Suppression of Vortex Shedding for Shear Flow Past a Rotating Bluff Body

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Project title

Code/計畫編號

NSC102-2221-E019-022-MY3

Translated Name/計畫中文名

剪流通過週期性旋轉鈍形體之渦街抑制研究

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=8124884

Year

2014

Start date/計畫起

01-08-2014

Expected Completion/計畫迄

01-07-2015

Bugetid/研究經費

670千元

ResearchField/研究領域

機械工程

"水流通過鈍形體（bluff body）所形成的渦街（vortex street）一直是工程應用與物理基礎研究的重要課題，因此等物理現象會導致物體周圍壓力的週期性變化，因而引致噪音的產生，同時也會導致鈍形物體周圍受力不均與振動，長期下來，造成結構體的彈性疲乏；更嚴重的情況是，週期性的渦街可能會與結構體發生共振，造成結構體的嚴重破壞。因此，如何減低渦街的強度、或是抑制渦街的效應，一直是工程研究亟需面對的問題。本計畫擬以三年的時間，透過週期性反覆旋轉的圓柱，來研究二維剪流通過鈍形物體的渦街抑制效應。我們將探討兩種不同的剪流，一為透過壓力梯度驅動的渠道剪流，其速度分布為對稱的拋物線，另一為透過拉動一平板驅動的Couette 剪流，其速度分布為非對稱的線性函數。另外，我們也要探討鈍形物體靠近邊壁時的狀況，這事實上也是不對稱的狀況，主要是要了解邊界層所造成的效應。同時我們也要探討抑制渦街的物理機制，並就上述的三種狀況進行比較。剪流下的渦流抑制機制是學術討論上的處女地。為探討此一問題，我們定義幾個不同的幾何參數、運動參數、與動力參數。在運動參數上，有圓柱的旋轉頻率、以及旋轉速比（即圓柱的最高旋轉速度與入流平均速度之比值）；幾何參數則有圓柱直徑與渠道寬度之比值、或是圓柱直徑與圓柱至邊壁間隙之比值；另外，動力參數則為雷諾數。我們將就雷諾數與幾何參數作適當的變化，以了解參數變化所造成的影響，其中雷諾數將限制在50‐200 之間，幾何參數將設定為大、中、小三類數值。" "The physical phenomenon of vortex shedding due to flow passing a bluff body is of much interest to engineering applications and fundamental research. Such a phenomenon results in a periodic pressure fluctuation around the body, which induces noise and vibration and finally leads to structural fatigue. What may be worse is that the structural system may also suffer from resonance due to the periodic vortex shedding and is seriously damaged. Therefore, it is vitally important in engineering applications to reduce or suppress vortex shedding. We propose in the present project to study the possibility of suppressing vortex shedding for a shear flow passing a periodically rotating bluff body. For simplicity, a cylinder will be employed to represent a typical bluff body throughout the study. Three kinds of different shear flows will be considered. They are the Poiseuille flow which is driven in a channel by a pressure gradient, the Couette flow which is driven between two parallel plates with one of them pulled with a constant velocity, and the flow with the bluff body close to a wall which is similar to a boundary‐layer flow. Of particular interest are the combination of frequency and maximum speed at which the cylinder rotates to suppress the vortex shedding, the mechanism which results in the vortex shedding suppression, and the comparisons among the three different shear flows. To elaborate the problem in details, we have a geometric parameter, two kinematic parameters, and one dynamic parameter. The geometric parameter is the ratio of the cylinder diameter to the channel width or the ratio of the gap length to the cylinder diameter. The kinematic parameters include the frequency at which the cylinder rotates and the ratio of the maximum speed of the cylinder to the average of incoming flow velocity. The dynamic parameter is the Reynolds number. In order to understand the physical phenomenon, we will vary the Reynolds number between 50 and 200 and values of the geometric parameter. Then will study the effects of the two parameters on the two kinematic parameters to suppress vortex shedding."

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Suppression of Vortex Shedding for Shear Flow Past a Rotating Bluff Body

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