Numerical simulation of freesurface flow in updraftfreeexitflow hydropower turbine
YANG Wei, LIU Zhu-Qing, WU Yu-Lin, GAO De-Yu
(1.College of Water Conservancy and Civil Engineering, China Agricultural University, Beijing 100083, China; 2. Department of Thermal Engineering, Tsinghua University, Beijing 100084, China； 3. College of Engineering, Iowa State University, Iowa 50011,USA)
Abstract：To study the turbine′s internal flow more accurately and improve its hydraulic performance, a geometrical model of the whole flow passage, including casing and runner, was established. An unstructured grid was applied to segment the runner, encrypt the grids on the inner surfaces of the runner blades and the casing guide vane. The sizes of grid clusters were made to meet the y+ for turbulence simulation. Based on RNG k-ε turbulence model, the internal flow was simulated. Taking the effect of free surface flow into consideration, by applying volume of fluid method, a simulated internal flow in an updraftfreeexitflow turbine was obtained. On the basis of the computation of simulation results, the internal flow loss was analysed. It was found that the largest loss was between the stay vanes and the runner inlet, which amounted to 73% of the total loss. The flow details show that the step structure of the area was the direct cause of the loss and exacerbated the runner′s inflow condition. Accordingly, where and how to improve the turbine′s energy performance was inferred.
［1］Brown J J , Pierre St R A. Restoration of American shad Alosa sapidissima populations in the Susquehanna and Delaware Rivers, USA［C］∥Proceedings of Oceans,MTS/IEEE Conference and Exhibition,2001:321-326.［2］Herzog A V, Lipman T E, Edwards J L, et al. Renewable energy: A viable choice［J］. Environment, 2001, 43(10): 8-20.［3］Gopala V R, Wachem B G. Volume of fluid methods for immisciblefluid and freesurface flows［J］. Chemical Engineering Journal, 2008, 141(1/2/3): 204-221.［4］Lopez J, Hernandez J, Gomez P, et al. A volume of fluid method based on multidimensional advection and spline interface reconstruction［J］. Journal of Computational Physics, 2004, 195(2): 718-742.［5］Garrioh S H, Baliga B R. A PLIC volume tracking method for the simulation of twophase flows［J］. International Journal for Numerical Methods in Fluids, 2006, 52(10): 1093-1134.［6］Lopez J, Hernandez J, Gomez P, et al. An improved PLIC-VOF method for tracking thin fluid structures in incompressible two phase flows［J］. Journal of Computational Physics, 2005, 208(1): 51-74.［7］Liovic P, Rudman M, Liow J L, et al. A 3D unsplitadvection volume tracking algorithm with planarity preserving interface reconstruction［J］. Computers ＆ Fluids, 2006, 35(10): 1011-1032.［8］Harvie D J E, Fletcher D F. A new volume of fluid advection algorithm the defined donating region scheme［J］. International Journal for Numerical Methods in Fluids, 2001, 35(2): 151-172.［9］李海峰,吴玉林,王正伟,等.新式环保型上流式水轮机的实验研究［J］.水力发电学报,2002,76(1):89-95.Li Haifeng, Wu Yulin, Wang Zhengwei, et al. Experimental analysis of a new updraft freeexitflow hydroturbine system［J］. Journal of Hydroelectric Engineering, 2002,76(1):89-95.(in Chinese)［10］Li Haifeng, Wu Yulin, Kao D T. Experimental research and turbulent flow simulation of the updraft freeexitflow hydropower turbine system［C］∥Proceedings of ASME 2002 Fluids Engineering Division Summer Meeting,2002.
