The Effect of Reflector with Sound-Absorbing Material on Supersonic Jet Noise

This paper describes an experimental work to investigate the effect of a reflector on supersonic jet noise radiated from a convergent-divergent nozzle with a design Mach number 2.0.In the present study,a metal reflector and reflectors made of three different sound-absorbing materials(grass wool and polyurethane foam)were employed,and the reflector size was varied.Acoustic measurement is carried out to obtain the acoustic characteristics such as frequency,amplitude of screech tone and overall sound pressure level(OASPL).A high-quality schlieren optical system is used to visualize the detailed structure of supersonic jet.The results obtained show that the acoustic characteristics of supersonic jet noise are strongly dependent upon the jet pressure ratio and the reflector size.It is also found that the reflector with sound-absorbing material reduces the screech tone amplitude by about 5-13dB and the overall sound pressure levels by about 2-5dB,compared with those of the metal reflector.

Effect of Duct Geometry on Shock Wave Discharge

This paper describes computational work to understand the unsteady flow-field of a shock wave discharging from an exit of a duct and impinging upon a flat plate. A flat plate is located downstream, and normal to the axis of the duct. The distance between the exit of the duct and flat plate is changed. In the present study, two different duct geometries （i.e., square and cross section） are simulated to investigate the effect of duct geometry on the un-steady flows of a shock wave. In computation, the total variation diminishing （TVD） scheme is employed to solve three-dimensional, unsteady, compressible, Euler equations. Computations are performed over the range of shock Mach number from 1.05 to 1.75. Computational results can predict the three-dimensional dynamic behaviour of the shock wave impinging upon the flat plate. The results obtained show that the pressure increase generated on the plate by the shock impingement depends on the duct geometry and the distance between the duct exit and plate, as well as the shock Mach number. It is also found that for the duct with cross-section, the unsteady loads acting on the flat plate are less, compared with the square duct.

Optimization of Mass Bleed Control for Base Drag Reduction of Supersonic Flight Bodies

The minimization of base drag using mass bleed control is examined in consideration of various base to orifice exit area ratios for a body of revolution in the Mach 2.47 freestream Axisymmetric, compressible, rmss-averaged Navier-Stokes equations are solved using the standard k-ω model, a fully implicit finite volume scheme, and a second order upwind scheme. Base flow charcteristics are explained mgaarding the base configuration as well as the injection parameter which is defined as the mass flow rate of bleed jet non-dimensionalized by the product of the base area and fieestream mass flux. The results obtained through the present study show that for a smaller base area, the optimum mass bleed condition leading to minimum base drag occurs at relatively larger mass bleed, and a lalger orifice exit can offer better drag control.