Triangular tabs for supersonic jet mixing enhancement

2014 ◽  
Vol 118 (1209) ◽  
pp. 1245-1278 ◽  
Author(s):  
Arun Kumar P. ◽  
E. Rathakrishnan
Keyword(s):  
Pressure Ratio ◽  
Supersonic Jet ◽  
Adverse Pressure Gradient ◽  
Mixing Enhancement ◽  
Jet Mixing ◽  
The Core ◽  
Core Length ◽  
Increase With Increase ◽  
Nozzle Pressure ◽  
Length Reduction

AbstractThe mixing promoting capability of right-angled triangular tab with sharp and truncated vertex has been investigated by placing two identical tabs at the exit of a Mach 2 axi-symmetric nozzle. The mixing promoting efficiency of these tabs have been quantified in the presence of adverse and marginally favourable pressure gradients at the nozzle exit. It was found that, at all levels of expansion of the present study though the core length reduction caused by both the tabs are appreciable, but the mixing caused by the truncated tab is superior. The mixing promoting efficiency of the truncated tab is found to increase with increase of nozzle pressure ratio (that is, decrease of adverse pressure gradient). For all the nozzle pressure ratios of the present study, the core length reduction caused by the truncated vertex tab is more than that of sharp vertex tab. As high as 84% reduction in core length is achieved with truncated vertex right-angled triangular tabs at moderately overexpanded level, corresponding to expansion levelpe/pa= 0·90. The corresponding core length reduction for right-angled triangular tabs with sharp vertex and rectangular tabs are 65% and 31%, respectively. The present results clearly show that the mixing promoting capability of the triangular tab is best than that of rectangular tabs at identical blockage and flow conditions.

Tab Aspect Ratio Effect on Supersonic Jet Mixing

2015 ◽  
Vol 32 (3) ◽  
Author(s):  
Mrinal Kaushik ◽  
E. Rathakrishnan
Keyword(s):  
Aspect Ratio ◽  
Pressure Ratio ◽  
Supersonic Jet ◽  
Small Scale ◽  
Jet Mixing ◽  
Core Length ◽  
Nozzle Pressure ◽  
The Waves ◽  
Length Reduction ◽  
Better Than

AbstractThe efficacy of introducing mixing promoting small-scale vortices by two rectangular tabs, of aspect ratio 1.0, 1.5 and 2.0, placed at diametrically opposite locations at the exit of a Mach 1.73 convergent–divergent circular nozzle has been experimentally investigated, for NPRs from 4 to 8, covering overexpanded, correctly expanded and underexpanded states of the jet. The area blockage due to the each tab was 2.5% of the nozzle exit area. Keeping the blockage constant, the aspect ratio (defined as the ratio of length to width of the tab) was varied. A maximum core length reduction of 84.6% was caused by the tabs of aspect ratio 1.0, at underexpanded conditions corresponding to NPR (nozzle pressure ratio) 6. At this NPR, tabs of aspect ratio 1.5 and 2.0 caused core length reduction of 76.9% and 61.5%, respectively. The mixing promoting efficiency of aspect ratio 1.0 is found to be better than 1.5 and 2.0, at all NPRs of the present study, except NPR 5. The shadowgraph pictures of the uncontrolled and controlled jets clearly demonstrate the effectiveness of the tabs in weakening the waves in the jet core.

Tab Geometry Effect on Supersonic Elliptic Jet Control

2016 ◽  
Vol 0 (0) ◽  
Author(s):  
Anuj Bajpai ◽  
Ethirajan Rathakrishnan
Keyword(s):  
Pressure Ratio ◽  
Major Axis ◽  
Minor Axis ◽  
Mixing Enhancement ◽  
Core Length ◽  
Nozzle Pressure ◽  
Expansion Level ◽  
Jet Control ◽  
The Waves ◽  
Length Reduction

AbstractThe efficiency of tabs of two geometries in promoting the mixing of a Mach 2 elliptic jet has been studied. Limiting tab of triangular and circular geometry (crosswire) of 5 % blockage placed along major and minor axis at the nozzle exit, are tested for nozzle pressure ratio from 4 to 8, in steps of one. Both tabs are efficient mixing promoters, at all the tested NPRs, when placed along the minor axis. But along major axis the crosswire retards the mixing, at all the NPRs. The triangular tab along the major axis is also found to retard the mixing at NPRs 4 and 5, but for nozzle pressure ratios above 5 it causes mixing enhancement even when placed along the major axis. The triangular tab is found to be a better mixing promoter than the crosswire. The maximum core length reduction of 88 % is caused by triangular tab along the minor axis is at NPR4. The corresponding core length reduction for the crosswire is only 72 %. Shadowgraph pictures of controlled jets show that both tabs weaken the waves in jet core. The geometry and orientation of the tab and the expansion level influence the mixing caused by the tab.

Experimental study of supersonic co-flowing jet

2018 ◽  
Vol 233 (4) ◽  
pp. 1237-1249 ◽  
Author(s):  
De Satyajit ◽  
Ethirajan Rathakrishnan
Keyword(s):  
Experimental Study ◽  
Pressure Ratio ◽  
Nozzle Pressure Ratio ◽  
The Core ◽  
Core Length ◽  
Nozzle Pressure ◽  
Supersonic Core Length ◽  
Presence And Absence ◽  
The Waves ◽  
Length Reduction

A detailed experimental study was carried out to investigate the behaviour of a Mach 2 primary jet in the presence of a Mach 1.6 annular co-flow. The lip thickness of the inner nozzle was 7.75 mm. The characteristics of jets were investigated at nozzle pressure ratios 3 to 8, in steps of 1. At nozzle pressure ratios 3 to 7, the centre jet is overexpanded; and at nozzle pressure ratio 8, it is marginally underexpanded. Both primary and secondary jets were operated at the nozzle pressure ratio. Centreline pressure distribution was measured to examine the supersonic core length of the centre jet in the presence and absence of the co-flow at all nozzle pressure ratios. It is found that the co-flow reduces the core length of the primary jet at all overexpanded states. A maximum core length reduction of about 61% is at nozzle pressure ratio 4, whereas the core increases by 5% at the marginally underexpanded state corresponding to nozzle pressure ratio 8. The co-flow jet merges with the primary jet at 4 D, at nozzle pressure ratio 3, and at 8 D for nozzle pressure ratios above 4. Shadowgraph images of the jet in the presence and absence of co-flow reveal that the waves in the core of the jet are strongly influenced by the co-flow.

Tab location effect on supersonic jet mixing

2018 ◽  
Vol 122 (1254) ◽  
pp. 1229-1243
Author(s):  
K. Maruthupandiyan ◽  
E. Rathakrishnan
Keyword(s):  
Nozzle Exit ◽  
Pressure Ratio ◽  
Supersonic Jet ◽  
Small Scale ◽  
Pressure Gradients ◽  
Jet Mixing ◽  
Core Length ◽  
The Waves ◽  
Length Reduction ◽  
Different Levels

ABSTRACTAerodynamic mixing of a Mach 2 jet controlled with rectangular flat tab with length equal to the nozzle exit diameter, placed at locations 0.25D, 0.5D and 0.75D, downstream of the nozzle exit, has been studied in the presence of different levels of pressure gradients corresponding to nozzle pressure ratio (NPR) range from 3 to 8. The mixing modification associated with shifted tabs is compared with the mixing caused by the same tab at the nozzle exit (0D). The aerodynamic mixing caused by the mass transporting small-scale vortices shed from the edges of the tab placed at the shifted position is found to be appreciably larger than the tab at nozzle exit, for some levels of pressure gradient. For some other levels of nozzle expansion, mixing caused by the shifted tab is comparable to that of tab at nozzle exit. The waves present in the core of the jet controlled with shifted tab were found to be weaker than that of the jet controlled with tab at nozzle exit. At a marginally underexpanded state corresponding to NPR 8, jet core length reduction caused by the tab at 0.75D is about 39.21%, which is closer to the reduction of 40.2%, caused by the tab at 0D. The corresponding core length reduction for tab at 0.25D and 0.5D are 38.16% and 20%, respectively.

Control of Subsonic and Sonic Jets with Limiting Tabs

2017 ◽  
Vol 34 (1) ◽  
Author(s):  
T. Berrueta ◽  
E. Rathakrishnan
Keyword(s):  
Nozzle Exit ◽  
Pressure Ratio ◽  
Nozzle Pressure Ratio ◽  
Jet Mixing ◽  
Downstream Distance ◽  
The Core ◽  
Maximum Reduction ◽  
Sonic Jet ◽  
Nozzle Pressure ◽  
Mach Numbers

AbstractAerodynamic mixing of subsonic and sonic jets with limiting tabs, with and without corrugations, has been studied experimentally. Limiting tab located at the nozzle exit and at a downstream distance of 0.5D has been considered in this study. Mixing caused by the tab at nozzle exit is found to be better that of tab at 0.5D, for both plain and corrugated geometries. Also, both tabs caused better mixing for underexpanded sonic jets than the correctly expanded sonic jet and subsonic jets. At nozzle pressure ratio 3 the plain tab at the nozzle exit reduced the core by about 56 % and the corrugated tab by about 51 %. But when the plain tab is placed at 0.5D the jet mixing is retarded. However, the corrugated tab at 0.5D enhances the mixing, though not up to the level of the same tab at 0D, at all Mach numbers except 0.6. The maximum reduction of core caused by shifted corrugated tab is 14 % for Mach 0.8 jet.

scholarly journals Experimental Assessment of Corrugated Rectangular Actuators on Supersonic Jet Mixing

Actuators ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 88
Author(s):  
Thillaikumar T. ◽  
Tamal Jana ◽  
Mrinal Kaushik
Keyword(s):  
Pressure Ratio ◽  
Supersonic Jet ◽  
Vortex Generators ◽  
Military Aircraft ◽  
Nozzle Pressure Ratio ◽  
Engine Exhaust ◽  
Jet Mixing ◽  
Noise Characteristics ◽  
Nozzle Pressure ◽  
The Waves

To improve the stealth capability of a military aircraft, the reduction in core length is essential to reduce the heat signature and the noise characteristics of the engine exhaust. The efficacy of rectangular vortex generators in achieving these objectives has been demonstrated by several researchers, owing to their simplicity. One way of producing the mixed-size vortices is by providing corrugations on the edge of the tab (actuator). Therefore, in the current study, two tabs of aspect ratio 1.5, mounted diametrically opposite to each other at the outlet of a Mach 1.73 circular nozzle, are examined at varying levels of expansions, ranging from overexpanded to underexpanded jet states. In addition, to generate the mixed-size vortices, three corrugation geometries, i.e., rectangular, triangular, and semicircular, are configured along the tab edges. Both quantitative and qualitative investigations are carried out by using the pitot probe to measure the stagnation pressures and by utilizing a shadowgraph technique to visualize the flow field. The corrugated tabs generated a significant mixing, and among them, the tabs with triangular corrugations are found to be most effective. A maximum reduction of about 99.7% in the supersonic core is obtained with triangular corrugated tabs at near-correct-expansion, corresponding to nozzle pressure ratio (NPR) 5. Interestingly, the semicircular corrugated tab significantly reduces the asymmetry near the nozzle exit plane. The shadowgraph images confirm the efficacy of different corrugated tabs in reducing the strength of the waves, prevalent in the supersonic core.

Supersonic jet control with shifted tabs

2016 ◽  
Vol 232 (3) ◽  
pp. 433-447 ◽  
Author(s):  
K Maruthupandiyan ◽  
E Rathakrishnan
Keyword(s):  
Pressure Gradient ◽  
Nozzle Exit ◽  
Supersonic Jet ◽  
Pressure Oscillation ◽  
Adverse Pressure Gradient ◽  
Mixing Enhancement ◽  
Aspect Ratios ◽  
Core Length ◽  
Expansion Level ◽  
Length Width

Mixing characteristics of a Mach 2 jet controlled by shifted tabs have been studied at different levels of expansion at the nozzle exit. Two identical rectangular flat tabs of aspect ratios (length/width) 3, 4, 5 and 6, offering 2.5% blockage each, located diametrically opposite, found that the mixing promotion caused by the shifted tab increases with increase of adverse pressure gradient (that is, below NPR 5). On the contrary, the mixing enhancement caused by tab placed at the nozzle exit decreases with increase of adverse pressure gradient. At higher NPRs from 5 to 8 for shifted tab configuration, the amplitude of centerline pitot pressure oscillation is considerably smaller than the uncontrolled jet. At lower NPRs, corresponding to expansion level pe /pa, from 0.383 to 0.511, shifted tab is found to be a better mixing promoter than the tab at the nozzle exit. But for expansion levels from 0.511 to 1.022, mixing promoted by tab at nozzle exit is better than the shifted tabs. Shifted tab at 0.5D results in about 55% reduction in core length, at NPR 3, and the corresponding core length reduction by tabs at 0.25D, 0.5D, and 0D is 25.93%, 22.2%, and 14.81%, respectively.

scholarly journals Assessment of Short Rectangular-Tab Actuation of Supersonic Jet Mixing

Actuators ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 72 ◽  
Author(s):  
Abhash Ranjan ◽  
Mrinal Kaushik ◽  
Dipankar Deb ◽  
Vlad Muresan ◽  
Mihaela Unguresan
Keyword(s):  
Coming Out ◽  
Nozzle Exit ◽  
Stokes Equations ◽  
Cell Structure ◽  
Pressure Ratio ◽  
Supersonic Jet ◽  
Three Dimensional ◽  
Shock Cell ◽  
Jet Mixing ◽  
Nozzle Pressure

This work explores the extent of jet mixing for a supersonic jet coming out of a Mach 1.8 convergent-divergent nozzle, controlled with two short rectangular vortex-generating actuators located diametrically opposite to each other with an emphasis on numerical methodology. The blockage ratio offered by the tabs is around 0.05. The numerical investigations were carried out by using a commercial computational fluid dynamics (CFD) package and all the simulations were performed by employing steady Reynolds-averaged Navier–Stokes equations and shear-stress transport k−ω turbulence model on a three-dimensional computational space for more accuracy. The numerical calculations are administered at nozzle pressure ratios (NPRs) of 4, 5, 6, 7 and 8, covering the overexpanded, the correctly expanded and the underexpanded conditions. The centerline pressure decay and the pressure profiles are plotted for both uncontrolled and the controlled jets. Numerical schlieren images are used to capture the barrel shock, the expansion fans and the Mach waves present in the flow field. Mach contours are also delineated at varying NPRs indicating the number of shock cells, their length and the variation of the shock cell structure and strength, to substantiate the prominent findings. The outcomes of this research are observed to be in sensible concurrence with the demonstrated exploratory findings. A reduction in the jet core length of 75% is attained with small vortex-generating actuators, compared to an uncontrolled jet, corresponding to nozzle pressure ratio 5. It was also seen that the controlled jet gets bifurcated downstream of the nozzle exit at a distance of about 5 D, where D is the nozzle exit diameter. Furthermore, it was fascinating to observe that the jet spread increases downstream of the nozzle exit for the controlled jet, as compared to the uncontrolled jet at any given NPR.

Flow Mixing and Screech Characteristics of Elliptical Supersonic Jet

2018 ◽  
Vol 0 (0) ◽  
Author(s):  
S. Manigandan ◽  
K. Vijayaraja
Keyword(s):  
Pressure Ratio ◽  
Expansion Ratio ◽  
Shock Cell ◽  
Nozzle Pressure Ratio ◽  
Potential Core ◽  
Appreciable Change ◽  
Jet Mixing ◽  
Screech Tone ◽  
Core Length ◽  
Nozzle Pressure

Abstract The acoustic and flow characteristics of a jet with elliptical throat is studied at different levels of nozzle expansion ratio. In this study, we have taken two types of CD nozzle configuration (circular and elliptical throat) and it is studied for various NPR ratios of 2, 3, 4 and 6. In addition, the acoustic characteristic of the jet flow is also measured for respective NPRs. Measurements of acoustic data are done using microphones placed at 30, 60 and 90 degrees to imprison the effects of screech tone. At NPR 2, 3 and 4, the jet with elliptical throat witnesses superior mixing and shorter core length compared to the circular throat. Its surprising to see both the configurations provides the identical oscillation at NPR 2, 3 and 4, however the efficiency of jet mixing is larger in elliptical throat jet. As the nozzle pressure ratio increased from 2 to 3 and 3 to 4, the potential core length of the jet reduces marginally about 5 to 10 % for every NPR until nozzle pressure ratio of 5. At NPR 2 and 3, the centerline pitot pressure profile shows, the decay of jet from the elliptical throat is healthier than a circular jet. At various levels of nozzle expansion, shock cell shows an appreciable change with an increase in NPR. Introduction of the elliptical throat on circular modifies the structure of shock cell which significantly changes the magnitude of screech tone due to the weakening of shock waves.

Control of a supersonic elliptical jet

2017 ◽  
Vol 122 (1247) ◽  
pp. 131-147 ◽  
Author(s):  
A. Bajpai ◽  
E. Rathakrishnan
Keyword(s):  
Nozzle Exit ◽  
Major Axis ◽  
Minor Axis ◽  
The Core ◽  
Core Length ◽  
Nozzle Pressure ◽  
Elliptical Jet ◽  
The Waves ◽  
Length Reduction ◽  
Different Levels

ABSTRACTMach 2 jet from a convergent-divergent elliptical nozzle, of aspect ratio 2, has been controlled with limiting flat and arc tabs. The mixing promoting capability of the flat and arc tabs were studied in the presence of different levels of pressure gradient, at the nozzle exit, corresponding to nozzle pressure ratios of 4 to 8, in steps of one. The geometrical blockage of both the tabs is 5% of nozzle exit area. For the flat tab along the minor axis, the waves in the core become weaker and the core length becomes shorter than the uncontrolled jet, at all the NPRs studied. But the flat tab along the major axis promotes mixing only for some NPRs and retards the mixing for the rest of the NPRs studied. At NPR 5, the flat tab along the minor axis causes the largest core length reduction of 86%. For circular arc tab, along the minor axis, the maximum core length reduction is 55% at NPR 6. Arc tab along the major axis protects the core length for the entire range of the nozzle pressure ratios tested and maximum extension in core length is found at NPR 4, which is 40%.

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