Experiences in Modeling Wind Loading on Photovoltaic (Pv) Modules and Solar Collectors

Abstract eng:
The aerodynamic characteristics of finite aspect ratio flat plates at moderate to high Reynolds numbers remains poorly investigated, despite the relatively simple geometry. This shortcoming is particularly surprising given such important applications as wind loading on roof appendages and solar panels. Previous studies focused on special cases of infinite aspect ratio (2D) plates [1, 4]. This research addresses the aerodynamics of flat plates at high angles of attack and Reynolds numbers, to estimate the wind loading on photovoltaic (PV) modules and solar collectors in an attempt to reduce their installation costs. The flow around a single PV module is modeled using Large Eddy Simulation as implemented following Rodi et al. [2]. The results are analyzed for the near and far wake structures, vortex interactions and their effect on instantaneous aerodynamic forces acting on the plate. Special consideration is given to the challenge of modeling the thin shear layers. This study investigates the flow around a thin rectangular flat plate of aspect ratio 0.607 normal to the flow at a Reynolds number of 1.6x106. The aim is to obtain accurate prediction of drag, Strouhal number, etc., while minimizing computational effort. Attention is brought on the influence of mesh density and near-wall y+ criterion in predicting the shear layer intensity, vorticity generation and diffusion and thus its impact on near-wake formation and far-wake evolution. The grid sensitivity study shows that the resolution of the shear layer over the thin plate edges is critical. A strong coupling exists between the plate lee and edge separation region, strongly modifying the rate of vorticity generation (circulation flux) and thus the intensity of wake vortices. For example, poor resolution leads to suppression of vortex shedding. This coupled behavior is a major challenge to CFD simulations and contrasts with that for very thick plates, where the pressure behind the separation point fluctuates slightly [4]. Resolved CFD results show good agreement with experiment. The wake velocity spectra evidence vortex shedding at a Strouhal number of 0.158, compared to 0.16 reported in [1]. The mean drag coefficient is found to be 1.209 while the mean lift coefficient is negligible, which agrees with those results from a parallel experimental study [1, 3]. In the wake, the vortices generated on the longer edges of the plate are shed obliquely from the plate surface due to induction by the secondary vortices formed on the short edges of the plate. They create a chain-shaped vortex bundle behind the plate, advecting in the wake. Since solar collectors and PV modules are normally installed in large arrays, these findings are significant in understanding wake interference effects from neighboring structures.

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