Fluids

Fluids

C-D Nozzle Analysis

    • Ka Ki Yuen
      Subscriber

      I want to see the flow on the downstream side of the nozzle, so I draw a big square behind the nozzle (not sure if it is correct). But the flow pattern is not right. Here's my setting: 

      1. Inlet static pressure: 101325Pa; Inlet total pressure: 120192.9955Pa  (based on Mach=0.5); Inlet temperature: 293K; Ai/A*=1.34
      2. From the geometry, Ae/A*=1.675, so from isentropic flow table (supersonic condition), pressure on exit plane: 15576.84Pa, temperature on exit plane: 171.61K; Expected mach is 1.99~2
      3. the nozzle is build in accordance with Ai/A* and Ae/A*

      In the result, I don't have any flow pattern, and the mach-contour is all in blue.

      Please advice, thanks!!!

       

    • Rob
      Ansys Employee

      A velocity field image (not Mach Number) might help. What is the gas density? Is this 2d or 2d-axisymmetric? 

    • Ka Ki Yuen
      Subscriber

      when I delete the huge rectangle, I can get nice result, although it was inconsistent with my calculation.

      FYI: for air, I set it as ideal gas

    • Ka Ki Yuen
      Subscriber

      and yes, 2D- axisymmetric 

    • Rob
      Ansys Employee

      Picture please. As a guess your initial condition isn't very good. With pressure in & out the mass flow becomes part of the solution, and with ideal gas that'll get even messier. What is your operating pressure?

    • Ka Ki Yuen
      Subscriber

    • Ka Ki Yuen
      Subscriber

      this setting is sightly different from what i've post but if i put this setting to the model with big rectangle, is doesn't work too

      without the rectangle, the contour is like this

    • Rob
      Ansys Employee

      With the box the core downstream of the nozzle will be moving, but the remainder of the region won't. 

    • Ka Ki Yuen
      Subscriber

      sorry I am new to ANSYS, didn't catch you quite well...so if I wanna investigate the flow behind the nozzle (oblique shock or expansion wave), how could I set up the simulation? I've read some articles, they have something like this:,

      but I have no ideas how to setup this properly...

    • Rob
      Ansys Employee

      As you have been, but you may need to patch a higher velocity region in the jet zone. 

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