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Experimental Analysis and Numerical Simulation on flow structures within Labyrinth Seal
|關鍵字:||non-contact sealing;非接觸式軸封;high speed spindle;labyrinth;高速軸承;迷宮||出版社:||機械工程學系||摘要:||
(1)直通式迷宮軸封(A模型):出口壓力大於入口壓力，呈現逆向壓力梯度( )。外來的流體不易流入軸封內部。當徑向間隙 時，對於外來流體的阻擋效果佳；反之， 時，阻擋外來流體的能力較差。當軸向寬度 時，空穴Ⅱ留滯氣體效果最好；反之， 者的留滯氣體效果則是最差。另外，針對楔形正、負倒角而言，在空穴Ⅰ的壓力差以負倒角者大於正倒角者；然而，在空穴Ⅱ以及空穴Ⅲ的壓力差反而是正倒角者大於反倒角者。比較進、出口的壓力差，正向楔形倒角系列具有較強的逆向壓力梯度，而負向楔形倒角系列的逆向壓力梯度則是較弱。對A模型而言，最佳組合為徑向間隙 ，配合軸向寬度 ，且無論正、負楔形倒角均可。
(2)階梯式迷宮軸封(B模型)：出口壓力小於入口壓力，呈現正向壓力梯度( )，使得外來的流體容易流入軸封內。當軸向位移 時，空穴Ⅱ右方空腔內留滯氣體的效果則是最好。究其原因是在空穴Ⅱ右方空腔內的壓力差會隨著軸向位移的增加而上升。反之，當 者，留滯氣體效果則是最差，另外，當徑向間隙 時，對於外來流體的阻隔效果佳。反之；當 時，阻隔外來流體的效果變差。所以對B模型而言，最佳的阻隔效果是當徑向位移 為0.45且徑向間隙 ，以及軸向位移 的組合。
The purposes of this study are to investigate the flow structures within and the associated pressure distributions along the wall of the labyrinth seal by experiments and numerical analysis .The rotational speed of the horizontal spindle is 10000 r.p.m .Two types of the labyrinth seal are employed: a straight-through (model A) type and a stepwise type (model B) of the labyrinth. It is the objective to study the influence of the geometric parameters, such as the radial clearance (h), the axial width (W1) between the cavities, and the effect of the wedge angle on the sealing performance of model A. Besides, the radial clearance (h), the amount of axial offset (d) and the radial displacement (s) for model B are also investigated.
(1) For a Straight-through type labyrinth seals (Model A):
The outlet pressure is greater than the inlet pressure, showing an adverse pressure gradient ( ). Thus, the outside flow cannot get into the seal easily. When the radial clearance is smaller than 0.003636, the overall trapping ability is good. On the other hand, for greater than 0.003636, the overall trapping ability is relatively poor. When the axial width is greater than 2, the trapping ability within the cavity Ⅱ of the seal is better than . The pressure differences of the cavityⅠfor the negative wedge angle are greater than those of the positive one. On the contrary, the pressure differences in cavities Ⅱ and Ⅲ for the positive wedge angle is greater than the negative one. Based on the pressure differences between the outlet and the inlet, the amount of adverse pressure gradient is stronger for positive wedge angle than that for negative one. When is smaller then 0.003636 and the axial width is greater than 2, we can get the best sealing performance of models A no matter what the wedge angle is positive or negative.
(2) For the stepwise type labyrinth seal (Model B):
The outlet pressure is smaller than the inlet pressure, showing a favorable pressure gradient ( ), thus, the outside flow can easily enter the passage of the seal. When the axial displacement is greater than 0.3, the trapping ability is good in cavity Ⅱ. Large volume of the right space in cavity Ⅱ allows the full development of the vortex and is primarily responsible for the improved trapping ability there. On the other hand, when is smaller than 0.3, the trapping ability in the right space of cavity Ⅱ is relatively poor. When the radial clearance is smaller than 0.003636, the overall sealing performance is good. On the other hand, for greater than 0.003636, the overall sealing performance is relatively poor. For a model B, the conditions of radial clearance smaller than 0.003636 and the axial displacement greater than 0.3 will lead to the best sealing performance.
|Appears in Collections:||機械工程學系所|
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