large eddy simulation(LES) for turbomachinary

tengf689 · March 7, 2017, 02:28

Hi all
I have a question for using LES in a turbomachinary. Normally, we impose "Total Pressure","Total Temprature" and "Flow Angle" as inlet boundary conditions (subsonic). So , if I impose these as inlet boundary conditions, how could I impose velocity fluctuations at inlet ?
May I give some fluctuations on Total Pressure or Total Temprature ?? Can anyone gime me the answer or some recommendation?

piu58 · March 7, 2017, 08:35

An easy to implement an obvious way ist to calculate small timesteps and modify the U file in the latestTime dir. Your controldict.startFrom should contain "latestTime".

tengf689 · March 13, 2017, 00:17

Quote:

Originally Posted by piu58

An easy to implement an obvious way ist to calculate small timesteps and modify the U file in the latestTime dir. Your controldict.startFrom should contain "latestTime".

Thank you for your answers ! But sorry, I don't quite understand. Could you please make it clear?

piu58 · March 13, 2017, 00:38

If you start the simulation you have to give initial values for U and p in the 0 directory. After running the simulation for a simulated time you get results in a directory which is named by the simulated time. This contains p and U.
If you change the values to the ones you want to haveand restart the simulation, these values will be used from this simulated time on.

juliom · March 13, 2017, 07:13

I agree with PIU58 the problem with LES are the boundary and initial conditions. For subsonic flows you can specify velocities at the inlet, why don't tu work with velocities instead ? Nonetheless, you can follow PIU58 recommendations.

tengf689 · March 15, 2017, 19:41

Thank you ! I will try it.

tengf689 · March 15, 2017, 19:57

Sorry for late reply. In my simulation, the flow is transonic. I want to use LES method, and compare the result with the experimental data. But in the experiment, the total pressure,total temprature,and flow angle are specified at the inlet. How should I specify the inlet velocities instead ?
I can find the Mach Number distribution at the inlet from the experimental data. Can I get the velocity and static pressure distributions by using isentropic relations ?

piu58 · March 16, 2017, 00:08

> in the experiment, the total pressure,total temprature,and flow angle are specified at the inlet.

In this case you define the pressure at the inlet and the outlet (probably 0 there). For the velocity you give the gradient: zero gradient at the outlet and the gradient according to your inflow angle for the inlet.

March 7, 2017, 02:28	large eddy simulation(LES) for turbomachinary	#1
tengf689 New Member FeiTeng Join Date: Jan 2017 Location: Beijing,China Posts: 12 Rep Power: 9	Hi all I have a question for using LES in a turbomachinary. Normally, we impose "Total Pressure","Total Temprature" and "Flow Angle" as inlet boundary conditions (subsonic). So , if I impose these as inlet boundary conditions, how could I impose velocity fluctuations at inlet ? May I give some fluctuations on Total Pressure or Total Temprature ?? Can anyone gime me the answer or some recommendation?

March 7, 2017, 08:35		#2
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	An easy to implement an obvious way ist to calculate small timesteps and modify the U file in the latestTime dir. Your controldict.startFrom should contain "latestTime". __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

March 13, 2017, 00:38		#4
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	If you start the simulation you have to give initial values for U and p in the 0 directory. After running the simulation for a simulated time you get results in a directory which is named by the simulated time. This contains p and U. If you change the values to the ones you want to haveand restart the simulation, these values will be used from this simulated time on. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

March 16, 2017, 00:08		#8
piu58 Senior Member Uwe Pilz Join Date: Feb 2017 Location: Leipzig, Germany Posts: 744 Rep Power: 15	> in the experiment, the total pressure,total temprature,and flow angle are specified at the inlet. In this case you define the pressure at the inlet and the outlet (probably 0 there). For the velocity you give the gradient: zero gradient at the outlet and the gradient according to your inflow angle for the inlet. __________________ Uwe Pilz -- Die der Hauptbewegung überlagerte Schwankungsbewegung ist in ihren Einzelheiten so hoffnungslos kompliziert, daß ihre theoretische Berechnung aussichtslos erscheint. (Hermann Schlichting, 1950)

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March 13, 2017, 07:13		#5
juliom Senior Member Julio Mendez Join Date: Apr 2009 Location: Fairburn, GA. USA Posts: 290 Rep Power: 18	I agree with PIU58 the problem with LES are the boundary and initial conditions. For subsonic flows you can specify velocities at the inlet, why don't tu work with velocities instead ? Nonetheless, you can follow PIU58 recommendations.

March 15, 2017, 19:41		#6
tengf689 New Member FeiTeng Join Date: Jan 2017 Location: Beijing,China Posts: 12 Rep Power: 9	Thank you ! I will try it.

March 15, 2017, 19:57		#7
tengf689 New Member FeiTeng Join Date: Jan 2017 Location: Beijing,China Posts: 12 Rep Power: 9	Sorry for late reply. In my simulation, the flow is transonic. I want to use LES method, and compare the result with the experimental data. But in the experiment, the total pressure,total temprature,and flow angle are specified at the inlet. How should I specify the inlet velocities instead ? I can find the Mach Number distribution at the inlet from the experimental data. Can I get the velocity and static pressure distributions by using isentropic relations ?