Modal Decomposition Analysis of Subsonic Unsteady Flow Around An Atmospheric Entry Capsule with Forced Oscillation

2019 ◽  
Author(s):  
Kenji Kobayashi ◽  
Yuya Ohmichi ◽  
Masahiro Kanazaki
AIAA Journal ◽  
2018 ◽  
Vol 56 (10) ◽  
pp. 3938-3950 ◽  
Author(s):  
Yuya Ohmichi ◽  
Takashi Ishida ◽  
Atsushi Hashimoto

2021 ◽  
Vol 33 (9) ◽  
pp. 092117
Author(s):  
Antonio Colanera ◽  
Alessandro Della Pia ◽  
Matteo Chiatto ◽  
Luigi de Luca ◽  
Francesco Grasso

Author(s):  
Bogdan C. Cernat ◽  
Sergio Lavagnoli

The present research focused on the analysis of the leakage flows developing from advanced blade tip geometries. The aerodynamic field of a contoured blade tip and of a high-performance rimmed blade were investigated against a baseline squealer rotor. Time-resolved numerical predictions were combined with high-frequency pressure measurements to characterize the tip leakage flow of each tip design. High spatial and temporal resolution measurements provided a detailed representation of the unsteady flow in the near-tip region and at the stage outlet. Numerical computations, based on the nonlinear harmonic method, were employed to assess the unsteady blade row interactions and identify the loss generation mechanisms depending on the tip design. The space- and time-resolved flow field was analysed by modal decomposition to identify the main periodicities of the near-tip and outlet flow and classify the most relevant sources of aerodynamic unsteadiness and entropy generation across the stage.


1967 ◽  
Vol 27 (1) ◽  
pp. 177-207 ◽  
Author(s):  
W. W. Willmarth ◽  
N. E. Hawk ◽  
A. J. Galloway ◽  
F. W. Roos

Detailed studies are reported of the free and forced oscillation of disks and a right-circular cylinder constrained to rotate about a fixed diametrical axis passing through the centre of the body and normal to the free-stream direction. When a disk is free to rotate, it oscillates at a definite frequency with slowly varying amplitude and phase. A right-circular cylinder also oscillates at a definite frequency but with rapidly increasing amplitude. When the amplitude becomes large, after a few cycles of oscillation, the cylinder rotates steadily in one direction.Analogue computer elements, position sensors and a dynamic moment balance were used to study the static restoring moment, dynamic restoring moment, average damping moment, statistical properties of the disk motion and power spectrum of the turbulent moment. The behaviour of the disk and cylinder are explained using the measurements and the theory for random excitation of a linear system. The turbulent exciting moment is caused by the unsteady flow in the wake and can be changed by placing disks and splitter plates in the wake. A model is proposed for the unsteady flow field in the wake behind the disk. The model relates the turbulent moment to the vortex shedding process in the wake.


Author(s):  
Yang Liang ◽  
Brian Feeny

A frequency domain decomposition method is formulated to extract modal information of multi-degree-of-freedom systems. Previously, state-variable modal decomposition (SVMD), smooth orthogonal decomposition (SOD), and also proper orthogonal decomposition (POD), have used time domain signals for modal decomposition. Analysis shows that similar formulas can be obtained in the frequency domain, with eigenvalues as the resonance frequencies, and the eigenvectors as the inverse of the linear normal modes (LNMs). The method can be expressed in symmetric or non-symmetric eigenvalue problem format. The symmetric format resembles SOD in the frequency domain, while the non-symmetric method is similar to SVMD. One of the advantages of a frequency-domain method is that signals can be divided into frequency segments to find out the existence of natural frequencies and normal modes within a limited frequency range, such that the noise influence can be reduced. Furthermore, the obtained eigenvectors can be used to check if they actually are normal modes or noises. The method was examined by a six degree-of-freedom mass-spring system under free vibration and random excitation conditions.


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