Please use this identifier to cite or link to this item: http://hdl.handle.net/11455/2694
標題: 吸氣式安全氣囊之充氣器模擬分析與設計
Numerical Simulation and Design of Aspirated Inflator in Airbag
作者: 謝錦昇
關鍵字: 充氣器;吸氣比;Coanda effect
出版社: 機械工程學系
摘要: 
吸氣式安全氣囊是利用其充氣器內部流場的設計,使化學爆發的氣體轉換成低壓超音速流體,而造成強大的吸力吸入外界空氣充填安全氣囊。可達到與直接充氣式等同的效果,同時減少化學爆發物的使用量,增加安全性並減少環保問題,同時降低灼傷的危險性。
本研究以Fluent套裝軟體計算,對軸對稱EXAIR與二維對稱充氣器之充氣過程進行模擬,流場為非穩態流場(unsteady),並假設流體為理想氣體使用紊流模式計算。模擬吸氣式充氣器獲得持續性的吸氣效果,數值結果說明流場特性中Coanda effect、震波效應與尺寸參數對吸氣比的影響。
另外,針對吸氣口溫度、高壓入口壓力與溫度三種環境參數的變化,分別來探討環境效應對吸氣比的影響。模擬所得的結果與一維吸氣理論比較其趨勢皆相同。因此一維吸氣理論用於估計二維充氣器的吸氣比,有相當高的適應性與價值。
綜合模擬結果與獲得之經驗,並依據吸氣式充氣器的設計條件,分別對軸對稱與二維對稱之充氣器模型提出修改的建議,有效的阻止逆流產生,對吸氣比與充氣量均有良好的改善。此結果可作為充氣器實驗與設計的重要參考,並有助於相關應用作進一步的研究。

The aspirated inflator in airbag basically uses the principle of Coanda effect in an interior flow field. The high-pressure gas flowing through the primary nozzle speeds up and lowers its pressure to entrain air from the environment. Then the gas flows through a diffuser that increases the static pressure of the gas so as to open the airbag. The aspirated inflator can lower the use of bursting charge, and may provide a safer means as well as less environmental pollution. The mixed gas will decrease the danger of burn.
Numerical analysis uses a computational fluid dynamic (CFD) package Fluent. The simulations are focused on the axisymmetric EXAIR and 2D symmetric inflators. The flow fields are unsteady with the assumption of ideal gas. The Standard k —εmodel is employed to solve the continuity and Navier-Stokes equations. Simulations results show that aspirated inflator can continue entrain environmental air. Discuss of the flow characteristics ranges from the aspiration ratio to the Coanda effect, shock wave and dimension of the inflator.
In this study, the environmental effects, including surrounding temperature, the high-pressure inlet temperature and pressure, on the aspirating process and aspiration ratio of the inflator are further examined. It is found that the effects due to the inlet temperature and pressure agree well with the predictions of one-dimensional theorem with a difference below 5 % except for the pressure variation. Consequently, the one-dimensional theorem is valuable to some extend for estimating the aspiration ratio of two-dimensional inflator.
This study addresses the suggestion of revising the axisymmetric EXAIR and 2D symmetric inflators. For the revised inflators, reversed flow is eliminated and therefore the aspiration capability is enhanced. This simulation analysis provides useful information for experiments and design of the aspirated inflator.
URI: http://hdl.handle.net/11455/2694
Appears in Collections:機械工程學系所

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