Sandia Modifies Delft3D Turbine Model

Delft3D is a state-of-the-art, open-source hydrodynamics software suite capable of modeling hydrodynamics, sediment transport, and water quality in rivers, lakes, estuaries, and coastal environments. Delft3D was developed by the Dutch company, Deltares.

Because it is actively developed and maintained and because it is held in high regard by researchers and practitioners alike, Sandia is developing Delft3D as a complementary replacement for the aging open-source-version of the Environmental Fluid Dynamics Code (EFDC), which was modified to include a current energy converter (CEC) module and renamed SNL-EFDC.

Figure 1. Overhead image of the Roza Canal and a color-map of the canal depth (left). Delft3D numerical domain of the Roza Canal (right) where the colormap is for water velocity (m/s).

The CEC module provides the ability to simulate energy generation (momentum withdrawal) by CEC devices while including the commensurate changes in the turbulent kinetic energy and its dissipation rate and has been demonstrated to accurately predict flow through and around laboratory-scale CEC devices and arrays of actuator disks.

To advance CEC-simulation capabilities in an actively maintained modeling framework, the equivalent CEC module will be developed for Delft3D.

Sandia has incorporated a momentum sink turbine model into Delft3D based off of the work by Thomas Roc [1]. The resulting equation representing the force imposed on the fluid due to the turbine (acting as a momentum sink) is shown below:

Figure 2. Overhead (left) and cross-sectional (right) con-tour plots of flow velocity around the Delft3D turbine model. — Figure 2. Overhead (left) and cross-sectional (right) contour plots of flow velocity around the Delft3D turbine model.

A Delft3D model, run with the Sandia-developed implementation of CEC devices, was designed to represent the Roza Canal. Figure 1 shows a satellite image of the Roza Canal (left), a close-up view of the Delft3D bathymetry representation (center), and the simulated velocities throughout the entire model domain (right).

Figure 2 presents Delft3D-simulated velocities near the CEC turbine. The image on the left is a plan view of the region around the turbine, while that on the right is a cross sectional profile just behind the turbine. The model is behaving as expected where a velocity deficit forms in the region downstream from the turbine (the wake) and velocities increase due to some portion of the flow being diverted around the turbine (due to device physically blocking portions of the flow).

Figure 3. Turbine centerline flow velocity versus downstream distance as predicted by the Delft3D simulation (green) against the measured data from the canal (blue dots).

Figure 3 further illustrates the turbine wake characteristics, by showing the centerline turbine wake velocity versus downstream distance. The simulated stream-wise flow velocity is shown (green line) against the measured data from the canal (blue dots) and appears to agree quite well.

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[1] Roc, T., D.C. Conley, and D. Greaves, “Methodology for tidal turbine representation in ocean circulation model,” Renewable Energy, 51, pp. 448–464 (2013).

[2] Rethore, Pierre-Elouan Mikael, et al., “Study of the atmospheric wake turbulence of a CFD actuator disc model,” 2009 European Wind Energy Conference and Exhibition, 2009.

[3] Gunawan, B., J. Roberts, and V. Neary, “Hydrodynamic effects of hydrokinetic turbine deployment in an irrigation canal,” Proceedings of the 3rd Marine Energy Technology Symposium (METS2015), Washington DC., 2015.

[4] Myers, L. E., and A. S. Bahaj, “Experimental analysis of the flow field around horizontal axis tidal turbines by use of scale mesh disk rotor simulators,” Ocean Engineering 37.2, pp. 218–227 (2010).

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July 29, 2015