Submerged Flow Below Sluice Gate
Introduction: Discharge through the irrigation canals is commonly controlled by means of gates. Based on the downstream water level, the flow is classified as free or submerged flow. Both the free and submerged flow below sluice gates without sill was studied extensively. When the gate height exceeds some specific design criterion, double or triple leaf gates are recommended. In cases where construction of double or triple leaf gates is not desirable for economic reasons, a sill is constructed under the gate to reduce its height to meet the design criterion of single leaf gate. The use of the under-gate sill affects the flow behavior below and downstream of the gate. Sills may improve or disapprove the flow characteristics below and downstream the gate depending upon the sill geometry and type of flow.
Theoretical Background: a typical definition sketch for submerged flow below a sluice gate with sill. Applying the principles of dimensional analysis, the following functional relationship for coefficient of discharge of submerged silled sluice gate, Cds, can be proved as:
Where Cds is the discharge coefficient of silled sluice gate; G is the gate opening height; H1 is the effective upstream water depth =H-Z; H is the total upstream water depth.
The discharge coefficient (Cds) of sluice gate with sill for submerged flow is computed using the following equation:
In which W is the width of the flume?
Experimental Set-Up: A glass sided tilting re-circulating flume of 2.5 m long was used to conduct the experiments of the present study. The flume bed is 10 cm wide and 20 cm deep. The water depths were measured by means of point gauges mounted on instrument carriages. The discharge was measured by means of a pre-calibrated V-notch. The flume has a sluice gate which was made from an aluminum plate, 5 mm thick with a sharp beveled lower edge to control the upstream water depth. The flume is supplied by water from a constant head tank. The tail water is controlled by a tail gate located at the downstream end of the flume. Trapezoidal sills of different heights (1, 2 and 3 cm) having constant upstream slope (1:1) and constant downstream slope (1:5) were tested under different gate openings and discharges. In addition, a flatbed model was included for the comparison purposes. The sills were made from plastic material. The gate was located at the center line of the top width of the under-gate sill which was 3 cm wide. The discharges range between 30 l/min to 198 lit/min
For each of the tested model, a specific gate opening was set and a certain flow rate was allowed to pass through the flume. After attaining stability conditions, the upstream, the downstream and the tail water depths were measured. The discharge and the gate opening were recorded.