The instability of the shear layer separating from a bluff body

摘要: Notwithstanding the fact that instability of separated shear layer in cylinder wake has been extensively studied, there remains some uncertainty regarding not only critical Reynolds number at which manifests itself, but also variation its characteristic frequency with (Re). A large disparity exists literature precise value number, quoted values ranging from Re = 350 to 3000. In present paper, we demonstrate spanwise end conditions control primary mode vortex shedding significantly affect shear-layer instability. For parallel conditions, itself ≈ 1200, whereas for oblique it is inhibited until a higher 2600, implying even absence free-stream turbulence level, angle influences onset instability, and contributes number. We confirm existence intermittency fluctuations show related transverse motion layers past fixed probe, as suggested previously. Such are due an intermittent streamwise movement transition point, or location develop rapidly layer.Following original suggestion Bloor (1964), generally assumed previous studies (normalized by frequency) scales Re1/2, although careful examination actual data points these does support such variation. have reanalysed all investigations include our own measurements, find none yields relationship close Re1/2. least-squares analysis includes previously available produces form Re0·67. Based on simple physical arguments account velocity length layer, predict normalized Re0·7, good agreement experimental measurements.