• 유체기계공업학회:학술대회논문집
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• 2006.08a
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• pp.371-374
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• 2006

The objective of this study is to determine the influence of free-stream turbulent intensity on the three-dimensional turbulent flow in a linear turbine cascade. The range of free-stream turbulence intensity considered is 0.7~10%. This study was performed numerically. The results show that the mass averaged loss coefficient increased according to the increase of free-stream turbulence intensity due to increased value of the mass averaged total pressure loss coefficient which was higher than the decreased value of the mass averaged secondary flow loss coefficient. The loss coefficient distribution was changed suddenly at a free-stream turbulence intensity of 10% while the loss coefficient distribution was rarely changed at a lower free-stream turbulence intensity of 5%.

• Ocean and Polar Research
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• v.41 no.3
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• pp.193-202
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• 2019

There have been various approaches for efficiency improvement of a Darrieus tidal stream turbine after it was introduced as an alternative of horizontal axis turbines. Among the approaches, the researches on the interaction effect of dual configuration were conducted. In this study, a dual Darrieus turbine with a coupling mechanism was proposed for investigating the interaction effect. Also, the effect of bi-directional tidal stream was analyzed with prototype fabrication, apparatus set-up and experiment conduction in indoor and offshore facilities. As the results of the experiments, the dual turbine in case of counter-rotation and inflow between the turbines improved efficiencies by 9.5% and 11.31%, respectively, as compared to the single turbine. Also, the dual turbine in case of the inflow improved efficiencies by 9.4% and 16.62%, respectively, as compared to that in case of outflow between the turbines which represented the case of 180 degrees change of flow direction after slack water. Therefore, the proposed dual turbine showed the advantage in terms of the efficiency as compared to the single turbine and the effect level of the slack water on the performance of the dual turbine was investigated.

• Journal of Mechanical Science and Technology
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• v.18 no.8
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• pp.1435-1450
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• 2004

Experimental data are presented which describe the effects of a combustor-level high free-stream turbulence on the near-wall flow structure and heat/mass transfer on the endwall of a linear high-turning turbine rotor cascade. The end wall flow structure is visualized by employing the partial- and total-coverage oil-film technique, and heat/mass transfer rate is measured by the naphthalene sublimation method. A turbulence generator is designed to provide a highly-turbulent flow which has free-stream turbulence intensity and integral length scale of 14.7% and 80mm, respectively, at the cascade entrance. The surface flow visualizations show that the high free-stream turbulence has little effect on the attachment line, but alters the separation line noticeably. Under high free-stream turbulence, the incoming near-wall flow upstream of the adjacent separation lines collides more obliquely with the suction surface. A weaker lift-up force arising from this more oblique collision results in the narrower suction-side corner vortex area in the high turbulence case. The high free-stream turbulence enhances the heat/mass transfer in the central area of the turbine passage, but only a slight augmentation is found in the end wall regions adjacent to the leading and trailing edges. Therefore, the high free-stream turbulence makes the end wall heat load more uniform. It is also observed that the heat/mass transfers along the locus of the pressure-side leg of the leading-edge horseshoe vortex and along the suction-side corner are influenced most strongly by the high free-stream turbulence. In this study, the end wall surface is classified into seven different regions based on the local heat/mass transfer distribution, and the effects of the high free-stream turbulence on the local heat/mass transfer in each region are discussed in detail.

• Ocean Systems Engineering
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• v.13 no.3
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• pp.247-268
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• 2023

Tidal stream energy extraction remains a site-specific resource due to the "first generation" criteria requiring high-velocity tidal streams. Most studies on tidal energy and turbine blade design heavily focus on installation sites with higher velocity conditions that are non-existent in tropical countries such as the Philippines. To shorten this gap, this review paper tackles tidal turbine design considerations for low-energetic regions such as the tropics. In-depth discussions of operating principles, methods of analysis, and designs of tidal turbine blades are presented. Notable tidal stream projects around the world are also mentioned in the paper. Also, it provides a perspective on the potential of this renewable energy to produce electricity for various sites in the Philippines. Finally, the paper emphasizes the need for new tidal turbine blade designs to be viable in tropical regions, such as the Philippines.

• Wind and Structures
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• v.32 no.2
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• pp.169-177
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• 2021

This study investigates the effects of blade configuration and solidity of Darrieus wind turbine on the starting torque characteristics. Generally, the configuration of Darrieus wind turbine is divided into Troposkien, parabola, Catenary, Sandia, modified-parabola and straight types. A numerical analysis has been carried out using Multiple Stream Tube (MST) method to investigate the effect of blade configuration and solidity of Darrieus wind turbine on the starting torque under the initial low range of rotational speed. The simulation results show that the starting torque of Darrieus wind turbine varies considerably depending on the blade configuration. The initial starting torque was larger with Troposkien, Parabola, Catenary, and Sandia configurations than with modified parabola or straight types. The increase in solidity with increasing number of blades raised the starting torque and improved the dynamic stability during the initial operational speed of Darrieus wind turbine. Additionally, these torque results represent basic data for fluid-structure interaction (FSI) simulation of the steady-dynamic operation of the turbine.

• Solar Energy
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• v.7 no.2
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• pp.74-85
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• 1987

Performances of 3 different aerodynamic analytical models, single multiple and double multiple stream tube, for vertical axis Darrieus turbine were analyzed comparatively. From the study it has been found that the models derived from stream tube assumptions can be useful for simple prediction of basic design characteristics of Darrieus turbine. But, for a large tip speed and solidity ratios, the models has shown a certain limit in its applicability according to the formulation scheme applied. The results have shown that for the case having large tip speed and solidity ratios the consideration due to stream conditions, such as trailing vortices or wakes, should be included for accurate prediction of the aerodynamic performances of Darrieus turbine.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.1442-1446
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• 2004

The heat (mass) transfer characteristics on the blade surface of a first-stage turbine rotor cascade has been investigated by employing the naphthalene sublimation technique. A four-axis profile measurement system is employed for the measurements of the local heat (mass) transfer coefficient on the curved blade surface. The experiments are carried out for two free-stream turbulence intensities of 1.2% and 14.7%. The high free-stream turbulence results in more uniform distributions of heat load on the both pressure and suction surfaces and in an early boundary-layer separation on the suction surface. The heat (mass) transfer enhancement on the suction surface due to the endwall vortices is found to be relatively small under the high free-stream turbulence.

• International Journal of Naval Architecture and Ocean Engineering
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• v.1 no.2
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• pp.64-69
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• 2009

The two-dimensional unsteady flow around a vertical axis turbine for tidal stream energy conversion was investigated using a computational fluid dynamics tool solving the Reynolds-Averaged Navier-Stokes equations. The geometry of the turbine blade section was NACA653-018 aiifoil. The computational analysis was done at several different angles of attack and the results were compared with the corresponding experimental data for validation and calibration. Simulations were then carried out for the two-dimensional cross section of a vertical axis turbine. The simulation results demonstrated the usefulness of the method for the typical unsteady flows around vertical axis turbines. The optimum turbine efficiency was achieved for carefully selected combinations of the number of blades and tip speed ratios.

• Journal of the Korean Society for Marine Environment & Energy
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• v.17 no.1
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• pp.20-26
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• 2014

It is essential to consider the effect of blade deformation in order to design a better tidal stream turbine being operated in off-design condition. Flow load causes deformation on the blade, and the deformation affects the turbine performance. In the present study, CFD analysis procedures were developed to predict open water performance of horizontal axis tidal stream turbine (HATST). The developed procedures were verified by comparing the results with existing experimental results. Fluid-structure interaction (FSI) analysis method, based on the verified CFD procedure, have been carried out to estimate the turbine performance for a turbine with flexible composite blades, and then the results were compared with those for rigid blades.

• Proceedings of the KSME Conference
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• 2001.11b
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• pp.746-751
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• 2001

We used a cylindrical model which simulates turbine blade leading edge to investigate the effects of free-stream turbulence intensity and blowing ratio on film cooling of turbine blade leading edge. Tests are carried out in a low-speed wind tunnel on a cylindrical model with three rows of injection holes. Mainstream Reynolds number based on the cylinder diameter was $7.1\times10^4$. Two types of turbulence grid are used to increase a free-stream turbulence intensity. The effect of coolant blowing ratio was studied for various blowing ratios. For each blowing ratios, wall temperatures around the surface of the test model are measured by thermocouples installed inside the model. Results show that blowing ratios have small effect on spanwise-averaged film effectiveness at high free-stream turbulence intensity. However, an increase in free-stream turbulence intensity enhances significantly spanwise-averaged film effectiveness at low blowing ratio.