In 'physical' (real) pitch regulated wind turbines, pitch actuators are motors that pitch (i.e. rotate) the blades to get the desired pitch. In a pitch regulated wind turbine, the actuators are active also when the pitch shall not change to keep the blade from rotating. Rotation is accomplished by applying torque at the blade root. The magnitude of the torque is calculated by a control system (software). Although there are typically as many pitch motors as there are blades, they typically have the same control system. In ASHES, a Rotor has one Pitch actuator part per blade. A Pitch actuator part represents the control system for the actuator torque and the torque that is being applied to the root of the blade to get the correct pitch. The correct pitch is set by another control system: Demanded pitch system.
If the RNA's Demanded pitch scheme parameter is set to Fixed, then there is no Pitch actuator parts (in a physical (real) wind turbine this means that the blades are bolted to the hub and cannot rotate).