Copyright © 2016 by the International Society of Offshore and Polar Engineers. The energy from a tidal stream is abundant and renewable resource whose power is predictable and sustainable. To generate power effectively from the stream a unique counter rotating type tidal stream power unit, whose tandem rotors drive inner and outer armatures in a generator, has been provided by the authors. At the tidal power station located in narrow straits, the unit needs to be reoriented so that useful output power can be obtained from both flood and ebbing tides. In this paper, the counter rotating tandem rotor turbine was designed for operation in a bidirectional tidal stream and the performance was analyzed. The maximum output power is somewhat lower than that of the rotors designed exclusively for a unidirectional stream. The relative flow has a positive angle of attack at the leading edge and discharges from the trailing edge along the blade camber. The angular momentum change, namely the rotor work, is seen to always be accompanied with a shock loss at the leading edge.

© Springer International Publishing Switzerland 2015. Importance of renewable energy has become paramount due to its perennial source and no adverse environmental impact. Ocean is one of the major source of renewable energy where the sun's energy is converted into various natural phenomenon. Southwestern sea in particular, in Korea, has large range of tidal currents with potential for tidal current power generation. Tidal power has great potential for future power and electricity generation because of the massive size of the oceans. The major benefit of tidal power and difference from most renewable energy sources is that it is independent of seasons and weather, that is, it is always constant which makes power generation predictable and makes tidal power a reliable energy source. Horizontal-axis-type turbine appears to be the most technologically and economically viable option for the generation of tidal power. Several studies have shown that single-rotor turbines can obtain a theoretical maximum power coefficient of 59.3 %, whereas dual rotor can obtain a maximum of 64? %. Hence, with the optimization of counter-rotating turbines, more power can be obtained than the single-rotor turbines. Previous studies focus on the performance analysis of the turbine with the variation of distance between the blades. This chapter primarily concentrates on the investigation of the performance analysis and power output of a counter-rotating current turbine by the variation of blade angles by both computational fluid dynamics (CFD) simulation and experiments. Numerical simulations were performed using a commercial finite volume method solver, ANSYS CFX ver.13.0. Experiments were conducted in the water tank with a vertically circulating water channel in the laboratory of Korea Maritime and Ocean University (KMOU) to validate the numerical results. Several experiments were conducted with the fixed front blade angle and varying the rear blade angle and vice versa at various water flow rate. Surface streamlines, torque, total power output, power coefficient ( Cp) etc., were characterized and compared for CFD and experimental cases. The results obtained find good agreement with each other.

© 2014 Elsevier Ltd. Among the various ocean energy resources in Korea, the tidal currents in the South western sea have a large potential for development tidal current power generation. The biggest advantage of tidal power is that it is not dependent on seasons or weather and is always constant. This makes power generation predictable and makes tidal power a more reliable energy source than other renewable energy sources. Marine current turbines convert the kinetic energy in tidal currents for power production. Single rotor turbines can obtain a theoretical maximum power coefficient of 59.3%, whereas dual rotor can obtain a maximum of 64%. Therefore by optimizing the counter rotating turbines, more power can be obtained than the single rotor turbines. In this study, we investigated the effect of varying the distance between the dual rotors on the performance and efficiency of a counter-rotating current turbine by using computational fluid dynamics (CFD) and experimental methods. It was found that the dual rotor produced more power than the single rotor. In addition, the blade gap distance affects the flow on the rear rotor blades as well as power output and performance of the turbine. The distance can be used a parameter for counter rotating turbine design. Finally, the numerical setup used for this study can be further used to evaluate the design of larger counter rotating blade designs.

Global warming is one of the issues in the world mainly due to the burning of fossil fuels and so alternative energy is now paramount in the 21st century. In Korea, the tidal currents in the South western sea has a large range of currents that are available for tidal current power generation. Single rotor turbines can obtain a theoretical maximum power coefficient of 59.3%, whereas dual rotor can obtain a maximum of 64%. In this study, we investigated the performance and efficiency of a Counter-rotating current turbine by different front and rear blade angle by water velocity by using CFD and experimental methods. Copyright © 2014 by the International Society of Offshore and Polar Engineers (ISOPE).

Renewable energy sources which are gaining popularity over conventional resources mostly produce intermittent power as they fall under the influence of natural phenomena as daily cycle or weather conditions. However, worldwide remarkable growth of electricity generation from renewable resources in the recent years has resulted in the decentralized production posing network load stability problems, which requires proper energy storage. Therefore, energy storage system can make more efficient utilization of renewable energies available and hence it will be more practical in application. This research work discusses about the energy storage system which comprises the concepts of combined pumped-storage hydro electricity and compressed air energy storage. The system consists of two tanks, one open tank to the air and one closed tank which stores water and compressed air using multistage pump. The energy of compressed air will be released to drive water which passes through the hydro turbine resulting in the generation of electricity when the grid power is insufficient. This study focuses on the CFD analysis on the closed tank of energy storage system during discharge.

There has been a considerable interest recently in the topic of renewable energy. This is primarily due to concerns about environmental impacts of fossil fuels. Moreover, fluctuating and rising oil prices, increase in demand, supply uncertainties and other factors have led to increased calls for alternative energy sources. Small hydropower, among other renewable energy sources, has been evaluated to have adequate development value because it is a clean, renewable and abundant energy resource. In addition, small hydropower has the advantage of low cost development by using rivers, agricultural reservoirs, sewage treatment plants, waterworks and water resources. The main concept of the tubular-type hydro turbine is based on the difference in water pressure levels in pipe lines, where the energy which was initially wasted by using a reducing valve at the pipeline of waterworks, is collected by turbine in the hydro power generator. In this study, in order to acquire the performance data of a pico tubular-type hydro turbine, the output power, head and efficiency characteristics by different runner blade shapes are examined. The pressure and velocity distributions with the variation of guide vane and runner vane angle on turbine performance are investigated by using a commercial CFD code. © Published under licence by IOP Publishing Ltd.

Micro hydraulic turbines have a growing interest because of its small and simple structure, as well as a high possibility of using in micro and small hydropower applications. The differential pressure existing in city water pipelines can be used efficiently to generate electricity in a way similar to that of energy being generated through gravitational potential energy in dams. The pressure energy in the city pipelines is often wasted by using pressure reducing valves at the inlet of water cleaning centers. Instead of using the pressure reducing valves, a micro counter-rotating hydraulic turbine can be used to make use of the pressure energy. In the present paper, a counter-rotating tubular type micro-turbine is studied, with the front runner connected to the generator stator and the rear runner connected to the generator rotor. The performance of the turbine is investigated experimentally and numerically. A commercial ANSYS CFD code was used for numerical analysis. © Published under licence by IOP Publishing Ltd.