Numerical and Experimental Investigations of the Flow Field Inside the Intake Duct of a Combined Cycle Engine for Hypersonic Flight

Detailed measurements inside the subsonic intake duct of a combined cycle engine have been performed in a subscale model wind tunnel. The experiments comprised pneumatic five hole probe measurements in several traverse planes, surface flow visualization, and the recording of wall pressure distributions. A computational study of the flow within the intake canal is presented for one selected combination of inflow conditions (Ma1 = 0.63, Re1/L = 2.72 · 107 m−1). The compressible 3D-Na-vier-Stokes equations were solved employing different turbulence models: the standard high-Re k-ε two-equation model and two modifications of it, a “RNG” model and a modification suggested by Kato and Launder (1993). The experimental results point out the existence of strong 3D-separation and attachment of the flow on the top wall of the intake duct. The complex interfering secondary flows generated by the curved canal lead to highly distorted flow fields at the engine face. The numerical simulations clearly indicate the crucial impact of turbulence on the development of the flow field inside the intake duct: Depending on the inflow boundary conditions and the chosen turbulence model totally different secondary flow patterns were obtained. None of the investigated turbulence models properly reproduced the measured structures of separation. Qualitative agreement between calculated and measured secondary flow patterns could only be achieved by modelling a possibly existing laminar-turbulent transition over the first quarter of the duct top wall by suppressing the production of turbulent kinetic energy in this region in conjunction with a conventional k-ε calculation in the remaining domain.