# Re: airfoil in OpenLB

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Hi balzar29,

the Indicator is a functor which is called at another point in the library, when the material numbers are set.

In the

IndicatorCircle2D<S>::IndicatorCircle2D

the functor is initialized, here is the place to hand in parameters required for the desired equation.

The indicator return for coordinates, whether this coordinates are inside or outside the object. This is done in

bool IndicatorCircle2D<S>::operator()

This is the place to implement the equation describing the airfoil. “input” is the physical coordinate (input[0] for x-coordinate and input[1] for y-coordinate) which needs to be checked. “output[0]” is a boolean value that is returned. “true” or “1” if the point is inside the airfoil and “false” or “0” if the point is outside the airfoil.

Best

Robin