On Similarity Law of the Crossflow Instability in Three-Dimensional Boundary Layers on Yawed Cylinders
Three-dimensional boundary layers are unstable to both stationary and traveling crossflow disturbances. Early experiments show the center frequency of traveling disturbances to shift according to experimental conditions such as freestream turbulence and surface roughness. A natural speculation is that the observed shift of the center frequency of traveling disturbances is due mainly to the presence of stationary vortices, which surely deform the basic flow; no frequency shift should be observed in the flow with no stationary vortices. On this speculation, special cares are paid to establish traveling-mode dominated flows free from the stationary mode on yawed-circular cylinders. Then, a series of parametric studies focusing on the center frequency of traveling disturbances is conducted in combination of three yawed cylinders with different size and three wind tunnels with different turbulence levels under a constant Reynolds number. Experimental results show that the nondimensional center frequencies in totally six cases tested are almost independent of freestream turbulence levels and their spectra, and of the size of models with different surface conditions, providing a strong support to the above speculation.
Key words3-D boundary layer Crossflow instability Traveling waves Stationary vortices
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