Ka. Juhany et al., INFLUENCE OF INJECTANT MACH NUMBER AND TEMPERATURE ON SUPERSONIC FILM-COOLING, Journal of thermophysics and heat transfer, 8(1), 1994, pp. 59-67
The current work is an experimental investigation of the dependence of
film cooling effectiveness on the injection Mach number, velocity, an
d mass flux. The freestream Mach number is 2.4, and the injection Mach
numbers range from 1.2 to 2.2 for both air and helium injection. The
adiabatic wall temperature is measured directly. The injection velocit
y and mass nux are varied by changing the total temperature and Mach n
umber while maintaining matched pressure conditions between the inject
ed flow and that of the freestream. The total temperature of the frees
tream is 295 K, and for the injection it ranges from 215-390 K. The re
sults indicate an increase in film cooling effectiveness as the inject
ion rate is increased. With the exception of heated helium runs, large
r injection Mach numbers slightly increase the effective cooling lengt
h per mass injection rate. The results for helium injection indicate a
n increase in effectiveness as compared to that for air injection. Hea
ted injection, with the injectant to freestream velocity ratios greate
r than 1, exhibit a rise in wall temperature downstream of the slot re
sulting in effectiveness values greater than 1. The experimental resul
ts are also compared with earlier studies in the literature.