Three-dimensional simulations

Wind-turbine blades are intended for generating power by harnessing kinetic energy through rotational effect, in which blades have variation in thickness from root to tip, allowing the blade to withstand higher stress and moment close to the root than that towards the tip. Similarly, twist to the blade is given along the span of the blade to get the maximum power coefficient. Presently, the optimization of the geometric parameters works productively in operational conditions when the turbine is rotating. However, when the turbine is not rotating, particularly in a situation when yaw and pitch control mechanism is disconnected or during a turbine-erection stage, the optimized blade twist will make the stream 3D misleadingly contrasted with the genuine rotor stream itself. Subsequently, During the shutdown, without a wind turbine control system, the α of the flow on the blade is dictated by the free wind direction, and the wind turbine may work outside the restricted operational range. In such stationary circumstances, complex 3D impacts may exist attributable to both the working conditions and the 3D complex turbine geometry. Thus, 2D simulation performed in the above section is sufficiently bad to comprehend flow dynamics in such conditions. It presently features the significance of performing stationary simulations which can represent the effect of bluffness of the turbine geometry and evolving cross-segment on optimal design parameters and flow physics. Therefore, this section provides the results of 3d simulation by considering stationary NREL PHASE VI wind turbine blade for analysis.
Figure 20 to figure 23 is highlighting the effect of pitch angles on various performance parameters like torque, power, and power coefficient. Each parameter has its own degree of significance in determining wind turbine reliability. Because of the wind turbine physics, for any wind speed, there is a most extreme power, and the power coefficient that happens when the blade pitch angle set at a specific value and free stream velocity strikes the span of the blade at a certain angle. Hence, in this study, seven-pitch angles -50, 100, -100, 100, 200,300 and 400 have been considered, to decide the wind speed at which the power output of the wind turbine to reach its greatest. Figure 20 illustrated the variation of torque with different wind speeds at different pitch angles. Herein, Torque increases with an increase in wind speed until the blade occupied a certain pitch angle where value drops down. The complete simulation is performed in multiple reference frames. Blade exhibiting pitch angle of -50, 100, -100, 100shown rise in torque value, but when the blade has given pitch angle of 200,300 and 400,the graph shows a different trend. Torque is an important parameter in determining the power of wind turbine blade and figure 20 is giving an idea that pitch angle has some impactful presence in getting torque and ascertaining wind turbine efficiency for free stream velocity. It is thus become important to see the impact of pitch angle on the performance parameter of the wind turbine blade. The variation in trend in the figure 20 is such that, there is an increase of 0.53% in the value of torque when wind velocity changes from 5 m/s to 7 m/s, but, it shows some significant decrease in torque value when velocity of the flow is 13 m/s, 15 m/s, 15.1 m/s and 20 m/s. However, there is a 2% increase in torque value when velocity changes from 20 m/s to 25 m/s and 25.1 m/s. Now, for pitch 30 and pitch 40 as the free stream velocity increases torque decreases accordingly. Figure 24 to figure 26, variation of angle of attack along the span of the blade and is calculated according to the method described in [40] and [41]. The detailed estimated data of performance parameters are given in table 3, table4, table5, table 6.
Table 3 Estimation of torque for different pitch angle and wind speed using CFD