SOLID PROPELLANT RESPONSE FUNCTIONS DEDUCED BY MEANS OF FORCED LONGITUDINAL WAVES IN ROCKET MOTORS

Research with the Forced Longitudinal Wave (FLW) motor has demonstrated that pressure and velocity measurements inside a solid propellant rocket chamber can be utilized to deduce simultaneously the propellant pressure-coupled and velocity-coupled responses. The FLW motor represents the first attempt to measure propellant response functions within a rocket motor environment. A linear analysis of steady-state oscillations within rocket chambers has shown that oscillatory pressure measurements at the head and nozzle ends of a rocket chamber and a midchamber oscillatory velocity measurement provide sufficient information for the deduction of both real and imaginary parts of the propellant burning rate response functions. The midchamber velocity measurement was made by means of a magnetic flowmeter, a technique previously untried within solid propellant rocket chambers. The magnetic flowmeter operates according to Faraday's Law in that the ionized combustion products pass through a stationary magnetic field thereby generating a voltage proportional to the flow velocity. The real and imaginary parts of the velocity-coupled response for two high solids loading AP HTPB propellants were deduced as a function of frequency by means of the two pressure measurements. The real and imaginary parts of the velocity-coupled response were obtained at a single frequency for ANB-3066 propellant provided by the Air Force Rocket Propulsion Laboratory for the velocity coupling round robin. The midchamber velocity measurement was utilized to deduce the real part of the pressure-coupled response as a function of frequency for a single AP/HTPB propellant. Results consistent with our previous knowledge of response function characteristics were obtained.