PREDICTION OF UNSTEADY HYDRAULIC FORCE IN A MIXED-FLOW PUMP WITH VOLUTE CASING BY USING LARGE EDDY SIMULATION

摘要

A mixed flow pump with a double volute casing whose specific speed was 800 was simulated. The calculated flow rates were Q/Q_d x 100 = 0, 40, 80, 100, 120%, where Q_d is the design point. The Smagorinsky model was used for the turbulent eddy viscosity model of Large Eddy Simulation (LES), and the model constant was 0.15. The total head, shaft power, and pump efficiency for each flow rate were predicted with accuracies of +8 to +12%, -3 to +11%, and -3 to +10% compared with the experimental data. The power spectrum of the unsteady radial hydraulic force predicted by LES showed that the higher harmonics of the blade passing frequency were computed accurately. That kind of spectrum was generated by the interaction between the rotating impeller and the stationary casing. And that result indicated that the unsteady flow of the pump was accurately resolved with our LES code. The unsteady radial hydraulic force for each flow rate was predicted with an accuracy of -3 to +11% compared with the experimental force. The largest force at the shut-off point (Q/Q_d x 100 = 0%) was predicted with high accuracy (+5%). This level of accuracy showed that the numerical simulation using our LES code was able to predict the unsteady hydraulic force with a practical level of accuracy.