Magnetic flowmeter measurement of pressure-coupled response of a plateau solid propellant

A magnetic flowmeter was used to measure the pressure-coupled response of a plateau solid propellant. The magnetic flowmeter measures the one-dimensional acoustic gas velocity as a function of the height above the surface of a burning-propellant strand subjected to forced pressure oscillations. The unsteady gas velocity was measured by externally imposing a strong magnetic field in a region containing the propellant surface. The combustion product gas has sufficient ionization to be electrically conductive and generates an electrical potential proportional to the gas velocity in a direction perpendicular to both the magnetic field and the gas velocity and measured by two electrodes at the edges of the combustion gas flow. The position of the propellant surface relative to the measurement station was measured with an ultrasound transducer. The acoustic velocity, together with an acoustic pressure measurement as a function of distance above the burning propellant, was combined with a one-dimensional acoustic analysis of the flow to obtain the acoustic admittance at the propellant surface and thus the propellant response. Responses were measured at pressures up to 2000 psi (13.8 MPa) for frequencies between 300 and 1800 Hz. Results for a nonaluminized composite plateau propellant formulation are shown.