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The purpose of this paper is the numerical study of the effects of the fluid interaction with the blades of the working bodies of the renewable energy conversion systems. The paper presents the results of numerical research regarding the influence of the blade shape (straight), the number of blades (2, 3, 4) or the wind speed in the area on the output power of the small capacity wind turbines. The validation of the simulation data was performed by comparison with the experimental data obtained on a Windtrainer Junior laboratory wind energy system. Computed power coefficients are in good agreement with the experimental results. Increasing the efficiency of energy conversion for small wind turbines for their implementation in green farms represents a significant step in the concept of sustainable rural development. REZUMAT Scopul acestei lucrări este studiul numeric al efectelor interacțiunii fluidului cu lamele corpurilor de lucru ale sistemelor de conversie a energiei regenerabile. Lucrarea prezintă rezultatele cercetărilor numerice cu privire la influența formei lamei (drepte), numărul de pale (2, 3, 4) sau viteza vântului în zona pe puterea de ieșire a turbinelor eoliene de mică capacitate. Validarea datelor simulate a fost efectuată prin comparație cu datele experimentale obținute pe un sistem de energie eoliană de laborator Windtrainer Junior. Coeficienții de putere calculați sunt în acord cu rezultatele experimentale. Creșterea eficienței conversiei energiei pentru turbinele eoliene mici pentru implementarea lor în ferme ecologice reprezintă un pas semnificativ în conceptul de dezvoltare rurală durabilă. INTRODUCTION The need to reach a higher standard of living and increase the world's population have produced a dramatic increase in energy consumption globally. All energy sources affect the environment to a greater or lesser extent. There is no completely "clean" power source. Most of our energy comes from 85% fossil fuels coal, oil and natural gas, and the burning of these fuels causes pollution of the environment in which we live. To reduce the long-term impact of the energy industry on the environment, strategies are developed and implemented to increase the efficiency of energy use, to capitalize on alternative sources and on sustainable development. Wind energy is one of the renewable energy sources that can be harnessed due to its quite good potential. Generating small scale electricity is closer to the final user, significantly reducing transport losses. This leads to lower energy costs for consumers and ensures greater efficiency. In isolated areas, where electricity grids are missing or are isolated and have low transport capacity, individual turbines or small groups of turbines of different sizes are located. Small-scale electricity generation can be considered to be more reliable, cheaper, more efficient and more environmentally friendly than centralized production. The ability of modern computing systems to operate quickly with a large volume of data offers the unique opportunity for researchers to investigate problems whose practical approach would be too costly, longlasting or even impossible. Thus, the researcher can obtain optimal technical solutions that approach the experimental reality in a reasonable time. Vol. 62, No. 3 / 2020 INMATEH – 326 Mara et al., (2014), study a model for aerodynamics simulation of Magnus wind rotor blades using Ansys CFX. They evaluated various strategies for obtaining the grid and models of turbulence to accurately validate the model in relation to the experimental data published by Bychkov et al. (2007). Rogowski et al., (2017), performed a numerical analysis of a small-size vertical-axis wind turbine performance. They developed a two-dimensional model of vertical-axis wind turbine based on the experimental Darrieus wind turbine, and show that velocity profile becomes more asymmetric in relation to upper tip speed ratios if the rotor is operating at lower tip speed ratios. Nigam et al., (2017), perform a CFD analysis of a Vestas V82-1.65 MW horizontal axis wind turbine blade and NACA 634 -221 airfoil profile of wind turbine using k-SST turbulence model in Ansys Fluent. The results obtained for the traction coefficient and the moment of depositing at different angles of attack or lift coefficient are compared with the experimental results and show a good correlation. They also concluded that the air velocity is higher on the upper surface of the wing, while the air pressure on the lower surface of the wing is also increased. Wenehenubun et al., (2015), studied the performance of Savonius wind turbines related with the number of blades. For this work the ANSYS 13.0 software simulations were used to show the pressure distribution of wind turbine. Wußow et al., (2007), studied the airflow around a wind turbine (WT) of the type Enercon E66 with emphasis on the turbulent wake by using CFD simulations. It was found that the local values of turbulence intensity and the amplitude of the velocity inside the trace fits quite well with the measurements. Bose et al., (2014), studied numerically, using a commercial CFD code, the effect of pitch angle on the performance of a three bladed straight H-Darrieus vertical axis wind turbine. They showed that the presence of vortices close to the trailing edge deteriorates the performance of the turbine. The main purpose of the present paper is the theoretical and experimental argumentation of the aerodynamic characteristics of a wind turbine in the aspect of increasing the energy conversion efficiency for low power wind turbines. In order to achieve the formulated purpose, CFD simulations were performed for different wind speeds to determine the performance factor of the developed rotor and the aerodynamic forces acting on the blade, or to model the fluid's interaction with the blade structure to verify the resistance of the blade in stationary regime. MATERIALS AND METHODS The wind turbine works due to the difference of forces exert on each blade according to Wenehenubun, (2007). The maximum power of wind turbine Pt is determined as: Pt = T ∙ ω [Watt] (1) where: T is the torque (Nm) and ω is the angular velocity of rotor (s-1). The performance of wind turbine can be expressed in the form of torque coefficient (Ct) and the coefficient of power (Cp). The tip speed ratio or TSR (λ) is a parameter related with rated wind speed and rotor diameter. As the ratio between the speed of tip blade and wind speed through the blade, TSR can be determined with relation (2) according to Hameed and Afaq, (2013):

NUMERICAL 3D ANALYSIS OF A MINI WIND TURBINE WITH HORIZONTAL AXIS, FOR IMPLEMENTATION IN AGRICULTURAL FARMS