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-   -   Shock wave Capture in a C-D Nozzle (http://www.cfd-online.com/Forums/cfx/116139-shock-wave-capture-c-d-nozzle.html)

F C April 13, 2013 19:12

Shock wave Capture in a C-D Nozzle
 
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I have been assigned the Sajben Transonic Diffuser, in which I am attempting to solve in Ansys CFX as a 2D case in Ansys 14.5, so far I have been unable to capture the shock wave which occurs in the nozzle.

Below is the link to the studies which can be found at the bottom of the page
http://www.grc.nasa.gov/WWW/wind/val.../transdif.html

With my set up I am running Similar conditions to the the studies

Inlet Velocity: 300m/s (~0.9 Mach)
Inlet Temperature: 500R (277.78K)
Inlet Pressure: 19.58 psia (134.999 kPa)
Outlet Pressure: 14.1 psia ( 97.21 kPa) This pressure is reported to create a strong shock wave

Turbulence Model: SST
Heat Transfer: Total Energy

I am currently using a structured mesh which is approximately the same density that is used by the studies, however I think this may not be dense enough to capture the shock wave.

I am now using a Transient Simulation which is working much better and getting me close but in regards to the convergence of the simulations, they get very close to the simulation criteria, 1E-05 in my case however heat transfer generally just floats right above this value which stops it fully converging.

I am currently thinking that it may be due to my mesh being too coarse, and I am now attempting a finer mesh but it may be a while before I obtain results!

Any help is appreciated

Many Thanks

Farzad

ghorrocks April 14, 2013 07:21

This FAQ is written for the zillions of posts whch ask this question on steady state simulations: http://www.cfd-online.com/Wiki/Ansys...gence_criteria

Most of the comments are relevant to your transient simulation.

Have you checked that you require convergence to this tolerance? I bet you will find that you do not need to converge this tightly for a transient simulation, and then your problem will disappear.

hesamking October 1, 2013 14:39

Farzad Jan,
How did you give both pressure and velocity at the inlet?
Do you mean you set either pressure or velocity in the initialization setting and
specified the other one at the inlet?
By the way, looking at the problem it seems that you can solve it as subsonic. why did you use Total energy?
have you been able to solve it?
thanks,

amalthevj November 29, 2013 03:23

Hello Farzad,

I am trying for a simulation just like yours,if you have problem in getting shocks,try the back up results from steady state analysis and of course in my view mesh should be fine enough for it.Then try using inlet conditions as mass flow rate as it's more robust in CFX..You can give pressure inlet conditions,but in most of the cases ,while running solver it shows message"Wall has been placed at portion of inlet".Its not weird,it do generate results.but i don't know how much its accurate......


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