Parametric Investigation of Racetrack-to-Circular Cross- Section Transition of a Dual-mode Ramjet Isolator

Reynolds Averaged Navier Stokes (RANS) simulation is used to parametrically evaluate the performance of a matrix of 3-D isolator configurations which transition from a racetrack entrance cross-section to a circular exit cross-section. The matrix includes isolators with l ength-to-height ratios of 6 to 16, divergence angles of 0 to 2 degrees, and different cross section shape transition functions. Generic isolator entrance flow conditions for a dual-mode ramjet (DMR) were provided by Pratt & Whitney Rocketdyne, and are used to impose a spatially-varying isolator inflow profile, and a mass -averaged uniform inflow profile, in two separate sets of matrix computations. Isolator performance is characterized by ma ximum allowable static pressure rise (without unstart), and related stagnation pressure recovery, exit flow distortion, and shock train onset sensitivity. The implications of the results for selecting a racetrack-to-circular, transitional isolator geometry are discussed.