Numerical simulations of compressible, turbulent jets at M = 0.75 using the Shear Stress Transport (SST) k-ω model have been carried out for baseline nozzle and chevron nozzles with 4, 6 and 8 lobes and three different penetration angles (0°, 5° and 10°). The predicted far field noise level at several observer locations are compared with experimental data. Overall sound pressure levels at far field observer locations have been calculated using Ffowcs Williams-Hawkings equation. Numerical prediction of aerodynamic quantities like centreline velocity, stagnation pressure, turbulent kinetic energy and axial vorticity are compared among the nozzles. The Unsteady Reynolds Averaged Navier Stokes (URANS) calculations are able to predict the trends in overall SPL, even though the absolute values are slightly under-predicted. Copyright © 2010 Inderscience Enterprises Ltd.

Viswanathan T. Babu

Department of Mechanical Engineering

Absolute values

AXIAL VORTICITY

Chevron nozzle

CHEVRONS

Experimental data

far field

FAR-FIELD NOISE

FFOWCS WILLIAMS-HAWKINGS EQUATION

Numerical investigations

Numerical predictions

numerical simulation

Overall sound pressure level

SHEAR-STRESS TRANSPORT

Stagnation pressures

SUBSONIC JET NOISE

SUBSONIC JETS

turbulent jet

Turbulent kinetic energy

UNSTEADY REYNOLDS-AVERAGED NAVIER-STOKES

Acoustic noise

Acoustic noise measurement

Computer simulation

Jets

Kinetic energy

Nozzles

Mathematical models

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Numerical investigation of the effect of chevrons in subsonic jets using URANS

Progress in Computational Fluid Dynamics

Results from 3D, compressible, unsteady Favre-averaged calculations of transverse injection into a supersonic cross flow are reported. Four injector geometries, namely, circular, wedge, diamond, and chevron, have been investigated. The effectiveness of the chevron injector is demonstrated by comparing performance metrics, such as degree of mixing and total pressure loss, against those of the other injectors. The results show that the chevron injector provides better mixing and spreading compared to other injectors, with almost the same total pressure loss. Furthermore, for the operating conditions studied, the chevron-penetration angle is shown to have a minimal impact on the mixing and the total pressure loss. © 2014 by ASME.

Journal of Fluids Engineering, Transactions of the ASME

Transverse injection into a supersonic cross flow through a circular injector with chevrons

Experimental investigations have been carried out on chevron nozzles to assess the importance of chevron parameters such as the number of chevrons (chevron count) and chevron penetration. Acoustic measurements such as overall sound pressure level, spectra, directivity, acoustic power, and broadband shock noise have been made over a range of nozzle pressure ratio from sub-critical to underexpansion levels. Shadowgraph images of the shock-cell structure of jets from various chevron nozzles have also been captured for different nozzle pressure ratios. The results indicate that a higher chevron count with a lower level of penetration yields the maximum noise suppression for low and medium nozzle pressure ratios. Of all the geometries studied, chevron nozzle with eight lobes and 0° penetration angle gives the maximum noise reduction. Chevron nozzles are found to be free from screech unlike regular nozzles. Acoustic power index has been calculated to quantitatively evaluate the performance of the various chevron nozzles. Chevron count is the pertinent parameter for noise reduction at low nozzle pressure ratios, whereas at high nozzle pressure ratios, chevron penetration is crucial. The results illustrate that by careful selection of chevron parameters substantial noise reduction can be achieved. © 2009 Elsevier Ltd. All rights reserved.

Applied Acoustics

Effect of chevron count and penetration on the acoustic characteristics of chevron nozzles

Numerical simulations of round, compressible, turbulent jets using the Shear Stress Transport (SST k-ω) model have been carried out. The three-dimensional calculations have been done on a tetrahedral mesh with 0.9 million cells. Two jets, one cold and hot, have been simulated. The Mach number for both the cases is 0.75. Overall sound pressure levels (SPL) at far-field observer locations have been calculated using Ffowcs Williams-Hawkings equation. The numerical predictions have been compared with experimental results available in the literature. Axial and radial variation of the mean axial velocity, axial variation of over(u′ u′, -)1 / 2, over(v′ v′, -)1 / 2, radial variation of over(u′ v′, -) and overall SPL levels are compared. The potential core length is predicted well, but the predicted centerline velocity decay is faster than the measured value. The URANS calculations are not able to predict the absolute values for the overall SPL, but predict the trends reasonably well. The calculations predict the trends and absolute values of the variations of the spectral amplitude well for the aft receivers, but not for the forward receivers. Effect of chevrons on the noise from the jet is also investigated for cold and hot jets. In each case, two chevron taper angles, namely, 0° and 5° are considered. The latter nozzle produces the most significant modification to the baseline spectra and is less effective at high frequencies in abating the noise. The present calculations predict a reduction in the overall SPL for the chevron nozzle with 0° taper angle and a slight increase for chevron nozzle with 5° taper angle, for both cold and hot jets. © 2008 Elsevier Ltd. All rights reserved.

Numerical predictions of noise due to subsonic jets from nozzles with and without chevrons

Numerical simulations of round, compressible, turbulent jets at Mach 0.75 have been carried out. Two jets, one cold and hot, have been simulated. Overall Sound Pressure Levels (SPL) at far-field observer locations have been calculated using Ffowcs Williams-Hawkings equation. Axial and radial variation of the mean axial velocity, axial variation of 1/2/u'u', 1/2/v'v', radial variation of 1/2/u'v' and overall SPL levels are compared with experimental data reported in the literature. The potential core length is predicted well, but the predicted centreline velocity decay is faster than the measured value. The URANS calculations are able to predict the absolute values for the overall SPL, and the trends to within ±4dB of the experimental value for most of the receivers. The calculations predict the trends as well as absolute values of the variations of the spectral amplitude for receivers at 30 Dj but not 50 Dj. Copyright © 2009, Inderscience Publishers.

Improved noise predictions from subsonic jets at Mach 0.75 using URANS calculations

47th AIAA Aerospace Sciences Meeting including The New Horizons Forum and Aerospace Exposition

Aerodynamic and Acoustic Predictions from Chevron Nozzles Using URANS Simulation

Journal of Fluid Mechanics

Low-frequency sound sources in high-speed turbulent jets

Journal	Progress in Computational Fluid Dynamics
ISSN	14684349
Open Access	No