Parametric optimisation of a vertical axis hydrokinetic turbine with shallow water application

Ranabhat, Bikash 2022. Parametric optimisation of a vertical axis hydrokinetic turbine with shallow water application. PhD Thesis, Cardiff University. Item availability restricted.

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Abstract

There is a growing interest in harnessing hydroelectricity sourced from shallow and slow-moving water currents, as many countries are aiming to end their reliance on fossil fuels and investing in renewable energy. With an aim of utilising such resources, this thesis investigates the early-stage design optimisation of a flapping blade vertical axis hydrokinetic turbine named CarBine. Parameters for optimisation included varying blade shape, blade numbers and the flow environment of the working fluid, including inflow speed and flow depth. Physical model testing data are acquired from the test rig and analysed for their uncertainties. Power coefficient vs tip speed (Cp-λ) curves were developed as a measure of model performance. The results show that a four-armed eight bladed CarBine with flat plate blades performed optimally (Cpmax/λmax = 0.146/0.409) at U∞ = 0.90 m/s. Its performance is enhanced to Cpmax/λmax = 0.171/0.623, when the blades are replaced by NACA 0018 hydrofoils. The power coefficients are also found to be highly sensitive to blockage effect. The performance results are Reynolds (ReD) dependent for ReD < 106 , with further tests required for a fully conclusive results beyond this value of ReD. A positive correlation between the performance and the flow depth cover over the model is observed until it surface-pierced the free water surface. The numerical modelling study devises a quasi-steady approach of CFD to deal with the two degrees of rotational freedom for CarBine at a lower cost of computation. 3D models are developed using the SST turbulence model and results are assessed for model uncertainties. The outcomes are then validated against the physical testing results. It is found that the computed results are in good agreement with the physical test results except for models with NACA 0018 blades. This approach of CFD modelling has provided an insight into its effectiveness for the two degrees of rotational freedom in CarBine. The research outcomes have revealed the optimum CarBine configuration with blade numbers and blade shape. The lower tip speed ratio (0.15 ≤ λ ≤ 0.70) characterises CarBine as a slow-rotating device with its possible application in ecologically sensitive rivers and estuaries for hydroelectricity generation.

Item Type:	Thesis (PhD)
Date Type:	Completion
Status:	Unpublished
Schools:	Engineering
Uncontrolled Keywords:	1) Hydrokinetic turbine 2) Parametric Optimisation 3) Flapping blade 4) Shallow Water 5) Quasi steady approach of CFD 6) Modified Savonius turbine
Date of First Compliant Deposit:	2 February 2024
Last Modified:	02 Feb 2024 16:37
URI:	https://orca.cardiff.ac.uk/id/eprint/166109

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