## 1 Introduction  
Using wind turbines in small-scale and urban environments is becoming increasingly relevant. Various turbine configurations, both vertical and horizontal axes, have been well investigated and summarized by many authors [1, 2, 3]. Vertical-axis wind turbines (VAWTs) were initially considered very promising before being superseded by modern horizontal-axis turbines. For various reasons, there is currently a rising tide of interest in VAWTs, in particular, in Darrieus turbines. Using modern design tools and computational approaches, the performance of traditional VAWTs can be significantly improved, reaching a level almost comparable to horizontal-axis turbines. Since VAWTs have many specific advantages (compact design, easier connection to gearboxes/generator, easier blade control, if necessary, maintainability), it is important to quantify the efficiency of such turbines. Of particular interest are small vertical-axis wind turbines, which are considered effective for micro-power generation [4]. In moderate wind conditions, such turbines are widely used as a reliable source of electricity [5]. To improve the efficiency of wind turbines, the design of blades with an airfoil profile that provides a good thickness ratio and aerodynamic characteristics plays a key role [6]. A properly selected blade profile helps to increase the lift coefficient of the turbine. To achieve the maximum torque and power factor, the blades must provide high lift with minimum drag. Thus, the correct selection of blade design is critical to improving the efficiency of vertical-axis wind turbines [4]. In recent years, various asymmetric blades have been found to have greater potential than the symmetric NACA (National Advisory Committee for Aeronautics) airfoils for three-bladed Darrieus rotors. To select the optimal blade profile, an analysis of existing studies was conducted to identify the characteristics of the proposed designs. [PERSON] and [PERSON] studied the effect of a modified NACA 0018 airfoil in the trailing edge region on the self-starting ability at a low tip speed ratio (TSR) using 2D computational fluid dynamics (CFD) analysis and compared the simulation results with NACA 2415, which has self-starting ability. They found that the modified airfoil showed better self-starting results under both transient and steady flow conditions for their turbine model [7]. Subsequently, [PERSON] and [PERSON] performed a 2D CFD analysis under unsteady conditions for a three-bladed Darrieus rotor with NACA 2415 asymmetric blades. The rotor exhibited average torque, sufficient for the self-starting of the blades [8]. [PERSON] and [PERSON] investigated the aerodynamic and energy characteristics of a three-bladed Darrieus rotor based on a NACA 0012 swirling airfoil. The simulations were carried out under steady-state conditions using 2D CFD analysis and the standard k-\(\varepsilon\) turbulence model [9]. [PERSON] and [PERSON] analyzed a three-bladed H-Darrieus rotor using two symmetric airfoils, i.e., NACA0018 and NACA0015, and an asymmetric airfoil, i.e., S1210, and noted several advantages of the asymmetric S1210 blades for a fixed-pitch rotor [10]. [PERSON] and [PERSON] conducted an experimental study on a Darrieus rotor with three asymmetric S818 blades featuring increased thickness and a high blade solidity ratio to assess its self-starting capability [11]. [PERSON] et al. experimentally investigated a three-bladed Darrieus rotor with asymmetric S1210 blades to evaluate its power coefficient and self-starting capability at various blade-to-diameter ratios and low wind speeds. However, these studies did not pay enough attention to the blade-flow interaction at different azimuthal positions of Darrieus rotors at low wind velocities [12]. [PERSON] et al. used CFD analysis to investigate the effect of blade curvature and thickness on the performance of a Darrieus rotor using two asymmetric airfoils, NACA 5522 and LS0421.