Experimental and Theoretical Studies for Improving the Performance of a Modified Shape Savonius Wind Turbine

Abstract

In this paper, measurements and computations are performed to study the performance of a 45-deg twisted Savonius rotor with a modified profile, at various overlap ratios (δ), aspect ratios (AR), and wind velocity (V). A free air jet test rig is used to carry out the experiments, while three-dimensional unsteady Reynolds-averaged Navier–Stokes (URANS) equations are used, in conjunction with the renormalization group (RNG) k–ɛ turbulence model, to perform the computations. The present experimental results successfully verify the simulation predictions obtained by the selected turbulence model. The RNG k–ɛ turbulence model has been chosen based on previous tests performed and published by the authors. Furthermore, both torque coefficient (CT) and power coefficient (CP) are numerically predicted at various tip speed ratios (λ) for overlap ratios (δ) ranging from 0.0 to 0.5, aspect ratios (AR) ranging from 0.75 to 3, and wind velocity values ranging from 4 to 18 m/s. Unlike the conventional rotor, the present twisted rotor with a modified profile produces significant performance improvement in the case of modified rotor without overlapping (δ = 0.0). Moreover, the peaks of CT and CP of the twisted rotor with the modified profile are enhanced with the increase in the aspect ratio. However, the percentage increase is noticed to be insignificant for AR greater than two. The maximum power coefficient (CPmax) for the twisted rotor with the modified profile and optimized design is 0.305 at a wind velocity of 6 m/s, with a performance gain of 75.3% compared to the conventional Savonius wind rotor which has CPmax=0.174.

Performance Investigation of Two Vertical-Axis Twisted Rotor Models

“…The exit of the computational domain, see Figure (2), is taken to be away 15D from the center of the rotor, where D is the rotor diameter. Hence, the outlet boundary is considered as an atmospheric pressure [27]. The turbulence intensity considered in the present computation is taken to be 5% based on our previous work [24].…”

Optimization of the Power Coefficient of a Savonius Wind Turbine by Changing the Shape of Blades

“…The power coefficient was found to be increased when the twist angle of the rotor is 45 degrees at specific conditions [6,7]. El-Askary et al [8] noted that increasing the aspect ratio to be more than 2 leads to an increase in the peak values of torque and power coefficients for a twisted rotor. Zhang et al [9] introduced a blade shape optimization analysis using a novel wake energy method.…”

Review of Specific Performance Parameters of Vertical Wind Turbine Rotors Based on the SAVONIUS Type

“…Energies 2021, 14,1962 2 of 23 All these advantages encourage studies aimed at constructive and functional optimization that can ensure increased operation performance for this rotor type. To achieve this goal, multiple studies and research activities have been conducted in which researchers used both numerical [15][16][17][18][19][20][21][22][23] and experimental methods [24][25][26][27][28][29][30][31][32][33][34][35] to establish and improve the performance of rotor construction variants directed towards blade shape optimization or determination of the optimal rotor blade number [36][37][38][39]. Additionally, the studies aimed to establish the optimum values related to the aspect ratio [40][41][42][43], and the overlap ratio [44][45][46][47][48][49], and to change the performance parameters in the case of end plates [50], and curtains mounted to the rotor assembly [51][52][53][54][55], with the scope of directing the air stream to the active blade, thereby avoiding the negative mom...…”