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 bound ary layer flow over riblets surface and to observe its coherent structure i n the near wall region. The experimental results indicate that, in comparis on with the turbulent boundary layer flow over a smooth surface, greater va lues are obtained for the thickness of viscous sublayer, the thickness of b uffer region and the integral constant C in the log-law. Moreover, the maxi mum value of turbulent intensity u'/U*, is increased by 6.7%, but its posit ion is decreased by 6.4%, the skewness factor and the flatness factor are h ardly affected by the riblets surface. The non-dimensional value of low-spe ed streak spacing is reduced by 20%, this is also an indication of turbulen t drag reduction. (C) 2000 The Japan Society of Fluid Mechanics and Elsevie r Science B.V. All rights reserved.