Toroidal bubble dynamics near a solid wall at different Reynolds number

2018 ◽  
Vol 100 ◽  
pp. 104-118 ◽  
Author(s):  
L.T. Liu ◽  
X.L. Yao ◽  
N.N. Liu ◽  
F.L. Yu
Keyword(s):  
Reynolds Number ◽  
Bubble Dynamics ◽  
Solid Wall ◽  
Toroidal Bubble

Vortex Shedding From a Bluff Body Adjacent to a Plane Sliding Wall

1991 ◽  
Vol 113 (3) ◽  
pp. 384-398 ◽  
Author(s):  
M. P. Arnal ◽  
D. J. Goering ◽  
J. A. C. Humphrey
Keyword(s):  
Reynolds Number ◽  
Vortex Shedding ◽  
Bluff Body ◽  
Solid Wall ◽  
Reynolds Numbers ◽  
Careful Examination ◽  
Recirculation Region ◽  
Stream Velocity ◽  
Flow Past ◽  
Lower Reynolds Number

The characteristics of the flow around a bluff body of square cross-section in contact with a solid-wall boundary are investigated numerically using a finite difference procedure. Previous studies (Taneda, 1965; Kamemoto et al., 1984) have shown qualitatively the strong influence of solid-wall boundaries on the vortex-shedding process and the formation of the vortex street downstream. In the present study three cases are investigated which correspond to flow past a square rib in a freestream, flow past a rib on a fixed wall and flow past a rib on a sliding wall. Values of the Reynolds number studied ranged from 100 to 2000, where the Reynolds number is based on the rib height, H, and bulk stream velocity, Ub. Comparisons between the sliding-wall and fixed-wall cases show that the sliding wall has a significant destabilizing effect on the recirculation region behind the rib. Results show the onset of unsteadiness at a lower Reynolds number for the sliding-wall case (50 ≤ Recrit ≤100) than for the fixed-wall case (Recrit≥100). A careful examination of the vortex-shedding process reveals similarities between the sliding-wall case and both the freestream and fixed-wall cases. At moderate Reynolds numbers (Re≥250) the sliding-wall results show that the rib periodically sheds vortices of alternating circulation in much the same manner as the rib in a freestream; as in, for example, Davis and Moore [1982]. The vortices are distributed asymmetrically downstream of the rib and are not of equal strength as in the freestream case. However, the sliding-wall case shows no tendency to develop cycle-to-cycle variations at higher Reynolds numbers, as observed in the freestream and fixed-wall cases. Thus, while the moving wall causes the flow past the rib to become unsteady at a lower Reynolds number than in the fixed-wall case, it also acts to stabilize or “lock-in” the vortex-shedding frequency. This is attributed to the additional source of positive vorticity immediately downstream of the rib on the sliding wall.

Three-Dimensional Fluid Flow and Coupled Heat Transfer in Simplified Bipolar Plates

2007 ◽  
Author(s):  
Jianfei Wu ◽  
Jianhu Nie ◽  
Yitung Chen
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Fluid Flow ◽  
Solid Wall ◽  
Three Dimensional ◽  
Cathode Side ◽  
Uniform Heat Flux ◽  
Bipolar Plates ◽  
Coupled Heat Transfer ◽  
Temperature Distributions

Numerical simulations were performed for three-dimensional fluid flow and coupled heat transfer in simplified bipolar plates. The Reynolds number of inlet flow is varied from 100 to 900 on the anode side while the Reynolds number is maintained as a constant of 100 on the cathode side. The solid wall surfaces of the bipolar plates are assumed to be adiabatically insulated, except that the active areas of the channels are supplied with uniform heat flux. Results of velocity and temperature distributions for different Reynolds numbers are presented and discussed. It is shown that effects of flow pattern on temperature distributions in channels becomes negligible when the Reynolds number is as high as 900.

scholarly journals Influence of Transient Thermal Response of Solid Wall on Bubble Dynamics in Pool Boiling

2014 ◽  
Vol 6 (4) ◽  
pp. 361-375 ◽  
Author(s):  
Liang Zhang ◽  
Zhen-Dong Li ◽  
Kai Li ◽  
Hui-Xiong Li ◽  
Jian-Fu Zhao
Keyword(s):  
Bubble Dynamics ◽  
Solid Wall ◽  
Pool Boiling ◽  
Thermal Response ◽  
Transient Thermal ◽  
Transient Thermal Response

Bubble Dynamics in Confined Spaces: Effect on Heating Surface

1987 ◽  
Vol 11 (4) ◽  
pp. 221-227
Author(s):  
Hassan E. S. Fath
Keyword(s):  
Bubble Dynamics ◽  
Solid Wall ◽  
Hot Spot ◽  
Local Heating ◽  
Heating Surface ◽  
Transient Heat Conduction ◽  
Surface Damage ◽  
Nucleate Boiling ◽  
Confined Spaces ◽  
Spot Temperature

A theoretical study of the dynamics of a single vapour bubble growing between two close surfaces is presented. The results show that the existence of a solid wall situated opposite to the heating surface influences the bubble shape and tends to divert its geometry from the spherical to the ellipsoidal one. One also observes a slower growth rate in the direction perpendicular to the surface. Considering the forces responsible for the bubble detachment, it was found that the bubble departure radius and departure time increase when the width of the gap between the two surfaces is reduced. A close look at the mechanism leading to the heating surface “Departure from Nucleate Boiling” (DNB) in confined spaces indicated that the heating surfaces DNB is increased and the local “Critical Heat Flux” (CHF) is considerably reduced. The development of this phenomenon is explained and supported by previous experimental findings. Two transient heat conduction models are used to estimate the local heating surface (hot spot) temperature in the confined dry areas. The results show that, within a few seconds, the hot spot temperature excursion occurs and may lead to local surface damage.

Numerical and Experimental Study of Bubble Impact on a Solid Wall

2015 ◽  
Vol 137 (3) ◽  
Author(s):  
B. Y. Ni ◽  
A. M. Zhang ◽  
G. X. Wu
Keyword(s):  
High Speed ◽  
Bubble Dynamics ◽  
Velocity Potential ◽  
Solid Wall ◽  
Rigid Wall ◽  
Rigid Surface ◽  
Severe Damage ◽  
Convergence Study ◽  
Numerical Difficulty ◽  
Contraction Stage

The dynamic characteristics of a bubble initially very close to a rigid wall, or with a very narrow gap, are different from those of a bubble away from the wall. Especially at the contraction stage, a high-speed jet pointing toward the wall will be generated and will impact the rigid surface directly, which could cause more severe damage to the structure. Based on the velocity potential theory and boundary element method (BEM), the present paper aims to overcome the numerical difficulty and simulate the bubble impact on a solid wall for the axisymmetric case. The convergence study has been undertaken to verify the developed numerical method and the computation code. Extensive experiments are conducted. Case studies are made using both experimental data and numerical results. The effects of dimensionless distance on the bubble dynamics are investigated.

Temperature Fluctuations Inside the Infinite Heated Slab Cooled With Turbulent Flow From Both Sides

2013 ◽  
Author(s):  
Iztok Tiselj
Keyword(s):  
Reynolds Number ◽  
Turbulent Flow ◽  
Solid Wall ◽  
Flow Direction ◽  
Temperature Fluctuations ◽  
Thermal Fluctuations ◽  
Temperature Fields ◽  
Slab Thickness ◽  
Computational Domain ◽  
Flux Boundary Condition

Direct Numerical Simulation (DNS) of fully developed velocity and passive scalar temperature fields in two-dimensional turbulent channel flow was coupled with the unsteady conduction in the idealized slab heated with constant volumetric heat source. Similar geometry can be found in some experimental nuclear reactors with fuel in the form of parallel slabs. Beside streamwise and spanwise directions, periodicity of the computational domain was assumed also in the wall-normal direction. Simulations were performed at constant friction Reynolds number 180 and Prandtl number 1, and with various geometrical and material properties of the heated slab. Due to the periodicity, the same Reynolds number and the same flow direction is assumed on both sides of the slab. Results of the simulations predict penetration of the turbulent temperature fluctuations into the solid wall. For thick slab, temperature fluctuations from both sides of the slab do not interfere. As the slab gets thinner, fluctuations from both sides interfere and tend to a finite value as the slab thickness limits toward zero. However, due to the non-coherent turbulent flows on each side of the slab, thermal fluctuations of the zero-thickness slab are actually lower than in the case of the zero-thickness wall heated by the same turbulent flow on one side but cooled by the constant heat flux boundary condition on the other side. Results of the present study can serve as benchmarks for less accurate mathematical models used to predict temperature fluctuations and thermal fatigue in realistic conditions.

scholarly journals Laminar separation bubble dynamics and its effects on thin airfoil performance during pitching-up motion

2021 ◽  
pp. 095441002199952
Author(s):  
Zhaolin Chen ◽  
Tianhang Xiao ◽  
Yan Wang ◽  
Ning Qin
Keyword(s):  
Reynolds Number ◽  
Dynamic Characteristics ◽  
Bubble Dynamics ◽  
Separation Bubble ◽  
Navier Stokes ◽  
Pitching Motion ◽  
Laminar Separation ◽  
Thin Airfoil ◽  
Flow Vortex ◽  
Static Conditions

This article reports an investigation into dynamic characteristics of the laminar separation bubbles (LSBs) associated with aerodynamic loads unsteadiness of a cambered thin airfoil in pitching-up motions at low Reynolds number flows. Unsteady Reynolds-averaged Navier–Stokes (URANS) simulations were conducted for a 4%c cambered thin airfoil at Reynolds number of 30,000 and 60,000. The airfoil pitches up from 0° to 25°angles of attack at dimensionless pitch rate [Formula: see text] of 0.0398 and 0.0199. The [Formula: see text] SST [Formula: see text] turbulence transition model was used to account for the effect of transition on LSBs’ development. The LSBs are shown to evolve in their shape and size during the pitching motion. The influence of the LSBs on the airfoil upper surface during pitching motion continues to a higher incidence in comparison with that under static conditions before developing into a fully detached flow. Vortex merging is observed in the rear part of the LSBs in the turbulent portion for a Reynolds number of 30,000. At Reynolds number 60,000, the changing of the LSB length during pitching-up motion is similar to that of steady cases, except a delayed transition is observed as incidence increases. The results show further insight into the dynamic characteristics of the LSBs and their relation to the aerodynamic performance of the airfoil.

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