The two dimensional unsteady structure including the interaction between a normal shock and turbulent boundary layer in a transonic diffuser is quantitatively and qualitatively visualized using a high-speed Mach-Zehnder interferometry. The experiment has been performed over a range of operating pressure ratios from 1.4 to 1.6 where the free-stream Mach number just ahead of the normal shock is below around 1.3. The shock oscillatory characteristics in the diffuser are also investigated by a high-speed schlieren method. Streamwise static pressures on the diffuser side wall are measured and the time-mean flowfield in the diffuser is compared with that from the RANS equation with the k-ω SST turbulence model. The dominant frequency of the normal shock oscillation obtained from the Mach-Zehnder interferometry is quantitatively identical to that from the schlieren method.
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