Bulletin of the American Physical Society
77th Annual Meeting of the Division of Fluid Dynamics
Sunday–Tuesday, November 24–26, 2024; Salt Lake City, Utah
Session T26: Aerodynamics - Wind Energy |
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Chair: James Brasseur, University of Colorado, Boulder Room: 251 D |
Monday, November 25, 2024 4:45PM - 4:58PM |
T26.00001: The Three Characteristic Frequency Responses to the Nonsteady Forcing of Wind Turbines by Atmospheric Turbulence James Brasseur, Jarred Kenworthy, Edward Hart, Jonathan Keller, Yi Guo Strongly time-varying spatially-nonuniform motions within the atmospheric winds drive large time changes in the force and moment vectors acting at the rotor hub on the wind turbine main shaft. In turn, these drive strong time changes in force acting on the main bearing, potentially underlying premature failure. The strongest nonsteady responses arise from the continual passage of energetic streak-like turbulence eddies in the atmospheric surface layer (ASL). With high-fidelity LES and advanced actuator line representation of rotor blade aerodynamics within a convective daytime ASL, we analyze the detailed frequency responses of the out-of-plane bending moment vector acting on the rotor hub (MH) and the corresponding force vector acting on the main bearing of a rigid NREL 5 MW rotor (FB). We find that the strongest responses result from combined interactions of three frequency ranges, each with different forcing mechanisms and response characteristics. The three-blade-per-revolution (3P) response results from blade rotation through a nonuniform velocity distribution. This strong quasi-periodic response is modulated by the advection of concentrations of high and low speed horizontal velocity fluctuations (“streaks”) at advection time scales (10s of seconds) much higher than the 3P period (seconds), creating lower-frequency responses in magnitude and direction of MH and FB. In contrast, we observe large peak-to-peak responses at small sub-second time scales created by the passage of rotor blades through local strong gradients in the velocity field over the rotor plane. These, we find, occur in bursts that are modulated by the 3P frequencies. Thus all three characteristic frequency responses interact in the generation of the strongest, potentially most detrimental, forcings on the main bearing. |
Monday, November 25, 2024 4:58PM - 5:11PM |
T26.00002: The effects of wind shear on rotor aerodynamics Storm A Mata, Kirby S Heck, Michael F Howland Wind speed and direction variations can affect rotor power, thrust force, and structural loading. The effects of wind shear increase as turbines become larger and extend farther into the atmospheric boundary layer, where wind conditions can be more complex than those in the surface layer. Conventional turbine power models, like those prescribed by the IEC for wind resource assessment, assume incident wind conditions do not affect airfoil efficiency or induced rotor velocity, which determines the coefficient of power. These models are therefore limited in their ability to account for the aerodynamic effects of shear that modify turbine power production. We find that the common rotor-equivalent wind speed (REWS) model predicts power with similar accuracy to estimating power based on hub height wind speed alone. In this study, we investigate an actuator disk in large eddy simulations to resolve the aerodynamic interactions between the disk and inflow wind profiles. These simulations demonstrate that induction increases monotonically as the magnitude of directional shear over the rotor increases, which lowers the disk velocity and power production of the turbine. For wind conditions near uniform, 1D momentum theory overpredicts induction on the rotor by 2%, and underpredicts by as much as 3% as average directional shear over the rotor increases. These results point to coupling between the rotor and sheared inflow wind that causes average induction to deviate nonlinearly from what is predicted by 1D momentum theory. |
Monday, November 25, 2024 5:11PM - 5:24PM |
T26.00003: Horizontal Axis Wind Turbines under Yaw-Misalignment at High Reynolds Numbers – Experimental and Model Performance Predictions John W Kurelek, Alexander Pique, Kirby S Heck, Marcus Hultmark, Michael F Howland This study examines yaw and tip-speed ratio effects on horizontal axis wind turbine thrust, power, and wake development through comparisons of experimental measurements and model predictions. The experiments are conducted in the High Reynolds number Test Facility at Princeton University, where field-relevant Reynolds numbers (ReD = 4 × 106) and tip-speed ratios (3.5 ≤ λ ≤ 7.5) are achieved by scaling pressure in place of velocity. Yaw angles spanning -45° ≤ γ ≤ 45° are explored, and turbine performance is characterized through measurements of the generated thrust, power, and wake. As the yaw-misalignment is increased, the thrust and power decrease and the wake deflects laterally; effects which show a tip-speed ratio dependence. Leveraging recent analytical modelling improvements, these trends are compared to a Unified Momentum Model (UMM) for rotors at arbitrary inflow angles and thrust coefficients. The experimental and model-predicted power outputs show good agreement across all yaw angles when the turbine is operated at its design tip-speed ratio and when power is maximized through tip-speed ratio control. Agreement between the experimental and model results is less at off-design conditions, however the UMM predictions are improved over those from classical momentum theory and other empirical methods. These results help identify promising directions for future model development, towards the goal of developing a robust, yet simple model for use in real-time wind farm control. |
Monday, November 25, 2024 5:24PM - 5:37PM |
T26.00004: Experimental study of boundary layer turbulence transition and flow separation of wind turbine blades due to leading edge roughness. Hugh Irving, Kevin Nolan, Vikram Pakrashi This research aims to characterise the aerodynamics of wind turbine blades with rough leading edges in experiment. This work is motivated by the increasing phenomenon of wind turbine leading edge erosion. Deployed wind turbine blades have been observed to experience deterioration at their leading edge due to impact with rain, hail and particulates. Despite significant research interest, experimental imaging of the boundary layer suitable for validation of numerical models is not found in the literature. |
Monday, November 25, 2024 5:37PM - 5:50PM |
T26.00005: Effect of roughness on the wake lenght of a wind turbine located on a Gaussian hill Andrea Torrejón, Luis Silva-Llanca, Sonia Montecinos, Charles Meneveau Several factors influence the efficiency of power generation in wind farms, such as wind speed and direction, turbine size, distribution, and topography. In particular, the irregularity of the topography affects the wake characteristics of each turbine, and the wake length impacts the power generation of the downstream turbines. We evaluated different topographic configurations for a wind tunnel by combining a Gaussian function with a sinusoidal function to represent a hill with complex topography. This approach allows us to control the complexity characteristics of the terrain to correlate the topography with the length of the wakes. We used the commercial software ANSYS Fluent™️ to study the fluid mechanics of turbulent flow over a Gaussian hill with small-scale surface waviness using Reynolds Averaged Navier Stokes, utilizing the k-ω SST turbulence model with the Actuator Disk model to represent a wind turbine. We validated the numerical results with experimental data presented by Cao and Tamura (2006). For an area of interest downstream (7D), we found that a smaller sinusoidal amplitude and greater wavelength favor the recovery of the wakes. Larger sinusoidal amplitude thickens the Gaussian hill’s boundary layer upstream of the turbine, which we believe is responsible for a smaller airflow and a lower production of kinetic energy. The latter leads to larger wakes due to lower momentum entrainment. |
Monday, November 25, 2024 5:50PM - 6:03PM |
T26.00006: Wake Dynamics and Synergistic Clustering Effects of Savonius Wind Turbines Alexander Scheffler-Murry, Mark Aaron Miller, Azar Panah
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Monday, November 25, 2024 6:03PM - 6:16PM |
T26.00007: Three-dimensional vortical structures of a vertical-axis wind turbine and their effects on the aerodynamic performance and wake Sangwoo Ahnn, Haecheon Choi We conduct large eddy simulation of flow past a vertical-axis wind turbine (VAWT) to investigate the flow structures around the blades affecting aerodynamic performance and wake. At the Reynolds number of 80,000 based on the free-stream velocity and turbine diameter, we consider the tip-speed ratios of 1.0, 1.2, and 1.7. We compare the flow fields with those from a VAWT with infinite span blades and examine the three-dimensional flow structures at the blade tips. Dynamic stall and large leading-edge vortices (LEVs) develop on the inner blade surfaces during rotation, while strong blade tip vortices (BTVs) form at the blade tips. As the tip-speed ratio increases, the strength of LEV decreases and that of BTV increases. Near the blade tips, the formation of LEV is suppressed by BTVs. The power generation near the tips decreases, but the area affected by BTVs reduces with increasing tip-speed ratio. In the wake region, the tip-speed ratio of 1.7 has broader streamwise velocity deficit transversely but wake recovery is faster than those at lower tip-speed ratios. |
Monday, November 25, 2024 6:16PM - 6:29PM |
T26.00008: Identifying the Safe Area for Thrown Ice from a Wind Turbine seyedehmahdis madahi, EHSAN KARIMIBADRABADI Throwing ice from a large and modern wind turbine located in frigid regions can result in significant human and financial damages due to its high velocity and long range. Consequently, the trajectory, rotation, velocity, and kinetic energy of thrown ice from a horizontal axis wind turbine are investigated while the movement of a thrown ice is simulated in three dimensions, including both rotation and translation. A method for calculating Euler angles is presented inversely, followed by the derivation of the equations of translation and rotation using Newton's second law and Euler's laws of motion, which make it possible to calculate and plot the position of any desired point on the ice at any given moment which fills a gap in the references. The calculations are conducted using a ballistic model with an average drag coefficient. The obtained ordinary differential equations (ode) are solved numerically using the 4th-order Runge-Kutta method, the results are verified with existing references, while applying lift in the equations and solving the nonlinear differential equations, comparing the movement of the ice under conditions where lift is considered versus when it is neglected has been done for the first time. Furthermore, the concept of terminal velocity is described, and the value of this velocity and the time it takes to reach it for the specific flying ice are provided. Lastly, various parameters, such as a change in angular velocity, drag coefficient, local wind velocity, and the concept of apparent mass and its effect on the movement of the thrown ice as well as the presence of lift force on the distances of ice impact with the ground are examined, and unsafe areas around the wind turbine by considering changes in influencing parameters where the probability of ice-ground collision exists are identified. |
Monday, November 25, 2024 6:29PM - 6:42PM |
T26.00009: Experimental Investigation of Geometric and Virtual Camber on Cross-Flow Turbine Performance and Loading Ari S Athair, Caelan C Consing, Jennifer A. Franck, Owen Williams Cross-flow turbines show promise for renewable energy generation from wind and tidal sources. Their rotating reference frame introduces curved streamlines resulting in a virtual camber, where symmetrical profiles in a rotating flow produce lift similar to cambered blades in straight flows. Adding geometric camber is therefore likely to alter performance and loading, however such geometries have seen limited exploration, with little indication of which camber direction might be most favorable. This study compares positive and negative 2% cambered blades (NACA 2418) with symmetrical NACA 0018 foils for a turbine with a 0.49 chord-to-radius ratio. Experimental performance and PIV measurements across a range of tip-speeds are explored. Contrary to expectations, blades with concave sides facing away from rotation, which enhance virtual camber and lift in the power stroke, exhibited suboptimal performance. Conversely, oppositely cambered blades slightly improved on symmetrical blade performance by enhancing downstream flow reattachment, compensating for reduced upstream power extraction. Moreover, these blades reduced peak loading, which may prove critical in future designs, especially at high tip-speed ratios. The current work suggests that flow recovery in the downstream region is critical to overall performance and that reducing total camber (geometric plus virtual) leads to overall gains. |
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