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A performance prediction model is developed for axial-type turbines that operate at partial admission. Losses generated within the turbine are classified into windage loss, expansion loss and mixing loss. This developed loss model is compared with an experimental result when a turbine operates with a rectangular-type nozzle at a partial admission rate from 22% to 37%. The present predicted results show better agreement with the experimental results than with those predicted by other models, as the expansion loss in this model is developed more closely to the real flow situation. If a turbine operates at a very low partial admission rate, a circular-type nozzle is more efficient than a rectangular-type nozzle. In this case, a performance prediction model is developed and an experiment is conducted with the circular-type nozzle. The predicted result is compared with the measured performance, and the developed model is found to be in good agreement with the experimental results. Thus, the developed model could be applied to predict the performance of axial-type turbines that operate at various partial admission rates or with different nozzle shapes.

A wind tower can augment the performance of a vertical-axis wind turbine since it can increase the wind velocity as well as adjust the wind direction. However, it is very important to correctly determine the configuration of the wind tower because the wind tower can also interrupt the wind flow toward the wind turbine. Hence, a numerical analysis was conducted to investigate an effective wind tower configuration using computational fluid dynamics. For practical reasons, a numerical algorithm using a reduced computational domain was applied because the full three-dimensional computational fluid dynamics required huge amounts of computation time for a transient analysis. This method was validated using experimental results and was then applied to the computation of a wind tower with an installed vertical-axis wind turbine. Three wind tower design parameters were chosen for investigation: the inner radius, outer radius, and relative angle of the guide wall. When these parameters were correctly determined, the wind tower always increased the performance of the vertical-axis wind turbine in an omnidirectional wind. In addition, the maximum power coefficient was increased from 0.261 (without the wind tower) to 0.436.

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The partial admission technique is widely used to control the output power of turbines. In some cases, it has more merits than full admission. However, additional losses, such as expansion, mixing, or pumping, are generated in partial admission as compared with full admission. Thus, an experiment was conducted in a linear cascade apparatus having a partial admission region in order to investigate the effect of partial admission on a blade row. The admission region was formed by a spouting nozzle installed at the inlet of the linear cascade apparatus. Its cross section was rectangular and its size is 200×200 mm2. The tested blade was axial-type and its chord was 200 mm. Nineteen identical blades were applied to the linear cascade for the partial admission experiment. The blades moved along the rotational direction in front of the admission region, and then operating forces and surface pressures on the blades were measured at the steady state. The experiment was conducted at a Reynolds number of 3×105 based on the chord. The nozzle flow angle was set to 65 deg with a solidity of 1.38 for performance test at the design point. In addition, another two different solidities of 1.25 and 1.67 were applied. From the experimental results, when the solidity was decreased, the maximum rotational force increased but the maximum axial force decreased.

In order to augment the performance of vertical axis wind turbines, wind power towers have been used because they increase the frontal area. Typically, the wind power tower is installed as a circular column around a vertical axis wind turbine because the vertical axis wind turbine should be operated in an omnidirectional wind. As a result, the performance of the vertical axis wind turbine depends on the design parameters of the wind power tower. An experimental study was conducted in a wind tunnel to investigate the optimal design parameters of the wind power tower. Three different sizes of guide walls were applied to test with various wind power tower design parameters. The tested vertical axis wind turbine consisted of three blades of the NACA0018 profile and its solidity was 0.5. In order to simulate the operation in omnidirectional winds, the wind power tower was fabricated to be rotated. The performance of the vertical axis wind turbine was severely varied depending on the azimuthal location of the wind power tower. Comparison of the performance of the vertical axis wind turbine was performed based on the power coefficient obtained by averaging for the one periodic azimuth angle. The optimal design parameters were estimated using the results obtained under equal experimental conditions. When the non-dimensional inner gap was 0.3, the performance of the vertical axis wind turbine was better than any other gaps.

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