Title:

Dynamic stall model called "Simple"


Author(s):



Published by:

Publication date:

ECN

1996


ECN report number:

Document type:

ECNC95060

ECN publication


Number of pages:

Full text:

48

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Abstract:
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 NavierStokes 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 RungeKutta 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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