Influence of a back-flow flap on the dynamic stall flow topology
Tóm tắt
Dynamic stall is a major concern for highly loaded helicopter rotors in fast forward flight. The potential of a back-flow flap for dynamic stall reduction is investigated. The flap assembly is mounted on the suction side of a helicopter main rotor-blade airfoil undergoing deep-stall pitch oscillations. Wind-tunnel experiments using high-speed particle image velocimetry were conducted to identify the flow topology and to investigate the flap’s method of operation. A phase-averaged proper orthogonal decomposition (POD) is used to identify relevant flow events and to compare test cases with and without flap. The evolution of the large-scale dynamic stall vortex in the initial phases of flow separation is analyzed in detail. The back-flow flap splits the vortex into two smaller vortices and thereby reduces the pitching-moment peak. This effect can be described through the eigenmode coefficients of the POD. The study closes with an analysis of different pitching frequencies, which do not affect the flap’s method of operation.
Tài liệu tham khảo
McCroskey, W.J., Carr, L.W., McAlister, K.W.: Dynamic stall experiments on oscillating airfoils. AIAA. J. 14(1), 57–63 (1976). https://doi.org/10.2514/3.61332
McCroskey, W.J.: The phenomenon of dynamic stall, NASA TM-81264 (1981)
Carr, L.W., McAlister, K. W., McCroskey, W.J.: Analysis of the development of dynamic stall based on oscillating airfoil experiments. NASA TN-D-8382 (1977)
Joubert, G., Le Pape, A., Heine, B., Huberson, S.: Deployable vortex generator dynamic stall alleviation through experimental and numerical investigations. J. Am. Helicopter. Soc. 58(3), 1–13 (2013). https://doi.org/10.4050/JAHS.58.032005
Le Pape, A., Costes, M., Richez, F., Joubert, G., David, F., Deluc, J.-M.: Dynamic stall control using deployable leading-edge vortex generators. AIAA J. 50(10), 2135–2145 (2012). https://doi.org/10.2514/1.J051452
Heine, B., Mulleners, K., Joubert, G., Raffel, M.: Dynamic stall control by passive disturbance generators. AIAA J. 51(9), 2086–2097 (2013). https://doi.org/10.2514/1.J051525
Greenblatt, D., Wygnanski, I.: Dynamic stall by periodic excitation, Part 1: NACA 0015 parametric study. J. Aircr. 38(3), 430–438 (2001). https://doi.org/10.2514/2.2810
Greenblatt, D., Nishri, B., Darabi, A., Wygnanski, I.: Dynamic stall control by periodic excitation, Part 2: Mechanisms. J. Aircr. 38(3), 439–447 (2001). https://doi.org/10.2514/2.2811
Post, M.L., Corke, T.C.: Separation control using plasma actuators: Dynamic stall vortex control on oscillating airfoil. AIAA. J. 44(12), 3125–3135 (2006). https://doi.org/10.2514/1.22716
Chandrasekhara, M.S., Wilder, M.C., Carr, L.W.: Unsteady stall control using dynamically deforming airfoils. AIAA J 36(10), 1792–1800 (1998). https://doi.org/10.2514/2.294
Gerontakos, P., Lee, T.: Dynamic stall flow control via a trailing-edge flap. AIAA J 44(3), 469–480 (2006). https://doi.org/10.2514/1.17263
Meyer, R. K. J.: Experimentelle Untersuchungen von Rückströmklappen auf Tragflügeln zur Beeinflussung von Strömungsablösung. PhD Thesis, Technical University of Berlin (2000). ISBN: 3898202054
Meyer, R., Hage, W., Bechert, D.W., Schatz, M., Knacke, T., Thiele, F.: Separation control by self-activated movable flaps. AIAA J. 45(1), 191–199 (2007). https://doi.org/10.2514/1.23507
Bramesfeld, G., Maughmer, M.D.: Experimental investigation of self-actuating, upper-surface, high-lift-enhancing effectors. J Aircr. 39(1), 120–124 (2002). https://doi.org/10.2514/2.2905
Höfinger, M.: Rotor blade with integrated passive surface flap. Patent US9193456 B2 (2015)
Kaufmann, K., Gardner, A. D., Richter, K.: Numerical investigations of a back-flow flap for dynamic stall control. In: Dillmann, A., Heller, G., Krämer, E., Kreplin, H.-P., Nitsche, W., Rist, U. (Eds.) New Results in Numerical and Experimental Fluid Mechanics IX, pp. 255-262. Springer, Heidelberg (2014). https://doi.org/10.1007/978-3-319-03158-3_26
Opitz, S., Gardner, A.D., Kaufmann, K.: Aerodynamic and structural investigation of an active back-flow flap for dynamic stall control. CEAS Aeronaut. J. 5(3), 279–291 (2014). https://doi.org/10.1007/s13272-014-0106-3
Opitz, S., Kaufmann, K., Gardner, A.: An active back-flow flap of a helicopter rotor blade. Adv. Aircr. Spacecr. Sci. 1(1), 69–91 (2014). https://doi.org/10.12989/aas.2014.1.1.069
Gardner, A.D., Opitz, S., Wolf, C.C., Merz, C.B.: Reduction of dynamic stall using a back-flow flap. CEAS Aeronaut. J. 8(2), 271–286 (2017). https://doi.org/10.1007/s13272-017-0237-4
Merz, C. B., Wolf, C. C., Richter, K., Kaufmann, K., Raffel, M.: Experimental investigation of dynamic stall on a pitching rotor blade tip. In: Dillmann, A., Heller, G., Krämer, E., Wagner, C., Breitsamter, C. (Eds.) New Results in Numerical and Experimental Fluid Mechanics X, pp. 339-348. Springer, Heidelberg (2016). https://doi.org/10.1007/978-3-319-27279-5_30
Gardner, A.D., Richter, K., Mai, H., Neuhaus, D.: Experimental Investigation of Air Jets to Control Shock-Induced Dynamic Stall. J Am Helicopter Soc 59(2), 1–11 (2014). https://doi.org/10.4050/JAHS.59.022003
Mai, H., Dietz, G., Geissler, W., Richter, K., Bosbach, J., Richard, H., de Groot, K.: Dynamic Stall Control by Leading Edge Vortex Generators. J Am Helicopter Soc 53(1), 26–36 (2008). https://doi.org/10.4050/JAHS.53.26
Martin, P., Wilson, J., Berry, J., Wong, T., Moulton, M., McVeigh, M.: Passive Control of Compressible Dynamic Stall. 26th AIAA Applied Aerodynamics Conference, Honolulu, HI, USA, AIAA 2008-7506 (2008). doi: 10.2514/6.2008-7506
Min, B.-Y., Lorber, P. F., Berezin, C. R., Wake, B. E., Scott, M. W.: Numerical Study of Retreating Side Blowing Concept for a Rotor in High Speed Flight. AHS 73rd Annual Forum, Fort Worth, TX, USA (2017)
Raffel, M., Willert, C. E., Wereley, S. T., Kompenhans, J.: Particle Image Velocimetry: A Practical Guide, 2nd ed., pp. 131-176, Springer-Verlag Berlin (2007). doi:10.1007/978-3-540-72308-0
Sirovich, L.: Turbulence and the dynamics of coherent structures pt I-III. Q Appl Math 45(3), 561–590 (1987). https://doi.org/10.1090/qam/910462
Berkooz, G., Holmes, P., Lumley, J.L.: The proper orthogonal decomposition in the analysis of turbulent flows. Annu Rev Fluid Mech 25, 539–575 (1993). https://doi.org/10.1146/annurev.fl.25.010193.002543
Mulleners, K., Raffel, M.: The onset of dynamic stall revisited. Exp. Fluids 52(3), 779–793 (2012). https://doi.org/10.1007/s00348-011-1118-y