Effect of impingement surface roughness on the noise from impinging jets
TL;DR: In this paper, the effects of roughness of the impingement plate widens the staging region of noise and the effect of nozzle-to-plate spacing distance and nozzle pressure ratio are investigated.
Abstract: This paper presents extensive acoustic measurements on jets impinging on surfaces of various surface roughness values. Besides surface roughness, the effects of nozzle-to-plate spacing distance and nozzle pressure ratio are also investigated. Turbulent mixing noise and tonal noise are explained using far-field wall-jet velocity and impingement region temperature fields. The results demonstrate that roughness of the impingement plate widens the staging region of impingement noise. In general, high speed jet impinging on a rough plate generates less noise compared to a smooth plate. When tones are removed from the spectra, it is found that acoustic power monotonically decreases with increasing surface roughness. Thermal imaging in the stagnation region indicates that whenever tones are present, the temperature at the stagnation region is high. Further, sound pressure directivity pattern of impingement noise is constructed by superimposing a wall-jet and a free jet in the appropriate orientations.
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TL;DR: In this paper , the authors review what has been learned about the physics of noise generation and radiation from free and impinging rocket plumes since the completion of NASA SP-8072.
Abstract: In 1971, the U.S. National Aeronautics and Space Administration (NASA) published a seminal report-NASA SP-8072-which compiled the results of the early supersonic jet noise studies and provided methods to calculate the noise produced from launch vehicles. Fifty years later and despite known limitations, SP-8072 remains the foundation for much of the launch vehicle noise modeling today. This article reviews what has been learned about the physics of noise generation and radiation from free and impinging rocket plumes since the completion of SP-8072. State-of-the-art methods for the mitigation of launch vehicle noise are also reviewed. A discussion of launch vehicle noise modeling, from empirical to numerical and including reduced-order models of supersonic jets, points to promising approaches that can describe rocket noise characteristics not captured by SP-8072.
11 citations
TL;DR: In this paper, the authors describe the appearance of instability modes on subsonic and supersonic impinging jets produced by convergent and convergent-and divergent nozzles.
Abstract: The appearance of instability modes on subsonic and supersonic impinging jets is a phenomenon of great interest that has been observed in jets produced by nozzles of different sizes. The present study describes these instabilities in millimeter-sized supersonic jets produced by convergent and convergent–divergent nozzles (
$$D_\mathrm{throat} = 2 \hbox { mm}$$
). The smaller nozzle sizes allowed for a comprehensive parametric study involving 378 impingement distance values between $$H{/}D=0.5$$
and $$H{/}D=9.9$$
, as well as 30 nozzle pressure ratio values for both nozzles, totaling a set of more than 22,000 experiments. The detailed resolution on the impingement distance parameter allowed for the observation of acoustic resonant tones that alternate between two or three distinct frequency bands. It was observed that very small changes in the impingement distance (
$$\Delta H{/}D \le 0.5$$
) are sufficient for resonant mode switching, which is related to the instability mode switching phenomenon. The complementary high-speed schlieren images, captured for a set of 36 cases, allowed for the effective observation and classification of the jet resonant modes via feature tracking. A correlation between the resonant mode shape (helical or axisymmetric) and the resonant tone was clearly observed and quantified. Further experiments with high-resolution schlieren images showed the shape of the acoustic waves produced, connecting the acoustic wave packets with the production of shear layer instabilities. In the helical instability mode, it was possible to observe what appears to be a helix-shaped acoustic wave.
8 citations
TL;DR: In this paper , experiments were carried out in a water-filled elongated cup of a "kitchen scale", where motion was created by a rotating disk with various micro-and nano-roughness in the top of the cup.
Abstract: Experiments were carried out in a water-filled elongated cup of a “kitchen scale,” where motion was created by a rotating disk with various micro- and nano-roughness in the top of the cup. The obtained results have shown that for some patterns of nanostructures, there is a noticeable growth of a vortex, generated by the disk, while other roughnesses do not make visible changes in the flow structure. The results are of interest in assessing the efficiency of surfaces with nanoscale roughnesses. Indeed, the first type of nano-roughness may become useful for enhancing soft mixing in chemical and bio-reactors, including in the preparation of special food delicacies. On the other hand, the use of nanostructured surfaces that do not affect the main flow can help to solve some industrial problems of water and ice erosion, for example, in wind turbines or any other objects where disturbances of the main flow are undesirable.
5 citations
TL;DR: In this paper, the authors compared the acoustic variations in jets impinging on a flat plate, and plates with a central protrusion, and found that the protrusion is more effective in reducing tones in supersonic impinging jets than the tones in subsonic impingement jets.
4 citations
TL;DR: In this paper, the acoustic far field and flow field characteristics of co-axial swirling pipe jets were analyzed in the presence of six vanes at angles of 0°, 20° and 40°.
Abstract: 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.
3 citations
Cites methods or result from "Effect of impingement surface rough..."
...The present results show only helical modes, in line with results of Dhamanekar and Srinivasan(21), who also observed only helical modes....
[...]
...At supersonic conditions, the screech frequency for the non-swirl pipe jet (L/D = 2) is validated with the results of Dhamanekar and Srinivasan(21) and the screech frequency formula given by Gao and Li(22)....
[...]
References
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TL;DR: In this paper, a theory for estimating the sound radiated from a fluid flow, with rigid boundaries, which as a result of instability contains regular fluctuations or turbulence is initiated, based on the equations of motion of a gas.
Abstract: A theory is initiated, based on the equations of motion of a gas, for the purpose of estimating the sound radiated from a fluid flow, with rigid boundaries, which as a result of instability contains regular fluctuations or turbulence. The sound field is that which would be produced by a static distribution of acoustic quadrupoles whose instantaneous strength per unit volume is ρv i v j + p ij - a 2 0 ρ δ ij , where ρ is the density, v i the velocity vector, p ij the compressive stress tensor, and a 0 the velocity of sound outside the flow. This quadrupole strength density may be approximated in many cases as ρ 0 v i v j . The radiation field is deduced by means of retarded potential solutions. In it, the intensity depends crucially on the frequency as well as on the strength of the quadrupoles, and as a result increases in proportion to a high power, near the eighth, of a typical velocity U in the flow. Physically, the mechanism of conversion of energy from kinetic to acoustic is based on fluctuations in the flow of momentum across fixed surfaces, and it is explained in § 2 how this accounts both for the relative inefficiency of the process and for the increase of efficiency with U . It is shown in § 7 how the efficiency is also increased, particularly for the sound emitted forwards, in the case of fluctuations convected at a not negligible Mach number.
4,697 citations
01 Dec 1953
TL;DR: In this paper, the authors examined the noise in two-dimensional flow with the aid of a dynamic Schlieren apparatus, verifying the suggested mechanism and showing the similarity to axially symmetric flow where discontinuities in frequency, partly analogous to edge tones, occur.
Abstract: The character of jet noise undergoes a marked change above choking, the noise due to turbulent mixing being dominated by a powerful whistle or screech whose wavelength is related to the regular shock wave spacing. The mechanism in two-dimensional flow is further examined (by the aid of a dynamic Schlieren apparatus), verifying the suggested mechanism and showing the similarity to that in axially symmetric flow where discontinuities in frequency, partly analogous to edge tones, occur. The resultant sound emitted as the periodic eddy system traverses the regular shock wave pattern is highly directional, producing a powerful beam at doubled frequency normal to the jet and an intense beam at eddy frequency in the upstream direction adjacent to the jet, resulting in fluctuations in jet velocity direction at the orifice which initiate new stream disturbances. A gain criterion for the self-maintained cycle is given, enabling certain qualitative deductions concerning the intensity to be made, and use will be made of this in considering methods of reducing the noise level.
587 citations
TL;DR: In this article, the mean properties of the flow field are established for three types of jet flow issuing from a circular convergent nozzle, and measured distributions of surface pressure are given which result when the jets impinge both normally and obliquely at various distances on several surface shapes.
Abstract: In this, the first part of a two-part experimental study of the behaviour of impinging jets, the mean properties of the flow field are established. Velocity profiles are given for three types of jet flow issuing from a circular convergent nozzle. Measured distributions of surface pressure are given which result when the jets impinge both normally and obliquely at various distances on several surface shapes. The pressure distributions are used to compute the radial velocity gradient at the impingement stagnation point. It is found that for normal impingement this gradient correlates with the free jet centreline velocity and half-radius at the same axial location. A fall-off in the correlated value is noted as the impingement is made oblique. Measurements of the azimuthal distribution of momentum flux in the resulting wall jet are also given. The general behaviour of all three types of jet is found to be similar at locations downstream of any local effects due to the shock waves present in the under-expanded types. A special study of the close-range impingement of an under-expanded jet containing a normal shock disk reveals a region of separated flow surrounding the stagnation point. This condition results in a negative value of the radial velocity gradient at the centreline.
549 citations
TL;DR: In this paper, the authors show that a feedback mechanism is responsible for the sudden change observed in the pressure fluctuations at the onset of resonance in a high-speed subsonic jet impinging on a flat plate.
Abstract: In a high-speed subsonic jet impinging on a flat plate, the surface pressure fluctuations have a broad spectrum due to the turbulent nature of the high-Reynolds-number jet. However, these pressure fluctuations dramatically change their pattern into almost periodic waves, if the plate is placed close to the nozzle (x0/d < 7·5). In the present study extensive measurements of the near-field pressure provide solid support for the hypothesis that a feedback mechanism is responsible for the sudden change observed in the pressure fluctuations at the onset of resonance. The feedback loop consists of two elements: the downstream-convected coherent structures and upstream-propagating pressure waves generated by the impingement of the coherent structures on the plate. The upstream-propagating waves and the coherent structures are phase-locked at the nozzle exit. The upstream-propagating waves excite the thin shear layer near the nozzle lip and produce periodic coherent structures. The period is determined by the convection speed of the coherent structures, the speed of the upstream-propagating waves as well as the distance between the nozzle and the plate. An instability process, herein referred to as the ‘collective interaction’, was found to be critical in closing the feedback loop near the nozzle lip.
436 citations
TL;DR: In this paper, the authors examined the flow and acoustic characteristics of an axisymmetric supersonic jet issuing from a Mach 1.5 converging-diverging (C-D) nozzle and impinging on a ground plane.
Abstract: This paper describes the results of a study examining the flow and acoustic characteristics of an axisymmetric supersonic jet issuing from a Mach 1.5 converging-diverging (C-D) nozzle and impinging on a ground plane. A large diameter circular plate was attached at the nozzle exit to measure the forces generated on the plate due to jet impingement. The experimental results described in this paper include lift loss, Particle Image Velocimetry (PIV) and acoustic measurements. Suckdown forces as high as 60% of the primary jet thrust were measured when the ground plane was very close to the jet exit. The PIV measurements were used to explain the increase in suckdown forces due to high entrainment velocities. The self-sustained oscillatory frequencies of the impinging jet were well-predicted using a feedback loop that utilizes the measured convection velocities of the large scale coherent vortical structures in the jet shear layer. Near field acoustic measurements indicate that the presence of the ground plane increases the OASPL by approximately 8 dB relative to a corresponding free jet. For moderately under expanded jets, the influence of the shock cells on the important flow features was found to be negligible except for close proximity of the ground plane.
293 citations