# Stability Problem with sonicFoam for Nozzle Flow

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 June 19, 2009, 05:25 Stability Problem with sonicFoam for Nozzle Flow #1 Member   Julian Krick Join Date: May 2009 Location: Guelph Posts: 88 Rep Power: 9 Hi, I have a stability problem in my flow simulation. Here's the configuration: I'd like to simulate the flow air through a convergent-divergent nozzle. The geometry starts at the inlet and stops at the outlet of the nozzle. The flow should be critical in the throat. For this I use a pressure difference of dp=300mbar, whereas at the inlet I apply atmospheric pressure. The the calculation I use the sonicFoam solver with 2nd order, bounded interpolation schemes (limitedLinear with phi=1/0.5 and MUSCL) for the divergence terms. I set the BCs as follows: /0/p: Code: ``` inlet { type totalPressure; p0 uniform 1.01325e+05; U U; phi phi; rho none; psi none; gamma 1.4; value uniform 1.01325e+05; } outlet { type fixedValue; value uniform 0.71325e+05; }``` /0/U: Code: ``` inlet { type pressureInletVelocity; value uniform (0 0 0); } outlet { type zeroGradient; } wall { type fixedValue; value uniform (0 0 0); }``` What happens is the following: The simulation starts fine. The p-, U- and T-fields develop as they should. Shocks occur, which cause a separation of the boundary layer resulting in a creation vortices, which are eventually transported towards the outlet. However, at some point the solution becomes unstable. At the outlet there is a drastic increase in velocity and pressure (of order > 10^30). Also negative pressure occurs near the outlet. Then the simulation crashes. I suppose the reason for this effect is the BC at the outlet. What I could do is to fix the pressure, velocity and temperature at the inlet and have 'zeroGradients' at the outlet. However, for my analysis it is necessary to induce the flow via a pressure difference between inlet and outlet. __________________ grid generation: ICEM CFD 13.0 solver: CFX 13.0

 June 19, 2009, 08:42 #2 Member   Julian Krick Join Date: May 2009 Location: Guelph Posts: 88 Rep Power: 9 As suggested by prapanj in this thread (Pressure Inlet Velocity) I used the 'waveTransmissive' BC for the pressure at the outlet. Now, the simulation seem to be stabilized, however it's still running so that, yet, I cannot tell if it works. I hope so . __________________ grid generation: ICEM CFD 13.0 solver: CFX 13.0

 June 29, 2009, 19:46 #3 New Member   Giro Join Date: Mar 2009 Posts: 13 Rep Power: 9 Hi I try to solve nozzle-flow and my sample-files are opened on my URL. http://giropenfoam.web.fc2.com/sample/index_sample.html This is how you can help?

 July 2, 2016, 04:57 LES sonicFoam #4 New Member   SIAN Join Date: Jun 2016 Posts: 5 Rep Power: 2 Dear Foamers: I need help in sonicFoam solver. I am working on a project with sonicFoam and an example like shocktube. I have run it with RAS turbulency model but the results have bad errors. I want to solve it with LES but I don't have the related files. who has the below files related to LES shocktube : 1- fvSolution 2- fvSchemes I need your helps please....

July 11, 2016, 08:14
#5
Member

Bruno Blais
Join Date: Sep 2013
Posts: 55
Rep Power: 4
Other than people trying to steal your topic, how did you results end up?

It seems like you had a bad case of a boundary condition polluting your simulations, which happens a lot for compressible flows.

Quote:
 Originally Posted by Julian K. As suggested by prapanj in this thread (Pressure Inlet Velocity) I used the 'waveTransmissive' BC for the pressure at the outlet. Now, the simulation seem to be stabilized, however it's still running so that, yet, I cannot tell if it works. I hope so .

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