A Study of Flow past a Circular Cylinder over a Backward-Facing Step

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基本資料

Project title

Code/計畫編號

NSC101-2221-E019-001-MY2

Translated Name/計畫中文名

背階圓柱流場特性分析

Project Coordinator/計畫主持人

Jiahn-Horng Chen

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Systems Engineering and Naval Architecture

Website

https://www.grb.gov.tw/search/planDetail?id=2853561

Year

2013

Start date/計畫起

01-08-2013

Expected Completion/計畫迄

01-07-2014

Bugetid/研究經費

759千元

ResearchField/研究領域

機械工程

"流體流動通過圓柱與背階（backward-facing step）所形成的流場，都是個古典基礎流體力學問題，這些流場的研究長久以來受到極多的關注，因其中所涵蓋的流動剝離（flow separation）與再附著（flow reattachment）現象是多數工程應用問題的基礎原型，這在造船工程與海洋工程自不例外。本研究擬結合此二流場的幾何特性，探討剝離流場與渦漩流場的性質，整體的流場形狀如圖一所示，圓柱立於背階上游的邊緣。此等組合過去並無文獻探討，但我們最近的初步實驗顯示，在適當的組合下，渦漩散逸頻率有大幅下降、且渦漩強度明顯降低的可能性，此等發現具有工程應用的價值。為了解此一現象，我們提出此一研究計劃，將運用適當的計算流體力學方法，建立適當的計算網格，詳細探討水流通過此一幾何構造時所形成的流動現象。探討的現象主要集中在低雷諾數下的流場結構特性，包括隨著雷諾數的增加，流場的剝離變化、迴流區的變化特性、以及渦漩散逸、頻率、與強度的變化特性。本研究計畫將以兩年的時間來執行兩種上邊界的狀況。在第一年，上邊界的設定為一壁面，此代表古典渠道流（channel flow）的狀況；在第二年，上邊界的設定則改為自由液面，代表一般的河流或海流的狀況。至於側面的邊界，我們將假設為週期邊界，這相當於是一排圓柱以等間距的距離立在下邊界上。另外，為探討此等現象，我們定義三個幾何參數。第一個參數是背階係數，定義為背階高度與圓柱直徑的比值，我們擬探討的範圍將侷限在較小的數值，暫定從0.2 變化到1.5，間距暫定為0.3；第二個參數跨距係數，定義為相鄰兩圓柱圓心間之距離與圓柱直徑之比值，我們擬探討的範圍將從2 變化到10，間距暫定為2，必要時可再往下降或往上升；第三個參數為沒水係數，定義為水位高度與圓柱直徑之比值，我們擬探討的範圍將暫定從1 變化到15，間距暫定為1~3 的範圍。" "The physical phenomena due to flow past a circular cylinder and a backward-facing step are classical problems in fluid mechanics. They have received considerable attention in the past because separated and reattached flows involved in these flows are typically encountered in most practical engineering applications, including naval architecture and ocean engineering. In the present project, we propose to combine these two geometries and study the flow past a circular cylinder which stands just upstream of the backward facing step, as shown in Figure 1. In the literature, few reports investigating such a flow are available. However, a recent experimental study in our research team seems to show that with the frequency of vortex shedding and strength are significantly reduced when some geometrical parameters were properly chosen. This observation has its value in engineering application. To understand such interesting flow phenomena in details, we propose to conduct a series of computations to reveal its fundamental mechanism and features. We will focus on the flow development at low Reynolds numbers, including separation, recirculating flow, vortex shedding, and frequency and strength of vortex shedding. The study will be carried out in two years. For the first year, we assume that the upper boundary in the flow geometry is a solid wall; for the second year, we assume the upper boundary is a free surface. In addition, we employ a symmetrical boundary condition on the side boundaries, signifying equally-spaced cylinders stand on the bottom boundary. Furthermore, we have three geometrical parameters in the present geometry. The first one is step coefficient, defined as the ratio of the step height to the cylinder diameter. We plan to vary its value from 0.2 to 1.5, with a step of 0.3. The second one is the span coefficient, defined as the ratio of the distance between two adjacent cylinders to the cylinder diameter. We also change its value from 2 to 10, with a step of 2. The third one is the immersion coefficient, defined as the ratio of the water depth to the cylinder diameter. We plan to vary its value from 1 to 15, with step of 1-3."

Keyword(s)

圓柱流場
背階流場
渦漩減降
Flow past a circular cylinder
flow past a backward-facing step
vortex reduction

DSpace CRIS

A Study of Flow past a Circular Cylinder over a Backward-Facing Step

基本資料

Description