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7/18/2019 Thrust Reverser Optimization for Safety With CFD
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Procedia Engineering 17 (2011) 595 – 602
1877-7058 © 2011 Published by Elsevier Ltd.
doi:10.1016/j.proeng.2011.10.075
Available online at www.sciencedirect.com
The 2nd International Symposium on Aircraft Airworthiness (ISAA 2011)
Thrust Reverser Optimization for Safety with CFD
QIAN Ruizhana,b
*, ZHU Ziqianga, DUAN Zhuoyi
b
aSchool of Aeronautics Science and Engineering, Beihang University, Beijing, 100191, P.R.China,
b Department of General Configuration and Aerodynamics design, AVIC the First Aircraft Institute, Xi’an, 710089, P.R.China
Abstract
With its function of decreasing the ground roll distance, thrust reverser (T/R) may cause safety problems in case of its
inadequate integration with the aircraft. Traditionally, designers rely on wind tunnel testing, which is expensive and
time-consuming and usually carried out only near the end of the design process, to verify their designs. This paper
addresses a numerical procedure for integration of the thrust reverser with the aircraft, in which the risk of ingestion
of the exhaust gas and foreign objects, the adverse effects on stability and control are evaluated for sequential thrust
reverser configurations so as to obtain an optimal design that meets airworthiness requirements, by means of
computational fluid dynamics (CFD) analysis performed on a complete aircraft model including fuselage, wing,
pylon, slats, flaps, spoilers, empennages and nacelle with thrust reverser deployed. The Reynolds averaged Navier-Stokes equations are solved using the commercial CFD flow solver, CFX5. The κ-ε two equations model has been
chosen to model the effect of turbulence. This procedure has been applied to the development of a regional jet,
yielding remarkable reduction of wind tunnel tests, providing a faster design-to-build cycle. The work indicates the
proposed procedure can be successfully used for reverser aerodynamic optimization to meet safety requirements.
© 2011 Published by Elsevier Ltd. Selection and/or peer-review under responsibility of Airworthiness
Technologies Research Center NLAA, and Beijing Key Laboratory on Safety of Integrated Aircraft and
Propulsion Systems, China
Keywords:Thrust reverser, Airworthiness standard, Safety, CFD, Navier-Stokes equations
* Corresponding author. Tel.: +86-029-86832360; fax: +86-029-86202493.
E-mail address: qianruizhan@sina.com
Open access under CC BY-NC-ND license.
Open access under CC BY-NC-ND license.
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596 QIAN Ruizhan et al. / Procedia Engineering 17 (2011) 595 – 602
1. Introduction
Modern aircraft are almost without exception equipped with thrust reverser systems to reduce break
wear and shorten landing length. The systems are built in to the nacelle system and uses the power of the
jet engine as a deceleration force by reversing the direction of the hot or cold stream airflows which
generate forward thrust in flight[1] (Fig 1). Thrust reverser systems are especially efficient for slippery
and wet runways.
(a) Forward Thrust (b) Reverse Thrust
Fig. 1 Section through jet engine nacelle with cold stream thrust reverser operating in forward and reverse thrust
Because of the interaction of the reverser efflux with the airframe and the effect the deployment of the
reverser can have on the engine cycle, thrust reverser design is a very complex and challenging task (Fig
2).
Generally the thrust reverser system is designed to provide as much reversed thrust as possible. The
constrains are associated with operational safety. The airworthiness requirements on thrust reverser
system are described in the following sections of FAR:
• §25.933 Reversing systems;
•
§25.934 Turbojet engine thrust reverser system tests;• §25.939 Turbine engine operating characteristics;
• §33.65 Surge and stall characteristics.
To summarize, the thrust reverser related safety problems are as follows[1,2,3]:
• Inlet distortion and Engine instability due to re-ingestion of reversed flows;
• Foreign object damage to engine structure due to ground debris lifted by strong inlet-ground vortex
caused by reversed flows;
• Loss of efficiency of the control surfaces due to changed flow field around the aircraft with the
deployment of thrust reverser;
• Vibration and fatigue due to impingement of reversed air flows on aircraft surfaces.
Thrust reverser wind tunnel tests are typically employed to investigate the combinability between the
thrust reverser and airframe[4] (Fig 3). But the tests are very expensive and time-consuming. Nowadays
only a few wind tunnels in the world can undertake these kinds of tests. Moreover, the tests are usually
performed in the late stage of aircraft design. Any safety problems appeared in the tests will lead to the
redesign of the thrust reverser and the delay of first flight.
During recent years, computational fluid dynamics (CFD) has made great progress in the simulation
of complex flow field. CFD brings about a new method in thrust reverser design[1-3,5-7].
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597QIAN Ruizhan et al. / Procedia Engineering 17 (2011) 595 – 602
This paper presents a CFD based procedure for thrust reverser/airframe integration. It can be used in
the early design stage to evaluate the combinability between the thrust reverser and airframe and detect
potential safety problems. It has found application in the development of a regional jet.
Fig 2. Interaction of the reverser efflux with the airframe
Fig 3. Thrust reverser wind tunnel test
2. CFD Model
The regional jet is powered by two aft-mounted engines equipped with a thrust reverser system which
is of the cascade type. Only the fan flow will be reversed. The cascade has 24 boxes placed
circumferentially around the nacelle with each box a tuned outflow direction. When reverse thrust is
engaged, the trans cowl moves back and a blocking mechanism is introduced to the cold stream flow
generated by the fan. The air flow is re-directed through 24 cascade boxes, forcing the flow back in the
direction of aircraft movement thereby reducing speed.
For safety assessment the reverser supplier gives aircraft manufacturer the baseline T/R CFD model,
which includes:
• Nacelle aero surface model with T/R deployed (Fig 4);
• Fan inlet flow rate;• 24 T/R efflux vectors (Fig 5);
• Cascade total pressure and temperature;
• Total pressure and temperature of fan and core exhaust.
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Fig 4. Thrust reverser cascade boxes
Fig 5. Efflux vector definition
From the view point of optimization the design variables are the 24 T/R efflux vectors. Adjusting the
beta angle can increase reverser thrust or avoid re-ingestion; changing the skew angle can avoid the efflux
impingement on particular surfaces.
The complete aircraft model includes fuselage, slats, wing, flaps, winglet, spoilers, HT, VT.
The Reynolds averaged Navier-Stokes equations were solved using the commercial CFD flow solver,
CFX5. The κ-ε two equations model has been chosen to model the effect of turbulence for its
compromise between robustness and use of computational resources. The grids are generated using ICEM
CFD (Fig 6).
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Fig 6. Computational grids
3. Integration of Thrust Reverser and Airframe
3.1. Optimization procedure
The thrust reverser optimization is a process by which the reverse thrust is maximized while the
aircraft safety is assured.
The CFD based procedure is as following:
1) The aircraft manufacturer puts forward the design requirements on the thrust reverser system.
2) The system supplier carries on the thrust reverser design and gives to the aircraft manufacturer the
baseline CFD model of the thrust reverser system.
3) The aircraft manufacturer carries on numerical investigation on complex flow field of complete
aircraft using CFD tool.
4) The effects of deployment of thrust reverser system on aircraft aerodynamics characteristics are
investigated based on CFD results while emphasis are placed on efflux re-ingestion and inlet distortion,stability and control, efflux impingement on control surfaces. Aircraft safety is evaluated according to
airworthiness standard.
5)If aircraft safety are meet according to airworthiness standard, the current design cycle will be
closed; Otherwise, the Technical discussion between the aircraft manufacturer and the system supplier
should be arranged to review the CFD results. De-emphasis on reverse thrust may be ineluctable to meet
safety requirements.
6) The system supplier starts a new design campaign based on the CFD results and suggestions from
aircraft manufacturer. The new CFD model of thrust reverser will be provided to aircraft manufacturer.
7)Do from 3) through 5) until the performance and safety requirements on the system are meet
simultaneously.
Integration of thrust reverser and airframe is a collaborative effort of the aircraft manufacturer and the
system supplier. The interface between the two sides is the thrust reverser CFD model. The key step is
complete aircraft flow field computation with thrust reverser deployment.
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3.2. CFD analysis
During the design of the regional jet, the aircraft manufacturer carries on CFD investigation for
baseline T/R configuration provided by the system supplier. Here only the re-ingestion of reversed flows
and inlet distortion are introduced briefly.
When the Mach number is 0.21, the T/R flow can not reach the wing. The free-stream encounters the
T/R flow around the top of the engine, then the high pressure air wall is appeared, leading to the augmentof the pressure on the upper and lower wing surface. When the Mach number is 0.21, the inlet distortion
index IDC is all below 0.06 (this is under the limitation of 0.07) whenever the fan inlet flow rate is large,
middle or small. The wake of spoiler is sunk into the engine, so the lower pressure region is appeared.
The T/R efflux does not enter the inlet (Fig 7).
Fig7. Isosurfaces of total temperature at M=0.21
When the Mach number is 0.09, the T/R flow reaches the front of the upper wing and body, the flow
structure is very complex. The free stream encounters the T/R flow in the front of the wing, then the high
pressure air wall is appeared. When the fan inlet flow rate is middle or large, the upper and lower surface
of the wing lie in the separate flow of air wall, so it will cause the reduction of the pressure, and the T/R
flow will enter the engine (as shown in fig8); But when the fan inlet flow rate is small, the front of upper
wing around the engine has not any separate flow, and the T/R flow does not enter the engine inlet. When
the Mach number is 0.09, the inlet distortion index IDC is below 0.06 (this is under the limit 0.07) if the
fan inlet flow rate is small, above 0.07 if the fan inlet flow rate is middle or large.
If the baseline T/R is employed when the Mach number is 0.09, the inlet distortion index IDC will be
above the value of the limitation, resulting in engine stability problems. The aircraft manufacturer
requests the system supplier to redesign cascade box 12~23 to avoid re-ingestion of reversed flows. The
system supplier then starts a new design campaign. After several iterations of cut and try, the safety
requirements are satisfied.
Total Temperature = 320K
Total Temperature = 308K Total Temperature = 306K Total Temperature = 310K
Total Temperature = 312K Total Temperature = 316K
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Fig 8. Efflux streamlines at M=0.09
4. Conclusions
A CFD based procedure of integration of thrust reverser system and airframe is presented to improve
aircraft safety in the early stage of aircraft design. The procedure is the team effort of aircraft
manufacturer and system supplier. The interface between the two sides is the thrust reverser CFD model.
The key step is complete aircraft flow field computation with thrust reverser deployment. Although wind
tunnel testing is still indispensable in the process of the development and checkout of thrust reverser
designs, the configurations to be chosen in the test can be considerably reduced by using this procedure.
The procedure has found successful applications in the development of a new regional jet.
Acknowledgements
The Authors would like to thank WANG Kaichun, JIANG Guangnan, ZUO Zhicheng and LIAO
Zhengrong for their outstanding support in CFD calculation.
Cascade 8 Cascade 11
Cascade 1 Cascade 4
Cascade 8 Cascade 11
Cascade 14 Cascade 19
Cascade 12 Cascade 13
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[3] Chen Chuck. Computational Procedures for Complex Three-Dimensional Geometries Including Thrust Reverser Effluxes
and APUs. AIAA 2001-3747.
[4] G.H. Hegen and J.W. Kooi. Investigation of Aircraft Performance with Deployed Thrust Reversers in DNW. AIAA 2005-
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Computed Flow field During Thrust Reversers Operation. AIAA 2006-3673.
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[7] Fernando Oliveira de Andrade Sandro Barros Ferreira, Luís Fernando Figueira da Silva. Study of the Influence of Aircraft
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