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popezmark June 26, 2011 10:16

Wave Rotor simulation
Hi everyone!
I'm an OpenFoam rookie and I'm tryng to use it for my thesis regarding the so called "Wave Rotor". I think you know what I'm talking about better than me, nevertheless I'll try to explain. The device is a cylindrical rotor with a certain number of straight channels. The rotor in enclosed in a case with ports that permit the passage of fluid through the channels. The rotor rotation ( :D ) determines the opening and closure of the inlet and outlet of the channels. The Wave Rotor can be used in a turboengine essentialy in two ways:
1) 4 port Wave Rotor ( NASA studies this case for 20 years) : the Wave Rotor is connected with the compressor (inlet), the combustor (inlet for hot gas and outlet for compressed air) and the turbine (outlet low pressure gas). The rotor work as a pressure exchanger, fresh air from the compressor enters the WR and is compressed by the hot exhaust gas coming from the combustor. The hot exhaust gas is then expanded (and cooled) and exits the WR to the turbine.
2) 2 port Wave Rotor Combustor : in this case the WR replaces entirely the combustor; the fresh air comes from the inlet (compressor) and in the channels, when inlet and outlet are closed, we can perform a costant volume combustion. The exhaust gas exit from the outlet and reach the turbine.
I hope I've explained clearly with my terrible English! :)
I want to perform a series of simulations of this two cases, starting with the first. I want to make a first very simple 2d approximation of a single straight channel of the rotor. At the instant 0, in the channel there is fresh low pressure air (zero velocity), the outlet is CLOSED, and from the inlet flows inside hot high pressure gas. I expect the formation af a shock wave moving from the inlet to the outlet and reflecting back, and of course there will be a contact surface between the two fluids at different temperature. An istant BEFORE the shock wave is reflected back, the outlet is opened, and the simulation go on with other fases...
So, I need to simulate a highly transient, compressible and probably turbolent flow, and I need to change the boundary conditions at inlet and outlet at specific istants (sigh!)
- Can you please suggest me what solver is more suitable for this application? I think of rhoPisoFoam with LES for turbolence, similar to the tutorial PitzDaily, but I note that in the new OpenFoam 2.0 this solver is no more... maybe rhoPimpleFoam?? And how can I describe correctly the conditions (pressure, temperature and velocity) at the boundary inlet and outlet?
- What are alphSgs, B, k, muSgs, muTilda? Can you suggest me some good information source to understand how rhoPiso (or rhoPimple) works? I coldn't find any...
- How can I perform the changing in course of the boundary conditions?
Thanks for your attention, I can't wait to read your answers! :)

immortality January 9, 2013 07:29

hello dear Marco
Im simulating wave rotor with rhoCentralFoam and by groovyBC and I want to obtain tokyo university results by Dr.Nagashima and Dr.Okamoto.
but I before that tried to simulate their experiment that the right wall is closed and some errors I reached so far.could you help me about this simulation?

immortality March 27, 2013 10:59

hello dear Marco
I have a doubt about timing of opening of air side port in high pressure part.
when primary shock wave
reaches to air exit port(in high pressure part) it should be fully
opened and whole of primary shock reflects of this port as secondary
shock,am I right?
if its so,the wall should begin to open when the primary shock has not
reached yet,and because of high pressure at air port side a shock wave
starting coming in the channel from air side before primary shock
reaches.isn't it correct?

9007754 November 13, 2013 05:42

wave rotor flow simulation
My thesis is on simulating flow in wave rotor.I think when primary shock reaches the end of the channel, the left port opens and we have reflected shock
i have problem in boundary condition,whether we have constant pressure in boundaries or we should obtain some of them?

immortality December 5, 2013 12:33

Hi Mahmud
on the entering ports you should set total pressure be constant and on the right(outgoing ports) pressures be constant and the solver calculates the velocities.
which dimensions and flow parameters you want to model?which experiment?

9007754 December 11, 2013 05:29

Hi immortality
I knew that, but all the efforts in this application is to find pressure not to force or maintain a specified pressure in the outlet, i think our simulation should be consistent,meaning that we must search for some limitations or criterias in the outlet and let the pressure be obtained according to that criterias. For instance we know that the maximum pressure drop in the combustion loop should be 5%.

immortality December 11, 2013 09:42

all conditions you set at outlet should satisfy CFD constraints in numerical aspects.
in outlet you should set pressure,its more stable than for example velocity there,but you can test it yourself.if you want to set 95% of the inlet pressure to outlet again you have set pressure there. a questionable problem is that what experiment or numerical results you want to follow in doing the thesis?
which university you were? and who is your adviser?

9007754 December 13, 2013 14:52

I am studying propulsion in khajeNasir university, my adviser is dr ebrahimi.Thank you for replying my question but i think in this problem we should have consistency.i want to know the strength of two shocks in my simulation,not to fix them with for example Prw=1.8

immortality February 4, 2014 19:00

do you obtain the total pressure of flow behind of reflected shock larger than total pressure of driver gas? is there an experiment like sod for reflected shock strength?

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