In this study, we experimentally investigate the effects of mainstream turbulence intensity (Ti) on a leading-edge separation bubble under low-Reynolds number (Rec) conditions range of 2.0 × 104 to 6.0 × 104. We used a flat plate to fix a separation point at the leading edge. Also, we visualized the behavior of the leading-edge separation bubble using the smoke wire technique and Particle Image Velocimetry (PIV) measurement. Furthermore, we measured the effect of Ti on the turbulent transition process in the separated shear layer using a hot-wire anemometer. The results indicate that the bypass transition for large Ti causes the turbulent transition, and so accelerates the reattachment of the separated shear layer. The results show that the bypass transition promotes the reattachment of the separated shear layer to maintain the leading-edge separation bubble on the upper surface even at high angles of attack, increasing the stall angle.
References
[1]
Mueller, T.J. (1999) Aerodynamic Measurements at Low Reynolds Numbers for Fixed Wing Micro-Air Vehicles. DTIC ADP010760, DTIC, Fort Belvoir.
[2]
Wood, R.J. (2008) The First Takeoff of a Biologically-Inspired At-Scale Robotic Insect. IEEE Transactions on Robotics, 24, 341-347.
https://doi.org/10.1109/TRO.2008.916997
[3]
Oyama, A. and Fuji, K. (2006) A Study on Airfoil Design for Future Mars Airplane. AIAA Paper 2006-1484, AIAA, Reston. https://doi.org/10.2514/6.2006-1484
[4]
Braun, R.D., Wright, H.S., Croom, M.A., Levine, J.S. and Spencer, D.A. (2006) Design of the ARES Mars Airplane and Mission Architecture. Journal of Spacecraft and Rockets, 43, 1026-1034. https://doi.org/10.2514/1.17956
[5]
Aono, H., Nonomura, T., Anyoji, M., Oyama, A. and Fujii, K. (2012) A Numerical Study of the Effects of Airfoil Shape on Low Reynolds Number Aerodynamics. Proceedings of the 8th International Conference on Engineering Computational Technology, Dubrovnik, 4-7 September 2012, 131.
[6]
Anyoji, M., Nonomura, T., Aono, H., Oyama, A., Fujii, K., Nagai, H. and Asai, K. (2014) Computational and Experimental Analysis of a High-Performance Airfoil under Low-Reynolds-Number Flow Condition. Journal of Aircraft, 51, 1864-1872.
https://doi.org/10.2514/1.C032553
[7]
Mueller, T.J. and Delaurier, J.D. (2003) Aerodynamics of Small Vehicles. Annual Review of Fluid Mechanics, 35, 89-111.
https://doi.org/10.1146/annurev.fluid.35.101101.161102
Schmitz, F.W. (1967) Aerodynamics of the Model Airplane: Part 1. Airfoil Measurements. NASA-TM-X-60976.
[11]
Schmitz, F.W. (1980) The Aerodynamics of Small Reynolds Numbers. NASA TM-75816, NASA, Washington DC.
[12]
Tsuchiya, T., Numata, D., Suwa, T. and Asai, K. (2013) Influence of Turbulence Intensity on Aerodynamic Characteristics of an NACA 0012 at Low Reynolds Numbers. AIAA Paper 2013-0065, AIAA, Reston. https://doi.org/10.2514/6.2013-65
[13]
Wang, S., Zohn, Y., Alam, M.M. and Yang, H. (2014) Turbulent Intensity and Reynolds Number Effects on an Airfoil at Low Reynolds Numbers. Physics of Fluids, 26, Article ID: 115107. https://doi.org/10.1063/1.4901969
[14]
Hoffmann, J.A. (1991) Effects of Freestream Turbulence on the Performance Characteristics of an Airfoil. AIAA Journal, 29, 1353-1354.
https://doi.org/10.2514/3.10745
[15]
Simoni, D., Lengani, D., Ubaldi, M., Zunino, P. and Dellacasagrande, M. (2017) Inspection of the Dynamic Properties of Laminar Separation Bubbles: Free-Stream Turbulence Intensity Effects for Different Reynolds Numbers. Experiments in Fluids 58, Article No.66. https://doi.org/10.1007/s00348-017-2353-7
[16]
Li, H. and Yang, Z. (2016) Numerical Study of Separated Boundary Layer Transition under Pressure Gradient. Proceedings of the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malaga, 11-13 July 2016, 1759-1764.
[17]
Balzer, W. and Fasel, H.F. (2016) Numerical Investigation of the Role of Free-Stream Turbulence in Boundary-Layer Separation. Journal of Fluid Mechanics, 801, 289-321.
https://doi.org/10.1017/jfm.2016.424
[18]
Abdalla, I.E. and Yang, Z. (2004) Numerical Study of the Instability Mechanism in Transitional Separating-Reattaching Flow. International Journal of Heat and Fluid Flow, 25, 593-605. https://doi.org/10.1016/j.ijheatfluidflow.2004.01.004
[19]
Yang, Z. and Voke, P.R. (2001) Large-Eddy Simulation of Boundary Layer Separation and Transition at a Change of Surface Curvature. Journal of Fluid Mechanics, 439, 305-333. https://doi.org/10.1017/S0022112001004633
[20]
Yang, Z. and Abdalla, I.E. (2009) Effects of Free-Stream Turbulence on a Transitional Separated-Reattached Flow over a Flat Plate with a Sharp Leading Edge. International Journal of Heat and Fluid Flow, 30, 1026-1035.
https://doi.org/10.1016/j.ijheatfluidflow.2009.04.010
[21]
Langari, M. and Yang, Z. (2013) Numerical Study of the Primary Instability in a Separated Boundary Layer Transition under Elevated Free-Stream Turbulence. Physics of Fluids, 25, Article ID: 074106. https://doi.org/10.1063/1.4816291
[22]
Lee, D., Kawai, S., Nonomura, T., Anyoji, M., Aono, H., Oyama, A., Asai, K. and Fuji, K. (2015) Mechanisms of Surface Pressure Distribution Within a Laminar Separation Bubble at Different Reynolds Numbers. Physics of Fluids, 27, Article ID: 023602. https://doi.org/10.1063/1.4913500
[23]
Burns, T.F. and Mueller, T.J. (1982) Experimental Studies of the Eppler 61 Airfoil at Low Reynolds Numbers. AIAA Paper 1982-345, AIAA, Reston.
https://doi.org/10.2514/6.1982-345
[24]
Tsuji, H. (1959) A Document on Turbulent Grid Design. Aeronautical Research Institute, University of Tokyo, Tokyo, 179-184. (In Japanese)
[25]
Anyoji, M., Nose, K., Ida, S., Numata, D., Nagai, H. and Asai, K. (2011) Aerodynamic Measurements in the Mars Wind Tunnel at Tohoku University. AIAA Paper 2011-0852, AIAA, Reston. https://doi.org/10.2514/6.2011-852
[26]
Sasaki, K. and Kiya, M. (1991) Three-Dimensional Vortex Structure in a Leading-Edge Separation Bubble at Moderate Reynolds Number. Journal of Fluids Engineering, 113, 405-410. https://doi.org/10.1115/1.2909510
[27]
Rinoie, K. (2003) Laminar Separation Bubbles Formed on Airfoils. Journal of Japan Society Fluid Mechanics NAGARE, 22, 15-22. (In Japanese)
[28]
Watmuff, J.H. (1999) Evolution of a Wave Packet into Vortex Loops in a Laminar Separation Bubble. Journal of Fluid Mechanics, 397, 119-169.
https://doi.org/10.1017/S0022112099006138
[29]
Bruun, H.H. (1995) Hot-Wire Anemometry: Principles and Signal Analysis. Oxford University Press, Oxford. https://doi.org/10.1088/0957-0233/7/10/024
[30]
Durst, F., Zanoun, E.S. and Pashtrapanska, M. (2001) in Situ Calibration of Hot Wires Close to Highly Heat-Conducting Walls. Experiments in Fluids, 31, 103-110.
https://doi.org/10.1007/s003480000264
[31]
Abdalla, I.E. and Yang, Z. (2005) Numerical Study of a Separated-Reattached Flow on a Blunt Plate. AIAA Journal, 43, 2465–2474. https://doi.org/10.2514/1.1317
[32]
Kiya, M. and Sasaki, K. (1983) Structure of a Turbulent Separation Bubble. Journal of Fluid Mechanics, 137, 83-113. https://doi.org/10.1017/S002211208300230X
[33]
Cherry, N.J., Hillier, R. and Latour, M.E.M.P. (1984) Unsteady Measurements in a Separated and Reattaching Flow. Journal of Fluid Mechanics, 144, 13-46.
https://doi.org/10.1017/S002211208400149X
[34]
Chandrasekhar, S. (1961) Hydrodynamic and Hydromagnetic Stability. Clarendon Press, Oxford.
[35]
Tani, I. (1964) Low Speed Flows Involving Bubble Separations. Progress in Aerospace Sciences, 5, 70-103. https://doi.org/10.1016/0376-0421(64)90004-1
[36]
O’Meara, M.M. and Mueller, T.J. (1987) Laminar Separation Bubble Characteristics on an Airfoil at Low Reynolds Number. AIAA Journal, 25, 1033-1041.
https://doi.org/10.2514/3.9739
[37]
Gerakopulos, R., Boutilier, M. and Yarusevych, S. (2010) Aerodynamic Characterization of a NACA 0018 Airfoil at Low Reynolds Numbers. AIAA Paper 2010-4629, AIAA, Reston. https://doi.org/10.2514/6.2010-4629
[38]
Garmann, D.J. and Visbal, M.R. (2014) Dynamics of Revolving Wings for Various Aspect Ratios. Journal of Fluid Mechanics, 748, 932-956.
https://doi.org/10.1017/jfm.2014.212
