Movement of gas slug in annular channels with different diameter ratios

Abstract The motion of gas slugs in annular channels was studied experimentally. The outer tube diameter was 32 mm. The inner tube diameter varied from 4 to 25 mm. The gas slugs were produced by injecting air through a capillary tube. The shapes of gas slugs were studied by high-speed videos. The paper presents data on the rise velocity of gas slugs in the channels, and wall shear stress measurements, performed by electrodiffusional technique. The probes were mounted on both walls of the channel. The evolution of wall shear stress during slug passage was recorded.

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Wall Shear Stress Measurements

Encyclopedia of Microfluidics and Nanofluidics ◽

10.1007/978-1-4614-5491-5_1760 ◽

2015 ◽

pp. 3479-3486 ◽

Cited By ~ 1

Author(s):

Christian Cierpka ◽

Massimiliano Rossi ◽

Christian J. Kähler

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Stress Measurements ◽

Wall Shear

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Particle-wall shear stress measurements within the standpipe of a circulating fluidized bed

10.33915/etd.1165 ◽

2001 ◽

Author(s):

Angela Marie Sarra

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Fluidized Bed ◽

Circulating Fluidized Bed ◽

Stress Measurements ◽

Wall Shear

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Modeling Reichardt’s Formula for Eddy-Viscosity in the Fluid Film of Tilting Pad Thrust Bearings

Volume 7: Fluids Engineering ◽

10.1115/imece2017-71749 ◽

2017 ◽

Author(s):

Xin Deng ◽

Brian Weaver ◽

Cori Watson ◽

Michael Branagan ◽

Houston Wood ◽

...

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Turbulence Model ◽

High Speed ◽

Eddy Viscosity ◽

The Other ◽

Fluid Film ◽

Suitable Model ◽

Velocity Gradients ◽

Wall Shear

Oil-lubricated bearings are widely used in high speed rotating machines such as those used in the aerospace and automotive industries that often require this type of lubrication. However, environmental issues and risk-adverse operations have made water lubricated bearings increasingly popular. Due to different viscosity properties between oil and water, the low viscosity of water increases Reynolds numbers drastically and therefore makes water-lubricated bearings prone to turbulence effects. The turbulence model is affected by eddy-viscosity, while eddy-viscosity depends on wall shear stress. Therefore, effective wall shear stress modeling is necessary in producing an accurate turbulence model. Improving the accuracy and efficiency of methodologies of modeling eddy-viscosity in the turbulence model is important, especially considering the increasingly popular application of water-lubricated bearings and also the traditional oil-lubricated bearings in high speed machinery. This purpose of this paper is to study the sensitivity of using different methodologies of solving eddy-viscosity for turbulence modeling. Eddy-viscosity together with flow viscosity form the effective viscosity, which is the coefficient of the shear stress in the film. The turbulence model and Reynolds equation are bound together to solve when hydrodynamic analysis is performed, therefore improving the accuracy of the turbulence model is also vital to improving a bearing model’s ability to predict film pressure values, which will determine the velocity and velocity gradients in the film. The velocity gradients in the film are the other term determining the shear stress. In this paper, three approaches applying Reichardt’s formula were used to model eddy-viscosity in the fluid film. These methods are for determining where one wall’s effects begin and the other wall’s effects end. Trying to find a suitable model to capture the wall’s effects of these bearings, with aim to improve the accuracy of the turbulence model, would be of high value to the bearing industry. The results of this study could aid in improving future designs and models of both oil and water lubricated bearings.

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Surface Pressure and Wall Shear Stress Measurements on a Wall Mounted Cylinder

Notes on Numerical Fluid Mechanics and Multidisciplinary Design - Imaging Measurement Methods for Flow Analysis ◽

10.1007/978-3-642-01106-1_20 ◽

2009 ◽

pp. 197-206 ◽

Cited By ~ 5

Author(s):

Christoph Dobriloff ◽

Wolfgang Nitsche

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Surface Pressure ◽

Stress Measurements ◽

Wall Shear

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Impinging jets array: an experimental investigation and numerical modeling

E3S Web of Conferences ◽

10.1051/e3sconf/20198505004 ◽

2019 ◽

Vol 85 ◽

pp. 05004

Author(s):

Nilesh Dhondoo ◽

Ştefan-Mugur Simionescu ◽

Corneliu Bălan

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Stagnation Point ◽

High Speed ◽

Jet Impingement ◽

Impinging Jets ◽

Stagnation Region ◽

Jet Mixing ◽

Point Pressure ◽

Wall Shear

This paper reports on the measurements of wall shear stress and static pressure along a smooth static wall upon which jet impingement occurs. The effect of a single circular jet, respectively an array of jets is studied using a high speed/resolution camera. The areas of interest are the stagnation region and the wall jet region, where the jet is deflected from axial to radial direction. The effect of increasing the distance between the inlets is also investigated. The results are obtained by performing direct flow experimental visualizations and CFD numerical simulations, using the Reynolds averaged Navier-Stokes (RANS) approach with the commercial software ANSYS Fluent. The findings suggest that the smaller the nozzle-to-wall distance is, the higher the pressure peak. The wall shear stress has a bimodal distribution; at stagnation point, the wall shear stress is 0. An increase in the number of inlets produces the effect of a decrease in the stagnation point pressure. The greater the inter-inlet distance is, the greater the stagnation point pressure (there is less inter-jet mixing, less energy is lost in vortices formed between jets).

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Wall shear stress measurements in high Reynolds number boundary layers from two facilities

10.2514/6.1999-3814 ◽

1999 ◽

Cited By ~ 8

Author(s):

Jens Osterlund ◽

Arne Johansson ◽

Hassan Nagib ◽

Michael Hites

Keyword(s):

Reynolds Number ◽

Shear Stress ◽

Wall Shear Stress ◽

Boundary Layers ◽

High Reynolds Number ◽

Stress Measurements ◽

Wall Shear ◽

High Reynolds

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Dynamic response of a hot-wire anemometer. Part II: A flush-mounted hot-wire and hot-film probes for wall shear stress measurements

Measurement Science and Technology ◽

10.1088/0957-0233/9/5/006 ◽

1998 ◽

Vol 9 (5) ◽

pp. 764-778 ◽

Cited By ~ 27

Author(s):

Y T Chew ◽

B C Khoo ◽

C P Lim ◽

C J Teo

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

Dynamic Response ◽

Hot Wire ◽

Stress Measurements ◽

Wall Shear ◽

Hot Film

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Comparison in High-Speed Droplet Impact Between Single and Multiple Collisions Against a Wall Covered With a Liquid Film

Volume 5: Multiphase Flow ◽

10.1115/ajkfluids2019-5200 ◽

2019 ◽

Author(s):

Yoichiro Fukuchi ◽

Tomoki Kondo ◽

Keita Ando

Keyword(s):

Shear Stress ◽

Wall Shear Stress ◽

High Speed ◽

Water Layer ◽

Liquid Jet ◽

Surface Erosion ◽

Single Droplet ◽

Cleaning Efficiency ◽

Droplet Impingement ◽

Wall Shear

Abstract In semiconductor industry, liquid jet cleaning plays an important role because of its high cleaning efficiency and low environmental load. However, its cleaning mechanism is not revealed in detail because the experimental observation of high-speed and sub-micron droplets is challenging. Furthermore, higher impact velocity may give rise to surface erosion due to water-hammer shock loading from the impingement. To study cleaning mechanisms and surface erosion, numerical simulation of droplet impingement accounting for both viscosity and compressibility is an effective approach. In the previous study, wall-shear-flow generation has evaluated from the simulation of high-speed single droplet impingement. To evaluate more practical model of jet cleaning application, simulation of two droplets simplifying mono-dispersed splay of droplet train is favorable. Here, we numerically simulated impingement of two droplets, which allows for evaluating water-hammer pressure and wall shear stress. We consider the case of two water droplets (200 μm in diameter) that collides continuously, at speed 50 m/s, at the inter-droplet distance from 250 to 400 μm, with a no-slip rigid wall covered with a water layer (100 μm in thickness). The simulation is based on compressible Navier-Stokes equations for axisymmetric flow and the mixture of two components appears in numerically diffusion interface expressed by the volume average and advection equation. The simulation is solved by finite-volume WENO scheme that can capture both shock waves and material interface. In our simulation, the impingement of second droplet impingement gain higher shear stress than the single droplet impingement. At the case that the inter-droplet distance is 300 μm, maximum shear stress is 30.22 kPa (at the second droplet impingement), which is much larger than at the first droplet impingement (8.42 kPa). This result indicates how the second droplet impingement make wall shear flow induced by first droplet impingement stronger. From the parameter study of the inter-droplet distance, we can say that wall shear stress gets stronger as water layer thickness decreases. Furthermore, the maximum wall pressure is 1.96 MPa at the second droplet impingement, which is larger than at the first droplet impingement (1.46 MPa). From this study, the evaluation of surface erosion caused by jet cleaning is expected. The simulation suggests that multiple droplets impingement continuously may gain higher cleaning efficiency, which will give us a fundamental insight into liquid jet cleaning technologies. For further study, simulation of water column impingement and comparing the result of impingement of two droplets are expected.

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