Question

What is the slope for C– characteristic line?

(a) u + a

(b) u – a

(c) ua

(d) \(\frac {u}{a}\)

I have been asked this question in an interview for job.

Origin of the question is Finite Waves topic in chapter Unsteady Wave Motion of Aerodynamics

Answer 1

Correct choice is (b) u – a

The best explanation: At a point (x,y) in an x – y plane there exists paths through this point known as C+ and C– characteristic lines. They represent the path of sound waves which are left and right running. The slope for a C– characteristic line is given by u – a and for C+ characteristic is u + a.