Investigation of Transonic Inlet Drag Characteristics

Fourteen subsonic axisymmetric inlet models with various forebody contours and geometry parameters were tested in the NASA-Langley Research Center 16-foot transonic wind tunnel. Test Mach numbers ranged from 0.59 to 0.96. A mass flow control throttle (translating plug) allowed mass flow ratios from 0.23 to 0.92. Force and pressure data were acquired for all fourteen inlets, with and without external boundary layer transition strips (grit). The force balance was found to be defective after completion of the test. However, drag data were calculated from wake pressure rake data. Various inlet geometry effects on drag characteristics were analyzed. In particular, drag divergence Mach number was found to correlate with inlet thickness ratio. Experimental pressure and drag data were also compared with predictions from full potential transonic flow codes to verify their reliability and accuracy. The computer codes were found to be useful design tools that can help significantly reduce the number of inlet configurations to be examined experimentally.