The rapid change in local blade angle produced the

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Unformatted text preview: esult of quasi-static mean CN participation at various spans, or a true three-dimensional dynamic effect resulting from geometry and/or separation behavior. Influence of the tower shadow was observed to have a greater effect than expected. The rapid change in local blade angle produced the expected dynamic stall events. However, the same effect was also observed to “bifurcate” the steady state aerodynamic response introducing “state” changes between attached and separated flow over the cycle. The number of occurrences was significant enough in the random sampling of pressure time series selected to warrant further investigation. This overview of key aerodynamic influences impacting wind turbine operation has highlighted some pressing problems and promising opportunities. The flow fields that most stubbornly resist comprehension and actively challenge design are three-dimensional, unsteady, and separated. Aerodynamics modeling strategies continue to advance, but cannot yet predict these types of flows with sufficient accuracy and reliability. Field experiments can successfully characterize these flow field effects. However, bounds on spatial and temporal resolution coupled with the impossibility of controlling inflow conditions limit the understanding thus gained. Cause exists for optimism, however. Later this year, the NWTC Unsteady Aerodynamics Experiment is projected to enter the NASA Ames 80 ft x 120 ft wind tunnel. This series of experiments will enable full-scale wind turbine flow field measurements, and allow command of inflow and other parameters that defy control in the field. Exploitation of the data thus acquired will augment comprehension of threedimensional unsteady separated flows elicited by wind turbines. In addition, these data will facilitate development of enhanced aerodynamic modeling strategies. Improved understanding of complex wind turbine aerodynamics formalized in accurate, robust models will constitute a powerful capability for analyzing and designing wind energy machines of the future. REFERENCES [1] Schepers, J.G.; Brand, A.J.; Bruining, A.; Graham, J.M.R.; Hand, M.M.; Infield, D.G.; Madsen, H.A.; Paynter, R.J.H.; Simms, D.A. (1997), “Final Report of IEA Annex XIV: Field Rotor Aerodynamics,” ECN-C-97-027, Petten, Netherlands. [2] Butterfield, C.P.; Musial, W.P.; Simms, D.A. (1992). “Combined Experiment Phase I Final Report.” NREL/TP257-4655. Golden, CO: National Renewable Energy Laboratory. [3] Huyer, S.A.; Simms, D.A.; Robinson, M.C. “Unsteady Aerodynamics Associated with a Horizontal-Axis Wind Turbine.” American Institute of Aeronautics and Astronautics Journal, Volume 34, No. 10, pp. 1410-1419, 1996. [4] Miller, M.S.; Shipley, D.E.; Young, T.S.; Robinson, M.C.; Luttges, M.W.; Simms, D.A. (1995), “The Baseline Data Sets for Phase II of the Combined Experiment.” NREL/TP 442-6915, Golden, CO: National Renewable Energy Laboratory. [5] Miller, M.S.; Shipley, D.E.; Young, T.S.; Robinson, M.C.; Luttges, M.W.; Simms, D.A. (1995), “Combined Experiment Phase II Data Characterization.” NREL/TP 4426916, Golden, CO: National Renewable Energy Laboratory. [6] Robinson, M.C.; Simms, D.A.; Hand, M.M.; Schreck, S.J. “Vortex/Blade Interaction from Tower Shadow Effects.” In preparation. [7] Carr, L.W.; “Progress in Analysis and Prediction of Dynamic Stall.” American Institute of Aeronautics and Astronautics Journal, Volume 25, No. 1, pp. 6-17, 1988. [8] McCroskey, W.J. “Some Current Research in Unsteady Fluid Dynamics-The 1976 Freeman Scholar Lecture.” Transactions of the ASME Journal of Fluids Engineering. March, 1977. [9] Somers, D.M. (1997), “Design and Experimental Results for the S809 Airfoil,” NREL/SR 440-6918, Golden, CO: National Renewable Energy Laboratory. 11...
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This note was uploaded on 11/13/2011 for the course AEE 495 taught by Professor O.uzol during the Spring '11 term at Middle East Technical University.

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