CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home >

CFD Journal Feeds

Annual Review of Fluid Mechanics top

► Fluid Dynamics of Polar Vortices on Earth, Mars, and Titan
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 265-289, January 2023.
► Particle Rafts and Armored Droplets
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 459-480, January 2023.
► Sharp Interface Methods for Simulation and Analysis of Free Surface Flows with Singularities: Breakup and Coalescence
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 707-747, January 2023.
► A Perspective on the State of Aerospace Computational Fluid Dynamics Technology
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 431-457, January 2023.
► 3D Lagrangian Particle Tracking in Fluid Mechanics
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 511-540, January 2023.
► Evaporation of Sessile Droplets
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 481-509, January 2023.
► Gas-Liquid Foam Dynamics: From Structural Elements to Continuum Descriptions
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 323-350, January 2023.
► Transition to Turbulence in Pipe Flow
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 575-602, January 2023.
► Icebergs Melting
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 377-402, January 2023.
► Elasto-Inertial Turbulence
  19 Jan, 2023
Annual Review of Fluid Mechanics, Volume 55, Issue 1, Page 675-705, January 2023.

Computers & Fluids top

► A parallel unstructured multi-color SOR solver for 3D Navier–Stokes equations on graphics processing units
    

Publication date: 30 June 2023

Source: Computers & Fluids, Volume 260

Author(s): Miguel Uh Zapata, Francisco J. Hernandez-Lopez, Reymundo Itzá Balam

► An integrated in-vitro and in-silico workflow to study the pulmonary bifurcation hemodynamics
    

Publication date: 30 June 2023

Source: Computers & Fluids, Volume 260

Author(s): Benigno Marco Fanni, Emanuele Gasparotti, Emanuele Vignali, Claudio Capelli, Vincenzo Positano, Simona Celi

► Lattice-Boltzmann modeling of the quiet and unstable PRECCINSTA burner modes
    

Publication date: 30 June 2023

Source: Computers & Fluids, Volume 260

Author(s): Song Zhao, Karthik Bhairapurada, Muhammad Tayyab, Renaud Mercier, Pierre Boivin

► Editorial Board
    

Publication date: 30 June 2023

Source: Computers & Fluids, Volume 260

Author(s):

► Computational analysis of unsteady flow features around a realistic Estate vehicle with hybrid RANS/LES methods
    

Publication date: Available online 19 May 2023

Source: Computers & Fluids

Author(s): Francois Delassaux, Iraj Mortazavi, Vincent Herbert, Charles Ribes

► A new type of weighted compact nonlinear scheme with minimum dispersion and adaptive dissipation for compressible flows
    

Publication date: Available online 25 May 2023

Source: Computers & Fluids

Author(s): Zhangbo Zhou, Juchun Ding, Shenghong Huang, Xisheng Luo

► Inertial migration of rigid red blood cell particles in Poiseuille flow
    

Publication date: 30 June 2023

Source: Computers & Fluids, Volume 260

Author(s): Weiyin Liang, Chengliang Xuan, Zhangrong Qin, Binghai Wen

► Unsteady vortex shedding dynamics behind a circular cylinder in very shallow free-surface flows
    

Publication date: 30 June 2023

Source: Computers & Fluids, Volume 260

Author(s): Fawaz Alzabari, Catherine A.M.E. Wilson, Pablo Ouro

► A multi-stage coupling adaptive method for thermochemical nonequilibrium gas
    

Publication date: 15 July 2023

Source: Computers & Fluids, Volume 261

Author(s): Peng Li, Jianqiang Chen, Mingsong Ding, Tao Jiang, Jie Mei, Yang'aoxiao Fu, Weizhong Dong

► Spurious currents suppression by accurate difference schemes in multiphase lattice Boltzmann method
    

Publication date: 15 July 2023

Source: Computers & Fluids, Volume 261

Author(s): Zhangrong Qin, Wenbo Chen, Chunyan Qin, Xin Xu, Binghai Wen

International Journal of Computational Fluid Dynamics top

► A Momentum-Conserving Weakly Compressible Navier–Stokes Solver for Simulation of Violent Two-Phase Flows with High Density Ratio
  21 Apr, 2023
Volume 36, Issue 9, November 2022, Page 776-796
.
► Evaluation Method for the Reasonableness of Countermeasures for Defective Products in the Negative-Pressure Molding Mechanism
  31 Mar, 2023
Volume 36, Issue 9, November 2022, Page 816-833
.
► Numerical Study of Compressible Wall-Bounded Turbulence – the Effect of Thermal Wall Conditions on the Turbulent Prandtl Number in the Low-Supersonic Regime
  30 Mar, 2023
Volume 36, Issue 9, November 2022, Page 797-815
.
► Correction
  27 Mar, 2023
Volume 36, Issue 9, November 2022, Page 834-834
.
► Application of Gas-Kinetic Scheme for Continuum and Near-Continuum Flow on Unstructured Mesh
  22 Mar, 2023
Volume 36, Issue 9, November 2022, Page 753-775
.
► Erratum
  18 Aug, 2014
.

International Journal for Numerical Methods in Fluids top

► Momentum exchange modeling for coarsely resolved interfaces in a multifield two‐fluid model
  27 May, 2023
Momentum exchange modeling for coarsely resolved interfaces in a multifield two-fluid model

With the proposed algorithm coarsely resolved gas-liquid interfaces in the multifield two-fluid model are characterized by direction of the flow relative to the interface orientation and by the dimensionless interface thickness defined in terms of the flow's shear length scale. Based on those two quantities an under-resolution indicator function is formulated. Via this information the interfacial momentum coupling is adapted to low grid resolutions in order to reduce the grid dependency of simulation results of interfacial multiphase flows.


Abstract

Morphology-adaptive multiphase models are becoming more established for the numerical description of complex gas-liquid flows adapting dynamically to the local flow morphology. In the present study, two different numerical methods originally designed for distinct flow morphologies are combined, namely the volume-of-fluid and the Euler–Euler method. Both edge cases have been proven to be capable of delivering reliable predictions in the respective use cases. The long-term goal is to improve the prediction of gas-liquid flows, regardless of the flow regime in a specific application. To capture the system dynamics with a given grid resolution, the flow fields need to be predicted as precise as possible, while the shape of structures such as gas bubbles need to be recovered adequately in topology and shape. The goal is to obtain reliable predictions on intermediate mesh resolutions rather than relying on fine meshes requiring more computational resources. Therefore, a procedure is proposed to locally measure the degree of resolution. With this information, the hydrodynamics in the interface region can be controlled by means of a dedicated interfacial drag formulation in order to improve simulation results across several levels of spatial resolution. A modified formulation of buoyancy is proposed to prevent unphysical oscillations of vertical velocity near a horizontal interface. The functionality is demonstrated in a three-dimensional case of a gas bubble rising in stagnant liquid and in a co-current stratified air-water channel flow in two-dimensional space. The choice of these different applications demonstrates the general applicability of the proposed model framework.

► Modeling of Darcy‐Forchheimer magnetohydrodynamic Williamson nanofluid flow towards nonlinear radiative stretching surface using artificial neural network
  26 May, 2023
Modeling of Darcy-Forchheimer magnetohydrodynamic Williamson nanofluid flow towards nonlinear radiative stretching surface using artificial neural network

In the present research, the Levenberg–Marquardt technique combined with backpropagated neural networks is used to assess the nanomaterial flow of the Darcy-Forchheimer Williamson nanofluid model. Results from the current study are compared with existing results, which support the validity of the present approach.


Abstract

Modern industries face a new challenge in cooling processes. Traditional cooling lubricants have limited heatconducting capacity. The development of nanofluids possessing superior properties such as high thermal conductivity, homogeneity, and long-term stability has revolutionized the cooling lubrication industry. The literature reports a wide range of applications of nanofluid, such as cooling devices, peristaltic pumps for diabetic treatments, accelerators, reactors, petroleum industry applications, solar collectors and so forth. Nanofluids like Williamson nanofluid are very important non-Newtonian fluids that have pseudoplastic properties. Williamson nanofluid has a number of applications in the medical and engineering sciences. It is used in food processing, inkjet printing, adhesives and emulsions, coated photographic films, and many other applications. In the current study, the nanomaterial flow of the Darcy-Forchheimer Williamson nanofluid model is evaluated using the Levenberg–Marquardt approach with backpropagated neural networks. Thermalphoresis and Brownian motion are incorporated into the nanofluid model. This system is converted into an analogous nonlinear ordinary differential system through the application of necessary transformations. A dataset for the proposed multilayer perceptron artificial neural network is generated by altering the necessary variables through a Runge–Kutta fourth-order shooting procedure. It has been created an artificial neural network called a multiple-layer perceptron in order to forecast the values of the multiple-layer perceptron. It is discovered that the SFClss$$ {\mathrm{SFC}}_{lss} $$ parameter had the highest mean deviation of 0.26%$$ 0.26\% $$ and the LNNnlss$$ {\mathrm{LNN}}_{nlss} $$ parameter had the lowest mean deviation of −0.004%$$ -0.004\% $$. Furthermore, MSE value of ANN model developed to estimate the skin friction coefficient value as 3.55×10−05$$ 3.55\times 1{0}^{-05} $$ and R value as 0.99954 whereas MSE and R values of the ANN model developed for the estimation of the LNN value were obtained as 3.09×10−09$$ 3.09\times 1{0}^{-09} $$ and 0.99999, respectively.

► Dry and wet boundary treatment and improvement of a TVD‐MacCormack scheme in shallow water flow
    8 May, 2023
Dry and wet boundary treatment and improvement of a TVD-MacCormack scheme in shallow water flow

A simple and efficient dry-wet boundary treatment method is proposed. We also improve difference scheme to solve the problem of distortion of left and right traveling waves propagating in the dry bed.


Abstract

To solve shallow water equation, this paper proposes a simple and easy-to-operate dry-wet boundary treatment method based on the total variation diminishing (TVD)- MacCormack scheme. The method requires to judge dry and wet nodes before the calculation of prediction step and correction step, respectively. Then, the dry nodes are fictitiously celled and the topographic variables are reset. Moreover, previous researches show that when the same differential scheme was used, the left and right traveling waves showed over predicted computational fluxes during the downstream dry bed flow evolution, which led to distorted values and non-real physical phenomena. To solve the problem, the difference scheme for prediction step and correction step is modified, and a new finite difference scheme improvement method is proposed. Finally, the numerical solutions are compared with the analytical solution results by five classical cases to verify the rationality of the proposed method in this paper.

► Assessment of high‐order IMEX methods for incompressible flow
    8 May, 2023
Assessment of high-order IMEX methods for incompressible flow

This paper investigates semi-implicit Runge-Kutta and spectral deferred correction methods up to order six for incompressible flow problems. A novel approach based on partitioned Runge-Kutta methods is proposed for embedding the projection scheme and to achieve a consistent treatment of nonlinear viscosity. Numerical experiments including laminar flow, variable viscosity and transition to turbulence demonstrate the accuracy, convergence and computational efficiency of the proposed methods and their superiority over second-order methods.


Summary

This paper investigates the competitiveness of semi-implicit Runge-Kutta (RK) and spectral deferred correction (SDC) time-integration methods up to order six for incompressible Navier-Stokes problems in conjunction with a high-order discontinuous Galerkin method for space discretization. It is proposed to harness the implicit and explicit RK parts as a partitioned scheme, which provides a natural basis for the underlying projection scheme and yields a straight-forward approach for accommodating nonlinear viscosity. Numerical experiments on laminar flow, variable viscosity and transition to turbulence are carried out to assess accuracy, convergence and computational efficiency. Although the methods of order 3 or higher are susceptible to order reduction due to time-dependent boundary conditions, two third-order RK methods are identified that perform well in all test cases and clearly surpass all second-order schemes including the popular extrapolated backward difference method. The considered SDC methods are more accurate than the RK methods, but become competitive only for relative errors smaller than ca 10−5$$ 1{0}^{-5} $$.

► Stability effect of multidimensional velocity components in numerical flux SLAU
    8 May, 2023
Stability effect of multidimensional velocity components in numerical flux SLAU

The computational stability effect of multidimensional velocity components in the all-speed numerical flux scheme SLAU is investigated by comparing it with the mSLAU (formulated with only a cell interface-normal velocity component). It was observed that the multidimensional velocity components contributed to stability against poor-quality grids by isotropically producing a larger amount of numerical dissipation, especially in low-subsonic and hypersonic flows.


Abstract

In computational fluid dynamics of compressible fluid flow, the simple low-dissipation advection upstream (SLAU) scheme formulated with multidimensional velocity components (normal and parallel to a cell interface) is a widely employed all-speed scheme. As a variant of SLAU, the mSLAU scheme, which adopts only a velocity component normal to the cell interface instead of multidimensional velocity components, is used for rotorcraft calculations. However, although mSLAU has been claimed to be empirically stable, it has been pointed out that using only the cell-interface-normal velocity component instead of the multidimensional velocity components causes numerical instability. Therefore, to clarify the roles of the multidimensional velocity components for computational stability, we solved some benchmark problems associated with using SLAU or mSLAU. We discovered that the multidimensional velocity components contributed to stability against poor-quality grids by isotropically producing enough amount of numerical dissipation, especially in low-subsonic and supersonic flows. Although mSLAU could practically treat moderate Mach number flows (approximately 0.1 < M < 1.0) when coupled with the minmod limiter, using only the cell-interface-normal velocity component can deteriorate convergence of calculations and lead to susceptibility in the grid geometry.

► Issue Information
    8 May, 2023
International Journal for Numerical Methods in Fluids, Volume 95, Issue 6, June 2023.
► An unconditionally stable third order scheme for mixed convection flow between parallel plates with oscillatory boundary conditions
    8 May, 2023
An unconditionally stable third order scheme for mixed convection flow between parallel plates with oscillatory boundary conditions

It was asserted that no multistep method with more than two steps is A-stable (Altunkaya et al. 2017). However, this article proposes a third-order multistep method that is always stable for time-dependent partial differential equations. A third-order numerical scheme has been proposed for solving parabolic equations. The scheme is linear and unconditionally stable. The comparison showed less error than the existing backward Euler scheme with fourth-order spatial discretization. The proposed scheme solves the nonlinearized partial differential equation due to the compact scheme implementation technique.


Abstract

This work proposes an unconditionally stable third-order multistep technique for time-dependent partial differential equations. Its unconditional stability is proved by employing von Neumann stability analysis, and constructed Matlab code is another solid proof of the existence of the such scheme. The scheme is constructed on three consecutive time levels, and a compact fourth-order scheme is considered for spatial discretization. The convergence conditions are found when applied to the system of parabolic equations. The scheme is tested on two examples of flow between parallel plates. The mathematical model of heat and mass transfer of flow between parallel plates under the effects of viscous dissipation, thermal radiations, and chemical reaction is given and solved by the proposed scheme. The impact of some parameters, including radiation and reaction rate parameters, on velocity, temperature, and concentration profiles is also illustrated by graphs. The proposed scheme is also compared with the existing scheme, providing faster convergence than an existing one. The fundamental benefit of the proposed scheme is that it can give a compact fourth-order solution to parabolic equations.

► A constrained proper orthogonal decomposition model for upscaling permeability
    8 May, 2023
A constrained proper orthogonal decomposition model for upscaling permeability

New Findings Applying the models to practical datasets, statistics from the error analysis shows classical POD algorithm seems to be more preferred for LRA. However, since non-negativity of permeability datasets is a priority, the constrained POD (non-negative POD) algorithm described in this article is more appropriate. Results shows that the NPOD model has the capability of using minimal number of modes to reconstruct the permeability image while still retaining the geological details from the original data as opposed to the POD model.


Abstract

Reservoir modeling and simulation are vital components of modern reservoir management processes. Despite the advances in computing power and the advent of smart technologies, the implementation of model-based operational/control strategies has been limited by the inherent complexity of reservoir models. Thus, reduce order models that not only reduce the cost of the implementation but also provide geological consistent prediction are essential. This article introduces reduced-order models based on the proper orthogonal decomposition (POD) coupled with linear interpolation for upscaling. First, using POD-based models, low rank approximate (LRA) are obtained by projecting the high dimensional permeability dataset to a low dimensional subspace spanned by its trajectories to decorrelate the dataset. Next, the LRA is integrated into the interpolation algorithm to generate upscaled values. This technique is highly scalable since low-rank approximations are achieved by the variation in the number of modes used for reconstruction. To test the validity and reliability of the model, we show its application to the practical dataset from SPE10 benchmark case2. From statistics of the error analysis, the classical POD algorithm seems to be more preferred for LRA; however, since non-negativity of the permeability data set is a priority, the constrained POD (non-negative POD) algorithm described in this article is more appropriate. Finally, we compared the POD-based models to a traditional industry-standard upscaling technique (e.g., arithmetic mean) to highlight our model benefits/performance. Results show that the POD-based models, particularly the non-negative POD model, produce considerably less error than the arithmetic mean model in the upscaling process.

► A high‐order stabilized solver for the volume averaged Navier‐Stokes equations
    8 May, 2023
A high-order stabilized solver for the volume averaged Navier-Stokes equations

We develop an arbitrary order finite element volume average Navier-Stokes solver that is stabilized with streamline upwind and pressure–stabilizing Petrov–Galerkin techniques and grad div stabilization. The solver is robust, globally mass conservative and supports both models A and B of the equations. Three verification cases with increasing complexity are developed using the method of manufactured solution to verify the solver while a packed bed test case is simulated to validate the solver.


Abstract

The volume-averaged Navier-Stokes equations are used to study fluid flow in the presence of fixed or moving solids such as packed or fluidized beds. We develop a high-order finite element solver using both forms A and B of these equations. We introduce tailored stabilization techniques to prevent oscillations in regions of sharp gradients, to relax the Ladyzhenskaya–Babuska–Brezzi inf-sup condition, and to enhance the local mass conservation and the robustness of the formulation. We calculate the void fraction using the particle centroid method. Using different drag models, we calculate the drag force exerted by the solids on the fluid. We implement the method of manufactured solution to verify our solver. We demonstrate that the model preserves the order of convergence of the underlying finite element discretization. Finally, we simulate gas flow through a randomly packed bed and study the pressure drop and mass conservation properties to validate our model.

► A new numerical approach to Gardner Kawahara equation in magneto‐acoustic waves in plasma physics
    8 May, 2023
A new numerical approach to Gardner Kawahara equation in magneto-acoustic waves in plasma physics

The basic idea of this article is to investigate the numerical solutions of Gardner Kawahara equation, a particular case of extended Korteweg-de Vries equation, by means of finite element method. For this purpose, a collocation finite element method based on trigonometric quintic B-spline basis functions is presented. The standard finite difference method is used to discretize time derivative and Crank–Nicolson approach is used to obtain more accurate numerical results. Then, von Neumann stability analysis is performed for the numerical scheme obtained using collocation finite element method. Several numerical examples are presented and discussed to exhibit the feasibility and capability of the finite element method and trigonometric B-spline basis functions. More specifically, the error norms L2$$ {L}_2 $$ and L∞$$ {L}_{\infty } $$ are reported for numerous time and space discretization values in tables. Graphical representations of the solutions describing motion of wave are presented.


Abstract

The basic idea of this article is to investigate the numerical solutions of Gardner Kawahara equation, a particular case of extended Korteweg-de Vries equation, by means of finite element method. For this purpose, a collocation finite element method based on trigonometric quintic B-spline basis functions is presented. The standard finite difference method is used to discretize time derivative and Crank–Nicolson approach is used to obtain more accurate numerical results. Then, von Neumann stability analysis is performed for the numerical scheme obtained using collocation finite element method. Several numerical examples are presented and discussed to exhibit the feasibility and capability of the finite element method and trigonometric B-spline basis functions. More specifically, the error norms L2$$ {L}_2 $$ and L∞$$ {L}_{\infty } $$ are reported for numerous time and space discretization values in tables. Graphical representations of the solutions describing motion of wave are presented.

Journal of Computational Physics top

► Efficient decoupling schemes for multiscale multicontinuum problems in fractured porous media
    

Publication date: 15 August 2023

Source: Journal of Computational Physics, Volume 487

Author(s): Maria Vasilyeva

► A robust and contact resolving Riemann solver for the two-dimensional ideal magnetohydrodynamics equations
    

Publication date: 15 August 2023

Source: Journal of Computational Physics, Volume 487

Author(s): Xun Wang, Hongping Guo, Zhijun Shen

► A generalized coupled level set/volume-of-fluid/ghost fluid method for detailed simulation of gas-liquid flows
    

Publication date: 15 August 2023

Source: Journal of Computational Physics, Volume 487

Author(s): Changxiao Shao, Shian Yuan, Kun Luo

► The immersed boundary method: A SIMPLE approach
    

Publication date: 15 August 2023

Source: Journal of Computational Physics, Volume 487

Author(s): Kirill Goncharuk, Oz Oshri, Yuri Feldman

► Generic five-equation model for compressible multi-material flows and its corresponding high-fidelity numerical algorithms
    

Publication date: 15 August 2023

Source: Journal of Computational Physics, Volume 487

Author(s): Zhiwei He, Huipo Liu, Li Li

► Time complexity analysis of quantum algorithms via linear representations for nonlinear ordinary and partial differential equations
    

Publication date: 15 August 2023

Source: Journal of Computational Physics, Volume 487

Author(s): Shi Jin, Nana Liu, Yue Yu

► Local-basis Difference Potentials Method for elliptic PDEs in complex geometry
    

Publication date: Available online 25 May 2023

Source: Journal of Computational Physics

Author(s): Qing Xia

► A combined immersed finite element and conservative semi-Lagrangian scheme for plasma-material interactions
    

Publication date: Available online 25 May 2023

Source: Journal of Computational Physics

Author(s): Hongtao Liu, Mengyu Chen, Xiaofeng Cai, Yong Cao, Giovanni Lapenta

► Editorial Board
    

Publication date: 15 August 2023

Source: Journal of Computational Physics, Volume 487

Author(s):

► An implicit, conservative and asymptotic-preserving electrostatic particle-in-cell algorithm for arbitrarily magnetized plasmas in uniform magnetic fields
    

Publication date: 15 August 2023

Source: Journal of Computational Physics, Volume 487

Author(s): G. Chen, L. Chacón

Journal of Turbulence top

► Toward the use of LES for industrial complex geometries. Part I: automatic mesh definition
  29 May, 2023
.
► Physical/numerical duality of explicit/implicit subgrid-scale modelling
  25 May, 2023
.
► Multi-fidelity parametric sensitivity estimation for large eddy simulation with the Spalart–Allmaras model
  18 May, 2023
Volume 24, Issue 5, May 2023, Page 195-212
.
► Influence of streamwise and spanwise wall magnet arrays on near-wall MHD turbulence
  21 Apr, 2023
Volume 24, Issue 5, May 2023, Page 173-194
.
► Correction
  13 Apr, 2023
Volume 24, Issue 5, May 2023, Page 213-213
.
► An EDQNM study of the dissipation rate in isotropic non-equilibrium turbulence
  16 Mar, 2023
.
► The effect of Prandtl number on decaying stratified turbulence
  16 Feb, 2023
.

Physics of Fluids top

► A sharp interface immersed edge-based smoothed finite element method with extended fictitious domain scheme
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
This paper proposes a versatile and robust immersed edge-based smoothed finite element method with the mass conservation algorithm (IESFEM/Mass) to solve partitioned fluid–structure interaction (FSI). A gradient smoothing technique was used to solve the system governing equations, which can improve the calculated capability of the linear triangular elements in two phases. Based on the quadratic sharp interface representation of immersed boundary, an extended fictitious domain constructed by a least squares method approximately corrected the residual flux error. The compatibility for boundary conditions on moving interfaces was satisfied, thus eliminating spurious oscillations. The results from all numerical examples were consistent with those from the existing experiments and published numerical solutions. Furthermore, the present divergence-free vector field had a faster-converged rate in the flow velocity, pressure, and FSI force. Even if in distorted meshes, the proposed algorithm maintained a stable accuracy improvement. The aerodynamics of one- and two-winged flapping motions in insect flight has been investigated through the IESFEM/Mass. It can be seen that the wing–wake interaction mechanism is a vital factor affecting the lift. The applicability of the present method in the biological FSI scenario was also well-demonstrated.
► Enhanced and reduced solute transport and flow strength in salt finger convection in porous media
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
We report a pore-scale numerical study of salt finger convection in porous media, with a focus on the influence of the porosity in the non-Darcy regime, which has received little attention in previous research. The numerical model is based on the lattice Boltzmann method with a multiple-relaxation-time scheme and employs an immersed boundary method to describe the fluid–solid interaction. The simulations are conducted in a two-dimensional, horizontally periodic domain with an aspect ratio of 4, and the porosity [math] is varied from 0.7 to 1, while the solute Rayleigh number [math] ranges from [math] to [math]. Our results show that, for all explored [math], solute transport first enhances unexpectedly with decreasing [math] and then decreases when [math] is smaller than a [math]-dependent value. On the other hand, while the flow strength decreases significantly as [math] decreases at low [math], it varies weakly with decreasing [math] at high [math] and even increases counterintuitively for some porosities at moderate [math]. Detailed analysis of the salinity and velocity fields reveals that the fingered structures are blocked by the porous structure and can even be destroyed when their widths are larger than the pore scale, but become more ordered and coherent with the presence of porous media. This combination of opposing effects explains the complex porosity dependencies of solute transport and flow strength. The influence of porous structure arrangement is also examined, with stronger effects observed for smaller [math] and higher [math]. These findings have important implications for passive control of mass/solute transport in engineering applications.
► On the instability of the magnetohydrodynamic pipe flow subject to a transverse magnetic field
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
The linear stability of a fully developed liquid–metal magnetohydrodynamic pipe flow subject to a transverse magnetic field is studied numerically. Because of the lack of axial symmetry in the mean velocity profile, we need to perform a BiGlobal stability analysis. For that purpose, we develop a two-dimensional complex eigenvalue solver relying on a Chebyshev–Fourier collocation method in physical space. By performing an extensive parametric study, we show that in contrast to the Hagen–Poiseuille flow known to be linearly stable for all Reynolds numbers, the magnetohydrodynamic pipe flow with transverse magnetic field is unstable to three-dimensional disturbances at sufficiently high values of the Hartmann number and wall conductance ratio. The instability observed in this regime is attributed to the presence of velocity overspeed in the so-called Roberts layers and the corresponding inflection points in the mean velocity profile. The nature and characteristics of the most unstable modes are investigated, and we show that they vary significantly depending on the wall conductance ratio. A major result of this paper is that the global critical Reynolds number for the magnetohydrodynamic pipe flow with transverse magnetic field is Re = 45 230, and it occurs for a perfectly conducting pipe wall and the Hartmann number Ha = 19.7.
► The turbulence development at its initial stage: A scenario based on the idea of vortices decay
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
In this paper, a model of the development of a quantum turbulence in its initial stage is proposed. The origin of the turbulence in the suggested model is the decay of vortex loops with an internal structure. We consider the initial stage of this process, before an equilibrium state is established. As result of our study, the density matrix of developing turbulent flow is calculated. The quantization scheme of the classical vortex rings system is based on the approach proposed by the author earlier.
► Interstage difference and deterministic decomposition of internal unsteady flow in a five-stage centrifugal pump as turbine
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
A five-stage centrifugal pump is utilized to investigate the interstage flow characteristics of the multistage centrifugal pump as turbine (PAT). The simulation results of performance are verified by comparing with the experimental results. Owing to the distinct structural attributes, significant differences in flow occur between the first stage and the other stages of the multistage PAT. To enhance the understanding of these disparities and explore their repercussions, this study focuses on analyzing the flow within the impellers in the first and second stages by a deterministic analysis. The main conclusions are as follows: The discrepancies in the inflow conditions are the major reason for the dissimilarities in the flow of impellers between stages. The impact loss generated by the misalignment between the positive guide vane outlet angle and the impeller inlet angle leads to flow deviation between impeller passages and affects the internal flow pattern. The unsteadiness under low flow rates is mostly produced by the spatial gradient of the blade-to-blade nonuniformities, which is relevant to the relative position between blades and the positive guide vanes. At high flow rates, especially in the second-stage impeller, the pure unsteady term is the primary cause of flow unsteadiness as a result of the flow separation induced by interactions between the blades and the positive guide vanes. This study can provide some references for the practical operation and performance optimization of the multistage PATs in the future.
► Effect of gravity on phase transition for liquid–gas simulations
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
Direct simulations of phase-change and phase-ordering phenomena are becoming more common. Recently, qualitative simulations of boiling phenomena have been undertaken by a large number of research groups. One seldom discussed limitation is that large values of gravitational forcing are required to simulate the detachment and rise of bubbles formed at the bottom surface. The forces are typically so large that neglecting the effects of varying pressure in the system becomes questionable. In this paper, we examine the effect of large pressure variations induced by gravity using pseudopotential lattice Boltzmann simulations. These pressure variations lead to height dependent conditions for phase coexistence and nucleation of either gas or liquid domains. Because these effects have not previously been studied in the context of these simulation methods, we focus here on the phase stability in a one-dimensional system, rather than the additional complexity of bubble or droplet dynamics. Even in this simple case, we find that the different forms of gravitational forces employed in the literature lead to qualitatively different phenomena, leading to the conclusion that the effects of gravity induced pressure variations on phase-change phenomena should be very carefully considered when trying to advance boiling and cavitation as well as liquefaction simulations to become quantitative tools.
► Entrapment and mobilization dynamics during the flow of viscoelastic fluids in natural porous media: A micro-scale experimental investigation
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
Capillary desaturation process was investigated as a function of wetting phase rheological signatures during the injection of Newtonian and non-Newtonian fluids. Two sets of two-phase imbibition flow experiments were conducted on a water-wet sandstone core sample using brine and viscoelastic polymer solutions. During the experiments, a high-resolution micro-computed tomography scanner was employed to directly map pore-level fluid occupancies within the pore space. The results of the experiments revealed that at a given capillary number, the viscoelastic polymer was more efficient than the brine in recovering the non-wetting oil phase. At low capillary numbers, this is attributed to the improved accessibility of the viscoelastic polymer solution to the entrance of pore elements, which suppressed snap-off events and allowed more piston-like and cooperative pore-body filling events to contribute to oil displacement. For intermediate capillary numbers, the onset of elastic turbulence caused substantial desaturation, while at high capillary numbers, the superimposed effects of higher viscous and elastic forces further improved the mobilization of the trapped oil ganglia by the viscoelastic polymer. In the waterflood, however, the mobilization of oil globules was the governing recovery mechanism, and the desaturation process commenced only when the capillary number reached a threshold value. These observations were corroborated with the pore-level fluid occupancy maps produced for the brine and viscoelastic polymer solutions during the experiments. Furthermore, at the intermediate and high capillary numbers, the force balance and pore-fluid occupancies suggested different flow regimes for the non-Newtonian viscoelastic polymer. These regions are categorized in this study as elastic-capillary- and viscoelastic-dominated flow regimes, different from viscous-capillary flow conditions that are dominant during the flow of Newtonian fluids. Moreover, we have identified novel previously unreported pore-scale displacement events that take place during the flow of viscoelastic fluids in a natural heterogeneous porous medium. These events, including coalescence, fragmentation, and re-entrapment of oil ganglia, occurred before the threshold of oil mobilization was reached under the elastic-capillary-dominated flow regime. In addition, we present evidence for lubrication effects at the pore level due to the elastic properties of the polymer solution. Furthermore, a comparison of capillary desaturation curves generated for the Newtonian brine and non-Newtonian viscoelastic polymer revealed that the desaturation process was more significant for the viscoelastic polymer than for the brine. Finally, the analysis of trapped oil clusters showed that the ganglion size distribution depends on both the capillary number and the rheological properties of fluids.
► Impact of wettability on interface deformation and droplet breakup in microcapillaries
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
The objective of this research paper is to relate the influence of dynamic wetting in a liquid/liquid/solid system to the breakup of emulsion droplets in capillaries. Therefore, modeling and simulation of liquid/liquid flow through a capillary constriction have been performed with varying dynamic contact angles from highly hydrophilic to highly hydrophobic. Advanced advection schemes with geometric interface reconstruction (isoAdvector) are incorporated for high interface advection accuracy. A sharp surface tension force model is used to reduce spurious currents originating from the numerical treatment and geometric reconstruction of the surface curvature at the interface. Stress singularities from the boundary condition at the three-phase contact line are removed by applying a Navier-slip boundary condition. The simulation results illustrate the strong dependency of the wettability and the contact line and interface deformation.
► Drag increase and turbulence augmentation in two-way coupled particle-laden wall-bounded flows
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
The exact regularized point particle method is used to characterize the turbulence modulation in two-way momentum-coupled direct numerical simulations of a turbulent pipe flow. The turbulence modification is parametrized by the particle Stokes number, the mass loading, and the particle-to-fluid density ratio. The data show that in the wide region of the parameter space addressed in the present paper, the overall friction drag is either increased or unaltered by the particles with respect to the uncoupled case. In the cases where the wall friction is enhanced, the fluid velocity fluctuations show a substantial modification in the viscous sub-layer and in the buffer layer. These effects are associated with a modified turbulent momentum flux toward the wall. The particles suppress the turbulent fluctuations in the buffer region and concurrently provide extra stress in the viscous sub-layer. The sum of the turbulent stress and the extra stress is larger than the Newtonian turbulent stress, thus explaining the drag increase. The non-trivial turbulence/particles interaction turns out in a clear alteration of the near-wall flow structures. The streamwise velocity streaks lose their spatial coherence when two-way coupling effects are predominant. This is associated with a shift of the streamwise vortices toward the center of the pipe and with the concurrent presence of small-scale and relatively more intense vortical structures near the wall.
► Partial and complete wetting of thin films with dynamic contact angle
  17 Apr, 2023
Physics of Fluids, Volume 35, Issue 4, April 2023.
The wetting of thin films depends critically on the sign of the spreading coefficient [math]. We discuss the cases S < 0, S = 0, and S > 0 for transient models with contact line dissipation and find that the use of a dynamic contact angle solves problems for S > 0 that models might otherwise have. For initial data with a non-zero slope and S > 0, we show that there exists a finite time [math] at which the contact angle of the thin film goes to zero. Then, a molecular precursor emerges from the thin film and moves outward at a constant velocity.

Theoretical and Computational Fluid Dynamics top

► Modal analysis of a fluid flowing over a porous substrate
  27 May, 2023

Abstract

We study the modal stability analysis for a three-dimensional fluid flowing over a saturated porous substrate where the porous medium is assumed to be anisotropic and inhomogeneous. A coupled system of time-dependent evolution equations is formulated in terms of normal velocity, normal vorticity, and fluid surface deformation, respectively, and solved numerically by using the Chebyshev spectral collocation method. Two distinct instabilities, the so-called surface mode instability and the shear mode instability, are identified. Modal stability analysis predicts that the Darcy number has a destabilizing influence on the surface mode instability but has a stabilizing influence on the shear mode instability. Similarly, the surface mode instability intensifies but the shear mode instability weakens with the increase in the value of the coefficient of inhomogeneity. Although the anisotropy parameter shows a stabilizing effect, increasing porosity exhibits a destabilizing effect on the shear mode instability. However, the anisotropy parameter and porosity have no significant impact on the surface mode instability. Spanwise wavenumber is found to have a stabilizing influence on both the surface mode and shear mode instabilities.

Graphical abstract

► Highly conservative Allen–Cahn-type multi-phase-field model and evaluation of its accuracy
  25 May, 2023

Abstract

In the engineering field, it is necessary to construct a numerical model that can reproduce multiphase flows containing three or more phases with high accuracy. In our previous study, by extending the conservative Allen–Cahn (CAC) model, which is computationally considerably more efficient than the conventional Cahn–Hilliard (CH) model, to the multiphase flow problem with three or more phases, we developed the conservative Allen–Cahn type multi-phase-field (CAC–MPF) model. In this study, we newly construct the improved CAC–MPF model by modifying the Lagrange multiplier term of the previous CAC–MPF model to a conservative form. The accuracy of the improved CAC–MPF model is evaluated through a comparison of five models: three CAC–MPF models and two CH–MPF models. The results indicate that the improved CAC–MPF model can accurately and efficiently perform simulations of multiphase flows with three or more phases while maintaining the same level of volume conservation as the CH model. We expect that the improved CAC–MPF model will be applied to various engineering problems with multiphase flows with high accuracy.

Graphic abstract

► Prediction of leading-edge-vortex initiation using criticality of the boundary layer
  13 May, 2023

Abstract

The initiation of leading-edge-vortex formation in unsteady airfoil flows is governed by flow criticality at the leading edge. While earlier works demonstrated the promise of criticality of leading-edge suction in governing LEV shedding, this criterion is airfoil and Reynolds number dependent. In this work, by examining results from Navier–Stokes computations for a large set of pitching airfoil cases at laminar flow conditions, we show that the onset of flow reversal at the leading edge always corresponds to the boundary-layer shape factor reaching the same critical value that governs laminar flow separation in steady airfoil flows. Further, we show that low-order prediction of this boundary-layer criticality is possible with an integral-boundary-layer calculation performed using potential-flow velocity distributions from an unsteady panel method. The low-order predictions agree well with the high-order computational results with a single empirical offset that is shown to work for multiple airfoils. This work shows that boundary-layer criticality governs LEV initiation, and that a low-order prediction approach is capable of predicting this boundary-layer criticality and LEV initiation.

Graphical Abstract

► Active chaotic mixing of yield stress fluids in an open channel flow
  11 May, 2023

Abstract

A numerical investigation of active mixing of yield stress fluids using a mixer recently proposed in El Omari et al. (Phys Rev Fluids 6(024):502, 2021. https://doi.org/10.1103/PhysRevFluids.6.024502) and tested experimentally with Newtonian fluids (Younes et al. in Int J Heat Mass Transf 187(122):459, 2022) is presented. As the Bingham number (defined by the ratio of the yield stress to the viscous stress) is increased past a critical value \(\text {Bn}_{\textrm{bulk}}^\textrm{crit}\approx 5\) , a dramatic decrease of both the efficiency of the mixing process and of the homogeneity of the final mixture is observed. Further physical insights into this observation are obtained by a systematic analysis of the space-time dynamics of the flow fields in both Eulerian and Lagrangian frames. The numerical results show that the cascade of the passive scalar fluctuations from the wave numbers associated to the integral scale at which the passive scalar is injected down to the diffusive scale is obstructed by the emergence of a supplemental space scale associated to the characteristic size of the un-yielded material elements. The study is complemented by the discussion of two plausible solutions for alleviating the dramatic loss of mixing efficiency induced by the viscoplastic fluid behavior.

Graphical abstract

► Flow dynamics in a model of a dilated thoracic aorta prior to and following prosthetic replacement
    9 May, 2023

Abstract

We numerically investigate the flow dynamics in a model of a dilated thoracic aorta, and compare the flow features with the case of a prosthetic replacement in its ascending part. The flow is characterized by an inlet jet which impacts the aortic walls and sweeps toward the aortic arch. Secondary flows generated by the transvalvular jet evolve downstream into a helical flow. The small curvature radius at the end of the aortic arch induces flow separation and vortex shedding in the initial part of the descending aorta, during the systole. The implantation of a prosthesis determines several modifications in the global and local flow patterns. An increase of the pulse wave velocity in the aorta leads to larger pressures inside the vessel, due to the geometrical and rigidity modifications. The sweeping jet is more aligned along the axial direction and propagates faster along the aortic arch. Consequently, a stronger separation of the flow downstream of the aortic arch is observed. By also exploiting manifold analysis, we identify regions characterized by near-wall disordered flows which may present intense accumulation and drop of concentration of biochemicals. These regions are localized downstream of the prosthetic replacement, in the aortic arch, and may be more prone to a new emergence of vessel dilation.

Graphical Abstract

► Effects of annulation on low Reynolds number flows over an orthocone
    6 May, 2023

Abstract

This study numerically examines the influences of transverse annulation around a cone surface on the characteristics of a flow over an orthocone. This work is inspired by Spyroceras, a fossilized genus of nautiloid cephalopods from the Paleozoic era, whose method of locomotion is understudied. As a baseline case, a flow over a smooth orthoconic model with a blunt cone end is investigated numerically at Reynolds numbers from 500 to 1500. As Reynolds increases, two different shedding mechanisms—hairpin-vortex wake and spiral-vortex wake—are captured. We notice that an introduction of annulation over the cone surface changes the critical Reynolds number for the transition of the shedding mechanism. The dominant shedding frequency increases with the Reynolds number for the smooth and annulated cone flows. Moreover, the annulation reduces the dominant frequency for the same Reynolds number and increases the time-averaged drag coefficient. Modal decompositions—Proper Orthogonal Decomposition (POD) and Spectral Proper Orthogonal Decomposition (SPOD)—are used to capture the coherent structures and their oscillating frequencies. We have captured modes corresponding to the hairpin-vortex wake and spiral-vortex wake shedding mechanisms. Comparing the leading POD modes for the smooth and the annulated cone flows, we find that the annulation can reduce the twisting effects of the coherent structures in the wake. Additionally, we find that the SPOD analysis can identify modes presenting both hairpin-vortex wake and spiral-vortex wake in one flow condition as leading modes, while the POD leading modes only reveal one shedding mechanism in each flow.

Graphical abstract

► Simulation of droplet impact dynamics on V-shaped walls
    5 May, 2023

Abstract

This paper presents the morphological evolution characteristics of a droplet impacting a V-shaped wall by using the lattice Boltzmann method (LBM). Four parameters are investigated comprehensively. The parameters vary over wide ranges: surface wettability ( \(60^\circ \le \theta ^{eq} \le 120^\circ \) ), Weber number ( \(102.27 \le \text {We} \le 3681.82\) ), bending angle of the V-shaped wall (90 \(^\circ \le \theta \le 180^\circ \) ), and eccentricity ratio (0 \(\le b \le \) 0.5). Two types of collision are observed: deposition and breakage. For breakage, the number of satellite droplets increases against the increment of We. The splashing occurs for a high We. And the lamella ejection is observed on the hydrophilic wall and the neutral wall. The lamella ejection will be slight against the increase of \(\theta ^{eq}\) , while it will become obvious against the increment of \(\theta \) . In addition, the nondimensional spreading length, width, and height are measured and analyzed. Regime maps are established based on We, Re, and \(\theta \) .

Graphic abstract

► Vortex dynamics of axisymmetric cones at high angles of attack
    4 May, 2023

Abstract

Vortex asymmetry, dynamics, and breakdown in the wake of an axisymmetric cone have been investigated using direct numerical simulation for a wide range of angles of attack. The immersed boundary method is employed with pseudo-body-conformal grids to ensure the accuracy and resolution requirements near the body while being able to account for topology changes near the cone tip. The separated shear layer originated from the surface of the cone swirls into a strong primary vortex. Beneath the primary vortex on the leeward surface of the cone, a well-coherent counter-rotating secondary vorticity is generated. Beyond a particular threshold of swirl, the attached vortex structure breaks and the flow undergoes a chaotic transformation. Depending on the angle of attack, the flow shows different levels of instabilities and the topology of the vortices changes in the wake. In addition to swirl, spiral vortices that revolve around the primary vortex core often merge with the core and play a role in developing the double-helix mode of instability at the onset of the vortex breakdown. At the angle of attack of 60 \(^\circ \) , the time-averaged side force becomes asymmetric at the stage where the drag overcomes the lift. At the angle of attack of 75 \(^\circ \) , the primary vortex governs the flow asymmetry and the side force. Flow asymmetry is independent of the vortex breakdown. Finally, the contribution of primary vortices to the total forces is quantified using a force partitioning method.

Graphical abstract

► Flow over a hydrofoil subjected to traveling wave-based surface undulation: effect of phase difference between surface waves and wave number
  29 Apr, 2023

Abstract

Flow around a traveling wave-based surface-undulating NACA0012 hydrofoil has been numerically studied. In particular, we determine the effect of the phase speed of the wave, the phase difference between the waves traveling on the top and bottom surfaces, and the wave number on flow dynamics around and behind the hydrofoil and propulsive performance. The flow results in a vortex sheet or a street behind the hydrofoil, where oppositely signed vortices are aligned in either forward or reverse direction. Apart from these, side vortices start forming on either side of the hydrofoil at a higher wave number. The phase difference analysis between the upper and lower surface undulation reveals the configuration better for the hydrofoil’s lateral and longitudinal stability. The hydrofoil can shift from high thrust to high lateral force configuration by changing the phase difference between waves on the top and bottom surfaces. Thrust increases with an increase in the wave number, and a threshold value of phase speed and wave number exists where the drag-to-thrust transition happens. The added mass force-based scaling analysis corroborates with the simulated results.

Graphic abstract

► Passive control of dynamic stall using a flow-driven micro-cavity actuator
  26 Apr, 2023

Abstract

A novel passive flow control strategy for the mitigation of transient separation and dynamic stall is demonstrated by means of high-fidelity large-eddy simulations. The control technique is based on a properly-sized micro-cavity cut into a wing’s underside near the leading edge, ahead of stagnation. This cavity remains essentially inactive at low incidence. However, as the wing effective angle of attack increases, the stagnation point displaces past the micro-cavity and the accelerating flow grazing the cavity induces a high-frequency resonance phenomenon or so-called Rossiter modes. The self-generated small-scale disturbances are carried around the leading-edge through the boundary layer to the wing’s upper side where the laminar separation bubble (LSB) amplifies these disturbances. This process delays LSB bursting and dynamic stall when the cavity size is selected such that its naturally occurring Rossiter modes are tuned to the receptivity of the LSB. Control effectiveness is explored for a harmonically pitching NACA 0012 wing section with freestream Mach number \(M_\infty = 0.2\) , chord Reynolds numbers \(\textrm{Re}_\textrm{c} = 5 \times 10^5\) , and maximum angle of attack of \(18^\circ \) . The flow fields are computed employing a validated overset high-order implicit large-eddy simulation (LES) solver based on sixth-order compact schemes for the spatial derivatives augmented with an eighth-order low-pass filter. Despite its simplicity, the micro-cavity resonance is found to be highly effective in preventing the deep dynamic stall experienced by the baseline airfoil. A significant reduction in the cycle-averaged drag and in the force and moment fluctuations is achieved. In addition, the negative (unstable) net-cycle pitch damping found in the baseline cases is eliminated.

Graphical abstract


return

Layout Settings:

Entries per feed:
Display dates:
Width of titles:
Width of content: