Discharge characteristics of orifice spillway under oblique approach flow

In the conventional practice of design of canal drops, long length of inlet and outlet transitions are provided for improving performance. They are very costly and their hydraulic performance too is not satisfactory. Analytical and experimental studies were undertaken by the author to find an economic and innovative method of design. Optimum fluming ratio and optimum length of transitions are found both for economy as well as good performance. An innovative and economic stilling basin with rapidly diverging side walls and adversely sloping floor which act simultaneously as energy dissipater and expanding transition has been recommended. An example has been worked out to illustrate the design procedure of a typical canal drop.

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Economic and innovative design of a canal drop

Reservoir sedimentation is significant for the efficiency and life of a dam. Flushing orifices have been used in many small dams and other hydraulic structures to remove deposited sediments. Tempor...

Time evolution of scour hole and flow characteristics upstream of a flushing orifice

Innumerable falls are to be provided in irrigation canals where ground slope exceeds the permissible bed slope of a canal. In the conventional method of design, fluming ratio is fixed arbitrarily irrespective of inflow Froude’s number. Long lengths of inlet and outlet transitions are provided to prevent flow separation. Transition and dissipation structures are kept separate resulting in high costs. Hydraulic performance of the conventional fall structure is also not so satisfactory. Analytical and experimental studies were conducted by the author to find an efficient and economic method of design of falls. Optimum fluming ratio and optimum length of transitions are found both for economy as well as efficiency. An efficient and economic stilling basin with rapidly diverging side walls and adversely sloping floor, which act simultaneously as energy dissipater and transition, has been recommended. An example has been worked out to illustrate the design procedure of the proposed canal fall.

Economic and efficient method of design of a flumed canal fall

The flow through a breast wall spillway is greatly affected by the centripetal force due to a downstream curved profile. Therefore, the mean vertical pressure distribution at the outlet section is not consistent with the hydrostatic pressure law. This distribution in turn affects the discharge capacity of the breast wall spillway. This paper experimentally studies the effect of a convex downstream profile on the mean pressure variation and the discharge of a breast wall spillway without gates. It is indicated that the effect of the curvilinear streamline on the mean vertical pressure variation is significant. The regression analysis method is used to determine the water head effect Zo of the orifice opening through the mean pressure variation. A discharge prediction formula of the breast wall spillway is obtained under the limited conditions of a laboratory flume. The predicted discharge is compared to the measured discharge. A good agreement is evidenced for the free orifice flow with errors within ±5%, while a big error (20% or even more) is obtained if the hydrostatic pressure law is used for the determination of Zo.

The effect of a curved bed on the discharge equation in a spillway with a breast wall

Conventional flow meters have several drawbacks which were overcome in the improved design. Geometry of the control section of the flow meter was determined theoretically in order to maintain normal depth—discharge relation upstream. Model dimensions were computed from prototype canal with a scale of 1:30. The improved flow meter has high modular limit and nearly constant coefficient of discharge under free flow condition. Conventional expansive transition provided at the outlet of the flow meter was replaced by straight expansion. Studies were made with four different lengths of expansion governed by side splays 0:1, 1:1, 2:1 and 3:1. With level bed, the hydraulic performance of expansions defined in terms of efficiency (η0) and Coriolis coefficient (α2) were found to be extremely poor. Separation of flow occurred right from the entry of the expansions resulting in highly non-uniform velocity downstream. By providing adverse slopes to the expansion floor, performance of the flow meter was found ...

Improved design of a proportional flow meter

Theoretical value of discharge for orifice flow in a gated Ogee spillway was computed using U.S.B.R. and Sinniger equations. Experimental values were found to be substantially different from the theoretical values. Pressure correction factor found to be a function of both head and gate openings, was calculated by least square curve fitting. Discrepancy between theoretical and experimental values of discharge were reduced substantially with the introduction of the pressure coefficient Cp.

Indroniel Deb Roy

Papers

Improved design of a proportional flow meter

Orifice flow in a gated spillway

Discussion on Improved Design of a Proportional Flow Meter