By using two high-speed cameras and a slightly extended visualization setup (typically based on a Toepler system) one can generate two simultaneous time-resolved records of the same flow, where these records can be obtained with different visualization methods, different spatial and different temporal resolutions. This allows one to generate visualizations that can complement each other in various ways and thus yield a considerably increased amount of information on the observed flow.
The rotational behavior of capsule-shaped models is investigated in the transonic wind tunnel of JAXA. A special support is developed to allow the model to rotate around the pitch, yaw and roll axes. This 3-DOF free rotational mounting apparatus achieves the least frictional torque from the support and the instruments. Two types of capsule models are prepared, one is drag type (SPH model) and the other is lift type (HTV-R model). The developed mounting apparatus is used in the wind tunnel tests with these capsule models. In a flow of Mach 0.9, the SPH model exhibits oscillations in pitch and yaw, and it rolls half a turn during the test. Similarly, the HTV-R model exhibits pitch and yaw oscillations in a flow of Mach 0.5. Moreover, it rolls multiple times during the test. In order to investigate the flow field around the capsule, the combined technique of color schlieren and surface tufts is applied. This visualization clearly shows the flow reattachment on the back surface of a capsule, which is suspected to induce the rapid rolling motion.
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.
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