Many full-size helicopters are fitted with ventilation slots; for example, the Bell 204 and Bell 205 feature horizontally and vertically arranged vents in the dome covers.
The air intakes provide an airflow to starter generators and the engine / turbine compartment, and are generally covered by aerodynamically shaped metal fairings.
To add this scale detail to your model, select the appropriate size of flexible vent slots and stick them to the fuselage in the desired position using cyano. This should be done before painting the model.
* Ventilation slots, 35 x 100 mm
* Slot width 23 mm