Preliminary Investigation of Stagnation Point Liquid Injection Influence on Blunt Body Aerodynamics

A preliminary investigation has been performed to determine the influence of stagnation point water injection on the hypersonic aerodynamic forces and moments for two-dimensional blunt bodies. This investigation was performed in the Langley 20-Inch Mach 6 Air Tunnel, and represents the qualitative first phase of a study to examine the potential benefits of water injection to reduce aerodynamic drag and aero-heating. Tests with a 4-inch diameter hemisphere cylinder and a 4-inch diameter cylinder with a span 1.5 times the diameter were performed over a range of free-stream unit Reynolds number from two million to six million per ft and of angle of attack (-5 deg to 5 deg) with water and gaseous nitrogen injection at the geometric stagnation point. The momentum flux ratio, that is, the ratio of the momentum flux of the jet to that of the free-stream flow, was varied from the non-blowing value of zero up to 0.00031 by maintaining the jet momentum fixed and varying the free-stream momentum, hence Reynolds number. The effect of water injection on the aerodynamic drag coefficient for the hemisphere cylinder was observed to be negligible as the momentum flux ratio was increased to 0.00017, but decreased significantly as this ratio increased above 0.00017; a nearly 50 percent reduction in drag occurred for a factor of two increase in momentum flux ratio.