A laboratory study of double eye-walled structure of typhoon under the environment of background vorticity
|Keywords:||旋轉水槽;雙眼牆;颱風;科氏效應;粒子影像追蹤測速法;Rotating tank;Double eye wall;Typhoon;Coriolis effect;Particle Image Velocimetr(PIV)||Issue Date:||2009||Abstract:||
本文嘗試以水工實驗模擬出自然界中颱風之雙眼牆現象，以水實驗模擬颱風雙眼牆現象，目前未曾於文獻中討論過。吾人以旋轉水槽提供背景渦度，在適當的類比條件下於旋轉水槽中產生一個類似颱風的穩定渦漩，藉著瞬間改變上升氣流的強度，從58.3 cm3s-1(虹吸)加強到116.6 cm3s-1(虹吸+幫浦抽取)，觀察並量測渦流場的變化。據實驗結果推斷雙眼牆的出現是因為渦心部分會先受到上升流的影響，急速往上運動。周圍環流在上升流突然增強的情況下，往的壓力梯度增加，則為了維持旋轉平衡(cyclostrophic blance)，離心力也會隨之增加，導致周圍環流旋轉速度加快。且因為渦心部分急速往上運動，流體達到自由液面後只能往下達到底部邊界層，一部分往內進入渦心，一部分則會往外環繞渦心上升。往外的部分則會影響內眼牆外的流體往上，形成眼牆間的空白區域，而阻擋外部的流體無法進入渦心部分，使得內眼牆得不到補充便會慢慢消散。為了達成平衡，外眼牆便會開始內縮，重新形成單眼牆結構。
In this study, the investigation of the double eye wall typhoon by means of hydraulic experiments has been conducted. Similar researches have not been observed in open literatures yet. Provide background vorticity by rotating sink, and produces A typhoon-like vortex vortex was produced under appropriated analog conditions in a rotating tank. By rapid-changing upper flow rate from 58.3 cm3s-1 (siphone) to 116.6 cm3s-1 (siphoge+pump), the changes of flow field changes were observed and measured. Results of experiments show that the appearance of double eye wall is due to the strengthening of vortex core affected by the increasing of upward flow. The sudden speed-up of horizontal circular flow around the vortex core leads to a sharp increase of inward pressure gradient. In order to maintain the cyclostrophic balance, centrifugal force will be increased resulting in the increasing of velocity of circular flow around vortex core. When the upward moving vortex core reaches the free surface, part of the upward flow will move outwardly and downward to the boundary layer of the bottom plate. Part of the downward flow will enters the vortex core inwardly, the rest will move outwardly and turn up around the vortex core. A double eye-walled structure is thus formed. Finally, inner eye wall disappears gradually due the short of fluid support from the boundary layer. Because of the cyclostrophic balance the outer eye wall will take over the inner one to reform a single eye-walled structure.
|Appears in Collections:||應用力學研究所|
Items in DSpace are protected by copyright, with all rights reserved, unless otherwise indicated.