Weichao Shi

Flow separation impacts on the hydrodynamic performance analysis of a marine current turbine using CFD

Although there are different strategies to control the operation of marine turbines, the so-called ‘stall-regulated strategy’ is one of the most widely used and mature control strategies. Since the stall phenomenon is closely related to flow separation around the turbine blades the treatment of this separation requires great care during the design and performance analysis of turbines when using computational fluid dynamics (CFD). This study investigates appropriate methodologies and approaches to simulate the hydrodynamic performance of horizontal marine turbines with a specific emphasis on the flow separation phenomena. The well-known viscous flow solver ANSYS-CFX was employed as the main CFD code to predict the power extraction coefficient of these turbines. The investigations were carried out by using both numerical and experimental methods applied on tidal stream turbine models tested in the Emerson Cavitation Tunnel of Newcastle University, UK and the circulating water channel of Harbin Institute of Technology, China. The measured power extraction coefficients generally agreed well with the numerically predicted ones except for one of the models with the lower pitch angle which displayed large discrepancies over the entire operating range. The detailed flow analyses from the CFD studies with this turbine and other model at higher pitch angles revealed that large-scale detached vortices developed downstream of the model with the lower pitch angle may have contributed to this large discrepancy. The study therefore draws attention to the importance of the combined use of the CFD and model test-based approaches in the design and performance analysis of marine turbines.

Numerical Simulation of a Tidal Turbine Based Hydrofoil With Leading-Edge Tubercles

The tubercles along the leading edges of the humpback whale flippers can provide these large mammals with an exceptional maneuverability. This is due to the fact that the leading-edge tubercles have largely a 3D benefit for the finite hydrofoils, which can maintain the lift, reduce the drag and delay the stall angle. Newcastle University launched a series study to improve a tidal turbine’s performance with the aid of this concept. This paper presents a numerical simulation of the tested hydrofoil, which is representative of a tidal turbine blade, to investigate the flow around the foil and also to numerically model the experiment. This hydrofoil was designed based on an existing tidal turbine blade with the same chord length distribution but a constant pitch angle. The model tests have been conducted in the Emerson Cavitation Tunnel measuring the lift and drag. The results showed that the leading-edge tubercles can significantly improve the performance of the hydrofoil by improving the lift-to-drag ratio and delaying the stall. By applying Shear Stress Transport (SST), Detached Eddy Simulation (DES) and Large Eddy Simulation (LES) via using the commercial CFD solver, Star-CCM+, the tested hydrofoil models were simulated and more detailed flow information has been achieved to complement the experiment. The numerical results show that the DES model is in close agreement with the experimental results. The flow separation pattern indicates the leading-edge tubercles can energize the flow around the hydrofoil to keep the flow more attached and also separate the flow into different channels through the tubercles.

The Hydrodynamic Analysis of Propeller Based on ANSYS-CFX

In this paper, the open water performance of a pod propeller in the viscous flow fields is numerically simulated by the Computational Fluid Dynamics (CFD) method. Based on the coordinate transformation formula for transforming the local to the global coordinate, mathematical model of a propeller is created. Thrust and torque coefficients corresponding to different advance coefficients of the model are calculated by ANSYS-CFX with three different turbulence models. The pressure distributions on the blade surface are also presented. Comparisons show that experimental results and numerical results agree well, with SST k-ω and RNG k-ε more accurate than the standard k-ε.

Learning from humpback whales for improving the energy capturing performance of tidal turbine blades

This paper summarizes a project on the potential of further improving the performance of horizontal axis tidal turbines via the application of leading-edge tubercles to the turbine blades inspired by humpback whales. Within this framework, a wide variety of experimental investigations, supported by numerical studies, have been conducted.

Similarity Laws and Model Test Approaches to Determine Hydrodynamic Performance of a Marine Turbine

The paper presents the methodologies and approaches used in a Cavitation Tunnel or any other circulation channel to investigate the power extraction performance of a marine stream turbine. The paper first introduced model test similarity laws used in the Emerson Cavitation Tunnel (ECT) of Newcastle University to test a marine turbine in marine propeller cavitation tunnel; then based on these similarity laws to investigate the power extraction performance of a marine turbine in different approaches to control the rotation speed, namely: Torque Control and Rotation-speed control. A comparison was made by the tested experimental results. Torque Control is referred to the speed control strategy of using a generator to absorb the torque building up from the stream, on the other hand Rotation-speed control is to use motor to control rotation speed of the turbine. It indicates that both methods can be employed to investigate the hydro performance of marine stream turbine, with wider range of TSR can Rotation-speed Control test.