[vivjk94]

Hello, i am trying to perform a 2D gear pump simulation as part of my project. I have modelled a gear pump where the gear has 13 teeth and rotating at 2000 rpm. I have used water as the fluid and used a fine mesh with triangular elements. The pump inlet boundary condition has 0 Pascal and outlet has 2000 psi pressure. the udf code used is as follows:

Rotating motion for gear 1

#include "udf.h"

DEFINE_CG_MOTION(gear_1_new,dt,vel,omega,time,dtim e)

{

real t = CURRENT_TIME;

NV_S (vel, = , 0.0);

NV_S (omega, = , 0.0);

omega[2] = -209.4395;

}

Rotating motion for gear 2

#include "udf.h"

DEFINE_CG_MOTION(gear_2_new,dt,vel,omega,time,dtim e)

{

real t = CURRENT_TIME;

NV_S (vel, = , 0.0);

NV_S (omega, = , 0.0);

omega[2] = 209.4395;

}

The dynamic mesh settings are as follows:

image.png


image.png
image.png
I have copied the mesh scale info to the parameters.

Now the issue lies when i try to run preview mesh motion. I get negative cell volume error. The timestep size used is 0.000000025 s and 10000 timesteps. I have tried to refine mesh further and reduce time step size. when i try to run calculation, i get negative cell volume error. Refining the mesh made no difference and reducing time step size allowed the simulation to run for a timestep or two and eventually end up with negative cell volume error.

I have even tried to run the simulation for a gear pump with lesser number of teeth and slower rotational speed (40 rpm). For this, i have taken a timestep size of 0.00025 s and 10000 timesteps. Doing so lets me run the simulation for a lot more timesteps and more accurate result but i still end up with negative cell volume error after like 200 timesteps(the gear doesn't complete one full rotation).

As per my observation, the error occurs when the gear is just about to finish one full rotation. My guess is that there is a problem with the dynamic mesh settings or the code but I might be wrong. After i get negative cell volume error, i click on check case and i get left handed cells detected and skewness exceeded 0.9 errors in the command box. I have tried using mesh repair command and that too doesn't improve anything.

Please guide me on resolving this issue. I am new to cfd.