# Aerodynamic Loads on Nacelle and hub

This section deals with the aerodynamic loads on the nacelle and the hub. For aerodynamic loads on the blades, see BEM algorithm. For aerodynamic loads on non-blade elements, see Aerodynamic Loads on Support section elements - Aero drag loads

In Ashes, it is possible to apply loads on the nacelle center of mass by ticking the Aero drag on the Nacelle/hub parameter in the Aerodynamics tab of the Analysis parameters window. For aerodynamic purposes, the nacelle and hub are modeled as a sphere. The aerodynamic loads are then computed with the drag term according to the Morison equation (Morison et al. (1950)):
$$F_{aero}=\frac{1}{2}\rho V^2 C_D \pi r^2$$

where
• $$\rho$$
is the air density, that can be changed in the Atmosphere part
• $$V$$
is the incoming wind at the nacelle center of mass
• $$C_D$$
is the drag coefficient, that can be changed in the Aerodynamics tab
• $$r$$
is the radius of the sphere modeling the nacelle and hub for aerodynamic purposes, that can be changed in the Aerodynamics tab

Note: since the nacelle and hub are modelled as a shpere, the direction of the drag load is always the same as the direction of the incoming wind at the nacelle center of mass

The position of the center of mass of the nacelle can be changed in the Nacelle frame part.

Note: the velocity of the nacelle center of mass (as a result of tower motion for example) is not taken into account when computing the aerodynamic drag. The drag load therefore only comes from the incoming wind and not the velocity of the node.

It is possible to add a sensor on the drag loads by following the procedure described in the Individual load sensor section. This sensor will also provide the wind velocity used to compute the aerodynamic load, i.e. the component of the incoming wind perpendicular to the element axis.