A Experimental Study of Passive Drag Reduction in a Turbulent Boundary Layer by a Riblet Surface.
Abstract
An experimental study was performed with a single sensor hotwire probe in the wall region of a nominally zero pressure gradient turbulent boundary layer over smooth and Vgroove riblet plates of h^{+ } ~ 14, s^{+} ~ 28 at Re_{theta } ~eq 1200. The shear stress variation in the spanwise direction and the alteration of the turbulent characteristics were directly measured. The spanwise average shear stress on riblet groove was obtained and contour lines were fitted to the measurement for all the statistics. Net drag reduction of about 4% was found for this case, in substantial agreement with previous direct measurement. The synthetic analysis, at y^{+} ~ 30, of a modified Kovasznaytype probe was performed and an improvement algorithm was developed. The performance of a crossshaped foursensor probe in the turbulent boundary layer in the highly sheared region ( y^{+} ~ 4) is also presented. To further understand the flow structure inside the riblet, foursensor hotwire probes of a modified version of the original Kovasznaytype and of a crossshaped were used over the two test surfaces at Re_{ theta} ~eq 2500 and 2100, respectively. Statistical properties of the fluctuating velocity components and the Reynolds stress, including joint probability density functions and frequency spectra of data obtained over the smooth and the peak and over the valley of the riblet plate are presented.
 Publication:

Ph.D. Thesis
 Pub Date:
 1992
 Bibcode:
 1992PhDT........37P
 Keywords:

 Engineering: Mechanical; Physics: Fluid and Plasma; Statistics;
 Drag Reduction;
 Flow Distribution;
 HotWire Flowmeters;
 Riblets;
 Shear Stress;
 Turbulent Boundary Layer;
 Flow Velocity;
 Probability Density Functions;
 Reynolds Stress;
 Statistical Distributions;
 Fluid Mechanics and Heat Transfer