Question

What is the static thrust for an engine as derived from the integral momentum equation?

(a) T = \(\dot {m}\)ue + Ae(pe – p0)

(b) T = \(\dot {m}\)Ae(pe – p0)

(c) T = Ae(pe – p0)

(d) T = \(\dot {m}\)Ae

This question was addressed to me in an interview.

Enquiry is from Jet Propulsion Engine Thrust in portion Integral Form of Conservation Equation for Inviscid Flow of Aerodynamics

Answer 1

Correct choice is (a) T = \(\dot {m}\)ue + Ae(pe – p0)

Easy explanation: Considering an engine in a control volume with ambient pressure p0, exit pressure pe and exit velocity of the fluid ue, the net force is given by:

∑Fx = T + Ae(p0 – pe)

Fx = \(\dot {m}\)ue

Thus, solving the equations we get,

T + Ae(p0 – pe) = \(\dot {m}\)ue

On rearranging the terms we get,

T = \(\dot {m}\)ue + Ae(pe – p0)