Experimental Analysis on Boundary Layer Growth Using Varying Configuration of Roughness Blocks and Spires in Wind Tunnel

Abstract

Flowing behaviour of real fluid is very complex to understand. When real fluid flows over a solid body or a solid plate, the fluid particles adhere to the boundary of the stationary surface and the phenomenon of no slip condition occurs. This results that the velocity of fluid near to the boundary will be same as that of boundary. If the boundary is stationary, the velocity of fluid at the boundary will be zero. The velocity of fluid increases from zero velocity on the stationary boundary to the free stream velocity of the fluid in the direction normal to the boundary .Boundary layer is defined by its parameters as boundary layer thickness, momentum and displacement thickness. In boundary layer region viscous effect is prominent; drag force and shear force act within this layer on the body. Study of boundary layer is important for design of stream line bodies such as air foils. Most wind tunnels, typically designed for the study of aeronautics with smooth laminar flow, lack the turbulence intensity and sufficient boundary layer depths. The present work shows how thick boundary layers can be produced in a wind tunnel with a view to simulate atmospheric flows. The wind loading on structures depends on the velocity and turbulence parameters of the approaching flow. Therefore, in order to obtain similitude between the model loading in the wind tunnel and the real structure, different types of thickening devices are used which are 2.5 cm cube blocks as a floor roughness and 45cm height spires of different configurations in test section. Analysed the effect of different patterns of spires and floor roughness blocks on boundary layer parameter in test section using velocity profiles at variable free stream velocity, were measured at five sections in test section. And roughness parameter was measured for all configurations of spires and blocks using log-law of velocity profiles.This paper summarizes the recent investigations involving the computations of effects of roughness thickness, mainstream velocity and distance from roughness plate on turbulent boundary layer along with the correlations.