A description is given of the principle and a preliminary embodiment of a flow-visualization technique in which the test body is pulled through water.

Initially, dyed and undyed parts of the water are separated by a plane horizontal interface; as the body emerges from below this interface, it carries dyed fluid upwards in its wake. A succession of photographs reveals the nature of the flow.

In principle, the flow is steady in a frame fixed relative to the body, and unsteady in one relative to the tank and the initial interface. Interpretation of the experimental results must therefore proceed by way of an analysis in which the steady-state equations are solved for velocity and turbulence quantities but an unsteady-state equation is solved for the dye concentration.

Preliminary results are reported for the flows behind a wedge and behind a bar. They reveal that these particular flows are unsteady even in the body-fixed coordinate frame, being strongly oscillatory.