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  • 1
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    Peak and Post-Peak Power Aerodynamics from Phase VI NASA Ames Wind Turbine Data (2005)
    American Society of Mechanical Engineers
    Details
    Publication Date: 2005-04-25
    Description: Constant speed/pitch rotor operation lacks adequate theory for predicting peak and post-peak power. The objective of this study was to identify and quantify how measured blade element performance characteristics from the Phase VI NASA Ames 24m×36m80ft×120ft wind tunnel test of a two-bladed, tapered, twisted rotor relate to the prediction of peak and post-peak rotor power. The performance prediction code, NREL’s Lifting Surface Prescribed Wake code (LSWT), was used to study the flow physics along the blade. Airfoil lift and drag coefficients along the blade were derived using the predicted angle of attack distribution from LSWT and Phase VI measured normal and tangential force coefficients. Through successive iterations, the local lift and drag coefficients were modified until agreement was achieved between the predicted and Phase VI measured normal and tangential force coefficients along the blade. This agreement corresponded to an LSWT angle of attack distribution and modified airfoil data table that reflected the measured three-dimensional aerodynamics. This effort identified five aerodynamic events important to the prediction of peak and post-peak power. The most intriguing event was a rapid increase in drag that corresponds with the occurrence of peak power. This is not currently modeled in engineering performance prediction methods.
    Print ISSN: 0199-6231
    Electronic ISSN: 1528-8986
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by American Society of Mechanical Engineers
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    PAPER CURRENT
  • 2
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    Navier-Stokes and Comprehensive Analysis Performance Predictions of the NREL Phase VI Experiment (2003)
    American Society of Mechanical Engineers
    Details
    Publication Date: 2003-11-01
    Description: A lifting-line code, CAMRAD II, and a Reynolds-Averaged Navier-Stokes code, OVERFLOW-D, were used to predict the aerodynamic performance of a two-bladed horizontal axis wind turbine. All computations were compared with experimental data that was collected at the NASA Ames Research Center 80-by-120-foot Wind Tunnel. Lifting-line computations were performed for both axial and yawed operating conditions while the Navier-Stokes computations were performed for only the axial conditions. Various stall delay models and dynamic stall models were used by the CAMRAD II code. For axial operating conditions, the predicted rotor performance varied significantly, particularly for stalled wind speeds. The lifting-line required the use of stall delay models to obtain the proper stall behavior, yet it still has difficulty in predicting the proper power magnitude in stall. The Navier-Stokes method captures the stall behavior and gives a detailed insight into the fluid mechanics of the stall behavior.
    Print ISSN: 0199-6231
    Electronic ISSN: 1528-8986
    Topics: Energy, Environment Protection, Nuclear Power Engineering
    Published by American Society of Mechanical Engineers
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    PAPER CURRENT
  • 3
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    Research and technology 1994 (1995)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Selected research and technology activities at Ames Research Center are summarized. These activities exemplify the Center's varied and productive research efforts for 1994.
    Keywords: General
    Type: NASA-TM-108858 , NAS 1.15:108858 , A-950019
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 4
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    Numerical simulation of helicopter engine plume in forward flight (1994)
    In:  CASI
    Details
    Publication Date: 2019-06-28
    Description: Flowfields around helicopters contain complex flow features such as large separated flow regions, vortices, shear layers, blown and suction surfaces and an inherently unsteady flow imposed by the rotor system. Another complicated feature of helicopters is their infrared signature. Typically, the aircraft's exhaust plume interacts with the rotor downwash, the fuselage's complicated flowfield, and the fuselage itself giving each aircraft a unique IR signature at given flight conditions. The goal of this project was to compute the flow about a realistic helicopter fuselage including the interaction of the engine air intakes and exhaust plume. The computations solve the Think-Layer Navier Stokes equations using overset type grids and in particular use the OVERFLOW code by Buning of NASA Ames. During this three month effort, an existing grid system of the Comanche Helicopter was to be modified to include the engine inlet and the hot engine exhaust. The engine exhaust was to be modeled as hot air exhaust. However, considerable changes in the fuselage geometry required a complete regriding of the surface and volume grids. The engine plume computations have been delayed to future efforts. The results of the current work consists of a complete regeneration of the surface and volume grids of the most recent Comanche fuselage along with a flowfield computation.
    Keywords: AERODYNAMICS
    Type: NASA-CR-197488 , NAS 1.26:197488
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 5
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    A numerical analysis of the British Experimental Rotor Program blade (1989)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Two Computational Fluid Dynamic codes which solve the compressible full-potential and the Reynolds-Averaged Thin-Layer Navier-Stokes equations were used to analyze the nonrotating aerodynamic characteristics of the British Experimental Rotor Program (BERP) helicopter blade at three flow regimes: low angle of attack, high angle of attack and transonic. Excellent agreement was found between the numerical results and experiment. In the low angle of attack regime, the BERP had less induced drag than a comparable aspect ratio rectangular planform wing. At high angle of attack, the blade attained high-lift by maintaining attached flow at the outermost spanwise locations. In the transonic regime, the BERP design reduces the shock strength at the outer spanwise locations which affects wave drag and shock-induced separation. Overall, the BERP blade exhibited many favorable aerodynamic characteristics in comparison to conventional helicopter rotor blades.
    Keywords: AERODYNAMICS
    Type: AHS Annual Forum; May 22, 1989 - May 24, 1989; Boston, MA; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 6
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    Numerical Predictions of Wind Turbine Power and Aerodynamic Loads for the NREL Phase II and IV Combined Experiment Rotor (1999)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: Accurate, reliable and robust numerical predictions of wind turbine rotor power remain a challenge to the wind energy industry. The literature reports various methods that compare predictions to experiments. The methods vary from Blade Element Momentum Theory (BEM), Vortex Lattice (VL), to variants of Reynolds-averaged Navier-Stokes (RaNS). The BEM and VL methods consistently show discrepancies in predicting rotor power at higher wind speeds mainly due to inadequacies with inboard stall and stall delay models. The RaNS methodologies show promise in predicting blade stall. However, inaccurate rotor vortex wake convection, boundary layer turbulence modeling and grid resolution has limited their accuracy. In addition, the inherently unsteady stalled flow conditions become computationally expensive for even the best endowed research labs. Although numerical power predictions have been compared to experiment. The availability of good wind turbine data sufficient for code validation experimental data that has been extracted from the IEA Annex XIV download site for the NREL Combined Experiment phase II and phase IV rotor. In addition, the comparisons will show data that has been further reduced into steady wind and zero yaw conditions suitable for comparisons to "steady wind" rotor power predictions. In summary, the paper will present and discuss the capabilities and limitations of the three numerical methods and make available a database of experimental data suitable to help other numerical methods practitioners validate their own work.
    Keywords: Numerical Analysis
    Type: Joint ASME/AIAA Wind Energy Symposium; Jan 01, 2000; Reno, NV; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 7
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    Helicopter Rotor Blade Computation in Unsteady Flows Using Moving Overset Grids (1996)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: An overset grid thin-layer Navier-Stokes code has been extended to include dynamic motion of helicopter rotor blades through relative grid motion. The unsteady flowfield and airloads on an AH-IG rotor in forward flight were computed to verify the methodology and to demonstrate the method's potential usefulness towards comprehensive helicopter codes. In addition, the method uses the blade's first harmonics measured in the flight test to prescribe the blade motion. The solution was impulsively started and became periodic in less than three rotor revolutions. Detailed unsteady numerical flow visualization techniques were applied to the entire unsteady data set of five rotor revolutions and exhibited flowfield features such as blade vortex interaction and wake roll-up. The unsteady blade loads and surface pressures compare well against those from flight measurements. Details of the method, a discussion of the resulting predicted flowfield, and requirements for future work are presented. Overall, given the proper blade dynamics, this method can compute the unsteady flowfield of a general helicopter rotor in forward flight.
    Keywords: Aerodynamics
    Type: NASA/TM-96-207307 , NAS 1.15:207307 , AIAA Paper 94-1922 , Applied Aerodynamics Conference; Jun 20, 1994 - Jun 22, 1994; Colorado Springs, CO; United States|Journal of Aircraft; 33; 1; 54-60
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 8
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    A Solution Adaptive Structured/Unstructured Overset Grid Flow Solver with Applications to Helicopter Rotor Flows (1995)
    In:  CASI
    Details
    Publication Date: 2019-07-13
    Description: This paper summarizes a method that solves both the three dimensional thin-layer Navier-Stokes equations and the Euler equations using overset structured and solution adaptive unstructured grids with applications to helicopter rotor flowfields. The overset structured grids use an implicit finite-difference method to solve the thin-layer Navier-Stokes/Euler equations while the unstructured grid uses an explicit finite-volume method to solve the Euler equations. Solutions on a helicopter rotor in hover show the ability to accurately convect the rotor wake. However, isotropic subdivision of the tetrahedral mesh rapidly increases the overall problem size.
    Keywords: Aerodynamics
    Type: NASA-CR-201053 , NAS 1.26:201053 , RIACS-TR-95-09 , AIAA Paper 95-1766 , AIAA Applied Aerodynamics Conference; Jun 19, 1995 - Jun 21, 1995; San Diego, CA; United States
    Format: application/pdf
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    NASA TECHNICAL REPORTS
  • 9
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    Navier-Stokes and Comprehensive Analysis Performance Predictions of the NREL Phase VI Experiment (2003)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: A vortex lattice code, CAMRAD II, and a Reynolds-Averaged Navier-Stoke code, OVERFLOW-D2, were used to predict the aerodynamic performance of a two-bladed horizontal axis wind turbine. All computations were compared with experimental data that was collected at the NASA Ames Research Center 80- by 120-Foot Wind Tunnel. Computations were performed for both axial as well as yawed operating conditions. Various stall delay models and dynamics stall models were used by the CAMRAD II code. Comparisons between the experimental data and computed aerodynamic loads show that the OVERFLOW-D2 code can accurately predict the power and spanwise loading of a wind turbine rotor.
    Keywords: Aerodynamics
    Type: AD-A520249 , AIAA Paper 2003-0355 , 2003 ASME Wind Energy Symposium; Jan 06, 2003 - Jan 09, 2003; Reno, NV; United States
    Format: text
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    NASA TECHNICAL REPORTS
  • 10
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    Experimental and numerical study of the British Experimental Rotor Programme blade (1990)
    In:  Other Sources
    Details
    Publication Date: 2019-07-13
    Description: Wind-tunnel tests on the British Experimental Rotor Programme (BERP) tip are described, and the results are compared with computational fluid dynamics (CFD) results. The test model was molded using the Lynx-BERP blade tooling to provide a semispan, cantilever wing comprising the outboard 30 percent of the rotor blade. The tests included both surface-pressure measurements and flow visualization to obtain detailed information of the flow over the BERP tip for a range of angles of attack. It was observed that, outboard of the notch, favorable pressure gradients exist which ensure attached flow, and that the tip vortex also remains stable to large angles of attack. On the rotor, these features yield a very gradual break in control loads when the retreating-blade limit is eventually reached. Computational and experimental results were generally found to be in good agreement.
    Keywords: AERODYNAMICS
    Type: AIAA PAPER 90-3008 , AIAA Applied Aerodynamics Conference; Aug 20, 1990 - Aug 22, 1990; Portland, OR; United States
    Format: text
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    NASA TECHNICAL REPORTS
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