Bulletin of the American Physical Society
67th Annual Meeting of the APS Division of Fluid Dynamics
Volume 59, Number 20
Sunday–Tuesday, November 23–25, 2014; San Francisco, California
Session D24: Industrial Applications II |
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Chair: Amos Winter, Massachusetts Institute of Technology Room: 2003 |
Sunday, November 23, 2014 2:15PM - 2:28PM |
D24.00001: Simulation of an Oscillating Hydrofoil near Boundaries Jennifer Franck, Ka Ling Wu An oscillating hydrofoil in freestream flow is computationally investigated for the application of a novel hydrokinetic energy device. The hydrofoil is prescribed a rigid body sinusoidal motion in pitch and heave, with the maximum efficiency occurring with a heave amplitude of 0.5 chord lengths, pitch amplitude of 75 degrees, a non-dimensional frequency of 0.15, and a phase difference of 90 degrees between pitch and heave. Simulations are performed using 2D direct numerical simulation with a moving mesh algorithm and compared to particle image velocimetry results of Strom et. al 2014 and previous computational results of Frank and Franck 2013. The high pitch angle during mid-downstroke and upstroke generates large coherent vortices that enhance the power generated from linear translation, yet remain on the wing during stroke reversal to also generate power from the angular motion. In order to assess the hydrofoil's performance in shallow tidal zones, a lower wall boundary is introduced into the simulation to investigate the ground effect on the unsteady vortex shedding and power generation. [Preview Abstract] |
Sunday, November 23, 2014 2:28PM - 2:41PM |
D24.00002: Parametric dependence of energy harvesting performance with an oscillating hydrofoil Benjamin Strom, Daegyoum Kim, Shreyas Mandre, Kenneth Breuer We report on experiments on tidal energy conversion from a open channel water flow using an oscillating hydrofoil. The hydrofoil is operated at high angles of attack such that the formation and capture of a leading edge vortex greatly enhances the energy conversion efficiency. A computer-controlled pitch and heave system allows for arbitrary position profiles to be imposed. Force and torque measurements are used to determine the energy harvesting efficiency as a function of Reynolds number, pitch and heave amplitudes, phase shift, the location of the pitching axis, position profile, and the cross sectional shape of the hydrofoil. PIV measurements are used to capture the vortex dynamics and these results are compared to the computational results of Frank and Franck (2013). Efficiency was found to be most sensitive to pitch amplitude, pitching axis and phase shift with relatively little dependence on Reynolds number, heave amplitude, and foil shape. [Preview Abstract] |
Sunday, November 23, 2014 2:41PM - 2:54PM |
D24.00003: The effect of aspect ratio on the performance of an energy harvesting hydrofoil Daegyoum Kim, Benjamin Strom, Yunxing Su, Shreyas Mandre, Kenneth Breuer We investigated the effect of aspect ratio on energy harvesting performance and flow structure of an oscillating hydrofoil. Power measurement and particle image velocimetry were performed in a water flume with a hydrofoil undergoing periodic heaving and pitching motions. Aspect ratio was varied from 2.5 to 4.5, and end plates were also mounted at the hydrofoil tips in order to suppress three-dimensional effects near the tips. For each aspect ratio, energy conversion efficiency was maximum at the same kinematics determined by reduced frequency and pitch amplitude. The efficiency is increased with the aspect ratio, and it is noticeably enhanced with the installation of the end plates. Leading-edge vortex formation and wake dynamics were compared at several spanwise sections among different aspect ratios. Their correlation with the efficiency was also examined. [Preview Abstract] |
Sunday, November 23, 2014 2:54PM - 3:07PM |
D24.00004: Real-time Coupled Ensemble Kalman Filter Forecasting {\&} Nonlinear Model Predictive Control Approach for Optimal Power Take-off of a Wave Energy Converter Daniele Cavaglieri, Thomas Bewley, Mirko Previsic In recent years, there has been a growing interest in renewable energy. Among all the available possibilities, wave energy conversion, due to the huge availability of energy that the ocean could provide, represents nowadays one of the most promising solutions. However, the efficiency of a wave energy converter for ocean wave energy harvesting is still far from making it competitive with more mature fields of renewable energy, such as solar and wind energy. One of the main problems is related to the difficulty to increase the power take-off through the implementation of an active controller without a precise knowledge of the oncoming wavefield. This work represents the first attempt at defining a realistic control framework for optimal power take-off of a wave energy converter where the ocean wavefield is predicted through a nonlinear Ensemble Kalman filter which assimilates data from a wave measurement device, such as a Doppler radar or a measurement buoy. Knowledge of the future wave profile is then leveraged in a nonlinear direct multiple shooting model predictive control framework allowing the online optimization of the energy absorption under motion and machinery constraints of the device. [Preview Abstract] |
Sunday, November 23, 2014 3:07PM - 3:20PM |
D24.00005: Numerical Simulations and Experimental Measurements of Scale-Model Horizontal Axis Hydrokinetic Turbines (HAHT) Arrays Teymour Javaherchi, Nick Stelzenmuller, Joseph Seydel, Alberto Aliseda The performance, turbulent wake evolution and interaction of multiple Horizontal Axis Hydrokinetic Turbines (HAHT) is analyzed in a 45:1 scale model setup. We combine experimental measurements with different RANS-based computational simulations that model the turbines with sliding-mesh, rotating reference frame and blame element theory strategies. The influence of array spacing and Tip Speed Ratio on performance and wake velocity structure is investigated in three different array configurations: Two coaxial turbines at different downstream spacing (5d to 14d), Three coaxial turbines with 5d and 7d downstream spacing, and Three turbines with lateral offset (0.5d) and downstream spacing (5d \& 7d). Comparison with experimental measurements provides insights into the dynamics of HAHT arrays, and by extension to closely packed HAWT arrays. The experimental validation process also highlights the influence of the closure model used (k-$\omega$ SST and k-$\epsilon$) and the flow Reynolds number (Re=40,000 to 100,000) on the computational predictions of devices' performance and characteristics of the flow field inside the above-mentioned arrays, establishing the strengths and limitations of existing numerical models for use in industrially-relevant settings (computational cost and time). [Preview Abstract] |
Sunday, November 23, 2014 3:20PM - 3:33PM |
D24.00006: Experimental assessment of blade tip immersion depth from free surface on average power and thrust coefficients of marine current turbine Ethan Lust, Karen Flack, Luksa Luznik Results from an experimental study on the effects of marine current turbine immersion depth from the free surface are presented. Measurements are performed with a 1/25 scale (diameter D$=$0.8m) two bladed horizontal axis turbine towed in the large towing tank at the U.S. Naval Academy. Thrust and torque are measured using a dynamometer, mounted in line with the turbine shaft. Shaft rotation speed and blade position are measured using a shaft position indexing system. The tip speed ratio (TSR) is adjusted using a hysteresis brake which is attached to the output shaft. Two optical wave height sensors are used to measure the free surface elevation. The turbine is towed at 1.68 m/s, resulting in a 70{\%} chord based Rec$=$4 x 10$^{5}$. An Acoustic Doppler Velocimeter (ADV) is installed one turbine diameter upstream of the turbine rotation plane to characterize the inflow turbulence. Measurements are obtained at four relative blade tip immersion depths of z/D $=$ 0.5, 0.4, 0.3, and 0.2 at a TSR value of 7 to identify the depth where free surface effects impact overall turbine performance. The overall average power and thrust coefficient are presented and compared to previously conducted baseline tests. The influence of wake expansion blockage on the turbine performance due to presence of the free surface at these immersion depths will also be discussed. [Preview Abstract] |
Sunday, November 23, 2014 3:33PM - 3:46PM |
D24.00007: Large-eddy simulation of turbulent flow past tri-frame configurations of hydrokinetic turbines in an open channel Saurabh Chawdhary, Xiaolei Yang, Craig Hill, Michele Guala, Fotis Sotiropoulos An effective way to develop arrays of hydrokinetic turbines in streams and tidal sites is to arrange them in tri-frame configurations, where three turbines are mounted together at the apexes of a triangular frame. Turbines mounted on a tri-frame can serve as the building block for rapidly deploying multi-turbine arrays. We employ large-eddy simulation (LES) to understand wake interactions of turbines mounted on tri-frame configurations and develop design guidelines for field deployment. We employ the computational framework of Yang et.al. (2013) to simulate the flow past turbines with the turbines modeled as actuator lines. The computed results are compared with experiments conducted at the Saint Anthony Falls Lab (SAFL) in terms of mean flow and turbulence characteristics. The flow fields are analyzed to elucidate the mechanisms of turbine interactions and wake evolution in tri-frame configurations and to develop design guidelines for maximizing the combined power output while reducing structural loads due to turbulent fluctuations. [Preview Abstract] |
Sunday, November 23, 2014 3:46PM - 3:59PM |
D24.00008: Experimental investigation on axial-flow turbine arrays in erodible and non-erodible channels: Performance, flow-field, and bathymetric interactions Craig Hill, Fotis Sotiropoulos, Michele Guala Natural channels ideal for hydrokinetic turbine installations present complex environments containing asymmetric flow, regions of high shear and turbulent eddies that impact turbine performance. To understand the impacts caused by variable topography, baseline conditions in a laboratory flume are compared to turbine performance, flow characteristics, and channel topography measurements from two additional experiments with small-scale and large-scale bathymetric features. Both aligned and staggered multi-turbine configurations were investigated. Small-scale axial-flow rotors attached to miniature DC motors provided measurements of turbine performance and response to i) complex topographic features and ii) flow features induced by upstream turbines. Discussion will focus on optimal streamwise and lateral spacing for axial-flow devices, turbine-topography interactions within arrays and inter-array flow-field measurements. Primary focus will center on results from turbines separated by a streamwise distance of 7dT. Additionally, results indicate possible control strategies for turbines installed in complex natural environments. [Preview Abstract] |
Sunday, November 23, 2014 3:59PM - 4:12PM |
D24.00009: The dynamic interaction of a marine hydrokinetic turbine with its environment Nitin Kolekar, Arindam Banerjee Unlike wind turbines, marine hydrokinetic and tidal turbines operate in a bounded flow environment where flow is constrained between deformable free surface and fixed river/sea bed. The proximity to free surface modifies the wake dynamics behind the turbine. Further, size {\&} shape of this wake is not constant but depends on multiple factors like flow speed, turbine blade geometry, and rotational speed. In addition, the turbulence characteristics of incoming flow also affects the flow field and hence the performance. The current work aims at understanding the dynamic interaction of a hydrokinetic turbine (HkT) with free surface and flow turbulence through experimental investigations. Results will be presented from experimental study carried out in an open channel test facility at Lehigh University with a three bladed, constant chord, zero twist HkT under various operating conditions. Froude number (ratio of characteristic flow velocity to gravitational wave velocity) is used to characterize the effect of free surface proximity on turbine performance. Experimental results will be compared with analytical models based on blade element momentum theory. Characterization of wake meandering and flow around turbine will be performed using a stereo-Particle Image Velocimetry technique. [Preview Abstract] |
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