A Single-stream Jet Noise Prediction Model for a Family of Chevron Nozzles

The Center for Reference on Gas Turbines (CRTG), at the Technological Institute of Aeronautics, carries out research in relevant areas of gas turbines, to provide the support for teaching and the ability to design high performance gas turbines. Noise prediction, by means of theoretical and empirical methods, is among such areas. Emphasis is given to the prediction of noise from new engines, to anticipate problems at very early design stage and to take the necessary actions to guarantee that the engine noise is below the recommended limits. Noise prediction is part of a high fidelity gas turbine performance prediction computer program, which provides the designer, at any time during the design phases, with information on the noise levels generated by each component and by the engine. This paper presents results obtained with such methodology incorporated to the high fidelity engine performance prediction computer code, and in the format usually used in the literature. The SPL — far-field one-third octave band sound pressure level — and the OASPL — overall sound pressure level — for single-stream jet were calculated for several engine rotational speeds and observer positions. Two methods have been for the single-stream jet noise prediction, namely: ESDU item 98019 and SAE ARP 876D. Nozzle details were taken from a 5 kN turbojet engine, designed at the CRTG, and which is being installed in the test rig for the preliminary evaluation. In this paper the influence of the observer position on the calculated SPL is presented, and the corresponding OASPL for steady engine operation, combined with the effect of the engine rotational speeds on exhaust jet noise. It is shown that they are in agreement with the noise of similar operating conditions. Ground reflection and atmospheric attenuation were not considered in this work. The results indicate that the noise prediction is adequate for use during the design phase and that the model derived in the SAE ARP 876D paper provides better single-stream jet noise prediction than ones predicted using the ESDU Item 98019.

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Determination of CFD Turbulence Scales for Lobed Mixer Jet Noise Prediction

Volume 6: Turbo Expo 2007, Parts A and B ◽

10.1115/gt2007-28334 ◽

2007 ◽

Author(s):

Sid-Ali Meslioui ◽

Mark Cunningham ◽

Patrick Germain

Keyword(s):

Jet Noise ◽

Prediction Method ◽

New Method ◽

Noise Model ◽

Excess Noise ◽

Scale Model ◽

Frequency Noise ◽

Noise Prediction ◽

Single Stream ◽

Noise Data

Many turbofan engine exhaust designs feature internal forced mixers to rapidly mix the hot core flow with the cold bypass flow before the nozzle exit, primarily to enhance mixing and thus improve Specific Fuel Consumption (SFC). Although the design is intended for performance improvement, it may also considerably reduce low frequency noise because of the lower relative mixed jet velocity compared to a confluent nozzle. In reality, the presence of the mixer adds complexity to the jet flow fields and additional high frequency source noise commonly labeled “mixer excess noise”. There is no industry standard on predicting such jet noise contribution. As a remedy to this, a new method was recently developed by the Institute of Sound and Vibration Research (ISVR), UK, and Purdue University, USA, under the AeroAcoustics Research Consortium (AARC) contract to predict jet noise of lobed mixers. The method essentially relies on SAE ARP876D or ESDU98019 far field noise spectra predicted for single stream jets, with appropriate filtering to decompose the spectrum into an enhanced jet spectrum and a fully mixed jet spectrum. The process is similar to the four source model earlier developed for the coplanar separate flow jets. In addition to mixer flow parameters, the prediction method requires the knowledge of two parameters related to mixer excess noise: a turbulence factor Fm, defined as the ratio of the turbulence in a forced mixer to the ‘normal’ turbulence in a single-stream mixed jet at equal distances downstream of the nozzle; and LenJ that represents the axial length of the effective jet over which Fm exceeds unity. Extensive analysis of NASA scale model lobed mixers noise data showed that the method is promising. RANS CFD was also performed to numerically determine equivalent turbulence scales based on the turbulent kinetic energy in forced mixer jets relative to confluent mixer jets. The present paper extends this work, refining the prediction method and providing validation of the new method with full-scale engine noise data. In addition, the potential of CFD to enhance noise prediction for lobed mixer jets by providing the turbulence scales needed for the empirical model is further investigated. A new definition of the equivalent CFD turbulence parameters is proposed that agrees well with those derived from empirical jet noise model. Comparison of the CFD results with NASA PIV data for a confluent mixer configuration showed that the CFD methodology is not yet fully mature and additional work is required. However, the resolution of the mixer turbulence scales predicted by CFD analysis is sufficient to identify noise trends between two mixer designs. As a result, CFD is seen as a tool with the potential to identify mixer designs that result in lower jet noise.

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Jet-Noise-Prediction Model for Chevrons and Microjets

AIAA Journal ◽

10.2514/1.j054546 ◽

2016 ◽

Vol 54 (12) ◽

pp. 3928-3940 ◽

Cited By ~ 6

Author(s):

N. K. Depuru Mohan ◽

A. P. Dowling

Keyword(s):

Prediction Model ◽

Jet Noise ◽

Noise Prediction

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Road Traffic Noise Prediction Model

PARIPEX-INDIAN JOURNAL OF RESEARCH ◽

10.15373/22501991/apr2014/34 ◽

2012 ◽

Vol 3 (4) ◽

pp. 110-112

Author(s):

Rahul Singh ◽

◽

Parveen Bawa ◽

Ranjan Kumar Thakur

Keyword(s):

Prediction Model ◽

Road Traffic ◽

Traffic Noise ◽

Road Traffic Noise ◽

Noise Prediction

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Jet-Surface Interaction Test: Far-Field Noise Results

Journal of Engineering for Gas Turbines and Power ◽

10.1115/1.4023605 ◽

2013 ◽

Vol 135 (7) ◽

Cited By ~ 44

Author(s):

Clifford A. Brown

Keyword(s):

High Speed ◽

Radial Distance ◽

Jet Noise ◽

Surface Interaction ◽

Shielding Effect ◽

Noise Prediction ◽

Far Field ◽

Wide Range ◽

Field Noise ◽

Surface Length

Many configurations proposed for the next generation of aircraft rely on the wing or other aircraft surfaces to shield the engine noise from the observers on the ground. However, the ability to predict the shielding effect and any new noise sources that arise from the high-speed jet flow interacting with a hard surface is currently limited. Furthermore, quality experimental data from jets with surfaces nearby suitable for developing and validating noise prediction methods are usually tied to a particular vehicle concept and, therefore, very complicated. The Jet-Surface Interaction Tests are intended to supply a high quality set of data covering a wide range of surface geometries and positions and jet flows to researchers developing aircraft noise prediction tools. The initial goal is to measure the noise of a jet near a simple planar surface while varying the surface length and location in order to: (1) validate noise prediction schemes when the surface is acting only as a jet noise shield and when the jet-surface interaction is creating additional noise, and (2) determine regions of interest for future, more detailed, tests. To meet these objectives, a flat plate was mounted on a two-axis traverse in two distinct configurations: (1) as a shield between the jet and the observer and (2) as a reflecting surface on the opposite side of the jet from the observer. The surface length was varied between 2 and 20 jet diameters downstream of the nozzle exit. Similarly, the radial distance from the jet centerline to the surface face was varied between 1 and 16 jet diameters. Far-field and phased array noise data were acquired at each combination of surface length and radial location using two nozzles operating at jet exit conditions across several flow regimes: subsonic cold, subsonic hot, underexpanded, ideally expanded, and overexpanded supersonic. The far-field noise results, discussed here, show where the jet noise is partially shielded by the surface and where jet-surface interaction noise dominates the low frequency spectrum as a surface extends downstream and approaches the jet plume.

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