Learning Forum

[D L]

Hi everyone, I am trying to study the effects of a moving body on the pressure drop of a fluid flowing within the moving body. The moving body should be undergoing rigid body motion. I have tried many ways to simulate this but I am having trouble getting it to work properly. I will list the methods I have tried thus far below.

Method #1:

I created a DEFINE_ZONE_MOTION UDF that models constant acceleration and added it to "mesh motion" in "cell zone conditions" for my solid. I then used a transient solver to be able to capture the difference in velocity with respect to time. This worked well for lower acceleration values for a while but as I increased the acceleration, the pressure drop started to remain constant, which should not be the case. I tried reducing time step and overall transient time but neither solved this issue.

An example of the UDF used is this:

#include "udf.h"
 DEFINE_ZONE_MOTION(acceleration_2_neg,omega,axis,origin,velocity,time,dtime)
{
 real a = 2.0;
 real cruise = 60.0 / 3.6;
 real currentvelo;

 if (time <= cruise / a)
 {
 currentvelo = a * time * -1.0;
 }
 else
 {
 currentvelo = cruise * -1.0;
 }

 N3V_D (velocity,=,currentvelo,0.0,0.0);
 return;
}

 

Method #2:
I tried to add a constant translational velocity to "mesh motion" in "cell zone conditions" for my solid. The problem with this is that no matter what magnitude I put as the velocity, the outlet pressure of the fluid remains constant as well.

Method #3:
I tried using a DEFINE_GRID_MOTION UDF and attached it to the solid via dynamic mesh. However, I can't get this to run at all because I will encounter a negative cell volume issue. I am reluctant to use dynamic mesh too because it would take way too long to process.

 

Are there other possible ways to add rigid body motion to a solid? My mentor suggested to simply use boundary conditions to add a constant velocity to the solid wall but I cannot find any way to do this directly within the software.

Any help will be greatly appreciated, thank you in advance! 

[Rob]

If the body is moving at a constant speed what is driving the fluid flow? Please can you post some images of what you're wanting to model?

[D L]

Here is an image of what i am trying to model:

The green part is the solid and the orange part is the fluid. The fluid flows in from the left inlet at the top and comes out from the right outlet. The main driving force is pressure where the initial pressure at inlet is 40000Pa gauge.

[Rob]

How does the solid motion alter the flow?