Vortex Breakdown in an Enclosed Cylinder With a Partially Rotating Bottom-Wall

2008 ◽  
Vol 130 (11) ◽  
Author(s):  
P. Yu ◽  
T. S. Lee ◽  
Y. Zeng ◽  
H. T. Low
Keyword(s):  
Aspect Ratio ◽  
Vortex Breakdown ◽  
Numerical Study ◽  
Axisymmetric Flow ◽  
Rotating Disk ◽  
Bottom Wall ◽  
Cylindrical Chamber ◽  
Noticeable Effect ◽  
Disk Radius ◽  
Boundary Curves

A numerical study of the axisymmetric flow in a cylindrical chamber of height H is presented, which is driven by a bottom disk rotating at angular velocity Ω. However, unlike most previous studies, the present rotating disk is of smaller radius than the bottom-wall. The boundary curves for the onset of vortex breakdown are presented using different definitions of the nondimensional parameters, depending on whether the cylinder radius R or the disk radius rd is used as the length scale. The study shows that the boundary curves are best correlated when presented in terms of the Reynolds number Ωrd2∕υ, aspect ratio H∕R, and cylinder-to-disk ratio R∕rd. The cylinder-to-disk ratio R∕rd up to 1.6 is found to have noticeable effect on vortex breakdown; this is attributed to the change of effective aspect ratio. The contours of streamline, angular momentum, and azimuthal vorticity are presented and compared with those of whole bottom-wall rotation.

Investigation on Convective Heat Transfer over a Rotating Disk with Bottom Wall Subjected to Uniform Heat Flux

2012 ◽  
Vol 249-250 ◽  
pp. 443-451
Author(s):  
Jing Zhou Zhang ◽  
Xiao Ming Tan ◽  
Xing Dan Zhu
Keyword(s):  
Heat Transfer ◽  
Heat Flux ◽  
Convective Heat Transfer ◽  
Convective Heat ◽  
Numerical Study ◽  
Rotating Disk ◽  
Outer Radius ◽  
Bottom Wall ◽  
Uniform Heat Flux ◽  
Uniform Heat

A three-dimensional numerical study on the flow and heat transfer characteristics over a rotating disk with bottom wall subjected to uniform heat flux was conducted with the use of RNG k- turbulent model. And some experiments were also made for validation. The effects of rotating angular speed and pin configuration on the temperature maps and convective heat transfer characte-ristics on rotating surface are analyzed. As the increase of rotating velocity, the impingement of pumping jet on the centre of rotating disk became stronger and the transition from laminar to turbu-lent occurred at the outer radius of rotating disk, which resulted in heat transfer enhancement. The pins on the disk made the pumping action of a rotating disk weaker. Simultaneously, they also acted as disturbing elements to the cyclone flow near the rotating disk surface, which made the overall heat transfer to be enhanced. Under the same extend areas of different pins, needle pin has higher convective heat transfer capacity than the discrete ring pin.

Friction Drag on Bladed Disks in Housings as a Function of Reynolds Number, Axial and Radial Clearance, and Blade Aspect Ratio and Solidity

1961 ◽  
Vol 83 (4) ◽  
pp. 719-723 ◽  
Author(s):  
Robert W. Mann ◽  
Charles H. Marston
Keyword(s):  
Reynolds Number ◽  
Aspect Ratio ◽  
Rotating Disk ◽  
Radial Clearance ◽  
Disk Radius ◽  
Moment Coefficient ◽  
Aspect Ratios ◽  
Direct Measurements ◽  
Partial Admission ◽  
The Moment

Extra losses from partial admission operation of a gas turbine occur both in the nozzle flow arc and away from it. The latter have been related to the theory of fluid flow over a rotating disk expressing a dimensionless moment coefficient as a function of Reynolds number. By direct measurements of drag torque, the moment coefficient has been determined over a range of Reynolds number from 2.0 × 104 to 4.5 × 106 for several aspect ratios, axial and radial shroud clearances, and solidities. Losses increase with increasing aspect ratio. Small increases from minimum practical clearance have little effect, but blade pumping losses become severe at radial and axial clearances of the order of half the disk radius. Typical changes in solidity have only small effects on losses.

scholarly journals Numerical Study on the Surface Plasmon Resonance Tunability of Spherical and Non-Spherical Core-Shell Dimer Nanostructures

Nanomaterials ◽  
2021 ◽  
Vol 11 (7) ◽  
pp. 1728
Author(s):  
Joshua Fernandes ◽  
Sangmo Kang
Keyword(s):  
Refractive Index ◽  
Optical Properties ◽  
Surface Plasmon Resonance ◽  
Aspect Ratio ◽  
Surface Plasmon ◽  
Plasmon Resonance ◽  
Shell Thickness ◽  
Numerical Study ◽  
Field Enhancement ◽  
Core Shell

The near-field enhancement and localized surface plasmon resonance (LSPR) on the core-shell noble metal nanostructure surfaces are widely studied for various biomedical applications. However, the study of the optical properties of new plasmonic non-spherical nanostructures is less explored. This numerical study quantifies the optical properties of spherical and non-spherical (prolate and oblate) dimer nanostructures by introducing finite element modelling in COMSOL Multiphysics. The surface plasmon resonance peaks of gold nanostructures should be understood and controlled for use in biological applications such as photothermal therapy and drug delivery. In this study, we find that non-spherical prolate and oblate gold dimers give excellent tunability in a wide range of biological windows. The electromagnetic field enhancement and surface plasmon resonance peak can be tuned by varying the aspect ratio of non-spherical nanostructures, the refractive index of the surrounding medium, shell thickness, and the distance of separation between nanostructures. The absorption spectra exhibit considerably greater dependency on the aspect ratio and refractive index than the shell thickness and separation distance. These results may be essential for applying the spherical and non-spherical nanostructures to various absorption-based applications.

Heat transfer characteristics of nanofluids from a sinusoidal corrugated cylinder placed in a square cavity

2021 ◽  
pp. 095440622110272
Author(s):  
Salaika Parvin ◽  
Nepal Chandra Roy ◽  
Litan Kumar Saha ◽  
Sadia Siddiqa
Keyword(s):  
Heat Transfer ◽  
Nusselt Number ◽  
Rayleigh Number ◽  
Aspect Ratio ◽  
Average Nusselt Number ◽  
Numerical Study ◽  
Heat Transfer Characteristics ◽  
Number Range ◽  
Transfer Characteristics ◽  
Wide Range

A numerical study is performed to investigate nanofluids' flow field and heat transfer characteristics between the domain bounded by a square and a wavy cylinder. The left and right walls of the cavity are at constant low temperature while its other adjacent walls are insulated. The convective phenomena take place due to the higher temperature of the inner corrugated surface. Super elliptic functions are used to transform the governing equations of the classical rectangular enclosure into a system of equations valid for concentric cylinders. The resulting equations are solved iteratively with the implicit finite difference method. Parametric results are presented in terms of streamlines, isotherms, local and average Nusselt numbers for a wide range of scaled parameters such as nanoparticles concentration, Rayleigh number, and aspect ratio. Several correlations have been deduced at the inner and outer surface of the cylinders for the average Nusselt number, which gives a good agreement when compared against the numerical results. The strength of the streamlines increases significantly due to an increase in the aspect ratio of the inner cylinder and the Rayleigh number. As the concentration of nanoparticles increases, the average Nusselt number at the internal and external cylinders becomes stronger. In addition, the average Nusselt number for the entire Rayleigh number range gets enhanced when plotted against the volume fraction of the nanofluid.

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