Experimental study of a round jet impinging on a convex cylinder

The flow physics of a free round air jet prior to impinging on a convex cylindrical surface is discussed. Two components of mean velocity, normal stress and shear stress profiles were obtained using a novel fibre- optic, two- simultaneous velocity component laser- Doppler velocimetry probe. Velocity profiles obtained at seven axial locations in the impinging jet case are compared to profiles obtained at eight axial locations away from the jet exit to determine the surface effects on the free jet. The Reynolds number of the flow based on the jet diameter was Re = 25 000 and the convex cylinder was located at x/d = 4.0 ( jet exit velocity, U-j = 24 m s(-1); jet diameter, d = 15.24 mm; circular cylinder diameter, D = 60.5 mm). Flow visualization results show that the initially axisymmetric jet becomes a three- dimensional flow, wraps itself on the cylinder across the cylinder and also behaves similar to a wall jet along the cylinder axis. The jet axial mean velocity starts reducing sharply one diameter ( 1d) away from the cylinder. The jet axial, radial, tangential normal stresses and the shear stress are not affected by the presence of the surface in the vicinity of the jet axis until 0.05d away from the surface, and are affected near the jet edge about 0.75d away from the surface.