Comparison of Sliding and Overset Mesh Techniques in the Simulation of a Vertical Axis Turbine for Hydrokinetic Applications

Abstract

The application of Computational Fluid Dynamics (CFD) to energy-related problems has increased in the last decades in both renewable and conventional energy conversion processes. In recent years, the application of CFD in the study of hydraulic, marine, tidal, and hydrokinetic turbines has focused on the understanding of the details of the complex turbulent flow and also in improving the prediction of the performance of these devices. There are several complexities involved in the simulation of Vertical Axis Turbine (VAT) for hydrokinetic applications. One of them is the necessity of a dynamic mesh model. Typically, the model used in the simulation of these devices is the sliding mesh technique, but in recent years the fast development of the overset (also known as chimera) mesh technique has caught the attention of the academic community. In the present paper, a comparison between these two techniques is done in order to establish their advantages and disadvantages in the two-dimensional simulation of vertical axis turbines. The comparison was done not only for the prediction of performance parameters of the turbine but also for the capabilities of the models to capture complex flow phenomena in these devices and computational costs.

Effects of upstream and downstream ramp on flow characteristics over a cylindrical weir

“…This study contributes to a variety of engineering fields such as cars designs and some hydrokinetic turbines. In addition, CFD techniques have proven their efficiency in simulating the flow and representing it very close to reality (Memon et al, 2012;Yuanyuan et al, 2012;Schleicher et al, 2013;Manafpour and Ebrahimnezhadian, 2019;Tokyay and Kurt, 2019;Lopez Mejia et al, 2021).…”

“…In order to acquire the discharge, qw, in the experimental flume, a rectangular non-contractile sharp crested weir of 10 cm height and the Rehbock equation (Humberto, 2009) were employed. The rectangular weir was placed at the end of the channel.…”

ExaWind: Open‐source CFD for hybrid‐RANS/LES geometry‐resolved wind turbine simulations in atmospheric flows

“…For simulating the near-body turbine fluid dynamics, the k À ω SST model (( 23) and ( 24)) was used to model the turbulence. The far-field turbulence is modeled using the LES model discussed in (18). The outerdomain boundary conditions imposed are slip along the top boundary, zero pressure at the outflow boundaries, and wall boundary conditions (( 19) -( 22)) along the bottom boundary.…”

“…To simulate the operation of turbines in the ABL, AMR-Wind only solves the one-equation model (18), while Nalu-wind solves ( 23) and ( 24)…”

“…From an engineering perspective, the primary challenge is to strike a balance between manageable computational cost and the accuracy requirements. The primary approaches to achieving geometry‐resolved wind farm simulations use either sliding grids 17–19 or overset grids 20–22 to resolve flow past the turbine geometry. During operation, turbine controllers can often cause the blade to rotate about its pitch axis or about the tower axis (yaw) resulting in rotor movement outside the turbine plane, rendering sliding‐grid frameworks impractical.…”