Study On Hydraulic Characteristic Of The Multioutlet Pipeline

Hydraulic calculation of multioutlet pipeline and tapered multioutlet pipeline wasinevitably involved in the hydraulic design of the manifold in Mountain gravity-fed dripirrigation system. The accrancy of hydraulic calculation of these two types of pipeline wasdetermined by estimation of head loss. Calculation of head loss was departed to the local headloss and the frictional head loss. The previous researches made a lot of progress on frictionalhead loss calculation. And the formula proposed was used efficiently with high accuracy. Forlocal head loss,it was usually treated as the constant percentage of local head loss in frictionalhead loss. However, in the hydraulic calculation of pipe network, the local head loss of thenodes had a significant impact on flow distribution and pressure distribution of each pipes,gnoring the local head loss or using the fixed local energy loss coefficient may lead todeciation from true results, the deciation had directly effect on the accrancy of hydrauliccalculation of pressure head distribution and the hydraulic design of the multioutlet pipeline.In order to improve the level of hydraulic calculation of the multioutlet pipeline, throughtheoretical analysis, experimental research and numerical simulation, Study was conducted totest the flow resistance and the pressure head distribution of the multioutlet pipeline in thispaper. The results was as follows:(1) the effects of Reynolds number on the local resistance coefficient of main branch toside branch1was not significant,1increased with increasing of flow rate, and1decreasedwith increasing of cross-section ratio. The effects of cross-section ratio on local resistancecoefficient of main branch to straight branch2was not significant, and decreased withincreasing of Reynolds number, and firstly decreased and then increased when flow ratio wasgrowing. Empirical equations were proposed simultaneously to calculate the local resistancecoefficient. The results showed that the local resistance of main branch to side branchincluded impact loss, contraction loss and the diffusion loss of the swerves, and the localresistance coefficient of main branch to straight branch was effected by turning loss and sidebend loss. (2) As compared with the experiment results of the pressure head distribution of multipleoutlets pipeline, the empirical equation proposed had a high calculation accuracy for lateralinlet pressure head along the manifold. Then the pressure head distribution of the multioutletpipeline was analyzed using the empirical equation of the local resistance coefficient in thispaper. The results showed that lateral inlet pressure head along the manifold decreased withincreasing of lateral inlet flow, decreased with increasing of number of lateral, decreased withincreasing of interval of lateral and increased with increasing of slope.(3) the effects of Reynolds number on the local resistance coefficient of reducing joint was not significant, and decreased with growing of cross-section ratio. Also empiricalequations were given simultaneously to calculate the local resistance coefficient. The resultsshowed that the vortex flow was generated near the wall of tube in the contraction Section,the streamline was bended and velocity obviously changed. The flow exactly came into thedownstream straight pipe, a pressure gradient was evidently generated near the wall, whichwas mainly due to generate flow detachment surface. with decreasing of cross-section ratio,the vortex flow was even more generated near the wall of tube in the contraction Section andthe streamline was seriously bended.(4) As compared with the experiment results of the pressure head distribution of thetapered multiple outlets pipeline, the empirical equation proposed had a high calculationaccuracy for lateral inlet pressure head along the manifold. The pressure head distribution ofthe tapered multioutlet pipeline was analyzed using the empirical equation of the localresistance coefficient in this paper. The results showed that lateral inlet pressure head alongthe manifold decreased with increasing of lateral inlet flow, decreased with increasing ofinterval of lateral and increased with increasing of slope.