Abstract: The body surface of some organisms has nonsmooth structure, which is related to drag reduction in moving fluid. To imitate these structures, models with a nonsmooth surface were made. In order to find a relationship between drag reduction and the nonsmooth surface, an orthogonal design test was employed in a low speed wind tunnel. Six factors likely to influence drag reduction were considered, and each factor tested at three levels. The six factors were the configuration, diameter/bottom width, height/depth, distribution, the arrangement of the rough structures on the experimental model and the wind speed. It was shown that the nonsmooth surface causes drag reduction and the distribution of nonsmooth structures on the model, and wind speed, are the predominant factors affecting drag reduction. Using analysis of variance, the optimal combination and levels were obtained, which were a wind speed of 44 m/s, distribution of the nonsmooth structure on the tail of the experimental model, the configuration of riblets, diameter/bottom width of 1 mm, height/depth of 0.5 mm, arranged in a rhombic formation. At the optimal combination mentioned above, the 99% confidence interval for drag reduction was 11.13 % to 22.30%.

Key words: drag reduction, non-smooth structure, orthogonal experiment, low speed wind tunnel