THE BIFURCATION OF CIRCULAR JETS IN CROSS-FLOW

An experimental study of an incompressible circular jet in a crossflow and theoretical analysis based on inviscid flow models are described. The jet exits from a rigidly mounted pipe projecting distant from the floor of a tunnel carrying a steady stream of water; density of the j et and the stream are the same. The results of scalar and velocity mea surements and visualizations showed that the jet bifurcated into two s eparated, counterrotating arms for values of epsilon=U-x/U-JET, the ra tio of the mean crossflow velocity U-x to the mean jet discharge veloc ity U-JET, less than or equal to 0.25. The angle of separation between the two arms of the bifurcated jet was found to vary inversely with e psilon. For higher values of epsilon the jet does not bifurcate but is dominated by a different mode of instability. The structure of the fl ow field, which is different for bifurcated and nonbifurcated jets, co mprised a variety of vortical structures which survived for very long distances x beyond x/2a>400, where a is the radius of the jet exit and x is distance downstream from the jet axis. The location of the point of bifurcation is predicted from consideration of potential flow mode ls and the characteristics of bifurcating elliptical jets. The locatio n of the point of bifurcation is more distant from the jet exit for sm aller values of epsilon, and experimental results were in good agreeme nt with the theoretical predictions. The initial jet trajectory is sho wn to be associated with the presence in the wake of vorticity shed fr om the pipe. The near-field geometry and centerline trajectory of the jet are also found to be in accord with predictions in that it is obse rved that z similar to x(1/2) and z similar to epsilon(-1). Dilutions of bifurcated jets are found to be greater than for nonbifurcated jets . (C) 1996 American Institute of Physics.