| 1. |
- Blackmore, Tom, et al.
(författare)
-
Influence of turbulence on the drag of solid discs and turbine simulators in a water current
- 2013
-
Ingår i: Experiments in Fluids. - : Springer Berlin Heidelberg. - 0723-4864 .- 1432-1114. ; 55:1, s. 1-10
-
Tidskriftsartikel (refereegranskat)abstract
- Laboratory experiments have been used to investigate the effects of turbulence on the drag of both solid discs and porous disc turbine simulators. These discs were introduced to turbulent flows, in a gravity-fed water flume, with various levels of turbulence intensity and integral length scales. The turbulence was generated using three different grid configurations, which produced intensities and scales comparable with previous wind tunnel studies. The drag measurements were taken with discs of two different diameters and porosities with and without the upstream grids. The experimental results have demonstrated that the drag coefficients, of all the discs tested, are significantly dependent on both the turbulence intensity and integral length scale. For small integral length scales, relative to the disc, the drag coefficients converged for turbulence intensities greater than 13 %, with an increase of around 20 % in drag coefficient over the low-intensity case. Experiments with turbulence intensities of 10 % demonstrated minimum drag coefficients when the integral length scale-to-disc diameter ratio was around 50 %. Significant variations in the drag coefficient of circular bluff bodies are therefore expected when operating in turbulent flows with different characteristics.
|
|
| 2. |
- Blackmore, Tom, et al.
(författare)
-
Turbulence generation and its effect in LES approximations of tidal turbines
- 2013
-
Konferensbidrag (refereegranskat)abstract
- Tidal flows suitable for the installation of tidal stream turbines are highly turbulent with a broad range of turbulent scales, and intensities of around 10%. It is important to understand how turbulent flows affect the performance and wake profiles for the accurate prediction of the performance of single devices and arrays. Previous studies have considered the effects of turbulence intensity, but the effects of turbulent eddy size have not been investigated. This paper presents a new method for generating turbulence in large eddy simulations of uniform actuator disc rotor models. The advantage of the gridded actuator disc is that the generated turbulence may be controlled, so the effects of turbulence length scale and intensity may be investigated. Initial results show the wake recovery is faster behind a rotor generating larger turbulent length scales and intensities, with a corresponding increase in axial induction and thrust. Therefore turbines may be positioned closer together if they generate more turbulence, increasing the power output of an array for a given area, although the individual device performance may be lower. Future work will consider the effects of free-stream turbulence on the performance and wake profiles of the gridded actuator disc, and validation against experimental data.
|
|
| 3. |
- Forslund, Johan, 1985-
(författare)
-
Experimental Results of a Load-Controlled Vertical Axis Marine Current Energy Converter
- 2015
-
Licentiatavhandling (övrigt vetenskapligt/konstnärligt)abstract
- This thesis investigates the load control of a marine current energy converter using a vertical axis turbine mounted on a permanent magnet synchronous generator. The purpose of this thesis is to show the work done in the so far relatively uncharted territory of control systems for hydro kinetic energy conversion. The work is in its early stage and is meant to serve as a guide forfuture development of the control system.An experimental power station has been deployed and the first results are presented.A comparison between three load control methods has been made; a fixedAC load, a fixed pulse width modulated DC load and a DC bus voltage control of a DC load. Experimental results show that the DC bus voltage control reduces the variation of rotational speed with a factor of 3.5. For all three cases, the tip speed ratio of the turbine can be kept close to the expected optimal tip speed ratio. However, for all three cases the average extracted power was significantly lower than the average power available in the turbine times the estimated maximum power coefficient. A maximum power point tracking system, with or without water velocity measurement, should increase the average extracted power.A simulation model has been validated using experimental data. The simulated system consists of the electrical system and a hydrodynamic vortex model for the turbine. Experiments of no load operation were conducted to calibrate the drag losses of the turbine. Simulations were able to predict the behaviour in a step response for a change in tip speed ratio when the turbine was operated close to optimal tip speed ratio. The start position of the turbine was varied in the simulation to view the influence on the step response from a changed turbine position relative to the direction of the water flow.
|
|
