Large-Scale Particle Image Velocimetry for Estimating Vena-Contracta Width for Flow in Contracted Open Channels

This paper presents the findings of a flume study using large-scale particle velocimetry (LSPIV) to estimate the top-width of the vena contracta formed by an approach open-channel flow entering a contraction of the channel. LSPIV is an image-based method that non-invasively measures two-dimensional instantaneous free-surface velocities of water flow using video equipment. The experiments investigated the requisite dimensions of two essential LSPIV components—search area and interrogation area– to establish the optimum range of these components for use in LSPIV application to contractions of open-channel flows. Of practical concern (e.g., bridge hydraulics) is flow contraction and contraction scour that can occur in the vena contracta region. The study showed that optimum values for the search area (SA) and interrogation area (IA) were 10 and 60 pixels, respectively. Also, the study produced a curve indicating a trend for vena-contracta width narrowing with a variable ratio of approach-channel and contracted-channel widths and varying bed shear stress of approach flow.

Experimental investigation of the effect of skew angle on partially or fully submerged deck scour

This paper presents the results of an experimental study investigating the effect of skew angle on clear-water contraction scour under a bridge deck at partially and fully submerged flow conditions. Two bridge deck models without a pier, one of which was located perpendicular to the flow while the other one was located with skewness of 15°, were used in the study. Forty experiments were performed for each deck model, 24 of which were under partially submerged and 16 were under fully submerged flow conditions. Analysis of the experimental data showed that as the discharge and approach flow depth increased, the maximum scour hole depth under the skewed deck model increased up to 25%–66% for fully submerged flow and 17%–57% for partially submerged flow conditions. Furthermore, the effect of skew angle significantly enlarged the width of the scour hole as you move along the skewed deck.

Experimental study of clear-water contraction scour

In this paper, experimental results of clear-water scour on a sand bed under short contractions were studied. Sequences of test runs were performed under clear-water conditions for three different contraction ratios. The outcomes of the experiments were employed to define the effects of various parameters on equilibrium scour depth under clear-water scour conditions. In this work, the precision of three maximum scour depth equations was tested from previous studies for contraction scour cases. Two new analytical equations were proposed to calculate time-dependent scour depth and maximum scour at equilibrium conditions, respectively, from the study. The proposed equations were validated using measurements from the present study as well as from previous literature, and the equations show a reasonable agreement between measured and computed values of scour depth under clear-water conditions in short contraction. The presented equations can be used for studying protection of the submerged portion at a bridge abutment or any similar structure.