The generation of 3D flows in a combined current and wave tank

Abstract

a b s t r a c tOne means of producing a 3D current in a circular tank is by using groups of conditioned axial flow impellers arranged around the perimeter to collectively create a sea representative bulk flow in a laboratory setting. Unfortunately to achieve the required bulk flow neighbouring impellers have to operate at different speeds resulting in steps in the plan view velocity profile. Therefore the underlying situation that governs tank behaviour is that of two fluid streams at different speeds combining, leading to a turbulent mixing layer which then dissipates and develops. Here a simulation of this flow is created using a 2D Reynolds Averaged Navier-Stokes method and then validated with physical experiments. The implications for accuracy and computational costs of various turbulence models, boundary conditions setups, and geometry representations are assessed. These findings are then used to produce a simplified 2D numerical model of the plan view flows in a 3D test tank which is then employed to demonstrate how a satisfactory device test zone might be generated from groups of stepped inputs. This finding helps prove that a combined current and wave tank can be created using the described configuration with the model providing a useful means of testing control scenarios.

Experimental Assessment of Flow, Performance, and Loads for Tidal Turbines in a Closely-Spaced Array

“…The flow is directed across the test volume of the tank by turning vanes mounted around the outside of the floor, below and in front of the wavemakers. Full details of the flow generation are given in Robinson et al [23,24]. Due to the method of generating flow in a circular tank, there is some spatial variation of the mean flow across the test area.…”

“…This can be attributed to the way I U is defined as a function of flow velocity (Equation (2)), and the reduced wake deficit for the triple turbine array. Due to the re-circulation of currents at FloWave [22,23], consideration was given to blockage in the tank and how this affects the flow re-circulation. Figure 5 shows the wake of a single turbine as a function of rpm, with more blockage and higher wake deficit at higher rpm, as would be expected.…”

Assessing extreme loads on a tidal turbine using focused wave groups in energetic currents

“…The facility is a circular, combined wave and current basin, with a diameter of 25 m and a nominal water depth of 2 m. Waves are generated using 168 active-absorbing force-feedback wavemakers around the entire circumference. A re-circulating flow system is generated using 28 impeller units mounted in the plenum chamber beneath the floor [27]. These enable the creation of a predominantly straight flow in any direction across the central test area [22], where waves can be added to the current field at any relative angle.…”

Re-Creating Waves in Large Currents for Tidal Energy Applications

“…The facility is a 25 m-diameter, circular, combined wave and current basin. Wave generation consists of 168 active-absorbing force-feedback wavemakers, with a nominal water depth of 2.0 m. A re-circulating flow system is implemented using 28 impeller units mounted in the plenum chamber beneath the floor [19]. These enable the creation of a predominantly straight flow in any direction across the central test area [20], where waves can also be added to the current field at any relative angle.…”

“…In this case, A i,measured is defined as the mean spectrum over the gauges obtained from an FFT. The error between target spectrum and measured is calculated from Equation (19). Table 3.…”