Effect of the Aspect Ratio on Flow over a Fence in a Duct

渠道寬高比對流過障礙體流場之影響研究

彭逸凡(Y. F. Peng) ； 黃榮鑑(Robert R. Hwang)

《中國航空太空學會學刊》 30卷4期 (1998/12) Pp. 253-260

https://doi.org/10.6124/TAASRC.199812_30(4).01

摘要

本論文以直接數值解析一個三維流場。在一個寬扁的東道中，渠道寬高比爲W/H=18；流體通過一道短牆的流場。這道短牆高度對渠道高度比爲0.5，短牆長度對渠道高度此爲0.2，流場雷諾數爲218。以往這個寬扁渠道中央對稱面的流動現象被認爲具有二維性質。但是，二維流場解析結果和實驗資料並不吻合。本文以三維數值解析的結果則和實驗資料吻合。論文中對於流場的三維結構分析相當完整。一些有趣的流場現象例如，主回流區與二次回流區中流體治螺旋線形由邊壁向中央對稱面流動，這是以往二維解析方法無法觀查到的現象。另外，論文中探討渠道寬高比，當W/H超過36時，中央對稱面流動具有三維性質；此結果對於中低雷諾數二維流場的實驗條件具有相當的參考價值。

關鍵字

三維流場 ； 直接數值解析 ； 渠道寬高比

並列摘要

Laminar flows over a fence of high ratio h/H=0.5 and length ratio l/H=0.2 in a duct are numerically solved by the three-dimensional (3-D) simulations. The Reynolds number of the duct flows are Re=218 and width to high aspect ratios of the duct are W/H=10, 18, 25, 36. Computations are conducted by solving the full Navier-Stokes equations and numerical solutions are obtained on basis of the chosen aspect ratios. Validations of the simulations are investigated by comparing the numerical results for the flow with aspect ratio equal to 18 to available measurements. Computational velocity profiles, primary reattachment length on bottom wall, and secondary reversed flow length on roof wall at the symmetrical plane fit the measured data of Tropea and Gackstatter (1987) well. Effects of aspect ratio on the flows are systematically investigated. Notably addressed is that the existence of side-walls increase the strength of primary reversed flow coherent on bottom wall and decrease that of the secondary reversed flow on roof wall. Typically for the flow of aspect ratio W/H=10，the secondary reversed flow on roof wall is only confined to regions near the side-walls and does not extend over the whole span. For the flow at larger aspect ratio, symmetry plane flows tend to be having a larger secondary reversed flow length on roof wall and a smaller primary reversed flow length on bottom wall. With an aspect ratio equal to 36. flow yields a nearly two-dimensional (2-D) flow at the symmetry plane.

並列關鍵字

three-dimensional ； numerical simulation ； side-wall effect ； aspect ratio