Analysis of tip-leakage flow in an axial fan at varying tip-gap sizes and operating conditions

Moghadam, Seyed Mohsen Alavi; Meinke, Matthias; Schröder, Wolfgang

doi:10.1016/j.compfluid.2019.01.014

Cited by 45 publications

(17 citation statements)

References 35 publications

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“…(1) Governing equation: the continuity equation and 3D steady Reynolds-averaged Navier-Stokes (RANS) equation are used; the convection term, diffusion term, and turbulent viscosity are all discretised by the second-order upwind scheme [28,29]. (2) Turbulence model: considering the complex internal flow dynamics of axial flow fans and the evolution of different vortices, including the passage vortex, tip leakage vortex, scraping vortex, and wakes [30][31][32][33][34], the Realisable k-ε model that effectively simulates the complex flow in the tip clearance and the rotational motion is applied [1,2,19,35]. The SIMPLE algorithm is used to achieve the coupling of velocity and pressure [36].…”

Section: Methodsmentioning

confidence: 99%

“…It can be seen from Figure 12 that the total pressure rise coefficient is relatively high in the range R = 0-0.8, indicating that it is the main working area of the blade. The range R = 0.8-1.0 is near the blade tip, in which the total pressure rise coefficient decreases rapidly, owing to tip leakage [30,33]. At the three blade pitch angles of β= 29 • , 32 • and 35 • , the total pressure rise coefficient with θ= 3.0 • across the entire blade height range is higher than that of the original fan with θ= 0 • , especially in the β= 35 • case, indicating that the forward-skewed blade can effectively improve the impeller total pressure rise, in agreement with Figure 7, and the improved effect is greater at larger blade pitch angles.…”

Section: Distribution Of Total Pressure Rise and Static Pressure Recomentioning

confidence: 99%

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Prediction of Performance of a Variable-Pitch Axial Fan with Forward-Skewed Blades

Ye¹,

Fan²,

Zhang³

et al. 2019

Energies

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For a single-stage variable-pitch axial fan, the aerodynamic performance and through flow with and without blade skewing are examined numerically. Simulated results show that the total pressure rise and efficiency increase by 2.99% and 0.16%, respectively, with the best forward-skewed angle of θ = 3° at the design conditions. At the blade pitch angles of β = 29° and 35°, the total pressure rises and efficiency of the fan with θ = 3.0° under the highest efficiency point change by −0.55%, −0.53% and 1.39%, 2.11%, respectively. At design and off-design conditions, the forward-skewed blades mitigate tip leakage and delay the emergence of separation flow at the blade root, these benefits are higher at the higher blade pitch angle. The θ = 3.0° forward skew effectively raises the stage performance of the impeller and guide vanes.

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Section: Methodsmentioning

confidence: 99%

Section: Distribution Of Total Pressure Rise and Static Pressure Recomentioning

confidence: 99%

Prediction of Performance of a Variable-Pitch Axial Fan with Forward-Skewed Blades

Ye¹,

Fan²,

Zhang³

et al. 2019

Energies

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“…Qiu et al executed a numerical study of hydrodynamic and cavitation performance of a pump-jet propulsor with different TCSs and different oblique flow angles and found an interesting point that the efficiency with cavitation was higher than with non-cavitation conditions in oblique flow [16]. By analyzing the tip vortex of a duct axial fan on the basis of a highly resolved large-eddy simulation, Moghadam et al found that there were a series of consequences relating to vortices at the tip-gap region when extending the clearance dimension, such as strong leakage flow, flow separation, and induced vortex that strengthens the main vortex intensity [17].…”

Section: Introductionmentioning

confidence: 99%

Effects of Tip Clearance Size on Energy Performance and Pressure Fluctuation of a Tidal Propeller Turbine

et al. 2020

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Unavoidable tip clearance between blade tip and casing shroud plays an important role in the performance and characteristics of a tidal propeller turbine. In this work, the tip-leakage vortex (TLV) induced in the end-wall region was numerically illustrated by using the shear-stress transport (SST) k–ω turbulence model at various flow conditions and different tip-clearance sizes (TCSs). The swirling strength criterion was employed to visualize the tip-leakage vortex trajectory and investigate vortex evolution according to clearance size change. Although TLV occurs in both design and off-design conditions, vortex intensity develops strongly under excess flow rate with increased tip gap. The extreme influence of TCS on the turbine’s generated power and efficiency was predicted in steady simulations for four TCS cases, namely, δ = 0%, 0.25%, 0.5%, and 0.75%. With the extension of the tip gap, turbine performance was drastically reduced because of vigorous turbulent leakage flow combined with considerable volumetric loss. The effect of TCS on pressure fluctuation intensity were also explored on the basis of the transient simulation statistic. Maximal pressure variation amplitude and dominant frequency were presented in spectrum analysis utilizing fast Fourier transform.

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“…[5][6][7] When mixed-flow pump operates at the design flow rate, the TLF and TLV are stable and approximately account for 15% of the total energy losses in impeller 6 as shown by Liu et al 7 Furthermore, it may also cause other performance problems as discussed later when the mixed-flow pump runs at flow rates different from design flow rate, especially near stall and stall condition. 8,9 For several decades, a great deal of research has been focused on developing correlations for tip leakage flow for various types of rotating fluid machinery [10][11][12] including axial compressors, 13 turbines, 14 and fan 15 etc. These findings have clearly demonstrated that the tip leakage flow has strong relationship with the pre-stall condition or stall inception in the rotating fluid machinery.…”

Section: Introductionmentioning

confidence: 99%

Transient characteristics of internal flow fields of mixed-flow pump with different tip clearances under stall condition

Shi

et al. 2020

Proceedings of the Institution of Mechanical Engineers, Part A:

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This paper investigates the influence of different tip clearances on the transient characteristics of mixed-flow pump under stall condition. The instantaneous internal flow fields of mixed-flow pump with four tip clearances (0.2 mm, 0.5 mm, 0.8 mm and 1.1 mm) are explored by conducting unsteady time accurate simulations. Reynolds-averaged Navier-Stokes (RANS) equations are employed in the simulations and the results of computations are compared with experimental data. The results show that the pump head decreases by 22.1% and the pump efficiency drops by 13.9% at design flow condition when the impeller tip clearance increases from 0.2 mm to 1.1 mm. The swirling flow occurs in the inlet pipe of the mixed-flow pump with different tip clearances under stall condition, and the initial starting point of the swirling flow gets further away from the impeller inlet with increase in tip clearance because of increase in circumferential velocity and change in momentum of the tip leakage flow (TLF). The high turbulent eddy dissipation (TED) regions in the flow are attributed to the TLF, swirling flow, back flow and stall vortex, and their intensity are affected by the change in tip clearance. The oscillating trend of time domain distribution of TED enhances first and then decreases with increase in tip clearance and it exhibits a propagation feature under the effect of stall vortex, while most of the energy in the frequency domain remains concentrated in the low frequency part under stall condition.

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Analysis of tip-leakage flow in an axial fan at varying tip-gap sizes and operating conditions

Cited by 45 publications

References 35 publications

Prediction of Performance of a Variable-Pitch Axial Fan with Forward-Skewed Blades

Prediction of Performance of a Variable-Pitch Axial Fan with Forward-Skewed Blades

Effects of Tip Clearance Size on Energy Performance and Pressure Fluctuation of a Tidal Propeller Turbine

Transient characteristics of internal flow fields of mixed-flow pump with different tip clearances under stall condition

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