Numerical simulation of the blade channel vortices in a Francis turbine runner

Abstract

Purpose This study analyzes the blade channel vortices inside Francis runner with a particular focus on the identification of different types of vortices and their causes. Design/methodology/approach A single-flow passage of the Francis runner with refined mesh and periodic boundary conditions was used for the numerical simulation to reduce the computational resource. The steady-state Reynolds-averaged Navier–Stokes equations closed with the k-ω shear–stress transport (SST) turbulence model were solved by ANSYS CFX to determine the flow field. The vortices were identified by the second largest eigenvalue of velocity. Findings Four types of vortices were identified inside the runner. Three types were related to the inlet flow. The last one (Type 4) was caused by the reversed flow near the runner crown and had the lowest pressure inside the core near the runner outlet. Thus, in the blade channel vortex inception line, Type 4 vortex would appear earlier than the other three ones. Besides, the Type 4 vortex emerged from the crown and shed toward the blade-trailing edge. And its location moved from near the crown down to near the band when the unit speed increased or unit discharge decreased. Research limitations/implications Although the refined mesh was used and the main vortices in the Francis runner were well predicted, the current mesh is not enough to accurately predict the lowest pressure in the channel vortex core. Practical/implications This knowledge is instructive in the runner blade design and troubleshooting related to the channel vortex. Originality/value This study gives an overview of the main observed blade channel vortices and their causes, and points out the important role the reversed flow plays in the formation of blade channel vortices. This knowledge is instructive in the runner blade design and troubleshooting related to blade channel vortices.

RANS and LES Simulations at Partial Load in Francis Turbines : Three-Dimensional Topology and Dynamic Behaviour of Inter-Blade Vortices

“…Then, the flow field at the inlet of the runner is strongly misaligned. These vortices are also already presented in the literature [6].…”

“…A small vortex in the junction between the leading edge and the shroud, identified by Zhou et al [6] as another type of vortex, has also been observed for all the operating points.…”

“…Flow analysis in the runner shows that this backflow region plays a major role in the formation of the inter-blade vortices. In another numerical investigation, Zhou et al [6] show with RANS computations and k-ω SST model that the vortex related to the reverse flow is the most prone to cavitation. Moreover this article suggests a classification of the inter-blade vortices appearing in the runner into four types.…”

Analysis of Channel Vortex and Cavitation Performance of the Francis Turbine under Partial Flow Conditions

“…Guo Pengcheng et al [17][18][19] carried out experiments with numerical models on Francis turbines to analyze the development mechanism of channel vortices and made a comparative analysis of the shapes of cavitation vortices inside the channel by using said models in experiments. Liu [20][21][22][23] et al used a high-speed camera to capture the channel vortex phenomenon during a test and found that the channel vortex occurs due to the influence of the attack angle at the blade inlet. Su Wentao et al [24] carried out numerical simulations and tests on a Francis turbine, which verified the feasibility and accuracy of the LES method based on a cavitation model in predicting the performance of Francis turbines under partial flow conditions, while Trivedi Chirag et al [25,26] used the LES method to simulate the load change of a Francis turbine and compared the results with experimental data.…”

Numerical simulation of pressure pulsation effects of a snubber in a CNG station for increasing measurement accuracy

“…Commonly used simulation programs are based on a numerical solution of the one-dimensional classical fluid mechanics equation by the method of characteristics. Zhou, Liu, Wang, Liu, and Zhao (2017) numerically investigated an unsteady multiphase flow in the whole passage of a Francis hydraulic turbine. In their research, pulsation of the pressure was forecast and compared with the data experimentally obtained.…”