Question

At which point is the initial data taken for nozzle flow?

(a) Downstream of the limiting characteristic

(b) Upstream of the limiting characteristic

(c) Expansion region

(d) Straightening section

This question was posed to me during an internship interview.

This intriguing question comes from Supersonic Nozzle Design in section Numerical Techniques for Nonlinear Supersonic Flow, Elements of Hypersonic Flow, Couette and Poiseuille Flow of Aerodynamics

Answer 1

The correct choice is (a) Downstream of the limiting characteristic

Easy explanation: For solving method of characteristic, it is important to choose an initial point where the flow field properties are known. The method os characteristic can thus be used to find the flow downstream point by point. For nozzle flor or internal flow, the initial point is taken downstream of the limiting characteristic which is approximately slightly downstream of the sonic line.