Compressible fluids

prajputprajput Admin Posts: 304

Hello Folks,

I recently started getting in to the area of Fluid Dynamics. I noticed that most textbooks divide the discussion of fluid behavior into two major segments: Incompressible and Compressible. Within compressible, there is further division based on whether the velocity of the fluid flow is slower or faster than the speed of sound. Being a beginner, I am unable to get my head around how the physics of fluid flow is different if its velocity is greater than speed of sound. can someone explain what happens in this regime?

This forum is a great place to get help. Thank you Ansys for creating such a wonderful platform to encourage technical discussions!


  • kkanadekkanade Forum Coordinator Posts: 3,088

    Hello @prajput ,

    For supersonic motion i.e when the speed of the fluid flow is greater than the speed of sound, the interaction between a body and the fluid will result in the formation of shock waves. A shock wave is a extremely thin region (of the order of the fluid molecules mean free path) where abrupt variations of the fluid properties happen. Moving across a shock wave the velocity drops, while pressure, temperature and density suddenly increase. Over the years, scientists were able to formulate analytical relations that can be used to determine how large those variations would be.

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  • prajputprajput Admin Posts: 304

    Hello @kkanade  ,

    Thank you very much for the response. So, if I understand correctly, as the air moves around a supersonically traveling object, shock waves are created. Is that correct? If so, are there different types of shock waves depending on high the velocity is?


  • kkanadekkanade Forum Coordinator Posts: 3,088
    Yes, That is correct. There are different types of shock waves, but their formation is not just dependent on the speed of the moving object. It depends on the object's geometry and other parameters. The most common forms of shock waves are the normal shock, the oblique shock and the bow shock. 
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