Investigation of Three-Dimensional Flow Structure in a Transonic Diffuser by the LIF Method

The three-dimensional flow structure induced by normal shock-wave/boundary-layer interaction in a transonic diffuser is investigated by a laser-induced fluorescence (LIF) method. This diagnostic system uses an argon-ion laser as a light source, and target gas is dry nitrogen with iodine seeded as a fluorescence material. The Mach-number distributions in the diffuser are obtained from the measured fluorescence intensity, and the three-dimensional shape of the boundary layers is obtained immediately behind the shock wave. The oil-flow surface visualization is also done, and the vortex-like patterns appear in the interaction region. These flow characteristics are reproduced very well by solving the Navier-Stokes equations numerically, and it is found that the vortices are generated at the foot of the shock wave and bended downstream. The calculated result also reveals that the complicated wave configuration is formed at the diffuser corner. The simple flow model is constructed by considering this wave configuration. This model can explain very well the three-dimensional flow characteristics