many turbine helicopters have VIGVs because the inlet airflow is often disrupted by the rotor wash.
the VIGVs direct the air onto the 1st stage of the compressor at the optimum angle based upon several factors such as N1 speed & acceleration, Fuel Flow, Power demand/required etc.
VIGVs don not rotate and are often hollow and fed bleed air to prevent inlet incing.
i dont know of any fixed wing aircraft with either VIGVs or variable N1 fans.