Sensitivity of wake parameters to diameter changes for a circular cylinder

2018 ◽  
Vol 29 (11) ◽  
pp. 1850087 ◽  
Author(s):  
Salwa Fezai ◽  
Fakher Oueslati ◽  
Nader Ben-Cheikh ◽  
Brahim Ben-Beya
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Stream Velocity ◽  
Low Reynolds Numbers ◽  
Variable Diameter ◽  
Cylinder Diameter ◽  
Flow Evolution ◽  
Low Reynolds

Two-dimensional, incompressible fluid flow past a circular cylinder, having a variable diameter, is analyzed numerically at low Reynolds numbers (Re). The Reynolds number is based on the cylinder diameter and free-stream velocity. Numerical outcomes demonstrate that at low Reynolds number, the flow remains steady. Analysis of the flow evolution also shows that with enhancing Re beyond a certain critical value, the flow becomes unstable and undergoes a Hop bifurcation. The critical Reynolds number beyond which the flow becomes unsteady is determined for each configuration by an extrapolation procedure. A nonuniform variation of the critical Reynolds number (Rec) with the diameter is observed. On the other hand, it is observed that elongating the diameter of the cylinder leads to increasing the critical Reynolds number. It was also noted that the variation of the diameter value has a significant influence on the different regimes criteria as well as on the vortex detachment. Besides, it is seen that the diameter variation may lead to the birth of vortices with different oscillating frequencies due to the increase of the cylinder diameter that modifies considerably the Strouhal number.

Low Reynolds number flow around and heat transfer from a heated circular cylinder

2010 ◽  
Vol 1 (1-2) ◽  
pp. 15-20 ◽  
Author(s):  
B. Bolló
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Lift Coefficient ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Reynolds Number Flow ◽  
Two Dimensional Flow ◽  
Number Flow ◽  
Low Reynolds ◽  
Increasing Temperature

Abstract The two-dimensional flow around a stationary heated circular cylinder at low Reynolds numbers of 50 < Re < 210 is investigated numerically using the FLUENT commercial software package. The dimensionless vortex shedding frequency (St) reduces with increasing temperature at a given Reynolds number. The effective temperature concept was used and St-Re data were successfully transformed to the St-Reeff curve. Comparisons include root-mean-square values of the lift coefficient and Nusselt number. The results agree well with available data in the literature.

Low Reynolds number heat transfer from a circular cylinder

1968 ◽  
Vol 32 (1) ◽  
pp. 21-28 ◽  
Author(s):  
C. A. Hieber ◽  
B. Gebhart
Keyword(s):  
Heat Transfer ◽  
Reynolds Number ◽  
Number Theory ◽  
Circular Cylinder ◽  
Prandtl Number ◽  
Experimental Work ◽  
Reynolds Numbers ◽  
Low Reynolds Numbers ◽  
Low Reynolds ◽  
Theoretical Results

Theoretical results are obtained for forced heat convection from a circular cylinder at low Reynolds numbers. Consideration is given to the cases of a moderate and a large Prandtl number, the analysis in each case being based upon the method of matched asymptotic expansions. Comparison between the moderate Prandtl number theory and known experimental results indicates excellent agreement; no relevant experimental work has been found for comparison with the large Prandtl number theory.

scholarly journals Hot-wire investigation of the wake behind cylinders at low Reynolds numbers

1949 ◽  
Vol 198 (1053) ◽  
pp. 174-190 ◽  
Keyword(s):  
Reynolds Number ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Sufficient Information ◽  
Hot Wire ◽  
Mean Velocity ◽  
Phase Measurements ◽  
Low Reynolds Numbers ◽  
Laminar Wake ◽  
Low Reynolds

The hot-wire technique has been used to measure the regular vortex street pattern behind a cylinder at low Reynolds number. Measurements of mean velocity distribution were made both below and above the critical Reynolds number at which the periodic motion appears. Amplitude and phase measurements gave sufficient information for computation of the instantaneous flow pattern of the vortex system. The important points resulting from the investigation are that (i) the critical Reynolds number at which vortices are shed is 40, (ii) in the range of Reynolds numbers investigated the vortices are not shed directly from the cylinder but appear some distance downstream as an instability of the laminar wake.

Bifurcation analysis of the primary instability in the flow around a flexibly mounted circular cylinder

2019 ◽  
Vol 880 ◽  
Author(s):  
Daiane I. Dolci ◽  
Bruno S. Carmo
Keyword(s):  
Reynolds Number ◽  
Circular Cylinder ◽  
Critical Reynolds Number ◽  
Reynolds Numbers ◽  
Nonlinear Analyses ◽  
Low Reynolds Numbers ◽  
Nonlinear Responses ◽  
Nonlinear Character ◽  
Lock In ◽  
Isolated Systems

The nonlinear character of the primary bifurcation is investigated for the flow around a flexibly mounted circular cylinder. We have considered the cases in which the cylinder can oscillate in the transverse direction only and in both transverse and in-line directions. Low and high values of mass ratio ($m^{\ast }=5$ and 50) were studied, and reduced velocity ($V_{r}$) values are chosen inside ($V_{r}=9$) and outside ($V_{r}=5$ and $V_{r}=13$) the lock-in range for low Reynolds numbers. For each combination of $m^{\ast }$ and $V_{r}$, a global linear stability analysis was applied to find the critical Reynolds number $Re_{c}$ of the fluid–structure system. For $V_{r}$ in the lock-in range, the values of $Re_{c}$ were noticeably less than the critical Reynolds number of the flow around a fixed circular cylinder ($Re_{c_{0}}\cong 47$). On the other hand, for $V_{r}$ outside the lock-in range, the values of $Re_{c}$ were close to $Re_{c_{0}}$. Next, nonlinear analyses were performed in the vicinity of $Re_{c}$ for each case. Subcritical character (with hysteresis) was observed for $V_{r}$ in the lock-in range, while for $V_{r}$ outside the lock-in region the bifurcations were found to be supercritical (without hysteresis). This shows that when the coupling between the structure and flow is strong, due to the proximity of the natural frequencies of the isolated systems, it significantly changes both the linear and nonlinear responses observed.

A Computational Study on Airfoils at a Low Reynolds Number

2000 ◽  
Author(s):  
Ajit Pal Singh ◽  
S. H. Winoto ◽  
D. A. Shah ◽  
K. G. Lim ◽  
Robert E. K. Goh
Keyword(s):  
Reynolds Number ◽  
Computational Analysis ◽  
Computational Study ◽  
Low Reynolds Number ◽  
Micro Air Vehicles ◽  
Reynolds Numbers ◽  
Aerodynamic Performance ◽  
Low Reynolds Numbers ◽  
Study Results ◽  
Low Reynolds

Abstract Performance characteristics of some low Reynolds number airfoils for the use in micro air vehicles (MAVs) are computationally studied using XFOIL at a Reynolds number of 80,000. XFOIL, which is based on linear-vorticity stream function panel method coupled with a viscous integral formulation, is used for the analysis. In the first part of the study, results obtained from the XFOIL have been compared with available experimental data at low Reynolds numbers. XFOIL is then used to study relative aerodynamic performance of nine different airfoils. The computational analysis has shown that the S1223 airfoil has a relatively better performance than other airfoils considered for the analysis.

Experimental characterization of three-dimensional corner flows at low Reynolds numbers

2012 ◽  
Vol 707 ◽  
pp. 37-52 ◽  
Author(s):  
J. Sznitman ◽  
L. Guglielmini ◽  
D. Clifton ◽  
D. Scobee ◽  
H. A. Stone ◽  
...  
Keyword(s):  
Reynolds Number ◽  
Numerical Solutions ◽  
Three Dimensional ◽  
Reynolds Numbers ◽  
Secondary Flows ◽  
Channel Cross Section ◽  
Experimental Characterization ◽  
Low Reynolds Numbers ◽  
Low Reynolds

AbstractWe investigate experimentally the characteristics of the flow field that develops at low Reynolds numbers ($\mathit{Re}\ll 1$) around a sharp $9{0}^{\ensuremath{\circ} } $ corner bounded by channel walls. Two-dimensional planar velocity fields are obtained using particle image velocimetry (PIV) conducted in a towing tank filled with a silicone oil of high viscosity. We find that, in the vicinity of the corner, the steady-state flow patterns bear the signature of a three-dimensional secondary flow, characterized by counter-rotating pairs of streamwise vortical structures and identified by the presence of non-vanishing transverse velocities (${u}_{z} $). These results are compared to numerical solutions of the incompressible flow as well as to predictions obtained, for a similar geometry, from an asymptotic expansion solution (Guglielmini et al., J. Fluid Mech., vol. 668, 2011, pp. 33–57). Furthermore, we discuss the influence of both Reynolds number and aspect ratio of the channel cross-section on the resulting secondary flows. This work represents, to the best of our knowledge, the first experimental characterization of the three-dimensional flow features arising in a pressure-driven flow near a corner at low Reynolds number.

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