A Detailed Analysis of the Centrifugal Pumping Phenomenon in HAWTs Through the Use of CFD Models

The centrifugal pumping, also known as rotational augmentation, is a 3D phenomenon which is of utmost importance in the aerodynamics of HAWTs. A clear physical explanation about the rise and development of this phenomenon is still missing in the scientific literature. Indeed, several empirical approaches have been proposed for taking into account the rotational effects inside 1D design codes. However, at the state, these approaches lead to results, which are quite different amongst each other. In the present paper the authors propose a thorough analysis of the rotational augmentation in an experimental micro HAWT. For this purpose, previously validated CFD 3D models were used. These models were developed using ANSYS Fluent solver with a calibrated RANS transition turbulence model. The post-processing analysis, presented in this paper, demonstrates that the strong increase of the aerodynamic forces is mainly due to the presence of a strong helical vortex which develops in the inner part of the blade. This vortex depressurizes the entire separated layer and it is found to be due to the combined effect of Coriolis and centrifugal forces along with the span-wise pressure gradient. Moreover, the essential contribution of the radial component of the Coriolis force was evidenced in contrast with the fact that this component is usually neglected.