Experimental study of square riblets effects on delta wing using smoke visualization and force measurement

Riblets are effective approach to improve the aerodynamic performance of low speed wing configurations. For a delta type wing, it is important to alleviate the flow features such as large rollup and tip vortices in low Reynolds number. In this paper, for first time, the effect of the square riblets on delta wings is studied. In the first step, flow visualization is accomplished to find out the effects of riblets on the flow pattern. For this purpose, two slender delta wings with and without riblet are examined in a vertical wind tunnel in which smoke stream lines are passed over the delta wings to visualize the flow pattern. The visualization tests are performed at five angles of attack; i.e., 0, 10, 20, 30 and 35 degrees. The results of flow visualization indicate that considerable improvements are obtained because of delaying flow separation at high attack angles. In the second step, the aerodynamic performance of the two delta wings are quantitatively evaluated by measuring the lift and drag forces using two load cells in another wind tunnel. The force tests are performed at attack angles of 5–65 degrees with 5-degree step sizes. The measured forces show that the riblets decreases the drag coefficient for all attack angles and increase the lift to drag ratio more than 12 percent for 5–20 degrees attack angles.Graphical Abstract

[1]  B. Bhushan,et al.  Shark-skin surfaces for fluid-drag reduction in turbulent flow: a review , 2010, Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences.

[2]  K. Rinoie,et al.  Flow field measurements of leading-edge separation vortex formed on a delta wing with vortex flaps , 2001 .

[3]  Myong Hwan Sohn,et al.  Delta-wing vortex visualization using micro-sized water droplets generated by an ultrasonic humidifier , 2008, J. Vis..

[4]  Christian Breitsamter,et al.  Turbulent and unsteady flow characteristics of delta wing vortex systems , 2013 .

[5]  Thomas L. Daniel,et al.  FISH MUCUS: IN SITU MEASUREMENTS OF POLYMER DRAG REDUCTION , 1981 .

[6]  Cja Kees Pulles.  Drag reduction of turbulent boundary layers by means of grooved surfaces , 1988 .

[7]  Promode R. Bandyopadhyay,et al.  Modeling how shark and dolphin skin patterns control transitional wall-turbulence vorticity patterns using spatiotemporal phase reset mechanisms , 2014, Scientific Reports.

[8]  A. M. Savill,et al.  Turbulent Skin Friction Drag Reduction By Active and Passive Means. Part 2 , 1992 .

[9]  Petter Krus,et al.  Implications of scale effect for the prediction of high angle of attack aerodynamics , 2005 .

[10]  E. Coustols,et al.  Synthesis of Experimental Riblet Studies in Transonic Conditions , 1990 .

[11]  M. J. Walsh.  Drag characteristics of V-groove and transverse curvature riblets , 1980 .

[12]  Chih-Ming Ho,et al.  Vortex Dynamics of Delta Wings , 1989 .

[13]  Gregroy D. Bixler.  Bioinspired Surface for Low Drag, Self-Cleaning, and Antifouling: Shark Skin, Butterfly and Rice Leaf Effects , 2013 .

[14]  J. Anderson,et al.  Fundamentals of Aerodynamics , 1984 .

[15]  J. Cousteix,et al.  Experimental Investigation of Turbulent Boundary Layers Manipulated with Internal Devices: Riblets , 1990 .

[16]  Jerome T. Kegelman,et al.  The flowfields of bursting vortices over moderately swept delta wings , 1990 .

[17]  J M Caram,et al.  Effect of riblets on turbulence in the wake of an airfoil , 1991 .

[18]  Parviz Moin,et al.  Direct numerical simulation of turbulent flow over riblets , 1993, Journal of Fluid Mechanics.

[19]  Ismet Gursul,et al.  Unsteady flow phenomena over delta wings at high angle of attack , 1994 .

[20]  M. J. Walsh,et al.  Riblets as a Viscous Drag Reduction Technique , 1983 .

[21]  M. J. Walsh,et al.  Optimization and application of riblets for turbulent drag reduction , 1984 .

[22]  Wolfram Hage,et al.  Experiments with three-dimensional riblets as an idealized model of shark skin , 2000 .

[23]  Michael S. Selig,et al.  Drag Reduction Using Riblet Film Applied to Airfoils for Wind Turbines , 2011 .

[25]  William L. Sellers,et al.  Riblet drag at flight conditions , 1989 .

[26]  D. W. Bechert,et al.  Experiments on drag-reducing surfaces and their optimization with an adjustable geometry , 1997, Journal of Fluid Mechanics.