Relationship between Shock-cell Length and Noise of Jets from Rectangular and Elliptic Disk Nozzles
01 Jan 2009-International Journal of Turbo & Jet-engines (Walter de Gruyter GmbH)-Vol. 26, Iss: 2, pp 145-153
TL;DR: In this paper, the effects of aspect ratio, measurement plane (major vs. minor) and directivity on the sound pressure levels of rectangular and elliptic disk nozzles of various aspect ratios have been analyzed.
Abstract: Jets issuing from rectangular and elliptic disk nozzles of various aspect ratios have been studied for their noise characteristics. The overall sound pressure level and directivity were measured for these jets. The effects of aspect ratio, measurement plane (majorvs. minor-) have been analyzed. The results show that the sound pressure levels are entirely different for higher and lower aspect ratio elliptic and rectangular jets. At lower aspect ratios (AR=2:1), the noise emissions from major axis plane dominate while for higher aspect ratios jets (AR>2), the noise from minor axis plane dominate. Further, the relationship between sound pressure level and average shock-cell length is observed to be quadratic at emission angles of 30° and 90° for both rectangular and elliptic jets.
Citations
More filters
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
TL;DR: In this paper, a proper scale for the average shock-cell length Ls¯ of circular and elliptic supersonic free jets is found as Ls*¯AR0.2e−0.15γMj2 and Lc*AR 0.5e− 0.11γmj2, where Lc is the nozzle throat diameter normalized by nozzle diameter Dth and Mj is the ideally expanded jet Mach number.
Abstract: A supersonic core length Lc and an average shock-cell length Ls¯ are experimentally investigated for the acoustic properties of supersonic jets. Following Kumar and Rathakrishnan [“Scaling law for supersonic core length in circular and elliptic free jets,” Phys. Fluids 33(5), 051707 (2021)], a proper scale for the average shock-cell length Ls¯ of circular and elliptic supersonic free jets is found as Ls*¯AR0.2e−0.15γMj2, where Ls*¯ is the average shock-cell length normalized by nozzle throat diameter Dth, AR is the nozzle aspect ratio, γ is the specific heat ratio, and Mj is the ideally expanded jet Mach number. The scaling law developed for Ls*¯ exhibits a close similarity with the scaling law for supersonic core length Lc*AR0.5e−0.11γMj2, where Lc* is the nozzle throat diameter normalized supersonic core length. The scaling laws Ls*¯AR0.2e−0.15γMj2 and Lc*AR0.5e−0.11γMj2 are valid across a wide range of parameters, such as γ from 1.28 to 1.6, the nozzle design Mach number Md from 1 to 2, AR from 1 to 6, and Mj corresponds to the absence of Mach reflection. Discussion conducted on the scaling laws provides important insight into the choice of AR. Furthermore, the relationship between Lc* and Ls*¯ with the intensity of shock-associated noise is also discussed; hence, new correlation functions are developed for Lc* and Ls*¯ that provide an analogous measure of the shock-associated noise.
4 citations
Journal Article•
TL;DR: In this paper, the influence of tab heads on the shock train of Underexpanded jet issuing through a convergent nozzle was investigated. Tabs were attached diametrically opposite.
Abstract: This paper presents the influence of tabs on shock trains of Underexpanded jet issuing through a convergent nozzle. The shadowgraph of flow is captured to have an insight of shock structure prevailed in Underexpanded jet. Tabs were attached diametrically opposite. Tabs used in the study were elliptical and perforated elliptical. The blockage ratio was 5%. Shadowgraph pictures were captured for tabs along and normal to the flow for nozzle pressure ratios (NPRs) of 3, 4, 5, 6 and 7. It was observed that elliptical tabs, highly distorts the shock train compared to perforated elliptical tabs. However perforated elliptical tabs are more influential to reduce noise level as well as compensation for thrust loss.
References
More filters
TL;DR: Gutmark and Ho as discussed by the authors investigated the near-field pressure fluctuations of an elliptic jet and found that the characteristics of the fluctuating pressure were only slightly different in the two planes containing the major and minor axes.
Abstract: Author(s): Gutmark, E; Ho, CM | Abstract: The near-field pressure fluctuations of an elliptic jet were experimentally investigated in this work. The characteristics of the fluctuating pressure were found to be only slightly different in the two planes containing the major and minor axes. A spectral analysis of the pressure fluctuations was performed and its relation to the velocity perturbations generated by vortex merging was examined. © 1985 American Institute of Aeronautics and Astronautics, Inc., All rights reserved.
38 citations
TL;DR: In this paper, the effects of nozzle geometry on the performance of an axisymmetric thrust augmentor have been investigated experimentally and a very slight improvement in the performance was observed when cruciform nozzles were used after the tests had been performed with circular nozzle.
Abstract: The mixing of single or multiple jets is relevant in several engineering applications ranging from flame stabilisation in combustion to high lift devices for V/STOL aircraft. In some of these applications, expeditious manufacturing and ease of installation may dictate the use of sharp-edged slots in preference to nozzles with contoured upstream shaping. It has been suggested that cruciform nozzle exit shapes may be suitable for improving mixing and thus thrust augmentation in STOL aircraft. The effects of nozzle geometry on the performance of an axisymmetric thrust augmentor have been investigated experimentally and a very slight improvement in the performance of the axisymmetric thrust augmentor was observed when cruciform nozzles were used after the tests had been performed with circular nozzles.
21 citations
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.
11 citations
TL;DR: In this article, the authors describe the design and construction of a medium-size, low-cost anechoic chamber for conducting experiments in jet-acoustics and demonstrate that the enclosure satisfied anechoics properties for frequencies above 630 Hz, beyond 16 cm from the sound source.
Abstract: Experiments in jet acoustics require free-field conditions for obtaining comparable results. This paper describes the design and construction of a medium-size, low-cost anechoic chamber for conducting experiments in jet-acoustics. The enclosure satisfied anechoic properties for frequencies above 630 Hz, beyond 16 cm from the sound source.
7 citations
TL;DR: In this article, the authors describe a short series of experiments investigating the nature and magnitude of the differences in the noise field from subsonic cold air jets having circular and elliptic orifices.
Abstract: This note describes a short series of experiments investigating the nature and magnitude of the differences in the noise field from subsonic cold air jets having circular and elliptic orifices. An anticipated increase in the noise level occurs in directions normal to the major axis, but other changes having more obscure origins are also revealed.
4 citations