Author(s): P Rudolf; B Oberta; D Stefan

Linked Author(s):

Keywords: Vortex rope; Hydraulic turbine; Draft tube; Shape optimization; Swirling flow

Abstract: Vortex rope is a typical undesired phenomenon occurring in draft tube of Francis turbines operated under off-design operating conditions. It is characterized by pressure pulsations (synchronous and asynchronous), which influence dynamics of the hydraulic turbine and often cause limiting of the turbine operation. Because vortex rope is result of flow instability, there is a chance to influence the instability onset by modification of boundary conditions. Present contribution is focusing on mitigation by proper shaping of the draft tube walls. The approach is based on automatic procedure using coupling of CFD simulations and mathematical optimization methods. Efficient, yet robust, combination of stochastic optimization PSO algorithm with direct search Nelder-Mead method makes up sufficiently global, but relatively fast optimization algorithm. To make the whole optimization loop feasible, only 2D axisymmetric domain is assumed and the goal is minimization of the backflow region, which is an indivisible feature of the vortex breakdown instability.

DOI: https://doi.org/10.1088/1755-1315/1483/1/012040

Year: 2023