A Study on the Aeroelastic and Aeroacoustic Effects of a Sonic Under-expanded Jet

Abstract

An experimental and computational study of a sonic and sub-sonic jet impinging on a flat plate is presented. Traditional techniques for acquiring surface pressure distributions on models call for embedded arrays of pressure taps and or transducers which can be costly and are limited in spatial resolution and by model geometry. Pressure sensitive paint (PSP) offers a costeffective non-intrusive alternative with superior spatial resolution over traditional techniques. Experimental pressure sensitive paint measurements are compared to CFD models using the Spalart-Allmaras single equation turbulence model. Attempts are made and conclusions are presented to correlate flow structures to noise sources such as screech tones. Jet noise has been characterized but its sources are not fully understood and this research aims to look experimentally at its origins.Introduction: Pressure Sensitive Paint (PSP) is an optical sensor used for surface pressure measurements. A paint-like coating is applied to a surface and illuminated by an LED lamp of a specific wavelength. The fluorescence of the paint is then imaged through a long-pass filter by a CCD camera and stored for conversion to pressure by use of a previously determined calibration. The paint fluorescence is a function of the local oxygen concentration in the air. Using PSP, each camera pixel acts as a pressure transducer. PSP was used to investigate the steady pressure distribution across the surface of an acrylic plate statically mounted normal to a sonic jet impinging on its surface. The study was done over a wide range of impingement distances and pressure ratios using to determine cases of interest where distinct tones were produced. A case of interest was modeled using CFD in FLUENT © for comparison with the PSP data.