Allowance for secondary flows in the 3 D numerical flow models of piping systems

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Allowance for secondary flows in the 3 D numerical flow models of piping systems

Klasinc, R. / Dum, T. / Knoblauch, H. / Reitbauer, R.

The subject of this paper is turbulent pipe flow, a phenomenon of great importance in the hydraulic structures of hydro power schemes. The aim of our studies was to test and adapt a three-dimensional numerical program for general use in hydraulics. A program has been developed that is based on the differential equations by Navier-Stokes, using the finite volume method for the discretization of the flow field. The numerical results were compared with the hydraulic parameters measured on the physical model. Two geometries were investigated: a sudden expansion of a pipe and a T-junction. A great number of pressure and velocity values were measured at different points, using the LDA system. For the sudden expansion, good agreement with the calculation using the k-epsilon model was obtained. As to the T-junction, a strong secondary flow was seen to be present. In order to improve the results of the numerical calculation, the k-epsilon model was substituted by a Reynolds stress model (RSM), which brought results that were considerably closer to the physical conditions. This study has shown that even for complex flows, appropriate turbulent models are of practical use.