A calibration method for downwind wake models accounting for the unsteady behaviour of the wind turbine tower shadow behind monopile and truss towers.

Abstract Traditionally wind turbines are built in the upwind configuration, but the alternative of a downwind rotor has distinct advantages. A main issue with such a configuration is the tower shadow effect. The presence of the tower generates a complex wind field, consisting of an averaged velocity deficit, unsteady fluctuations from vortex shedding processes and turbulence. Since this tower shadow is commonly implemented using parametric steady wake models, the dynamic behaviour of the wake is not directly accounted for. The present paper introduces a general method for calibrating the parametric steady wake models and an effective turbulence intensity (accounting both for the velocity profile and the unsteady effects) from computational fluid dynamic simulations of the unsteady structural shadow. To demonstrate its potential the method is used in a blade fatigue comparison study. A 15 percent more flexible and lighter blade for the downwind mounted rotors showed a decrease in blade fatigue loads of three, four, and two percent compared to the conventional upwind mounted rotor on a monopile tower for the monopile tower and truss towers at 0 and 22.5 degrees, respectively. This example shows that the truss tower at 0 degree angle seems to result in the lowest blade fatigue loads. The proposed calibration method is completely general and can be used to obtain efficient, effective engineering models for the aerodynamic flow behind complex, multi-membered structures.

[1]  Richard G. J. Flay,et al.  Compliant Blades for Wind Turbines , 1998 .

[2]  Ervin Bossanyi,et al.  Wind Energy Handbook , 2001 .

[3]  R. Blevins,et al.  Flow-Induced Vibration , 1977 .

[4]  J. Jonkman,et al.  Definition of a 5-MW Reference Wind Turbine for Offshore System Development , 2009 .

[5]  H. Schlichting.  Boundary Layer Theory , 1955 .

[6]  Dag Myrhaug,et al.  Numerical simulation of flow around a smooth circular cylinder at very high Reynolds numbers , 2009 .

[7]  Michael Muskulus,et al.  The simultaneous effect of a fairing tower and increased blade flexibility on a downwind mounted rotor , 2013 .

[8]  Helge Madsen Aagaard,et al.  Simulation of Low frequency Noise from a Downwind Wind Turbine Rotor , 2007 .

[9]  Frank N. Coton,et al.  An investigation of the aerodynamic response of a wind turbine blade to tower shadow , 2004 .

[10]  Akihiko Nakayama,et al.  Large-eddy simulation of flows past complex truss structures , 2010 .

[11]  Michael Muskulus,et al.  Numerical Analysis of Turbulent Flow Past a Truss Tower For Offshore Downwind Turbines , 2011 .

[12]  Anders Ahlström,et al.  Influence of wind turbine flexibility on loads and power production , 2006 .

[13]  Frank N. Coton,et al.  A high resolution tower shadow model for downwind wind turbines , 2001 .

[14]  Michael Muskulus,et al.  Resolution of tower shadow models for downwind mounted rotors and its effects on the blade fatigue , 2014 .

[15]  Seikan Ishigai,et al.  Experimental Study on Structure of Gas Flow in Tube Banks with Tube Axes Normal to Flow : Part 1, Karman Vortex Flow from Two Tubes at Various Spacings , 1971 .

[16]  Frank N. Coton,et al.  An examination of key aerodynamic modelling issues raised by the NREL blind comparison , 2002 .

[17]  F. Menter.  Two-equation eddy-viscosity turbulence models for engineering applications , 1994 .

[18]  J. Ferrari,et al.  NUMERICAL SIMULATION OF FLOW INTERFERENCE BETWEEN TWO CIRCULAR CYLINDERS IN TANDEM AND SIDE-BY-SIDE ARRANGEMENTS , 2001 .

[19]  Salim Mohamed Salim,et al.  Wall y + Strategy for Dealing with Wall-bounded Turbulent Flows , 2009 .

[20]  S. Powles.  The effects of tower shadow on the dynamics of a horizontal-axis witn turbine , 1983 .

[21]  M. M. Zdravkovich,et al.  REVIEW—Review of Flow Interference Between Two Circular Cylinders in Various Arrangements , 1977 .

[22]  Geir Moe,et al.  Blade Response on Offshore Bottom Fixed Wind Turbines With Down-Wind Rotors , 2010 .

[23]  Masanobu Shinozuka,et al.  Monte Carlo solution of structural dynamics , 1972 .

[24]  Michael Muskulus,et al.  Numerical Tower Shadow Modeling for a Downwind Wind Turbine Truss Tower , 2011 .

[25]  Geir Moe,et al.  Tower Shadow - Experiment Comparing Wake Behind Tubular and Truss Towers , 2011 .

[26]  Patrick Moriarty,et al.  AeroDyn Theory Manual , 2005 .