Seyed Alireza Jalali CHIMEH, Hassan Karimi Mazareh SHAHI, Mohammad Shafiei DEHAJ

Frequency Analysis of Launch Vehicle Oscillation Absorbent Configuration on Performance of Liquid Propellant Engine

Pogo phenomenon is considered as low-frequency instability at system level in heavy satellite launchers. This instability results from the frequency interactions between structure and propulsion subsystems. To compensate for or prevent the occurrence of this instability in a satellite launcher, an element that reduces the frequency interaction effects of these two systems is used. This element, which is known as ‘accumulator’, absorbs the pogo vibrations in satellites. In this paper, by dynamically modeling the engine elements (tank, supply line, accumulator, pump, and thrust chamber), and by considering the connection of structure to engine at two points of tank and pump, the effects of the accumulator element and parameters on the natural frequency of the propulsion system have been investigated and the considerations related to operating conditions and the placement of this element along the supply line of the propulsion system have been determined. The findings indicate that placing the accumulator near the pump assembly and along the suction path reduces the natural frequency of the propulsion system; which contributes to a greater stability of the satellite launcher. With the increase in the compliance and inertance of accumulator, accumulator’s influence on the natural frequency of the propulsion system becomes more significant.

Fırlatma Aracı Salınım Absorb Konfigürasyonunun Sıvı Yakıtlı Roket Performansına Etkisinin Frekans Analizi

Büyük uydu fırlatıcılarda Pogo olgusu düşük frekanslı bir dengesizlik seviyesi olarak görülür. Bu dengesizliğin sebebi yapısal ve yakma-itki sistemlerinin frekansları arasındaki değişim ve etkileşimdir. Bu kuvvet dengesizliğinin oluşumunu engellemek veya etkisini azaltmak için uydu fırlatma sisteminde bir element kullanılır. “Akümülatör” olarak da adlandırılan bu element Pogo titreşimlerini uydu yapısında absorbe eder. Bu çalışmada, akümülatörün etkisi ve itki sisteminin doğal frekans üzerindeki etkisi, motora ait dinamik modellemeler yardımıyla (tank, besleme sistemleri, akü, pompa ve itki halkası) ve motorun ana yapıya bağlandığı noktalar dikkate alınarak motorun nasıl konumlanması gerektiği ve sistemin tepkisi ölçülmüştür. Bu sayede varılan bulgular değerlendirildiğinde oluşan sonuçlar şunu göstermektedir ki, akümülatörün pompanın hemen yanına veya yakınına yerleştirilmesi, emilim yolunda kullanılan tüplerle birlikte, itki sisteminin yarattığı doğal frekansın azalmasına yardımcı olmaktadır ve bu da istenildiği üzere bütün yapının daha stabil bir hal almasında ve özellikle uydunun fırlatma anına yardımcı olmaktadır. Akümülatör ve ana yapı arasındaki uyumluluktaki bu artış ile akümülatörün itki sisteminin doğal frekansı üzerindeki etkisi de daha dikkate değer bir hal almıştır.

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