CFD study of blockage ratio and boundary proximity effects on the performance of a tidal turbine

Abstract

The effects of blockage ratio and boundary proximity on tidal turbine performance are quantified in this study using computational fluid dynamics (CFD). Reynold averaged Navier-Stokes (RANS) equations are solved using the commercial CFD code ANSYS CFX. Steady-state analyses are performed using a rotating frame of reference technique, and a shear stress transport turbulence model is used. Results from the numerical model are validated with experimental data. RANS CFD simulations are performed over tip speed ratios (TSRs) from 1 to 9. The simulation-based performance curve approximately match the experimental performance curve, with errors ranging from 4 to 9%. Blockage ratios from 0.02 to 0.19 are evaluated for a constant depth of two rotor diameters to study the effect of blockage on turbine performance. Results show that shaft power increased by 13 and 47% for TSRs of 5.11 and 9.05, respectively, when the blockage ratio increased from 0.02 to 0.19. Additionally, for these TSRs and blockage ratios the turbine thrust increased by 7 and 10%. The presence of a boundary layer resulted in a calculated thrust increases between 1.6 and 2.3% and power between 2.7 and 3.5% for the entire range of evaluated blockage ratios. Nomenclature A swept area of the rotor (m 2) C P turbine power coefficient C T turbine thrust coefficient P mechanical power generated by the turbine, W R turbine radius (m) V mean upstream flow velocity (m/s) Y + dimensionless wall distance ω blade tip angular velocity (rad/s) ρ density of water, (kg/m 3) programme developed a TCT design called RM1. This is a nonproprietary RM developed as a study object for open-source research [19]. Experiments using RM1 were conducted in the open channel of the University of Minnesota's St. Anthony Falls Laboratory (UMN-SAFL) [19]. These high-resolution laboratory

The Effects of a Morphed Trailing-Edge Flap on the Aeroacoustic and Aerodynamic Performance of a 30P30N Aerofoil

“…The C-shaped computational domain boundaries are located at 13 chord lengths in front, above, and below the aerofoil, and 25 chord lengths behind. The boundaries perpendicular to the flow can generate a blockage ratio of around 2% according to past research (e.g., Badshah et al [12]). In the present work, it was found that when blockage is below 10% there is little or no effect on results, but when blockage increases above 10%, rapid changes in results occur.…”

“…The boundary conditions used for the flow domain were as follows: the front and bottom boundaries were set as velocity inlets with specified velocity components and standard mean sea level values for pressure and temperature; turbulent intensity was set at 0.25% (similar to what was used by Jawahar et al [4]); solid The C-shaped computational domain boundaries are located at 13 chord lengths in front, above, and below the aerofoil, and 25 chord lengths behind. The boundaries perpendicular to the flow can generate a blockage ratio of around 2% according to past research (e.g., Badshah et al [12]). In the present work, it was found that when blockage is below 10% there is little or no effect on results, but when blockage increases above 10%, rapid changes in results occur.…”

Numerical investigation of inter‐blade cavitation vortex for a Francis turbine at part load conditions

“…The finite volume method integrated inside ANSYS CFX is used to carry out the numerical simulations. The unsteady Reynolds-Averaged Navier-Stokes (URANS) equation is closed by the two-equation shear stress transport (SST k-ω) model [27][28][29] with automatic near-wall treatment that automatically switches from wall-functions to a low-Re near-wall formulation as the mesh is refined. The SST k-ω turbulence model has been embedded into the commercial code ANSYS CFX and, thus, is convenient to be selected to carry out the simulations in this study.…”

Coupled Fluid-Structure Interaction Modelling of Loads Variation and Fatigue Life of a Full-Scale Tidal Turbine under the Effect of Velocity Profile

“…This model has the capability of gradually changing from the standard K − ω model in the inner region of the boundary layer flow to a high Reynolds-number version of the K − ε model in the outer part of the boundary layer so that advantages of both models can be utilized. The SST model is known to predict the onset and amount of flow separation under adverse pressure gradient with better convergence [42] and has been successfully used to model the near wake of tidal turbines [43][44][45]. An SST model with automatic wall function is also utilized for the work presented in this paper.…”