3D Numerical Simulation versus Experimental Assessment of Pressure Pulsations Using a Passive Method for Swirling Flow Control in Conical Diffusers of Hydraulic Turbines

28th IAHR symposium on Hydraulic Machinery and Systems

Tanasa, C.^1 ; Muntean, S.^2 ; Ciocan, T.^3 ; Susan-Resiga, R.F.^3

Politehnica University of Timisoara, Research Institute for Renewable Energy - RIRE, Victoriei Square, No.2, Timisoara, Romania^1

Romanian Academy, Center of Advanced Research in Engineering Sciences, Timisoara Branch, Bv. Mihai Viteazu, No.24, Timisoara, Romania^2

Politehnica University of Timisoara, Department of Hydraulic Machinery, Bv. Mihai Viteazu, No.1, Timisoara, Romania^3

关键词: 3-D numerical simulation;    Adjustable cross sections;    Circular diaphragms;    Cross-sectional shape;    Experimental assessment;    Operating regimes;    Pressure pulsation;    Pressure recovery coefficient;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/49/8/082018/pdf
DOI  :  10.1088/1755-1315/49/8/082018

来源: IOP

【 摘 要 】

The hydraulic turbines operated at partial discharge (especially hydraulic turbines with fixed blades, i.e. Francis turbine), developing a swirling flow in the conical diffuser of draft tube. As a result, the helical vortex breakdown, also known in the literature as "precessing vortex rope" is developed. A passive method to mitigate the pressure pulsations associated to the vortex rope in the draft tube cone of hydraulic turbines is presented in this paper. The method involves the development of a progressive and controlled throttling (shutter), of the flow cross section at the bottom of the conical diffuser. The adjustable cross section is made on the basis of the shutter-opening of circular diaphragms, while maintaining in all positions the circular cross-sectional shape, centred on the axis of the turbine. The stagnant region and the pressure pulsations associated to the vortex rope are mitigated when it is controlled with the turbine operating regime. Consequently, the severe flow deceleration and corresponding central stagnant are diminished with an efficient mitigation of the precessing helical vortex. Four cases (one without diaphragm and three with diaphragm), are numerically and experimentally investigated, respectively. The present paper focuses on a 3D turbulent swirling flow simulation in order to evaluate the control method. Numerical results are compared against measured pressure recovery coefficient and Fourier spectra. The results prove the vortex rope mitigation and its associated pressure pulsations when employing the diaphragm.