Goji Etoh

Development of High-speed Video Cameras for Dynamic PIV

The most promising next generation Image Velocimtry (IV) is the high-speed Dynamic PIV. It requires the development of innovative high-speed video camera sensors. We started by specifying the required performance of these new sensors, for measurements in air and water flows. These criteria founded on the most recent developments in PIV algorithms and incorporate results from a large questionnaire survey of users of high-speed video cameras in Japan. The results suggest that the followings are required: (1) frame rate of 1,000,000 fps, (2) pixel count of 1,000,000 pixels, (3) frame storage capacity of 100–200 frames for tracing a single event and 10,000 frames for turbulent measurements, (4) gray levels of 4–8 bits for PTV; 12 bits for observation. Finally, we reviewed the state of the art of high-speed video-image sensors. Currently the standard parallel-readout sensors can operate at 1 Kfps with a pixel count of approximately 1 Kpixels. The In-situ Storage Image Sensor (ISIS) developed by the authors has recently achieved frame rates of 1 Mfps.

Flow instability induced by spiked bodies

In order to investigate the unsteady flow field around a spiked body in supersonic flow, time-resolved color schlieren visualization was applied using a high-speed video camera which could take up to 1 000 000 frames per second at full frame resolution. Conically and spherically tipped spikes of six different lengths could be attached at the center of the model and their effect on the flow unsteadiness was visually observed. The obtained images revealed in great detail the interaction between the incoming free stream flow and the high-pressure region near the model base, which could make its presence known upstream at the tip of the spike by means of displacing the boundary layer on the spike and subsequently inducing a large-scale instability of the flow.