Performance Prediction of Hydraulic Turbomachinery

Abstract

In this paper an accurate and efficient numerical algorithm for simulation of three-dimensional turbomachinery flows is presented. This model is used later for turbomachinery performance prediction. Mathematical model is based on the RANS equations that are written in non-inertial frame of reference. Reynolds stresses are approximated with Boussinesq hypothesis using two-equation k-ω near-wall turbulence closure. Discretization of convective fluxes of the mean flow equation is performed using central differences, by explicitly added eigenvalue scaling non-isotropic matrixvalued artificial dissipation. In turbulence closure equations, numerical convective fluxes are approximated according to Roe second order upwind scheme in conjunction with monotone (TVD) variable extrapolations. The semi-discrete equations are advanced in time using a four stage explicit Runge-Kutta scheme enhanced with local time stepping, variable coefficient implicit residual smoothing and multigrid acceleration. Developed software is applied for numerical analysis of work processes in the model of NEL mixed-flow bowl pump. Obtained numerical results are in good agreement with the available experimental data in the operating conditions at the best efficiency point (BEP). Also, turbopump performances are simulated for number flow rates and constant shaft speed, corresponding to the off-design operating conditions. According to information from numerical experiment, methodology for design performance characteristics is shown. By further improvement of mathematical model, the developed methodology enables that, from an engineer's perspective, numerical experiment could be a useful, low-cost tool in comparison with the expensive measurements. Using the dimensionless characteristics as well as theory of conformity, the turbopump performance can be calculated within the wide operating regimes in a relatively simple way.