Self-Starting Analysis of an OWC Axial Impulse Turbine in Constant Flows: Experimental and Numerical Studies

Marine energy is a major source of renewable energy and yet remains untapped. As the ocean covers about two-thirds of the Earth’s surface, it contains a large amount of energy. Energy can be extracted from the sea exploiting several phenomena, such as salinity gradient (energy from the difference in the salt concentration between seawater and fresh water), temperature gradient, waves, and ocean currents. Among these, ocean waves have tremendous potential as a source of renewable energy. The vast amount of of energy from the waves could meet an important part of the energy demand for humankind. Wave energy is enormous, reliable, and has higher energy density compared to wind power and solar power, and thus offers a good correlation between resource and demand. Waves also offer multiple locations for energy harvesting from the shoreline to deep water. There has been worldwide interest in harnessing this immense power from the ocean that can play a major part to solve our energy problems.

Marine power technology—wave energy

The geometry modification of a bidirectional flow Wells turbine used in a wave energy converter can assist in overcoming the mammoth stall triggered by tip leakage, secondary flow on the blade surface, corner vortex, passage vortex, tip scrubbing, tip trailing edge vortex, boundary layer formation on hub and casing, and combination of all the listed making it a complex 3D flow. As the flow varies almost sinusoidally in each wave cycle in the ocean, it is inevitable to get a turbine having a higher operating range and average power output. Skewing a blade reduces the radial flow on the blade suction surface. A casing groove and endplate reduce tip leakage flow. These modifications give a significant improvement in the turbine performance. There are several design alternatives reported in the articles, and they have shown different results. In this article, the modifications and their effects are discussed in detail and concluded for future recommendations.

Effect of blade skew, endplate and casing groove on the aerodynamic performance of Wells turbine for OWC: a review

We recognize three reasons for making measurements as indicated in Fig. 1.1. From the point of view of the present book, measurements for commerce is outside its scope. Engineers design physical systems in the form of machines to serve some specified functions. The behavior of the parts of the machine during the operation of the machine needs to be examined or analyzed or designed such that it functions reliably. Such an activity needs data regarding the machine parts in terms of material properties. These are obtained by performing measurements in the laboratory.

Measurements and Errors in Measurement

With the growing menace of increase in population and pollution, renewable sources of energy are being preferred over the fast depleting fossil fuels. Ocean wave energy is one such form of renewable source with a huge potential all around the globe. Wave energy conversion (WEC) devices are used to harness the energy from ocean waves. An oscillating water column (OWC) is a WEC device, which uses an axial turbine to convert wave energy into useful electrical energy. The experimental setup designed and assembled at Wave Energy and Fluids Engineering Laboratory, IIT Madras tested the turbine subjected to bidirectional airflow. The objective of the preliminary experiment is to measure the rotational speed and pressure drop across the turbine. The variable parameters are stroke length and time period of the oscillating piston, which simulates different ocean wave conditions. A comparative study of the parameters is carried out and reported in this article.

Experimental Study of an Axial Turbine for Wave Energy Conversion

Experimental analysis of turbine‐chamber coupling for wave energy conversion

A bidirectional impulse turbine is a self-rectifying air turbine used in an oscillating water column wave energy converters. Most of the study on bidirectional impulse turbines involves steady-state performance analysis; however, the performance under oscillating airflow conditions is necessary to understand its behavior. The objective of this study is to experimentally analyze an optimized and numerically investigated bidirectional impulse turbine with fixed guide vane subjected to oscillating airflow conditions. A bidirectional airflow test facility developed at Indian Institute of Technology Madras, Chennai, India is employed to determine the aerodynamic characterization of the turbine and the dynamics involved in each of the coupling stages. The test rig consists of a piston chamber assembly, which provides different airflow rates by varying the stroke length (SL) and cycle time. Emphasis is made on the pressure and flow rate coefficients of the turbine, turbine-generator coupling, and power developed for different input conditions. The operating range of the turbine is mapped for four different frequencies and three SLs. Different electrical loading and the power output were analyzed for accelerations and decelerations of inflow and outflow. The preliminary dynamic characterization of the turbine with respect to nondimentionalized pressure coefficient and flow coefficient was determined for inflow and outflow. The power output is found to be in strong correlation with the flow rate and angular rotation of the rotor. The turbine analyzed in the experimental test rig will be proceeded with real sea testing on the Indian coast by the National Institute of Ocean Technology, Chennai, India.

Experimental Investigation of a Bidirectional Impulse Turbine for Oscillating Flows at Various Resistive Loads

Evaluation of Impulse Turbines for a Wave Energy Converter

The oscillating water column (OWC) based wave energy devices require a turbine for the conversion of wave energy to electrical energy. Customarily, Wells and impulse turbines have been widely accep...

Aravind George

Papers

Experimental analysis of turbine‐chamber coupling for wave energy conversion

Experimental Investigation of a Bidirectional Impulse Turbine for Oscillating Flows at Various Resistive Loads

Evaluation of Impulse Turbines for a Wave Energy Converter

Numerical analysis of damping induced by impulse turbines for wave energy conversion