FLOW ANALYSIS OF PENSTOCK FOR MULTIPLE OUTLETS USING COMPUTATIONAL FLUID DYNAMICS

Abstract

Penstock is used for transporting water from intake to the turbine. In case of two or three turbines being fed through a common penstock, it will be generally bifurcated or trifurcated to supply water to turbines respectively. It is mostly recommended to keep the angle of trifurcation between 30-60 degree, however not much information is available for the angle of orientation between the b ifurcat ion/trifurcat ion and ground level. Normally the penstock is oriented in line with the topography of site and the location of its branching does not depend on the angle of orientation at that point. In this work, the effect of orientation angle of trifurcation on the flow held has been investigated numerically. The orientation angle has been changed from 10-90 degree, in step of 10 degree. Commercial CFD code of ANSYS has been used to develop hexahedral mesh in the computational domain and k-epsilon turbulence model has been used to solve N-S equation by applying second order upwind scheme. Velocity inlet and pressure outlet have been used as boundary conditions. It is observed that the average velocity through each branch pipe remains unaffected till the angle of orientation reaches 50 degree. The velocity starts decreasing from 50 degree orientation angle, reaches the minimum at 60 degree and then rises till 70 degree. The velocity in the region of 0-50 degree and 70-90 degree remains constant while it shows a fall in the region of 50-70 degree, owing to effect of generation turbulence in the flow. It has been noticed that flow separation is taking place inside the trifurcation when the orientation angle is kept 60 degree, resulting in turbulent flow inside the trifurcation. l-Ience it would be better to avoid 60 degree orientation angle.