Numerical Simulation of the Lux Vertical Axis Wind Turbine
Date
2019-04-16
Authors
Journal Title
Journal ISSN
Volume Title
Publisher
ORCID
0000-0003-0227-0832
Type
Thesis
Degree Level
Masters
Abstract
Wind energy can be characterized as a cheap, clean, and renewable energy source that is absolutely
sustainable. With increasing demand for wind energy, it is productive to investigate the structural and operational
factors that undermine the proficiency and the characteristic performance of the wind turbine. Of
paramount importance to efficient wind energy generation is the aerodynamics of the wind turbine blades.
The aerodynamic factors, such as drag, airfoil pro files, and wake interactions that often reduce the performance of the wind turbines, can be investigated through computational mathematics using computational fluid dynamics (CFD). CFD offers basic techniques and tools for simulating physical processes and proffers
important insights into the
ow data, which are demanding and costly to measure experimentally.
In this thesis, we develop a simulation model in an open-source software package called OpenFOAM to investigate the performance characteristics of the Lux Vertical Axis Wind Turbine (VAWT). The Lux VAWT has a simpler design than its horizontal counterparts; however, its performance is affected by the unsteady
aerodynamic due to a complex flow field. The turbulent flow field is governed by the incompressible Navier-
Stokes equations. Simulations are carried out with an unsteady incompressible and dynamic
flow solver, PimpleDyMFoam, on an unstructured mesh surface of the Lux VAWT geometry. The computational domain
includes both the stationary and rotating mesh domains to accommodate the rotating motion of the
turbine blades and the free-stream zone. The arbitrary mesh interface is applied as a boundary condition for the patches between the two domains to enable computation across disconnected but adjacent mesh domains.
Meshing was done using two separate meshing tools, snappyHexMesh and ANSYS Mesher. The
snappyHexMesh tool offered the most
flexible and effective control over the mesh generation and quality. In
order to derive the maximal power output from the Lux VAWT simulations, the Unsteady Reynolds Averaged Navier--Stokes (URANS) equations are solved with different time-stepping methods; the objective is to reduce
the computational costs. While attempting to reduce the numerical diffusion from the non-transient terms
of URANS, a stabilized trapezoidal rule with a second-order backward differentiation formula (TR--BDF2) time-stepping method was implemented in OpenFOAM.
As a result, the transient aerodynamic forces of the blades, the torque, and power output are evaluated.
The findings demonstrate that most of the transient aerodynamic force is generated along the axis of rotation of the rotor during one complete revolution. Similarly, the computations indicate that the BDF2 method results in the least computational cost and predicts a turbine power that is somewhat comparable to the
experimental results. The difference between the simulation results and the experimental data is attributed partly to the pressure fluctuations on the turbine blades due to the mesh topology.
Description
Keywords
CFD, Lux VAWT, OpenFOAM, FVM, Discretization, Meshing, Simulation
Citation
Degree
Master of Science (M.Sc.)
Department
Mathematics and Statistics
Program
Mathematics