Drawdown curve and incipient aeration for chute flow

Abstract

Turbulent rough flows in spillway chutes are considered in the first part. The drawdown curve is demonstrated to be identical with those of flows in the turbulent smooth regime. It is further shown that all drawdown curves can be expressed with a normalized streamwise coordinate that involves the bottom slope and the uniform and critical flow depths. An explicit solution is presented. The computational results are verified with model observations. Also, previous derivations are generalized and a universal drawdown curve for chute flow is introduced. The results are readily applicable for design. In the second part of this paper, incipient aeration on a spillway chute is investigated, based on the data of Bauer for the boundary-layer thickness. Predictions for the flow depth and location of incipient aeration are in agreement with observations. The effects of bottom slope and relative roughness are demonstrated to be comparably small, whereas the critical depth has a major influence on both flow depth and location of incipient aeration. Typical examples illustrate the computational procedure.Key words: aeration, chute, drawdown, spillway, supercritical flow.