Variation of drag coefficients in an interacting drop stream

Variation of the drag coefficient of closely spaced drops in a stream injected into a turbulent flow is studied experimentally. Three different regions are identified. In the first region, close to the injector, drops flow in the wake of each other. The drag coefficient in this region is much smaller (by a factor of 4 to 5) than the standard drag coefficient, and its magnitude is dependent on the drop initial spacing. Shortly downstream of the injection point, the transition region starts, where the drag coefficient increases rapidly approaching the drag coefficient of a single isolated drop. And further down-stream when drops are dispersed significantly, the drag coefficient will behave the same way as a single isolated drop.