How can I set velocity in the outflow?

- May 21, 2019 at 1:49 pm
  
  jack1wang
  Subscriber
  
  I am doing a simulation of the fluid dynamics in a water supply tank. The geometry and meshing have been done. The tank has only one inlet and one outlet. Now I have only the observed data of initial water level, inflow velocity and outflow velocity. How can I set velocity in the outflow? Define the outlet boundary condition as a velocity inlet?
- May 21, 2019 at 2:00 pm
  
  Kalyan Goparaju
  Ansys Employee
  
  You can impose a velocity inlet boundary condition on your outflow plane. In the input options, select Magnitude as the velocity specification method and input a negative velocity value.
  
  Please be very sure that this is exactly what you want as two velocity BC's is not a recommended boundary condition pair.
- May 22, 2019 at 1:23 am
  
  jack1wang
  Subscriber
  
  Hello Kalyan Goparaju,
  
  Sry for the late response. I have tried the velocity inlet BC for my outlet, but the volume balance in the tank is a bit strange and the simulated volume variation shows a significant difference against the observed one. Is it caused by two velocity BCs in the model?
- May 22, 2019 at 4:57 am
  
  DrAmine
  Ansys Employee
  
  Yes that might be caused by this combination. Does your run include more than one phase?
- May 22, 2019 at 5:10 am
  
  jack1wang
  Subscriber
  
  Hello Amine,
  
  Yes. It is a multiphase model with water (bottom) and air (top) in a storage tank.
  
  Best regards,
  
  Zhenyu
- May 22, 2019 at 6:14 am
  
  DrAmine
  Ansys Employee
  
  Velocity at outlet would only work if only one phase is leaving that outlet othersie it does not make sense. Moreover as my colleague highlighted if you are providing inflow and outflow velocities of the water phase into the system it might be overconstraining the problem.
- May 22, 2019 at 6:42 am
  
  jack1wang
  Subscriber
  
  In my case, the inlet is in the air phase at the top while the outlet at the bottom is submerged by the water phase. Therefore, only the water phase is leaving the outlet. Is the air caused the problem?
  
  Best regards,
  
  Zhenyu
- May 22, 2019 at 9:21 am
  
  DrAmine
  Ansys Employee
  
  How are you evaluating the run? Do you have an outlet somewhere for the air? As I said velocity outlet is only sensible if only one phase is leaving that.
  
  Add more details about the model, BC, Geo, Mesh..