Acoustic Characteristics of Non-Circular Slot Jets
TL;DR: In this paper, the acoustic characteristics of non-circular jets are investigated in terms of the spectra, directivity of sound pressure, tonal properties, and broadband shock associated noise.
Abstract: Experimental investigations on the acoustic characteristics of non-circular jets are carried out. Non-circular geometries include triangular, rounded triangular, square, and elliptic configurations, with a circular jet serving as the baseline case. Acoustic characteristics in terms of the spectra, directivity of sound pressure, tonal properties, and broadband shock associated noise are obtained to unravel the basic differences in these jets. Experiments are carried out for various pressure ratios ranging from 2 to 6, corresponding to fully expanded jet Mach numbers ranging from 1.04 to 1.82. The reduced effects of screech and broadband shock associated noise in triangular and square jets render them quieter than circular jet by up to 10 dB. The broadband shock associated noise levels are higher along flat edge planes than vertex planes, at all pressure ratios. Tonal analysis of the acoustic radiation from elliptic jet reveals that the screech tones along the major axis plane are more intense than those along minor axis plane.
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TL;DR: In this paper, 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.
15 citations
01 Jan 2009
TL;DR: Chevron nozzles are known to be excellent attenuators of jet noise as mentioned in this paper, and they use triangular serrations at the trailing edge of the nozzle to attenuate jet noise.
Abstract: Chevron nozzles are known to be excellent attenuators of jet noise. Conventional chevron nozzles use triangular serrations at the trailing edge of the nozzle. This article proposes two nove...
11 citations
TL;DR: In this article, the authors used shadowgraph technique to investigate the shock evolution from non-circular slot jets at various underexpansion levels and found that the shock cell structures of noncircular jets strongly depend upon the initial shape of the topology.
Abstract: Flow visualization studies using shadowgraph technique are carried out to investigate the shock evolution from non-circular slot jets at various under-expansion levels. The non-circular topologies considered are triangular, square and elliptic, and the circular jet is taken as the baseline case for the study. These jets are underexpanded in the pressure ratio (R) range of 2–6 corresponding to a fully expanded jet Mach number up to 1.85. Results indicate that the shock cell structures of non-circular jets strongly depend upon the initial shape of the topology. The shock structures of triangular jet have additional secondary oblique shocks that are distinct from those of other non-circular jets. Mach disk is almost absent in a shock cell structure of triangular jet, which is unlike the case of other jets used in the study. The study suggests that square jet undergoes faster diffusion process compared with the triangular jet. Axis-switching phenomenon is predicted for the elliptical jet at a distance of 3–7 equivalent diameters.
7 citations
TL;DR: In this article, a semi-empirical frequency formula for the dominant tone is proposed based on the present experimental data for small edge angles, which is defined as the minimum distance of the edge from the nozzle for the first tone to be generated.
Abstract: Experimental and theoretical investigations of the high speed jets impinge on a wedgeshaped edge have been conducted. Sonic circular and square jets of the same hydraulic diameter are examined in the present study. Edge-tones produced due to a wedgeshaped edge having different angles, specifically, 10o, 20o, 60o and 180o, have been investigated. Experiments reveal that several instability modes exist simultaneously in the microphone-captured acoustic signal. The minimum breadth is defined as the minimum distance of the edge from the nozzle exist for the first tone to be generated. Experiments showed that at small edge angle, the minimum breadth is approximately half of its equivalent two-dimension case. Semi-empirical frequency formula for the dominant tone is proposed based on the present experimental data for small edge angles. The theoretical results based on the vortex-sheet model proposed by Tam and Ahuja(1) showed that both helical and axisymmetric stability modes exist during jet impingement. The dominant tone usually has helical stability mode which is the well known edge-tone. Other tones are known as impinging-tones in the literatures and have axisymmetric stability modes. Finally, it has been shown that the experimentally obtained mean Strouhal numbers for helical and axisymmetric modes show good agreement with the Strouhal number of the least dispersive wave of the same mode calculated at various Mach numbers.
6 citations
TL;DR: In this paper, the influence of nozzle profile on heat transfer for underexpanded impinging jets was explored and it was observed that plate shock and pressure distribution over the plate have significant influence on the local heat transfer.
Abstract: Experimental study is carried out to explore the influence of nozzle profile on heat transfer for underexpanded impinging jets. Circular and elliptical orifices are used to generate underexpanded jets for underexpantion ratio ranging from 1.25 to 2.67. The supply pressure maintained in the present study ranges from 2.36 to 5.08 times the ambient pressure.
IR thermal imaging camera is used to measure surface temperature of thin foil at different nozzle to plate distances. Shadowgraph and pressure distribution are used to understand the flow structure and distribution of circular and elliptical nozzle. It is observed that plate shock and pressure distribution over the plate have significant influence on the local heat transfer. The performance of the circular orifice is far better at lower z/d. The axis switching is observed for an elliptical orifice. Correlation for local heat transfer predicts Nusselt number comparable within 15 % of experimental results.
5 citations