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Novel Flow Control Strategies for High-Speed Inlets and Isolators


RT&L FOCUS AREA(S): Hypersonics

TECHNOLOGY AREA(S): Air Platforms; Weapons

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 section 3.5 of 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: Conceive, develop, and demonstrate innovative flow control methodologies that increase inlet system recovery and operability while decreasing inlet-isolator length and combustor-entrance flow distortion without requiring bleed.

DESCRIPTION: The performance of high-speed air-breathing weapons is highly dependent on the inlet performance and operability under a range of inflow Mach numbers, altitudes, and vehicle angles-of-attack and yaw angles. [Ref 1]

Fixed-geometry inlets are desirable due to their mechanical simplicity, but on-design operation is limited to a narrow range of conditions. Off-design modes of inlet operation occurring during acceleration and maneuvers generate highly complex and potentially unstable flowfields that can lead to unpredictable consequences such as inlet unstart. [Refs 2, 3] The unstarted inlet flowfield is characterized by a large separated region and supersonic flow spillage. In general, an unstarted inlet captures less airflow with lower efficiency and higher aerodynamic and thermal loads compared to a started inlet. [Ref 1]

This SBIR topic aims to develop flow control strategies to improve the inlet flow delivered to scramjet or ramjet combustors. Promising control strategies are not limited to, but may include, mechanical protuberances and fluid injection devices [Ref 4], and their optimal placement in an inlet/isolator system in conjunction with inlet and isolator duct shaping. Figures of merit for flow control strategies include improved flow uniformity at the inlet throat and exit of the isolator, improved inlet flow stability, increased inlet compression efficiency or compression ratio capability, and reduced inlet-isolator system length. Solutions that enable or enhance the performance and operability of a fixed-geometry inlet without bleed are especially attractive. While an unstart detection system is not the focus of this SBIR topic, there is benefit in developing control methodologies that provide the ability to rapidly add pressure margin to the inlet operation if insipient unstart of the inlet is detected.

Recent improvement in high-fidelity simulations [Refs 5, 6] and optimization methodologies [Ref 7] provide new avenues to design, analyze and optimize novel inlet-isolator control devices. The design of the control devices needs to be guided by numerical simulations and optimization methodologies that includes aerodynamics and thermo-structural considerations. Validation of the analytical and numerical toolsets against wind-tunnel experiments under relevant high-supersonic and hypersonic flight conditions is also needed.

Work produced in Phase II may become classified. Note: The prospective contractor(s) must be U.S. owned and operated with no foreign influence as defined by DoD 5220.22-M, National Industrial Security Program Operating Manual, unless acceptable mitigating procedures can and have been implemented and approved by the Defense Counterintelligence Security Agency (DCSA). The selected contractor and/or subcontractor must be able to acquire and maintain a secret level facility and Personnel Security Clearances, in order to perform on advanced phases of this project as set forth by DCSA and ONR in order to gain access to classified information pertaining to the national defense of the United States and its allies; this will be an inherent requirement. The selected company will be required to safeguard classified material IAW DoD 5220.22-M during the advanced phases of this contract.

PHASE I: Develop a conceptual design for innovative flow control strategies to improve the performance and operability of the inlet-isolator system. The proposed flow control solution(s) shall be developed using suitable computational methodologies to estimate improvements in the relevant performance metrics such as flow uniformity, inlet-isolator length and compression efficiency. The suitability of the computational methodologies for the design and analysis of inlet-isolator control solutions must be demonstrated. Therefore, validation against relevant experimental data for hypersonic inlets and isolators will be a key consideration towards successful phase transition. The analysis must show that the proposed flow control solution(s) enable a significant improvement in the performance metrics outlined above in the Description as the inlet-isolator design is driven toward more compact configurations. Develop a Phase II plan.

PHASE II: Refine, optimize and validate the proposed flow control strategies. Mature the computational design and optimization methods. Perform required validation against wind-tunnel experiments under relevant high-supersonic and hypersonic flight conditions to gain confidence in the design methodology and to accurately quantify the improvements to the performance metrics. Perform successful execution of ground tests validating the flow control solution(s), refinement of numerical simulation tools incorporating experimental data, and a detailed plan towards integrating the proposed concept(s) in a Navy relevant flight vehicle in Phase III  all criteria for phase transition.

It is probable that the work under this effort will be classified under Phase II (see Description section for details).

PHASE III DUAL USE APPLICATIONS: Seek further maturation of the flow control solution(s), including its manufacturability. Demonstrate the flow control solution(s) on a relevant Navy weapons geometry once a sufficient TRL is achieved.

In the near term, this technology is geared toward military applications, but in the longer term, it could be used to enable commercial hypersonic flight. Commercial hypersonic platforms will likely rely on a turbine-based combined cycle (TBCC) propulsion system that requires inlet operation over a wide range of Mach numbers and low flow distortion for turbine operation.

Commercialization can include both flow control devices, and the toolset for design, analysis and optimization (devices geometry, placement and integration) of these devices.


  1. Van Wie, D.M. "Scramjet Inlets." Scramjet Propulsion, AIAA, 2000, pp. 447-511.  
  2. Zvegintsev, V.I. "Gas-dynamic problems in off-design operation of supersonic inlets (review)." Thermophysics and Aeromechanics, vol. 24, no. 6, 2017, pp. 807-834.  
  3. Chang, J.; Li, N; Yu, K.; Bao, W. and Yu, D. "Recent research progress on unstart mechanism, detection and control of hypersonic inlet." Progress in Aerospace Sciences, vol. 89, February 2017, pp. 1-22, 2017.  
  4. Valdivia, A.; Yuceil, K.B.; Wagner, J.L.; Clemens, N.T. and Dolling, D.S. "Control of Supersonic Inlet-Isolator Unstart Using Active and Passive Vortex Generators." AIAA Journal, vol. 52, no. 6, 2014.  
  5. Bisek, N.J. "High-Fidelity Simulations of the HIFiRE-6 Flow Path." AIAA 2017-1480, 2016.  
  6. Lyubimova, D.A. and Chestnykha, O.A. "Flow in a High-Velocity Mixed Compression Inlet Studied by the RANS/ILES Method in Different Operation Modes." High Temperature, vol. 56, no. 5, 2018, pp. 702–710.  
  7. Kline, H.L. and Alonso, J.J. "Adjoint of Generalized Outflow-Based Functionals Applied to Hypersonic Inlet Design." AIAA Journal, vol. 55, no. 11, 2017.
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