Aidan Wimshurst - Academia.edu (original) (raw)
Papers by Aidan Wimshurst
On the outboard sections of horizontal axis rotor blades (that are not enclosed within a duct or ... more On the outboard sections of horizontal axis rotor blades (that are not enclosed within a duct or shroud), vorticity is shed into the wake of the rotor. The shed vorticity induces a downwash at the rotor plane and spanwise flow accelerations along the blade, which causes the blade loading to drop off as the tip is approached. These tip flow effects are currently not adequately accounted for by reduced order rotor models (such as the blade element momentum and actuator line methods) which are frequently used to represent wind and tidal turbine rotors in large simulations. Hence, the rotor thrust and torque may be considerably over-predicted by these models if they are not corrected appropriately for tip flow effects. In this thesis, the tip loss mechanism experienced by both wind and tidal turbine rotor blades is examined directly in a series of simulations, using computational fluid dynamics. Two different correction methods that can account for tip flow effects are then presented an...
Blade boundary layer resolved simulations of two different tidal turbine rotor designs are presen... more Blade boundary layer resolved simulations of two different tidal turbine rotor designs are presented. The first rotor was designed to achieve its maximum power coefficient at tip speed ratio of 5 in unblocked conditions and the other was designed to achieve its maximum power coefficient at a tip speed ratio of 5 but at a higher local blockage ratio of 0.197. Both designs achieve their maximum power coefficient close to a tip-speed-ratio of 5 for which they were originally designed. In addition, the maximum power coefficients for both rotors operating in an unblocked domain compare favourably with full-scale deployed horizontal axis tidal turbines. With increasing blockage ratio, it is observed that greater power coefficients can be achieved, 0.62 to 0.63, but that this requires an increased thrust. The blockage designed rotor can provide this extra thrust naturally , primarily as it is designed with greater solidity. In contrast, the rotor designed for unblocked flow must be made to operate at a significantly higher tip-speed-ratio to achieve the required thrust.
Wind Energy, 2017
Low order rotor models such as the actuator line method are desirable as an efficient method of c... more Low order rotor models such as the actuator line method are desirable as an efficient method of computing the large range of operating and environmental conditions, required to design wind and tidal rotors and arrays. However, the integrated thrust and torque predictions for each rotor are dominated by the blade loading on the outboard sections, where three-dimensional (3D) effects become increasingly significant, and the accuracy of the reduced order methods remains uncertain. To investigate the accuracy of the spanwise blade loading on an individual rotor, actuator line and blade boundary layer resolved computations of the Model Rotor Experiments in Controlled Conditions (MEXICO) rotor are presented. The high fidelity blade-resolved simulations give good agreement with measured pressure coefficient and particle image velocimetry data. Alternative lift and drag polars are extracted from the 3D simulated flow fields as a function of radial position. These are then used as replacemen...
Computations of the blade loading and the local flow field around the Model Rotor Experiments In ... more Computations of the blade loading and the local flow field around the Model Rotor Experiments In Controlled Conditions (MEXICO) rotor are presented using an actuator line method, implemented within the open source code OpenFOAM. The nacelle and near wake mesh refinement are shown to have little influence on the computed blade loads but a significant impact on the near wake flow field. In addition, the blade loads and near wake flow field calculated with 3 different distributions of the Gaussian smearing parameter ǫ are compared with experimental measurements. Local chord and lift coefficient scaled smearing distributions are shown to yield a significant improvement in the representation of the computed tip vortices and also a small improvement in the blade loading prediction, when compared with a spanwise constant smearing distribution. Despite these improvements in performance prediction, the performance of the rotor is shown to be more strongly influenced by the tip correction fac...
On the outboard sections of horizontal axis rotor blades (that are not enclosed within a duct or ... more On the outboard sections of horizontal axis rotor blades (that are not enclosed within a duct or shroud), vorticity is shed into the wake of the rotor. The shed vorticity induces a downwash at the rotor plane and spanwise flow accelerations along the blade, which causes the blade loading to drop off as the tip is approached. These tip flow effects are currently not adequately accounted for by reduced order rotor models (such as the blade element momentum and actuator line methods) which are frequently used to represent wind and tidal turbine rotors in large simulations. Hence, the rotor thrust and torque may be considerably over-predicted by these models if they are not corrected appropriately for tip flow effects. In this thesis, the tip loss mechanism experienced by both wind and tidal turbine rotor blades is examined directly in a series of simulations, using computational fluid dynamics. Two different correction methods that can account for tip flow effects are then presented an...
Blade boundary layer resolved simulations of two different tidal turbine rotor designs are presen... more Blade boundary layer resolved simulations of two different tidal turbine rotor designs are presented. The first rotor was designed to achieve its maximum power coefficient at tip speed ratio of 5 in unblocked conditions and the other was designed to achieve its maximum power coefficient at a tip speed ratio of 5 but at a higher local blockage ratio of 0.197. Both designs achieve their maximum power coefficient close to a tip-speed-ratio of 5 for which they were originally designed. In addition, the maximum power coefficients for both rotors operating in an unblocked domain compare favourably with full-scale deployed horizontal axis tidal turbines. With increasing blockage ratio, it is observed that greater power coefficients can be achieved, 0.62 to 0.63, but that this requires an increased thrust. The blockage designed rotor can provide this extra thrust naturally , primarily as it is designed with greater solidity. In contrast, the rotor designed for unblocked flow must be made to operate at a significantly higher tip-speed-ratio to achieve the required thrust.
Wind Energy, 2017
Low order rotor models such as the actuator line method are desirable as an efficient method of c... more Low order rotor models such as the actuator line method are desirable as an efficient method of computing the large range of operating and environmental conditions, required to design wind and tidal rotors and arrays. However, the integrated thrust and torque predictions for each rotor are dominated by the blade loading on the outboard sections, where three-dimensional (3D) effects become increasingly significant, and the accuracy of the reduced order methods remains uncertain. To investigate the accuracy of the spanwise blade loading on an individual rotor, actuator line and blade boundary layer resolved computations of the Model Rotor Experiments in Controlled Conditions (MEXICO) rotor are presented. The high fidelity blade-resolved simulations give good agreement with measured pressure coefficient and particle image velocimetry data. Alternative lift and drag polars are extracted from the 3D simulated flow fields as a function of radial position. These are then used as replacemen...
Computations of the blade loading and the local flow field around the Model Rotor Experiments In ... more Computations of the blade loading and the local flow field around the Model Rotor Experiments In Controlled Conditions (MEXICO) rotor are presented using an actuator line method, implemented within the open source code OpenFOAM. The nacelle and near wake mesh refinement are shown to have little influence on the computed blade loads but a significant impact on the near wake flow field. In addition, the blade loads and near wake flow field calculated with 3 different distributions of the Gaussian smearing parameter ǫ are compared with experimental measurements. Local chord and lift coefficient scaled smearing distributions are shown to yield a significant improvement in the representation of the computed tip vortices and also a small improvement in the blade loading prediction, when compared with a spanwise constant smearing distribution. Despite these improvements in performance prediction, the performance of the rotor is shown to be more strongly influenced by the tip correction fac...