Hi, I suspect this is your radiator fan. Radiator fans are normally secured by two bolts ( on the upper portion of the radiator), while the bottom part of the fan are secured by two slots. I am not really sure if the fan can fell down, unless someone repaired the radiator and forgot to tighten up the bolts or the two anchors in the bottom were not properly placed in the slots.
To fix this you will need to make sure that the fan is still in good condition. If so, you will need to buy a nylon or plastic radiator fan mounting kit as shown here.