Acoustically Induced Shock Oscillations in a Low-Boom Inlet

Abstract

Experimental unsteady centerbody surface pressures measured in a low-boom inlet have been analyzed and compared with an unsteady computational flow approach. The experimental dataset was gathered at the 8 × 6 ft supersonic wind tunnel at the NASA John H. Glenn Research Center in 2010. The axisymmetric external compression inlet considered herein featured a relaxed isentropic centerbody compression spike followed by a short subsonic diffuser to the aerodynamic interface plane. The axisymmetric inlet computational domain comprised a 10 deg sector, starting with the freestream inflow region, and included both the internal flowpath up to the mass flow plug and the external flow past the sharp-edged cowl for external flow. The selected inlet test conditions were based on a 1.67 freestream Mach number at a zero angle of attack with a near-design spillage rate of approximately 4%. Both experiments and simulations revealed temporal shifts between pressure peaks at different streamwise locations, indicating upstream-running compression waves that moved at acoustic speeds. These waves became amplified near the geometric throat and produced streamwise oscillations of the external normal shock. The simulations also revealed a second smaller shock on the centerbody at the geometric throat, for which the complex dynamics suggested an opportunity for further study. Nomenclature a = speed of sound D = diameter L = length N = number of unsteady pressure readings p = pressure r = radial direction coordinate t = time u = streamwise velocity component x = streamwise direction coordinate y = normal direction coordinate z = spanwise direction coordinate τ = timescale Subscripts AC = acoustic AIP = aerodynamic interface plane CB = centerbody cowl = inner cowl diff = averaged over low-speed diffuser end = wave end peak = local peak RMS = root mean square sh = shock start = wave start tip = spike tip ∞ = freestream condition Superscripts 0 = fluctuation = normalized

Analysis of shock oscillations of an external compression supersonic inlet through unsteady numerical simulations

“…In the aforementioned studies, no attempt in simulating the flow regime at which little buzz takes place has been reported. The most advanced study dedicated to hybrid RANS-LES simulation of little buzz is due to Candon et al [12]. Those author focused on a low-boom cylindrical external compression inlet for which shock oscillations have been seen to take place for a mass flow ratio close to the design configuration.…”