Fixed-Cone Valves, New Melones Dam, California. Hydraulic Model Investigation

摘要

This model study was conducted with the major emphasis on determining the differential pressures acting on the vanes of the valves. Pressures were measured along the vane, and the differential acting across the vane was used in a structural analysis. Flow entering the 66-in.-diam valves in the low-level outlet works was highly distorted by the combined bends located just upstream of the valves. The upstream bifurcations in the flood control and irrigation outlet system caused substantial fluctuation of flow entering the 78-in.-diam valves. Discharge characteristics of the valves showed that the eight-vaned valves (without the center connecting hub design) used in the New Melones Dam outlet works have discharge coefficients slightly higher than conventional four- and six-vaned valves with center connecting hub. Approach conduit pressures were measured at all potential low pressure zones and no low pressures were measured. The original hood design was modified to reduce backsplash on the valves. In the low-level outlet works, the backsplash plate was moved downstream 4 ft from the original location and backsplash was substantially reduced. In the flood control and irrigation outlet system a divergent cone was used in lieu of the plate to reduce backsplash. Results of the study are considered valid for use in designing against fatigue failure of the vanes. Although frequency spectra determined that predominant frequencies were low, the possibility of a resonant failure cannot be ruled out.