Modelling Wind Turbines via Actuator Lines in High-Order h/p Solvers

TL;DR

This paper evaluates two actuator line methods for wind turbine modeling using high-order solvers and LES, demonstrating that weighted sums improve force distribution and wake resolution at higher polynomial orders.

Contribution

It introduces a comparison of actuator line methodologies in high-order solvers, highlighting the benefits of weighted sums and the influence of polynomial order and smoothing parameters.

Findings

Weighted sum method yields smoother force distributions.

Higher polynomial order improves physics capture without mesh refinement.

Cell averaging causes nonphysical oscillations at high polynomial orders.

Abstract

This paper compares two actuator line methodologies for modelling wind turbines employing high-order h/p solvers and large-eddy simulations. The methods combine the accuracy of high-order solvers (in this work the maximum order is 6) with the computational efficiency of actuator lines to capture the aerodynamic effects of wind turbine blades. Comparisons with experiments validate the actuator line methodologies. We explore the effects of the polynomial order and the smoothing parameter associated with the Gaussian regularization function, and use them to blend the actuator line forcing in the high-order computational mesh, to show that both parameters influence the distribution of forces along the blades and the turbine wake. The greatest impact is obtained when the polynomial order is increased, allowing one to better capture the physics without requiring new meshes. When comparing the actuator line methodologies, we show the advantages of performing weighted sums, over element averages, to compute the blade velocities and forces in high-order solvers. For low-order simulations (low polynomial orders), both methods provide similar results, but as the polynomial order is increased, the weighted sum method shows smoother thrust/torque distributions and better wake resolution. Furthermore, cell averaging introduces nonphysical oscillations when increasing the polynomial order beyond 3 (4th order accuracy).