Simulation-based investigation of unsteady flow in near-hub region of a Kaplan Turbine with experimental comparison

Abstract

This paper presents a detailed comparison of steady and unsteady turbulent flow simulation results in the U9 Kaplan turbine draft tube with experimental velocity and pressure measurements. The computational flow domain includes the guide vanes, the runner and the draft tube. A number of turbulence models were studied, including the standard k − ε, RNG k − ε, SST and SST-SAS models. Prediction of the flow behavior in the conical section of the draft tube directly below the runner cone is very sensitive to the prediction of the separation point on the runner cone. The results demonstrate a significant increase in precision of the flow modeling in the runner cone region by using unsteady flow simulations compare to stage simulation. The prediction of the flow in the runner cone region, however, remains delicate, and no turbulence model could accurately predict the complex phenomena observed experimentally.

Simulation of steady and unsteady flows through a small‐size Kaplan turbine

“…Examination of the variation of efficiency with turbulence intensity showed a slight sensitivity with levels of 1%, 5%, and 10%, and thus an intensity level of 5% was selected. Mulu et al adopted a similar value and concluded that the turbulence intensity has a slight effect.…”

Numerical analysis of fluid-added parameters for the torsional vibration of a Kaplan turbine model runner

“…The fluid part has been experimentally and numerically investigated in detail by Mulu and colleagues [22][23][24] , Jonsson et al 25 and Amiri et al [26][27][28] This model is a 1:3.1 scale of the 10 MW prototype turbine, which has a runner diameter of 1550 mm. The turbine is composed of 18 unequally distributed stay vanes, 20 guide vanes, and 6 runner blades.…”

“…The computational model used in this study is presented in Figure 1, which was extracted from the numerical simulations of Mulu et al 24 The spiral casing and stay vanes are omitted because their presence is not required to capture the flow near the runner.…”

“…According to the numerical simulation of Mulu et al, 24 who investigated many turbulence models (k2e, re-normalisation group (RNG) k2e, shear stress transport (SST) and scale-adaptive simulation-shear stress transport (SAS-SST)) to simulate the Porjus U9 model at the BEP, the standard k2e model with a scalable wall function is suitable and was used to perform the simulations. A scalable wall function can handle fine meshes near the wall regardless of the Reynolds number.…”

“…The mesh used in the simulations was selected based on the mesh study of Mulu et al 24 Hexahedral-type elements were used for all parts, including the guide vanes, runner, and draft tube. The mesh resolution at the hub clearance and tip clearance is shown in Figure 2.…”