| Three-dimensional aspects of the wakes of long cylinders have been investigated from low to moderately high Reynolds numbers, using extensive flow visualization and wake measurements.;By acoustically forcing the two-dimensional wave, we find that a whole series of oblique wave resonances can be generated in the far wake. Surprisingly, the oblique resonance waves are preferentially amplified even when the forcing frequency is identical to that of the oblique waves. The effect of increasing the forcing amplitude is to cause the nonlinear interactions to occur further upstream, and also to increase the amplitude of the oblique wave response.;The effect of the cylinder end boundary conditions on the vortex shedding pattern at moderate to high Reynolds numbers, between 200 and 10000, has been investigated. We find that oblique and parallel vortex shedding can be controlled over long spanlengths in a manner similar to that used at low Reynolds numbers. Such control has practical significance as one can decorrelate the shedding along the span thereby delivering smaller spanwise-integrated unsteady fluid forces on the body.;The separating shear layers from a cylinder develop an instability for Reynolds numbers of order 1000. We have also found that the oblique angle of vortex shedding influences the shear-layer instability and may contribute to the large disparity in quoted values, observed in the literature, for the Reynolds number at which this instability manifests itself. Regarding the variation of the normalized shear-layer frequency with Reynolds number (Re), we find that the power-law ;We have found that there exists a connection between the near and far wakes, at low Reynolds numbers of the order of 150, through the sensitivity to free-stream disturbances. These disturbances are instrumental in the generation of an 'oblique resonance wave', which is found to dominate the far wake. The oblique resonance wave is the result of a nonlinear interaction between oblique vortex shedding waves from upstream and two-dimensional waves that are amplified in the far wake and have an acoustic origin. |
