Numerical and Experimental Study of the Unsteady Friction Influence on Water Level Oscillation in the Simple Hydraulic Circuit with a Surge Tank

The hydraulic transient in pipes is an important study subject for the correct choice and design of the damping structure which protects the circuit from the abrupt variation of the internal pressure caused by the change in the average flow velocity. This paper shows the influence of unsteady friction on water level oscillation generated by the abrupt closing valve. For this purpose, the computational fluid dynamics (CFD) is applied to modeling the 3D problem, and to evaluate the transient flow or water level oscillation inside the protection structure called Surge Tank. The experimental investigation includes water level measurements in a simple surge tank model of the hydraulic circuit installed at the Hydraulic Laboratory of the Civil Engineering Department, in Polytechnic School - University of São Paulo. Collected data were compared with theory and results of the numerical modeling, and used to calibrate model parameters to determine the unsteady friction. Good agreement between data and numerical results was obtained. This work applies Ansys CFX software that uses the finite volume technique to solve the 3D fields of velocity and pressure in both steady and transient flows.