The excitation of thin planar liquid sheets formed by impinging two collinear water jets to acoustic waves was studied at varying frequencies and sound pressure levels ͑SPLs͒. Experiments were conducted over a range of liquid velocities that encompassed the stable and flapping regimes of the sheet. For a given frequency, there was a threshold value of SPL below which the sheet was unaffected. The threshold SPL increased with frequency. Further, the sheet was observed to respond to a set of specific frequencies lying in the range of 100-300 Hz, the frequency set varying with the Weber number of the liquid sheet. The magnitude of the response for a fixed pressure level, characterized by the reduction in the extent of the sheet, was larger at lower frequencies. The droplet sizes formed by the disintegration of the sheet reduced with an increase in the measured response and the drop-shedding frequency was near the imposed frequency. Model equations for inviscid flow and accounting for the varying pressure field across the moving liquid sheet of constant thickness was solved to determine the linear stability of the system. Numerical solution shows that the most unstable wavelengths in the presence of the forcing to be smaller than in the absence, which is in line with observations. Both the dilatational and sinuous modes are coupled at the lowest order and become significant for the range of acoustic forcing studied. The model calculation suggests that the parametric resonance involving the dilatational mode may be responsible for the observed instability although the model was unable to predict the observed variation of threshold SPL with frequency.

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The present study involves simulation of a single compressor rotor with a high hub-to-tip ratio blade. The study includes the effect of variation of tip gap, of tip shapes and of inlet axial velocity profiles, with inflows simulated similar to that of a typical rear stage environment of a multi-stage axial compressor. Numerical studies were carried out on a baseline rotor blade (without sweep or dihedral) and then on blades with sweep and dihedral applied at the tip region of the rotor. Simulation of these part-span sweep and dihedral shapes are done to study their effects on blade tip leakage flow. Results show that sweep and dihedral, in some cases, produce favorable tip flows, improving blade aerodynamics. Positive dihedral caused weakening of tip leakage vortex at design point as well as at peak pressure point. Negative dihedral may help postpone stall at the high pressure, low flow operation. Backward sweep weakened tip vortex at the design point. Contrary to some of the studies reported earlier forward sweep, when applied at the tip region, showed performance deterioration over the most of the operating range of the high hub-to-tip rotor.