Numerical investigation of airflow through a Savonius rotor

Abstract

The aim of this report is to present a model of a rigid-rotor system based on computational fluid dynamics (CFD), which is applied on a vertical axis wind turbine (VAWT) research. Its originality results from the use of the average value of the variable rotational speed method taken in a periodic steady-state (PSS) of the VAWT rotor instead of the classical fixed rotational speed method. This approach was chosen in order to determine the mechanical and aerodynamic parameters of the wind turbine. The modeling method uses an implicit Euler iterative solution strategy, which resolves the coupling between fixed and moving rotor domains. The main methods that were adopted are based on the three-dimensional modeling of the interaction of the fluid flow with a rigid-rotor. The strategy consists of using the Reynolds averaged Navier Stokes (RANS) equations with the standard k-" and SST k-! models to solve the fluid flow problem. To perform the rigid-rotor motion in a fluid, the one degree of freedom (1-DOF) method was applied. In the present study, the steady-state and dynamic CFD simulations of the Savonius rotor are adopted to contribute to the validation elements of the VAWT models that are used. The dynamic study allows the investigation of the rotor behavior and the relation between velocity, pressure, and vorticity fields in and around the rotor blades. The flow fields generated by the rotation of the Savonius rotor were investigated in the half revolution period of the rotor angle  from 0 ı to 180 ı . In this range of  , the focus is on generating and dissipating vortices. Copyright © 2013 John Wiley & Sons, Ltd. NOMENCLATURE

Enhancement of Savonius wind rotor aerodynamic performance: a computational study of new blade shapes and curtain systems

“…This numerical model takes advantage of resolving the angular velocity of the rotor as a time-varying variable, according to the unsteady aerodynamics of the Savonius rotor. This is a key point since performing unsteady simulations by means of coupling fluid-flow equations with the rigid-body ones allows to achieve a proper and reliable reconstruction of the dynamic behaviour of the Savonius wind rotor [19]. The same computational model has been also applied to investigate a more complex flow field, such as the case of a Savonius rotor with conventional semi-cylindrical blades, provided with an innovative conveyor-deflector curtain system, selforienting relative to the wind direction.…”

Experimental Study of the Performance of a Novel Vertical-Axis Wind Turbine

“…Zanon et al [15] solved potential flow equations in conjunction with integral boundary layer equations formulated for VAWT rotors, using a semi-inverse iterative algorithm. From their simulations, they inferred that VAWTs can be designed to avoid the occurrence of dynamic stall resulting from blade-vortex interaction in the downward part of rotor rotation during gusts and normal operation, and even at low tip-speed ratios [16]. Scheurich et al [14] implemented a CFD scheme based on the vortex transport model (VTM).…”

“…The governing momentum equation is expressed in terms of the vorticity and velocity and is the result of finding the curl of the velocity and pressure-based N-S momentum equation. In their work on the steady-state and dynamic simulations of Savonius rotors, Jaohindy et al [16] found that the best approximations of the static torque coefficient, the dynamic torque coefficient and the power coefficient were obtained using the shear stress transport-k-ω model rather than the k-ε turbulence model. At startup, dynamic torque coefficient curves of a Savonius rotor oscillate around fixed values in polar coordinates [16].…”

“…In their work on the steady-state and dynamic simulations of Savonius rotors, Jaohindy et al [16] found that the best approximations of the static torque coefficient, the dynamic torque coefficient and the power coefficient were obtained using the shear stress transport-k-ω model rather than the k-ε turbulence model. At startup, dynamic torque coefficient curves of a Savonius rotor oscillate around fixed values in polar coordinates [16]. There is a significant difference between simulated and experimental values of the power coefficient of a DVAWT at high tip-speed ratios, even though simulation and experimental power coefficient values follow the same trend as the tip-speed ratio varies [17].…”

Numerical Study of Savonius Wind Turbine with Fluid-Rotor Interactions

“…Numerical steps of Savonius wind turbine simulation in 1-DOF DBFI method are applied by using polyhedral mesh [7]. In the research, 2 blades straight Savonius is simulated in STAR CCM+ program.…”