Abstract
Tubular turbine is a type of turbine with low-head. Due to the fact that the runner of a tubular turbine is of axial-flow type, there will be a certain width of blade tip between the blade and the chamber. In order to explore the influence of tip clearance width on the flow inside the turbine, taking the model tubular turbine as the research object, six different tip clearance widths were compared and analyzed. The research shows that the increase in blade tip clearance width affects the performance of the turbine, reduces the minimum pressure at blade tip and causes cavitation in advance. Larger tip clearance width significantly increases pressure pulsation intensity inside the turbine, especially in the vaneless region between the runner and guide vane and the area of the runner tip. However, the increase in tip clearance width can greatly reduce the axial force for about 100 N and radial excitation force for about 50% of rotating parts. Therefore, during the design and processing of tubular turbines, the blade tip clearance width should be carefully selected to ensure safe and stable operation of the unit.
Highlights
Tubular turbines are used for low-head hydropower stations
The results show that the tip clearance width is directly proportional to the axial velocity, momentum and flow of the tip leakage vortex and inversely proportional to turbulent flow energy
1 is the flow passage of tubular turbine studied in this paper study takes a model turbine of tubular turbine as the research object and analyzes
Summary
Tubular turbines are used for low-head hydropower stations. It has a large size and suits large flow rate and low rotational speeds [1,2,3]. Conducted numerical simulation calculation and analysis on the operation of the blades of axial flow pumps under different rotating speed conditions and found that the cantilever blade root is prone to fracture, and the deformation of the blade tip is large and can occur, which is not conducive to the safe and stable operations of the unit Another problem includes unstable tip leakage flow. Dreyer and Decaix et al [21,22] analyzed the tip leakage vortex (TLV) structure and strength of hydrofoil flow field with different tip clearance widths by using an experimental method and numerical simulation, respectively. CFD simulations and model experiments, and the influence of the runner tip leakage width in the high efficiency turbine mode is in-depth discussed; the visualization of internal flow characteristics of a tubular turbine is realized, which has a clear guiding significance for engineering.
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