Air Influence on Similarity of Hydraulic Transients and Vibrations

Abstract

The effects of wave speed variation due to air content on the validity of similarity laws for model studies of hydraulic transients and hydraulic vibrations were investigated. Studies show that hydraulic similarities between geometrically similar model and prototype are reduced substantially for cases involving two- or three-phase flow. For flow with intensive cavitation, analysis shows that there is no hydraulic similarity between model and prototype. For pump discharge pipeline and turbine draft tube where two phase flow of air-water mixture occurs, analysis shows that the natural frequency and the response characteristics of the fluid system are a strong function of the local wave speed variation within the fluid system. This local wave speed variation is a function of the local transient air content and transient pressure.