Question

Select the incorrect statement out of the following.

(a) limτs→0⁡ is the case of an incompressible flow

(b) Speed of sound in incompressible medium is zero

(c) Mach number for finite velocity object, in incompressible flow is zero

(d) Incompressible flow is theoretically zero-Mach number flows

The question was asked in exam.

The query is from The Basic Normal Shock Equations topic in division Normal Shock Waves of Aerodynamics

Answer 1

Right choice is (b) Speed of sound in incompressible medium is zero

To explain I would say: Incompressible flow is the limiting case of isentropic compressibility being zero. This gives an infinite speed of sound and a zero Mach number in that medium. Thus, theoretically, zero-Mach number flows are incompressible.