Hydrodynamic analysis of a ducted, open centre tidal stream turbine using blade element momentum theory

Abstract

This paper analyses two different configurations of horizontal axis Tidal Stream Turbines (TST) using a Blade Element Momentum Theory (BEMT) model. Initially, a 'conventional' 3 bladed and bare turbine is assessed, comparing predictions of turbine power and thrust forces against experimental measurements and existing literature. Excellent agreement is seen, increasing confidence in both the implementation of the theory into the code and the applicability of the method to represent the turbine physical behaviour. The focus of the paper lies on the analysis of a ducted and open centre turbine, where the BEMT model is adapted to take into account the increased mass flow through a duct (or augmenter). This is based on an analytical framework, where empirical expressions are devised based on Computational Fluid Dynamics (CFD) studies to approximate the inlet efficiency, diffuser efficiency and base pressure. This is applied to a bi-directional ducted case, where calibration of certain duct parameters is performed through modelling the OpenHydro device and comparing results with blade resolved CFD studies. The results are validated with a comparison of this ducted BEMT model to a coupled CFD blade element model (RANS BEM). Both models align very closely for most Tip Speed Ratios, capturing the peak power at optimal conditions. Slight over predictions for thrust and power are seen at higher TSRs, where higher velocities are seen at localised elements around the hub. This is due to the model limitations in fully replicating the complex flow interactions in and around the hub and open centre. The presented approach has the benefit of significantly lower computational requirements, in the order of CPU-minutes, rather than CPU-days required for RANS BEM, allowing practicable engineering assessments of turbine performance and reliability

Investigation of the Possibilities to Improve Hydrodynamic Performances of Micro-Hydrokinetic Turbines

“…The analytical model for ducted turbines coupled with numerical methods is presented in [19]. The ducted Blade Element Momentum Theory model is applied to a bi-directional ducted tidal turbine in [20] to benefit from significantly lower computational requirements when compared to the RANS-BEM approach. The BEM model is adopted for the design of diffuser-augmented hydro turbines in [21] by inserting the effect of diffuser efficiency into the BEM model.…”

Studi Eksperimental Performance Kavitasi Waterjet Propulsi

“…Waterjet propulsion sistem memiliki tiga komponen utama: inlet, pump and nozzle [11] [14]. Water jet propulsor termasuk dalam pompa aksial yang terdiri dari sudu-sudu impeller dan sudu-sudu pengarah [14] setiap penampang secara teoritis dihitung dengan pendekatan aliran turbulen yang diekspresikan ulang oleh Creswell et al [18] dan Steven Alshop et al [19], yaitu :…”

The effects of shape and size on duct-augmented horizontal axis turbine performance

“…The duct-rotor interaction can add axial momentum on the boundary layer on the internal flow near the duct wall and thereby delay the onset of flow separation with the beneficial consequence of increasing the flow augmentation under loaded condition (Hansen et al, 2000;Oman et al, 1977;Phillips, 2003;Shives and Crawford, 2011). A few studies (Allsop et al, 2017;Palmer et al, 2017;Shives and Crawford, 2011) have accounted for the influence of the duct-rotor interaction by incorporating empirical expressions (obtained from an experiment) that link the rotor loadings and the augmentation parameters into their models. However, the developments of such an empirical model require many experimental or computational data to be generated for specific duct design.…”