Experimental study on the turbulent boundary layer flow over riblets surface

The laser Doppler velocimeter (LDV) and hydrogen bubble flow visualization techniques have been used to measure the characteristics of turbulent boundary layer flow 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 flow over a smooth surface, greater values are obtained for the thickness of viscous sublayer, the thickness of buffer region and the integral constant C in the log-law. Moreover, the maximum value of turbulent intensity u'/U*, is increased by 6.7%, but its position is decreased by 6.4%, the skewness factor and the flatness factor are hardly affected 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. (C) 2000 The Japan Society of Fluid Mechanics and Elsevier Science B.V. All rights reserved.