标题: | 空气喷流冲击至一加热旋转圆盘之稳定及不稳定涡流特性研究 Steady and Unstable Vortex Flow Characteristics Affected by Disk Rotation in an Air Jet Impinging onto a Confined Heated Horizontal Disk |
作者: | 谢泛钧 Fan-Chun Hsieh 林清发 Tsing-Fa Lin 机械工程学系 |
关键字: | 涡流;流场观测;底盘旋转;冲击喷流;vortex flow;flow visualization;disk rotation;jet impinging |
公开日期: | 2007 |
摘要: | 在本论文中,利用实验流场观及温度场量测,探讨底盘旋转在垂直圆柱容器中空气喷流冲击至一加热圆盘之稳定与不稳定涡流特性研究。主要关注底盘旋转对由惯性力及浮力所驱动的稳定涡流特性及其发生条件之影响。此外,也对底盘旋转如何抑制在较高的惯性力及浮力所驱动的涡流进行研究。特别的是,本实验研究操作范围分别是:雷诺数0~811,雷利数0~120,260,而旋转雷诺数0~2335,另外喷流出口到加热底板间的距离比上喷流的直径HDj(=H/Dj)为2~5。 由流场观测可以清楚显示典型喷流冲击旋转圆盘的结果有三种涡流,靠近喷流中心,产生了由于惯性力所驱动的涡流称为Primary inertia-driven roll,而流道中间的涡流是由于底盘旋转的离心泵送效应,称之为Rotation-driven roll。而靠近炉体壁面的涡流是由于加热圆盘与入口冷空气间的温度所形成的浮力效应所引起,称之为Buoyancy-driven roll。由实验的结果清楚地了解在较高的底盘转速下产生惯性力所驱动之涡流的临界雷诺数也跟着提高而延迟。在HDj=3~4时,在足够高的喷流雷诺数下所形成的secondary和tertiary inertia-driven rolls亦会随着底盘转数提高至大于10转后而消失。而HDj=2时,在高转速下( rpm),由浮力所形成的Buoyancy-driven roll会变得较小且强度较弱。同时,由惯形力所形成的primary inertia-driven roll会变得较细长且较弱。此外,Secondary inertia-driven roll则完成被消除。但在HDj=3跟4,由于高度增加,需要更高的转速才能有效抑制由浮力所驱动的涡流。因此,底盘旋转台有效抑制由惯性力驱动的不稳定涡流,但对在HDj=5由于惯性力及浮力互相推挤所驱动的不稳定涡流则无法稳定流场。最后,针对在HDj=2,由于高浮惯比所驱动的type-1 buoyancy-driven unstable vortex flow可以藉由一定高的底盘转速而达稳定。 此外,我们以流谱图描述在炉体内存在三种型式的涡流结构,也发表了区分这些涡流结构之边界的经验公式。 An experiment combining flow visualization and temperature measurement is carried out here to explore the effects of disk rotation on the vortex flows resulting from a round jet of air impinging onto a heated horizontal disk confined in a vertical cylindrical chamber. Attention is paid to investigating how the disk rotation affects the onset of the inertia- and buoyancy-driven vortex rolls and their steady characteristics. Moreover, the unstable vortex flows prevailed at high jet inertia and buoyancy force affected by the disk rotation are explored to investigate the possible suppression of the unstable flows by the disk rotation. Specifically, the present experiment is conducted for the jet Reynolds number, Rayleigh number and rotational Reynolds number range respectively from 0 to 811, 0 to 120,260, and 0 to 2,335 for HDj(=H/Dj)=2 to 5. The results from the flow visualization clearly show that typically the steady vortex flow resulting from the mixed convective air jet impinging onto the heated rotating disk consists of three circular vortex rolls. The inner vortex roll is generated by the deflection of the impinging jet at the disk surface and is mainly driven by the jet inertia. The middle vortex roll is mainly formed by the centrifugal pumping action produced by the disk rotation and hence termed as the rotation-induced roll. The buoyancy-induced vortex roll results from the temperature difference between the heated disk and the inlet air and prevails in the outer zone of the processing chamber. The results from the present study clearly reveal that the critical jet Reynolds numbers for the onset of the inertia-driven rolls are slightly higher for the disk rotated at a higher speed. Besides, at the disk rotation rate ≥ 10 rpm the secondary and tertiary inertia-driven rolls are completely wiped out for HDj=3 and 4. For HDj=2 at higher disk rotation rate for ≥ 20 rpm the buoyancy-driven roll can be substantially squeezed by the disk rotation to become smaller and weaker. Meanwhile, the primary inertia-driven roll is stretched out to become slender and weaker. Moreover, the secondary inertia-driven rolls are completely wiped out. But for HDj=3 and 4, due to a stronger buoyancy-driven vortex flow at a higher jet-disk separation distance a higher is needed to stabilize the buoyancy-driven roll. The disk rotation can effectively stabilize the inertia-driven unstable vortex flow. But the mutual roll-pushing unstable vortex flow is not stabilized by the disk rotation for a larger jet-disk separation distance with HDj=5. Finally, we note that the type-1 buoyancy-driven unstable vortex flow prevailed at high buoyancy-to-inertia ratio for HDj=2 can be suppressed and even completely stabilized by the disk rotated at a high speed. Moreover, we identify three different types of vortex flows in the chamber. Flow regime maps delineating various types of vortex flow are provided. Besides, empirical correlations are proposed for the boundaries separating three different types of vortex flows. |
URI: | http://140.113.39.130/cdrfb3/record/nctu/#GT009114812 http://hdl.handle.net/11536/48434 |
显示于类别: | Thesis |