CFD simulation of transient startup for a low specific-speed pump-turbine

29th IAHR Symposium on Hydraulic Machinery and Systems

Casartelli, E.^1 ; Ryan, O.^1 ; Schmid, A.^1 ; Mangani, L.^1

Lucerne University of Applied Sciences and Arts, Department of Mechanical Engineering, Technikumstrasse 21, Horw

CH-6048, Switzerland^1

关键词: Dynamic operations;    Increased flexibility;    Low specific speed pumps;    Mechanical integrity;    Pressure fluctuation;    Storage capability;    Transient start-up;    Unsteady vortices;   

Others  :  https://iopscience.iop.org/article/10.1088/1755-1315/240/8/082007/pdf
DOI  :  10.1088/1755-1315/240/8/082007

来源: IOP

【 摘 要 】

Hydropower plants are very well suited for the modern electricity market which depends on increased flexibility and storage capabilities. Nevertheless, increased dynamic operation leads to new challenges in the design as well as the mechanical integrity of the equipment. In particular, the number of start and stops has significantly increased in recent years. The startup of the machine is a transient procedure with considerable load-oscillations which can affect the lifespan of the machine. Detailed understanding of transient effects in pump-turbines is therefore useful for improved prediction of loads and an important tool in pump-turbine layout and design. This study discusses the application of unsteady RANS CFD to fully transient pump-turbine operations. A low specific-speed pump-turbine during startup is investigated and results are discussed accordingly. The boundary conditions are imposed from 1D hydro-acoustic results of the power plant, using time dependent quantities like guide-vane angle, rotational speed and flow rate. Previous studies of the same authors contain simulations such as runaway or load-rejection, where the same method has been successfully applied. Turbine-startup results in terms of head and torque can be compared to the 1D model data for the validation of the CFD procedure. Instantaneous fluctuation of the same quantities can be observed as runner speed increases. A flow feature analysis shows that partial pumping takes place in all individual runner passages, resulting in significant global pressure fluctuations. This phenomenon can be associated with unsteady vortex formation as the characteristic reaches the speed-no load curve close to the S-shape of the characteristic.