[Me_1989]

Hello,

I've recently tried to simulate an external gear pump ( with two gears) and used a "DEFINE_CG_MOTION" code for defining the angular velocity of the gears. I solved all the code errors and I could see the rotation of the gears in the dynamic mesh preview. But, when I change the rotation speed to see its effect on the inlet mass flow rate ( any changes in the rotation speed of the gears must result in the changes of the input mass flow rate), I could not see any effects in the result. I mean with all of the rotation speeds, I have a constant amount of mass flow rate which is absolutely wrong!!

Thus, I would be so thankful if anybody could have any suggestions enabled me to solve this issue.

Kind Regards

[vinerm]

What conditions are you using at the boundaries?

[Me_1989]

I use Pressure Inlet and Pressure outlet. Also wall for the outer case and the gears as a solid. The model is 2-D and I also use K-e turbulence model and there is nothing else. In case of dynamic mesh, I use two rigid body for defining the upper and lower gears and also the stationary one for the case of the pump.

[vinerm]

Try with very low rotational speed. The fact is that the flow might be pressure driven and not pump driven. If you get same flow rate even with almost nil rotation speed, then that's what is happening.

[Me_1989]

Good suggestion. But, actually yes, that's true since we use this external gear pump as a turbine on a high pressure line. The problem is that in the experiments, we record different mass flow rate in different input pressures and so we have different rotation speed!

[vinerm]

Then you should simulate it as a turbine; you may use 1DOF for that. And it will certainly show different speeds at different flow rates.

[Me_1989]

How could I use 1DOF? should I use it from boundary conditions to add rotational moving wall? or you mean I have to add something in UDF code of "Define-CG-Motion"?
Would you please just extend your explanation a little bit?

[vinerm]

You have to enable 6DOF under Dynamic Mesh and then you can constrain it to 1D rotation within 6DOF settings. No UDF is needed.

[Me_1989]

I will try it for sure. Thanks a bunch dear Vinerm.


Best Regards

[Me_1989]

Dear Vinerm,

Do you mind if I have another question in this regard?

I try 1DOF rotation but I faces some warnings and so there is no motion in the preview. The warning is: "Warning: unable to read motion history file".

I think the problem is that I have to define the gears (driver and driven) as a solid zone in Gambit. To do so, I defined 3 face comprising Driver gear, Driven gear and the interior region where the fluid flows between the gears as you could see in the image attached. Since the fluid behavior is important for me, I just meshed the region between gears without meshing the inner area of the gears. At last, I defined one fluid zone and two solid zone. I did just like this but when I import the mesh file to Fluent, there is no gears in boundary condition. In other word, the Fluent named them as wall. So, I would be really grateful if I have your recommendation for this problem?

<>

Thank you again

Regards