Supersonic partially-covered cavity flow frequency estimation with proper orthogonal decomposition on schlieren photography슐리렌 사진 및 적합직교분해법을 통한 초음속 공동 유동의 주파수 예측

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Cavity flow has been identified to have intricate relationship between fluid dynamics and acoustics. High speed flow over cavities would result in strong pressure fluctuations at certain discrete frequencies known as cavity tones. In certain cases, i.e. weapons bay, cavity tone resonance may damage local structures and therefore cavity tone estimation is essential. In present work, a set of cavity models of 3 different length-to-depth ratio (L/D = 3, 4.5, and 6) with 4 different cover configurations (baseline-no cover, BP-back cover, FP-front cover, and CP-center uncovered) are investigated. Supersonic flowfield on each model is visualized with Schlieren photography and 5 typical types of shockwaves and acoustic waves unique to supersonic cavity flow can be identified. While schlieren images could only provide qualitative information, the use of Proper Orthogonal Decomposition (POD) is proposed to obtain quantitative components of acoustic waves inside the cavity. Subsequently, 16 POD bases of highest Relative Information Content (RIC) are shortlisted and presented in this work. Stripe-like patterns are visible in most POD bases and were surmised to be made of acoustic waves. Thus, wavelength of each pattern can be obtained with autocorrelation and Rossiter analogy is applied to obtain POD frequency. Numerical cavity tones are also obtained from CFX Scale-Adaptive Simulation (SAS) for comparison with POD frequencies, which are found to be in good agreement aside from minor discrepancies, especially for the shortest cavity. We have found that the use of thick covers on the cavity models altered either shear layer thickness, shear layer length, or both. Furthermore, more discrete tones are produced by partially-covered cavities when compared with those of uncovered models. It is also concluded that characteristic length in Rossiter equation for supersonic cavity flow was identified as shear layer length.
Advisors
Lee, Duck Jooresearcher이덕주researcher
Description
한국과학기술원 :항공우주공학과,
Publisher
한국과학기술원
Issue Date
2017
Identifier
325007
Language
eng
Description

학위논문(석사) - 한국과학기술원 : 항공우주공학과, 2017.2,[vi, 150 p. :]

Keywords

supersonic cavity flow; schlieren photography; proper orthogonal decomposition; turbulence model; CFX; 초음속 공동 흐름; 슐리렌 사진; 견적 직교 해석법; 난류 모델

URI
http://hdl.handle.net/10203/243566
Link
http://library.kaist.ac.kr/search/detail/view.do?bibCtrlNo=675526&flag=dissertation
Appears in Collection
AE-Theses_Master(석사논문)
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