Improvement of Air Flow in Duct Elbow Using Bulge-Modulated Blockage Ratio

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Project title

Code/計畫編號

MOST107-2221-E019-030

Translated Name/計畫中文名

改善彎角管道效能以受隆突體調控阻塞比的設計

Project Coordinator/計畫主持人

Shun-Chang Yen

Funding Organization/主管機關

National Science and Technology Council

Department/Unit

Department of Mechanical and Mechatronic Engineering

Website

https://www.grb.gov.tw/search/planDetail?id=12676862

Year

2018

Start date/計畫起

01-08-2018

Expected Completion/計畫迄

01-07-2019

Bugetid/研究經費

601千元

ResearchField/研究領域

機械工程

本計畫書擬議一個實驗研究方式，進行以隆突體(Bulge entity)的流動被動控制裝置，來改善彎角管道的流量效能；以隆突體在不同形狀、尺度、位置、粗糙度的條件下，對不同彎角管道的流量進行提升之研究。申請人基於去年度計畫‒以曲翼型導葉片改善彎角管道效能的設計，過程中以彎曲薄板及曲翼型(Cambered-airfoil)的導葉片在不同間距比的條件下，對不同彎角度管道的流量效能提升之研究。結果發現，裝置曲翼型導葉片能在尾流區後約五倍距離後，會趨近彎角管道前的流場行為、壓力損失、流量、速度等特性較彎曲薄板導葉片好。但因阻塞比原因，仍然無法回復到彎角管道前的流場特性，此一障礙仍有待克服。申請人近三年來協助合作企業—和光工業公司，開發新穎靜音型烘手機的流道設計，過程中發現烘手機內部空間狹小，致使烘手空氣流路的管道方向變化相當大；尤其是空氣流過彎道時，是否流暢，會影響烘手機的出風口風量及機器本體的振動與噪音。因此計畫將嘗試，以「技術發展」層面的觀點，結合申請人先前研究的結果，以隆突體在不同尺度、位置的條件下，覆蓋彎角管道所產生二次分離流的回流泡為依據。改善傳統彎管道內，因導葉片所衍生壓力降、阻塞高的困慮；進行彎管道的流量效能提升之研究。有鑑於此，專題研究中以隆突體在不同尺度、位置的條件下，構置於開放下吹式風洞的測試區具有彎角管道中，進行不同隆突鈍體形狀、尺度、位置、粗糙度、及速度等的研究。藉由調制隆突體的參數，進而抵銷彎角管道所產生二次分離流的回流泡大小。過程中將以煙線流場可視化技術、PIV量測系統、拓樸理論的分析應用、熱線風速儀、壓力掃描器、與噪音分貝計等交互應用，以尋找出最佳化的設計規則與操作條件，探討受隆突體所調控的彎角管道的幾何配置選取、流場行為、壓力降頭損、紊流動能特性、及非穩態流動與尾流的調制能力。煙線流場可視化技術、PIV系統觀察量測隆突體的流場特徵模態，並運用拓樸學的分析應用，確定複雜的流場結構模態。熱線風速儀以偵測隆突體的流場行為，包含由壓力及速度梯度所產生的渦街及剪流層不穩定波之間機制的差異。利用壓力掃描器擷取彎角管道受隆突體所產生壓力分佈，並經由理論的計算得到壓力損失的大小。使用噪音分貝計偵測彎角管道的音頻譜與分貝。將流體流過彎角管道受隆突體在不同尺度、位置的條件所調制時，彎角管道中的流場行為、壓力降頭損、流量、速度特性與噪音的關聯性做討論。 This project will experimentally utilize a bulge entity to passively improve the flow behaviors in the duct elbows. The controlling parameter will be set on the bulge size and location. The previous study on the cambered airfoil shows that the flow behaviors recover to in-duct one about 5-fold of duct diameter. The in-duct recovery, pressure loss, flow rate, flow velocity in the cambered airfoil is better than those of curved thin plate. However, the flow properties cannot recover completely to the in-duct condition due to the blockage ratio. The previous experience on the industrial cooperation — HOKWANG Industrial Company (和光工業公司) — of flow-path design in a innovative high-efficient and low-noised hand dryer triggered this study interest. The research results revealed that the flow channel changed abruptly in the cramped space. Specifically, the airflow passing through the flow channel will influence apparently the exit flow rate, the vibration and noise of dryer body. The centrifugal effect occurring at the duct elbow causes the flow-speed difference between the inner and outer walls. Furthermore, the second separation and pressure loss result in the non-uniformity of velocity distribution. This project will utilize different bulge dimension and location to control the duct elbow efficiency. The research results will be applied in the design and manufacture of flow channel. Furthermore, in this project, the controlling parameters of bulge shape, bulge size, bulge location and flow velocity will explored to decrease the secondary separation. These experimental factors will be considered comprehensively to shrink the second-separation bubble. The contraction of second-separation bubble will feedback the control factors on the upstream/down-stream flow distribution, pressure distribution and noise decibel. The experimental tools include the smoke-streak flow visualization, particle-image velocimetry (PIV), topological analysis, hot-wire velocimetry, linear pressure scanner and decibel meter. The flow performance considers the geometrical arrangement of turning vane in the duct elbows, flow behaviors, pressure head loss, turbulence characteristics, unstable flow and wake modulation. The smoke-streak flow visualization and PIV explore the flow characteristic patterns around the turning vanes. The topological flow analysis utilizes the critical point theorem to determine the flow structures. The hot-wire velocimetry examines the velocity distribution and vortex street caused from the velocity gradient and the difference between the shear-layer instability. The pressure scanner will be utilized to measure the pressure distribution resulted from the existence of turning vane. Furthermore, the pressure head loss will be determined. The decibel meter detect the noise spectrum and noise level; and multiple-frequency phenomenon of turning vanes. Consequently, the flow behaviors, pressure head loss, flow rate, velocity property and noise level in the duct elbows will be comprehensively discussed with considering the bulge shape, bulge dimension and the bulge location.

Keyword(s)

彎角管道
隆突體
阻塞比
二次分離流
Duct elbows
Bulge entity
Blockage ratio
Second separation

DSpace CRIS

Improvement of Air Flow in Duct Elbow Using Bulge-Modulated Blockage Ratio

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