Page History

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• Obtain the diamond shocks on a nozzle using an axisymmetric geometry.
• Apply more advanced concepts of Compressible Flows and generate a more sophisticated simulation
• Qualitatively verify the CFD results from FLUENT by comparing the contour plots to the expected shape. The Verification & Validation section will give insights on how one could get a more precise comparison with real data and other more accurate simulations.

Problem Specification

We want to simulate an over-expanded nozzle in FLUENT, and try to obtain the this cool "Diamond Shock" pattern shown in the this figure below:

For that, we need to design a Nozzle that has a measured exit pressure smaller than the ambient pressure.  Therefore, This means that the nozzle is "too big" and ended will end up expanding the flow too much.

The flow , trying to accommodate to that will form exits the nozzle with a lower pressure, and will try to accommodate to the higher ambient pressure, forming an oblique shock outside the nozzle. The shock will then reflect "on the axis" (on another shock instance, actually), and the reflected shock will now make the pressure become too high (compared to the ambient). This will lead to expansion waves, making the flow with the correct pressure again. These expansion waves, however, will reflect "on the axis" as well, dropping too much the pressure of the flow, what will lead to another oblique shock, like the first one. This is then repeated, resulting on a series of diamond shaped shocks/expansion waves.

Another characteristic of over-expanded nozzle is that the "plume" of the jet gets contracted, opposed to an under-expanded nozzle where the plume "diverges" in the radial direction. 

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