Numerical study on the flow around a cold cylinder at low Reynolds numbers

doi:10.7523/j.ucas.2024.036

Abstract

Abstract:

This article utilizes three-dimensional numerical simulations on the flow around a cold cylinder with a constant Reynolds number （Re=80） and a Richardson number （Ri） ranging from -5 to -0.5， to investigate the formation mechanism of the wake structure and the influence of buoyancy on the wake structure. The results indicate that within the range of -2.5≤Ri≤-0.5， the wake structure around the cold cylinder exhibits a consistent cyclic pattern due to the influence of buoyancy. As $R i$ reaches a certain threshold （e.g.， Ri=-5）， the cyclic pattern of the cold cylinder flow undergoes a change. With the decrease of Ri， the overall wake structure of the cold cylinder deflects in the direction of gravity， while the number of rib structures exhibits a non-monotonic variation， and the wall-attached flow of the cylinder wake intensifies. When Ri decreases to a certain threshold， flow separation occurs solely from beneath the cylinder. The lift and drag coefficients， along with the Nusselt number on the cylinder’s surface， increase monotonically as Ri decreases.

Key words: cold cylinder, Re, Ri, cyclical mode, flow separation

CLC Number:

O357

Ruida ZHANG, Long CHEN. Numerical study on the flow around a cold cylinder at low Reynolds numbers[J]. Journal of University of Chinese Academy of Sciences, 2026, 43(2): 173-185.

Figures/Tables 19

Fig.1 View of the WCLL blanket design

Fig.2 Calculation model

Table 1 Comparison among Cd， Cl， and Nu of a cylinder

	C_d	C_l	Nu
文献[8]	1.196	-1.129	6.366
本文	1.259	-1.183	6.473
误差/%	2.3	3.1	1.7

Fig.3 Distribution of double O-type grids

Table 2 Effects of grid parameters on flow characteristics

	C_d	C_l	Nu
G₁	1.472	-0.025	2.004
G₂	1.474	-0.025	2.005
G₃	1.476	-0.025	2.006

Fig.4 Temporal variation of axial velocity Uz at the point （2.5，0，0） and spectral analysis

Fig.5 Iso-thermal surfaces （Θ=0.1） for various Ri values（colored by streamwise velocity）

Fig.6 Temperature and velocity fields on the cross section y=0 at t/T=0for different Ri values

Fig.7 Temperature field contours at t/T=0 for different Ri values

Fig.8 Distribution of baroclinic vorticity and streamwise vorticity on the cross section x=0.51 for Re=80

Fig.9 Numerically calculated iso-vorticity surfaces（ ωx=0.2） for Ri=-1

Fig.10 Numerically calculated iso-vorticity surfaces（ ωx=0.4） for Ri=-2.5

Fig.11 Velocity vectors at y=0 for Ri=-1（colored by temperature）

Fig.12 Velocity contours on the cross section y=0 for Re=80 and Ri=-1

Fig.13 Velocity contours at t/T=1/4 for Re=80 and Ri=-1 on the cross sections y=（a）0.5，（b）-0.5

Fig.14 Contours of temperature fields and velocity vectors of the plume at t/T=0

Fig.15 Skin lines （blue） and separation lines （black） on cylinder at t/T=0 for different Ri values

Fig.16 Variation of time-averaged lift and drag coefficients with Ri values

Fig.17 Variation of average Nu on cylinder with Ri values

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