Investigating the Level of Fidelity of an Actuator Line Model in Predicting Loads and Deflections of Rotating Blades under Uniform Free-Stream Flow

Nikos Spyropoulos,George Papadakis,John M Prospathopoulos,Vasilis A Riziotis

doi:10.3390/app112412097

Nikos Spyropoulos, George Papadakis + Show 2 more

Open Access

https://doi.org/10.3390/app112412097

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Journal: Applied sciences	Publication Date: Dec 19, 2021
Citations: 6	License type: CC BY 4.0

Affiliation: National Technical University of Athens

Abstract

In this paper, the accuracy of an in-house Actuator Line (AL) model is tested on aeroelastic simulations of a Wind Turbine (WT) rotor and a helicopter Main Rotor (MR) under uniform free-stream flow. For the scope of aeroelastic analyses, the AL model is coupled with an in-house multibody dynamics code in which the blades are modeled as beams. The advantage from the introduction of CFD analysis in rotorcraft aeroelasticity is related to its capability to account in detail for the interaction of the rotor wake with the boundary layer developed on the surrounding bodies. This has proven to be of great importance in order to accurately estimate the aerodynamic forces and thus the corresponding structural loads and deflections of the blades. In wind turbine applications, a good example of the above is the rotor/ground interaction. In helicopter configurations, the interaction of MR with the ground or the fuselage and the interaction of tail rotor with the duct in fenestron configurations are typical examples. Furthermore, CFD aerodynamic analysis is an obvious modeling option in which the above mentioned asset can be combined with the consideration of the mutual interaction of the rotor with the ambient turbulence. A WT rotor operating inside the atmospheric boundary layer under turbulent free-stream flow is such a case. In the paper, AL results are compared against Blade Element Momentum (BEM) and Lifting Line (LL) model results in the case of the WT, whereas LL and measured data are considered in the helicopter cases. Blade loads and deflections are mainly compared as azimuthal variations. In the helicopter MR cases, where comparison is made against experimental data, harmonic analysis of structural loads is shown as well. Overall, AL proves to be as reliable as LL in the canonical cases addressed in this paper in terms of loads and deflections predictions. Therefore, it can be trusted in more complex flow conditions where viscous effects are pronounced.

Highlights

The Actuator Line (AL) method [1] is a renowned CFD technique widely used in the aerodynamic analysis of Wind Turbine (WT) rotors
Results obtained by the investigated AL-based aeroelastic tool are compared against reference results obtained using lower fidelity aerodynamic tools or through wind tunnel measurements
In WT cases, benchmark simulations are performed for the rotor of the conceptual DTU 10 MW reference wind turbine developed by DTU and employed as a reference turbine in a number of research projects (e.g., INNWIND.EU see [28])

Summary

Introduction

The Actuator Line (AL) method [1] is a renowned CFD technique widely used in the aerodynamic analysis of Wind Turbine (WT) rotors. The broad application of AL stems from the high fidelity level that the CFD context provides, alongside with the limited computational requirements of the methodology. The latter originates in the fact that the rotor blades are not fully resolved, rather than modeled as a set of blade elements along their axis. Just by a simple blade element analysis, together with the use of predefined airfoil polars, the blade forces can be calculated in a cost effective manner and applied to the flow as source terms of the Navier–Stokes equations In this way, the effect of the rotor on the flow can be accounted for in great detail [7,8]

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