A COMPARATIVE STUDY OF PENSTOCK TRIFURCATION MODELS

Abstract

A power tunnel feeding three hydroelectric units may necessitate the use of a penstock trifurcation if branching is not done by the conventional Wye arrangement. The hydraulic design of a suitable penstock trifureation has to be arrived at on the basis of a comparative study of different alternatives. The results of model studies of only a few trifurcation models are available, This thesis deals with the experimental study of the losses at trifurcations of three different types (1) trifurcation with suitable transition, (ii) two Wye junctions and (iii) trifurcation with an'abrupt junction. A compara-tive study of different trifurcation models including model studies carried out elsewhere is presented in this thesis. The present study of trifurcation models has been made with air as the fluid on a 1 I 13 scale-model of the proposed penstock trifurcation for Ram Gangs ProjeCt in Uttar PradeSh. The energy.loss coefficients for different operating conditions have been determined. Dimensionless plots of the pressure distribution along the arc length are drawn for different Reynold's numbers. The results indicate ,Goe,Sc■ 0- that for Reynold's number greater than 103, head lossLis almost independent of the Reynold's number, The energy loss coefficient for trifurcation provided with transition is appreciably less than for the trifuroation with abrOpt Juno.. tion or two Wye junctions for the condition of all the three pipes running, Where as the superiority of trifurcation with transition is established beyond doubt over trifurca. tion with abrupt entry, the Wye model is adjudged suprior to other two for single pipe running condition, A trifurca tion model shaped so. that the stagnation point is shifted in the flow direction seems to be preferable to a trifur• cation model in Which transition begins at one transverse section. This is because the flew is better guided into the different branches in the former case