Experimental investigation of tip-leakage flow in an axial flow fan at various flow rates

Lee, Hongkwon; Park, Keuntae; Choi, Hyo Geun

doi:10.1007/s12206-019-0227-z

Cited by 16 publications

(11 citation statements)

References 36 publications

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“…In addition, loss evaluations based on turbulent kinetic energy have been discussed not only in numerical analyses but also in relation to tip leakage vortices captured by particle image velocimetry (PIV) measurements (Lee et al, 2019), which has been found to be effective as a means to clarify pressure drop mechanisms. As shown in Fig.…”

Section: Resultsmentioning

confidence: 99%

Pressure drop mechanisms in a cooling system enclosure

Kawano

Fuchiwaki

2022

JFST

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A potential way to reduce the noise generated by construction machinery cooling systems is to satisfy the flow rate required for cooling at lower fan speeds, and a promising approach to achieving this goal involves finding ways to reduce the pressure drop that occurs in the cooling system ventilation passages. Towards that end, approaches using computational fluid dynamics (CFD) have proven effective for estimating three-dimensional (3D) spatial pressure drops, but there have been few reports on actual loss mechanisms. In this study, the mechanisms of pressure drops that occur inside a cooling system enclosure and around exhaust port vents were investigated by capturing the flow discharged by the axial fan within the enclosure into the atmosphere via the exhaust port. We found that portions of the fan outlet flow divert significantly inside the enclosure and are exhausted at exhaust port outlets located some distance away from the fan. We also found that the pressure drops in such locations are larger than experienced by flow discharged via the shortest path. Since flows within the enclosure collide with each other and become unsettled around the exhaust port, turbulent kinetic energy increases, thus intensifying the pressure drop. Hence, by expelling the flow at the exhaust port via the shortest path without allowing it to mix chaotically inside the enclosure, the flow rate can be increased using the same fan speed.

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Section: Resultsmentioning

confidence: 99%

Pressure drop mechanisms in a cooling system enclosure

Kawano

Fuchiwaki

2022

JFST

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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%

“…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 10–12 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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“…In addition, the extremely reduced gaps were a serious handicap for the development of reliable and practicable sensors. Recent investigations have used particle Image velocimetry systems to identify and track the evolution of tip vortex structures in axial turbomachinery (Jin et al, 2011;Miorini et al, 2012;Lee et al, 2019). These investigations have reported notable findings, highlighting the physical mechanisms behind the mixing out of the TLF and analyzing the impact of different parameters, especially the size of the tip gap and the inclusion of tip plates to control the leakage flow (Bae et al, 2005;Aktürk and Camci, 2010;Corsini et al, 2010).…”

Section: Introductionmentioning

confidence: 99%

Stator–rotor interaction in the tip leakage flow of an inlet vaned low-speed axial fan

Gonzalez

Meana-Fernández

Fernández

2020

HFF

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Purpose The purpose of the paper is to quantify the impact of the non-uniform flow generated by the upstream stator on the generation and convection of the tip leakage flow (TLF) structures in the passages of the rotor blades in a low-speed axial fan. Design/methodology/approach A full three dimensional (3D)-viscous unsteady Reynolds-averaged Navier-stokes (RANS) (URANS) simulation of the flow within a periodic domain of the axial stage has been performed at three different flow rate coefficients (φ = 0.38, 0.32, 0.27) using ReNormalization Group k-ε turbulence modelling. A typical tip clearance of 2.3 per cent of the blade span has been modelled on a reduced domain comprising a three-vaned stator and a two-bladed rotor with circumferential periodicity. A non-conformal grid with hybrid meshing, locally refined O-meshes on both blades and vanes walls with (100 × 25 × 80) elements, a 15-node meshed tip gap and circumferential interfaces for sliding mesh computations were also implemented. The unsteady motion of the rotor has been covered with 60 time steps per blade event. The simulations were validated with experimental measurements of the static pressure in the shroud of the blade tip region. Findings It has been observed that both TLF and intensities of the tip leakage vortex (TLV) are significantly influenced by upstream stator wakes, especially at nominal and partial load conditions. In particular, the leakage flow, which represents 12.4 per cent and 11.3 per cent of the working flow rate, respectively, has shown a clear periodic fluctuation clocked with the vane passing period in the relative domain. The periodic fluctuation of the TLF is in the range of 2.8-3.4 per cent of the mean value. In addition, the trajectory of the tip vortex is also notably perturbed, with root-mean squared fluctuations reaching up to 18 per cent and 6 per cent in the regions of maximum interaction at 50 per cent and 25 per cent of the blade chord for nominal and partial load conditions, respectively. On the contrary, the massive flow separation observed in the tip region of the blades for near-stall conditions prevents the formation of TLV structures and neglects any further interaction with the upstream vanes. Research limitations/implications Despite the increasing use of large eddy simulation modelling in turbomachinery environments, which requires extremely high computational costs, URANS modelling is still revealed as a useful technique to describe highly complex viscous mechanisms in 3D swirl flows, such as unsteady tip flow structures, with reasonable accuracy. Originality/value The paper presents a validated numerical model that simulates the unsteady response of the TLF to upstream perturbations in an axial fan stage. It also provides levels of instabilities in the TLV derived from the deterministic non-uniformities associated to the vane wakes.

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Experimental investigation of tip-leakage flow in an axial flow fan at various flow rates

Cited by 16 publications

References 36 publications

Pressure drop mechanisms in a cooling system enclosure

Pressure drop mechanisms in a cooling system enclosure

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

Stator–rotor interaction in the tip leakage flow of an inlet vaned low-speed axial fan

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