Bulletin of the American Physical Society
69th Annual Meeting of the APS Division of Fluid Dynamics
Volume 61, Number 20
Sunday–Tuesday, November 20–22, 2016; Portland, Oregon
Session A2: Wind Turbines: Airfoils |
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Chair: Jonathan Naughton, University of Wyoming Room: A106 |
Sunday, November 20, 2016 8:00AM - 8:13AM |
A2.00001: Design and analysis of small wind turbine blades with wakes similar to those of industrial scale turbines Arash Hassanzadeh, Jonathan Naughton A new design approach has been developed for wind turbine blades to be used in wind tunnel experiments that study wind turbine wakes. The approach allows wakes of small scale (2 m diameter) wind turbine rotors to simulate the important physics of wakes generated by a ``parent'' industrial scale wind turbine rotor despite the difference in size. The design approach forces the normalized normal and tangential force distributions of the small scale wind turbine blades to match those of the ``parent'' industrial scale wind turbine blades. The wake arises from the interaction between the flow and the blade, which imparts a momentum deficit and rotation to the flow due to the forces created by the blade on the flow. In addition, the wake dynamics and stability are affected by the load distribution across the blade. Thus, it is expected that matching normalized force distributions should result in similar wake structure. To independently assess the blades designed using this approach, the ``parent'' industrial scale and small scale wind turbine rotors are modeled using a free vortex wake method to study the generation and evolution of the two wakes. [Preview Abstract] |
Sunday, November 20, 2016 8:13AM - 8:26AM |
A2.00002: Three-dimensional effects on airfoil measurements at high Reynolds numbers Janik Kiefer, Mark Miller, Marcus Hultmark, Martin Hansen Blade Element Momentum codes (BEM) are widely used in the wind turbine industry to determine a turbine’s operational range and its limits. Empirical two-dimensional airfoil data serve as the primary and fundamental input to the BEM code. Consequently, the results of BEM simulations are strongly dependent on the accuracy of these data. In this presentation, an experimental study is described in which airfoils of different aspect ratios were tested at identical Reynolds numbers. A high-pressure wind tunnel facility is used to achieve large Reynolds numbers of $Re_c=3\times10^6$, even with small chord lengths. This methodology enables testing of very high aspect ratio airfoils to characterize 3-D effects on the lift and drag data. The tests were performed over a large range of angles of attack, which is especially important for wind turbines. The effect of varying aspect ratio on the aerodynamic characteristics of the airfoil is discussed with emphasis on the outcome of a BEM simulation. [Preview Abstract] |
Sunday, November 20, 2016 8:26AM - 8:39AM |
A2.00003: Wind turbine airfoil investigations in customized turbulent inflow Hendrik Heisselmann, Joachim Peinke, Michael Hoelling Experimental airfoil characterizations are usually performed in laminar or unsteady periodical flows. Neither of these matches the flow conditions of natural atmospheric flows as experienced by wind turbine blades. In the presented experimental study, an active grid is used to generate turbulent inflow with customized properties, like reduced frequencies or inflow angles. This is used not only to tune flow properties, but also to mimic time series of measured atmospheric wind speeds and inflow angles in the wind tunnel. Experiments were performed on a wind turbine dedicated DU 00-W-212 airfoil to obtain highly resolved force data and chord-wise pressure distributions at Re=500,000 and Re=900,000. Additional to a laminar baseline case, unsteady sinusoidal inflow fluctuations were applied as well as three different turbulent inflows with comparable turbulence intensity, but different inflow angle fluctuations to grasp the impact of inflow characteristics on the airfoil performance. In comparison with the laminar inflow case, the lift peak of the polar is shifted to higher angles of attack in the turbulent flows. While the laminar lift polars show a rather sudden transition to stall, a softer transition with an extended stall region is found for all turbulent cases. [Preview Abstract] |
Sunday, November 20, 2016 8:39AM - 8:52AM |
A2.00004: Comparison of Blade Element Momentum Theory to Experimental Data Using Experimental Lift, Drag, and Power Data Tara Nealon, Mark Miller, Janik Kiefer, Marcus Hultmark Blade Element Momentum (BEM) codes have often been used to simulate the power output and loads on wind turbine blades without performing CFD. When computing the lift and drag forces on the blades, the coefficients of lift and drag are normally calculated by interpolating values from standard airfoil data based on the angle of attack. However, there are several empirical corrections that are needed. Due to a lack of empirical data to compare against, the accuracy of these corrections and BEM in general is still not well known. For this presentation, results from an in-house written BEM code computed using experimental lift and drag coefficient data for the airfoils of the V27 wind turbine will be presented. The data is gathered in Princeton University's High Reynolds Number Testing Facility (HRTF) at full scale Reynolds numbers and over a large range of angles of attack. The BEM results are compared to experimental data of the same wind turbine, conducted at full scale Reynolds number and TSR, also in the HRTF. Conclusions will be drawn about the accuracy of the BEM code, and the corrections, regarding the usage of standard airfoil data versus the experimental data, as well as future applications to potentially improve large-eddy simulations of wind turbines in a similar manner. [Preview Abstract] |
Sunday, November 20, 2016 8:52AM - 9:05AM |
A2.00005: ABSTRACT WITHDRAWN |
Sunday, November 20, 2016 9:05AM - 9:18AM |
A2.00006: Synthetic-jet-based dynamic stall control on a scaled finite span wind turbine S817 blade Thomas Rice, Keith Taylor, Michael Amitay As wind turbines increase in size, so do many of the adverse effects associated with unsteady flow fields. Yawed flow, unsteady gusts, atmospheric boundary layers, and even free stream turbulence can cause unsteady loading, which are detrimental to the blades' structure. In order to decrease unsteady loading, synthetic jet actuators were installed on a scaled finite span cantilevered wind turbine blade having an S817 airfoil shape. The S817 airfoil shape is of the blade tips on the NREL CART3, which will be used next year on full scale field testing of active flow control. The model has been tested in the wind tunnel with and without active flow control, using load, surface pressure, and PIV measurements to characterize the airfoil's stall behavior during static and dynamic conditions, and the effect of flow control on its aerodynamic performance. Surface-mounted microphones were also used to detect dominant frequencies in the flow field. Dynamic stall was also simulated by pitching the airfoil through stall in a sinusoidal pitching motion. Synthetic jets, placed near the leading edge, were shown to increase lift both in the static and dynamic cases, in addition to attaching the flow and reducing hysteresis during dynamic pitching, showing a decrease in structural loading. [Preview Abstract] |
Sunday, November 20, 2016 9:18AM - 9:31AM |
A2.00007: A comparison between 2-and 3-bladed wind turbine rotors with focus on wake characteristics Franz Mühle, Muyiwa Samuel Adaramola, Lars Sætran Due to cost benefit and weight reduction, 2-bladed wind turbines have the potential to become more important for offshore wind applications. In order to optimize the arrangement of wind turbines in wind farms and for accurate forecasts of the power production, a detailed knowledge of the wake flow is needed. In the presented study, three different rotors with varying number of blades and similar performance behavior have been designed and manufactured using the 3-dimensional (3D) printing technology. The performance characteristics of these rotors as well as their wake features are measured experimentally in wind tunnel tests and compared. The velocity deficit is seen to vary only insignificantly for the wakes in distances of 3D (where D is the rotor diameter), 5D and 7D behind the turbine. However, higher turbulence intensity levels are recorded in the wake of the 2-bladed rotors. This could have potential for a faster wake recovery and thus a narrower turbine spacing. [Preview Abstract] |
Sunday, November 20, 2016 9:31AM - 9:44AM |
A2.00008: Evolution of the shear layer during unsteady separation over an experimental wind turbine blade Matthew Melius, Raul Cal, Karen Mulleners Unsteady flow separation in rotationally augmented flow fields plays a significant role in the aerodynamic performance of industrial wind turbines. Current computational models underestimate the aerodynamic loads due to the inaccurate prediction of the emergence and severity of unsteady flow separation in the presence of rotational augmentation. Through the use of time-resolved particle image velocimetry (PIV), the unsteady separation over an experimental wind turbine blade is examined. By applying Empirical Mode Decomposition (EMD), perturbation amplitudes and frequencies within the shear-layer are identified. The time dependent EMD results during the dynamic pitching cycle give insight into the spatio-temporal scales that influence the transition from attached to separated flow. The EMD modes are represented as two-dimensional fields and are analyzed together with the spatial distribution of vortices, the location of the separation point, and velocity contours focusing on the role of vortex shedding and shear layer perturbation in unsteady separation and reattachment. [Preview Abstract] |
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