ECN publication
Dynamic stall model called "Simple"
Published by: Publication date:
ECN 1996
ECN report number: Document type:
ECN-C--95-060 ECN publication
Number of pages: Full text:
48 Download PDF  

The development and implementation of a method for the calculation ofdynamic stall to be applied to horizontal axis wind turbines are described. In the project on the title subject several countries participated, covering the three aspects of measurements, scientific type of flow field solving (typically of Navier-Stokes type) and so called 'engineering models'. The latter type should be viewed as models that require a minimum of computer code and calculation time. Such models are invariably heavily dependent on measured data. The model presented in this report is of the engineering type. A computer program called 'Simple' was generated, tuned and tested against measured data. The initial intent was to generate a model being as simple as possible for fast calculation and simple interfacing with aeroelastic codes. The core of the created model focuses around a differential equation which expresses the time derivative of the lift coefficient. Two terms are used for this purpose. One term corresponds to a simple dynamic delay with reference to the delayed action of the value of the dynamic lift to move toward the steady state lift level. The other term corresponds to an immediate response of lift to angle of attack changes using a slope similar to 2#pi#. For best fit to measured data, both the delay parameter and the slope are manipulated to be functions of both angle of attack and its time derivative. The differential equation is solved using a Runge-Kutta 4th order routine. Several simulation runs were made using the code as described. The important conclusions are largely derivable from the corresponding output graphs showing comparisons between calculations and measurements from several dynamic cases of three different 2D airfoils and one free air full scale turbine. The experience from comparing the model with the measured results leads to the conclusion that dynamic lift can easily be well modeled in this simple manner. The behavior of calculated drag, however, can be considerably improved. A discussion on that topic is presented while its consequences were not modeled. 28 figs., 1 tab., 18 refs.

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