Flow characteristics of three-dimensional concave-wall jet

doi:10.11949/j.issn.0438-1157.20180836

Abstract

Abstract:

To improve the mechanical separation efficiency of the heterogeneous material, a semi-circular cross-section tangential inlet is arranged in the vertical cylindrical separator to form a three-dimensional concave-wall jet. The concave-wall jet flow characteristics are studied by tracer concentration experiment and large eddy simulation. The aim is to reveal the three-dimensional concave-wall jet flow mechanism. The concentration field spread is evaluated along the streamwise and spanwise flow. The results show that the half-value width of the tracer concentration increases with the increase of the inlet Reynolds number. The streamwise spread ratio is in the range of 0.019—0.033 and the spanwise spread ratio is in the range of 0.079—0.161. Under the action of centrifugal force, the concentration half-value width shrinks to 2/3 of the jet width within the scope of 60° in the inlet circumferential direction. There are several streamwise vortices developed from the inner surface of the cylinder, however no vortex along spanwise flow is found. The peak values of tangential velocity half-value width and the vorticity boundary locates at the center of the streamwise vortex. There is not obvious fluctuation in spanwise direction. Secondary flow vortex is not found in the range of 180° in the inlet circumferential direction. The reason is that the ratio of the tangential velocity half-value width to the cylindrical radius is less than 0.1 along streamwise flow. Thus the forming condition of the secondary flow that caused by centrifugal instability is not reached. The concave wall tangential jet effectively reduces the disturbance of the main fluid in the stratifier by the vortex.

Key words: concave-wall jet, vortex, large eddy simulation, tracer concentration, jet spread

摘要：

在立式圆筒体分层器内设置半圆形截面切向入口，形成三维凹壁面切向射流，以提高非均相物料机械分离效率。为了揭示三维凹壁面切向射流流动机理，利用示踪剂浓度实验和大涡模拟研究了凹壁面切向射流流动特性，并对浓度场沿流向和展向扩展进行了评价。研究结果表明，示踪剂浓度半值宽随着入口Reynolds数的提高扩展范围增加，流向扩展率为0.019～0.033，展向扩展率为0.079～0.161。在离心力作用下，入口周向60°范围内浓度半值宽沿流向收缩至射流宽度的2/3。圆筒体内壁面存在多个周向滚动发展的流向涡旋，但无展向涡旋。切向速度半值宽和涡量边界值在流向涡旋中心位置出现峰值，展向无明显波动。入口周向180°范围内，未发现二次流涡旋，沿射流流向的切向速度半值宽与圆筒体半径之比小于0.1，未达到离心不稳定性二次流的形成条件。凹壁面切向射流有效降低了涡旋对分层器内主流体的扰动。

关键词: 凹壁面切向射流, 涡旋, 大涡模拟, 示踪剂浓度, 射流扩展

CLC Number:

O 358

Jing ZHANG, Yuanyuan ZHOU, Bin GONG, Yaxia LI, Hailiang LIU, Jianhua WU. Flow characteristics of three-dimensional concave-wall jet[J]. CIESC Journal, 2019, 70(4): 1340-1348.

张静, 周圆圆, 龚斌, 李雅侠, 刘海良, 吴剑华. 三维凹壁面切向射流流动特性分析[J]. 化工学报, 2019, 70(4): 1340-1348.

Figures/Tables 14

Fig.1 Separation of dyed wall jet issuing from capillary nozzle in rotating tank of water

Fig.2 Model of wall jet on concave wall

Table 1 Structure and flow parameters

Structure parameter	Value	Flow parameter	Value
D ₀ /mm	800	Re	2864—14320
H /mm	800	T /℃	20
R /mm	15	ν ×10⁶/(m²·s^-1)	1.006

Fig.3 Experimental system

Fig.4 Multiple block structured grid

Table 2 Statistics analysis for cells (Re=5728)

Mesh number

y _p/

Average

of y ⁺

Proportion

of y ⁺<5

t ₁₈₀/s

Fig.5 Half width based on concentration

Table 3 Spread characteristics based on concentration

Re	b _ct/L		b _cz/L
Re	Experimental	LES	Experimental	LES
2864	0.020	0.019	0.084	0.079
5728	0.023	0.022	0.092	0.098
8592	0.027	0.028	0.117	0.116
11456	0.030	0.031	0.142	0.139
14320	0.032	0.033	0.161	0.152

Fig.6 Vortices along streamwise at t=50 s (Re=5728)

Fig.7 Center position of streamwise vortices (Re=5728)

Fig.8 Distribution of maximum velocity along streamwise (Re=5728)

Fig.9 Distribution of half-value width along streamwise (Re=5728)

Fig.10 Distribution of maximum vorticity along streamwise(Re=5728)

Fig.11 Jet boundary based on vorticity (Ω/(2u in/R 0)>1)

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