Experimental results axe presented for a laboratory study of the effectiveness of hydraulic breakwaters in dissipating deep water waves. Test data are reported for a range of wave steepnesses for wave length: water depth ratios ranging from 0.375 to 1.343. It is shown that the effectiveness of hydraulic breakwaters depends upon the steepness of the incident wave and upon the ratio of the momentum of the opposing surface current created by the breakwater to the momentum of the incident waves. Results also are compared with the theoretical predictions of Taylor which are appropriate to deep water waves. Data are presented in a form allowing the determination of hydraulic breakwater manifold discharge characteristics in order to achieve specified attenuation for a particular incident wave. It is concluded that while the hydraulic breakwater is better adapted to deep water waves than to shallow water waves upon which prior studies of the device have concentrated, it is generally inefficient for most practical cases because of excess power requirements. Some possible field applications are indicated.

The effects of surface roughness on the frictional resistance of enclosed rotating disks have been studied experimentally. Torque data were obtained over the range of disk Reynolds numbers 4 × 103 to 6 × 106 for three different relative roughnesses a/k of 1000, 2000, and 3200 at three axial-clearance-to-disk-radius ratios s/a of 0.0227, 0.0609, and 0.112 for a constant, small, radial tip clearance. The existence of four possible basic flow regimes in the axial gap between the disk and casing wall was verified. Empirical expressions have been presented which predict the initial point of onset of turbulence in the flow within the boundary layer on the disk, the point at which the surface roughness becomes fully effective, and the magnitudes of the resistance coefficients in the zone of fully rough turbulent flow. The similarities and differences between smooth and rough-disk torque behavior, and to a limited extent boundary-layer behavior, have been noted.

The fundamental fluid mechanics associated with the rotation of a smooth plane disk enclosed within a right-cylindrical chamber have been studied both experimentally and theoretically. In order to acquire further and systematic information pertinent to this problem, which has received much attention in the past, torque data were obtained over a range of disk Reynolds numbers from 103 to 107 for axial clearance-disk radius ratios s/a from 0.0127 to 0.217 for a constant small radial tip clearance and velocity and pressure data were obtained for laminar and turbulent flows. The existence of four basic flow regimes in the axial gap between the disk and casing wall was verified, and these regimes, the existence and extent of which are governed by the Reynolds number-axial spacing combinations, have been delineated. A new approximate theoretical analysis has accounted for axial-clearance effects for the case of separate boundary layers on the disk and end wall; this theory has been checked against test results. Velocity and pressure data have shown that the concept of a fluid “core” rotation in the case of separate boundary layers must be modified because of secondary flows and skewed boundary layers.