Aerodynamic drag spinning disc
Aerodynamic drag spinning disc
(OP)
Hi guys, im looking for a simple formula to calculate the aerodynmaic drag on a spinning disc. The disc is basically the rotor for a mechanical centrifuge where the test tubes are hanging downwards and experience drag at 3000RPM.
Any help would be very nice thanks
Any help would be very nice thanks





RE: Aerodynamic drag spinning disc
RE: Aerodynamic drag spinning disc
TTFN
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RE: Aerodynamic drag spinning disc
is this clear??
RE: Aerodynamic drag spinning disc
RE: Aerodynamic drag spinning disc
Worst case - assume area is the length times the diameter of each tube, * no of tubes. Assume Cd=1
assume v= tip speed of tube
power=v^3*1/2*Cd*A*rho
If that is absurdly high (it should be) then find an equation for a fan.
Cheers
Greg Locock
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RE: Aerodynamic drag spinning disc
RE: Aerodynamic drag spinning disc
Secondly I understand what your saying about the sofisticated software to study drag. Could I use Solidworks CosmosFlow works and tr maybe a CFD analysis??
To GregLocock, thanks for that formula but how can i get power when i know the torque and energy??
RE: Aerodynamic drag spinning disc
Forget about energy. The moment, or torque if you'd rather, to keep the rotor spinning at a given speed (against the resistance of air) is in units of N-m. You'll find equations to get a good estimate of the aero torque, for a shrouded rotor, from the link posted. A shroud is a smooth cover (think fairing, or cowling) surrounding your centrifuge wheel, to make it look more aerodynamic, more like a wheel and less like a fan.
In calculating the torque, you had to know the speed of your wheel. The rotational speed is in revolutions per minute, which you then convert to units of radians/sec, or 1/sec, by multiplying rpm by (2*pi/60).
Multiply torque by rotational speed, and the units are
N-m/sec, which is watts, i.e. Power = Torque x Rot. Speed