Abstract
To study the effect of tip clearance on unsteady flow in a tubular turbine, a full-channel numerical calculation was carried out based on the SST k–ω turbulence model using a power-plant prototype as the research object. Tip leakage flow characteristics of three clearance δ schemes were compared. The results show that the clearance value is directly proportional to the axial velocity, momentum, and flow sum of the leakage flow but inversely proportional to turbulent kinetic energy. At approximately 35–50% of the flow direction, velocity and turbulent kinetic energy of the leakage flow show the trough and peak variation law, respectively. The leakage vortex includes a primary tip leakage vortex (PTLV) and a secondary tip leakage vortex (STLV). Increasing clearance increases the vortex strength of both parts, as the STLV vortex core overlaps Core A of PTLV, and Core B of PTLV becomes the main part of the tip leakage vortex. A “right angle effect” causes flow separation on the pressure side of the tip, and a local low-pressure area subsequently generates a separation vortex. Increasing the gap strengthens the separation vortex, intensifying the flow instability. Tip clearance should therefore be maximally reduced in tubular turbines, barring other considerations.
Highlights
TLVflow structure axial on flow pumps high-speed to study the tip leakage vortex (TLV) structure pumpsofbased different based on different tip clearances
To improve the reliability of the numerical results, this study considers the tubular turbine of a power station as the research object and uses UG NX 12.0 commercial software to complete the model design
To study theResults leakage flow leakage vortex characteristics of the hydraulic turbine underTo different clearances, unsteady numericalvortex calculation results of threeof structures studytipthe leakagethe flow and leakage characteristics the hydraulic with tip clearance δ1 = 5 mm, δ2 = 10 mm, and δ3 = 20 mm were analyzed under the rated under different tip clearances, the unsteady numerical calculation results of thre flow condition Qr
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. The tubular turbine has the advantages of a short construction period, small investment, large excess flow, high efficiency, good cavitation performance, and fewer blades. It is widely used in the development of low-head water resources [7,8,9]. Processes 2021, 9, 1481 of 14 studied the formation mechanism and geometric influence of the tip leakage vortex 2(TLV). Taha et al [17] studied the performance of a Wells turbine under different tip clearances using the computational fluid dynamics method. TLVflow structure axial on flow pumps high-speed to study the TLV structure pumpsofbased different based on different tip clearances.
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