Learning Forum

[cyassopoulos]

Problem Statement

Description of Physical System

For the physical system, a pump will be used to send a fluid at a defined inlet temperature and flow rate into a loop. After a predetermined volume of fluid is pumped into the loop, a valve will close so that only a fixed volume of the liquid is flowing within the loop. Also, within this loop, another pump will continuously pump the fluid at the same inlet flow rate. I hope this description is clear. 

CFD Requirements

The team would like to use Fluent within ANSYS to simulate and analyze this system. Ideally, we would like to do a transient study, but if this is overly complicated, a steady-state analysis of the flow in the closed-loop is also acceptable. We are having trouble with two key areas of the simulations:

1.     For the steady-state analysis – imposing boundary conditions that model closed-loop flow

2.     For the transient analysis – imposing boundary conditions that model a valve opening and closing

For the closed-loop flow, we originally made a small cut in the loop to create two surfaces. We defined one surface as the inlet with a defined fluid velocity. We then defined the other surface as an outflow boundary condition. However, this led to a massive drop in pressure across the loop that seems unrealistic for closed-loop flow. I think the error may be that Fluent is assuming the outflow is open to atmospheric pressure when in reality the outlet would be flowing into a pump to go through the loop again.

Similarly, for the transient analysis, we are not sure how to define time-dependent boundary conditions. Or how to define a boundary condition that simulates a valve turning off to stop the flow into the loop.

Any insight on how to solve these problems would be greatly appreciated. Thanks.