An experimental study of Rayleigh-B

Due to the very fine space resolution and high noise-reduction capability of the improved laboratory-made laser Doppler anemometer, the temporal mean velocity and velocity fluctuation in uniform, rough bed open channel turbulent flows were measured in full detail and a large amount of information about the wall region was obtained. The influence of boundary roughness on flow characteristics was examined by changing the relative smoothness scale, H/ks, of the flow. It is proposed that there are three sorts of bed roughness, namely, the large scale roughness, the mediuin one and the small one. The small scale roughness is of more universal significance to engineering practice, and much attention is devoted to the characteristics of the flow over boundaries of such a sort of roughness.

In this paper, the systematic longitudinal turbulent intensity measurements of flow in a gravel open-channel have been conducted with a highly accurate one-dimensional LDA-system. The channel bed was roughened with gravels of uniform and non-uniform diameters respectively, and a wide range of H/Ks were considered. In comparison with the smooth bed results, it was found that the bed roughness makes the flow turbulence become well-distributed in the region near the bed and in the case of small H/Ks values. With regard to the flow over a non-uniform gravel bed, only the flow region below the maximum gravels is affected by the rough bed, and outside this region, the turbulent intensity distributions could collapse on to a single curve.

Experimental investigations were conducted on a NACA0012 airfoil to determine the influences of mounting angles and mounting locations on the lift-enhancing effects of Gurney flaps at a Reynolds number of 2.1

The laser Doppler velocimeter (LDV) and hydrogen bubble ow visualization techniques have been used to measure the characteristics of turbulent boundary layer ow over riblets surface and to observe its coherent structure in the near wall region. The experimental results indicate that, in comparison with the turbulent boundary layer ow over a smooth surface, greater values are obtained for the thickness of viscous sublayer, the thickness of bu er region and the integral constant C in the log-law. Moreover, the maximum value of turbulent intensity u0=U is increased by 6.7%, but its position is decreased by 6.4%, the skewness factor and the atness factor are hardly a ected by the riblets surface. The non-dimensional value of low-speed streak spacing is reduced by 20%, this is also an indication of turbulent drag reduction.