Article
Engineering, Civil
Yong Cao, Huan Ping, Tetsuro Tamura, Dai Zhou
Summary: This study focuses on the flow mechanism of negative peak pressures on a square-section cylinder at a Reynolds number of 22,000, particularly those immediately upstream of the trailing edges. Trailing-edge peak pressures are observed to have minimum coefficients as low as -5 and show a close correlation within a streamwise length of approximately 0.1D (where D is the width of the cylinder). The formation of small trailing-edge vortices, characterized by highly concentrated vorticity, is found to be responsible for the occurrence of trailing-edge peak pressures. Standard proper orthogonal decomposition (POD) is used to identify the inherent spatial modes associated with sharp peak pressures upstream of the trailing edges. Higher-order modes, rather than the first mode corresponding to vortex shedding, are found to significantly contribute to the trailing-edge peak pressures, with mode coefficients exhibiting harmonics of the vortex shedding frequency. At least nine POD modes are needed to reconstruct the trailing-edge peak pressures. The recently proposed conditional space-time POD, a variant of POD, is effective in studying the average evolution of wind peak pressures and provides information about the relative phase and frequency ratio between the trailing-edge peak pressure and vortex shedding.
JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS
(2022)
Article
Mechanics
Sanjay Mittal, Jawahar Sivabharathy Samuthira Pandi, Mainak Hore
Summary: The study investigates the flow past a cylinder with side walls at various Reynolds numbers and aspect ratios, finding that the complexity of wake transitions increases with aspect ratio. The vortex structures and shedding characteristics change with Reynolds number and aspect ratio, showcasing different flow patterns and shedding modes.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Mechanics
Yongliang Yang, Zhe Feng, Mengqi Zhang
Summary: This paper presents the results of numerical simulations and linear stability analyses on the flow past a cylinder. The effects of aspect ratios and Reynolds numbers on vortex shedding are investigated, and a new steady wake pattern is discovered.
JOURNAL OF FLUID MECHANICS
(2022)
Article
Engineering, Marine
Behzad Forouzi Feshalami, Shuisheng He
Summary: This study investigates the effects of divergence ratio on flow characteristics around a confined square cylinder, finding that vortex shedding can be completely suppressed within a specific range of divergence ratio, leading to drag reduction.
Article
Mechanics
Shijun Chu, Chao Xia, Hanfeng Wang, Yajun Fan, Zhigang Yang
Summary: The study reveals that the seal-vibrissa-shaped cylinder has a more stable three-dimensional separation wake, longer vortex formation length, and weaker vortex strength compared to a circular cylinder at a Reynolds number of 20000. The mean drag and fluctuation of the lift coefficient of the seal-vibrissa-shaped cylinder are significantly reduced, and SPOD can extract four typical vortex shedding patterns.
Article
Mechanics
Dianfang Bi, Yingjie Wei, Raf Theunissen, Hao Xu
Summary: The paper experimentally investigates the dynamics of an annular disk falling freely in steady water, revealing three distinct falling motions. Proper Orthogonal Decomposition (POD) is used to extract the forces and torques governing the falling motion of annular disks. By decomposing the flow field into different POD modes, the study illuminates the reasons for the disparity between different falling motions.
EUROPEAN JOURNAL OF MECHANICS B-FLUIDS
(2021)
Article
Mathematics, Applied
Xiaodong Li, Steven Hulshoff, Stefan Hickel
Summary: Proper Orthogonal Decomposition (POD) is crucial for analyzing complex nonlinear systems governed by partial differential equations (PDEs). Traditional POD methods face challenges in storing high-dimensional solutions, leading to the development of incremental Singular Value Decomposition (SVD). To reduce the total computing cost, the proposed enhanced algorithm for incremental SVD incorporates POD mode truncation. The effectiveness of this algorithm is demonstrated through numerical experiments.
COMPUTERS & MATHEMATICS WITH APPLICATIONS
(2022)
Article
Thermodynamics
Ali Mohammadi, Chris Morton, Robert J. Martinuzzi
Summary: This study compares the benefits of time-domain spectral proper orthogonal decomposition (SPOD) with traditional proper orthogonal decomposition (POD) in separating coherent contributions within narrow spectral bandwidth. The results show that SPOD allows for a better interpretation of the related dynamics by representing each identified frequency in a separate mode pair, while POD does not separate the frequencies in the modes and makes it difficult to associate each frequency with specific phenomena within the wake region.
INTERNATIONAL JOURNAL OF HEAT AND FLUID FLOW
(2023)
Article
Mechanics
R. J. Crane, A. R. Popinhak, R. J. Martinuzzi, C. Morton
Summary: This study investigates the wake of a finite wall-mounted circular cylinder, revealing the relationship between periodically shed vortices and the quadrupole structure in the wake. The influence of H/D on the development of the quadrupole is characterized, showing that it emerges as an imprint of shed full-loop structures. The results reconcile mean and instantaneous interpretations satisfying the solenoidal condition on the vorticity field.
JOURNAL OF FLUID MECHANICS
(2021)
Article
Engineering, Marine
Zhenhua Lin
Summary: This study validates the influence of ambient density stratification on vortex shedding frequency through numerical simulations and experimental measurements. The numerical results show that the Strouhal number decreases with increasing ambient density gradient. The experimental measurements confirm the expectations from numerical simulations.
Article
Thermodynamics
Li Shen, Kwee-Yan Teh, Penghui Ge, Fengnian Zhao, David L. S. Hung
Summary: In-cylinder flow fields and their temporal evolution are crucial for the combustion dynamics of internal combustion engines. Proper orthogonal decomposition is a statistical tool that decomposes flow fields into patterns and coefficients to analyze their energy contributions, but current approaches fail to capture the temporal behavior of the flow fields. This study aims to understand the temporal behavior of tumble flow fields by analyzing low-order phase-dependent decomposition modes and proposing a low-order approximation model for in-cylinder tumble flow.
INTERNATIONAL JOURNAL OF ENGINE RESEARCH
(2021)
Article
Mathematics, Applied
Maria Kulikova, Gennady Yu Kulikov
Summary: This paper explores the design of accurate nonlinear Bayesian filters and proposes a numerical method for solving mean and error covariance of dynamic state. The key idea is to use methods with discretization error control to ensure accurate implementation of the filters' moment differential equations. The new method, tested on various application examples including stiff systems, utilizes a numerically stable square-root approach within singular value decomposition for a hybrid filter.
APPLIED NUMERICAL MATHEMATICS
(2022)
Article
Engineering, Mechanical
Cong Chen, Shengzhe Mao, Klaus Thiele
Summary: This paper investigates the spanwise correlation of unsteady lift in slender structures. Hilbert transform and Wavelet transform are used as time-frequency analysis tools to extract the instantaneous shedding frequency of vortex shedding. The results show that the extracted frequencies are stochastic and correlated between different cross sections.
JOURNAL OF FLUIDS AND STRUCTURES
(2023)
Article
Engineering, Civil
Yong Cao, Weizhi Li, Tao Tao, Shiyu Wang, Dai Zhou
Summary: This study applies the conPOD method to investigate the temporal evolution of peak suction on wall-mounted square cylinders under different incident angles. It reveals that the occurrence of peak pressures at the upper and lower windward corners is not synchronized when the incident angle is smaller than the critical angle. However, a strong correlation is observed at a greater angle. The conPOD method systematically clarifies the location, time of occurrence, and flow mechanism of the trailing-edge peak suction at different incident angles.
JOURNAL OF WIND ENGINEERING AND INDUSTRIAL AERODYNAMICS
(2023)
Article
Engineering, Ocean
Marek Jan Janocha, Lukas Philip Fabricius, Guang Yin, Muk Chen Ong
Summary: This paper presents a numerical simulation of the flow around a cylinder undergoing vortex-induced vibration, analyzing the effects of different reduced velocities. The results are compared with experimental data and validated using previous studies. The dominant wake flow features are discussed using proper orthogonal decomposition.
JOURNAL OF OFFSHORE MECHANICS AND ARCTIC ENGINEERING-TRANSACTIONS OF THE ASME
(2022)
Article
Engineering, Mechanical
Naoki Kanda, Chihaya Abe, Shintaro Goto, Keigo Yamada, Kumi Nakai, Yuji Saito, Keisuke Asai, Taku Nonomura
Summary: This paper presents the results of researching sparse processing particle image velocimetry (SPPIV) as a real-time flow field estimation method, which can estimate the flow velocity field from a small number of processing points. However, it is necessary to set the optimal number of processing points and select the appropriate number of modes to achieve the best estimation accuracy and processing efficiency.
EXPERIMENTS IN FLUIDS
(2022)
Article
Chemistry, Analytical
Yoshinori Oka, Takayuki Nagata, Miku Kasai, Yuta Ozawa, Keisuke Asai, Taku Nonomura
Summary: We developed a new pressure-sensitive paint with a short fluorescent lifetime, high pressure sensitivity, and low temperature sensitivity. The paint showed good performance under different excitation light sources.
Article
Instruments & Instrumentation
Chiharu Inomata, Masahide Kuwata, Sho Yokota, Yoshiaki Abe, Hideo Sawada, Shigeru Obayashi, Keisuke Asai, Taku Nonomura
Summary: A new model-position-sensing method is proposed for magnetic suspension of low fineness ratio models. The method utilizes two line sensors parallel to the central axis of the model image and achieves high-resolution position measurements. Experimental results demonstrate the effectiveness of the method in levitating low fineness ratio circular cylinder and reentry capsule models.
REVIEW OF SCIENTIFIC INSTRUMENTS
(2023)
Article
Chemistry, Analytical
Kazuki Uchida, Yuta Ozawa, Keisuke Asai, Taku Nonomura
Summary: This study applied antioxidants to a dual-luminophore pressure-sensitive paint and found that one type of antioxidant can significantly reduce the degradation rate, highlighting the importance of singlet oxygen in the photodegradation mechanism.
Article
Engineering, Mechanical
Yoshinori Oka, Yuta Ozawa, Takayuki Nagata, Keisuke Asai, Taku Nonomura
Summary: The pressure distribution inside a two-dimensional rectangular cavity with a ratio L/D=5.0 of the cavity length L to the depth D over a supersonic flow was measured using improved fast anodized-aluminum pressure-sensitive paint (AA-PSP). The freestream Mach number was M-infinity = 1.9 and the frequencies of the dominant cavity modal phenomena, called Rossiter modes, were on the order of 1-10 kHz. The measurement system used a fast AA-PSP with a 60 kHz sampling rate and validated the results with time-resolved pressure transducer data.
EXPERIMENTS IN FLUIDS
(2023)
Article
Engineering, Multidisciplinary
Miku Kasai, Takayuki Nagata, Kazuki Uchida, Taku Nonomura, Keisuke Asai, Yasuhiro Egami
Summary: Fast-response polymer-ceramic pressure-sensitive paints (PC-PSP) were developed and evaluated for pressure measurement under low-pressure conditions. The PC-PSP using poly[1-trimethylsilyl)-1-propyne] (poly(TMSP)) showed high oxygen permeability and improved dynamic characteristics compared to conventional binders and ruthenium-complex-based PC-PSPs. The particle mass content and composition of the PC-PSPs were adjusted to optimize the frequency response and local Stern-Volmer coefficient.
MEASUREMENT SCIENCE AND TECHNOLOGY
(2023)
Article
Multidisciplinary Sciences
Shu Tsuchiya, Hikaru Aono, Keisuke Asai, Taku Nonomura, Yuta Ozawa, Masayuki Anyoji, Noriyasu Ando, Chang-kwon Kang, Jeremy Pohly
Summary: The flapping flight of animals has been extensively studied and now researchers have successfully demonstrated the lift-off of a flapping wing robot in a low-density environment. By scaling wing size and motion, the robot was able to maintain high lift despite reduced air density. The results suggest that a coordinated increase in wing size and reduction in flapping frequency enable flight in lower density conditions, and this finding may have implications for flight in high-altitude environments and even in the ultra-low density Martian atmosphere.
SCIENTIFIC REPORTS
(2023)
Article
Physics, Fluids & Plasmas
Sho Yokota, Keisuke Asai, Taku Nonomura
Summary: This study investigates the influence of angle of attack on the aerodynamic characteristics of a freestream-aligned circular cylinder. Experimental tests were conducted using a magnetic suspension and balance system, and the aerodynamic forces and velocity fields were obtained. The results indicate that flow reattachment occurs at an angle of 9 degrees or higher, which alters the aerodynamic characteristics, particularly the lift and pitching moment coefficients, as well as the fluctuations in lift force.
PHYSICAL REVIEW FLUIDS
(2023)
Article
Thermodynamics
Akitoshi Matsui, Miku Kasai, Yosuke Sugioka, Keisuke Asai, Taku Nonomura
Summary: The sound-pressure level of acoustic waves and the pressure-fluctuation distribution of the bogie bottom surface were simultaneously measured using a microphone and a pressure-sensitive paint. A high-pressure-fluctuation area was observed on the upstream side of the bogie bottom surface at the peak sound frequency. The phase distribution of the peak frequency showed uniformity in the spanwise direction and delay in the downstream direction.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2023)
Article
Thermodynamics
Kodai Tashiro, Sho Yokota, Keisuke Asai, Taku Nonomura
Summary: This study investigates the effects of strut support on a slanted cylinder afterbody using a magnetic suspension and balance system in a wind tunnel. The findings suggest that the aerodynamic characteristics significantly change at the critical Reynolds number where the flow field and aerodynamic forces change. The presence of a dummy strut decreases the range of the critical Reynolds number, which depends on the location of the strut. The size of the recirculation region and the separation bubble on the wake center plane also varies based on the strut location. Additionally, weak vortices formed behind the strut alter the wake structure and contribute to the observed power spectral density peaks.
EXPERIMENTAL THERMAL AND FLUID SCIENCE
(2023)
Article
Engineering, Aerospace
Rui Aoki, Ikuhiro Fujimura, Taro Handa, Chungil Lee, Yuta Ozawa, Yuji Saito, Taku Nonomura, Keisuke Asai
Summary: An experimental study investigates the feasibility of controlling supersonic boundary-layer flows using a high-frequency flapping jet. The results show that the flapping jet effectively increases the boundary layer fullness, with the most significant increase observed at a flapping frequency of 30 kHz.
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES
(2022)
Article
Computer Science, Information Systems
Yuto Iwasaki, Taku Nonomura, Kumi Nakai, Takayuki Nagata, Yuji Saito, Keisuke Asai
Summary: In this study, we organize the existing sparsity-promoting dynamic mode decomposition (DMDsp) based on noise robustness, propose a faster optimization algorithm for DMDsp, and evaluate its characteristics. Two types of DMDsp, namely system-based DMDsp (sDMDsp) and observation-based DMDsp (oDMDsp), combined with three optimization algorithms, namely the fast iterative shrinkage thresholding algorithm (FISTA), the alternating direction method of multipliers (ADMM), and a greedy algorithm, are investigated. The results show that FISTA algorithm achieves the shortest processing time for both sDMDsp and oDMDsp. The original data reconstruction errors are similar among the three optimization algorithms for both sDMDsp and oDMDsp. The noise robustness of sDMDsp and oDMDsp is evaluated, with oDMDsp outperforming sDMDsp in systems with large system and observation noise.
Article
Computer Science, Information Systems
Keigo Yamada, Yuji Saito, Taku Nonomura, Keisuke Asai
Summary: In this study, optimization of sensor selection for monitoring complex and large-scale systems using data-driven linear reduced-order modeling is investigated. A greedy sensor selection algorithm is proposed under the assumption of correlated noise in the sensor signals, and sensor positions optimal for generalized least squares estimation are selected using an optimization approach. The results of numerical experiments using randomly generated data and real-world data demonstrate the effectiveness of the selection algorithm in accurately estimating the states of large-dimensional measurement data.
Article
Engineering, Mechanical
Kodai Tashiro, Sho Yokota, Fernando Zigunov, Yuta Ozawa, Keisuke Asai, Taku Nonomura
Summary: This study successfully magnetically levitated a cylinder with a slanted afterbody using a magnetic suspension and balance system, and investigated its aerodynamic characteristics through measuring aerodynamic force and visualizing the wake.
EXPERIMENTS IN FLUIDS
(2022)
Article
Engineering, Aerospace
Takayuki Nagata, Taku Nonomura, Kiyonobu Ohtani, Keisuke Asai
Summary: In this study, the visualization of compressible flow around a particle/particles, including wake vortices and drag estimation, was conducted through shock-particle interaction experiments. The experimental method allowed for the investigation of flow over isolated and clustered particles interacting with a planar shock. Flow structures for shock waves and wake structures were successfully visualized, and the mean drag coefficient was estimated and found to be close to previous values.
TRANSACTIONS OF THE JAPAN SOCIETY FOR AERONAUTICAL AND SPACE SCIENCES
(2022)
