A simple fixed geometry impulse turbine has been studied as a suitable power converter in Oscillating Water Column based wave power plants. Comparison with the Wells turbine, which is the commonly used self-rectifying turbine in such applications, shows it to be superior in performance under irregular flow conditions. Optimum guide vane angle for maximum efficiency has been arrived at based on the five angles tested.

Sundarm Moses Santhakumar

GUIDE VANES

IMPULSE TURBINE

OSCILLATING WATER COLUMN

WELLS TURBINE

Aspect ratio

Hydraulic turbines

Hydroelectric power plants

Torque

WAVE POWER

WAVE ENERGY CONVERSION

turbine

WATER COLUMN

IIT Madras is a public technical and research university located in Chennai, Tamil Nadu. Founded in 1959, it is recognised as an Institute of National Importance.

IIT Madras has been ranked as the top engineering institute in India for four years in a row by the National Institutional Ranking Framework of the MHRD

It currently offers undergraduate, postgraduate and research degrees across 16 disciplines in Engineering, Sciences, Humanities and Management. About 596 faculty belonging to science and engineering departments and centres of the Institute are engaged in teaching, research and industrial consultancy.

IIT Madras

Performance of an impulse turbine with fixed guide vanes for wave power conversion

Renewable Energy

This paper deals with the efficiency maximization of a wave energy converter (WEC). The WEC is an oscillating water column (OWC) device and drives a permanent magnet synchronous generator (PMSG) through a bidirectional flow impulse-turbine. The converter faces challenges such as large peak-to-average power ratio, low overall efficiency, and inefficient energy absorption for regular and irregular sea states. In this context, a higher order sliding mode controller (HOSMC) was proposed, and its gains were optimized to control through the best efficiency point tracking (BEPT) of the turbine. The flow through the turbine-passage was simulated by the computational fluid dynamics (CFD) technique, and the BEPT characteristics were obtained. An adaptive inertia-weight particle-swarm algorithm and a grouped grey-wolf algorithm were used for optimization. The Optimized HOSMC reduced chattering, minimized the reaching time and improved the mean efficiency by about 67% compared to the uncontrolled cases. In addition, the relative improvement of the mean efficiency was at least 4.8% compared to conventional controllers. The controller reduced the peak-to-average power ratio of at least 35.6% relative to the uncontrolled case of the turbine under different sea states. © 2019 Elsevier Ltd

Energy

Optimization based higher order sliding mode controller for efficiency improvement of a wave energy converter

Oscillating water column wave energy converter is having low efficiency because of its principal component, a bidirectional turbine. An analysis of the internal flow of the turbine gives an idea of improving the performance through optimization of geometrical parameters. In this study, an impulse turbine of 0.3 m diameter with fixed guide vanes is numerically simulated by solving three-dimensional incompressible steady Reynolds averaged Navier-stokes equation with two-equation turbulence closure model. This study shows that the numerical results very well match with the experimental results. The detailed flow physics demonstrates that different types of losses occur in this type of turbine and shows that the downstream diverging path of the rotor and guide vane is responsible for low performance. In this study, the effect of guide vane lean, as well as the combined rotor and guide vane lean on the performance of the turbine, has been discussed in detail and found to increase the efficiency of the turbine. © IMechE 2018.

Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy

High-performance ocean energy harvesting turbine design – Detailed flow analysis with blade leaning strategy

This work deals with unsteady analysis and control of a bi-directional impulse turbine equipped in oscillating water column (OWC) wave energy converter (WEC). The Unsteady Reynolds-averaged Navier-Stokes equations (URANS) were solved to get the turbine characteristics and the maximum efficiency tracking for different axial velocities. The grouped grey wolf optimization (GGWO) algorithm finds the optimal gains of proportional-integral-derivative (PID) controllers of a permanent magnet synchronous generator (PMSG), such that a maximum efficiency tracking can be achieved. The URANS analysis show that the best efficiency point (BEP) occurs at a flow coefficient of 1.25. The GGWO based controller increases efficiency by 61.5% and 4% compared to the uncontrolled and conventionally controlled case, respectively and limits the peak-to-average power ratio by 38.6% compared to the uncontrolled case. © 2019 Elsevier Ltd

Ocean Engineering

Performance enhancement of an impulse turbine for OWC using grouped grey wolf optimizer based controller

A bidirectional axial-flow impulse turbine installed in an oscillating water column raises the question of damping at different wave conditions. This article reports unsteady performances of such a turbine in an airflow test rig. The rig has a piston-cylinder arrangement, and the piston, when reciprocating, generates the oscillatory airflow. At a very low wave height (piston stroke length, <0.4 m), the turbine speed is very low. Time series analysis of pressure drop and speed are reported for higher stroke lengths, which shows the rate of increase and decrease in velocity of the turbine. Furthermore, the turbine pressure coefficient and the damping characteristics of the test rig chamber were estimated. Finally, the chamber damping verifies that the turbine-chamber coupling effect is reciprocal. © 2018 John Wiley & Sons, Ltd.

International Journal of Energy Research

Experimental analysis of turbine-chamber coupling for wave energy conversion

Wave energy harvesting systems mostly have low power production capability because of unoptimized design of the system components. A bidirectional flow impulse-turbine used in such a system has efficiency less than 40%, and it is required to design the turbine for a higher efficiency. Present work finds an optimal design and shows design-variable sensitivity to the turbine efficiency. The problem is solved using numerical analysis technique. The flow through the turbine was analyzed by solving the Reynolds-averaged Navier-Stokes equations (RANSE). The design variables; namely number of rotor blades and number of guide vane, guide vane angle and guide vane profile were modified to maximize the turbine efficiency. Using the Latin hypercube sampling technique, sample points were selected from a design space defined by lower and upper limits of the variables. Then, several surrogates were constructed using the RANSE calculated results, and the turbine performance was optimized. The results show that guide vane angle is the most sensitive parameter, while the guide vane profile has negligible effect on efficiency. A hybrid genetic algorithm searched the optimal design point. The relative mean efficiency enhancement over a wide range of flow coefficient was approximately 24%, while it was 28% at maximum efficiency point. © 2018 Elsevier Ltd

High efficiency design of an impulse turbine used in oscillating water column to harvest wave energy

Journal of Energy Resources Technology

Performance of a High-Solidity Wells Turbine for an OWC Wave Power Plant

International Journal of Heat and Fluid Flow

The wells air turbine subjected to inlet flow distortion and high levels of turbulence

4th Joint Fluid Mechanics, Plasma Dynamics and Lasers Conference

Simulation of starting characteristics of the Wells turbine

Bulletin of JSME

Studies on Wells Turbine for Wave Power Generator : 4th Report, Starting and Running Characteristics in Periodically Oscillating Flow

Journal	Renewable Energy
ISSN	09601481
Open Access	No