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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 613 records · Page 34
All sourcesNASA NTRSDOE OSTI
DOE OSTI2015

The Influence of Sliding and Contact Severity on the Generation of White Etching Cracks

White etching cracks (WECs) have been identified as the dominant mechanism of premature failure for bearings within wind turbine gearboxes. Though WECs have been observed in the field for over a decade, the exact mechanisms which lead to this failure are still debated, and benchtop replication has proven difficult. In previously published work, WECs have been replicated only through the use of component level test rigs, where complete bearings are tested. In these tests, the factors that are thought to drive the formation of WECs, such as slide-to-roll ratio (SRR) and lubricant film thickness, cannot not be easily altered or controlled. In this paper, WECs have been replicated on a three rings on roller, benchtop test rig, which allowed for a direct investigation into the influence that SRR magnitude, sliding direction, and the lubricant film thickness have on surface failures and WEC generation. It was determined that WEC were formed in samples that experienced -30% SRR at various lubrication conditions, however, at lower levels of negative SRR and positive SRR up to 30% no white-etching cracks were observed.

17 WIND ENERGY↗
DOE OSTI2017

Real-time monitoring, prognosis, and resilient control for wind turbine systems

This special issue aims to provide a platform for academic and industrial communities to report recent results and emerging research in real-time monitoring, fault diagnosis, prognosis, and resilient control and design of wind turbine systems. After a strict peer-review process, 20 papers were selected, which represent the most recent progress of the real-time monitoring, diagnosis, prognosis, and resilient control methods/techniques in wind turbine systems.

17 WIND ENERGY↗
DOE OSTI2022

Characterization and repair of core gap manufacturing defects for wind turbine blades

Various wind turbine blade components, such as shear webs and skins, commonly use fiber-reinforced composite sandwich structures with a core material like balsa or foam. During manufacturing, core gap defects may result from the misalignment of adjacent foam or balsa core sheets in the blade mold. It is important to understand the influence that core gaps have on the structural integrity of wind turbine blades and how to mitigate their influence. This research characterized the effects of core gap defects at the manufacturing and mechanical levels for both epoxy and next-generation thermoplastic composites. Common repair methods were assessed and compared. Multiple defect sizes were compared using temperature data gathered with thermocouples embedded during manufacturing to core gap defect characteristics obtained using image-mapping techniques, optical microscopy, and mechanical characterization by long beam flexure. Results showed that peak exothermic temperatures during curing were closely related to core gap size. The long beam flexure tests determined that transverse core gaps under pure bending loads can have a substantial effect on the ultimate facesheet strength of both epoxy and thermoplastic composite sandwich structures (up to 25% strength reduction), although the size of the defect itself had less of an influence on the magnitude of the strength reduction. The supporting image-mapping techniques indicated that the distortion of the composite facesheets by the core gaps contributed to the premature failures. The repair methods used in this study did very little to improve the ultimate strength of the sandwich panels that previously had core gap defects. The repair of the thermoplastic panel resulted in a further loss in ultimate facesheet strength. This research demonstrated that there is a vital need for the development of a compatible thermoplastic polymer repair resin system and appropriate resin specific repair procedures for the next generation of recyclable thermoplastic wind blades.

17 WIND ENERGY↗
DOE OSTI2022

Demonstration of NREL Modeling Capability to Design the Next Generation of Floating Offshore Wind Turbines with Stiesdal and Magellan Wind (Cooperative Research and Development Final Report)

This Technology Commercialization Fund (TCF) CRADA involved demonstration of NREL modeling capability using OpenFAST (formerly known as FAST) to design the next generation of floating offshore wind turbines (FOTW) with Stiesdal’s TetraSpar design. The objective of the project was to enable the design and optimization of next generation FOWT that show promise to make FOWT cost-competitive with other energy technologies by upgrading, verifying, and validating improvements to OpenFAST. This objective was achieved by (1) upgrading OpenFAST to compute floating substructure flexibility and member-level loads, which is critical to enable the design of floating substructures—especially newer designs that are streamlined, flexible, and cost-effective; (2) verifying the new OpenFAST capabilities through model-to-model comparisons and validating the capabilities through comparisons to empirical data generated with wave-tank testing, using TetraSpar data provided by Stiesdal; and (3) making available the upgraded OpenFAST tool to the wind energy community to enable next-generation floating wind designs.

17 WIND ENERGY↗
DOE OSTI2021

On the scaling of wind turbine rotors

This paper formulates laws for scaling wind turbine rotors. Although the analysis is general, the article primarily focuses on the subscaling problem, i.e., on the design of a smaller-sized model that mimics a full-scale machine. The present study considers both the steady-state and transient response cases, including the effects of aerodynamic, elastic, inertial, and gravitational forces. The analysis reveals the changes to physical characteristics induced by a generic change of scale, indicates which characteristics can be matched faithfully by a subscaled model, and states the conditions that must be fulfilled for desired matchings to hold. Based on the scaling laws formulated here, the article continues by considering the problem of designing scaled rotors that match desired indicators of a full-scale reference. To better illustrate the challenges implicit in scaling and the necessary tradeoffs and approximations, two different approaches are contrasted. The first consists in a straightforward geometric zooming. An analysis of the consequences of zooming reveals that, although apparently simple, this method is often not applicable in practice, because of physical and manufacturing limitations. This motivates the formulation of scaling as a constrained optimal aerodynamic and structural matching problem of wide applicability. Practical illustrations are given considering the scaling of a large reference 10 MW wind turbine of about 180 m in diameter down to three different sizes of 54, 27, and 2.8 m. Results indicate that, with the proper choices, even models characterized by very significant scaling factors can accurately match several key performance indicators. Additionally, when an exact match is not possible, relevant trends can at least be captured.

17 WIND ENERGY↗
DOE OSTI2016

Characterization of the High-Speed-Stage Bearing Skidding of Wind Turbine Gearboxes Induced by Dynamic Electricity Grid Events: Preprint

Bearing behavior is an important factor for wind turbine drivetrain reliability. Extreme loads and dynamic excitations pose challenges to the bearing design and therefore its performance. Excessive skidding of the bearing rollers should be avoided because it can cause scuffing failures. Excitations coming from wind and the electricity grid can subject the drivetrain to fluctuating torque and nontorque loads. Wind-induced excitations have been investigated predominantly in literature. However, modern wind turbines are subjected more and more to grid-induced loads because of stricter electricity grid regulations. For example, during fault-ride-through events, turbines are required to stay connected for a longer period of time during the grid failure. This work investigates the influence of electrically induced excitations on the skidding behaviour of the tapered roller bearings on the high-speed stage of a wind turbine gearbox. This skidding behaviour during dynamic events is described as a potential bearing failure initiator by many researchers; however, only limited full-scale dynamic testing is documented. Therefore, a dedicated gridloss-type event is defined in the paper and conducted in a dynamometer test on a full-scale wind turbine nacelle. During the event, a complete electricity grid failure is simulated while the turbine is at rated speed and predefined torque levels. Particular focus is on the characterization of the high-speed shaft tapered roller bearing slip behavior. Strain-gauge bridges in grooves along the circumference of the outer ring are used to characterize the bearing load zone in detail. It is shown that during the torque reversals of the transient event, roller slip can be induced. This indicates the potential of the applied load case to go beyond the preload of the tapered roller bearing. Furthermore, the relation between the applied torque and skidding level is studied.

17 WIND ENERGY↗
DOE OSTI2018

Assessment of Wind Parameter Sensitivity on Ultimate and Fatigue Wind Turbine Loads: Preprint

Wind turbines are designed using a set of simulations to ascertain the structural loads that the turbine could encounter. While mean hub-height wind speed is considered to vary, other wind parameters such as turbulence spectra, sheer, veer, spatial coherence, and component correlation are fixed or conditional values that, in reality, could have different characteristics at different sites and have a significant effect on the resulting loads. This paper therefore seeks to assess the sensitivity of different wind parameters on the resulting ultimate and fatigue loads on the turbine during normal operational conditions. Eighteen different wind parameters are screened using an Elementary Effects approach with radial points. As expected, the results show a high sensitivity of the loads to the turbulence standard deviation in the primary wind direction, but the sensitivity to wind shear is often much greater. To a lesser extent, other wind parameters that drive loads include the coherence in the primary wind direction and veer.

17 WIND ENERGY↗
NASA NTRS1991

Results of the space shuttle vehicle ascent air data system probe calibration test using a 0.07-scale external tank forebody model (68T) in the AEDC 16-foot transonic wind tunnel (IA-310), volume 2

A recalibration of the Space Shuttle Vehicle Ascent Air Data System probe was conducted in the Arnold Engineering and Development Center (AEDC) transonic wind tunnel. The purpose was to improve on the accuracy of the previous calibration in order to reduce the existing uncertainties in the system. A probe tip attached to a 0.07-scale External Tank Forebody model was tested at angles of attack of -8 to +4 degrees and sideslip angles of -4 to +4 degrees. High precision instrumentation was used to acquire pressure data at discrete Mach numbers ranging from 0.6 to 1.55. Pressure coefficient uncertainties were estimated at less than 0.0020. Additional information is given in tabular form.

Collette, J. G. R.↗
NASA NTRS1980

Full-scale wind tunnel-investigation of the Advanced Technology Light Twin-Engine airplane (ATLIT)

An investigation was conducted to evaluate the aerodynamic performance, stability, and control characteristics of the Advanced Technology Light Twin Engine airplane (ATLIT). Data were measured over an angle of attack range from -4 deg to 20 deg for various angles of sideslip between -5 deg and 15 deg at Reynolds numbers of 0.0000023 and 0.0000035 for various settings of power and flap deflection. Measurements were also made by means of special thrust torque balances to determine the installed propeller characteristics. Part of the investigation was devoted to drag cleanup of the basic airplane and to the evaluation of the effect of winglets on drag and stability.

Hassell, J. L., Jr.↗
NASA NTRS1994

Measurements of Forward Flight Effects on the Advanced Ducted Propulsion Demonstrator Engine

The performance of the Pratt & Whitney Advanced Ducted Propulsion (ADP) UHB concept has been recently evaluated with studies of a 17 in. diameter fan simulator. Following the model scale tests, a 118 in. diameter demonstrator was tested at the NASA Ames 40- by 80-Foot Wind Tunnel. The 18 blade fan was driven by the low compressor shaft of a PW2037 core through a reduction gear system fabricated by Fiat with approximately 1:3.7 reduction ratio. ne variable pitch fan was hydraulically actuated with settings for take-off, cruise, feather, and reverse thrust. The low-pressure turbine was built by MTU to provide higher shaft power in comparison with the standard PW2037. The demonstrator was provided with 45 vanes located 2.6 fan chords downstream of the rotor, and 10 case struts approximately 1 fan chord downstream of the vanes. The inlet, mid-duct, and exhaust linings were acoustically treated. Acoustic surveys were taken in the for-ward thrust mode for fan speeds of 898, 1120, 1205, and 1302 R.P.M., and at tunnel speeds of 25, 50, 100, and 140 kts. The lowest speed was achieved with the wind tunnel fans at flat pitch, but with the engine pumping the test section Microphone signals were recorded for 30 seconds at 5 deg. increments. These measurements will be used to assess the effects of forward speed on UHB engines, to compare these effects with the corresponding characteristics of conventional bypass ratio engines, and to discuss the various aspects of testing large engines in the wind tunnel.

Horne, W. C.↗
NASA NTRS1950

Investigation of Effects of Inlet-air Velocity Distortion on Performance of Turbojet Engine

To determine effect of nonuniform inlet-air velocities, a full scale, axial-flow turbojet engine was investigated in Lewis altitude wind tunnel at altitudes from 20,000 to 50,000 feet, 0.21 flight Mach number and corrected engine speeds from 77.3 percent of rated speed to rated speed. Total-pressure variations as large as 103 pounds per square foot in radial direction and 90 pounds per square foot in circumferential direction at 30,000 feet were obtained. With the distortions investigated, net thrust varied between 0.95 and 1.03 of the thrust with uniform inlet-air distribution. Similarly the ratio of specific fuel consumption varied from 1.00 to 1.04. Within the arrange of this investigation the effects of nonuniform inlet velocity were not serious for the engine investigated.

AIR INLETS↗