Turbomachinery

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A 2D numerical study is conducted to assess the effect of outer stators on the performance of a vertical wind turbine and the acoustical noise radiation. The model wind turbine is 3 straight blades Giromill type with a NACA 0015 airfoil. The stators are composed of 4 straight plates. The flow interaction mechanism between the turbine blades and the stator blades and the acoustic characteristics are analyzed applying the finite difference lattice Boltzmann method. From the results, it is observed that the increase of the incident flow velocity guided by the stator blades increases the rotor blade lift at a certain azimuth angle interval. The cycle averaged torque coefficient of the turbine with the stators is greater by maximum 40% compared to the no stator turbine. The mean sound pressure observed at a distance of 10m from the center around the turbine with the stators is 1.5 times i.e. 3.5 dB larger compared to the pressure of the no stator turbine.

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In order to research the discharge coefficient of a balancing hole C_d for a wide range of axial flow velocity v in the hole and rotational speed u, we carried out CFD simulations. Some of the results and the reported experimental data agree within the difference of about 5.3% on the pressure difference of the hole. Flow in a balancing hole is influenced by not only v but also u. Therefore the parameter v/u is considered as an important parameter of C_d. Furthermore, for very low range of v/u, we found a rare flow situation with S-shaped streamlines. Due to the strong pumping effect by rotating disk, C_d is greatly different in this region.

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