An approach to hydraulic design of Conical Central Baffle Flumes

Abstract

Design methodology for providing a Conical Central Baffle flume (CCBF) has not yet been found in the literature, though it is required by the hydraulic engineers considering the increased popularity of the baffled flumes, now-a-days. Some guidance for discharge prediction using CCBF is only found in the literature. The main objective of the present research is to address the issue of hydraulic design of CCBFs. A measuring flume serves as a device for quantifying the flow rate in an open channel. These flumes operate on the basis of principles of critical flow and energy conservation. Conventionally, it is assumed that the critical flow occurs at location of the minimum flow cross-section or throat. In the current investigation, a CCBF is employed to gauge the flow discharge. The CCBF configuration involves placing one conical obstruction in a trapezoidal channel, thus creating a throat. One of the objectives of the study is to scrutinize the prevailing location of the critical section and introduce a refining approach to discharge prediction. Through a series of experiments and numerical simulations, the present study endeavors to ascertain the true location of the critical section in CCBF. Contrary to the traditional belief that the critical section is always at the throat, the investigation revealed that the critical section tends to shift upstream with increased discharge. The theoretical analysis, employing energy expression and critical flow concepts, unveiled that despite this shifting nature, the energy-critical depth ratio of the flume remains constant. Based on these findings, a discharge prediction model is proposed. The model demonstrates a mean relative error of ±1.42 % and a maximum relative error of 3.5 % in discharge prediction. The theoretical investigation also highlighted that the critical section occurring at the throat signifies the minimum discharge value, and induced a threshold choking flow condition in the flume. The present study also proposes the expressions for minimum as well as maximum discharge measuring capacity of a CCBF which leads to its proper design methodology, which has never been presented so far in the literature. Additionally, a design example is presented, elucidating the process of designing a conical CCBF for a trapezoidal channel based on the understanding of the limiting discharge.