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D.Stratmann January 22, 2001 04:35

shocks / oblique reflection
hello cfd`ler !!!

a) thanks to mr Chien, Larsson and alain for our help

b) situation / case : i want to simulate the internal flow through very thin duct. it consists of an nozzle and a diffusor. indeed it is a model for an air gap in a compressor with a gap depth of 0.4

mm (nozzle > gap > diffusor). inlet pressure is 2 bar and outlet pressure 1 bar

experience data :

as we detected from experience there is a transient flow. as the flow-speed increases and reaches the gap, there appears a shock that is refleceted at the walls several


please visit :

question :

1) should i use turbulent simulation for these velocity ? ( v > 1.3 Ma)

2) Does anyone have similar kind of streaming phenomedia (espacially shocks / refection) using fluent ? i would like to look foward any suggestions and data

3) can i continue a laminar calculation switching then to turbulent ?

4) i calculated laminar flow (becaus the cell reynolds numbers in the gap are < 1), but the residuals are running horizontal (even after 100.000 iterations). the values are between 1e-03 and 1e-06. Does this mean that there is no static solution (using 2nd order scheme, because any shocks dissapear using 1st) ?

many thanks for any kind of commentary

dirk (university of dortmund, germany)

John C. Chien January 22, 2001 05:22

Re: shocks / oblique reflection
(1). I do not know whether the code you are using can solve this problem or not. (2). So, the best way to do is to contact the support engineer first. So, that they can tell you how to use their code in the best way. (3). I don't know what's in the code. It's hard to tell you whether the turbulence model will give you a better result. (4). As a user of a commercial code, the best you can do is to refine the mesh to see if you can get a better result. (you have to determine what is a better result.) By the way, what you are getting is fairly common. Fluid dynamics problems are very difficult problems to solve, especially with the presence of shocks.

Vitaliy Pavlyk January 23, 2001 04:12

Re: shocks / oblique reflection
Hello, Dirk!

I have looked at the link to your Project. Please, what is a "trockenlaufende Schraubenmaschine"?

thanks, Vitaliy.

D.Stratmann January 23, 2001 05:06

Re: shocks / oblique reflection
sorry, but the description on this page is only in German. sorry about that.

"trockenlaufende Schraubenmaschine" is an screw-type machine (compressor). in most cases it is used as an compressor for gases, i.e. air. "trockenlaufend" means that there is no oil in the working area of the machine. these machines are also available to work with oil. you can also use this machine as an engine. this vision has been developed by my prof, mr k. kauder.

do you know this machine ? or more information ?

are you something like mechanical engineer ? if not, it becomes more difficult ? but to solve this fluid flow problem it does not matter...


dirk (university od dortmund, germany)

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