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Description of Driving Event:

For many years, LARC has been studying cavity flow fields at supersonic speeds. This research has included various flow visualization wind tunnel tests to document both the cavity surface and offbody flow fields. During one of these tests, water was injected through pressure measurement orifices located on the model surface in an attempt to visualize vortices that typically form above certain cavity configurations. Because of the low static pressure in the tunnel, it was anticipated that the water would vaporize as it exited the orifice and the resulting vapor would be entrained into the vortices and render them visible. This technique did not work, and the water instead flowed along the model surface. Although the water was difficult to discern against the model surface, it was obvious that the water was being entrained by the model surface flows and had a fast response to the cavity flow unsteadiness. This impetus led to the development of a technique that uses colored water as a medium to visualize surface flows over wind tunnel models.

The colored water surface flow visualization technique basically involves injecting colored water through the pressure measurement orifice tubes installed in a wind tunnel model. The colored water exits the orifices and flows along the model surfaces to form streaklines. The resulting flow patterns are then photographed for later analysis. This method has several advantages over the conventional oil flow and tuft techniques that can make it a useful procedure for routine testing.