Hydrodynamic Performance Analysis of the Vertical Axis Twin-Rotor Tidal Current Turbine

Abstract

The goal of this manuscript is to investigate the influence of relative distance between the twin rotors on the hydrodynamic performance of the vertical axis twin-rotor tidal current turbine. Computational fluid dynamics (CFD) simulations based on commercial software ANSYS-CFX have been performed to enhance the understanding of interactions between the twin-rotors. The interactions between the twin rotors are known to have increased the power output efficiency as a whole, and it is, therefore, of great significance to undertake deeper research. The simulation results are found to be consistent with similar research results in the literature in some aspects. The simulation results of stand-alone turbine and twin rotors are compared from three different aspects, including blade forces, power output efficiency and wake flow field. The results showed that the cyclic variations tendency of blade force coefficients of twin rotors is close to that of the stand-alone turbine. The average power output efficiency of the twin-rotors system is higher than that of the stand-alone turbine. The interactions between the turbines increase the power output of the twin turbine system as whole in a wide relative distance range. However, smaller relative distance between the twin rotors does not mean a bigger power output efficiency of such a system. The power out efficiency of such a system would decrease when the relative distance between the twin rotors exceeds the critical point. The power output of the twin rotors reaches the peak value when the ratio between the two main axis distance and diameter of the turbine is around 9/4. This research can provide a reference for the design and development of larger tidal power stations.

Computational Fluid Dynamic Simulation of Vertical Axis Hydrokinetic Turbines

“…Nevertheless, the use of numerical methods associated with different algorithms of CFD to analyze complex fluid flow applications has grown in recent years due to the rapid development of computer technology. Therefore, the analysis of vertical axis hydrokinetic turbines is also being conducted using CFD simulation [18][19][20][21][22][23].…”

“…The CFD tools transform the governing equations of the fundamental physical principles of the fluid flow in discretized algebraic forms, which are solved to find the flow field values in time and space. The simulation results can be very sensitive to the wide range of computational parameters that must be set by the user; for a typical simulation, the user needs to select the variables of interest, turbulence models, computational domain, computational mesh, boundary conditions, methods of discretization, and the convergence criteria, among other simulation setup parameters [20][21][22][23]. In general, the CFD tools compute the flow field values by the equations of the fundamental physical principles of a fluid flow.…”

“…The physical aspects of any fluid flow are governed by three principles: mass is conserved, Newton's second law (momentum equation) is fulfilled, and energy is conserved. These principles are expressed in integral equations or partial differential equation (continuity, momentum and energy equation), being the most common form of momentum equation, the Navier-Stokes equations for viscous flows and the Euler equations for inviscid flows [20][21][22][23].…”

“…The hydrodynamics and performance of these turbines are governed by several parameters such as (i) the tip-speed ratio (TSR or λ ¼ Rψ=V, which is defined as the ratio between the blade tip speed and the fluid speed (V), being R the turbine radius and ψ the rpm); (ii) the aspect ratio AR ðÞ , defined as the ratio between the hydrokinetic turbine height H ðÞ and its diameter D ðÞ ; and (iii) the solidity σ ¼ Bc=2R ðÞ , which refers to the ratio of the product of the blade chord length c ðÞand the number of blades B ðÞ , the blade profiles, and the chord Reynolds number Re ¼ ρVc=μ ðÞ , where ρ and μ are the water density and viscosity, respectively. In the literature, there are several studies including experimental, numerical (computational fluid dynamics) and theoretical studies, focused on optimizing the hydrokinetic turbine geometric parameters, mainly the blade profiles, using different techniques [8,[16][17][18][19][20][21][22][23]. Figure 1 shows the typical power curves for the most common types of turbine.…”

Experimental, Numerical and Application Analysis of Hydrokinetic Turbine Performance with Fixed Rotating Blades

“…Comparing by the finite element method, MATLAB/Simulink can analyze the performance parameters of the model easily. Commercial software can perform analysis to study the performance parameters of turbines in a various engineering aspect although they raise the cost of the study [25].…”