Calculating Inlet Pressure for Multi-Outlet Horizontal Irrigation Laterals Considering Variable Outflow in Outlets

Precise calculation of inlet pressure into sprinkler laterals is an important problem for proper distribution of uniformity. The adjusted average friction correction factor، FaAVG، provides the possibility of calculating the inlet pressure to mutli-outlet pressurized irrigation pipelines when the first outlet spacing from the pipe entrance is arbitrary. To investigate the effect of allowable head-loss in the lateral pipeline on inlet pressure، a new equation was developed for calculating this factor. A progression coefficient was assumed for variable discharge of the outlets. The results showed that though the inlet pressure of the lateral depends on the head loss between the outlets، it is negligible when more than 15 outlets are used. It was also concluded that when N is less than 15 and the ratio of distance between inlet and first outlet to outlet spacing is less than 1، the conventional approaches overestimate the inlet pressure. In this research، a new equation was also developed for Christiansen friction factor in which the first outlet is located at a fraction of outlet spacing. This new factor is dependent on the head loss between the first and last outlets، in addition to the number of outlets and the power of velocity equation. The results of applying this new factor showed good correlation with other researchers’ numerical results when a large number of outlets are coalesced.