Numerical prediction and similarity study of pressure fluctuation in a prototype Kaplan turbine and the model turbine

• Published in: Computers & fluids Vol. 56; pp. 128 - 142
• Main Authors: Wu, Yulin, Liu, Shuhong, Dou, Hua-Shu, Wu, Shangfeng, Chen, Tiejun
• Format: Journal Article
• Language: English
• Published: Kidlington Elsevier Ltd 15.03.2012; Elsevier
• Subjects: Applied sciences; Computational methods in fluid dynamics; Draft tubes; Engines and turbines; Exact sciences and technology; Fluctuation; Fluid dynamics; Frequency; Fundamental areas of phenomenology (including applications); Hydraulic turbines; Mathematical models; Mechanical engineering. Machine design; Navier-Stokes equations; Physics; Pressure fluctuation; Prototype Kaplan turbine; Prototypes; Similarity; Turbines; Turbulence simulation and modeling; Turbulent flow; Turbulent flows, convection, and heat transfer; Unsteady flow simulation; Pressure fluctuation; Frequency; Similarity; Prototype Kaplan turbine; Unsteady flow simulation; Turbulent flow; Computational fluid dynamics; Navier Stokes equation; Numerical simulation; Unsteady flow; Kaplan turbine; Modeling; Mesh generation; Turbulence structure; Hydraulic turbine
• ISSN: 0045-7930; 1879-0747
• DOI: 10.1016/j.compfluid.2011.12.005

► Pressure fluctuation in a Kaplan turbine is predicted at several survey points. ► Similarity of pressure fluctuation between prototype and model turbines is found. ► Pressure difference on each section is indication of relative pressure fluctuation. ► Pressure suddenly rising is found in the draft tube at a frequency. ► Resonance of the water body system may be related to the pressure suddenly rising. In this paper, the Reynolds averaged Navier–Stokes equations coupled with the RNG k– ε turbulence model are employed to simulate the unsteady turbulent flow throughout the whole flow passage of a prototype Kaplan turbine. The behavior of the pressure fluctuation in the prototype Kaplan turbine, which includes the amplitude and frequency, is predicted and analyzed at several survey points in the turbine. Then, the mechanisms of generation and transmission of the main pressure fluctuation in the prototype turbine are discussed. After that, the frequency and amplitude of pressure fluctuation in the prototype turbine are compared with those of the model turbine. It is found that there is a similarity of pressure fluctuation between the prototype Kaplan turbine and the model turbine except at low frequency. At low frequency, the similarity of the pressure fluctuation fails due to the difference of the Reynolds number between the prototype turbine and the model turbine. It is observed from the simulation results that the pressure difference between the maximum and the minimum of pressure on each section of the draft tube can be utilized to estimate the relative pressure fluctuation in the draft tube for both the model and prototype turbines. It is also found in the frequency domain that there is a pressure fluctuation frequency at which the pressure suddenly rises in the draft tube. It is possible that this phenomenon is induced by the resonance nature of the water body system in the draft tube. At last, the comparison of pressure fluctuation at on-cam and non on-cam operation conditions of the prototype turbine is also carried out.