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Tailored Supersonic Flow Fields

Description:

TECHNOLOGY AREA(S): Air Platform 

OBJECTIVE: Develop and demonstrate experimental techniques to reproduce complex flow fields determined by Computational Fluid Dynamics (CFD) solutions of integrated vehicle/inlet configurations for use in direct connect testing of supersonic inlets. 

DESCRIPTION: The Air Force Research Laboratory’s Aerospace Vehicles Division (AFRL/RQV) wishes to break the problem of analyzing modern supersonic external compression inlets (such as inlets on the F-15) into three distinct steps, 1) simulating the flow entering the inlet, including the forebody effect and forward portion of the inlet, especially at angles of attack and yaw, using CFD, 2) using the predicted CFD flowfield just upstream of the terminal normal shock inside the inlet, and mimicking this flow just upstream of the shock using a variety of physical techniques (blowing, suction, wall shaping, etc) inside of a duct, and then 3) simulating the rest of the inlet and diffuser conventionally, in a direct connect rig. AFRL is essentially looking for innovative ways of simulating the distorted flow ingested in inlets at angle of attack or yaw (pressure distortion and swirl) in a direct connect rig, without having to test the actual forebody and inlet front end. This would allow for the inexpensive study of inlets at off design, at smaller scale, and reduced cost. In the direct connect rig being considered at AFRL, it is envisioned that the desired pressure/swirl distortion pattern would be evaluated before the simulated cowl lip, but the flow control used to create the pattern can be contained anywhere between the beginning of a bellmouth to accelerate the inflow, to the constant area section behind the converging/diverging nozzle. Being able to accurately reproduce these distorted flow fields in both pressure distortion intensity and location, as well as, swirl intensity, location and direction in the intended rig would allow experimental measurements of the highly viscous flow field of a complete inlet design. The measurements at the end of the diffuser have historically been very difficult to simulate computationally and expensive to determine experimentally. The combination of robust computational predictions upstream of the terminal shock of a full size aircraft, the technologies created in this effort, and experimental measurements downstream of the terminal shock will allow RQV to simulate a range of maneuver conditions for future aircraft. This experimental data is critical to determine installed performance parameters at key flight points in a relatively low cost, rapid turnaround test rig as compared to prohibitively expensive (10 ft. to 16 ft.) wind tunnel facilities. Historically, pressure/swirl distortions have been generated using multiple techniques including screens, jets, vanes, and bellmouth designs. For screens, wire size and screen density were chosen using prior experience developed in a proprietary manner. Another method was to use air jets where the pressure of the jet was individually adjusted based upon the required distortion. Swirl has been generated in various ways but recently has used aerodynamic vanes. A rapid turnaround system that can produce distortion generation at low cost is desired. It is preferred that firms avoid extensive research into how each individual distortion generation device should be arranged to accomplish the desired flow profile goals. Distortion generation performance just prior to the simulated cowl will be validated. Another change from historical testing would be the change in internal flow path shape. As shown in SAE 1419, typical screens/jets/vanes are done on relatively large axis-symmetric shapes at subsonic Mach numbers. In contrast, the shape of ADAC diffuser will be a much smaller rectangular cross section (4.21x6 inches near terminal shock) and the intended flow field where the distortion is needed will be supersonic. 

PHASE I: Design/develop a range of techniques to provide arbitrary supersonic flow fields. Fundamental patterns will be provided to replicate. Using computational techniques and/or lab testing, the most promising techniques will be selected. 

PHASE II: Further refine technology for generating arbitrary supersonic flow fields. Design/develop hardware for generating a specific flow field for use in AFRL ADAC rig. Document performance of system through flow field measurements. In order to perform proof of concept test program, offerors may request use of the ADAC test rig (subject to availability) located at Wright-Patterson AFB. Only U.S. Citizens will be permitted to work within AFRL Facilities. 

PHASE III: Develop refined system and methodology for generating a range of supersonic flow fields typical of both military and commercial vehicle supersonic inlet systems. System should be capable of being used in DOD, NASA and commercial aircraft company test facilities. 

REFERENCES: 

1. Advisory Group for Aerospace Research and Development. Aerodynamics of Power Plant Installation Part 1, AGARDograph 103. AGARD, 1965. http://www.dtic.mil/dtic/tr/fulltext/u2/656569.pdf; 2. J. Koncsek, "An Approach to Conformal Inlet Diffuser Design for Integrated Propulsion Systems", 17th Joint Propulsion Conference, Joint Propulsion Conferences. https://doi.org/10.2514/6.1981-1395; 3. D. Beale, S. Wieland, J. Reed, and L. Wilhite, "Demonstration of a Transient Total Pressure Distortion Generator for Simulating Aircraft Inlet Distortion in Turbine Engine Ground Tests", ASME Turbo Expo 2007: Power for Land, Sea, and Air, Vol. 1, pp. 39-50.; 4. SAE International, "Inlet Total-Pressure-Distortion Considerations For Gas-Turbine Engines AIR 1419C", 2017.

KEYWORDS: Flow Distortion, Intake Aerodynamics, Pressure Distortion, Propulsion Integration, Direct-connect 

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