A Momentum Integral Method to Predict the Frictional Torque of a Rotating Disk With Protruding Bolts

Abstract

A momentum integral method was developed to predict the frictional torque of a disk rotating in quiescent air with cylindrical protrusions mounted on its surface. The predicted torque is compared to experimental data taken for the protrusions placed on two different radii on the disk with two different numbers of protrusions on each radius. A critical review of the calculated results reveals that caused by the protrusions the predicted thickness of the boundary layer on the disk is of the same magnitude as the radius of the disk. Since in this case Prandtl’s simplifications for the boundary layer on which the momentum integral equations are based upon are not valid their use appears to be doubtful. However, the predicted frictional torque is in good agreement with the measurements for all configurations tested except for that with the smallest circumferential distance between the protrusions where the torque is overpredicted by the method. The application of the method for a disk rotating in a stationary housing is briefly discussed.