THE EFFECT OF AN INTERMITTANT FLAPPING MOTION ON THE PROPERTIES OF MERGING PLUMES

Experiments with merging buoyant jets revealed the existence of an int ermittent flapping motion in the flow trajectory. The flapping commenc es beyond the point where the initially axi-symmetric buoyant jets mer ge to form a plane plume. The size and relative positions of large-sca le vortices on either boundary of the plane plume determine whether th e flapping flow state occurs. The effect of-the flapping on the short term time-averaged Bow properties was measured and the flapping was fo und to increase the spreading rate and also change the shape of the co ncentration fluctuation distribution in the plane plumes. The intermit tent presence of flapping in plane plumes is shown to be the cause of widely accepted differences between plane and axisymmetric plumes. The new findings on the flapping behaviour were used to improve an integr al model which describes merging buoyant jets.