[silviuskt]

i ran a 2D Single phase Laminar Flat Plate incompressible flow. The basic Laminar Flat plate from tutorials, with a different mesh. same BCs and all.


The density is 1 kg/m3 instead of 1.225 at is supposed to be, which i presume influences the velocity of the flow.

The freestream velocity should be 1.16 m/s.
Kin Visc is 14.84 m2/s
Re 54k
flow is laminar


I ran it with SOLVER= INC_NAVIER_STOKES and got better results than the original SOLVER= INC_RANS

% ------------- DIRECT, ADJOINT, AND LINEARIZED PROBLEM DEFINITION ------------%
%
% Physical governing equations (EULER, NAVIER_STOKES,
%                               WAVE_EQUATION, HEAT_EQUATION, FEM_ELASTICITY,
%                               POISSON_EQUATION)
SOLVER= INC_NAVIER_STOKES
%
% If Navier-Stokes, kind of turbulent model (NONE, SA)
KIND_TURB_MODEL= NONE
%
% Mathematical problem (DIRECT, CONTINUOUS_ADJOINT)
MATH_PROBLEM= DIRECT
%
% Restart solution (NO, YES)
RESTART_SOL= NO

% ---------------- INCOMPRESSIBLE FLOW CONDITION DEFINITION -------------------%
%
% Initial density for incompressible flows (1.2886 kg/m^3 by default)
INC_DENSITY_INIT= 1.225
%
% Initial velocity for incompressible flows (1.0,0,0 m/s by default)
INC_VELOCITY_INIT= ( 1.16, 0.0, 0.0 )
%
% List of inlet types for incompressible flows. List length must
% match number of inlet markers. Options: VELOCITY_INLET, PRESSURE_INLET.
INC_INLET_TYPE= VELOCITY_INLET
%
% Damping coefficient for iterative updates at pressure inlets. (0.1 by default)
INC_INLET_DAMPING= 0.1
%
% List of outlet types for incompressible flows. List length must
% match number of outlet markers. Options: PRESSURE_OUTLET, MASS_FLOW_OUTLET
INC_OUTLET_TYPE= PRESSURE_OUTLET PRESSURE_OUTLET
%
% Damping coefficient for iterative updates at mass flow outlets. (0.1 by default)
INC_OUTLET_DAMPING= 0.1

% --------------------------- VISCOSITY MODEL ---------------------------------%
%
% Viscosity model (SUTHERLAND, CONSTANT_VISCOSITY).
VISCOSITY_MODEL= CONSTANT_VISCOSITY
%
% Molecular Viscosity that would be constant (1.716E-5 by default)
MU_CONSTANT= 1.48592e-05
 ---------------------- REFERENCE VALUE DEFINITION ---------------------------%
%
% Reference origin for moment computation
REF_ORIGIN_MOMENT_X = 0.175
REF_ORIGIN_MOMENT_Y = 0.00
REF_ORIGIN_MOMENT_Z = 0.00
%
% Reference length for pitching, rolling, and yawing non-dimensional moment
REF_LENGTH= 1.0
%
% Reference area for force coefficients (0 implies automatic calculation)
REF_AREA= 0.7

% -------------------- BOUNDARY CONDITION DEFINITION --------------------------%
%
% Navier-Stokes wall boundary marker(s) (NONE = no marker)
MARKER_HEATFLUX= ( wall, 0.0 )
%
% Inlet boundary marker(s) (NONE = no marker) 
% Format: ( inlet marker, total temperature, total pressure, flow_direction_x, 
%           flow_direction_y, flow_direction_z, ... )
MARKER_INLET= ( inlet, 0, 1.16, 1.0, 0.0, 0.0 )
%
% Outlet boundary marker(s) (NONE = no marker)
% Format: ( outlet marker, back pressure, ... )
MARKER_OUTLET= ( outlet, 0.0, farfield, 0.0 )
%
% Symmetry boundary marker(s) (NONE = no marker)
MARKER_SYM= ( symmetry )
%
% Marker(s) of the surface to be plotted or designed
MARKER_PLOTTING= ( wall )
%
% Marker(s) of the surface where the functional (Cd, Cl, etc.) will be evaluated
MARKER_MONITORING= ( wall )

PICTURES:

https://ibb.co/0snRd6j
https://ibb.co/682PCTj

So my question is. why is my density stuck at 1 kg/m3 ? This is my first post so please let me know if i missed anything and thanks in advance guys

[silviuskt]

somebody on reddit said it might show the normalised density.


I think it's wrong because the 0.82 pa pressure difference should produce a free stream velocity of 1.16 m/s and it does not.

[bigfootedrockmidget]

The default is to nondimensionalize the results.
You can use dimensionalized values using:

INC_NONDIM = DIMENSIONAL

[silviuskt]

Hello,

so it was actualy nondimensionalised.

using this,you can set it to have the actual values :
INC_NONDIM = DIMENSIONALINC_NONDIM = DIMENSIONAL
the solution proposed by u/kpisagenius i think its actually this one
WRT_FORCES_BREAKDOWN=YES

which even though it didnt give me a straight answer, it was very helpful in pointing me to why the velocity is wrong, due to having a bigger Re number than expect.