Discharge measurement in terms of pressure differences at bridge piers

[摘要] ENGLISH ABSTRACT: This study entailed the investigation and evaluation of a new methodology for measuring highdischarges passing through bridges. Pressure differences generated around bridge piers have beenmeasured and related to the discharges. These pressure differences are mainly functions ofdownstream flow conditions. The pressure differences have been converted into velocities byapplying Newton's second law expressed in terms of the laws of conservation of energy;momentum; and of power.The energy principle was re-evaluated following a preVIOUSstudy (Retief, 1999) on a limitednumber of model pier combinations and flow conditions. Comparison of the energy approach withnewly developed theories in terms of the momentum and power laws respectively led to theconclusion that the energy principle gave the best results. The question of applicability of thetheory to practical pier/stream width and length ratios as well as its validity under flow conditionscommonly found under flood conditions required that additional laboratory tests be done.The energy-based discharge equation was calibrated in terms of newly selected measuring points,different pier width and length ratios, as well as pier rotations for both super and sub-criticaldownstream conditions. According to the new tests performed at the Hydraulics Laboratory of theUniversity of Stellenbosch on model piers, clear relationships were found between discharges andpressure differences measured against the pier. Calibration curves for practical flow measurementapplication were derived in terms of principle dimensionless parameters.Application of the energy approach at the prototype level needs further investigation.

[发布机构] Stellenbosch University