Analysis of hydraulic noise characteristics of large mixed-flow turbines based on runner blade modification

Abstract

[Objective] The aim is to investigate the hydraulic noise characteristics and control strategies of large mixed-flow turbines, specifically targeting the hydraulic whistling noise generated during the operation of a specific large mixed-flow turbine. [Methods] The Reynolds-averaged Navier-Stokes(RANS) method was used to perform numerical simulations of the large mixed-flow turbine under hydraulic whistling conditions, both before and after modifying trailing edges of the runner blades. Pressure pulsations were monitored at internal measurement points of key flow-passing components. Using fluid-acoustic coupling, the distribution of external sound pressure levels and internal sound power levels in flow-passing components such as the runner and draft tube were analyzed. The flow field distribution patterns and mechanisms of hydraulic noise reduction before and after the modification of the runner blade trailing edges were analyzed. [Results] The result showed that abnormal pressure pulsation frequencies in the range of 300 to 400 Hz were detected in flow-passing components including the volute, runner, and draft tube. Areas with high sound power levels were mainly located near the trailing edges of the runner blades. [Conclusion] The findings indicate that complex vortex structure is one of the causes of hydraulic noise in turbines. Modifying the trailing edges of the runner blades can achieve hydraulic noise reduction in turbines.

Keywords

hydraulic turbine / numerical simulation / blade modification / pressure pulsation / hydraulic noise / Reynolas-Averaged-Navier-Stokes(RANS) method / fluid-structure-acoustic coupling / operational stability