FLOW CHARACTERSTICS OF VERTICAL GATES WITH DIFFERENT LIP SHAPES

Abstract

The present work has been mainly an experimental investigation with the broad objectives of studying the discharge and pressure characteristics of vertical gate with different types of non-stream lined and stream lined lip shapes at gate bottom. These lips have been placed at the gate bottom and experiments have been conducted in total for fourteen types of lip shapes and four types of bed conditions including three raised ogee crests, marked by variations in the upstream face and one plane bed. In total, six non-stream lines lip shapes and eight steam lined lip shapes have been tested for their discharge and pressure characteristics. Certain simplifications to the existing relationships for computation of discharge through gates are done to bring out similarity between these relationships and relationships based on field data. It is also observed that higher discharge coefficients are obtained in the case of weirs located above raised crest. Discharge coefficient variations are found sensitive to the lip effects. To account for lip effects, correction factors are developed which can be used for different bed conditions and lip types. These correction factors, when multiplied with existing relationships of discharge coefficient, lead to a better match with the observed values of discharge coefficient. Among non-streamlined lip types, lip having equal lip width to lip length is found effective as leads to higher coefficient of discharge than other non-streamlined lip types for a given relative gate opening. For a given lip type, the discharge coefficient is found to be higher when the gate is located above raised crest than the plane bed. This behavior is observed for all the lip types. Regarding pressure variation, the ratio of observed to hydrostatic pressure is found below one. This is influenced by the type of bed profile. For example: ogee weir having upstream face as 2H: 3V is found to experience a lesser pressure than type 1H: 3 V and upstream face vertical. Ratio of observed pressure (P) to gate opening (a) is found to have an increasing trend with the ratio of upstream specific energy (E) to gate opening. Also, this trend is found to be non-linear for different lip types. Only few lip types have been identified which have uniform distribution of pressure across the gate thickness. Based on the Cd variation, ratio of observed to hydrostatic pressure and uniformity of pressure variation, ranking of overall performance of various lip shapes is done. The best performing lip types are identified among non-stream lined and stream lined lip types