This is the 11188th most frequent Turkish word.
dönüyordu
"Was turning" or "was rotating."
Here, 'dönüyordu' describes the physical action of the bus changing direction.
Otobüs köşeyi dönüyordu, yolcular sabırsızlanıyordu.
The bus was turning the corner, and the passengers were getting impatient.
Here, 'dönüyordu' is used in the context of a continuous action describing the spinning movement of the fan.
Güneş doğar doğmaz, pervane hızla dönüyordu.
As soon as the sun rose, the fan was spinning rapidly.
In this case, 'dönüyordu' is metaphorical, indicating going back to a past time or mental state.