Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 28
Book Description
An Improved Method for Predicting the Effects of Flight on Jet Mixing Noise
Scientific and Technical Aerospace Reports
Author: NASA Technical Paper
Author: NASA Reference Publication
Author: STAR
Author: The Prediction and Analysis of Jet Flows and Scattered Turbulent Mixing Noise about Flight Vehicle Airframes
Author: National Aeronautics and Space Administration (NASA)Publisher: Createspace Independent Publishing Platform
ISBN: 9781719506496
Category :
Languages : en
Pages : 58
Book Description
Jet flows interacting with nearby surfaces exhibit a complex behavior in which acoustic and aerodynamic characteristics are altered. The physical understanding and prediction of these characteristics are essential to designing future low noise aircraft. A new approach is created for predicting scattered jet mixing noise that utilizes an acoustic analogy and steady Reynolds-averaged Navier-Stokes solutions. A tailored Green's function accounts for the propagation of mixing noise about the airframe and is calculated numerically using a newly developed ray tracing method. The steady aerodynamic statistics, associated unsteady sound source, and acoustic intensity are examined as jet conditions are varied about a large flat plate. A non-dimensional number is proposed to estimate the effect of the aerodynamic noise source relative to jet operating condition and airframe position.The steady Reynolds-averaged Navier-Stokes solutions, acoustic analogy, tailored Green's function, non-dimensional number, and predicted noise are validated with a wide variety of measurements. The combination of the developed theory, ray tracing method, and careful implementation in a stand-alone computer program result in an approach that is more first principles oriented than alternatives, computationally efficient, and captures the relevant physics of fluid-structure interaction. Miller, Steven A. E. Langley Research Center AEROACOUSTICS; GREEN'S FUNCTIONS; JET MIXING FLOW; LOW NOISE; TURBULENT MIXING; AERODYNAMIC CHARACTERISTICS; AERODYNAMIC NOISE; REYNOLDS AVERAGING; NAVIER-STOKES EQUATION; RAY TRACING; NOISE GENERATORS; PREDICTIONS
Prediction of Jet Mixing Noise for High Subsonic Flight Speeds
Author: Ulf MichelPublisher:
ISBN:
Category :
Languages : en
Pages : 9
Book Description
A method for the prediction of single stream jet mixing noise in flight is presented that can be used for flight Mach numbers up to 0.9. The method is similar to the empirical SAE method. However, two important results of the theoretical scaling law of Michalke and Michel are incorporated: (1) the total noise of heated jets is separated into quadrupole and dipole noise components because they are influenced differently by the flight Mach number and, (2) the influence of the stretching of the jet plume in flight on the overall sound pressure and the frequency of the emitted sound is considered. A relative velocity exponent law is used to correlate experimental flyover data. The correlation is based on all available data for combat aircraft with fuselage mounted engines and flight Mach numbers between 0.5 and 0.9. The difference between predictions with this new method and measured overall flyover levels is generally less than two decibels. The spectra are also well predicted.
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