Peer Review Paper

For Peer Review

Computational analysis of subsonic flow in aircraft engine

intake with auxiliary air intake configuration

Journal: Aircraft Engineering and Aerospace Technology

Manuscript ID: AEAT-02-2014-0022

Manuscript Type: Research Paper

Keywords: Aircraft engine, Auxiliary air intake, Pressure recovery, Computational fluid dynamics, Take-off performance, Auxiliary interference plane (AIP)

Aircraft Engineering and Aerospace Technology

For Peer Review

Abstract:

With the objective to reduce the take off distance in naval aircrafts by using auxiliary intake door

in the engine duct and thereby maximizing total pressure recovery. Computational studies on

aerodynamic performance over an auxiliary air intake fitted in a typical aircraft S-intake were presented in

this paper. The aerodynamic performances of auxiliary air intake were calculated at Mach number of 0.1

and Reynolds number based on inlet duct length is of 0- 9.8 *105. Unstructured mesh was done with

Ansys ICEM-CFD using tetra-triangular cells and all the computations were done with commercial

computational package Ansys Fluent. Pressure recovery for 3D-Ducts with and without auxiliary air intake

was studied computationally with good accuracy using k- epsilonturbulence model. The performance

parameters like total pressure recovery, static pressure were calculated at aerodynamic interference

plane (AIP). The aircraft inlet duct with auxiliary air intake shows a better efficient at low range operation

end.

Keywords: Air intake, pressure recovery, Computational fluid dynamics, auxiliary interference plane (AIP)

Introduction:

Naval aircrafts has only short run way distance which demands better engine performance during

take-off. The proper supply of air into the aircraft engine under various operational conditions of aircraft is

a fundamental role of aerodynamics. The feeding of fresh air into the aircraft is carried out by passage

enclosed through intake lip and duct called air intake.

But due to various factors like flow separation, spillage at lip, pressure loss, friction, boundary

layer, interaction with mounting arrangement the supply of air into the engine getsaffected. During the

take-off condition, the air supply into the engine is limited by the area of intake is while at high speed

spillage plays a main role in dragging air supply.

At lower subsonic speeds, especially during takeoff, it is necessary that allow the engine to have

a high mass flow of air to produce required thrust. But during take-off, since there is no much pressure

difference between engine face and inlet lip face there is no ramming effect produced, also air is

required to force to enter into the engine. Hence, during take-off the engine must depend on its gathering

Page 1 of 28 Aircraft Engineering and Aerospace Technology

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For Peer Review

ability to fulfill its appetite of large volume of air.This fulfilling ability of engines air demandduring take-

off ability is mainly depends on the area of the inlet, thus the larger the area of the inlet throat, greater the

gathering ability of the engine.

The capture area and its influence on pressure recovery and drag is an issue with both

supersonic and subsonic designs. If the intake which has a large captures area, or, more to the point, a

high capture/throat area ratio, this is optimized for low speeds, the excess airflow spilling it around it at

high speeds will separate and thus will create spillage drag. But increasing the area of intake affects the

performance of aircraft engine at cruise speed and altitude for which it is designed. Equally sizing the

capture area for high speed operation will mean loss of performance at low speeds, due to insufficient air

reaching the engine. This issue can be solved in generally two ways as intermittently operating auxiliary

intakes and variable inlet geometry depending on airflow available. Since later is a non-cost effective and

riskiest, some designers ruled out second option.For the foregoing reasons, it is desirable to be able to

enlarge the minimum total cross-sectional area of the inlet passageway, such as by providing

intermittently operating auxiliary airflow passageways to the engine. These types of doors opens at low

speeds to effectively increase the capture area and close when they are not needed and they usually take

the form of blow-in doors.

Understanding of aerodynamics over inlet is necessary for the design an inlet with good balance

between good pressure recovery and low inlet drag. Even 1% increment in the pressure recovery yields

the 1% increment in thrust, thus study of pressure recovery in air intake is necessary. The present

computational study only focuses on the effect of auxiliary air intake in the S-duct at takeoff conditions.

The auxiliary air intake is of blow-in type and has a shape of three airfoils so that engine damage caused

by foreign objects can be prevented and flow separation at auxillary door lips can be avoided.

Literature survey:

Since most of research in auxiliary air intake was carried out by defense organizations, in spite of

remarkable progress in auxiliary air intake research, the publication and access are limited. Sobester[1]

reviewed the historical survey of scientific and technical developments in aerodynamics of jet engines and

Page 2 of 28Aircraft Engineering and Aerospace Technology

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For Peer Review

its influence on inlet designs. The transformation of freestream flow conditions into the engines required

conditions is the measuring scale for the efficiency of intake. Better inlet comprises of good total pressure

recovery along with minimum drag, fan face pressure distribution, weight, complexity and cost. TheIn

terms of pressure recovery Scoop type inlet is found to be better than flush-mounted submerged

intakes.The main source of pressure loss at inlet is frictional effect between airflow and aircraft body.

MiG-29 had the feature of intermittently operating auxiliary air intake with a sealed door to stop the engine

damage might have been caused by foreign object when operating near ground.So in this study a scoop

type inlet likely of S-shaped along with auxiliary air intake attached with complete typical aircraft is

considered for study.

Mujumdaret al [5] presented the design optimization of Y-shaped intake ducts which are

symmetrical about their central plane embedded in the fuselage. The two arms of the Y are typically ducts

with double bends (S-shaped) and the two arms merges downstream and beyond which the duct is a

single symmetrical tube. In our work the computation model is selected such that the single S-duct which

form an arm of Y- shaped intake and symmetrical boundary condition is used to analyze the flow in the

merged portion of Y-shaped intake.

Fattah et al [2 & 3] works on auxiliary air intake in Jindivik aircraft is detailed with wind tunnel

values at velocity ranges from 0 85 m/s and angle of attack from 00to 10

0. The effect of geometry,

shape and location of different auxiliary air intake were tested and found that rectangular with the

curvature similar to the cowl is found to have best. The sharp lip profile auxiliary air intake was found

have a better pressure recovery capability at all speed tests. Also pressure recovery ability is in

decreasing from fully closed door configuration to half closed door configuration and then to fully open

configuration. Test with cross wind found that the auxiliary air take effect on it was found as negligible.

The variation of static pressure on the length of the inner duct is compared with the model without

auxiliary duct and found to have a better raise. Hence the auxiliary air intake of rectangular shape and

sharp lipped profile is considered in this study.

Computational analysis for the flow field within the three-dimensionalS-duct is done with the

extended k- turbulence model at Mach number of 0.6 was carried out by yongchoetal [3].A straight duct


123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

For Peer Review

of 4.6 Diis attachedbefore the S-duct to get the boundary layer thickness equivalent to aircraft body at the

inlet of S-duct. The computed static pressure, total pressure fields are compared with the experimental

values of Vakili et al [7].From velocity vectors the separation regions are calculated and it is found that

computed flow separation region is farther downstream than the experimentally measured values.Also, on

comparison of circumferential static pressure with the experimental values the agreement was not good.

The deviation of computed results from experimental was due to the boundary layer growth originated

from installation of straight duct and henceadditional computational study is needed for correctly

predicting the turbulent flow inside the duct. Hence in our study to compute the boundary layer growth

correctly we are attaching the inlet with typical aircraft likely of Mig-29.

Numerical simulation was carried out around the wing-body configurations was found to be

effective method for boundary layer growth [Kanazaki,8-10]. Some studies were done for inlet studies

with wing-body configuration[dinesh] to study the coupled internal and external flow.

Geometry:

The geometry adopted for present study is a symmetrical portion ofatypical aircraft(similar to MiG

29) having aY-shaped duct with its two of arms shapedinto two S ducts as shown in figure 1. The length

of each S-duct is of 4m and has an inlet area of 0.18m2 and exit area of 0.22m

2 i.e., area ratio of inlet to

exit is 0.8. Arectangular shaped auxiliary air intake of dimension 0.3*0.6 m is attached on curvature of

intake as shown in figure 2a. The auxiliary intake has splitsinto three streamlined doors with equally

spacing between themso that the incoming flow can be channel to reduce the boundary layer growth as

shown in figure 2b.


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Fig. 2a :S- Duct

Fig. 2b : S- Duct with a rectangular auxiliary duct

Grid Generation:


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For Peer Review

The unstructured grid generation were done using Ansys ICEM CFD commercial software to

obtain a surface and volume mesh consist of tetra and triangular cells the quality of the mesh is around

0.23 and the nodes and cells around 200000 with the scale factor of 0.3 as shown in figure 3.

Fig. 3a : Unstructured Mesh on the surface of S - Duct

Fig. 3b : Cut sectional view of Mesh on the surfaceFig. 3c : Cut sectional view of Mesh on the surface


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Fig. 3d : Cut sectional view of Mesh on the surface

Computational:

Three dimensional numerical computational were performed using commercial CFD package

Fluent. In present investigation, steady state computations have been made adopting k- turbulent

model. The use of the turbulent model has been arrived after making necessary grid sensitivity tests,

convergence history.

The first cell distance near the wall boundary conditions was of order of 5*103mm and y

+ of 0.4.

The pressure far-field boundary condition at the inlet, no slip wall boundary condition with

suitable near wall treatment for turbulent flows were enforced in fuselage air intake, auxiliary air intake,

doors. In order to save the computational time only half of aircraft were considered with symmetrical

boundary condition was applied at mid plane of fuselage. The overall grid, computational domain and

boundary condition adopted is shown in fig. 4. The residuals of continuity, energy, and turbulent kinetic

energy with mass flux between the inflow and outflow and y+ values were monitored. The convergence

history of mass weighted average was monitored during the entire solution period. Results were analyzed

only when it was ascertained that the residuals has converged to the order of 10-5.

Results:

Fig.5a and 5b shows the static pressure distributions at inner surface of duct with and without

channel opening of auxiliary intake duct. The surface static pressure rises along the inner duct for both

configuration. From the comparison it is clear that that the presence of auxiliary air intake affect the static

pressure ahead of it and aft it.

Fig. 6a and 6b shows the comparison of total pressure at the inner surface of duct for with and

without channel opening of auxiliary duct respectively. Further fig. 6c shows the closure view of total

pressure distribution near the channel opening. From the calculation of mass weighted average it is found

that the total pressure raised form a value of 94 KPa to 96Kpa on comparing the door closed and door

open configuration.


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Velocity profiles normal to the surface of the duct is shown in fig. 6. It is found the a secondary

fluid is developed on aft portion of bend of S-duct which is primary due to movement of fluid particles

towards the center of duct to satisfy constant mass flux.

Velocity contour on mid plane of S-Duct in door closed and open configuration along the flow

direction are shown in the fig. 7a and 7b respectively. Velocity at inlet is decreased by the presence of

auxiliary opening so that average velocity reduced which will lead to less spillage drag. Near the lower

wall it is found that low energy is found. The non-uniform flow at the exit of S-duct is clearly predicted from

the contour. From the closure view near the channel it is found that the flow between first channel is

having lesser velocity and the second channel has higher velocity and so does the third channel.

Fig. 5a : Static pressure contour on mid plane of S-Duct in door closed configuration.

Fig. 5b : Static pressure contour on mid plane of S-Duct in door open configuration.


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Fig. 6a : Total pressure contour on mid plane of S-Duct in door closed configuration.

Fig. 6b : Total pressure contour on mid plane of S-Duct in door open configuration.

Fig. 6c :Closure view of Total pressure contour on mid plane of S-Duct in door open configuration.


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Fig. 7a: Velocity contour on mid plane of S-Duct in door closed configuration.

Fig. 7b: Velocity contour on mid plane of S-Duct in door open configuration.

Fig. 7c: Closure view of Velocity contour on mid plane of S-Duct in door open configuration.


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Fig. 8a: Velocity vector on mid plane of S-Duct in door closed configuration.

Fig. 8b: Velocity vector on mid plane of S-Duct in door closed configuration near inlet.

Fig. 8b: Velocity vector on mid plane of S-Duct in door open configuration near inlet.


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Conclusion:

Because of Auxiliary air intake doors the total pressure at Aerodynamic Interference Plane (AIP)

improves from 94.5KPa to 97.5KPa at 0 degree AOA and at 0.1 Mach number.

The study clearly captures the flow structures in the Y- duct with each arm consists of S-duct with

an auxiliary air intake. From the total pressure recovery comparison it is found that the auxiliary air intake

shows a better aerodynamic efficiency during the takeoff regime of aircraft.

It reduces the flow separation at the intake lip experimental study on the intake duct with auxiliary

air intake is necessary for the validation of computational results with the AAID. Also we are continuing

this work at different angle of attacks and at different Mach numbers.

References:

1. Tradeoffs in Jet Inlet Design: A Historical Perspective, AndrsSbester, JOURNAL OF

AIRCRAFTVol. 44, No. 3, MayJune 2007.

2. Modification of Jindivikairintake duct with an auxiliary intake static aerodynamic tests, A. M.

Abdel-fathah, propulsion technical memorandum august 1991.

3. Wind tunnel tests on jindivik air intake duct with and without an auxiliary intake, A. M. Abdel

fetah, Y.Y. Link, propulsion memorandum 472, march 1992.

4. Soo-yongcho ., Byung kyu park, Numerical study of three dimensional compressible flow within

an S- duct for aircraft engine inlet, KSAS international journal, Vol. 1., No. 1, May 2000.


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For Peer Review

5. AERODYNAMIC DESIGN OPTIMIZATION STUDIES AT CASDE , P.M. Mujumdar, K.

Sudhakar, A.G. Marathe, A. Isaacs, D. Ghate& N. Nigam , Proceedings of the Symposium on

Applied Aerodynamics and Design of Aerospace Vehicles 15-16 December 2003, Bangalore,

India

6. Inlet Drag Prediction for Aircraft Conceptual Design Paul Malan and Eugene F. Brownt

,JOURNAL OF AIRCRAFT Vol. 31, No. 3, May-June 1994

7. Vakili, A. D., Wu, J. M., Bhat M. K. and Liver, P. A., 1987, Compressible flow in diffusing S-duct

with flow seperatiom, in Heat transfer and fluid flow in rotating Machinery edited by Yang, W.J.,

Hemisphere publishing corporation, pp. 201-211.

8. Dinesh kumar

9. 9. NUMERICAL SIMULATION OF SUPERSONIC FLOW AROUND WING-BODY

10. CONFIGURATION WITH INTEGRATED ENGINE NACELLE ,Masahiro Kanazaki*, Shigeru

Obayashi and Kazuhiro Nakahashi, AIAA-2002-0836

11. Doyle Knight, Wei-Li Zhang and Don Smith, Automated Design of a three-dimensional subsonic

diffuser, J. of Propulsion and Power, Vol. 16 No.6, Nov.-Dec. 2000.

12. Doyle Knight, Automated optimal design of supersonic and subsonic diffusers using CFD,

European Congress on Computational Methods in Applied Sciences and Engineering,

ECCOMAS 2000.

13. Richard C. Jenkins and Albert L. Loeffler Jr., Modeling of subsonic flow through a Compact

Offset Inlet diffuser, AIAA Journal, Vol. 29, No. 3, March 1991.


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Computational analysis of subsonic flow in aircraft engine intake with auxiliary air intake configuration

Computational analysis of subsonic flow in aircraft engine intake with auxiliary air intake configuration Author 1 Name: Rajasekar J. Department: Department of Aeronautical Engineering University: Mount Zion College of Engineering and Technology Town/City: Pudukkottai State (US only): Country: India Author 2 Name: Senthilkumar R. Department: Department of Aeronautical Engineering University: Mount Zion College of Engineering and Technology Town/City: Pudukkottai State (US only): Country: India [email protected]

Please check this box if you do not wish your email address to be published NOTE: affiliations should appear as the following: Department (if applicable); Institution; City; State (US only); Country. No further information or detail should be included Acknowledgments (if applicable): We thank the management and administration of Mount Zion College and Technology for giving their encouragement and support for this work. Biographical Details (if applicable): Nil Abstract Purpose The aim of this paper is to increase the take-off performance and to reduce the take-off distance in aircrafts by using auxiliary intake door in the engine duct and thereby maximizing total pressure recovery. Design/methodology/approach Computational studies on aerodynamic performance over an auxiliary air intake fitted in a typical aircraft S-intake were presented in this paper. Unstructured mesh was done with Ansys ICEM-CFD using tetra-triangular cells and three dimensional numerical computational were performed using commercial computational software Ansys Fluent. The aerodynamic performances of auxiliary air intake were calculated at Mach number of 0.1 and range of Reynolds number based on inlet duct length is of 0 - 9.8 *10

5.

Findings - Pressure recovery and flow separation at cowl lip for three dimension inlet ducts with and without auxiliary air intake were studied computationally with good accuracy. The performance parameters like total pressure recovery, static pressure were calculated at aerodynamic interference plane (AIP). The aircraft inlet duct with auxiliary air intake shows a better efficient at low range operation end.

Research limitations/implications - The present computational study only focuses on the effect of auxiliary air intake in the S-duct at take-off conditions. Practical implications Aircraft engine with auxiliary air intake will be a stronger solution for the short take off aircraft such as naval aircrafts. Originality/value Computational study on auxiliary air intake is very few in the academic community. Paper type Research paper Keywords [Mandatory]: Aircraft engine, Auxiliary air intake, Pressure recovery, Computational fluid dynamics, Auxiliary interference plane (AIP), Take-off performance


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For Peer Review

Type footer information here

Type header information here

For internal production use only Running Heads:

Abstract:

With the objective to reduce the take off distance in naval aircrafts by using auxiliary intake door in the engine

duct and thereby maximizing total pressure recovery. Computational studies on aerodynamic performance over an

auxiliary air intake fitted in a typical aircraft S-intake were presented in this paper. The aerodynamic performances of

auxiliary air intake were calculated at Mach number of 0.1 and Reynolds number based on inlet duct length is of 0- 9.8

*105. Unstructured mesh was done with Ansys ICEM-CFD using tetra-triangular cells and all the computations were

done with commercial computational package Ansys Fluent. Pressure recovery for 3D-Ducts with and without auxiliary

air intake was studied computationally with good accuracy using k- epsilonturbulence model. The performance

parameters like total pressure recovery, static pressure were calculated at aerodynamic interference plane (AIP). The

aircraft inlet duct with auxiliary air intake shows a better efficient at low range operation end.

Keywords: Air intake, pressure recovery, Computational fluid dynamics, auxiliary interference plane (AIP)

Introduction:

Naval aircrafts has only short run way distance which demands better engine performance during take-off. The

proper supply of air into the aircraft engine under various operational conditions of aircraft is a fundamental role of

aerodynamics. The feeding of fresh air into the aircraft is carried out by passage enclosed through intake lip and duct

called air intake.

But due to various factors like flow separation, spillage at lip, pressure loss, friction, boundary layer, interaction

with mounting arrangement the supply of air into the engine getsaffected. During the take-off condition, the air supply

into the engine is limited by the area of intake is while at high speed spillage plays a main role in dragging air supply.

At lower subsonic speeds, especially during takeoff, it is necessary that allow the engine to have a high mass

flow of air to produce required thrust. But during take-off, since there is no much pressure difference between engine

face and inlet lip face there is no ramming effect produced, also air is required to force to enter into the engine.

Hence, during take-off the engine must depend on its gathering ability to fulfill its appetite of large volume of air.This

fulfilling ability of engines air demandduring take-off ability is mainly depends on the area of the inlet, thus the larger

the area of the inlet throat, greater the gathering ability of the engine.

The capture area and its influence on pressure recovery and drag is an issue with both supersonic and

subsonic designs. If the intake which has a large captures area, or, more to the point, a high capture/throat area ratio,

this is optimized for low speeds, the excess airflow spilling it around it at high speeds will separate and thus will create


123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

For Peer Review



spillage drag. But increasing the area of intake affects the performance of aircraft engine at cruise speed and altitude

for which it is designed. Equally sizing the capture area for high speed operation will mean loss of performance at low

speeds, due to insufficient air reaching the engine. This issue can be solved in generally two ways as intermittently

operating auxiliary intakes and variable inlet geometry depending on airflow available. Since later is a non-cost

effective and riskiest, some designers ruled out second option.For the foregoing reasons, it is desirable to be able to

enlarge the minimum total cross-sectional area of the inlet passageway, such as by providing intermittently operating

auxiliary airflow passageways to the engine. These types of doors opens at low speeds to effectively increase the

capture area and close when they are not needed and they usually take the form of blow-in doors.

Understanding of aerodynamics over inlet is necessary for the design an inlet with good balance between good

pressure recovery and low inlet drag. Even 1% increment in the pressure recovery yields the 1% increment in thrust,

thus study of pressure recovery in air intake is necessary. The present computational study only focuses on the effect

of auxiliary air intake in the S-duct at takeoff conditions. The auxiliary air intake is of blow-in type and has a shape of

three airfoils so that engine damage caused by foreign objects can be prevented and flow separation at auxillary door

lips can be avoided.

Literature survey:

Since most of research in auxiliary air intake was carried out by defense organizations, in spite of remarkable

progress in auxiliary air intake research, the publication and access are limited. Sobester[1] reviewed the historical

survey of scientific and technical developments in aerodynamics of jet engines and its influence on inlet designs. The

transformation of freestream flow conditions into the engines required conditions is the measuring scale for the

efficiency of intake. Better inlet comprises of good total pressure recovery along with minimum drag, fan face pressure

distribution, weight, complexity and cost. TheIn terms of pressure recovery Scoop type inlet is found to be better than

flush-mounted submerged intakes.The main source of pressure loss at inlet is frictional effect between airflow and

aircraft body. MiG-29 had the feature of intermittently operating auxiliary air intake with a sealed door to stop the

engine damage might have been caused by foreign object when operating near ground.So in this study a scoop type

inlet likely of S-shaped along with auxiliary air intake attached with complete typical aircraft is considered for study.

Mujumdaret al [5] presented the design optimization of Y-shaped intake ducts which are symmetrical about

their central plane embedded in the fuselage. The two arms of the Y are typically ducts with double bends (S-shaped)

and the two arms merges downstream and beyond which the duct is a single symmetrical tube. In our work the

computation model is selected such that the single S-duct which form an arm of Y- shaped intake and symmetrical

boundary condition is used to analyze the flow in the merged portion of Y-shaped intake.


123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

For Peer Review



Fattah et al [2 & 3] works on auxiliary air intake in Jindivik aircraft is detailed with wind tunnel values at velocity

ranges from 0 85 m/s and angle of attack from 00to 10

0. The effect of geometry, shape and location of different

auxiliary air intake were tested and found that rectangular with the curvature similar to the cowl is found to have best.

The sharp lip profile auxiliary air intake was found have a better pressure recovery capability at all speed tests. Also

pressure recovery ability is in decreasing from fully closed door configuration to half closed door configuration and then

to fully open configuration. Test with cross wind found that the auxiliary air take effect on it was found as negligible. The

variation of static pressure on the length of the inner duct is compared with the model without auxiliary duct and found

to have a better raise. Hence the auxiliary air intake of rectangular shape and sharp lipped profile is considered in this

study.

Computational analysis for the flow field within the three-dimensionalS-duct is done with the extended k-

turbulence model at Mach number of 0.6 was carried out by yongchoetal [3].A straight duct of 4.6 Diis attachedbefore

the S-duct to get the boundary layer thickness equivalent to aircraft body at the inlet of S-duct. The computed static

pressure, total pressure fields are compared with the experimental values of Vakili et al [7].From velocity vectors the

separation regions are calculated and it is found that computed flow separation region is farther downstream than the

experimentally measured values.Also, on comparison of circumferential static pressure with the experimental values

the agreement was not good. The deviation of computed results from experimental was due to the boundary layer

growth originated from installation of straight duct and henceadditional computational study is needed for correctly

predicting the turbulent flow inside the duct. Hence in our study to compute the boundary layer growth correctly we are

attaching the inlet with typical aircraft likely of Mig-29.

Numerical simulation was carried out around the wing-body configurations was found to be effective method

for boundary layer growth [Kanazaki,8-10]. Some studies were done for inlet studies with wing-body

configuration[dinesh] to study the coupled internal and external flow.

Geometry:

The geometry adopted for present study is a symmetrical portion ofatypical aircraft(similar to MiG 29) having

aY-shaped duct with its two of arms shapedinto two S ducts as shown in figure 1. The length of each S-duct is of 4m

and has an inlet area of 0.18m2 and exit area of 0.22m

2 i.e., area ratio of inlet to exit is 0.8. Arectangular shaped

auxiliary air intake of dimension 0.3*0.6 m is attached on curvature of intake as shown in figure 2a. The auxiliary intake

has splitsinto three streamlined doors with equally spacing between themso that the incoming flow can be channel to

reduce the boundary layer growth as shown in figure 2b.


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Fig. 2a :S- Duct

Fig. 2b : S- Duct with a rectangular auxiliary duct

Grid Generation:


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For Peer Review



The unstructured grid generation were done using Ansys ICEM CFD commercial software to obtain a surface

and volume mesh consist of tetra and triangular cells the quality of the mesh is around 0.23 and the nodes and cells

around 200000 with the scale factor of 0.3 as shown in figure 3.

Fig. 3a : Unstructured Mesh on the surface of S - Duct

Fig. 3b : Cut sectional view of Mesh on the surfaceFig. 3c : Cut sectional view of Mesh on the surface

Fig. 3d : Cut sectional view of Mesh on the surface

Computational:

Three dimensional numerical computational were performed using commercial CFD package Fluent. In present

investigation, steady state computations have been made adopting k- turbulent model. The use of the turbulent

model has been arrived after making necessary grid sensitivity tests, convergence history.


123456789101112131415161718192021222324252627282930313233343536373839404142434445464748495051525354555657585960

For Peer Review



The first cell distance near the wall boundary conditions was of order of 5*103mm and y

+ of 0.4.

The pressure far-field boundary condition at the inlet, no slip wall boundary condition with suitable near wall

treatment for turbulent flows were enforced in fuselage air intake, auxiliary air intake, doors. In order to save the

computational time only half of aircraft were considered with symmetrical boundary condition was applied at mid plane

of fuselage. The overall grid, computational domain and boundary condition adopted is shown in fig. 4. The residuals of

continuity, energy, and turbulent kinetic energy with mass flux between the inflow and outflow and y+ values were

monitored. The convergence history of mass weighted average was monitored during the entire solution period.

Results were analyzed only when it was ascertained that the residuals has converged to the order of 10-5.

Results:

Fig.5a and 5b shows the static pressure distributions at inner surface of duct with and without channel opening

of auxiliary intake duct. The surface static pressure rises along the inner duct for both configuration. From the

comparison it is clear that that the presence of auxiliary air intake affect the static pressure ahead of it and aft it.

Fig. 6a and 6b shows the comparison of total pressure at the inner surface of duct for with and without channel

opening of auxiliary duct respectively. Further fig. 6c shows the closure view of total pressure distribution near the

channel opening. From the calculation of mass weighted average it is found that the total pressure raised form a value

of 94 KPa to 96Kpa on comparing the door closed and door open configuration.

Velocity profiles normal to the surface of the duct is shown in fig. 6. It is found the a secondary fluid is

developed on aft portion of bend of S-duct which is primary due to movement of fluid particles towards the center of

duct to satisfy constant mass flux.

Velocity contour on mid plane of S-Duct in door closed and open configuration along the flow direction are

shown in the fig. 7a and 7b respectively. Velocity at inlet is decreased by the presence of auxiliary opening so that

average velocity reduced which will lead to less spillage drag. Near the lower wall it is found that low energy is found.

The non-uniform flow at the exit of S-duct is clearly predicted from the contour. From the closure view near the

channel it is found that the flow between first channel is having lesser velocity and the second channel has higher

velocity and so does the third channel.


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Fig. 5a : Static pressure contour on mid plane of S-Duct in door closed configuration.

Fig. 5b : Static pressure contour on mid plane of S-Duct in door open configuration.

Fig. 6a : Total pressure contour on mid plane of S-Duct in door closed configuration.


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Fig. 6b : Total pressure contour on mid plane of S-Duct in door open configuration.

Fig. 6c :Closure view of Total pressure contour on mid plane of S-Duct in door open configuration.

Fig. 7a: Velocity contour on mid plane of S-Duct in door closed configuration.


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Fig. 7b: Velocity contour on mid plane of S-Duct in door open configuration.

Fig. 7c: Closure view of Velocity contour on mid plane of S-Duct in door open configuration.

Fig. 8a: Velocity vector on mid plane of S-Duct in door closed configuration.


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Fig. 8b: Velocity vector on mid plane of S-Duct in door closed configuration near inlet.

Fig. 8b: Velocity vector on mid plane of S-Duct in door open configuration near inlet.


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Conclusion:

Because of Auxiliary air intake doors the total pressure at Aerodynamic Interference Plane (AIP) improves from

94.5KPa to 97.5KPa at 0 degree AOA and at 0.1 Mach number.

The study clearly captures the flow structures in the Y- duct with each arm consists of S-duct with an auxiliary

air intake. From the total pressure recovery comparison it is found that the auxiliary air intake shows a better

aerodynamic efficiency during the takeoff regime of aircraft.

It reduces the flow separation at the intake lip experimental study on the intake duct with auxiliary air intake is

necessary for the validation of computational results with the AAID. Also we are continuing this work at different angle

of attacks and at different Mach numbers.


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References:

1. Tradeoffs in Jet Inlet Design: A Historical Perspective, AndrsSbester, JOURNAL OF AIRCRAFTVol. 44, No.

3, MayJune 2007.

2. Modification of Jindivikairintake duct with an auxiliary intake static aerodynamic tests, A. M. Abdel-fathah,

propulsion technical memorandum august 1991.

3. Wind tunnel tests on jindivik air intake duct with and without an auxiliary intake, A. M. Abdel fetah, Y.Y. Link,

propulsion memorandum 472, march 1992.

4. Soo-yongcho ., Byung kyu park, Numerical study of three dimensional compressible flow within an S- duct for

aircraft engine inlet, KSAS international journal, Vol. 1., No. 1, May 2000.

5. AERODYNAMIC DESIGN OPTIMIZATION STUDIES AT CASDE , P.M. Mujumdar, K. Sudhakar, A.G.

Marathe, A. Isaacs, D. Ghate& N. Nigam , Proceedings of the Symposium on Applied Aerodynamics and

Design of Aerospace Vehicles 15-16 December 2003, Bangalore, India

6. Inlet Drag Prediction for Aircraft Conceptual Design Paul Malan and Eugene F. Brownt ,JOURNAL OF

AIRCRAFT Vol. 31, No. 3, May-June 1994

7. Vakili, A. D., Wu, J. M., Bhat M. K. and Liver, P. A., 1987, Compressible flow in diffusing S-duct with flow

seperatiom, in Heat transfer and fluid flow in rotating Machinery edited by Yang, W.J., Hemisphere publishing

corporation, pp. 201-211.

8. Dinesh kumar

9. 9. NUMERICAL SIMULATION OF SUPERSONIC FLOW AROUND WING-BODY

10. CONFIGURATION WITH INTEGRATED ENGINE NACELLE ,Masahiro Kanazaki*, Shigeru Obayashi and

Kazuhiro Nakahashi, AIAA-2002-0836

11. Doyle Knight, Wei-Li Zhang and Don Smith, Automated Design of a three-dimensional subsonic diffuser, J. of

Propulsion and Power, Vol. 16 No.6, Nov.-Dec. 2000.

12. Doyle Knight, Automated optimal design of supersonic and subsonic diffusers using CFD, European

Congress on Computational Methods in Applied Sciences and Engineering, ECCOMAS 2000.

13. Richard C. Jenkins and Albert L. Loeffler Jr., Modeling of subsonic flow through a Compact Offset Inlet

diffuser, AIAA Journal, Vol. 29, No. 3, March 1991.


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