Learning Forum

[mmmaada00]

I am trying to simulate a 2D inviscid external compression intake to study the effect of different back pressures on the position of the normal shock within the intake duct/throat. Using a density based solver.

The boundary conditions are as follows:

• Pressure inlet with inputs signifying Mach 2.2.
• Pressure farfield for the external domain.
• Pressure outlet at the exit of the intake with static pressure applied.

The problem is that the flow at the exit of the intake is still wholly supersonic and therefore FLUENT ignores the pressure outlet BC and no normal shock is formed in the duct. I have attached a screenshot of the result.

How do I solve this issue?

Any help will be greatly appreciated, thanks!

[RK]

Hello,
Can you please give a brief description of the problem setup? What are looking to achieve using simulation? Thanks!

[2587521004]

I have the same problem here.

[mmmaada00]

I am trying to achieve a normal shock across the inlet/throat which will decrease the flow to subsonic conditions in order to compare the pressure recovery of different external compression geometries after the shock system. This normal shock should be achieved by imposing a back pressure at the outlet, however ANSYS is ignoring any condition I impose there - no matter what pressure I set. I believe there may be an issue with the problem initialisation as the flow starts supersonic through the whole domain and therefore the back pressure is ignored? Although when I change inlet conditions to subsonic and set a back pressure, I get reversed flow across the outlet.
The setup is a steady inviscid density based solver with ideal gas law for density. Implicit formulation and second order upwind for the flow. The reference values and solution initialisation are computed from the pressure inlet at Mach 2.2.
An example of what I am trying to achieve is this:
Where the normal shock will change location based on the value of the back pressure ratio.
Thanks for any help!

[mmmaada00]

here is a good example of the flow structure I am trying to achieve

[mmmaada00]

Hi
Did you ever manage to solve this issue?

[2587521004]

Yes I did. Try use k-w sst mode, make sure wall y+ is lower than 30.

[mmmaada00]

Using the k-w SST model, a normal shock does form but eventually moves out of the front of the intake rather than sitting across the throat/entry. Did you encounter this issue? How did you fix it?

[2587521004]

I never had that kind of problem. Sounds like you need to reduce the static pressure of pressure outlet.