Wind tunnel testing of an axisymmetric isentropic relaxed external compression inlet at Mach 1.97 design speed

An alternative inlet design method employing isentropic relaxed compression has been developed by Gulfstream Aerospace Corporation for improving net propulsion system performance and reducing sonic boom strength. To substantiate results from prior analytical studies and to provide an experimental database for subsequent research, a wind tunnel test was conducted using a family of subscale axisymmetric relaxed compression inlet models designed for an incoming flow speed of Mach 1.97. All tests were performed in the 1 ft by 1 ft supersonic wind tunnel at NASA Glenn Research Center. Focusing on internal flow characteristics, a large database comprising nearly 1500 test runs was acquired, covering a range of subsonic diffuser Mach numbers, diffuser lengths, mass flow rates, and angles-of-attack. Differences in flow properties between inlet models were surprisingly modest despite significant changes in hardware geometry. Strut effects were noteworthy for all model designs. Comparisons with CFD proved the analytical methodology to be reliable for this application. The large experimental database will be used for additional analytical methodology development, design work, test planning at larger scale, and the development of non-bleed surface treatment concepts for boundary layer control.