Now showing 1 - 10 of 27
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    Introducing Gurney flap to Wells turbine blade and performance analysis with OpenFOAM
    (01-09-2019)
    Kumar, P. Madhan
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    A Gurney flap (GF) placed at pressure side of the trailing edge of an airfoil and perpendicular to the chord line enhances lift in aircraft wings, helicopter rotors, and wind turbines, etc. In this article, the GF concept was introduced for Wells turbine blade used to harvest wave energy with special consideration as the blades are having symmetric airfoil and faces bidirectional flow. Hence, the flap was extended to both pressure and suction sides of the trailing edge (TE) to maintain blade symmetry, and the turbine performance was evaluated using opensource computational fluid dynamics code OpenFOAM 4.0. Different GF-lengths (0.5–3% chord length) were considered, and the performance parameters such as non-dimensional torque, pressure drop and efficiency were evaluated. The GF blades produced a counter-rotating vortex pair behind the TE which modified the TE Kutta condition and increased the circulation and lift. In addition, the GF blades increased the blade loading and enhanced the torque generated. However, the increased pressure drop lead to decrement in efficiency.
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    High performance ocean energy harvesting turbine design-A new casing treatment scheme
    (15-06-2015)
    Halder, Paresh
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    Kim, Jin Hyuk
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    Choi, Young Seok
    Delaying a stall improves the performance of any turbomachinery system. TC (tip clearance), which is used in a bi-directional flow Wells turbine of an ocean wave energy device, changes the flow pattern on the turbine blade suction surface, while changing or modifying the TC zone can help obtaining a delayed stall. In the present work, a new tip grooving scheme is introduced and the performance is compared for different tip groove depths and TCs of a Wells turbine. The performance is defined in terms of wider operating range or stall delay, power production and efficiency. The problem was solved by a numerical analysis technique. A multi-block meshing scheme was employed to generate structured and hexahedral elements in the computational domain and the flow was solved in ANSYS CFX® v14.5 by solving Reynolds-averaged Navier Stokes equations. It was found that the grooves improve the turbine operating range and power production as compared to those of the turbine without a groove. The groove depth of 3% of the chord length produced highest power and widest operating range. Using the circumferential groove, 26% increase in turbine power output for a particular operating point is achieved.
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    Wave energy harvesting turbine: Effect of hub-to-tip profile modification
    (01-01-2018)
    Madhan Kumar, P.
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    Halder, Paresh
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    Rhee, Shin Hyung
    The present paper investigates the leading edge (LE) undulations of a Wells turbine blade through numerical analysis. The aspiration for this modification came from humpback whales, which have uneven protrusions at the LE of their pectoral flippers. The flippers help whales to maneuver during swimming. The work is performed by using three-dimensional steady, incompressible Reynolds Averaged Navier-Stokes (RANS) equations with turbulent closer model. The LE of the turbine blades is modified with undulations of three different amplitudes: 1mm, 2.5mm, and 4mm. The results show that the undulation changes the turbine performance. The amplitude 2.5mm gives the peak performance. The comparison between blades with different amplitudes and the reference blade has been discussed throughout this study.
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    Numerical optimization of wells turbine for wave energy extraction
    (01-01-2017)
    Halder, Paresh
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    Rhee, Shin Hyung
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    The present work focuses multi-objective optimization of blade sweep for a Wells turbine. The blade-sweep parameters at the mid and the tip sections are selected as design variables. The peak-torque coefficient and the corresponding efficiency are the objective functions, which are maximized. The numerical analysis has been carried out by solving 3D RANS equations based on k-w SST turbulence model. Nine design points are selected within a design space and the simulations are run. Based on the computational results, surrogate-based weighted average models are constructed and the population based multi-objective evolutionary algorithm gave Pareto optimal solutions. The peak-torque coefficient and the corresponding efficiency are enhanced, and the results are analysed using CFD simulations. Two extreme designs in the Pareto solutions show that the peak-torque-coefficient is increased by 28.28% and the corresponding efficiency is decreased by 13.5%. A detailed flow analysis shows the separation phenomena change the turbine performance.
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    Effect of blade leading-edge microcylinder in a Wells turbine used for wave energy converters
    (01-08-2023)
    Sadees, P.
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    Madhan Kumar, P.
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    The present study attempts to enhance a Wells turbine performance by adopting a leading-edge microcylinder (LEM) as a passive flow control device. The microcylinder is placed near the blade leading edge so that its axis lies on the chord line of the rotor blade. The influence of turbine performance, due to parameters such as microcylinder diameter and the distance between the cylinder and the blade leading edge, is evaluated by solving the steady Reynolds-averaged Navier–Stoke (RANS) equations with the k-ω SST turbulence model. The performance parameters of the microcylinder rotor were compared with the reference rotor. It was found that the pair of counter-rotating and co-rotating vortices shed from the microcylinder feed kinetic energy to the separated flow and re-energize the boundary layer. This phenomenon delays the flow separation and enhances the operating range. Moreover, a parametric investigation of the microcylinder rotor reveals that the diameter and space between the microcylinder and the rotor blade are instrumental in delaying flow separation. It was found that a cylinder diameter equal to 0.02C (C is blade chord) and a distance between the leading edge and the micro cylinder equal to 0.035C resulted in increases in the working range and in the average torque equal to about 22% and 49%, respectively.
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    Effect of microcylinder and d-cylinder at the leading edge of a wells turbine harvesting wave energy
    (01-01-2021)
    Sadees, P.
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    Kumar, P. Madhan
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    Wells turbine is a self-rectifying axial flow reaction turbine used to harvest energy from the ocean waves. It suffers from a premature stall at higher flow rates. The present study discusses a comparative performance analysis with a turbine-blade leading-edge (LE) microcylinder (LEM) and D-cylinder (LED). The space between the LE and the cylinder was fixed as 1.5% of chord length (c). The sizes of the cylinder were varied from 0.5% to 0.75% of the chord. The unstructured tetrahedral mesh elements were used to discretize the computational flow domain that consists of a single blade passage with periodic boundary conditions. The Reynolds-Averaged Navier-Stokes equations with the k-? shear stress transport (SST) turbulence equations were solved in a commercial CFD code Ansys CFX 18.1. The flow was considered incompressible. The present numerical study was compared with available open literature. The modified rotor blades showed a significant performance enhancement compared to the reference turbine. The peak efficiency was improved by 11.29% at a particular flow coefficient in 0.5%c radius LED-turbine. The presence of the cylinders delayed the flow separation and enhanced the operating range up to 11.11%.
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    Experimental study of Wells turbine with multiparameter modification for wave energy conversion
    (01-01-2021)
    Kumar, Amit
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    Das, Tapas K.
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    In this article, a Wells turbine geometry is created with the modification of multiple geometric parameters, i.e., blade sweep/skew, endplate, casing groove, and guide vane. The experiment of a bidirectional turbine is conducted at the wave and fluid engineering laboratory, IIT Madras. The preliminary objective of the study is to measure the starting characteristics and corresponding flow velocity, revolution per minute (rpm), differential pressure of higher and lower pressure sides of the turbine. The output parameters are measured at different cycle times and the stroke length of a piston-cylinder combination, which simulates different wave conditions. After starting the Wells turbine, rotational and axial speeds increase for some time. After that, it will fluctuate between a specific range, and pressure is prepositional to the airflow rate. The wave energy can be converted into pneumatic energy with the help of wave energy converting(WEC) devices, i.e., oscillating water column(OWC) that can be further converted into mechanical energy and then into electrical energy with some appropriate devices. In this article, an experimental analysis of the turbine geometry is reported.
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    Effect of guide vane angle on wells turbine performance
    (01-01-2014)
    Halder, Paresh
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    Wells turbines are used in oscillating water column wave energy system and the turbine has a stagger angle of 90o. Numerical analysis is performed to analyze the performance of the turbine in the present work. A commercial code ANSYSCFX ® v14.0 was used for the simulations at different flow coefficient, different angles and a constant rotational speed. The turbulence model was k-ω SST. Higher guide vane angle produced higher efficiency of the turbine and the efficiency (enhanced) change was contributed because of the vortex formation in different locations in the flow passage or near the blade surface.
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    Performance improvement of a Wells turbine through an automated optimization technique
    (01-12-2022)
    Das, Tapas K.
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    Kerikous, Emeel
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    Venkatesan, Nithya
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    Janiga, Gabor
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    Thevenin, Dominique
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    The present article reports optimization of the performance of a Wells turbine, which is an axial turbine utilized for wave energy conversion, through a computational fluid dynamics (CFD) based automated optimization technique. The in-house optimization library OPAL++ was coupled to a commercial CFD solver to get the Pareto front defining the relationships between two objectives. Four different geometric parameters of the turbine with ring-type endplate were used, and the objectives were to maximize the torque coefficient and simultaneously minimize the pressure drop coefficient. From the Pareto front, two designs (G1 and G2) were chosen for further analysis. G1 improved the peak torque-coefficient by more than 120 % and delayed the stall point from φ = 0.225 to φ = 0.3, while the peak efficiency dropped. Whereas, G2 improved the peak efficiency by 9.1 %, but the peak torque coefficient was reduced by about 50 %. The main contribution of the study is to develop an optimum Wells turbine geometry through the coupling of CFD and automated optimization algorithm - first of its kind applied to a Wells turbine with endplate. A detailed flow analysis, the influence of the endplate, and a comparison of the optimized geometries are presented.
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    Effect of stall fence on the performance of an axial turbine for wave energy conversion
    (01-01-2019)
    Das, Tapas K.
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    Wells turbine is one type of axial turbine exclusively used for wave energy conversion in Oscillating Water Column type wave energy conversion device. It is a bi-directional turbine which can rotate in one direction irrespective of the direction of airflow. One of the main disadvantages of this turbine is the stall phenomenon, where the torque, as well as efficiency, drops drastically at a particular angle of attack. The postponement of stall can be achieved by installing fences along the chord of the blade at a distance from the hub. In the present work, a numerical analysis of Wells turbine with the stall fence is carried out using commercial CFD tool ANSYS. The performance characteristics of the turbine are investigated for different number of stall fences at different distances along the span of the blade. A detail flow analysis is presented to explain the effect of the stall fence on this particular turbine.