Investigations of Reactive and Non Reactive Acoustic Boundary Layers in Porous Walled Ducts,
GEORGIA INST OF TECH ATLANTA SCHOOL OF AEROSPACE ENGINEERING
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This paper investigates the acoustic boundary layer in porous walled ducts with side wall gas injection which is of interest in studies of propellant driving in unstable solid propellant rocket motors. The characteristics of the acoustic boundary layer are investigated both in the presence and absence of a premixed, laminar flame located in the vicinity of the duct walls. The formulation, valid for low injection Mach numbers, is two dimensional and includes the effects of viscosity, thermal conductivity, steady state velocities and chemical reaction. It is shown that with increase of the steady wall injection velocity, the acoustic boundary layer thickness at a given frequency increases and its tendency to damp acoustic motions within the duct also increases. Whereas in the non reactive case the effect of the boundary layer is generally damping, in the reactive flow case substantial driving of acoustic motions can occur in the region of high release rate. The analysis also shows that the acoustic admittance at the boundary layer edge depends upon axial location varying most rapidly in regions adjacent to an acoustic pressure minimum. Results of experimental studies carried out for the non reactive case are also reported and shown to be in good agreement with the theory.