ISESCO JOURNAL of Science and Technology
The Official Journal of ISESCO Centre for Promotion of Scientific Research

Abstract

S avonius turbine, a Vertical Axis Wind Turbine (VAWT), is self starting, Omni-directional, and has high starting tor que. In this paper, an attempt was made to study the flow behaviour (static pressure and velocity con tours) of a rotating two bucket Savonius rotor using Computational Fluid Dy namics. CFD analysis was car ried out to model the complex flow physics around the rotating rotor, as it consumes less time and computational cost. For this purpose, data wer e taken from the experiments conducted earlier on the rotor in a subsonic wind tunnel for five overlap conditions, namely 16.2%, 20%, 25%, 30% & 35%. The rotor was 20cm in height and the buckets were 8 cm in diameter. A two-dimensional computational un str uctured mesh (triangular mesh) model was developed for the rotor in Gambit 2.3.16 package of Fluent 6.3.26 software. A k ε turbulence closure model with standard wall treatment function was selected. A second order upwind discretization scheme was adopted for pressure velocity coupling of the flow. The sequential algorithm, Semi-Implicit Method for Pressure-Linked Equation (SIMPLE) was used for solving all the scalar va riables. The flow was simu lated under steady-state condition, and the single rotating reference frame (MOVING WALL) was considered for the buckets. From the simulations done in Fluent 6.3.26 software, the flow patterns through the rotating rotor at 00 rotor angle for the above overlap conditions were analyzed with the help of static pr essure and velocity contours. The pressure dr op acr oss the rotor from upstream to downstream side was the maximum in case of 16.2% overlap indicating maximum power extraction from the wind at that overlap condition. Vortices formed on the concave side of the advancing bucket due to flow separations from adverse pressur e gradient were less up to 16.2% overlap, which increased with higher overlaps leading to reduction in positive torque by the advancing bucket. Mor eover, for 16.2% overlap, maximum pr essure difference was obtained across the returning bucket, thereby increasing the overall aerodynamic torque and power for the rotor

Keywords: CFD,Pressure Contours, Savonius rotor, Velocity Vectors.