The purpose of the inlet in a ramjet engine is to slow the incoming air to subsonic conditions so that it can be mixed and reacted with the fuel. Often, this is accomplished via a system of shock waves that are stabilized in the inlet. As an example, consider the compression process taking place in the inlet of a ramjet engine pictured in Figure 9.47. Two oblique shocks followed by a normal shock are used to decelerate the Mach 3.5 flow. The aircraft is flying at \(10 \mathrm{~km}\), where the static pressure and temperature are

\(26500 \mathrm{~N} / \mathrm{m}^{2}\) and \(223.3 \mathrm{~K}\), respectively. Assume that the flow is two-dimensional.

a. Determine the Mach number, static temperature, static pressure, and total temperature and total pressure at each stage of the compression process (i.e., from stations 1 to 4 ).

b. Compare the compression process with that due to a single normal shock.

c. Make a T-S diagram (Temperature-Entropy) for the compression process in the inlet.
i. Compute the entropy change across each shock.
ii. Plot the static temperature (y axis) against the entropy for each part of the flow field. (Choose the initial value of the entropy equal to zero.)
iii. Add contours corresponding to the total pressure at each station.
iv. How does this compression process compare to the "ideal" process?
v. Compute the total pressure and entropy change if the inlet was replaced with a single normal shock.
vi. Add the normal shock to your T-S diagram.
vii. Would you want to use a normal shock to do the compression instead of the shock system?

Transcribed Image Text:

M = 3.5 2 MA 30 10 Figure 9.47 Sketch of a planar ramjet inlet showing shock and expansion wave structures.