Effect of Tip Clearance Size on Tubular Turbine Leakage Characteristics

Li, Xinrui; Li, Zhenggui; Zhu, Baoshan

doi:10.3390/pr9091481

Cited by 13 publications

(11 citation statements)

References 29 publications

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“…The continuity equation was as follows [ 29 ]:

where ρ is the density of PCM kg/m 3 , and u is the PCM flow rate (m/s).…”

Section: Methodsmentioning

confidence: 99%

“…The momentum equation was as follows [ 29 ]:

where β is the liquid-phase rate in the range of 0–1, μ is the dynamic viscosity (Pa·S), A mush is the paste-phase region constant (generally taken as 10 5 ), ω is a constant used to avoid introducing a value of 0 into the formula (generally taken as 10 4 –10 7 ), and α is the coefficient of thermal expansion.…”

Section: Methodsmentioning

confidence: 99%

See 1 more Smart Citation

Study of the Phase-Change Thermal-Storage Characteristics of a Solar Collector

Deng¹,

Xu²,

Li³

et al. 2022

Materials

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A combined solar phase-change thermal-storage heating system is proposed, wherein erythritol is used as the phase-change material (PCM) used to fill the thermal-storage device, and the storage cavity is heated and stored with a disc concentrator. The Solidification/Melting, Volume-of-Fluid (VOF) model of ANSYS Fluent software was used to simulate the phase-change process of erythritol inside the thermal-storage device. The thermal-storage device was designed based on our numerical calculations, and its performance was tested. We found that larger PCM-volume fractions correlated with lower PCM volume-expansion rates and longer total melting times during the heat storage process. When the φ value equaled 80%, the PCM solid–liquid-phase interface and temperature distribution were most uniform and showed the best heat storage. In addition, the size of the heat-storage device affected the heat-exchange area, and the total melting time of the PCM decreased and then increased as the width-to-height ratio (I) increased. With this design capacity, the late stage of the charging process of the heat-storage device accounted for 70% of the total time, and the heat energy-utilization rate during the boiling process was 66.3%. Overall, this combined heating system can be considered a very efficient solar energy-utilization terminal for basic domestic energy needs.

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“…The continuity equation was as follows [ 29 ]:

where ρ is the density of PCM kg/m 3 , and u is the PCM flow rate (m/s).…”

Section: Methodsmentioning

confidence: 99%

“…The momentum equation was as follows [ 29 ]:

Section: Methodsmentioning

confidence: 99%

Study of the Phase-Change Thermal-Storage Characteristics of a Solar Collector

Deng¹,

Xu²,

Li³

et al. 2022

Materials

View full text Add to dashboard Cite

show abstract

“…In this study, the SST k-ω model is chosen as the turbulence model, considering the viscosity of the inner wall of the model compared with the standard k-ε model and the RNG k-ε model. This model has an improved turbulent shear stress transport, a more stable algorithm, and an improved simulation performance for the flow in narrow spaces [26].…”

Section: Methodsmentioning

confidence: 99%

Research on Energy Loss Characteristics of Pump-Turbine during Abnormal Shutdown

Deng¹,

Xu²,

Li³

et al. 2022

Processes

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Pumped-storage hydropower (PSH) stations are an efficient emission-free technology to balance renewable energy generation instabilities. The pump-turbine is a core component of PSH stations requiring frequent start-up, shutdown, and working conditions for regulation tasks, making it prone to instabilities. Based on entropy production theory and vortex dynamics, we analyzed the energy loss characteristics for three working conditions of the pump, pump brake, and turbine when shutting down the pump-turbine. The results showed that the entropy production and vorticity of the spiral casing and draft tube remain almost constant, while the entropy production and vorticity of the runner region substantially change from the late pump braking to the late turbine condition. The entropy production and vorticity are derived from the guide vane transitioning to the runner flow channel through the vaneless space. The change law of energy loss through entropy production agrees with the change law of internal flow turbulence through vorticity. The entropy production analysis can quantify the energy loss and mark its location, while the vorticity analysis can quantify the degree of flow disturbance and show its location. The entropy production theory and vortex dynamics combination provide insights into the connection between undesirable flow phenomena and energy loss.

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“…The shear stress transport k-ω model [27,28] is developed by coupling high Reynolds number k-ε model on the basis of the Wilcox's k-ω model. The additional transport equations for the turbulence kinetic energy (k) and the specific dissipation rate (ω) are as follows:…”

Section: Cfd Governing Equationsmentioning

confidence: 99%

Numerical Study of Effect of Sawtooth Riblets on Low-Reynolds-Number Airfoil Flow Characteristic and Aerodynamic Performance

et al. 2021

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Riblets with an appropriate size can effectively restrain turbulent boundary layer thickness and reduce viscous drag, but the effects of riblets strongly depend on the appearance of the fabric that is to be applied and its operating conditions. In this study, in order to improve the aerodynamic performance of a low-pressure fan by using riblet technology, sawtooth riblets on NACA4412 airfoil are examined at the low Reynolds number of 1 × 105, and the airfoil is operated at angles of attack (AOAs) ranging from approximately 0° to 12°. The numerical simulation is carried out by employing the SST k–ω turbulence model through the Ansys Fluent, and the effects of the riblets’ length and height on aerodynamic performance and flow characteristics of the airfoil are investigated. The results indicate that the amount of drag reduction varies greatly with riblet length and height and the AOA of airfoil flow. By contrast, the riblets are detrimental to the airfoil in some cases. The most effective riblet length is found to be a length of 0.8 chord, which increases the lift and reduces the drag under whole AOA conditions, and the maximum improvements in both are 17.46% and 15.04%, respectively. The most effective height for the riblet with the length of 0.5 chord is 0.6 mm. This also improves the aerodynamic performance and achieves a change rate of 12.67% and 14.8% in the lift and drag coefficients, respectively. In addition, the riblets facilitate a greater improvement in airfoil at larger AOAs. The flow fields demonstrate that the riblets with a drag reduction effect form “the antifriction-bearing” structure near the airfoil surface and effectively restrain the trailing separation vortex. The ultimate cause of the riblet drag reduction effect is the velocity gradient at the bottom of the boundary layers being increased by the riblets, which results in a decrease in boundary thickness and energy loss.

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Effect of Tip Clearance Size on Tubular Turbine Leakage Characteristics

Cited by 13 publications

References 29 publications

Study of the Phase-Change Thermal-Storage Characteristics of a Solar Collector

Study of the Phase-Change Thermal-Storage Characteristics of a Solar Collector

Research on Energy Loss Characteristics of Pump-Turbine during Abnormal Shutdown

Numerical Study of Effect of Sawtooth Riblets on Low-Reynolds-Number Airfoil Flow Characteristic and Aerodynamic Performance

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