|streamlines and pressure on the spats|
Time = 403
smoothSolver: Solving for Ux, Initial residual = 5.14663e-05, Final residual = 4.49128e-06, No Iterations 3
smoothSolver: Solving for Uy, Initial residual = 0.000128727, Final residual = 1.06587e-05, No Iterations 3
smoothSolver: Solving for Uz, Initial residual = 7.15543e-05, Final residual = 5.27129e-06, No Iterations 3
GAMG: Solving for p, Initial residual = 0.000129478, Final residual = 6.41391e-06, No Iterations 2
time step continuity errors : sum local = 3.84464e-10, global = 1.62637e-11, cumulative = 7.5432e-07
smoothSolver: Solving for omega, Initial residual = 5.26723e-07, Final residual = 3.78036e-08, No Iterations 3
smoothSolver: Solving for k, Initial residual = 3.84651e-06, Final residual = 2.74064e-07, No Iterations 3
ExecutionTime = 10837.4 s ClockTime = 11064 s
I learned that CFD people usually use a reduced pressure: p/rho. This originates from Bernoulli: the dynamic pressure p = rho/2*v^2. p/rho equals 1/2*v^2. I set the air density rho to 1.2 [kgm^-3]. This would mean that the pressure range is -226*1.2 to 50*1.2, -271 to 60 [Pa]. Atmospheric pressure is 1e5 [Pa]. In the CFD only relative pressures are calculated. (I found a declaration of pressure in a file initialConditions somewhere, it was set to 0). The lowest pressure is 1e5 -271 [Pa], the highest 1e5 +60 Pa. The pressure change is very small relative to the atmospheric pressure. ~200/1e5=2e-3=0.002 (0.2 %). Please correct me if I'm wrong.
|Pressure on the body. p/rho [m^2/s^2]|
|Something went wrong. Is is the mesh or is it paraview ?|
|The bottom view shows low pressure spots. p/rho [m^2s^-2]|
|Air speed [m/s] in a slice of the air 60 mm above the ground. (vehicle speed is 10m/s)|
|The pressure distribution in mid plane p/rho [m^2s^-2]|
The air is moving through the narrow space between wheel 'pants' bottom and road. In this narrow space the air velocity rises and pressure falls.
Now I would like to find out:
- are my statements about the pressure above correct?
- is there something wrong with the mesh?
- how do I check the quality of the simulation using the lines on Final residual?
- how do I calculate the forces on the body due to kinematic pressure and viscosity (skin friction)?
- in the boundary layer what is the type of flow: laminar or turbulent?
- I found out that the mesh is in [mm]. Both in the blockMeshDict and the snappyHexMeshDict the geometry is in mm. But shouldn't it be in [meter]. I know I can use to keyword convertToMeter in blockMeshDict but what about the snappyHexMeshDict?