خصوصيات جريان در سرريزهاي جانبي و نرمال لبه تيز مستطيلي

چكيده انگليسي :

Characteristics of Flow over Rectangular Sharp Crested Side and Normal Weirs Sara Bagheri s bagheri@ag iut ac ir September 29 2010 Department of Water Engineering College of Agriculture Isfahan University of Technology Isfahan 84156 83111 Iran Degree M Sc Language Farsi Dr Manouchehr Heidarpour heidar@cc iut ac ir Abstract The weirs are the simplest least expensive and probably most accurate hydraulic structures for controlling and measuring water flow in open channels The most common types of weirs are rectangular sharp crested weirs This kind of weirs could be investigated in two types of side and normal weirs Side weirs set into the side of a channel for diverting a portion of the discharge when the water surface rises above the weir crest level Side weirs are used in irrigation and drainage networks urban sewage systems storm relief separating of sediment and reduction of bed load Flow over side weirs is a typical case of spatially varied flow in which discharge is reduced along of the main channel Normal weirs set perpendicular to the flow direction and raise the upstream water level In this situation the spilling velocity increases and a two dimensional flow occurs over the crest of weir In this study the hydraulic characteristics of 15 physical models of rectangular sharp crested side weirs in subcritical flow were considered Discharge coefficient flow nappe profiles variation of specific energy three dimensional velocity distributions over the crest variation of boundary layer thickness variation of discharge and angle of the spilling jet along the crest of weir were investigated The results show that at the upstream and downstream of the side weir which are far from the weir plane the flow could be considered to be almost horizontal and the values of Vy and Vz are small The results revealed that the highest values of Vx that referred to the longitudinal velocity occur near the beginning of the weir while the lowest values of this component of velocity would take place close to the end of the weir The velocity Vy shows the vertical velocity over the crest of weir The values of Vy demonstrated that the flow moves upward near the crest of weir With increasing the depth the y velocity gradually decreases until the downward flow is generated at the water surface The Vz that implies the velocity of spill flow over the side weir increases along the crest of weir from the beginning of the weir toward the end of it The maximum of Vz was observed close to the end of the weir Analyzing the velocity profiles indicates that elementary discharge increases along the crest of weir When the weir width decreases the elementary discharge increases but the upstream Froud number does not have significant effect on this parameter Opposite of the elementary discharge the difference of flow depths at upstream and downstream of the weir and the angle formed by the spilling jet with the normal to the plane of weir are increased by increasing the Froud number Analyzing the data shows that the thickness of boundary layer varies along the crest and the highest values of take place near the middle of side weir For comparison between side and normal weirs flow nappe profiles and discharge coefficients of 19 physical models of rectangular sharp crested normal weirs were measured It was found that the upper and lower nappe profiles could be approximated very closely by quadratic and cubic equations respectively The variation of discharge coefficient of normal weirs with Froud number is not considerable but this coefficient is dependent to the dimensionless head of flow to weir height h P In contrast with normal weirs side weirs discharge coefficient is closely related to the upstream Froude number and the influence of h P is small In addition the discharge coefficients of normal weirs are higher than side weirs for the same condition Ultimately two semi empirical methods for estimating discharge coefficient of normal weirs and three empirical meth

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خصوصيات جريان در سرريزهاي جانبي و نرمال لبه تيز مستطيلي

ضريب دبي , نيم رخ سطح آب , توزيع سرعت سه بعدي