Particle image velocimetry study of a cloud-like flow

This study employs particle image velocimetry (PIV)13; on a jet with and without subjection to internal heating.13; The effects of buoyancy enhancement on the13; entrainment coefficient and on the streamline structures13; responsible for it are investigated. PIV results13; for the unheated jet are in good agreement with earlier13; studies. It is shown that when internal heating is13; present in the flow, the mean entrainment coefficient13; decreases from a value of 0.057 characterizing a standard13; jet to 0.017, at a heating rate of 1400 W corresponding13; to a Richardson number of 0.24. It is also13; shown that the mingling of the entrained fluid with13; the main flow is different in heated and unheated jets

Turbulence and noise suppression of a high-speed jet by water injection

An experimental investigation has been carried out on a supersonic jet of air issuing from an M =1.44 convergingx2013;diverging rectangular nozzle of aspect ratio 4. Particle13; image velocimetry measurements of the flow field along with near-field acoustic measurements were made. The effect of injection of a small amount of water (x223C;5% of the mass flow rate of the jet) into the shear layer of the jet, on the unsteady flow structure and sound generation were examined. The presence of water droplets in the jet modified the turbulence structure significantly, resulting in axial and normal r.m.s.velocity reductions of about 10% and 30%, respectively, as compared to that of a13; normal jet. An even larger effect is found on the peak values of the turbulent shear stress with a reduction of up to 40%. The near-field noise levels (OASPL) were found13; to reduce by about 2x2013;6 dB depending on the location of the injection and the water mass flow rate. Far-field acoustic measurements carried out on a heated M =0.9 (jet13; exit velocity=525msx2212;1) jet show significant (6 dB) reductions in the OASPL with moderate amounts of water injection (17% of the mass flow rate of the jet) suggesting13; that the technique is viable at realistic engine operating conditions

Supersonic jet noise suppression by water injection 13;

An experimental investigation was carried out on a supersonic jet of air issuing from an M = 1.44 converging-diverging rectangular nozzle of aspect ratio 4. Particle Image Velocimetry measurements of the flow field, along with acoustic measurements, were obtained. The effects of a small amount of water (about 5 percent of the mass flow rate of the jet), injected into the shear layers of the jet, on the unsteady flow structure and sound generation were examined. The presence of the water droplets in the jet modified the turbulence structure significantly, resulting in rms velocity reductions greater than 30 percent as compared to those of a normal jet. Similar reductions of the forcing term of the Phillip's equation, which represents the generation of the pressure fluctuations in the jet, were also found. The changes observed in the near-field noise measurements, due to water injection, are consistent with the unsteady flow modifications. (Author) 13; 13