Experimental study on the flow and noise characteristics of underexpanded notched slot jets

AbstractAn experimental investigation has been carried out to study the effect of notches on the flow and noise characteristics of 2:1 elliptic-slot jets. The effect of variation in notch geometry is also investigated. The presence of the notch is found to provide low-velocity regions in the notched-minor-axis plane thereby intensifying the jet growth along that plane. The interaction of these low-velocity regions with the mean flow results in shorter core-lengths. At under-expansion, the shock-cell lengths are weakened considerably in notched jets resulting in significant reductions in the overall jet noise level. Azimuthal directivity of elliptic jets indicate higher noise intensity radiated along major-axis ends relative to minor-axis sides. Notches seem to circumferentially modify the noise emission characteristics and significantly bring down the noise levels along major-axis-unnotched plane. Polar directivity indicates reduction in both shock noise and jet mixing noise in the forward quadrant.

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Flow field and acoustics characteristics of elliptical jet

Aircraft Engineering and Aerospace Technology ◽

10.1108/aeat-04-2017-0111 ◽

2018 ◽

Vol 90 (9) ◽

pp. 1364-1371 ◽

Cited By ~ 13

Author(s):

S. Manigandan ◽

Vijayaraja K.

Keyword(s):

Flow Field ◽

Large Scale ◽

Rapid Change ◽

Supersonic Jet ◽

Major Axis ◽

Minor Axis ◽

Shock Cell ◽

Potential Core ◽

Content Type ◽

Elliptical Jet

Purpose The purpose of this paper is to present the results of mixing promotion and screech frequency of controlled elliptical supersonic jet. Design/methodology/approach Flow field characteristics of low-aspect-ratio elliptical jets are examined at over-expanded, under-expanded and correctly expanded conditions. The tabs are placed at elliptical jet exit along the major and minor axes. Findings The results show that the mixing done by the minor axis is superior to the tabs along major axis. At all pressure ratios, the content of jet noise and the frequency are high for the tabs along the major axis because of increase in the amplitude of screech frequency. Further the tabs along minor axis show a dominance of large-scale vertical structures. In under-expanded conditions, the shock cell shows the rapid change because of the presence of tabs. The tabs along minor axis are making the shock weaker, hence no evidence of axis switching. Practical implications To achieve the greater performance of jet, the authors need to reduce the potential core length of the issuing jet. This can be achieved by implementing different types of tabs at the exit of the nozzle. Originality/value The present paper represents the flow of controlled jet using inverted triangular tabs. By achieving the controlled jet flow, the performance of propulsion systems can be improved. This can be used in systems such as combustion chamber, missile’s noise reduction and thrust vector control.

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Flow Regimes and Drag Characteristics of Yawed Elliptical Cavities With Varying Depth

Journal of Fluids Engineering ◽

10.1115/1.2801365 ◽

2007 ◽

Vol 129 (12) ◽

pp. 1577-1583 ◽

Cited By ~ 2

Author(s):

Thomas Hering ◽

Eric Savory

Keyword(s):

Flow Regime ◽

Flow Regimes ◽

Major Axis ◽

Minor Axis ◽

Radius Of Curvature ◽

Minor Effect ◽

Streamwise Direction ◽

Low Velocity ◽

Cavity Depth ◽

Yaw Angle

The effect of yaw angle and cavity depth on the resulting flow field of cavities with elliptical planform areas embedded in a low velocity turbulent boundary layer was investigated experimentally. A 2:1 elliptical cavity with depth to minor axis ratios ranging from 0.1 to 1.0 was tested in a wind tunnel facility. Surface pressure measurements and wake velocity measurements, using hot-wire anemometry, were conducted to examine the resulting flow regimes. The results indicated several different flow regimes for the different yaw angle and cavity depth configurations. Cellular structures were observed when the minor axis was aligned with the streamwise direction. Yawing the cavity with respect to the streamwise direction resulted in a highly asymmetric flow regime. This flow regime was also associated with high drag for certain cavity depth configurations. A nominally two-dimensional flow regime was observed for large yaw angles, when the major axis of the cavity was aligned with the streamwise direction. The yaw angle had only a minor effect on the flow regimes associated with the shallowest and deepest cavities examined. A strong resemblance was found between the flow regimes associated with elliptical and rectangular cavities for similar yaw and depth configurations. This similarity was also observed in the lift and drag coefficients for the different yaw angles and cavity depths. This indicated that the wall radius of curvature of elliptical cavities has a negligible effect on the resulting flow regimes when compared to rectangular cavities.

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Computation of jet mixing noise due to coherent structures: the plane jet case

Journal of Fluid Mechanics ◽

10.1017/s0022112096004582 ◽

1997 ◽

Vol 335 ◽

pp. 261-304 ◽

Cited By ~ 58

Author(s):

F. BASTIN ◽

P. LAFON ◽

S. CANDEL

Keyword(s):

Coherent Structures ◽

Large Scale ◽

Supersonic Jet ◽

Low Frequency ◽

Coherent Motion ◽

Mean Flow ◽

Jet Mixing ◽

Deterministic Modelling ◽

Plane Jets ◽

Mixing Noise

A computational approach to the prediction of jet mixing noise is described. It is based on Lighthill's analogy, used together with a semi-deterministic modelling of turbulence (SDM), where only the large-scale coherent motion is evaluated. The features of SDM are briefly illustrated in the case of shear layers, showing that suitable descriptions of the mean flow and of the large-scale fluctuations are obtained. Aerodynamic calculations of two cold fully expanded plane jets at Mach numbers 0.50 and 1.33 are then carried out. The numerical implementation of Lighthill's analogy is described and different integral formulations are compared for the two jets. It is shown that the one expressed in a space–time conjugate (κ, ω)-plane is particularly convenient and allows a simple geometrical interpretation of the computations. Acoustic results obtained with this formulation are compared to relevant experimental data. It is concluded that the radiation of subsonic jets cannot be explained only by the contribution of the turbulent coherent motion. In this case, directivity effects are well recovered but the acoustic spectra are too narrow and limited to the low-frequency range. In contrast at Mach number 1.33, especially in the forward quadrant, results are satisfactory, showing that coherent structures indeed provide the main source of supersonic jet mixing noise.

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The Effect of wall on subsonic non-circular jets

International Journal of Scientific Research and Management ◽

10.18535/ijsrm/v6i11.ec01 ◽

2018 ◽

Vol 6 (11) ◽

Author(s):

Bhatia Devansh Pradeep ◽

Imanbir Singh ◽

Sonam Eden Bhutia

Keyword(s):

Surface Roughness ◽

Major Axis ◽

Minor Axis ◽

Ambient Fluid ◽

Potential Core ◽

Jet Mixing ◽

The Core ◽

Mixing Characteristics ◽

Circular Jets ◽

Jet Axis

The present experimental study aims at characterizing the mixing characteristics of subsonic elliptic and rectangular orifice jets (Ve = 51 m/s) in the presence of wall of different surface roughness, namely smooth, fine and coarse, placed parallel to the jet axis at the edge of the orifice exit. The wall of length 120 cm of different surface roughness was oriented either parallel to the minor axis plane or major axis plane if the orifice. The wall had a strong effect on the mixing characteristics of elliptic and rectangular jets. The centerline velocity measurement showed that the potential core of elliptic and rectangular orifice jets was around 3De and 3.5De. For both jets, all the wall configurations retarded the mixing of jet with the ambient fluid only in the characteristic decay zone but not in the core and fully developed zones. The level of mixing retardation was found to be maximum when wall was placed parallel to the major axis plane of the jet. The effect of wall on jet mixing was intense for rectangular jet compared to elliptic jet.

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Elliptic jet control with triangular tab

Proceedings of the Institution of Mechanical Engineers Part G Journal of Aerospace Engineering ◽

10.1177/0954410016652921 ◽

2016 ◽

Vol 231 (8) ◽

pp. 1460-1477 ◽

Cited By ~ 5

Author(s):

SM Aravindh Kumar ◽

Ethirajan Rathakrishnan

Keyword(s):

Aspect Ratio ◽

Major Axis ◽

Minor Axis ◽

Mixing Enhancement ◽

Jet Mixing ◽

Pitot Pressure ◽

Nozzle Pressure ◽

Jet Control ◽

The Waves ◽

Different Levels

Elliptic jet mixing influenced by triangular tabs is demonstrated in this work. Mixing modification of a Mach 2 jet from a convergent-divergent elliptic nozzle of aspect ratio 2, in the presence of two triangular tabs along the major and minor axis at the nozzle exit, at different levels of nozzle expansion has been studied. The results show that the mixing caused by tabs along the minor axis is impressive compared to the uncontrolled jet at all the pressure ratios. But for tabs along the major axis, mixing enhancement is significant only for nozzle pressure ratios above 5. Tabs along the minor axis cause better mixing than tabs along the major axis. The iso-pitot pressure contours reveal that the tabs along the minor axis enhance the mixing by bifurcating the jet. Shadowgraphs show that the tabs render the waves in the jet weaker. The present study demonstrates the superior mixing promotion caused by triangular tab than rectangular tab, studied by Aravindh Kumar and Rathakrishnan (2015).

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The Noise Radiated by High-Speed Jets: Recent Insights From Numerical Simulations (Keynote Paper)

Volume 2: Symposia, Parts A, B, and C ◽

10.1115/fedsm2003-45061 ◽

2003 ◽

Author(s):

Sanjiva K. Lele

Keyword(s):

Numerical Simulations ◽

High Speed ◽

Large Scale ◽

Jet Flows ◽

Shock Cell ◽

Jet Mixing ◽

Large Scale Structures ◽

Mixing Noise ◽

Open Issues

The noise emanating from high-speed jets consists of jet mixing noise and shock-associated noise with its tonal and broadband components. This paper summarizes well-known features of high-speed jet flows and their relationship to the noise radiated by the jet. Open issues on which different opinions exist are also noted. In this context key findings from numerical simulations of jet flows, and model problems related to jet flows are highlighted. The mechanism responsible for the generation of strong screech noise is discussed, and the role of large-scale structures in jet mixing noise and broadband shock-associated noise are stressed. Implications of a new analytical model of shock-cell noise generation are discussed, and in particular the scaling of shock-associated noise from heated jets.

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Experimental studies on rectangular jets with trapezoidal tabs

The Aeronautical Journal ◽

10.1017/s0001924000008150 ◽

2013 ◽

Vol 117 (1191) ◽

pp. 505-517 ◽

Cited By ~ 1

Author(s):

A. Arokkiaswamy ◽

S. B. Verma ◽

S. Venkateswaran

Keyword(s):

Flow Structure ◽

Flow Direction ◽

Experimental Studies ◽

Major Axis ◽

Minor Axis ◽

Equivalent Diameter ◽

Jet Mixing ◽

Rectangular Nozzle ◽

Flow Development ◽

Jet Characteristics

Abstract An experimental investigation was carried out to study the flow development of a jet issuing from a 2:1 rectangular nozzle with mixing tabs using two-component hotwire anemometry. A pair of tabs of trapezoidal configuration (with 2% total blockage area) is placed on the minor-axis side of the rectangular nozzle and tested for two tab inclination angles of 135° and 45°, with respect to the flow direction. Tests were conducted for a nominal jet exit velocity of 20m/sec corresponding to a Reynolds number based on nozzle equivalent diameter of 5·013 × 104. Relative to the plain jet, the jet with tabs show significant reduction in jet-core length (by 67%) followed by a faster decay in jet centreline velocity (U/Ue ). This is also accompanied by a significant upstream shift in peak centreline turbulence intensity (u’/Ue ). The presence of tabs is observed to inhibit the jet growth along the minor-axis plane thereby introducing large distortion in the jet cross-sectional development that ultimately leads to jet-core bifurcation along its major-axis. While a mushroom-like flow structure develops behind the tab with 135° inclination, the flow structure behind a 45° inclined tab rather takes the shape of the tab itself. The former flow development is seen to enhance the jet growth more along the minor-axis while the latter improves the jet growth more along the major-axis plane. From application point of view, since both tab inclinations result in more or less similar jet characteristics, a 135° inclined tab would be preferable over a 45° inclined tab from the view of improved jet mixing.

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Experimental investigation of the turbulent density – Far-field sound correlations in compressible jets

International Journal of Aeroacoustics ◽

10.1177/1475472x18778274 ◽

2018 ◽

Vol 17 (4-5) ◽

pp. 521-540 ◽

Cited By ~ 3

Author(s):

Bertrand Mercier ◽

Thomas Castelain ◽

Christophe Bailly

Keyword(s):

High Speed ◽

Rayleigh Scattering ◽

Photon Counting ◽

Supersonic Jet ◽

Density Fluctuations ◽

Far Field ◽

Noise Emission ◽

Jet Mixing ◽

Cross Correlations ◽

Mixing Noise

Jet mixing noise is experimentally investigated by means of cross-correlations between density fluctuations inside the turbulent jet flow and the far-field acoustic pressure. The time-resolved density fluctuations are measured by an experimental device based on Rayleigh scattering, which is mounted in the large anechoic wind tunnel of Ecole Centrale de Lyon. An original signal processing developed in a previous study is implemented for the photon counting, combined with the use of a single photomultiplier to remove shot noise. A high-speed subsonic jet and a perfectly expanded supersonic jet with a subsonic convective velocity are considered to characterize mixing noise sources. In order to go beyond the classical Fourier analyses, conditional cross-correlations are determined, and the signature of turbulent events linked to the noise emission in the downstream direction is extracted.

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