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Aerodynamic Analysis of Deployed Bay Doors on Modern High-Speed Aircraft


OBJECTIVE: Develop a cost effective way (process or tool) to evaluate unsteady aero loading on deployed aircraft bay doors, to allow designers to evaluate early in design process. DESCRIPTION: The U.S. Air Force is required to open doors on many of its aircraft during flight. This ranges from an aircraft's low-speed opening of landing gear doors and speed brakes to opening weapons bay doors in supersonic flight. This sets up a situation for unsteady aerodynamic loading of these surfaces due to their motion into the flow path as well as the potential for unsteady flow oscillations in and around the exposed opening in the aircraft. Deploying weapons bay doors is particularly complex in that the separated flow from the doors themselves interacts with the highly unsteady weapons bay flow which is known to exhibit strong tonal content under many of the flight conditions at which the U.S. Air Force operates its aircraft. These weapons bay tones and the oscillatory nature of the separated flow on the doors have the potential to excite structural modes of the doors, aircraft surfaces, or externally carried munitions and fuel tanks and can lead to buffet, flutter, or fatigue induced failures. Currently, significant effort is taken to substantiate structural loads design analysis and to demonstrate structural integrity for critical loadings of all aircraft components. This can involve a multitude of testing from finite element modeling to wind tunnel testing of dynamically scaled doors to actual flight testing. The focus here is the generation of the aerodynamic loading on the weapons bay doors and the surrounding aircraft surfaces. Typically steady door loads are collected during sub-scale wind tunnel testing. When model scale permits static pressure mapping and, on rare occasion, dynamic pressure transducers are applied to weapons bay doors to collect mean and fluctuating pressures on rigid doors for detailed analysis. The coupling of the unsteady weapons bay flowfield with the highly complicated three-dimensional (3-D) aircraft surfaces (reference 4) drive the need to accurately model this highly unsteady aerodynamic phenomenon. To improve the analysis of deploying aircraft surfaces, with specific focus on weapons bay doors, both computational modeling and wind tunnel testing to establish steady and unsteady surface loadings are needed. It is critical that this modeling of a rigid model capture the unsteady character of the fluid dynamics prior to considering deploying doors, transient loading due to store separation, and eventually fully coupled aero-structural modeling during a store separation event. The key aspect of this effort is to accurately capture the magnitude and frequency content of the unsteady surface pressures due to the weapons bay, transient surface motions, and eventually the fluid structure interaction. A geometric build-up approach is recommended in order to isolate the incremental contributions. It is desired that the software and supporting documentation be delivered at the completion of the Phase II effort for additional evaluation by U.S. Government personnel. PHASE I: Devise a plan to develop a process/tool to obtain unsteady aerodynamic surface loads in and around open aircraft weapons bays. Demonstrate feasibility of these techniques to address flight conditions Mach 0.6 to 5.0 at altitude and experimentally validate to the extent possible during Phase I. PHASE II: Unsteady aerodynamic surface loads due to weapons bay doors cycling and store separation will be incorporated into the tool. Demonstrate in the transonic and supersonic (Mach 2+) flow regime. Planning will include provisions for coupling of the unsteady analysis tool with structural modeling to provide a unified capability to analyze a fully flexible dynamic store separation with door cycling, leading to a tool to address sonic fatigue, buffet, limit cycle oscillation, and flutter. PHASE III: Military Application: landing gear aerodynamics, air brake, weapons configuration, and aircraft modifications for sensors, antennas etc. Commercial Application: landing gear aerodynamics, automobile design opening/closing of windows/sunroofs and auto racing movable aerodynamic surfaces. REFERENCES: 1. R.E. Little,"Aerodynamic Characteristics of Open Weapon Bays on The B-1,"Aircraft/Stores Compatibility Symposium Proceedings, Vol. 2, September 2-4 1975, ADA084870 available in DTIC, pp. 791-836. 2. S.J. Lawson, G.N. Barakos,"Review of Numerical Simulations for High-Speed, Turbulent Cavity Flows,"Progress in Aerospace Sciences 47 (2011), Elsevier, Ltd., pp. 186-216. 3. Kannepalli, C., Chartrand, C., Birkbeck, R., Sinha, N., and Murray, N.,"Computational Modeling of Geometrically Complex Weapons Bays,"AIAA 2011-2774 ,17th AIAA/CEAS Aeroacoustics Conference, 32nd AIAA Aeroacoustics Conference, Portland, Oregon, June 5-8 2011. 4. Flight test photos of a modern fighter aircraft weapons bay 5. Murray, N., Jansen, B., and Rich, D.,"Effect of Door Configuration on Cavity Flow Modulation Process,"AIAA-2011-2773, 17th AIAA/CEAS Aeroacoustics Conference, 32nd AIAA Aeroacoustics Conference, Portland, Oregon, June 5-8 2011.
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