Construction of a reduced-order dynamic model for prospective swirling flow control in hydraulic turbine draft tube

Abstract

Vortex rope in Francis turbine draft tubes poses serious problems. Emphasis on operation of the turbines in wide operating range, quite far from the design point, is a challenge for both the turbine designers and power plant owners. While flow control becomes popular in aircraft and automotive industry, it is still feared in turbomachinery. Present paper brings results of investigations aimed on construction of a reduced order model, which describes dynamics of the swirling flow in the draft tube. First step is assesing the dominant modes of the flow, second step is projection of those modes onto a transport equation. Final set of ordinary differential equations is a relatively simple model of the time evolution of the flow dynamics, which is basis for the flow control aiming on mitigation of the instabilities (e.g. vortex rope).