Examination of Pressure and Velocity Fields and Their Relationships to Radiated Noise in a Jet

University Of Florida, Gainesville FL

Investigators

Abstract

Noise production from turbulent flow represents a fundamental flow phenomena that has wide reaching practical applications including transportation vehicles. One specific example is the noise produced by the turbulent flow exiting from the jet of an aircraft. Jet noise can be the dominant aircraft noise during takeoff and can be a limiting factor for the number of flights, the time of day, and the flight path for aircraft leaving the airport because of regulations focused on quality of life (acceptable noise pollution) for residence adjacent to an airport. Significant reductions in jet noise over the past many years has primarily been achieved by increasing the fan flow in turbo-fan engines. Other advances in jet noise reduction have been achieved by the introduction of corrugated nozzles to alter the mixing in the jet shear layer. In general, however, there is still a lack of a fundamental understanding of the underlying physics in the turbulent flow that leads to noise production and hence how to reduce it in an efficient fashion. The proposed experimental effort is designed to identify noise producing events within the turbulence of the free shear flow of an axisymmetric jet using novel experimental instrumentation and analysis techniques. Although jet flows are the focus of this investigation, the fundamental understanding of relationships between the pressure and velocity fields and how they relate to noise generation should directly impact many other applications where there is free shear flow generated noise. The project will provide high school students an opportunity to work in the laboratory and to develop noise and sensing modules for a summer program. The presence of noise generated by free shear layers in turbulent flows is ubiquitous throughout engineering applications. In this effort a new and novel MEMS sensor will be developed that can measure static pressure fluctuations, with minimal flow disturbances. Measurements from this sensor will be coupled with planar velocity measurements from particle image velocimetry to shed insight into the noise produced by turbulent motions in a jet shear layer. The analysis of the data will involve single and multi-point measurements of the inflow pressures to examine the spatio-temporal nature of wave-packet events in the flow. Additionally, synchronous velocity and fluctuating static pressure measurements will be examined to correlate flow events associated with pressure field through direct analysis along with an examination of the pressure-strain rate correlations. Stochastic estimation techniques of the time-dependent velocity events conditioned to the static pressure fluctuations will be used to elucidate the large scale turbulent flow features associated with the flow pressure events. Further analysis will involve causality studies relating the pressure events in the flow to the far field noise.