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I'm trying to understand why the drag coefficient decreases in the supersonic regime with Mach number. While it is easy show this using supersonic, potential flow theory, I'm looking for a more physical explanation.

My initial thought is, as freestream Mach number increases, the shocks should become stronger (even though they are more oblique, the normal component to the shock is still larger). Where is this train of thought going wrong?

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  • $\begingroup$ Read this and then let me know if anything is still unclear. $\endgroup$ – Peter Kämpf Jul 23 '20 at 21:03
  • $\begingroup$ The answer indicates why wave drag occurs, but I'm still a little unclear on why it would decrease with Mach number. It doesn't really dive into why the drag would decrease, just that drag would occur as Mach number increases to sonic velocity and past it. $\endgroup$ – Nick Hill Jul 23 '20 at 22:12
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    $\begingroup$ With speed well above Mach 1, the change in density is large enough to let the aircraft pass. Only around Mach 1 is the contraction of the streamlines low because the change in pressure and density compensate each other. In fully supersonic flow the change in density is dominant and makes it easier again for the aircraft to squeeze through. $\endgroup$ – Peter Kämpf Jul 24 '20 at 3:17

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