Drag Reduction In Turbulent Flow using Different Kinds of Riblets

In the present work the characteristics of a turbulent flow field over a riblet surface plate models have been investigated experimentally and compared with a smooth surface. Experiments tests were carried out in a low speed open-typed wind tunnel at constant air speed 20m/s and Reynolds number 4.9◊10 5 based on length of plate. Drag reduction investigations in a turbulent flow over a riblet-coverd surface is performed for two models: straight riblets and sinusoidal riblets with ratio ( a/λ=0.01). A parametric investigations show that the riblet shape, height (h), width (w) and lateral spacing (s) are main factors affecting drag reduction. With straight riblets model, skin fricti on drag reduction in the range of 10-14% have been obtained, and the best dimension are (h=0.25mm, s=1mm and w=1mm). The results show that more significant drag reduction is achieved with sinusoidal riblets due to an oscillatory spanwise component added to the mean flow, and it is found that drag reduction depend strongly on the a/ λ ratio. Sinusoidal riblet surface reduces drag coefficient by 19%, and the best dimensions for this riblet model to give high drag reduction are (h=0.125 & 0.25mm, s=2mm and w=2mm).