Low frequency instability and oscillating boundary layer in hybrid rocket combustion
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DOI 10.1007/s12206-020-1039-x
Journal of Mechanical Science and Technology 34 (11) 2020 Original Article DOI 10.1007/s12206-020-1039-x Keywords: · Low frequenccy instability · Hybrid rocket combustion · Proper orthogonal decomposition · Boundary layer perturbation
Correspondence to: Changjin Lee [email protected]
Citation: Kim, J., Lee, C. (2020). Low frequency instability and oscillating boundary layer in hybrid rocket combustion. Journal of Mechanical Science and Technology 34 (11) (2020) 4831~4839. http://doi.org/10.1007/s12206-020-1039-x
Received April 10th, 2020 Revised
August 11th, 2020
Accepted August 23rd, 2020 † Recommended by Editor Yong Tae Kang
Low frequency instability and oscillating boundary layer in hybrid rocket combustion Jina Kim and Changjin Lee Department of Aerospace Engineering, Konkuk University, 120 Neungdong-ro, Gwangjin-gu, Seoul, Korea
Abstract
The resonance of thermal lags of solid fuel with heat transfer oscillations in a boundary layer flow is the primary cause of low-frequency instability initiation in hybrid rocket combustion. A detailed study of two cases was conducted experimentally to investigate how the boundary layer is disturbed and leads to low-frequency instability (LFI); combustion with swirl injection and combustion with the frequency jump. The fluctuating boundary layer was successfully captured by visualizing images and proper orthogonal decomposition analysis was performed. The results show that swirl injection with an appropriate intensity substantially reduces the amplitudes of high frequency p', and no boundary layer perturbation is found in the spectral analysis of mode 2, and Rayleigh index amplifications disappear. While the frequency jump occurs, the coupling status between p' and q' became weakly positive and the driving force disturbing the upstream flow was not made. As a result, oscillatory heat transfer was difficult to occur. Therefore, the appearance of boundary layer perturbation is the necessary precondition for the initiation of the low-frequency instability. And the resonance with the thermal lag characteristic leads to the occurrence of LFI.
1. Introduction
© The Korean Society of Mechanical Engineers and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Hybrid rockets have recently attracted many attentions because of their safety nature in operation as well as low development costs compared to other conventional rockets. Nonetheless, poor nature in density specific impulses and inferior regression rate are major issues that needs to be addressed to make hybrid rockets practical. In addition, the occurrence of low-frequency instability in combustion shows a different characteristic from that of other chemical rockets. In combustion instability, the combustion pressure shows low frequency peaks much lower than 100 Hz, which is called low frequency instability (LFI), and is accompanied by a non-linear characteristic of successive occurrences and disappearances. Karabeyoglu et al. [1] confirmed that LFI is caused by the physical re
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