Physcial hydraulic model investigation of critical submergence for raised pump intakes

[摘要] ENGLISH ABSTRACT: Various design guidelines have been published over the past four decades to calculate the minimum submergence required at pump intakes to prevent vortex formation. These design guidelines also require the suction bell to be located not higher than 0.5 times the suction bell diameter (D) above the floor. Sand trap canals are an integral part of large river abstraction works, with the pump intakes located at the end of the sand trap canals. The canals need to be flushed by opening a gate, typically 1.5 m high, that is located downstream of the pump intake. This requires the suction bell be raised to not interfere with the flushing operation, which leads to the question – what impact does the raising of the suction bell have on the minimum required submergence? A physical hydraulic model constructed at 1:10 scale was used to determine the submergence required to prevent types 2, 5 and 6 vortices for prototype suction bell inlet velocities ranging from 0.9 m/s to 2.4 m/s, and for suction bells located at 0.5D, 1.0D and 1.5D above the floor. The tests were undertaken for four suction bell configurations with a conventional flat bottom suction bell, fitted with a long radius bend, being the preferred suction bell configuration in terms of the lowest required submergence levels. The experimental test results of the preferred suction bell configuration were compared against the published design guidelines to determine which published formula best represents the experimental test results for raised pump intakes. It became evident from the experimental test results that the required submergence increased markedly when the suction bell was raised higher than a certain level above the floor. It was concluded that this 'discontinuity in the required submergence occurred for all the suction bell configuration types when the ratio between the prototype bell inlet velocity and the approach canal velocity was approximately 6.0 or higher. It is recommended that, for pump intakes with a similar geometry to that tested with the physical hydraulic model, critical submergence is calculated using the equation published by Knauss (1987), i.e. S = D(0.5 + 2.0Fr), if the prototype bell inlet velocity/approach canal velocity ratio is less than 6.0, and that the equation published by the Hydraulic Institute (1998), i.e. S = D(1 + 2.3Fr), can be used where the ratio, as determined with Knauss' (1987) equation, exceeds 6.0. It is also recommended that prototype bell inlet velocities be limited to 1.5 m/s.

[发布机构] Stellenbosch University