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-   -   Jet in Supersonic Crossflow, controlling mass flow rate (http://www.cfd-online.com/Forums/openfoam-solving/109136-jet-supersonic-crossflow-controlling-mass-flow-rate.html)

ChrisA November 10, 2012 00:10

Jet in Supersonic Crossflow, controlling mass flow rate
 
I'm trying to model the seeding of a gas in a supersonic cross flow using a modified rhoCentralFoam solver (species conservation equation and diffusion coefficient modelling have been added). The gas is seeded from a small slit on a wedge inserted in a supersonic flow. The wedge is modelled as a flat plate with the incoming flow at the wedge angle. I want to be able to control the mass flow rate of the seeded gas. I've attempted to use FlowRateInletVelocity but, as it mentions in the header file, it's proving to be unstable with the supersonic flow (at least I think that's the issue). Solve attempts would crash shortly after starting, exceeding iterations on temperature.

I have managed to solve the system with the jet specifying velocity as a value at the jet inlet as well as the totalpressure/temperature for the jet. However, the mass flow from the jet rate is not as expected.

Ideally I would like to get FlowRateInletVelocity to work for my case, but I haven't been able to find much information on the corresponding pressure/temperature boundary conditions required to properly model the jet. I've tried quit a few combinations, too many to list here and nearing on exhaustive. I've also tried solving the case, with no jet, to a steady state condition, then turning on the jet and solving from there.

The boundary conditions for the wall that the jet is contained in are zero velocity, zero gradient pressure and the static temperature for the case as a fixed value.

I guess what I'm looking for is some information on how FlowRateInletVelocity would work for my case (if it's even the correct boundary condition) and any tips on the temperature/pressure BC's to hopefully obtain a stable solution or any alternatives that may work better.

Moslem November 12, 2012 05:10

Hi Chris,
Have you found a solution?
I'm eager to know about the B.c.'s for a mixing application I'm working on.

ChrisA November 12, 2012 18:50

I appear to have gotten it to run for my case with no free stream velocity (just the jet discharging to stagnant air). I'm specifying a total temperature/pressure and mass flow rate with flowRateInletVelocity at the jet. It's solving right now and I'll see if the results are as I expect.

As for when I have a supersonic cross-flow above the jet, I still have had no luck stabilizing it.

ChrisA November 13, 2012 19:20

I managed to get it to work with starting the jet from a previous case with an already established shock structure. The mass flux at the boundary is close to what I expect so everything looks good to go!


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