Elliptic jet control with triangular tab

2016 ◽  
Vol 231 (8) ◽  
pp. 1460-1477 ◽  
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).

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.

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%.

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.

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.

Aspect ratio effect on elliptical sonic jet mixing

2016 ◽  
Vol 120 (1230) ◽  
pp. 1197-1214 ◽  
Author(s):  
V. Chauhan ◽  
S.M. Aravindh Kumar ◽  
E. Rathakrishnan
Keyword(s):  
Aspect Ratio ◽  
Mach Disk ◽  
Jet Mixing ◽  
Disk Formation ◽  
Aspect Ratios ◽  
Sonic Jet ◽  
Nozzle Pressure ◽  
Expansion Level ◽  
Elliptical Jet ◽  
Different Levels

ABSTRACTThe effects of aspect ratio on elliptical sonic jet decay at different levels of under-expansion has been studied experimentally. Elliptical sonic jets from orifices of same area with aspect ratios (AR) 2, 4 and 6 at nozzle pressure ratios 2 to 5 in steps of 1 have also been studied. A circular jet from an orifice with an area equal to that of elliptical orifice was also studied for comparison. Jet centreline pressure decay, spread and waves present in the jet core were analysed. The results show that the mixing of the elliptical jet is superior to the circular jet, at all the nozzle pressure ratios of the present study. Also, the aspect ratio of the elliptical orifice has a strong influence on the jet mixing. Elliptical jets of aspect ratio 4 and 6 experience a significantly higher mixing than the aspect ratio 2 jet, till the under-expansion level corresponding to Mach disk formation. For higher under-expansion levels, the mixing of AR 4 and 6 jets become inferior to that of the AR 2 jet.

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.

Mixing Characteristics and Enhancement of Sonic Elliptic Jets from a Twin Elliptic Orifice

2020 ◽  
Vol 12 (2) ◽  
Author(s):  
S. Parameshwari ◽  
Pradeep Kumar ◽  
S. Thanigaiarasu ◽  
E. Rathakrishnan
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
System Design ◽  
Pressure Ratio ◽  
Jet Noise ◽  
Nozzle Pressure Ratio ◽  
Jet Mixing ◽  
Nozzle Pressure ◽  
Mixing Characteristics ◽  
Ir Signature

The knowledge of jet mixing and its enhancement of elliptic jet are important in a propulsion system of aircraft, rocket, and missile’s system design for advancement of combustion via fuel-air mixture increment, lowering the jet noise and reduction of the plume infrared (IR) signature. The jet issuing from a twin elliptic orifice is non-uniform in shape that promotes the faster mixing and it influences by orifice exit conditions, so knowledge of absence of boundary layer and jet mixing characteristics is important. Hence, an experimental work helps to study the jet mixing for a twin elliptic orifice of aspect ratio two at nozzle pressure ratios of one, two, and three. The proximity between the orifices kept as one to 3mm in steps of one. The experimental readings were taken using pitot probe. The results revealed that jet mixing is faster and effective when the proximity between the orifices is closer to each other than the faraway distances at measured nozzle pressure ratios. Difference in orifice jet core exerted a noticeable influence at high proximity levels of nozzle pressure ratio of three and four for elliptic orifice.

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.

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.

Bubble Formation in a DC Electric Field

2008 ◽  
Author(s):  
Feng Chen ◽  
Yaozu Song ◽  
Yao Peng
Keyword(s):  
Aspect Ratio ◽  
Field Strength ◽  
Electric Field ◽  
Electric Field Strength ◽  
Bubble Growth ◽  
Growth Process ◽  
Major Axis ◽  
Minor Axis ◽  
Electric Stress ◽  
Dc Electric Field

The effect of a DC electric field on the formation and the characteristics of a nitrogen bubble injected from an orifice were studied experimentally and theoretically. This study was the first to divide the bubble growth process into four stages (waiting, expansion, deformation and detachment) according to the variation of the bubble shape in order to analyze the bubble behavior in the electric field. During the waiting stage, the waiting interval decreases significantly as the electric field strength rises. In the expansion stage, the minor axis reaches a maximum that decreases with increasing the electric field strength. Within the deformation stage, the major axis achieves its maximum and so does the aspect ratio. As the electric field strength rises, both the maximums of the major axis and the aspect ratio increase. At the detachment stage, as the electric field strength is intensified, the major axis lengthens, the minor axis shortens and the aspect ratio lengthens. From the waiting stage to the detachment stage, the effect of the electric field on the major axis of the bubble is marginal, while with increasing the electric field strength, the minor axis decreases distinctly and thus the aspect ratio increases. To employ the four-stage model, the bubble growth process was analyzed in detail under the electric field. The electric stress exerted on the bubble surface was calculated. The results show that the electric stress compresses the bubble equator and elongates the poles of the bubble, causing the bubble to elongate along the electric field direction.

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