TO STUDY THE EFFECT OF CANTED ANGLE IN TURBULENCE …

© 2018 JETIR June 2018, Volume 5, Issue 6 www.jetir.org (ISSN-2349-5162)

JETIRC006021 Journal of Emerging Technologies and Innovative Research(JETIR)www.jetir.org 114

TO STUDY THE EFFECT OF CANTED ANGLE

IN TURBULENCE MIXING IN SUPERSONIC

TWIN JET

1Jubin Shaji, 2Mubarak A.K. 1 PG Student, Dept. of Mechanical Engineering , Government Engineering, College Thrissur, Kerala, India

2Assistant Professor, Dept. of Mechanical Engineering , Government Engineering, College Thrissur, Kerala, India

ABSTRACT-The pressing environmental issue of modern public is jet noise. Air travel is becoming common and affordable

globally. The airport authority set endurable limits of jet noise near airports. The review paper concentrate on twin jet interaction,

aeroacoustics and fluid flow physics. The computational and experimental investigation on supersonic jet noise is discussed;

consist of turbulent mixing noise, screech tones and broadband noise. CFD 2D simulation of axisymmetric converging diverging

nozzles of Mach number of 1.76 and canted twin jet has lower turbulence level due to jet interaction in the inter nozzle region.

The main objective of this study is to compare the jet structure, turbulence quantities of twinjets and the effect of canted angle in

turbulence mixing in supersonic twinjet.

KEYWORDS-Canted twinjet, supersonic nozzle, jet noise, twin jet, Axisymmetric converging diverging nozzles,potential core

length, jet interaction, Acoustic shielding

INTRODUCTION Canted nozzle from the basic definition has the meaning of a nozzle positioned so that its line of thrust is not parallel to the

direction of flight. The methods to lower turbulence in a nozzle is an active area of research. Greatrex and Brown [1958] put the

use of twinjets as a configuration to reduce jet noise. They found that two parallel co-planar jets placed sufficiently far apart to

avoid any interaction between the jets resulted in less noise radiation in the plane containing the axis of the jets than that

measured perpendicular to it. This phenomenon is called acoustic shielding.

Earlier research in twinjet, Lower turbulence levels were observed as compared to a single jet. The turbulence in the inter

nozzle region of the canted twin jets was significantly reduced due to increased jet interaction. The twin jet configuration leads to

reduction in sound pressure levels. This reduction in jet noise was attributed to two separate aeroacoustic phenomena. First is the

reduction due to acoustic shielding, where noise from one jet is suppressed in the sideline direction by the other jet. Second is the

reduction in noise due to increased jet interaction leading to reduced turbulence in the inter-nozzle region.

Raman panickar and chelliah[1] done a review on history of twinjet coupling, nozzle spacing, fatigue failure of components

due to dynamic pressure build up in inter nozzle region. To overcome above problems various techniques were employed.A

detailed review on twin rectangular supersonic jets and twin jet noise suppression was discussed.

R. W. Wlezien[2] studied jet interaction on various geometry and found that The noise produced by interaction of two

supersonic plumes is a strong function of nozzle spacing and jet Mach number.Yin zhao-qin[3] conducted a experimental work

related to the mixing region of twin jets and made a conclusion that the interference between the two jets increases as the spacing

between two nozzles decrease. The commercial computational fluid dynamic software packages have been widely accepted as a

research tool for jet interaction simulation. Sandeep yerapotina[4] studied the jet interaction between single and twin jet and their

acoustics characteristics K.M. Pandey et al[5] conducted simulation for multiple jet intraction in 2D using CFD softwareLater

2016 Justin D. Valentiet al[6] done simulation of dual jet flow using CFD software (StarCCM+ by CDAdapco).In this simulation

adaptive mesh refinement (AMR) approach was used. andVarious turbulence model were studied, compared with experimental

results. The twin jet CFD 2D simulation is done to compare the jet structure, turbulence quantities of twinjets and the effect of

canted angle in turbulence mixing in supersonic twinjet.

NOZZLE GEOMETRY AND COMPUTATIONAL DOMAIN

The CFD simulation of twinjet is carried out in axisymmetric converging diverging with exit diameter (d) of 21.3 mm. the exit

to throat area ratio for all the nozzle was 1.4, yielding a design

FIGURE 1:Schematic diagram of straight (left) and canted (right) twinjet

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mach number of 1.76. the spacing(s) between the twin nozzle is 37.3 mm or 1.75d. the converging angle is 350 and diverging

angle 50. The inlet pressure and temperature is 370000 Pa and 350F. The symmetry conditions where taken on opposite side of

the domain.

FIGURE 2:Computational domain

NUMERICAL METHODOLOGY

The fluent software employs finite volume based numerical method to solve the physics laws governing the flow through

nozzle. The mathematical equation that represent the physical laws, namely continuity equation, momentum equation, energy

equation and turbulence equation, are solved numerically along with appropriate constitute relation.

Continuity Equation 𝜕𝜌

𝜕𝑡+ 𝛻 ∙ (𝜌𝑢) = 0

Momentum Equation

𝜌𝜕𝑢

𝜕𝑡+ 𝜌𝑢. ∇𝑢 = −∇𝑝 + ∇ ∙ 𝜏 + 𝜌𝑓𝑥

Energy Equation

𝜌𝜕𝑒

𝜕𝑡+ 𝜌𝑢. ∇𝑒 = −𝑝∇ ∙ 𝑢 − ∇ ∙ 𝑞 + 𝜏: ∇𝑢 + 𝜌�̇�

In the above equations [8], ρ is the mass density; u is the velocity vector; p is the pressure; fk is the body force. In this study,

the turbulence is modeled using the k-ω sst turbulence model and the transport equations of turbulent kinetic energy, k and its

dissipation rate, ε are also solved along with aforementioned governing equations. The transport equations of k and ω are not

shown here for brevity.

COMPUTATIONAL MESH AND MESH STUDIES

A 2D computational mesh generated by ANSYS ICEM CFD applied to the axisymmetric converging-diverging nozzle. In

order to get mesh independent results a grid independency study is done are given in table 1

TABLE 1:Grid independency

Mesh No. Cell Velocity at exit

1 922600 434.6

2 752800 434.2

3 567895 430

Richardson Extrapolation methodused for grid independency study and Grid Convergence Index is 0.0001387589. the mesh

number 2 is used for study.

VALIDATION

Axis symmetric convergent divergent twinjet nozzle is validated [1] and found percentage error of




FIGURE 3:Validation of twin nozzle

6.04.

RESULTS AND DISCUSSIONS

(a) Velocity Distributions

The centre line velocity for axis symmetric twinjet and canted twinjet is shown in figure 4. Twinjet with canted angle

6,08,0100is plotted from results we can find canting of angle decreases the turbulence level. The turbulence level in the inter

region of the twin jets (canted) was significantly reduced due to increased jet interaction.

FIGURE 4:Center line velocity

the contour plot ofcenter line velocityshows the mean axial velocity. While canting thre twin jet the potential core of the exit

of the nozzle decreases. Shock cell structure is clearly seen. The structure of the jet exit is now elliptical. In twin jet we can see

that the separate single jet exit is now converging into simple jet.

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25

u/U

j

x/d

Center Line velocity

Numerical

experimental

0

0.2

0.4

0.6

0.8

1

1.2

0 5 10 15 20 25

u/U

j

x/d

Center line velocity

TWIN JET

CANTED ANGLE 8

CANTED ANGLE 10

CANTED TWINJET 6




FIGURE5: Velocity contour

(b) Turbulence Quantities

FIGURE6: Turbulence intensity

0

0.02

0.04

0.06

0.08

0.1

0.12

0 5 10 15 20

u/U

j

x/d

Trbulence Intencity

CANTED ANGLE 6

TWINJET

CANTED ANGLE 8

CANTED ANGLE10




FIGURE7: Turbulence intensity contour

Axial fluctuating velocity, u′/Uj vs diameter length Dis plotted in figure 6 were the turbulence intensity is seen decreasing as

the angle of canting is increased. Spacing ratio decreased between jets. The figure 7 shows contour of turbulence intensity were

lower turbulence level were found due to canting.

CONCLUSION

As the canting of twinjet is done the potential core length decreased between the jet. As the turbulence level lowers which

leads to lower noise levels due to acoustics shielding. the jet structure, turbulence quantities of twinjets and the effect of canted

angle in turbulence mixing in supersonic twinjet is studied. As canting of the jet in a practical case is much to be studied but

implementation can be more helpful for maintaining the regulation done by the various international bodies.

REFERENCES [1] Ganesh Raman, Praveen Panickar, Kanthasamychelliah“ Aeroacoustics of twin supersonic jets: a review” (2012), pp 957-

984.

[2] R. W. Wlezien, “Nozzle Geometry Effects on Supersonic Jet Interaction” ,AIAA Journal vol 27, (1989), pp 1361-1367.

[3] Yin Zhao-qin, “Experimental Study on the Flow Field Characteristics in the Mixing Region of Twin Jets” Science Direct

journal of hydrodynamics ,(2007) pp. 309-313.

[4] Sandeep Yerapotina, “Aeroacoustic Characteristics of Supersonic Twin Jets” Florida state university (2005), pp 1-72.

[5] K. M. Pandey, Virendra Kumar, Prateek Srivastava, “CFD Analysis of Twin Jet Supersonic Flow With Fluent Software”

Current Trends in Technology and Sciences, (2012), pp 84-91.

[6] Justin D. Valenti, Melissa Fronzeo “A Validation Effort of Dual Jet Flow Simulations” AIAA (2016) pp 1-15.


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