Influence of riblets on airfoils
 

Hi,

does anybody know any references on the usage of riblets on airfoils ?

Could it be possible, that beside reduction of friction drag riblets could have a positive influence on stall angle ? (increasing it)

Any opinions on that topic ?

Ron

Re: Influence of riblets on airfoils
 

Riblets would make the surface non-smooth and induce turbulence in the boundary layer at an earlier stage. A turbulent boundary layer would detach itself later than a non-turbulent boundary layer, therefore making it possible to increase the angle of attack. So the stall angle would be increased. I am not an aeronautical engineer, but I am familiar with boundary layers, so that's a guess.

Any comment and/or addition from the aeronautical engineers?

Cheers, Patrick

Re: Influence of riblets on airfoils
 

Hi,

You can check the following articles:

"Direct Numerical Simulation of turbulent flow over riblets" Choi, H., Moin, P. and Kim. J. J. Fluid Mech., Vol 225, 1993, pp 503-539.

"DRAG REDUCTION DUE TO RIBLETS ON A GAW(2) AIRFOIL". Subaschandar, N.; Kumar, Rajeev; Sundaram, S. Journal of Aircraft v36 n5 1999, pp 890-892

"VISCOUS DRAG REDUCTION USING RIBLETS ON A SWEPT WING". Sundaram, S.; Viswanath, P.R.; Subaschandar, N. AIAA Journal v 37 n 7 Jul 1999, pp 851-856

"BASE DRAG REDUCTION CAUSED BY RIBLETS ON A GAW(2) AIRFOIL". Raju, Channa; Viswanath, P.R. Journal of Aircraft v 35 n 6 Nov-Dec 1998, pp 988-991

"EFFECTS OF SURFACE RIBLETS AND FREE-STREAM TURBULENCE ON HEAT TRANSFER IN A LINEAR TURBINE CASCADE". Maciejewski, Paul K.; Rivir, Richard B. American Society of Mechanical Engineers (Paper) Proceedings of the International Gas Turbine and Aeroengine Congress and Exposition Jun 13-16 1994 Hague Publ by ASME New York NY USA p 1-9 Paper : 94-GT-245

"EFFECT OF RIBLETS ON AXISYMMETRIC BASE PRESSURE". Krishnan, V.; Viswanath, P.R.; Rudrakumar, S.; Journal of Spacecraft and Rockets v 34 n 2 Mar-Apr 1997, pp 256-258

"DEVELOPMENT OF THE WAKE OF AN AIRFOIL WITH RIBLETS". Caram, J.M.; Ahmed, A. AIAA Journal v 30 n 12 Dec 1992, pp 2817-2818

"EFFECT OF RIBLETS ON SAILS". Alving, A.E.; Freeberg, P. Experiments in Fluids v19 n6 Oct 1995, pp 397-404

"EFFECT OF RIBLETS ON TURBULENCE IN THE WAKE OF AN AIRFOIL". Caram, J.M.; Ahmed, A. AIAA Journal v 29 n 11 Nov 1991, pp 1769-1770

"TURBULENT DRAG REDUCTION USING RIBLETS ON A SUPERCRITICAL AIRFOIL AT TRANSONIC SPEEDS". Viswanath, P.R.; Mukund, R. AIAA Journal v33 n5 May 1995, pp 945-947

"EXPERIMENTAL INVESTIGATION OF LOSS REDUCTION WITH RIBLETS ON CASCADE BLADE SURFACES AND ISOLATED AIRFOILS". Fang, Chen; Yan-Ping, Tang; Mao-Zhang, Chen American Society of Mechanical Engineers (Paper) International Gas Turbine and Aeroengine Congress and Exposition Jun 11-14 1990 1990 Brussels.

I hope this will help.

Sincerely,

Frederic Felten CFD Laboratory UT Arlington, TX, USA. http://utacfdb.uta.edu/

Re: Influence of riblets on airfoils
 

Hi,

thanks for your comments.

Patrick, you talked about transition to turbulence and delaying of separation by that fact. What do you think about the following. If you assume that the boundary layer is turbulent at an early stage due to by-pass transition. So the riblets are not necessary to cause transition. If I remember my fluid mechanics lessons right separation is caused by the fact that the boundary looses too much kinetic energy due to wall friction to overcome the positive pressure gradient on the upper side of the airfoil. But if the riblets reduce the wall friction the energy loss is reduced and so the separation is delayed as well.

Do these thoughts make sense in your opinion ?

Ron