Structural effects of unsteady aerodynamic forces on horizontal-axis wind turbines
Abstract
Due to its renewable nature and abundant resources, wind energy has the potential to fulfill a large portion of this nation's energy needs. The simplest means of utilizing wind energy is through the use of downwind, horizontal-axis wind turbines (HAWT) with fixed-pitch rotors. This configuration regulates the peak power by allowing the rotor blade to aerodynamically stall. The stall point, the point of maximum coefficient of lift, is currently predicted using data obtained from wind tunnel tests. Unfortunately, these tests do not accurately simulate conditions encountered in the field. Flow around the tower and nacelle coupled with inflow turbulence and rotation of the turbine blades create unpredicted aerodynamic forces. Dynamic stall is hypothesized to occur. Such aerodynamic loads are transmitted into the rotor and tower causing structural resonance that drastically reduces the design lifetime of the wind turbine. The current method of alleviating this problem is to structurally reinforce the tower and blades. However, this adds unneeded mass and, therefore, cost to the turbines. A better understanding of the aerodynamic forces and the manner in which they affect the structure would allow for the design of more cost effective and durable wind turbines. Data compiled by the National Renewable Energy Laboratory (NREL) for a downwind HAWT with constant chord, untwisted, fixed-pitch rotors is analyzed. From these data, the actual aerodynamic characteristics of the rotor are being portrayed and the potential effects upon the structure can for the first time be fully analyzed. Based upon their understanding, solutions to the problem of structural resonance are emerging.
- Publication:
-
NASA STI/Recon Technical Report N
- Pub Date:
- August 1994
- Bibcode:
- 1994STIN...9516939M
- Keywords:
-
- Aerodynamic Forces;
- Aerodynamic Stalling;
- Rotors;
- Turbine Blades;
- Turbulence;
- Unsteady Aerodynamics;
- Wind Direction;
- Wind Tunnel Tests;
- Wind Turbines;
- Windpower Utilization;
- Aerodynamic Characteristics;
- Cost Effectiveness;
- Durability;
- Nacelles;
- Resonance;
- Stress Distribution;
- Supports;
- Structural Mechanics