Effect of dynamic and thermal prehistory on aerodynamic characteristics and heat transfer behind a sudden expansion in a round tube
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- 作者：V. I. Terekhov ; T. V. Bogatko
- 刊名：Heat and Mass Transfer
- 出版年：2017
- 出版时间：March 2017
- 年：2017
- 卷：53
- 期：3
- 页码：775-785
- 全文大小：
- 刊物类别：Engineering
- 刊物主题：Engineering Thermodynamics, Heat and Mass Transfer; Industrial Chemistry/Chemical Engineering; Thermodynamics;
- 出版者：Springer Berlin Heidelberg
- ISSN：1432-1181
- 卷排序：53
文摘
The results of a numerical study of the influence of the thicknesses of dynamic and thermal boundary layers on turbulent separation and heat transfer in a tube with sudden expansion are presented. The first part of this work studies the influence of the thickness of the dynamic boundary layer, which was varied by changing the length of the stabilization area within the maximal extent possible: from zero to half of the tube diameter. In the second part of the study, the flow before separation was hydrodynamically stabilized and the thermal layer before the expansion could simultaneously change its thickness from 0 to D1/2. The Reynolds number was varied in the range of \(\text{Re}_{{{\text{D}}_{1} }} = 6.7 \cdot 10^{3} \,{\text{to}}\,1.33 \cdot 10^{5}\), and the degree of tube expansion remained constant at ER = (D2/D1)2 = 1.78. A significant effect of the thickness of the separated boundary layer on both dynamic and thermal characteristics of the flow is shown. In particular, it was found out that with an increase in the thickness of the boundary layer the recirculation zone increases and the maximal Nusselt number decreases. It was determined that the growth of the heat layer thickness does not affect the hydrodynamic characteristics of the flow after separation but does lead to a reduction of heat transfer intensity in the separation area and removal of the coordinates of maximal heat transfer from the point of tube expansion. The generalizing dependence for the maximal Nusselt number at various thermal layer thicknesses is given. Comparison with experimental data confirmed the main trends in the behavior of heat and mass transfer processes in separated flows behind a step with different thermal prehistories.