Isolated columnar vortex generation: influence of momentum impulsion characteristics and wall roughness

AbstractCavitation is a phenomenon that occurs easily during rotation of fluid machinery and can decrease the performance of a pump, thereby resulting in damage to flow passage components. To study the influence of wall roughness on the cavitation performance of a centrifugal pump, a three-dimensional model of internal flow field of a centrifugal pump was constructed and a numerical simulation of cavitation in the flow field was conducted with ANSYS CFX software based on the Reynolds normalization group k-epsilon turbulence model and Zwart cavitation model. The cavitation can be further divided into four stages: cavitation inception, cavitation development, critical cavitation, and fracture cavitation. Influencing laws of wall roughness of the blade surface on the cavitation performance of a centrifugal pump were analyzed. Research results demonstrate that in the design process of centrifugal pumps, decreasing the wall roughness appropriately during the cavitation development and critical cavitation is important to effectively improve the cavitation performance of pumps. Moreover, a number of nucleation sites on the blade surface increase with the increase in wall roughness, thereby expanding the low-pressure area of the blade. Research conclusions can provide theoretical references to improve cavitation performance and optimize the structural design of the pump.

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An instability mechanism for channel flows in the presence of wall roughness

Journal of Fluid Mechanics ◽

10.1017/jfm.2020.493 ◽

2020 ◽

Vol 899 ◽

Cited By ~ 1

Author(s):

Philip Hall

Keyword(s):

Channel Flows ◽

Wall Roughness ◽

Instability Mechanism ◽

Image Position

Abstract

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Investigation of Side Wall Roughness Effect on Optical Losses in a Multimode Si3N4 Waveguide Formed on a Quartz Substrate

Photonics ◽

10.3390/photonics7040104 ◽

2020 ◽

Vol 7 (4) ◽

pp. 104

Author(s):

Anastasia Yakuhina ◽

Alexey Kadochkin ◽

Vyacheslav Svetukhin ◽

Dmitry Gorelov ◽

Sergey Generalov ◽

...

Keyword(s):

Optical Waveguides ◽

Quartz Substrate ◽

Side Wall ◽

Wall Roughness ◽

Roughness Parameters ◽

Optical Losses ◽

Waveguide Width ◽

Integration Density ◽

Frequency Domain Reflectometry ◽

Multimode Operation

This article presents the results of the study of the influence of the most significant parameters of the side wall roughness of an ultra-thin silicon nitride lightguide layer of multimode integrated optical waveguides with widths of 3 and 8 microns. The choice of the waveguide width was made due to the need to provide multimode operation for telecommunication wavelengths, which is necessary to ensure high integration density. Scattering in waveguide structures was measured by optical frequency domain reflectometry (OFDR) of a backscattering reflectometer. The finite difference time domain method (FDTD) was used to study the effect of roughness parameters on optical losses in fabricated waveguides, the roughness parameters that most strongly affect optical scattering were determined, and methods of its significant reduction were specified. The prospects for implementing such structures on a quartz substrate are justified.

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Microfluidic Channel Fabrication With Tailored Wall Roughness

ASME 2012 International Manufacturing Science and Engineering Conference ◽

10.1115/msec2012-7328 ◽

2012 ◽

Author(s):

Jing Ren ◽

Sriram Sundararajan

Keyword(s):

Flow Behavior ◽

Surface Texturing ◽

Microfluidic Channel ◽

Dip Coating ◽

Etch Depth ◽

Wall Roughness ◽

Random Surface ◽

Lab On Chip ◽

On Chip ◽

Autocorrelation Length

Realistic random roughness of channel surfaces is known to affect the fluid flow behavior in microscale fluidic devices. This has relevance particularly for applications involving non-Newtonian fluids, such as biomedical lab-on-chip devices. In this study, a surface texturing process was developed and integrated into microfluidic channel fabrication. The process combines colloidal masking and Reactive Ion Etching (RIE) for generating random surfaces with desired roughness parameters on the micro/nanoscale. The surface texturing process was shown to be able to tailor the random surface roughness on quartz. A Large range of particle coverage (around 6% to 67%) was achieved using dip coating and drop casting methods using a polystyrene colloidal solution. A relation between the amplitude roughness, autocorrelation length, etch depth and particle coverage of the processed surface was built. Experimental results agreed reasonably well with model predictions. The processed substrate was further incorporated into microchannel fabrication. Final device with designed wall roughness was tested and proved a satisfying sealing performance.

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