Hisataka Tamura

Vortex shedding from a circular cylinder in moderate-Reynolds-number shear flow

The frequency of vortex shedding from a circular cylinder in a uniform shear flow and the flow patterns around it were experimentally investigated. The Reynolds number Re , which was defined in terms of the cylinder diameter and the approaching velocity at its centre, ranged from 35 to 1500. The shear parameter, which is the transverse velocity gradient of the shear flow non-dimensionalized by the above two quantities, was varied from 0 to 0·25. The critical Reynolds number beyond which vortex shedding from the cylinder occurred was found to be higher than that for a uniform stream and increased approximately linearly with increasing shear parameter when it was larger than about 0·06. In the Reynolds-number range 43 Re Re

Forces acting on circular cylinders placed in a turbulent plane mixing layer

Abstract Time-averaged pressure distributions along the surface of a circular cylinder placed in a turbulent plane mixing layer were measured in order to clarify the time-averaged aerodynamic forces acting on the cylinders, together with the flow patterns around them. The Reynolds number based on the diameter of the cylinder d and the mainstream velocity U outside the mixing layer was in the range (2.16–4.06) × 10 4 . Both the angular position of the stagnation point and the stagnation-pressure coefficient were well correlated with a parameter d δ , δ being the width of the mixing layer, if the location of the cylinders was expressed in terms of the ratio u c U , where u c is the velocity of the otherwide undisturbed mixing layer at the centre of the cylinders. The drag coefficient was found to be rather insensitive to the parameter d δ , whereas a slight dependence of thedrag coefficient on the cylinder diameter was observed owing to the effect of turbulence in the mixing layer. The lift force was always directed from the high-velocity side to the low-velocity side of the mixing layer, its magnitude being approximately proportional to the parameter d δ .