FLAPPING MOTION OF A PLANAR JET IMPINGING ON A V-SHAPED PLATE

The behavior of a planar jet impinging on a V-shaped plate is studied experimentally by means of pressure and velocity measurements and flow visualization. The plate with a symmetrically variable opening angle is located downstream at distance L from the jet exit. Data indicate t hat, for the presence of the plate, not only the large-scaled coherent structures in the shear layers exist in the jet, but also the whole j et column exhibits a prominent periodic flapping motion with a preferr ed frequency f(F) in the flowfield. Results also show an unstable regi me occurring for the flapping motion, in which the criteria to determi ne the boundary of the regime are governed by the location and the ope ning angle of the plate. Moreover, the nondimensional Strouhal number f(F)L/U(j) is found to maintain a constant value of 0.11, and this val ue is nearly insensitive to the opening angle of the plate in the oper ating Reynolds number range.