Pressure mode analysis of nonuniform cross-sectional pipes and preliminary evaluation of a pogo suppressor

The pogo phenomenon is a type of instability that arises when the longitudinal modes of a space launch vehicle fuselage resonate with the pressure modes of the feedline in its propulsion system, with such resonance re-exciting the fuselage structure. To analyze this phenomenon, this paper specifically focuses on an analysis of the pressure modes in the space shuttle interpump line included in the LOX engine system. Because the interpump line is connected to pipes in different cross-sectional areas, the pressure modes are analyzed as a nonuniform cross-sectional pipe. Further, by applying a pogo suppressor in the feedline system, the possibility of preventing the pogo phenomenon is demonstrated. In order to design the suppressor, the resistive accumulator inertance, compliance, and resistance are considered as variables. Resistive accumulator compliance and inertance are determined and the pressure perturbation of the engine is prevented by lowering the inlet pressure amplitude of the high-pressure oxidizer pump (HPOP) in the space shuttle LOX system interpump line. When the resistive accumulator resistance is increased, the pressure frequencies of the interpump line gradually decrease, avoiding the resonance region with the fuselage. As a result, the resonance region with the fuselage is prevented by varying the pressure amplitude and natural frequencies of the interpump line. In this way, the capability of the present pogo suppression is evaluated.