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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

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