两个反向旋转盘片间剪切层不稳定性的实验和数值模拟研究
The shear layer instability in the flow between two counter-rotating disks enclosed bya cylinder is investigated experimentally and numerically, for radius-to-height ratioΓ =R/h between 2 and 21. For sufficiently large rotation ratio, the internal shear layerthat separates two regions of opposite azimuthal velocities is prone to an azimuthalsymmetry breaking, which is investigated experimentally by means of visualizationand particle image velocimetry. The associated pattern is a combination of a sharpcorneredpolygonal pattern, as observed by Lopez et al. (2002) for low aspect ratio,surrounded by a set of spiral arms, first described by Gauthier et al. (2002) for highaspect ratio. The spiral arms result from the interaction of the shear layer instabilitywith the Ekman boundary layer over the faster rotating disk. Stability curves andcritical modes are experimentally measured for the whole range of aspect ratios, andare found to compare well with numerical simulations of the three-dimensional timedependentNavier–Stokes equations over an extensive range of parameters. Measurementsof a local Reynolds number based on the shear layer thickness confirm that ashear layer instability, with only weak curvature effect, is responsible for the observedpatterns. This scenario is supported by the observed onset modes, which scale as theshear layer radius, and by the measured phase velocities.