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At least 19 records

Wind plant wake losses: Disconnect between turbine actuation and control of plant wakes with engineering wake models

Wake losses from neighboring plants may become a major factor in wind plant design and control as additional plants are constructed in areas with high wind resource availability. Because plant wakes span a large range of physical scales, from turbine rotor diameter to tens of kilometers, it is unclear whether conventional wake models or turbine control strategies are effective at the plant scale. Wake steering and axial induction control are evaluated in the current work as means of reducing the impact of neighboring wind plants on power and levelized cost of electricity. FLOw Redirection and Induction in Steady State (FLORIS) simulations were performed with the Gauss–Curl Hybrid and TurbOPark wake models as well as two operation and maintenance models to investigate control setpoint sensitivity to wake representation and economic factors. Both wake models estimate losses across a range of atmospheric conditions, although the wake loss magnitude is dependent on the wake model. Annual energy production and levelized cost of electricity are driven by wind direction frequency, with frequently aligned plants experiencing the greatest losses. However, both wake steering and axial induction are unable to mitigate the impact of upstream plants. Wake steering is constrained by plant geometry, since wake displacement is much less than the plant wake width, while axial induction requires curtailing the majority of turbines in upstream plants. Individual turbine strategies are limited by their effective scale and model representation. New wake models that include plant-scale physics are needed to facilitate the design of effective plant wake control strategies.

Scott, Ryan (ORCID:0000000328107574)

Comparison of steady-state analytical wake models implemented in wind farm analysis software

A common set of mathematical wind turbine wake models are implemented in a few, well-adopted computational tools for wind farm wake modelling. Although the referenced mathematical formulations are common, implementation details may lead to differences in results. This study presents a systematic comparison of the implementation of mathematical wake models in open source, Python-based wind turbine wake modelling software, and a set of the models are directly compared. Despite aligning only the mathematical model parameters and retaining the default computational model parameters, good agreement is found across most of the model implementations, and additional agreement is expected upon further parameters alignment.

17 WIND ENERGY

Airloads and wake models for a comprehensive helicopter analysis

Fundamental considerations regarding the theory of modeling of rotary wing airloads, wakes, and aeroelasticity are presented. The topics covered are: airloads and wakes, including lifting-line theory, wake models and nonuniform inflow, free wake geometry, and blade-vortex interaction; aerodynamic and wake models for aeroelasticity, including two-dimensional unsteady aerodynamics and dynamic inflow; and airloads and structural dynamics, including comprehensive airload prediction programs. Results of calculations and correlations are presented.

Johnson, Wayne

Benchmarking of three DWM-based wake models at below-rated wind speeds

Wind turbine wake models are essential tools for predicting power losses and structural loads in wind farms. Among these, the dynamic wake meandering (DWM) model, included as a recommended approach in the International Electrotechnical Commission design standard, is a widely used engineering-fidelity method that balances accuracy and computational cost. This study compares the performance of three DWM-based wake model implementations (from the Technical University of Denmark, the National Renewable Energy Laboratory, and the Institute for Energy Technology) under below-rated wind speed conditions. Model predictions of wake flow, power output, and structural loads for a four-turbine row are evaluated across different ambient turbulence levels and wind-direction misalignments and compared against high-fidelity large-eddy simulation results. All three models captured the overall wake evolution and mean turbine performance with reasonable accuracy; their predicted time-averaged thrust and power were typically within 5 %–10 % of the large-eddy simulation benchmark. However, notable differences emerged in wake structure and unsteady load predictions, with discrepancies increasing for turbines further downstream. These differences highlight the importance of modelling choices such as wake summation and turbulence treatment, which strongly influence power-deficit and fatigue-load predictions. Comparison with large-eddy simulations reveals each approach's strengths and weaknesses, indicating where improvements are needed. Overall, the findings point to specific refinements for DWM models to improve their fidelity, ultimately enabling more robust wake predictions for wind farm design and operation.

17 WIND ENERGY

Introduction to and comparison of deep learning and optimization approaches to analytical wake modeling of a tilted wind turbine

This paper introduces innovative optimization and deep learning techniques to enhance the prediction of complex wake dynamics in the downstream wind velocity of tilted wind turbines. Traditional methods for calibrating the Bastankhah wake model often lead to increased errors in wind velocity distribution due to overfitting of the local wake characteristics. To address this issue, we propose an additional global optimization step to reduce errors in wind velocity predictions with respect to various wake parameters. Despite this improvement, the Bastankhah model's axisymmetric Gaussian wake shape limits its accuracy for complex wake structures. Therefore, we also propose a deep learning approach, which demonstrates promising results by accurately modeling complex wake shapes across a broader range of tilt angles with minimal computational cost. The deep learning approach achieves near-identical predictions to high-fidelity large-eddy simulations, representing a promising advancement in wake modeling.

17 WIND ENERGY

An unsteady wake model for a hingeless rotor

A simple nonsteady wake model derived from the unsteady moment of the momentum equation for zero advance ratio is correlated with cyclic pitch frequency response tests conducted with a small hingeless rotor model. Two and three or more bladed rotor analyses are presented.

Crews, S. T.

Gaussian FLOWERS: Wind-rose-based analytical integration of Gaussian wake model for extremely fast AEP estimation

A major cost in the study of wind farm layout optimization is the repeated evaluation of the annual energy production (AEP). The current approach to estimating AEP requires a large set of flow simulations to be performed that cover each discrete wind speed and direction combination contained within the wind rose, followed by a probability-weighted sum of the power production resulting from each simulation. Even with inexpensive engineering wake models, this numerical integration scheme can lead to high computational costs. In this paper, we derive an analytical formulation for estimating farm AEP across every wind direction, based on a Gaussian wake velocity model, which reduces the number of wind farm simulations to a single function evaluation. As a result, we find that the Gaussian-FLOWERS approach reduces the time for AEP calculations by more than two orders of magnitude with a small trade-off in accuracy when compared to a conventional approach. This massive reduction in computation cost is useful to reduce overall costs in wind farm layout optimization studies.

17 WIND ENERGY

Implementation and validation of a wake model for vortex-surface interactions in low speed forward flight

The wake model was implemented using a VAX 750 and a Microvax II workstation. Online graphics capability using a DISSPLA graphics package. The rotor model used by Beddoes was significantly extended to include azimuthal variations due to forward flight and a simplified scheme for locating critical points where vortex elements are placed. A test case was obtained for validation of the predictions of induced velocity. Comparison of the results indicates that the code requires some more features before satisfactory predictions can be made over the whole rotor disk. Specifically, shed vorticity due to the azimuthal variation of blade loading must be incorporated into the model. Interactions between vortices shed from the four blades of the model rotor must be included. The Scully code for calculating the velocity field is being modified in parallel with these efforts to enable comparison with experimental data. To date, some comparisons with flow visualization data obtained at Georgia Tech were performed and show good agreement for the isolated rotor case. Comparison of time-resolved velocity data obtained at Georgia Tech also shows good agreement. Modifications are being implemented to enable generation of time-averaged results for comparison with NASA data.

Komerath, Narayanan M.

Evaluation of Fast-Time Wake Vortex Models using Wake Encounter Flight Test Data

This paper describes a methodology for the integration and evaluation of fast-time wake models with flight data. The National Aeronautics and Space Administration conducted detailed flight tests in 1995 and 1997 under the Aircraft Vortex Spacing System Program to characterize wake vortex decay and wake encounter dynamics. In this study, data collected during Flight 705 were used to evaluate NASA's fast-time wake transport and decay models. Deterministic and Monte-Carlo simulations were conducted to define wake hazard bounds behind the wake generator. The methodology described in this paper can be used for further validation of fast-time wake models using en-route flight data, and for determining wake turbulence constraints in the design of air traffic management concepts.

Ahmad, Nashat N.

Computation of rotor aerodynamic loads with a constant vorticity contour free wake model

An analytical method is presented which facilitates the study of isolated rotors with an improved approach to wake simulation. Vortex filaments are simulated along contours of constant sheet strength for the sheet of vorticity resulting from each rotor blade. Curved vortex elements comprise the filaments which can be distorted by the local velocity field. Called the Constant Vorticity Contour wake model, the approach permits the simulation of the blades' wakes corresponding to the full span of the rotor blade. The discretization of the wake of the rotor blade produces spacing and structure that are consistent with the spatial and temporal variations in the loading. A vortex-lattice aerodynamic model of the blade is also included which introduces a finite-element structural model of the blade and consideration of the force and moment trim analysis. Results of the present version of the simulation, called RotorCRAFT, are found to correlate well with H-34 flight-test data.

Quackenbush, Todd R.

Implementation and validation of a wake model for low-speed forward flight

The computer implementation and calculations of the induced velocities produced by a wake model consisting of a trailing vortex system defined from a prescribed time averaged downwash distribution are detailed. Induced velocities are computed by approximating each spiral turn by a pair of large straight vortex segments positioned at critical points relative to where the induced velocity is required. A remainder term for the rest of the spiral is added. This approach results in decreased computation time compared to classical models where each spiral turn is broken down in small straight vortex segments. The model includes features such a harmonic variation of circulation, downwash outside of the blade and/or outside the tip path plane, blade bound vorticity induced velocity with harmonic variation of circulation and time averaging. The influence of various options and parameters on the results are investigated and results are compared to experimental field measurements with which, a resonable agreement is obtained. The capabilities of the model as well as its extension possibilities are studied. The performance of the model in predicting the recently-acquired NASA Langley Inflow data base for a four-bladed rotor is compared to that of the Scully Free Wake code, a well-established program which requires much greater computational resources. It is found that the two codes predict the experimental data with essentially the same accuracy, and show the same trends.

Komerath, Narayanan M.

Numerical solution of the full-potential equation for rotors and oblique wings using a new wake model

A three-dimensional, full-potential, quasi-steady code TFAR1 is proposed for calculating the transonic flow past a lifting helicopter rotor blade and oblique wing. The TFAR1 uses a two-dimensional nonlinear wake-model that allows a jump in velocity potential to propagate with the local fluid flow in the wake. Rotor calculations were made for a single blade at an advance ratio of 0.3, a rotational tip Mach number of 0.7, and at 0-degree incidence. A 1/7-scale model of the Cobra Operational Load Survey (OLS) rotor blade is calculated, and the pressure distributions are compared to the measurements for azimuth angles 0, 30, 60, 90, 120, and 150 degrees at the 95 percent spanwise station of the OLS blade. Furthermore, an oblique wing with Korn airfoil was calculated at the high transonic free-stream Mach number of 0.9791, zero incidence, and yaw angle of 40 degrees. The TFAR1, coupled with a helicopter performance code CAMRAD (Johnson, 1981), provides a full-potential code for calculating the entire flow field for a multiple-bladed rotor in transonic lifting forward flight.

Chang, I.-C.

Computation of high resolution unsteady airloads using a constant vorticity contour free wake model

Recent work in the study of helicopter aerodynamic loading for acoustics applications has involved research on the development of an exceptionally efficient simulation of the velocity field induced by the rotor's vortex wake. This paper summarizes the work to date on the development of this analysis, which builds on the refined constant vorticity contour (CVC) free wake model recently developed for application to the study of vibratory loading. The particular focus of this paper is on demonstrations of a reconstruction approach that efficiently computes both the flow fields and airloads induced by CVC wakes on lifting rotor blades. Results of recent calculations on both main rotor and tail rotors are presented. These calculations show that by employing flow field reconstruction it is possible to apply the CVC wake analysis with temporal and spatial resolution suitable for acoustics applications while reducing the computation time required by one to two orders of magnitude relative to the direct calculations used in traditional methods.

Quackenbush, T. R.

A comparison of the Gurevich et al. and the Liu-Jew wake models for the ion flux around a satellite

Observations of ion currents obtained by a retarding potential analyzer on board the Explorer 31 satellite were used to compare the Liu-Jew (Liu, 1969) and Gurevich et al. (1970) wake models with experiment. The quantitative degree of agreement is shown and discussed. The Gurevich et al. 'neutral approximation' was tested via the observations and was found to be fairly good for regions where the hydrogen ions constitute more than 20 per cent of the plasma and the Mach number is low. For the case of high Mach number, the Liu-Jew computations are in better agreement with the observations over the angle of attack range which could be studied, namely, 100-130 degrees.

Samir, U.

Influence of Wake Models on Calculated Tiltrotor Aerodynamics

The tiltrotor aircraft configuration has the potential to revolutionize air transportation by providing an economical combination of vertical take-off and landing capability with efficient, high-speed cruise flight. To achieve this potential it is necessary to have validated analytical tools that will support future tiltrotor aircraft development. These analytical tools must calculate tiltrotor aeromechanical behavior, including performance, structural loads, vibration, and aeroelastic stability, with an accuracy established by correlation with measured tiltrotor data. The recent test of the Tilt Rotor Aeroacoustic Model (TRAM) with a single,l/4-scale V-22 rotor in the German-Dutch Wind Tunnel (DNW) provides an extensive set of aeroacoustic, performance, and structural loads data. This paper will examine the influence of wake models on calculated tiltrotor aerodynamics, comparing calculations of performance and airloads with TRAM DNW measurements. The calculations will be performed using the comprehensive analysis CAMRAD II.

Johnson, Wayne

Intercomparison among plasma wake models for plasmaspheric and ionospheric conditions

The angular distributions of ions in the wake of a body moving through a space plasma computed from three different models are compared in order to investigate wake current depletion ratios under conditions simulating the topside ionosphere and plasmasphere. Results demonstrate the importance of taking into account the thermal flux at low Mach numbers and the angular acceptance of ion detectors in making theory-experiment comparisons. For all models considered, gradients in the angular variations of the fluxes are shown to be steeper near the wake-ambient interface than closer to the maximum rarefaction region.

Samir, U.

Evaluation of Fast-Time Wake Models Using Denver 2006 Field Experiment Data

The National Aeronautics and Space Administration conducted a series of wake vortex field experiments at Denver in 2003, 2005, and 2006. This paper describes the lidar wake vortex measurements and associated meteorological data collected during the 2006 deployment, and includes results of recent reprocessing of the lidar data using a new wake vortex algorithm and estimates of the atmospheric turbulence using a new algorithm to estimate eddy dissipation rate from the lidar data. The configuration and set-up of the 2006 field experiment allowed out-of-ground effect vortices to be tracked in lateral transport further than any previous campaign and thereby provides an opportunity to study long-lived wake vortices in moderate to low crosswinds. An evaluation of NASA's fast-time wake vortex transport and decay models using the dataset shows similar performance as previous studies using other field data.

Ahmad, Nash’at N.

Recent developments in rotor wake modeling for helicopter noise prediction

A preliminary test/theory correlation evaluation is conducted for wake measurement test results obtained by LDV for a B360 helicopter rotor, at conditions critical to the understanding of wake-rollup and blade-vortex interaction phenomena. The LDV data were complemented by acoustic, blade pressure, rotor performance, and blade/control load measurements.

Poling, D.