Simulation and ground testing mark progress
By Howard “Greg” Johnston and Leslie Smith|December 2017
The High-Speed Air-Breathing Propulsion Technical Committee works to advance the science and technology of systems that enable supersonic and hypersonic air vehicle propulsion.
Interest in the science and engineering of high-speed air-breathing propulsion systems is surging across the globe. Strides have been made in areas of aerodynamics, thermal management, materials development and improved flight efficiency through both simulation and ground testing. Various international research teams are exploring multiple ways to develop ground test methodologies, ground-flight correlations and specific trajectory optimization.
At the Arc-Heated Scramjet Test Facility at NASA’s Langley Research Center in Virginia in April, several classes of high-speed fuel injector concepts for scramjet applications were investigated using planar laser-induced fluorescence. The resulting, high-quality, non-intrusive, experimental data provided insight about mixing and allowed the validation of computational fluid dynamics models used in the analytical studies.
The U.S. Department of Defense’s desire to field hypersonic vehicles powered by air-breathing propulsion systems has resulted in the need for an analysis-driven knowledge base with an applied engineering focus. The Aerospace Systems Directorate of the Air Force Research Laboratory at Wright-Patterson Air Force Base in Ohio has been working to extend the state-of-the-art beyond the X-51A Scramjet Engine Demonstrator since its last flight in 2013. Throughout 2017, AFRL has been preparing direct-connect testing of two unique powerhead concepts through the Medium Scale Critical Components program in the Aerodynamic and Propulsion Test Unit at the Arnold Engineering Development Complex in Tennessee.
The two engine test articles have an air mass capture approximately 10 times that of the X-51A engine and employ common isolator and combustor components. Flow characterization through the facility nozzle and distortion generator at the simulated M=4 flight condition was completed in May. Initial engine tests were expected in late 2017.
AFRL also made significant strides throughout the year in developing and using advanced high-frequency optical diagnostic techniques to elucidate the fundamental physics involved in supersonic reactive flows. Researchers used simultaneous schlieren, chemiluminescence and hydroxide planar laser-induced fluorescence for the same field of view at bandwidths of 40 kilohertz in studies of the ignition process of a cavity-based flame holder in supersonic flow. The spatially and temporally resolved measurements provide an unprecedented perspective of the starting transients that each diagnostic alone cannot achieve.
The German Aerospace Center, or DLR, has conducted tests throughout the year in Lampoldshausen that characterized the interaction between wedge flame-holders at test bench M11.1. Investigation of high-speed transpiration cooling systems for scramjets has been ongoing since 2014, with earlier work in 2000 on rocket combustion chambers. In September, DLR researchers carried out cold air tests on a variable geometry inlet for operation from Mach 3.0 to Mach 4.5 in DLR’s trisonic wind tunnel.
The National Natural Science Foundation of China funded an eight-year research project valued at $23 million to foster technology, multidisciplinary optimization and integrate hypersonic technology for a near-space maneuverable vehicle. China’s turbo-aided rocket-augmented ram/scramjet combined cycle engine, or TRRE, was set for free-jet testing at the end of 2017.
Russia’s Central Aerohydrodynamic Institute, or TsAGI, and its Central Institute of Aviation Motors, or CIAM, designed and performed direct-connect and aerodynamic testing in their facilities on a civil hydrogen powered-vehicle concept program in T-131 and C-16VK wind tunnels, respectively, demonstrating positive net thrust at Mach 7. Testing began in 2014; the last tunnel entry was in August.
Contributors: Kevin R. Jackson, Dean R. Eklund, Timothy M. Ombrello, J. Philip Drummond, Erik Axdahl, Johan Stellant, Venkat Tangirala, Ali Gülhan, Friedolin Strauss and Dvoynikov Alexander