Acoustic Losses of a Subscale, Cold-Flow Rocket Motor for Various 'J' Values

Abstract

Acoustic dissipation studies were undertaken using a subscale, cold-flow rocket motor model to determine the effect of purely geometric variables on the acoustic performance leadi~ng to axial mode combustion instability. Cold air served as the working fluid to simulate the internal flow and to obtain a critical nozzle throat condition. Using interchangeable metal parts, it was possible to simulate the geometry of a cylindrical-bore grain at various real motor burn times and also to vary the nozzle throat diameter. The results confirmed the speculation that, for practical motor designs, the radiation of acoustic energy through the nozzle is the largest source of loss for the axial mode and increases with the J of the motor. In view of the change in J with time during burning, this loss can vary-conspicuously during the motor burn time. SU.

Reduced Order Modeling Approach to Combustion Instabilities of Liquid Rocket Engines

“…In a rocket engine these are thermal, viscous, turbulent dissipation mechanisms and energy transport driven out of the geometric domain across the nozzle. Admittance has been extensively studied theoretically and experimentally ( [27][28][29][30][31]) and it is still today the subject of ongoing investigations. Thermal dissipation is the process by which a part of acoustic energy is converted into thermal energy.…”

Low order modeling of vortex driven self-sustained pressure pulsations in solid rocket motors

“…However, it differs due to the inclusion of an extra source term. This extra term proves essential to recover the expression for radiative acoustic losses at the nozzle including convection losses (Buffum et al 1966;Culick 2006). During the derivation a term is neglected (Eq.…”

“…However, using Howe's approximation to construct a global lumped element model one finds that it neglects convective acoustic radiation losses at the nozzle. These are essential (Buffum et al 1966;Culick 2006). In order to recover these loss terms the second term on the righthand side of Eq.…”

“…which can be substituted in I n , one finds the nozzle radiation losses as calculated by Culick 5 (Buffum et al 1966;Culick 2006) including convection effects:…”