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 Aspect Ratio Driven Relationship between Nozzle Internal Flow and Supersonic Jet Mixing

Aerospace ◽  
2021 ◽  
Vol 8 (3) ◽  
pp. 78
Author(s):  
Kalyani Bhide ◽  
Kiran Siddappaji ◽  
Shaaban Abdallah
Keyword(s):  
Boundary Layer ◽  
Aspect Ratio ◽  
Nozzle Exit ◽  
Supersonic Jet ◽  
Internal Flow ◽  
Shear Stresses ◽  
Loss Mechanism ◽  
Potential Core ◽  
Jet Mixing ◽  
Aspect Ratios

This work attempts to connect internal flow to the exit flow and supersonic jet mixing in rectangular nozzles with low to high aspect ratios (AR). A series of low and high aspect ratio rectangular nozzles (design Mach number = 1.5) with sharp throats are numerically investigated using steady state Reynolds-averaged Navier−Stokes (RANS) computational fluid dynamics (CFD) with k-omega shear stress transport (SST) turbulence model. The numerical shadowgraph reveals stronger shocks at low ARs which become weaker with increasing AR due to less flow turning at the throat. Stronger shocks cause more aggressive gradients in the boundary layer resulting in higher wall shear stresses at the throat for low ARs. The boundary layer becomes thick at low ARs creating more aerodynamic blockage. The boundary layer exiting the nozzle transforms into a shear layer and grows thicker in the high AR nozzle with a smaller potential core length. The variation in the boundary layer growth on the minor and major axis is explained and its growth downstream the throat has a significant role in nozzle exit flow characteristics. The loss mechanism throughout the flow is shown as the entropy generated due to viscous dissipation and accounts for supersonic jet mixing. Axis switching phenomenon is also addressed by analyzing the streamwise vorticity fields at various locations downstream from the nozzle exit.

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.

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.

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 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.

Exit Geometry Effect on Jet Mixing

2014 ◽  
Vol 598 ◽  
pp. 151-155 ◽  
Author(s):  
Jatin Mitruka ◽  
Pranav Kumar Singh ◽  
E. Rathakrishnan
Keyword(s):  
Aspect Ratio ◽  
Nozzle Exit ◽  
Azimuthal Asymmetry ◽  
Continuous Variation ◽  
Mixing Process ◽  
Geometry Effect ◽  
Jet Mixing ◽  
Elliptical Shape ◽  
Elliptical Jet ◽  
The Waves

An elliptical nozzle of 3:1 aspect ratio (AR) issuing a Mach 1.5 jet has been used to investigate its mixing promoting efficiency under over-expanded and under-expanded conditions at the nozzle exit. Azimuthal asymmetry of the elliptical shape is interpreted as a benefit to the mixing process, which is significantly enhanced in comparison to an equivalent circular jet under identical conditions. The elliptical jet decays faster than its circular counterpart throughout the jet field. It is found that continuous variation in the size of the mixing promoting vortices shed from the nozzle exit, as a result of its azimuthal asymmetry, is responsible for faster decay of elliptical jet. The visualization of elliptic jet corroborates the fact that the waves prevailing in the elliptical jet are significantly weaker than those in the circular jet.

Influence of nozzle exit geometrical parameters on supersonic jet decay

2021 ◽  
Vol 0 (0) ◽  
Author(s):  
Prasanta Kumar Mohanta ◽  
B. T. N. Sridhar ◽  
R. K. Mishra
Keyword(s):  
Aspect Ratio ◽  
Nozzle Exit ◽  
Ambient Air ◽  
Schlieren Image ◽  
Geometrical Parameters ◽  
Image Study ◽  
Aspect Ratios ◽  
Core Length ◽  
Supersonic Core Length ◽  
The Impact

Abstract Experiments and simulations were carried on C-D nozzles with four different exit geometry aspect ratios to investigate the impact of supersonic decay characteristics. Rectangular and elliptical exit geometries were considered for the study with various aspect ratios. Numerical simulations and Schlieren image study were studied and found the agreeable logical physics of decay and spread characteristics. The supersonic core decay was found to be of different length for different exit geometry aspect ratio, though the throat to exit area ratio was kept constant to maintain the same exit Mach number. The impact of nozzle exit aspect ratio geometry was responsible to enhance the mixing of primary flow with ambient air, without requiring a secondary method to increase the mixing characteristics. The higher aspect ratio resulted in better mixing when compared to lower aspect ratio exit geometry, which led to reduction in supersonic core length. The behavior of core length reduction gives the identical signature for both under-expanded and over-expanded cases. The results revealed that higher aspect ratio of the exit geometry produced smaller supersonic core length. The aspect ratio of cross section in divergent section of the nozzle was maintained constant from throat to exit to reduce flow losses.

Comparative study on interfacial oscillations of rectangular and elliptical liquid jets

2020 ◽  
Vol 234 (7) ◽  
pp. 1272-1286 ◽  
Author(s):  
Amin Jaberi ◽  
Mehran Tadjfar
Keyword(s):  
Aspect Ratio ◽  
Weber Number ◽  
High Speed ◽  
Nozzle Geometry ◽  
Liquid Jets ◽  
High Speed Photography ◽  
Aspect Ratios ◽  
Water Jets ◽  
Switching Phenomenon ◽  
Axis Switching

The instability characteristics and flow structures of water jets injected from rectangular and elliptical nozzles with aspect ratios varying from 2 to 6 were experimentally studied and compared. Shadowgraph technique was employed for flow visualization, and structures on the liquid jet surface were captured using high speed photography. It was found that disturbances originating from the nozzle geometry initially perturbed the liquid column, and then, at high jet velocities, disturbances generated within the flow dominated the jet surface. It was also found that rectangular nozzles introduced more disturbances into the flow than the elliptical ones. The characteristic parameters of axis-switching phenomenon including wavelength, frequency, and amplitude were measured and compared. Axis-switching wavelength was found to increase linearly with Weber number. Also, the wavelengths of rectangular jets were longer than the elliptical jets. Further, the frequency of axis-switching was shown to be reduced with increase of both Weber number and aspect ratio. It was observed that the axis-switching amplitude increased monotonically, reached a peak, and then decreased gradually. It was also found that the axis-switching amplitude varied with Weber number. At lower values of Weber number, the rectangular nozzles had higher amplitude than the elliptical nozzles. However, at higher values of Weber number, this relation was reversed, and the elliptical nozzles had the higher axis-switching amplitudes. This reversal Weber number decreased with the orifice aspect ratio. The reversal Weber number for aspect ratio of 4 was about 289, and it had decreased to 144 for the aspect ratio of 6.

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.

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.

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