Actuator line method applied to grid turbulence generation for large-Eddy simulations

Abstract

The constant growth of computational resources allows performing Large-Eddy Simulation (LES) on realistic flow configurations. In this context, it is important to properly model boundary conditions and particularly inflow turbulence. This study addresses wind tunnel applications where the object under investigation is downstream of a turbulence grid. This grid aims at generating a highly turbulent sheared flow for further use in wind turbines applications. In this work, an original strategy based on the actuator line method (ALM) is proposed to emulate the grid and generate realistic flow structures downstream at a moderate computational cost. As a first validation test of the proposed method, the LES of a single square rod is performed and the results are compared to a scale resolving simulation. In a second phase, the method is applied to a passive grid with non-homogeneous spacing, which generates fully-developed turbulence. Results are compared to experimental data and other state-of-the-art turbulence injection strategies such as homogeneous isotropic turbulence injection and also scale resolving simulations.

Towards an automated framework for Aero-Servo-Elastic Large Eddy Simulation of wind turbine wakes

“…Consequently, an alternative and more robust approach is preferred, which relies on Accurate Conservative Level Set (ACLS) functions [16] known for their strictly conservative behavior with low diffusion errors [17]. Such functions have already been used to track wind turbine wake mixing layers [7] or provide mean kinetic energy budget over streamtubes [15]. The ACLS function is set to be a hyperbolic tangent profile, ψ, where the interface is located at the iso-level 1/2 depicted in figure 3 with the marker (•).…”

“…The ACLS function is set to be a hyperbolic tangent profile, ψ, where the interface is located at the iso-level 1/2 depicted in figure 3 with the marker (•). Here, the level set initialization is based on the mean regularized forces of the wind turbine on the Eulerian grid [15,7], ensuring that the fluid crossing the rotor is flagged. Furthermore, the signed distance function ϕ(x, t) defining the distance to the front of the level set is inherent to the ACLS.…”

“…The developed workflow is here implemented around a two-way coupling [7,8] between the simulation codes YALES2 and BHawC. On the flow side, YALES2 [9] is a massively parallel finite-volume library used to solve the Navier-Stokes equations making it specifically tailored for LES.…”

“…In the following applications, the SWT-6.0-154 turbine is used. Designed for offshore applications, this industrial turbine features a rated power of 6 MW and a rotor diameter D = 154 m. The coupling between YALES2 and BHawC was initially validated using this same turbine design [7,8]. Depending on the application (see section 4), one of the two following inflow generation methods was selected:…”

Turbulent Eddy Generation for the CFD Analysis of Hydrokinetic Turbines

“…An interesting study on this subject is presented in [31], where the characteritics of the turbulent flow generated by a single bar in a grid is investigated in details.…”