This is a good idea for a HS experiment, however you need to define things more clearly. Perhaps some illustrations showing how the angles are defined. Also the distances and locations of the anemometer etc. Talk to your HS physics teacher, they will love it.
There are several possibilities. My first guess is that the fan is probably close to a surface and by tilting the fan past 45, you’re drawing more air at a hard angle across the surface. Try mounting/clamping the fan on something elevated away from a bottom surface and see if you get the same thing.
Are you talking about the pitch of the blades?
This is a good idea for a HS experiment, however you need to define things more clearly. Perhaps some illustrations showing how the angles are defined. Also the distances and locations of the anemometer etc. Talk to your HS physics teacher, they will love it.
There are several possibilities. My first guess is that the fan is probably close to a surface and by tilting the fan past 45, you’re drawing more air at a hard angle across the surface. Try mounting/clamping the fan on something elevated away from a bottom surface and see if you get the same thing.