2. Characteristics of the VAWT
2.1. Vertical Axis Wind Turbine Concept and Aerodynamic Characteristics
3. Wind Turbine and Computational Model
3.1. Experimental Test Case
3.2. Wind Turbine Overview
3.3. Computational Domain and Boundary Conditions
4.1. Aerodynamic Blade Loads
4.2. Aerodynamic Wake Characteristics
4.3. Revolution Convergence Analysis
4.4. Impact of Time Step Size
4.5. Mesh Convergence Study
- The SST k-ω turbulence model provides the results of the normal aerodynamic force component that appears to be satisfactory by comparing it with experimental results. However, slightly overestimated results of this force component may be due to 3D effects, which are not included in this work.
- The reason why the calculated velocity profiles (the velocity component parallel to the wind direction) downstream behind the rotor are not asymmetrical as in the case of the experimental studies it is not entirely clear. One possible reason is the simplification of the numerical model.
- The results of the second velocity component profiles agree much better with experimental research.
- The flow field around the wind turbine rotor is highly three-dimensional. The occurrence of flow separation is very likely in such conditions that are not favorable for URANS approach. Nevertheless, for the two-equation k-ω SST turbulence model and the URANS model, that were used here, the instantaneous velocity fields are consistent with the PIV studies.
- The influence of the rotating shaft is visible mainly in the central part of the velocity profiles and rapidly decreases with the distance downstream from the axis of rotation.
- The drop in the mean velocity for each Ux velocity profile is linear for six distances x/R downstream behind the rotor from 1.5 to 4.0. The average value of the velocity component parallel to the wind direction decreased by 13% for the given x/R range.
- The rotor in a non-shaft configuration achieves a power coefficient of 2.468% compared to a rotor equipped with a shaft.
- The frequency of the aerodynamic force acting on the shaft is 113.6% higher compared to the frequency of aerodynamic force of the rotor blade.
- Ten full rotor revolutions are sufficient to obtain repeatable results of the torque coefficient and almost constant values of the averaged rotor power coefficients. However, in order to obtain appropriate velocity profiles at the distance of 4R downstream behind the rotor, 15 full rotor revolutions are required for simulation.
- The selection of the appropriate time step size has the greatest impact on the estimation of the aerodynamic blade loads of the blade moving in the rotor shaft. If the time step size is too large, the shaft influence is invisible. Below the time step size corresponding to the angle step size of 0.05 degrees, the rotor power coefficient begins to be constant.
Conflicts of Interest
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|Number of blades, N||2|
|Rotor diameter, D=2R||1 m|
|Chord length, c||0.06 m|
|Rotor shaft diameter, DS||0.04 m|
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