Choked Flows through Short Contractions
Publication: Journal of Hydraulic Engineering
Volume 127, Issue 8
Abstract
This paper presents a study on choked flows through short, lateral contractions in subcritical open channels. A new discharge equation is developed based on the conservation of energy and experimental data with a wide range of opening ratios (ratio of contracted width-to-total width). The theoretical derivation accounts for the critical flow conditions that take place in the contraction under choking conditions. The effects of opening ratio σ, encroachment structure shape, inlet angle α, and relative contraction length L* on discharge coefficients are considered. The coefficients of the newly developed discharge equation are determined using a total of 186 sets of choking experiments conducted by various researchers. The analysis shows that the discharge coefficient is mainly affected by σ and may vary between 0.29 and 0.54 for the range of σ values used in the study (0.12–0.88). It is shown that the discharge coefficient (correspondingly the discharge) can vary up to 16% for encroachment-structure shape changing from sharp corner to rounded corner conditions—up to 11% for α going from 30° to 90° and up to 6% for L* ranging from 0 to 1.33. This study extends the traditional choking analysis to severe contractions. The proposed equation fits previous experimental data well and can be used to predict either the water discharge through a contraction for a given upstream depth or the water depth upstream from a contraction corresponding to a given discharge under choking conditions.
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Information & Authors
Information
Published In
Journal of Hydraulic Engineering
Volume 127 • Issue 8 • August 2001
Pages: 657 - 662
History
Received: May 8, 2000
Published online: Aug 1, 2001
Published in print: Aug 2001
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