Unsteady flow motions of an oscillating jet in crossflow

Abstract

The temporal and spatial variations of the flow behavior and velocity field of an oscillating jet in a crossflow were experimentally investigated. A pulsed jet issuing into a crossflow caused the deflected jet to oscillate. The instantaneous oscillating flow patterns in the symmetry plane at several specific phase angles were identified using smoke flow visualization method. The instantaneous flow velocities were measured using the high-speed particle image velocimetry (PIV) and presented as phase-averaged velocity vectors and streamlines. Owing to the variation of jet exit velocity, the near tube-tip jet column flapped up and down within one cycle of jet pulsation and induced a periodic wavy flow structure in the downstream area. By identifying the variations of near-wake velocity vectors and streamline patterns within one excitation cycle, four characteristic flow modes (downwash, crossflow-dominated, jet-dominated, and transitional) were found at different excitation phase angles. Around the mid-oscillation cycle, the wavy flow structure was characterized by two adjacent vorticity concentrated areas of opposite signs in the phase-averaged vorticity contour. The turbulence properties of the excited elevated transverse jet at large jet-to-crossflow momentum flux ratio were larger than those at low jet-to-crossflow momentum flux ratio.