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
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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.
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TL;DR: Experimental studies of incompressible elliptic jets of different aspect ratios and initial conditions are summarized along with the effects of excitations at selected frequencies and amplitudes in this paper, where the experimental facilities and procedures are described and jet spread and decay are discussed.
Abstract: Experimental studies of incompressible elliptic jets of different aspect ratios and initial conditions are summarized along with the effects of excitations at selected frequencies and amplitudes. The experimental facilities and procedures are described and jet spread and decay are discussed. The instability of elliptic shear layers, the behavior of the jet column under controlled excitation, and the time-average measures of unexcited jets are addressed.
483 citations
TL;DR: In this article, the authors developed a linear shock cell model for non-axisymmetric supersonic jets from convergent-divergent nozzles operating at off-design conditions, where the mixing layer of the jet is approximated by a vortex sheet.
166 citations
TL;DR: In this article, Schlieren photographs of the flow field along with hot-wire measurements in the jet were obtained at different pressure ratios and it was shown that the self-excitation helps to induce large scale vortical motions in a converging rectangular nozzle.
164 citations
TL;DR: In this article, sound generation by vortex pairing in circular and elliptic cold-air jets at Mach 015-035 is investigated experimentally, with a focus on the effects of initial conditions.
137 citations
TL;DR: In this paper, the authors studied the behavior of unexcited and excited elliptic jets and found that their characteristics are noticeably different from circular jets, suggesting potential applications of excited elliptical jets for enhanced mixing and chemical reaction, and control of aerodynamic noise.
Abstract: Studies of unexcited and excited elliptic jets reveal their characteristics to be noticeably different from circular jets, suggesting applications of excited elliptic jets for enhanced mixing and chemical reaction, and control of aerodynamic noise. The near‐field turbulence characteristics, jet spread, and locations of switching of major and minor axes of the jet cross section can be drastically altered by forcing. The preferred mode and the stable pairing mode of an elliptic jet scale with the exit equivalent diameter.
128 citations