Direct measurement of high frequency, solid propellant, pressure-coupled admittances

This paper presents an experimental method that is capable of directly measuring solid propellant pressurecoupled responses at the high frequencies associated with tangential mode instabilities inside solid propellant rocket motors. The method utilizes a magnetic flowmeter to measure the velocity oscillation above a burning propellant surface simultaneously with a pressure oscillation measurement within an externally excited combustion chamber. A magnetic flowmeter burner was designed and constructed to evaluate this method of pressurecoupled response measurement. Response measurements were obtained for two formulations of AP/HTPB composite propellant at pressure oscillation frequencies of 4000 and 8000 Hz. The measurement data displayed repeatable trends in both the real and imaginary parts of the pressure-coupled response function.