We are currently working on CFD solutions on ANSYS Fluent for the drag on our sounding rocket. We are modeling its drag profile through out its velocity range. We currently hit a top speed of approx 290m/s.

At subsonic speeds, as expected for a streamlined body, the component of viscous drag is greater than that of pressure drag.

When we performed simulations at 0.7,0.8 mach, the component of pressure drag is greater than that of viscous drag.

Is this what should happen at such high speeds?

We've been using the k-epsilon model with standard wall functions for all the simulations. We only accept the solution if the residuals are below e-5 and the drag coefficient has become constant. This occurred for our transonic simulations.

After post processing the results, there seems to be no separation of the boundary layer and the flow doesn't expand enough for it to accelerate to the speed of sound(so no wave drag).

So finally what I'm asking is, does pressure drag dominate at these high speeds vs viscous for a streamlined body, or is our solution wrong?

Edit: Misused the word transonic, so removed it.

Thank you.

  • 2
    $\begingroup$ What do you mean by "the flow doesn't expand enough for it to accelerate to the speed of sound"? If the flow is transonic, by definition there is a place that the flow becomes at least sonic. Otherwise it is still just subsonic. $\endgroup$ – tpg2114 Sep 27 '19 at 19:59
  • $\begingroup$ What I meant was, unlike in an airfoil, the flow is not reaching the velocity of sound when it is expanding over certain surfaces. Hmm so if it is still subsonic,does that mean our solution is wrong? $\endgroup$ – Rishi Chauhan Sep 28 '19 at 5:49
  • $\begingroup$ Also, thank you for the clarification on the transonic bit. Messed that up didn't I. $\endgroup$ – Rishi Chauhan Sep 28 '19 at 6:04

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