[cfdprojects]

I am developing a simple fortran solver in finite difference. My domain is 2pi*2pi*1 as taken by S. Chandrasekhar. My equations are having non dimensional parameters as Reynolds Number, Rayleigh Number and Prandtl No.
The code is running well but w- velocity contours(heating at bottom and cold at top) are coming only positive and negative alternatively and i am not getting rolls as expected. Can someone explain it.? Thanks in advance

[FMDenaro]

Originally Posted by cfdprojects

I am developing a simple fortran solver in finite difference. My domain is 2pi*2pi*1 as taken by S. Chandrasekhar. My equations are having non dimensional parameters as Reynolds Number, Rayleigh Number and Prandtl No.
The code is running well but w- velocity contours(heating at bottom and cold at top) are coming only positive and negative alternatively and i am not getting rolls as expected. Can someone explain it.? Thanks in advance

please, provide much more details about your code such as formulation, type of discretization, grid arrangement, values of the non-dimensional parameters, etc

[cfdprojects]

I am implementing Pressure- velocity method, and using pressure poisson equation for divergence free flow. Ra=1800, Re=1.0, Pr=1. Grid is uniform in x and y while clustered with cos function in z direction(gravity). discreatisation is done utilizing fourth order Central differencing for diffusion terms, while third order Kawamura and K. Kuwahara upwinding for convective terms. thanks for reply.

[FMDenaro]

Originally Posted by cfdprojects

I am implementing Pressure- velocity method, and using pressure poisson equation for divergence free flow. Ra=1800, Re=1.0, Pr=1. Grid is uniform in x and y while clustered with cos function in z direction(gravity). thanks for reply.

if you use a second order discretization and a colocated arrangement, you could have experienced a decoupling-mode solution in the pressure equation.
Could you post some figures of velocity and pressure fields?

[cfdprojects]

Originally Posted by FMDenaro

if you use a second order discretization and a colocated arrangement, you could have experienced a decoupling-mode solution in the pressure equation.
Could you post some figures of velocity and pressure fields?

Here are the figures encl :

[FMDenaro]

it is a decoupling along the gravity axis, you can see the pressure field oscillating ... why don't you try using a staggered grid?

[cfdprojects]

Originally Posted by FMDenaro

it is a decoupling along the gravity axis, you can see the pressure field oscillating ... why don't you try using a staggered grid?

Yes i am using collocated grid till now. Would you please suggest me some writeup on staggered grid implementation in view of this problem.

[FMDenaro]

Originally Posted by cfdprojects

Yes i am using collocated grid till now. Would you please suggest me some writeup on staggered grid implementation in view of this problem.

a second order discretization on staggered grid is a very old and well suited formulation, you can find that in any CFD textbook. For example, see the book of Peric & Ferziger

[cfdprojects]

Originally Posted by FMDenaro

a second order discretization on staggered grid is a very old and well suited formulation, you can find that in any CFD textbook. For example, see the book of Peric & Ferziger

Thankyou. I will apply it and come back.

[cfdprojects]

Now i applied staggered grid, please see w-velocity profile , i can see rolls still. Will they apper after long time ?

[FMDenaro]

Originally Posted by cfdprojects

Now i applied staggered grid, please see w-velocity profile , i can see rolls still. Will they apper after long time ?

from this plot I see still oscillations