2D Numerical Simulations of Blade-Vortex Interaction in a Darrieus Turbine

Abstract

The aim of this work is to provide a detailed two-dimensional numerical analysis of the physical phenomena occurring during dynamic stall of a Darrieus wind turbine. The flow is particularly complex because as the turbine rotates, the incidence angle and the blade Reynolds number vary, causing unsteady effects in the flow field. At low tip speed ratio, a deep dynamic stall occurs on blades, leading to large hysteresis lift and drag loops (primary effects). On the other hand, high tip speed ratio corresponds to attached boundary layers on blades (secondary effects). The optimal efficiency occurs in the middle range of the tip speed ratio where primary and secondary effects cohabit. To prove the capacity of the modeling to handle the physics in the whole range of operating condition, it is chosen to consider two tip speed ratios (λ=2 and λ=7), the first in the primary effect region and the second in the secondary effect region. The numerical analysis is performed with an explicit, compressible RANS k-ω code TURBFLOW, in a multiblock structured mesh configuration. The time step and grid refinement sensitivities are examined. Results are compared qualitatively with the visualization of the vortex shedding of Brochier (1986, “Water channel experiments of dynamic stall on Darrieus wind turbine blades,” J. Propul. Power, 2(5), pp. 445–449). Hysteresis lift and drag curves are compared with the data of Laneville and Vitecoq (1986, “Dynamic stall: the case of the vertical axis wind turbine,” Prog. Aerosp. Sci., 32, pp. 523–573).

3D CFD Analysis of a Vertical Axis Wind Turbine

“…Ferreira et al [22] use detached eddy simulation (DES) focusing on 2D dynamic stall and validate the results with particle image velocimetry data. It is to be noted that in the Darrieus-type VAWT, a cyclic phenomenon of dynamic stall and vortex separation is present [8,22,23]. Amet et al [23] provided a detailed numerical analysis of the physical phenomena that occur during dynamic stall where the compressible RANS κ − ω model and multi-block mesh structure were used.…”

“…It is to be noted that in the Darrieus-type VAWT, a cyclic phenomenon of dynamic stall and vortex separation is present [8,22,23]. Amet et al [23] provided a detailed numerical analysis of the physical phenomena that occur during dynamic stall where the compressible RANS κ − ω model and multi-block mesh structure were used. Furthermore, studies of dynamic stall show that the Shear Stress Transport (SST) κ − ω turbulence model performs better than the κ − ω model, as reported by Ekaterinaris and Platzer [24] and Qian et al [25].…”

Flow characteristics on the blade channel vortex in the Francis turbine

“…Zhang Hongming et al present numerical simulation of blade channel vortex in a low head Francis turbine using OpenFoam code, the simulation results have shown that using cavitation model to analyze blade channel vortex is very effective [3]. A 2D numerical simulations of blade-vortex interaction in a darrieus turbine is given for instance by Amet E. et al [4], and the results are compared qualitatively with the visualization of the vortex shedding of Brochier. The occurrence of the blade channel vortex between the turbine runner blades is discussed depending on the mechanism calculation, and the frequency of vortex cavity is analyzed form Chen jinxia et al [5] 2.…”

Comparative assessment of the harmonic balance Navier–Stokes technology for horizontal and vertical axis wind turbine aerodynamics

“…The periodic nature of the flow past the blades is due to the cyclic variation (every rotor revolution) of modulus and direction of the relative velocity perceived by their airfoils [4], and also the interactions between the blades traveling in the downwind region of the rotor and the vorticity shed by the blades in the upwind rotor region [5]. These complex 125 unsteady flow patterns are further complicated by the occurrence of dynamic stall [6] over a significant portion of the entire turbine operating range [5].…”

“…The report shows that the agreement between NS CFD analysis and measured data is substantially better than that between low-fidelity analyses and measured data, as expected. Early assessments of the NS CFD technology for Darrieus rotor aerodynamics, aiming primarily at thoroughly investigating the complex fluid mechanics of these machines, include the articles [16,5,6].…”