Research of wall roughness effects based on Q criterion

Zhou, Hao; Cai, Guobiao; Zhang, Jianhua; Zhang, Mingxing; He, Bijiao

doi:10.1007/s10404-017-1951-2

Cited by 13 publications

(11 citation statements)

References 30 publications

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“…The RANS model is usually used to calculate the time-averaged flow field. The RANS model essentially changes the actual problem, abandons the simulation of unsteady turbulence information, and only seeks the flow results in the average time [18][19][20][21][22]. Hence, it is impossible to simulate unsteady turbulent flow accurately.…”

Section: Transient Simulation Methodsmentioning

confidence: 99%

“…Different vortex structures reflect the flow characteristics of fluids in various computational domains. The Q criterion is regarded as providing significant physical insight into understanding the internal flow law and the local flow loss in the flow field [19][20][21][22]. To better analyze the internal flow of a centrifugal fan, the Q criterion is considered as a rule of discriminating eddy current in this paper.…”

Section: Q Criterionmentioning

confidence: 99%

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Unsteady Characteristics of Forward Multi-Wing Centrifugal Fan at Low Flow Rate

Lun

Ye²,

Lin³

et al. 2019

Processes

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The unsteady flow characteristics of a forward multi-wing centrifugal fan under a low flow rate are studied using the computational fluid dynamics (CFD) method. This paper emphasizes the eddy current distribution in terms of the Q criterion method, as well as pressure fluctuation, frequency spectrum, and kinetic energy spectrum analysis of internal monitoring points in a forward multi-wing centrifugal fan. The numerical results show that abnormal eddies mainly appear at the volute outlet and near the volute tongue, boundary layer separation occurs near the suction surface of the blade, and shedding eddies appear at the trailing edge of the blade with the time evolution. The unsteady flow characteristics of a forward multi-wing centrifugal fan at a small flow rate provide significant physical insight into understanding the internal flow law.

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Section: Transient Simulation Methodsmentioning

confidence: 99%

Section: Q Criterionmentioning

confidence: 99%

Unsteady Characteristics of Forward Multi-Wing Centrifugal Fan at Low Flow Rate

Lun

Ye²,

Lin³

et al. 2019

Processes

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“…It is well known that centrifugal fans have been widely adopted to industrial application, such as cooling units in air-conditioning, heating, ventilating and air conditioning systems, and home appliance machines [1][2][3][4][5]. In general, it is essential for the centrifugal fan to improve its aerodynamic performance to achieve the purpose of energy conservation [5][6][7][8][9]. Many centrifugal fans with moderate efficiency and low aero-acoustic performances still need to be improved by making use of today's technology.…”

Section: Introductionmentioning

confidence: 99%

Effects of Single-arc Blade Profile Length on the Performance of a Forward Multiblade Fan

Wei

Ying²,

Xu³

et al. 2019

Processes

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The effects of single-arc blade profile length on the performance of a forward multiblade fan are investigated in this paper by computational fluid dynamics and experimental measurement. The present work emphasizes that the use of a properly reduced blade inlet angle (β1A) and properly improved blade outlet angle (β2A) is to increase the length blade profile, which suggests a good physical understanding of internal complex flow characteristics and the aerodynamic performance of the fan. Numerical results indicate that the gradient of the absolute velocity among the blades in model-L (reducing the blade inlet angle and improving blade outlet angle) is clearly lower than that of the baseline model and model-S (improving the blade inlet angle and reducing blade outlet angle), where a number of secondary flows arise on the exit surface of baseline model and model-S. However, no secondary flow occurs in model-L, and the flow loss at the exit surface of the volute (scroll-shaped flow patterns) for model-L is obviously lower than that of the baseline model at the design point. The comparison of the test results further shows that to improve the blade profile length is to increase the static pressure and the efficiency of the static pressure, since the improved static pressure of the model-L rises as much as 22.5 Pa and 26.2%, and the improved static pressure efficiency of the model-L rises as much as 5 % at the design flow rates. It is further indicated that increasing the blade working area provides significant physical insight into increasing the static pressure, total pressure, the efficiency of the static pressure and the total pressure efficiency.

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“…A few studies on the impact of surface roughness on gas flows in microchannels have been published. [38][39][40][41] At the micro/nano-meter scale, the surface roughness, albeit small, may be comparable to the channel height and play an important role in gas hydrodynamic bearings.…”

Section: Introductionmentioning

confidence: 99%

Rarefaction cloaking: Influence of the fractal rough surface in gas slider bearings

Liu

Zhang

et al. 2017

Physics of Fluids

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This version is available at https://strathprints.strath.ac.uk/61934/ Strathprints is designed to allow users to access the research output of the University of Strathclyde. Unless otherwise explicitly stated on the manuscript, Copyright © and Moral Rights for the papers on this site are retained by the individual authors and/or other copyright owners. Please check the manuscript for details of any other licences that may have been applied. You may not engage in further distribution of the material for any profitmaking activities or any commercial gain. You may freely distribute both the url (https://strathprints.strath.ac.uk/) and the content of this paper for research or private study, educational, or not-for-profit purposes without prior permission or charge.Any correspondence concerning this service should be sent to the Strathprints administrator: strathprints@strath.ac.ukThe Strathprints institutional repository (https://strathprints.strath.ac.uk) is a digital archive of University of Strathclyde research outputs. It has been developed to disseminate open access research outputs, expose data about those outputs, and enable the management and persistent access to Strathclyde's intellectual output. PHYSICS OF FLUIDS 29, 102003 (2017)Rarefaction cloaking: Influence of the fractal rough surface in gas slider bearings For ultra-thin gas lubrication, the surface-to-volume ratio increases dramatically when the flow geometry is scaled down to the micro/nano-meter scale, where surface roughness, albeit small, may play an important role in gas slider bearings. However, the effect of surface roughness on the pressure and load capacity (force) in gas slider bearings has been overlooked. In this paper, on the basis of the generalized Reynolds equation, we investigate the behavior of a gas slider bearing, where the roughness of the slider surface is characterized by the Weierstrass-Mandelbrot fractal function, and the mass flow rates of Couette and Poiseuille flows are obtained by deterministic solutions to the linearized Bhatnager-Gross-Krook equation. Our results show that the surface roughness reduces the local mass flow rate as compared to the smooth channel, but the amount of reduction varies for Couette and Poiseuille flows of different Knudsen numbers. As a consequence, the pressure rise and load capacity in the rough bearing become larger than the ones in the smooth bearing in the slip and early transition flow regimes, e.g., a 6% roughness could lead to an increase of 20% more bearing load capacity. However, this situation is reversed in the free-molecular flow regime, as the ratio of the mass flow rates between Couette and Poiseuille flows is smaller than that in the smooth channel. Interestingly, between the two extremes, we have found a novel "rarefaction cloaking" effect, where the load capacity of a rough bearing equals to that of a smooth bearing at a certain range of Knudsen numbers, as if the roughness does not exist.

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Research of wall roughness effects based on Q criterion

Cited by 13 publications

References 30 publications

Unsteady Characteristics of Forward Multi-Wing Centrifugal Fan at Low Flow Rate

Unsteady Characteristics of Forward Multi-Wing Centrifugal Fan at Low Flow Rate

Effects of Single-arc Blade Profile Length on the Performance of a Forward Multiblade Fan

Rarefaction cloaking: Influence of the fractal rough surface in gas slider bearings

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