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 article, the authors present an overview on progress and perspectives of the jet impingement research for rocket launching and discuss the interaction of impinging jets with multiphase flows.
31 citations
TL;DR: In this article, a developed Shear Stress Transport (SST) model has been used for numerically simulating the problem of turbulent round jet impingement heat transfer, and the results showed that the inner peak of heat transfer is connected with the radial pressure gradient at the stagnation point.
Abstract: In this work, a developed Shear Stress Transport (SST) model has been used for numerically simulating the problem of turbulent round jet impingement heat transfer. Based on the cross-diffusion correction activated in the logarithmic and wake parts of a region by using a blending function in the destruction term of turbulent kinetic energy k, the developed SST model is capable of recovering the effect of the pressure gradient ignored by the standard SST model. Also, the Kato-Launder model is added in the production term of k to consider the stagnating flows. The developed model has been investigated for turbulent round jets with the nozzle-plate spacing of 2, 4, and 6. The model is verified by comparing with the measurements and the results of the standard SST model, the SST with low-Re model, the Launder and Sharma model with the Yap model, the k-ω model, and the Reynolds-averaged Navier-Stokes/large eddy simulation model. Comparing with other referred methods, the developed model obtains accurate prediction in terms of velocity and pressure. As for heat transfer, it also possesses appropriate performance. Moreover, the developed model is sensitive to the pressure gradient, which helps the model be capable of reproducing accurate flow structures. By using the present model, it has been found that the velocity profiles are dominated by the turbulent kinetic energy away from walls. Meanwhile, the results show that the inner peak of heat transfer is connected with the radial pressure gradient at the stagnation point.
20 citations
TL;DR: In this paper, an under-expanded supersonic jet impinging on a flat plate is investigated by means of acoustic, particle image velocimetry and wall pressure measurements.
Abstract: Experiments on the aeroacoustics of an under-expanded supersonic jet impinging on a flat plate are presented and thoroughly discussed. A wide range of nozzle pressure ratios and of nozzle-to-plate distances has been analyzed with particular attention to the behavior of the discrete component of the noise. The investigation has been carried out by means of acoustic, particle image velocimetry and wall pressure measurements. The analysis of the relationship between the acoustic data and the fluid dynamic fields allows to examine the different source mechanisms of the discrete component of the noise and to evaluate the link between the jet flow structure and the acoustic tone features. Specifically, two ranges of nozzle pressure ratio have been observed showing different acoustic behaviors, characterized by distinct mechanisms of discrete noise generation. These regions are separated by a range of nozzle pressure ratios where impinging tones are not observed. The present experimental data extend previously published results, improving the analysis of the connection between fluid dynamic and acoustic fields and leading to a better comprehension of the impinging tone source mechanisms.
20 citations
TL;DR: In this article, the authors summarized the state of the art of the process of multiple jet impingement onto flat plate and highlight the future scope of research space in this field.
15 citations
TL;DR: In this article, an experimental study of average heat transfer from air jet impinging on a rough plate by a micro cubic pin is investigated, and the main objective of the present study is to investigate the effect of...
Abstract: An experimental study of average heat transfer from air jet impinging on a rough plate by a micro cubic pin is investigated. The main objective of the present study is to investigate the effect of ...
12 citations
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TL;DR: In this article, a theory for the instability mechanism of the Hartmann air jet generator is presented, and it is found that the result calculated from the theory are in good agreement with the experimental observations.
Abstract: The Hartmann air jet generator (Hartmann 1939) is sound wave generator in which the sound is generated by oscillations of a shock developed in an over-expanded air jet by means of a blunt body: a resonator. A theory for the instability mechanism is advanced, and it is found that the result calculated from the theory are in good agreement with the experimental observations.
46 citations
TL;DR: In this paper, a passive control technique was used to suppress the self-sustained oscillations in a supersonic impinging jet, where a rigid plate was placed in the ambient region close to the jet exit to interrupt the upstream propagating acoustic waves originating from the impingement region.
Abstract: A passive control technique was used to suppress the self-sustained oscillations in a supersonic impinging jet. A rigid plate, placed in the ambient region close to the jet exit, was used to interrupt the upstream propagating acoustic waves originating from the impingement region. The effectiveness of this technique was examined using the particle image velocimetry. The results clearly showed that the large-scale coherent vortical structures, which dominated the normal impinging jet, are completely suppressed with the passive control technique. As a result, a signie cant reduction in induced entrainment velocity was found. A recovery of about 16% of the lift loss on the attached lift plate was achieved when compared to an uncontrolled impinging jet. A reduction of about 11 dB in the near-e eld overall sound pressure level was observed.
43 citations
38 citations
TL;DR: In this article, the sound produced during low Mach number turbulent flow over a roughened section of a nominally plane, rigid wall is analyzed. But the authors focus on the noise generated by the same turbulence convecting over a forward facing step of rounded profile, and are concerned only with the case in which the turbulence Reynolds stress sources are the same.
32 citations
TL;DR: In this article, a theory of the production of sound by turbulent boundary layer flow over a rough wall is proposed, where the roughness elements are embedded entirely within the viscous sublayer, and the radiation is determined by estimating the diffraction of the turbulence nearfield by those elements.
29 citations