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Advanced Dynamic Inlet Distortion Generators


OUSD (R&E) CRITICAL TECHNOLOGY AREA(S): Quantum Science;Microelectronics;Advanced Materials


The technology within this topic is restricted under the International Traffic in Arms Regulation (ITAR), 22 CFR Parts 120-130, which controls the export and import of defense-related material and services, including export of sensitive technical data, or the Export Administration Regulation (EAR), 15 CFR Parts 730-774, which controls dual use items. Offerors must disclose any proposed use of foreign nationals (FNs), their country(ies) of origin, the type of visa or work permit possessed, and the statement of work (SOW) tasks intended for accomplishment by the FN(s) in accordance with the Announcement. Offerors are advised foreign nationals proposed to perform on this topic may be restricted due to the technical data under US Export Control Laws.


OBJECTIVE: The objective of this topic is to develop an advanced dynamic inlet-distortion generator capable of producing time-varying pressure, swirl, or combined pressure and swirl flowfields in front of a turbine engine or fan rig for ground test evaluations. Phase I efforts shall focus on ideation of the concept and development of design parameters that scale to the application. Phase II shall focus on prototyping development and culminate with a rig demonstration with or without turbomachinery. Phase III efforts will focus on commercialization for the military application as well as the urban air mobility and next gen commercial airliner applications.


DESCRIPTION: Next generation air platform designs pose critical challenges to propulsion systems due to the complex integration of the engine into the airframe.  The use of boundary-layer-ingesting inlets and integrated airframe-propulsion designs that eliminate podded propulsion in favor of drag-reducing streamlined designs can reduce the propulsion system performance and life.


Current practices for airframe-propulsion integration utilize advanced design tools and modeling software to predict performance and structural response of the propulsion system integrated with the airframe, but many conditions must be thoroughly tested to validate the predictions. Previous experience has shown the installation effects and the resulting inlet distortion ingested by the engine can lead to costly development efforts with sub-optimal results.


A broad spectrum of complex inlet distortions comprising non-uniform total pressures and velocities must be evaluated for performance and operability changes and aeromechanic responses of representative compression systems to fully understand the impact on conventional fan designs.  Based on evaluation of component designs, design practices will be adjusted to account for complex total pressure and velocity fields.


Current methods for producing inlet distortion have mainly focused on producing total pressure distortions with porous screens.  This method utilizes the natural pressure drop and velocity reduction that occurs as the inlet air passes through the screen [1-3]. Less common are inlet distortion generators designed for producing non-axial velocities, or swirl, at the inlet of the turbomachinery [4, 5].  These swirl generators have historically relied on turning vanes with prescribed placement such that the desired swirl profile is recreated at the face of the turbomachinery.  In most cases, the resulting distortion pattern is assumed to be static, and may represent a time-averaged flowfield.


This SBIR/STTR topic aims to develop an advanced inlet distortion generator for turbine engine ground testing that can produce user-prescribed time-varying pressure, swirl, or both simultaneously within one-and-a-half-duct diameters downstream of the generating device.  The distortion generator should be compatible with existing SAE ARP 1420 [6] best practices for distortion testing and evaluation as well as standard practices for engine and fan rig testing.  The distortion generator should be capable of producing standard inlet distortion patterns as defined in SAE AIR 1419 [7] (pressure distortion) and SAE AIR 5686 [8] (swirl distortion) as well as capable of generating complex aircraft patterns. Design concepts should be scalable to accommodate various sizes of turbine engines as well as fan and compressor component rigs. The device should be able to reproduce an end user’s defined pattern which may include localized areas with a time-varying reduction in total pressure and/or time-varying swirl flowfield. Knowledge of the flowfield interaction involving deficits of total pressure and non-uniform velocities as it develops axially will be critical for the success of the distortion generator. The device may use fixed geometry to match desired flow fields at one condition or contain movable geometry capable of reproducing numerous flow fields. The device should have a mechanical design with low risk of failure and a low cost for research programs.


PHASE I: Develop methodology and feasibility of a low-cost concept for a novel distortion generator system capable of producing a user-prescribed time-varying total-pressure loss or time-varying non-uniform velocity field within one-and-a-half duct diameters downstream of the device. Methodology should be model-based and build upon fundamental concepts and literature. Governing equations and design parameters should be specified that show how the device can be scaled for different sizes, time scales, and magnitudes. Direct to Phase II proposals should demonstrate existing methodologies and concepts mature enough for prototype demonstration.


PHASE II: Develop proof of concept prototype using the methodology developed in Phase I and test under relevant conditions the ability to reproduce a complex flowfield with a time-varying component with localized pressure deficits of at least 10% at tunable frequencies up to 2x of the fan speed or with non-axial velocities equivalent to 10 degrees of swirl with a periodic variation at half the rotor speed.  Continue development of design methodology to accurately predict and place complex flow features with a specified frequency up to one-and-a-half duct diameters downstream of the device. Continue development of the commercial merit of the device and its application to both civilian and military sectors.


PHASE III DUAL USE APPLICATIONS: Develop commercialization of the device, manufacturing methods, and finalize device form factor and capabilities. Evaluate market potential for military and civilian applications and assess required infrastructure for continued technology readiness level (TRL) and manufacturing readiness level (MRL) development. It is expected that this technology will be at a TRL of 4 at Phase III entry. AFRL/RQTT is a potential transition customer that may purchase a functional product. AFRL/RQTT plans to use this technology in a fan rig for Phase III efforts, demonstrating TRL of 6 for this planned technology.



  1. Barlow, J. B., Rae, W. H. Jr., Pope, A., Low-Speed Wind Tunnel Testing, 3rd Edition, John Wiley & Sons, Inc., 1999.;
  2. D. G. DeVahl, “The Flow of Air Through Wire Screens,” Hydraulics and Fluid Mechanics, R. Sylvester, Pergamon, New York, 1964, pp. 191-212;
  3. Pinker R.A., and Herbert M.V., “Pressure Loss Associated with Compressible Flow Through Square-Mesh Wire Gauzes,” Journal of Mechanical Engineering Science, Vol 9, No 1, 1967;
  4. Sanders D. D., Nessler, C. A., Copenhaver, W.W., List, M.G., and Janczewski, T.J., “Computational and Experimental Evaluation of a Complex Inlet Swirl Pattern Generation System”, AIAA Propulsion & Energy Exposition, AIAA 2016-5008, Salt Lake City, UT, 2016.;
  5. Nessler C. A, Sanders D. D., List M. G., Janczewski T. J., and Copenhaver W. W., “Axial Extent of Flowfield Variation from the StreamVaneTM Swirl Pattern Generation System”, 55th AIAA Aerospace Sciences Meeting, AIAA 2017-1621, Grapevine, TX, 2017.;
  6. SAE S-16 Committee, “Gas Turbine Engine Inlet Flow Distortion Guidelines,” ARP 1420, Society of Automotive Engineers, 1998.;
  7. SAE S-16 Committee, “Inlet Total-Pressure-Distortion Considerations for Gas-Turbine Engines”, AIR 1419B, Society of Automotive Engineers, 2013.;
  8. SAE S-16 Committee, “A Methodology for Assessing Inlet Swirl Distortion”, AIR 5686, Society of Automotive Engineers, 2010


KEYWORDS: Inlet distortion generator; dynamic inlet distortion generator; time varying inlet distortion; embedded engine; turbine engine inlet distortion; distortion tolerant fans

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