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Analytical determination of local surface heat-transfer coefficients for cooled turbine blades from measured metal temperatures

Description: From Summary: "Procedures for applying these analytical methods to experimentally measured blade-metal temperatures are presented. Data are presented for the leading and trailing edge of a symmetrical water-cooled blade to illustrate the validity of the methods for those portions of the blade. In addition to the application to turbine blades, the methods can be applied to any heat-transfer apparatus having a profile that can be approximated by the shape discussed."
Date: April 10, 1950
Creator: Brown, W. B. & Esgar, J. B.
Partner: UNT Libraries Government Documents Department

Application of supersonic vortex-flow theory to the design of supersonic impulse compressor- or turbine-blade sections

Description: From Introduction: "The purpose of this paper is to present an analytical method for the design of two-dimensional related selection of a blade for particular rotor conditions may be made quickly and easily and its performance deduced from tests of representative sections in cascade."
Date: April 24, 1952
Creator: Wlodarski, John; Sterrett, James R & Boxer, Emanuel
Partner: UNT Libraries Government Documents Department

Analytical investigation of distribution of centrifugal stresses and their relation to limiting operating temperatures in gas-turbine blades

Description: From Introduction: "Analyses that provide a basis for comparing the centrifugal-stress distributions inherent in jet-engine turbine blades of several designs currently in use were therefore made and are presented."
Date: April 12, 1948
Creator: Kemp, Richard H & Morgan, William C
Partner: UNT Libraries Government Documents Department

Analytical investigation of effect of water-cooled turbine blades on performance of turbine-propeller power plants

Description: From Introduction: "Finally the work of the report is applied exclusively to consideration of the turbine-propeller power plant because previous performance analyses of the various gas-turbine propulsion systems combine with recent improvements in propeller design indicate that it is this combination which, will give the best over-all performance in the speed ranges considered."
Date: August 16, 1948
Creator: Bowman, William D
Partner: UNT Libraries Government Documents Department

An analytical method for evaluating factors affecting application of transpiration cooling to gas turbine blades

Description: From Introduction: "A survey of some of the advantages and problems associated with transpiration cooling of gas-turbine engines is given in reference 1, and its is shown therein that high pressure gradients around the periphery of gas-turbine blades require that the blade wall permeability be varied around the blade periphery in order for uniform cooling to be obtained over the entire blade surface. This fact is verified in experimental investigations of transpiration-cooled turbine blades mounted in a static cascade (references 2 and 3) where it is shown that although transpiration cooling results in extremely effective cooling in the midchord region of the blade, there are very large variations in the chordwise temperature distribution because of improper permeability variation."
Date: September 8, 1952
Creator: Esgar, Jack B
Partner: UNT Libraries Government Documents Department

Active load control techniques for wind turbines.

Description: This report provides an overview on the current state of wind turbine control and introduces a number of active techniques that could be potentially used for control of wind turbine blades. The focus is on research regarding active flow control (AFC) as it applies to wind turbine performance and loads. The techniques and concepts described here are often described as 'smart structures' or 'smart rotor control'. This field is rapidly growing and there are numerous concepts currently being investigated around the world; some concepts already are focused on the wind energy industry and others are intended for use in other fields, but have the potential for wind turbine control. An AFC system can be broken into three categories: controls and sensors, actuators and devices, and the flow phenomena. This report focuses on the research involved with the actuators and devices and the generated flow phenomena caused by each device.
Date: July 1, 2008
Creator: van Dam, C.P. (University of California, Davis, CA); Berg, Dale E. & Johnson, Scott J. (University of California, Davis, CA)
Partner: UNT Libraries Government Documents Department

Final Technical Report

Description: This variable length wind turbine blade project met the project objectives by successfully completing the task schedule. A set of variable length blades (8 to 12 meters in length) is now flying, in a configuration that is representative of a commercial blade designed to replace a standard 9 meter blade. Static testing and operations show that the blades are durable and stiff enough to prevent tower strikes. Power curve testing shows significant gains in low wind speed power production. An improved controller and drive mechanism have now been working for six months. Moving forward, we continue to monitor power curve, controller performance, and durability data. The project has made good progress towards understanding the costs and challenges associated with commercial production of variable length blades. Items that will require further study are: tip airfoil; blade pitching, tip and root interface design; jigs for more efficient construction, and optimization of subsystems
Date: June 30, 2005
Creator: Dawson, Mark H.
Partner: UNT Libraries Government Documents Department

Non-Destructive Evaluation of Wind Turbine Blades Using an Infrared Camera

Description: The use of a digital infrared as a non-destructive evaluation thermography camera (NDE) tool was ex- plored in two separate wind turbine blade fatigue tests. The fwst test was a fatigue test of part of a 13.1 meter wood-epoxy-composite blade. The second test was on a 4.25 meter pultruded fiber glass blade section driven at several mechanical resonant frequencies. The digital infrared camera can produce images of either the static temperature distribution on the surface of the specimen, or the dynamic temperature distribution that is in phase with a specific frequency on a vibrating specimen. The dynamic temperature distribution (due to thermoplastic effects) gives a measure of the sum of the principal stresses at each point on the surface. In the wood- epoxy-composite blade fatigue test, the point of ultimate failure was detected long before failure occurred. The mode shapes obtained with the digital infrared camera, from the resonant blade tests, were in very good agree- ment with the finite-element calculations. In addition, the static temperature images of the resonating blade showed two areas that contained cracks. Close-up dy- namic inf%red images of these areas showed the crack structure that agreed with subsequent dye-penetrant analysis.
Date: December 17, 1998
Creator: Beattie, A.G. & Rumsey, M.
Partner: UNT Libraries Government Documents Department

The Effect of Peel Stress on the Strength of Adhesively Bonded Joints

Description: Composite wind turbine blades are often attached to a metallic structure with an adhesive bond. The objective of this investigation is to determine which parameters affect the durability of these adhesively bonded joints. The composite-to-steel joint considered in this study typically fails when the adhesive debonds from the steel adherend. Previously, this joint was monotonically loaded in either compression or tension. Compressive and tensile axial loads of the same magnitude produce adhesive stresses with very similar magnitudes but opposite signs. (For the joint considered, tensile loads produce compressive peeh stresses in the adhesive at the location where debonding initiates.) The tensile specimens failed at much higher loads, establishing that the sign of the adhesive peel stresses strongly influences the single-cycle strength of these joints. Building on this earlier work, this study demonstrates that the adhesive peel stresses are also critical for fatigue loading. The results of low-cycle (axial) and high- cycle (bending) fatigue tests are presented. To complement the test results, finite element analyses demonstrate the localized nature of the peel stresses that develop in the adhesive. In addition, these analyses are used to investigate some of the causes of these peel stresses.
Date: October 14, 1998
Creator: Guess, T.R. & Metzinger, K.E.
Partner: UNT Libraries Government Documents Department

Design studies for twist-coupled wind turbine blades.

Description: This study presents results obtained for four hybrid designs of the Northern Power Systems (NPS) 9.2-meter prototype version of the ERS-100 wind turbine rotor blade. The ERS-100 wind turbine rotor blade was designed and developed by TPI composites. The baseline design uses e-glass unidirectional fibers in combination with {+-}45-degree and random mat layers for the skin and spar cap. This project involves developing structural finite element models of the baseline design and carbon hybrid designs with and without twist-bend coupling. All designs were evaluated for a unit load condition and two extreme wind conditions. The unit load condition was used to evaluate the static deflection, twist and twist-coupling parameter. Maximum deflections and strains were determined for the extreme wind conditions. Linear and nonlinear buckling loads were determined for a tip load condition. The results indicate that carbon fibers can be used to produce twist-coupled designs with comparable deflections, strains and buckling loads to the e-glass baseline.
Date: June 1, 2004
Creator: Valencia, Ulyses (Wichita State University, Wichita, KS) & Locke, James (Wichita State University, Wichita, KS)
Partner: UNT Libraries Government Documents Department

Dynamic stall occurrence on a horizontal axis wind turbine blade

Description: Surface pressure data from the National Renewable Energy Laboratory`s ``Combined Experiment`` were analyzed to provide a statistical representation of dynamic stall occurrence on a downwind horizontal axis wind turbine (HAWT). Over twenty thousand blade rotational cycles were each characterized at four span locations by the maximum leading edge suction pressure and by the azimuth, velocity, and yaw at which it occurred. Peak suction values at least twice that seen in static wind tunnel tests were taken to be indicative of dynamic stall. The occurrence of dynamic stall at all but the inboard station (30% span) shows good quantitative agreement with the theoretical limits on inflow velocity and yaw that should yield dynamic stall. Two hypotheses were developed to explain the discrepancy at 30% span. Estimates are also given for the frequency of dynamic stall occurrence on upwind turbines. Operational regimes were identified which minimize the occurrence of dynamic stall events.
Date: July 1, 1995
Creator: Shipley, D.E.; Miller, M.S. & Robinson, M.C.
Partner: UNT Libraries Government Documents Department

Wind-tunnel test of the S814 thick root airfoil

Description: The objective of this wind-tunnel test was to verify the predictions of the Eppler Airfoil Design and Analysis Code for a very thick airfoil having a high maximum lift coefficient (c{sub 1,max} designed to be largely insensitive to leading edge roughness effects. The 24-percent-thick S814 airfoil was designed with these characteristics to accommodate aerodynamic and structural considerations for the root region of a wind-turbine blade. In addition, the airfoil`s maximum lift-to-drag ratio was designed to occur it a high lift coefficient. To accomplish the objective, a two-dimensional wind-tunnel test of the S814 thick root airfog was conducted in January 1994 in the low-turbulence wind tunnel of the Delft University of Technology Low Speed Laboratory. Data were obtained for transition-free and transition-fixed conditions at Reynolds numbers of 0.7, 1.0, 1.5, 2.0, and 3.0 {times} 10{sup 6}. For the design Reynolds numbers of 1.5 {times} l0{sup 6}, the transition-free c{sub 1,max} is 1.3 which satisfies the design specification. However, this value is significantly lower than the predicted c{sub 1,max} of almost l.6. With transition-fixed at the is 1.2. The difference in c{sub 1,max} between the transition-free and transition-fixed conditions demonstrates the airfoil`s minimal sensitivity to roughness effects. The S814 root airfoil was designed to complement existing NREL low c{sub 1,max} tip-region airfoils for rotor blades 10 to 15 meters in length.
Date: January 1, 1995
Creator: Somers, D.M. & Tangler, J.L.
Partner: UNT Libraries Government Documents Department

Effects of grit roughness and pitch oscillations on the NACA 4415 airfoil

Description: A NACA 4415 airfoil model was tested in The Ohio State University Aeronautical and Astronautical Research Laboratory 3 x 5 subsonic wind tunnel under steady state and unsteady conditions. The test defined baseline conditions for steady state angles of attack from {minus}10{degree} to +40{degree} and examined unsteady behavior by oscillating the model about its pitch axis for three mean angles, three frequencies, and two amplitudes. For all cases, Reynolds numbers of 0.75, 1, 1.25, and 1.5 million were used. In addition, these were repeated after the application of leading edge grit roughness (LEGR) to determine contamination effects on the airfoil performance. Steady state results of the NACA 4415 testing at Reynolds number of 1.25 million showed a baseline maximum lift coefficient of 1.30 at 12.3{degree} angle of attack. The application of LEGR reduced the maximum lift coefficient by 20% and increased the 0.0090 minimum drag coefficient value by 62%. The zero lift pitching moment of {minus}0.0967 showed a 13% reduction in magnitude to {minus}0.0842 with LEGR applied. Data were also obtained for two pitch oscillation amplitudes: {+-}5.5{degree} and {+-}10{degree}. The larger amplitude consistently gave a higher maximum lift coefficient than the smaller amplitude, and both unsteady maximum lift coefficients were greater than the steady state values. Stall is delayed on the airfoil while the angle of attack is increasing, thereby causing an increase in maximum lift coefficient. A hysteresis behavior was exhibited for all the unsteady test cases. The hysteresis loops were larger for the higher reduced frequencies and for the larger amplitude oscillations. As in the steady case, the effect of LEGR in the unsteady case was to reduce the lift coefficient at high angles of attack. In addition, with LEGR, the hysteresis behavior persisted into lower angles of attack than for the clean case.
Date: July 1, 1996
Creator: Hoffmann, M.J.; Reuss Ramsay, R. & Gregorek, G.M.
Partner: UNT Libraries Government Documents Department

Effects of grit roughness and pitch oscillations on the S815 airfoil

Description: Horizontal axis wind turbine rotors experience unsteady aerodynamics due to wind shear when the rotor is yawed, when rotor blades pass through the support tower wake, and when the wind is gusting. An understanding of this unsteady behavior is necessary to assist in the calculation of rotor performance and loads. The rotors also experience performance degradation due to surface roughness. These surface irregularities are cause by the accumulation of insect debris, ice, and the aging process. Wind tunnel studies that examine both the steady and unsteady behavior of airfoils can help define pertinent flow phenomena, and the resultant data can be used to validate analytical computer codes. A S815 airfoil model was tested in The Ohio State University Aeronautical and Astronautical Research Laboratory (OSU/AARL) 3 x 5 subsonic wind tunnel (3 x 5) under steady flow and stationary model conditions, as well as with the model undergoing pitch oscillations. To study the possible extent of performance loss due to surface roughness, a standard grit pattern (LEGR) was used to simulate leading edge contamination. After baseline cases were completed, the LEGR was applied for both steady state and model pitch oscillation cases. The Reynolds numbers used for steady state conditions were 0.75, 1, 1.25, and 1.4 million, while the angle of attack ranged from {minus}20{degree} to +40{degree}. With the model undergoing pitch oscillations, data were acquired at Reynolds numbers of 0.75, 1, 1.25, and 1.4 million, at frequencies of 0.6, 1.2, and 1.8 Hz. Two sine wave forcing functions were used; {+-}5.5{degree} and {+-}10{degree}, at mean angles of attack of 8{degree}, 14{degree}, and 20{degree}. For purposes herein, any reference to unsteady conditions means that the model was in pitch oscillation about the quarter chord.
Date: July 1, 1996
Creator: Reuss Ramsay, R.; Hoffman, M.J. & Gregorek, G.M.
Partner: UNT Libraries Government Documents Department

Effects of surface roughness and vortex generators on the NACA 4415 airfoil

Description: Wind turbines in the field can be subjected to many and varying wind conditions, including high winds with rotor locked or with yaw excursions. In some cases the rotor blades may be subjected to unusually large angles of attack that possibly result in unexpected loads and deflections. To better understand loadings at unusual angles of attack, a wind tunnel test was performed. An 18-inch constant chord model of the NACA 4415 airfoil section was tested under two dimensional steady state conditions in the Ohio State University Aeronautical and Astronautical Research Laboratory (OSU/AARL) 7 x 10 Subsonic Wind Tunnel (7 x 10). The objective of these tests was to document section lift and moment characteristics under various model and air flow conditions. These included a normal angle of attack range of {minus}20{degree} to +40{degree}, an extended angle of attack range of {minus}60{degree} to +230{degree}, applications of leading edge grit roughness (LEGR), and use of vortex generators (VGs), all at chord Reynolds numbers as high as possible for the particular model configuration. To realistically satisfy these conditions the 7 x 10 offered a tunnel-height-to-model-chord ratio of 6.7, suggesting low interference effects even at the relatively high lift and drag conditions expected during the test. Significantly, it also provided chord Reynolds numbers up to 2.0 million. 167 figs., 13 tabs.
Date: December 1, 1995
Creator: Reuss, R.L.; Hoffman, M.J. & Gregorek, G.M.
Partner: UNT Libraries Government Documents Department

Elasticity tailoring of a composite D-Spar: Progress report for calendar year 1998

Description: There are many potential benefits to be gained from the aeroelastic behavior of a wind-turbine blade with bend-twist coupling. However, the ability to manufacture blades with sufficient coupling to provide the desired benefits has yet to be established. This report investigates the feasible (or practical) range of the coupling coefficient that can be obtained on a uniform cross-section composite D-spar, which could be the backbone of a wind-turbine-blade. The most critical parameters are identified and studied across a range of possible values. Various features, such as the geometry, skin thickness, ply distribution, ply materials, and ply orientations, are evaluated for their effect on twist-bend coupling of a D-spar. It is found that sufficient coupling can be built into the D-spar shape, but that carbon-fiber composite plies angled between 15 and 30 degrees to the longitudinal axis may be required.
Date: August 1, 1998
Creator: Ong, Cheng-Huat & Tsai, Stephen W.
Partner: UNT Libraries Government Documents Department

Estimation of uncertain material parameters using modal test data

Description: Analytical models of wind turbine blades have many uncertainties, particularly with composite construction where material properties and cross-sectional dimension may not be known or precisely controllable. In this paper the authors demonstrate how modal testing can be used to estimate important material parameters and to update and improve a finite-element (FE) model of a prototype wind turbine blade. An example of prototype blade is used here to demonstrate how model parameters can be identified. The starting point is an FE model of the blade, using best estimates for the material constants. Frequencies of the lowest fourteen modes are used as the basis for comparisons between model predictions and test data. Natural frequencies and mode shapes calculated with the FE model are used in an optimal test design code to select instrumentation (accelerometer) and excitation locations that capture all the desired mode shapes. The FE model is also used to calculate sensitivities of the modal frequencies to each of the uncertain material parameters. These parameters are estimated, or updated, using a weighted least-squares technique to minimize the difference between test frequencies and predicted results. Updated material properties are determined for axial, transverse, and shear moduli in two separate regions of the blade cross section: in the central box, and in the leading and trailing panels. Static FE analyses are then conducted with the updated material parameters to determine changes in effective beam stiffness and buckling loads.
Date: November 1, 1997
Creator: Veers, P.S.; Laird, D.L.; Carne, T.G. & Sagartz, M.J.
Partner: UNT Libraries Government Documents Department

Mechanical properties of Hysol EA-9394 structural adhesive

Description: Dextor`s Hysol EA-9394 is a room temperature curable paste adhesive representative of the adhesives used in wind turbine blade joints. A mechanical testing program has been performed to characterize this adhesive. Tension, compression stress relaxation, flexural, butt tensile, and fracture toughness test results are reported.
Date: February 1, 1995
Creator: Guess, T.R.; Reedy, E.D. & Stavig, M.E.
Partner: UNT Libraries Government Documents Department

A simple method of estimating wind turbine blade fatigue at potential wind turbine sites

Description: This paper presents a technique of estimating blade fatigue damage at potential wind turbine sites. The cornerstone of this technique is a simple model for the blade`s root flap bending moment. The model requires as input a simple set of wind measurements which may be obtained as part of a routine site characterization study. By using the model to simulate a time series of the root flap bending moment, fatigue damage rates may be estimated. The technique is evaluated by comparing these estimates with damage estimates derived from actual bending moment data; the agreement between the two is quite good. The simple connection between wind measurements and fatigue provided by the model now allows one to readily discriminate between damaging and more benign wind environments.
Date: June 1, 1995
Creator: Barnard, J.C. & Wendell, L.L.
Partner: UNT Libraries Government Documents Department