This paper investigates the flow resonance while the jet is issued out from a nozzle at transonic Mach numbers. In present study the jets emerging out from orifice and pipe nozzles are considered. The jet flow diameter of orifice and pipes is 10 mm, and the length of the pipe is varied in the range of 1 â‰ L/D â‰ 6. The pressure ratio of the jet flow is varied in the range of subsonic to supersonic Mach numbers; however the study predominantly concentrates on transonic regimes. Results indicate that distinct transonic resonance tones occur in the range of transonic Mach numbers (0.95 to 1.01). Unlike screech that occurs during the presence of shock cells, the transonic frequencies slightly increase with Mach number. Moreover numerous multiple non-harmonic frequency tones are observed during this transonic resonance thus indicating the non-linearity in the flow resonance. In case of pipe nozzles, the transonic tones tend to diminish with increase in pipe length and cease to exist beyond a certain length.

K. Srinivasan

Department of Mechanical Engineering

FLOW RESONANCE

FREQUENCY TONES

jet flow

jet noise

PIPE JET

PRESSURE RATIO

SHOCK-CELL

TRANSONIC REGIME

Mach number

Nozzles

Orifices

Resonance

Supersonic aerodynamics

Fulltext

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IIT Madras

Transonic Resonance Tones in Orifice and Pipe Jets

International Journal of Aeroacoustics

Experimental studies in the acoustic far field and flow visualization are carried out on circular and non-circular impinging jets at a nozzle to plate distance ratio of 5, for the nozzle pressure ratios of 1.8, 4, and 6. Spectra and directivity of the overall sound pressure level of circular jets are compared with those of non-circular jets for the same nozzle pressure ratios, at various emission angles. Non-circular jets mitigate the transonic impinging tones at around the critical pressure ratio, compared to the circular jet. Square jet is quieter at low nozzle pressure ratios by 5–8 dB compared to the circular jet. At higher under expansion conditions, the triangular and square jets almost completely eliminate the supersonic impinging tones. Elliptical jet is noisy at a nozzle pressure ratio of 6, even compared to the circular jet. Elliptical minor axis plane is quieter at lower nozzle pressure ratios compared to the major axis plane and the trend is reversed for the higher nozzle pressure ratios. Schlieren flow visualization studies reveal that the shock cell structures are weakened and symmetry of the shock cells are lost for the non-circular jets compared to the circular jet. © 2018 Elsevier Ltd

Applied Acoustics

Impinging jet noise reduction using non-circular jets

Experimental studies are carried out to reduce the jet noise using co-axial swirlers in the form of curved vanes fixed in an annular passage. The swirl numbers considered for the present work ranged from 0 to 1.31, and the corresponding swirl vane angles ranged from 0 to 60°. The nozzle pressure ratios studied ranged from 1.8 to 6. The acoustic far field study at subsonic conditions revealed the presence of transonic tones for the non-swirl jet. However, swirl eliminates the transonic tones and a weak swirl is most efficient for noise reduction at subsonic conditions. The centerline total pressure measurements indicate the reduced core length for the swirl jets compared to the non-swirl jets. At supersonic conditions, the non-swirl jet emits the highest noise at all the emission angles compared to the swirl jets. The swirl jets are free from screech tones, and have lower amounts of shock associated noise, even at high nozzle pressure ratios. The centerline total pressure measurements and schlieren visualization studies show that shock cell spacing and the number of shock cells are reduced in the swirl jets compared to the non-swirl jet. © 2017 Elsevier Ltd

Jet noise reduction using co-axial swirl flow with curved vanes

The present experimental work highlights the acoustic far field and flow field characteristics of confined co-axial swirling pipe jets. Co-axial confinements with six vanes at angles of 0°, 20° and 40° are considered here. Two pipe lengths of L/D=0.5 and 2 are studied. The Mach numbers studied range from 0.85 to 1.83. An increase in the pipe length causes suppression of the transonic tones in non-swirl pipe jets. Swirl reduces the low frequency noise components and increases the high-frequency components compared to non-swirl jet. The broadband shock associated noise is mitigated by the swirl pipe jets. However, the screech tone is completely eliminated by the swirl pipe jets. Further, swirl pipe jets radiate low levels of noise at all the emission angles compared to non-swirl pipe jets, for both the pipe length cases at supersonic Mach numbers. Increase in the pipe length enhances the shock associated noise and OASPL for the non-swirl pipe jet. Centreline pitot survey and schlieren visualisation show a reduction in core length, reduction in the number of shock cells, weakening/destruction of the shock cells by the swirl pipe jets compared to the non-swirl pipe jets. © Copyright Royal Aeronautical Society 2017.

Aeronautical Journal

Pipe jet noise reduction using co-axial swirl pipe

An experimental study of the acoustic far field and flow field of co-axial circular and non-circular jets with the vane angles of 0° and 30° are presented in this paper. Flat vanes are fixed in the annular passage of the coaxial jets, which cause trailing edge vortices and/or swirl flow. The co-axial jets with vane angles of 0° and 30° almost eliminate the transonic tones and screech tones entirely, in contrast to non-swirl jet. The broadband shock associated noise is also mitigated by the co-axial jets, irrespective of the vane angles. The co-axial jets are efficient in overall noise suppression at both subsonic and supersonic conditions. The co-axial jets diminish the low frequency noise and enhance the high frequency noise. Reduction in core length is highest for the co-axial jets compared to the non-swirl jet. The flow visualization study also confirms that the co-axial jets weaken or destroy the shock cells and reduce the number of the shock cells compared to non-swirl jet. © 2017 The Author(s). Published by S. Hirzel Verlag EAA.

Acta Acustica united with Acustica

Noise reduction of circular and non-circular jets surrounded by annular swirl flow

Experimental investigations are carried out with an objective of reducing impingement jet noise using coaxial swirl jets. Two nozzle-to-plate distances have been considered and the Mach number values ranged from 0.95 to 1.83. The vane angles of the coaxial swirlers ranged from 0 deg to 60 deg, corresponding to swirl numbers that ranged from weak to high. Flow visualization has also been conducted to understand the shock-cell structure for each case. The results indicate that swirl jets are highly efficient in the control of impingement noise. Transonic, screech, and impinging tones are completely eliminated by the swirl jets. A weak swirl seems efficient for lower Mach numbers while higher amounts of swirl are efficient at higher Mach numbers. © 2016 by ASME.

Journal of Vibration and Acoustics, Transactions of the ASME

Reduction of Jet Impingement Noise by Addition of Swirl

The Journal of the Acoustical Society of America

Whistling of an orifice in a reverberating duct at low Mach number

Journal of Thermal Science

Study on transonic tone in an axisymmetric supersonic nozzle

Mechanism of Pipe-Tone Excitation by Flow through an Orifice in a Duct

AIAA Journal

Numerical Investigation of Transonic Resonance with a Convergent-Divergent Nozzle

Journal of Fluid Mechanics

The elliptic whistler jet

Transonic resonance tones in orifice and pipe jets

Journal	International Journal of Aeroacoustics
ISSN	1475472X
Open Access	No