Year

2023

Degree Name

Doctor of Philosophy

Department

School of Mechanical, Materials, Mechatronic and Biomedical Engineering

Abstract

Duct augmented horizontal axis water current turbine (DAHAWCT) has emerged as a promising decentralized renewable power technology suitable for rural communities in remote regions with access to waterways. However, its application is often limited in small waterways due to the size of the device and its power generation capabilities. Therefore, it is necessary to develop a turbine design that can effectively harness the available energy in such constrained environments.

The role of the duct in a DAHAWCT is to augment the mass flow hence improving the coefficient of performance. The extent of flow augmentation depends on geometrical parameters such as duct length, angle, profile, and duct-turbine interaction. These parameters have been extensively studied in the literature on wind and water domains. However, there is still no consensus on which of these parameters are significant, and our understanding of their effects on turbine performance is limited.

In the deployment of turbines in small channels, the placement is a crucial factor in maximizing the utilization of kinetic energy available in the water current. The installation of turbines near the water surface is advantageous due to the reduced velocity caused by the shear flow near the channel bed having a minimum effect on the turbine. However, it is important to note that the maximum available energy of the water current is not exactly at the surface, but slightly below it due to the shear flow effect near the surface and the secondary flow effect. Moreover, other complex phenomena must also be considered that can affect turbine performance in such small open channels. The interaction of the turbine with the surroundings, such as channel walls, both sides, bed, and water surface, can occur when a water turbine is deployed in a small waterway. This phenomenon can affect turbine performance. The presence of channel walls in a turbine creates an additional confinement that enables the flow between the wake of the turbine and the walls, commonly referred to as the bypass flow to accelerate, a phenomenon known as the blockage effect. This phenomenon has been found to contribute to the acceleration of the flow through the turbine. This acceleration can increase the power generated, relative to an unconfined environment. As an artificial wall, the free surface and its deformation can also add the flow confinement effect. However, the free surface can also have an undesirable effect on turbine performance. The surface can limit wake expansion, hence the energy extraction on the turbine decreases. Nonetheless, much about DAHAWCT still needs to be explored since most studies of the environmental interaction effect on turbine performance are generally for the bare turbine.

In this thesis, the effect of duct geometrical parameters on ducted turbine performances is studied, together with the performance characteristic of the DAHAWCT in a small square channel with an aspect ratio of 1, especially the interaction of the turbine with the water surface. A developed mathematical model is utilized to investigate the effects of the duct geometrical parameters. Meanwhile, computational fluid dynamics (CFD) simulation and experiment are utilized to study the free surface effect of the DAHAWCT's performance. The selected duct for this investigation is a short duct with three proposed installations; the blade tip 0.05D, 0.3D and 1D below the water surface.

FoR codes (2008)

091305 Energy Generation, Conversion and Storage Engineering

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Unless otherwise indicated, the views expressed in this thesis are those of the author and do not necessarily represent the views of the University of Wollongong.