Question

For the flow over an airfoil, which of the following is the incorrect statement if the fluid is liquid?

(a) High pressure change

(b) Incompressible fluid

(c) Compressibility is very small

(d) Density is constant

I got this question during an internship interview.

This interesting question is from Definition of Compressibility topic in section Compressible Flow – Preliminary Aspects of Aerodynamics

Answer 1

The correct option is (a) High pressure change

The best I can explain: The pressure change can be both high or low and we can’t ascertain it with the given information. Moreover, for liquids the compressibility is negligible and so we can assume that density change is also small. Hence, the flow is compressible.