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.

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.

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.

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%.

Nozzle Aspect Ratio Effect on Supersonic Elliptic Jet Mixing

2017 ◽  
Vol 139 (10) ◽  
Author(s):  
S. M. Aravindh Kumar ◽  
E. Rathakrishnan
Keyword(s):  
Aspect Ratio ◽  
Nozzle Exit ◽  
Pressure Gradients ◽  
Ratio Effect ◽  
Jet Mixing ◽  
Free Jet ◽  
Aspect Ratios ◽  
Nozzle Pressure ◽  
Axis Switching ◽  
The Waves

Nozzle aspect ratio effect on the mixing of Mach 2 elliptic free jet, issuing from convergent–divergent elliptic nozzles of aspect ratios 2, 3, and 4, in the presence of adverse and marginally favorable pressure gradients at the nozzle exit has been studied experimentally. The results show that AR4 jet enjoys better mixing than AR2 and AR3 jets at all nozzle pressure ratios. The AR2 and AR3 jets displayed axis switching, whereas there is no axis switching for AR4 jet. The shadowgraph shows that the waves in AR4 jet are weaker than those in AR2 and AR3 jets.

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.

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.

Study of Decay Characteristics of Hexagonal and Square Supersonic Jet

2017 ◽  
Vol 34 (2) ◽  
Author(s):  
Prasanta Kumar Mohanta ◽  
B. T. N. Sridhar
Keyword(s):  
Pressure Ratio ◽  
Supersonic Jet ◽  
Ambient Air ◽  
Hydraulic Diameter ◽  
Schlieren Image ◽  
Image Study ◽  
Jet Mixing ◽  
Core Length ◽  
Supersonic Core Length ◽  
The Impact

AbstractExperiments were carried on nozzles with different exit geometry to study their impact on supersonic core length. Circular, hexagonal, and square exit geometries were considered for the study. Numerical simulations and schlieren image study were performed. The supersonic core decay was found to be of different length for different exit geometries, though the throat to exit area ratio was kept constant. The impact of nozzle exit geometry is to enhance the mixing of primary flow with ambient air, without requiring tab, wire or secondary method to increase the mixing characteristics. The non-circular mixing is faster comparative to circular geometry, which leads to reduction in supersonic core length. The results depict that shorter the hydraulic diameter, the jet mixing is faster. To avoid the losses in divergent section, the cross section of throat was maintained at same geometry as the exit geometry. Investigation shows that the supersonic core region is dependent on the hydraulic diameter and the diagonal. In addition, it has been observed that number of shock cells remain the same irrespective of exit geometry shape for the given nozzle pressure ratio.

Corrugated Truncated Triangular Tabs for Supersonic Jet Control

2013 ◽  
Vol 135 (9) ◽  
Author(s):  
P. Arun Kumar ◽  
E. Rathakrishnan
Keyword(s):  
Experimental Investigation ◽  
Pressure Gradient ◽  
Near Field ◽  
Supersonic Jet ◽  
Adverse Pressure Gradient ◽  
Small Scale ◽  
Nozzle Pressure ◽  
Jet Control ◽  
The Waves ◽  
Different Levels

An experimental investigation has been carried out to assess the effectiveness of truncated triangular tabs, provided with corrugations (semicircular, triangle, and square shapes) all along their edges, capable of shedding small-scale vortices of continuously varying size, in enhancing the mixing of axi-symmetric Mach 2 jet, at different levels of expansion. The performance of all the tabs were found to be effective only in the near-field of the jet at all levels of expansion of the present investigation. Both the semicircular and square corrugated tabs were found to bifurcate the jet, in two parts (lobes), at x/D ≤ 1, than the triangular corrugated tab, at all the nozzle pressure ratios (NPRs) of the present study. Among the controlled jets, the semicircular corrugated tab is found to be the best mixing promoter at NPRs 6 and 7, for the Mach 2 jet. However at NPRs 4, 5 and 8, the mixing promoting performance of uncorrugated tabs is the best; as high as 91% reduction in jet core length is achieved with semicircular corrugations. Therefore, the mixing promoting capability of truncated triangular tabs with semicircular corrugated tab assumes a maximum, around the overexpansion level with adverse pressure gradient of around 10% (corresponding to NPR7). Shadowgraph images reveal, that the waves prevailing in the near-field for the controlled jets are rendered weaker than those of uncontrolled jet.

Control of Supersonic Elliptic Jet with Ventilated Tabs

2020 ◽  
Vol 37 (3) ◽  
pp. 267-283 ◽  
Author(s):  
Saif Akram ◽  
E. Rathakrishnan
Keyword(s):  
Pressure Gradient ◽  
Pressure Ratio ◽  
Adverse Pressure Gradient ◽  
Mixing Enhancement ◽  
Pressure Gradients ◽  
Favorable Pressure Gradient ◽  
The Difference ◽  
The Waves ◽  
Different Levels ◽  
Better Than

AbstractControl of Mach 1.5 elliptic jet with ventilated triangular tabs is studied experimentally, in the presence of different levels of pressure gradient at the nozzle exit. Three different sets of ventilated tabs with circular, triangular and trapezoidal ventilations were studied. Two tabs were placed, at the ends of major and minor axes, at the exit of the elliptic nozzle of aspect ratio 3.37. The mixing enhancement caused by these tabs was studied in the presence of adverse and favorable pressure gradients, corresponding to nozzle pressure ratio (NPR) from 3 to 8. For Mach 1.5 jet NPR 3 corresponds to 18 % adverse pressure gradient and NPR 8 corresponds to 118 % favorable pressure gradient. The results of ventilated tabs are compared with unventilated truncated triangular tabs of identical geometry. The difference between the mixing promoting efficiency of the unventilated and ventilated tabs is only marginal (around 5–6 %). All tabs cause jet bifurcation and weaken the waves in the jet core. The tab with trapezoidal ventilation, at NPR 3, promotes mixing to an extent of reducing the core to about 92 %. At higher NPRs the mixing caused by unventilated tab is slightly better than the ventilated tabs.

Supersonic jet flow control using semi-circular corrugated tabs

2019 ◽  
Vol 91 (10) ◽  
pp. 1340-1352 ◽  
Author(s):  
Sathish Kumar K. ◽  
Senthilkumar Chidambaram
Keyword(s):  
Supersonic Jet ◽  
Expansion Ratio ◽  
Small Scale ◽  
Mixed Effect ◽  
Content Type ◽  
Jet Mixing ◽  
Axisymmetric Jet ◽  
Core Length ◽  
Pitot Pressure ◽  
Practical Implications

Purpose The purpose of this study is to increase the jet mixing effectiveness of Mach 1.6 axisymmetric jet using semi-circular corrugated triangular tabs (Tabs A, B and C), in which the locations of the semi-circular corrugations are varied along the leaned sides of the triangular tabs. Design/methodology/approach The tabs are fixed at the exit of the nozzle facing each other 180° apart. To quantify the jet mixing effectiveness of the semi-circular corrugated tabs, Pitot pressure measurements were carried out for the cases of over-expansion, marginally over-expansion and under-expansion levels of Mach 1.6 jet, along the jet centerline and the jet spread, along and normal to the tab axis. Findings The results exhibit that the semi-circular corrugated Tab A augments the jet mixing when compared to Tabs B and C. This impact in jet mixing is strongly due to the small-scale vortices shed from the tabs and the mixed effect of the corrugation locations and expansion ratio. The maximum percentage reduction in core length is about 73.6 per cent for the jet with semi-circular corrugated Tab A at NPR 5, whereas it is 71.4 and 67.1 per cent for Tabs B and C, respectively. Practical implications The reduction in core length of the jet with minimum thrust loss is obtained by controlling the jet used with semi-circular corrugated triangular tabs of equal blockage ratio 5.12 per cent with respect to the nozzle exit diameter. Originality/value The locations of the semi-circular corrugations varied systematically at the equally leaned sides of the triangular tab ensure the novelty of this study.

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