Author(s)

Soichiro Yagi^*, Saya Inoue, Shinichiro Nakao, Daisuke Ono, Yoshiaki Miyazato

Faculty of Environmental Engineering, The University of Kitakyushu, Kitakyushu, Japan.

Two-dimensional critical nozzle flows at low Reynolds numbers are visualized by the rainbow schlieren deflectometry. Experiments have been performed in a region of overexpanded nozzle flow. The variation of the shock structure against the back pressure ratio can be clearly visible with color gradation. Static pressure rises due to the shock-induced flow separation are compared with the previous theories. The unsteady characteristics of overexpanded critical nozzle flows at low Reynolds numbers are quantitatively and qualitatively visualized using laser schlieren and Mach-Zehnder interferometer systems combined with a high-speed digital camera. It was found that an oscillating normal shock wave appears inside the nozzle, and that the shock wave has a specified dominant frequency. Also the time-history of the oscillating shock wave is obtained from both the systems and compared with each other.

Compressible Flow, Micro Nozzle Flows, Optical Flow Visualization, Rainbow Schlieren Deflectometry, Mach-Zehnder Interferometry, Shock Wave Oscillation, Flow Separation

Yagi, S. , Inoue, S. , Nakao, S. , Ono, D. and Miyazato, Y. (2017) Optical Measurements of Shock Waves in Critical Nozzles at Low Reynolds Numbers. Journal of Flow Control, Measurement & Visualization, 5, 36-50. doi: 10.4236/jfcmv.2017.52003.