Coast Down Testing Methods

[elliott87]

I was looking into using a coast down test method to calculate the mechanical friction in the driveline of a wind turbine. I know the coast down test is used probably most frequently for testing cars, which is why I posted here.

In the coast down test, is there a known method of finding the value of the frictional force if I know the velocity profile of the rotating turbine coasting down?

What i'm thinking is that if I have a plot of rotational kinetic energy (KE = 1/2Iw^2) vs. time, the slope will be negative and will represent the power loss (energy/time). Since Power = Fv (or Power = Frw), knowing the slope of the energy vs. time graph (Power) and the velocity, F (force of friction) can be calculated. This is assuming that F is relatively constant with speed. Am I on the right track?

 

[GregLocock]

Yes, except that your friction is likely to vary with speed, depending on your bearing type.

measuring the efficincy of power transmission devices is tricky - differential amnufacturers use a method based on measuring the heat radiated by each bearing, for example.

Cheers

Greg Locock

SIGlease see FAQ731-376 for tips on how to make the best use of Eng-Tips.