"wind speed 7mph is 3miles per second"
you might want to check your math with this one! 3 miles per second is something on the order of 3x60 seconds x 60minutes=10,800mph?
lets see what we have here
"rpm=windspeed x tsr x 60/circumference". (assuming this is correct)
lets take the windspeed in ft/min
10mph would work out to 10x 5280 = 52800ft/hr
52800 / 60 min = 880ft/min
so... rpm = 880 x tsr x (60 x circumference)
(looks like something is wrong with your equation don't you think?)
rpm = 880 x tsr 5 = 4400 (60 x circumference)
rpm = 4400 x (60 x circumference)
lets solve for circumference and it needs to be in feet.
so for a 10 ft rotor we have 10 x 3.14159 = 31.42ft
now
rpm = 4400 x (60 x 31.42) = an insane rpm!
what we should have is the following
rpm = windspeed in ft/min * tsr / rotor/blade circumference (i think, so lets see)
from above a 10 mph windspeed works out to 880ft/min
so
rpm = 880 * tsr (lets use 5) = 4400 / circumference
rpm = 4400/ circumference ( lets use a 10ft rotor diameter)
circumference = 10ft * 3.14 (pi) = 31.4 ft
therefore
rpm = 4400/ 31.4 = 140rpm
so lets cross check
a 10 ft rotor turning 140
a 10 ft rotor is 31.4 ft in circumference
31.4 * 140= 4396 ft/min
4396 /5280 = .8325 mile/min
.8325 x 60 = 49.95mph
49.95 / tsr 5= 9.99 mph
so that works out, i rounded the numbers off so that is why we don't get exactly 10mph wind in the cross check.
i think i have this right, someone will correct me if i am wrong
fwiw
bob g