EFFECTS OF THICKNESS AND CAMBER RATIO ON FLOW CHARACTERISTICS OVER AIRFOILS

Abstract

This study ensures experimental and numerical investigation of different airfoils to observe and understand how camber ratio affects the flow characteristics over surface of different airfoils. Experimental results in the previous studies were used while the numerical study was performed for present investigation. Reynolds numbers based on the airfoil chords were 1x105 and the angle of attack of 8°. Instantaneous voltage output data were used in order to detect transition location for NACA 4412, oil surface visualization experiments were presented for NACA 2415. In the numerical analysis, values of u/U∞ and turbulent kinetic energy were presented for NACA 4415 airfoil. The experimental results denoted that the change of camber ratio and thickness significantly affected the flow phenomenon such as boundary layer separation or formation and progress of the laminar separation bubble. The long bubble was clearly observed with accumulation of pigments at oil-flow measurement experiment. By increasing the camber ratio with the use of NACA 4412 airfoil, the long bubble turned into the short bubble. Briefly, not only the progress and formation of laminar separation bubble was being affected, but also the onset of transition point was obviously influenced by changing of camber ratio.

Keywords

• Camber Ratio,Thickness,Laminar Separation Bubble

References

1. [1] Arcara P.C., Bartlett D.W., McCullers L.A. Analysis for the application of hybrid laminar flow control to a long-range subsonic transport aircraft. SAE Technical 1991; Paper No. 912113
2. [2] Carmichael B.H. Low Reynolds number airfoil survey, 1981, volume 1
3. [3] Mueller T.J., DeLaurier J.D. Aerodynamics of small vehicles. Annu. Rev. Fluid Mech. 2003; 35(1): 89-111.
4. [4] Hu H., Yang Z. An experimental study of the laminar flow separation on a low-Reynolds-number airfoil. J Fluid Eng 2008; 130(5): 051101.
5. [5] Gaster M. The structure and behaviour of laminar separation bubbles. HM Stationery Office 1969.
6. [6] Tani I. Low-speed flows involving bubble separations. Prog. Aerosp. Sci. 1964; 5: 70-103.
7. [7] Dovgal A.V., Kozlov V.V., Michalke A. Laminar boundary layer separation: instability and associated phenomena. Prog. Aerosp. Sci. 1994; 30(1): 61-94.
8. [8] Diwan S.S., Ramesh O.N. On the origin of the inflectional instability of a laminar separation bubble. J Fluid Mech. 2009; 629: 263-298.

9. [9] Brinkerhoff J.R., Yaras M.I. Interaction of viscous and inviscid instability modes in separation–bubble transition. Phys. Fluids 2011; 23(12): 124102.
10. [10] Cherry N.J., R. Hillier, Latour M.E.M. Unsteady measurements in a separated and reattaching flow. J Fluid Mech. 1984; 144(1): 13
11. [11] Hain R., Kähler C.J., Radespiel R. Dynamics of laminar separation bubbles at low-Reynolds-number aerofoils. J Fluid Mech. 2009; 630: 129-153.
12. [12] McAuliffe B.R., Yaras M.I. Separation-bubble-transition measurements on a low-Re airfoil using particle image velocimetry. ASME, 2005; Paper No. GT2005-68663.
13. [13] Burgmann S., Schröder W. Investigation of the vortex induced unsteadiness of a separation bubble via time-resolved and scanning PIV measurements. Exp. Fluids 2008; 45(4): 675.
14. [14] Genç, M.S., Kaynak, Ü., Yapıcı, H. Performance of transition model for predicting low Re aerofoil flows without/with single and simultaneous blowing and suction. Eur. J. Mech. (B/Fluids) 2011; 30(2): 218-235.
15. [15] Genç, M.S. Numerical simulation of flow over a thin aerofoil at a high Reynolds number using a transition model. Proceedings of the Institution of Mechanical Engineers, Part C: J. Mech. Eng. Sci. 2010; 224(10):2155-2164.
16. [16] Genç, M.S., Kaynak, Ü., Lock, G.D. Flow over an aerofoil without and with a leading-edge slat at a transitional Reynolds number. Proceedings of the Institution of Mechanical Engineers, Part G: J. Aerosp. Eng. 2009; 223(3): 217-231.
17. [17] Genc, M., Lock, G., Kaynak, U. An experimental and computational study of low Re number transitional flows over an aerofoil with leading edge slat. In The 26th Cong. of ICAS and 8th AIAA ATIO, 2008; p. 8877.
18. [18] Genc, M.S., Koca, K., Açikel, H. H. Investigation of pre-stall flow control on wind turbine blade airfoil using roughness element. Energy 2019; 176: 320-334.
19. [19] Alpman, E. Aerodynamic performance of small-scale horizontal axis wind turbines under two different extreme wind conditions. J.Therm. Eng. 2015; 1(3): 420-432.
20. [20] Mahmoud, H. Stability of Turbine Blades, Aircraft Wings and Their Acoustic Radiation. J.Therm. Eng., 2015; 1:6
21. [21] Kaboglu, C. The effect of different types of core material on the flexural behavior of sandwich composites for wind turbine blades. J. Therm. Eng. 2017; 3(2): 1102-1109.
22. [22] Celik, A., Javani, N. Wind turbine blade flapwise and edgewise bending vibration analyses using energy methods. J. Therm. Eng. 2016, 2(6): 983-989.
23. [23] Genç, M.S., Koca, K., Demir, H., Açıkel, H.H. Traditional and New Types of Passive Flow Control Techniques to Pave the Way for High Maneuverability and Low Structural Weight for UAVs and MAVs. In: Unmanned Aerial Vehicles. IntechOpen, 2020.
24. [24] Cherrared, D. Numerical simulation of film cooling a turbine blade through a row holes. J. Therm. Eng., 2017; 3(2): 1110-1120.
25. [25] Bodur, T.M., Genç, M.S., Koca, K. Elimination of tip vortex using air holes at wind turbine blade. In: International Symposium on Sustainable Aviation. 2015.
26. [26] Maheri, A. Simulation of wind turbines utilizing smart blades. J. Therm. Eng. 2016; 2(1): 557-565.
27. [27] Karasu, İ., Özden, M., Genç, M.S. Performance Assessment of Transition Models for 3D Flow over NACA4412 Wings at Low Reynolds Numbers. J Fluid Eng Trans ASME 2018; 140: 12
28. [28] Koca K. The flow control with roughness devices over wind turbine airfoil, MSc. Thesis 2016 Graduate School of Natural and Applied Sciences. Turkey: Erciyes University, Kayseri,.
29. [29] Genç M.S., Koca K., Açıkel H.H., Ozkan G, Kırıs¸ MS, Yıldız R. Flow characteristics over NACA 4412 airfoil at low Reynolds number. In: EPJ web of conf. 2016, Vol. 114. EDP sciences,
30. [30] Poels A., Rudmin D., Benaissa A. Poirel D., Localization of flow separation and transition over a pitching NACA0012 airfoil at transitional Reynolds numbers using hot-films. J Fluid Eng. 2015; 137(12): 124501.
31. [31] Haghiri A.A., Mani M., Fallahpour N. Unsteady boundary layer measurement on an oscillating (pitching) supercritical airfoil in compressible flow using multiple hot-film sensors. Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerosp. Eng. 2015; 229(10): 1771-1784.
32. [32] Bruun H.H., Hot-wire anemometry-principles and signal analysis, 1995.
33. [33] Hodson H.P., Howell R.J. Unsteady flow: its role in the low-pressure turbine. Minnow brook III, Workshop on Boundary Layer Transition in Turbomachines 2000, Syracuse University
34. [34] Zhang X.F., Mahallati A., Sjolander S.A. Hot-film measurements of boundary layer transition, separation and reattachment on a low-pressure turbine airfoil at low Reynolds numbers. AIAA P. 2002; 36: 2002.
35. [35] Koca, K., Genç, M.S., Açikel, H.H., Çağdaş, M., Bodur, T.M. Identification of Flow Phenomena over NACA 4412 Wind Turbine Airfoil at Low Reynolds Numbers and Role of Laminar Separation Bubble on Flow Evolution. Energy 2017; 144: 750-764
36. [36] Genç M.S., Karasu I., Açıkel H.H. An experimental study on aerodynamics of NACA 2415 aerofoil at low Re numbers. Exp. Therm. Fluid Sci. 2012; 39: 252-264.
37. [37] Karasu I. Experimental and numerical investigations of transition to turbulence and laminar separation bubble over aerofoil at low Reynolds number flows, MSc. Thesis 2011, Graduate School of Natural and Applied Sciences, Erciyes University, Kayseri, Turkey.