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The Science of Making Torque from Wind (TORQUE 2018)

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Room: BL.28 Carassa e Dadda
Chaired by:
Philippe Chatelain | UCL
Topic: AA. Aerodynamics and Aeroacoustics
Form of presentation: Oral
Duration: 110 minutes

Authors:
Franck Bertagnolio, Helge Aa. Madsen, Andreas Fischer

Abstract:
The influence of the wake of an upstream turbine impinging another one located further downstream is studied focusing on the latter’s noise emission. Measurement data as a well as numerical results from a wind turbine noise model are investigated. It is shown that the wake velocity deficit reduces noise in certain circumtances. This can compensate, or even sometime more than compensate, the additional noise emission expected as a result of the wake turbulence. Furthermore, noise amplitude modulation appears to increase when the turbine is impacted by the wake flow.

Authors:
Zhu Wei Jun Zhu, Jiufa Cao, Emre Barlas, Wen Zhong Shen, Lei Zhang, Zhenye Sun, Hua Yang, Haoran Xu

Abstract:
The purpose of the paper is to present an efficient numerical method that predicts: (a) wind turbine aerodynamic loads and power; (b) wind turbine noise source; (c) long distance wind turbine noise source propagation. The numerical methods involved in this study are a combination of Computational Fluid Dynamics (CFD) and wind turbine aeroacoustic methods. The results from the CFD simulation provide necessary information of wind turbine power and thrust etc. The novel 2D Actuator Disc (AD) theory is applied for such a purpose. The computational efficiency becomes very high while using a time domain 2D CFD approach. The flow geometry at each blade element position is required for wind turbine noise source calculations. The predicted wind turbine noise source is the starting field for long distance noise propagation model which is based on solving the Parabolic Equations (PE) in frequency domain. Preliminary results shown that the integrated wind turbine flow-acoustic prediction method is effective and accurate.

Authors:
Niels Nørmark Sørensen

Abstract:
For large wind turbines with rotor radii of the order of 100 meters, the blade tip might reach inflow velocities approaching to thirty percent of the speed of sound and the velocity is further increased along the suction side of the blade.  Most engineering codes are relying on airfoil data taken at Mach numbers below 0.2, and several of the advanced CFD codes applied to wind turbines are based on the assumption of incompressibility.  It is therefore important to evaluate the effect of the local Mach numbers that surpasses the value of 0.2 which is normally taken as the limit below which the incompressible assumption is valid.In the present work 2D incompressible and compressible CFD computations are compared with classical compressibility corrections to evaluate the effect of free stream Mach numbers close to 0.3.

Authors:
SeungJoon Yang, James Baeder

Abstract:
Wind turbine blade inboard flow was improved by modifying its trailing edge shape. A combined trailing edge modification design with blunt trailing edge and a span-wise wavy trailing edge was used. Designing blunt trailing edge at the blade inboard makes the flow become more attached than the conventional sharp trailing edge. The span-wise wavy trailing edge breaks up the Karman vortex shedding generated by the blunt trailing edge. The Sandia National Laboratory 100 meter blade, SNL100-03 was used as a baseline model. Rotating blade simulations were performed in the full-scale isolated rotor condition. Aerodynamic performance analysis and aeroacoustic performance analysis of the modified turbine blades were performed. By using the blunt and wavy combined trailing edge modification, the massive flow separation on the inboard of the baseline blade was prevented successfully. Delayed Detached Eddy Simulation (DDES) with a modified laminar-turbulent transition model (Medida – Baeder model) is applied to predict the separated flow behind these blades.

Authors:
Özge Sinem Özçakmak

Abstract:
The surface imperfections and the inflow turbulence in real operational conditions can cause significant deviations from the predicted wind turbine aerodynamic performance and energy yield. In this study, particular emphasis was placed on the effect of these parameters on the laminar-turbulent transition on wind turbine blades. For this purpose, the DAN-AERO wind tunnel measurements, with high frequency microphones flush mounted on the both suction and pressure sides of the NACA 63-418 airfoil profile, were used. Typical operating condition Reynolds numbers, turbulence grid and boundary layer control devices on the surface were implemented. The results indicate a high dependency of the transition process on these parameters. The analyses show that the critical height of the leading edge roughness (LER) is to be met in order to have a bypass transition to turbulent flow at the angle of attacks, where the stagnation point is upstream of the LER location. The transition location moves closer to the leading edge with increasing Reynolds number when the roughness height is smaller than the critical height. Inflow turbulence is observed to have a larger effect on the transition location than the predicted numerical results.

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