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Статті в журналах з теми "Unsteady mode"

Автор: Grafiati

Опубліковано: 2 грудня 2022

Оновлено: 25 липня 2025

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1

Wynn, A., D. S. Pearson, B. Ganapathisubramani, and P. J. Goulart. "Optimal mode decomposition for unsteady flows." Journal of Fluid Mechanics 733 (September 24, 2013): 473–503. http://dx.doi.org/10.1017/jfm.2013.426.

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AbstractA new method, herein referred to as optimal mode decomposition (OMD), of finding a linear model to describe the evolution of a fluid flow is presented. The method estimates the linear dynamics of a high-dimensional system which is first projected onto a subspace of a user-defined fixed rank. An iterative procedure is used to find the optimal combination of linear model and subspace that minimizes the system residual error. The OMD method is shown to be a generalization of dynamic mode decomposition (DMD), in which the subspace is not optimized but rather fixed to be the proper orthogon

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2

Ibraheem AlQadi, Ibraheem AlQadi. "Investigation of Flow Around a Slender Body at High Angles of Attack." journal of King Abdulaziz University Engineering Sciences 30, no. 1 (2019): 51–61. http://dx.doi.org/10.4197/eng.30-1.4.

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Анотація:

A numerical investigation of flow around a slender body at high angles of attack is presented. Large eddy simulation of the flow around an ogive-cylinder body at high angles of attack is carried out. Asymmetric vortex flow was observed at angles of attack of α = 55◦ and 65◦ . The results showed that the phenomenon is present in the absence of artificial geometrical or flow perturbation. Contrary to the accepted notion that flow asymmetry is due to a convective instability, the development of vortex asymmetry in the absence of perturbations indicates the existence of absolute instability. An in

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3

Li, Yi-bin, Chang-hong He, and Jian-zhong Li. "Study on Flow Characteristics in Volute of Centrifugal Pump Based on Dynamic Mode Decomposition." Mathematical Problems in Engineering 2019 (April 16, 2019): 1–15. http://dx.doi.org/10.1155/2019/2567659.

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To investigate the unsteady flow characteristics and their influence mechanism in the volute of centrifugal pump, the Reynolds time-averaged N-S equation, RNG k-ε turbulence model, and structured grid technique are used to numerically analyze the transient flow-field characteristics inside the centrifugal pump volute. Based on the quantified parameters of flow field in the volute of centrifugal pump, the velocity mode contours and oscillation characteristics of the mid-span section of the volute of centrifugal pump are obtained by dynamic mode decomposition (DMD) for the nominal and low flow-r

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4

Ling, Meiting, Ting Zhao, Wenguo Luo, Jianfeng Zhu, and Yancheng You. "Analysis of Aerodynamic Characteristics of Rotating Detonation Turbine Based on Proper Orthogonal Decomposition Method." Aerospace 12, no. 5 (2025): 406. https://doi.org/10.3390/aerospace12050406.

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The unsteady interactions in rotating detonation turbine engines (RDTE) remain poorly understood. To address this, a 2D numerical model integrating a rotating detonation combustor (RDC) with a first-stage turbine is established to analyze flow structures and aerodynamics under various detonation modes. Proper orthogonal decomposition (POD) reveals intrinsic links between flow features and performance metrics. Results show that while the RDC generates total pressure gain, it induces significant unsteady flow. Guide vanes partially suppress pressure fluctuations but cannot eliminate total pressu

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5

Corrochano, Adrián, Donnatella Xavier, Philipp Schlatter, Ricardo Vinuesa, and Soledad Le Clainche. "Flow Structures on a Planar Food and Drug Administration (FDA) Nozzle at Low and Intermediate Reynolds Number." Fluids 6, no. 1 (2020): 4. http://dx.doi.org/10.3390/fluids6010004.

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Анотація:

In this paper, we present a general description of the flow structures inside a two-dimensional Food and Drug Administration (FDA) nozzle. To this aim, we have performed numerical simulations using the numerical code Nek5000. The topology patters of the solution obtained, identify four different flow regimes when the flow is steady, where the symmetry of the flow breaks down. An additional case has been studied at higher Reynolds number, when the flow is unsteady, finding a vortex street distributed along the expansion pipe of the geometry. Linear stability analysis identifies the evolution of

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6

Hall, K. C., and P. D. Silkowski. "The Influence of Neighboring Blade Rows on the Unsteady Aerodynamic Response of Cascades." Journal of Turbomachinery 119, no. 1 (1997): 85–93. http://dx.doi.org/10.1115/1.2841014.

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Анотація:

In this paper, we present an analysis of the unsteady aerodynamic response of cascades due to incident gusts (the forced response problem) or blade vibration (the flutter problem) when the cascade is part of a multistage fan, compressor, or turbine. Most current unsteady aerodynamic models assume the cascade to be isolated in an infinitely long duct. This assumption, however, neglects the potentially important influence of neighboring blade rows. We present an elegant and computationally efficient method to model these neighboring blade row effects. In the present method, we model the unsteady

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7

STEWART, B. E., M. C. THOMPSON, T. LEWEKE, and K. HOURIGAN. "Numerical and experimental studies of the rolling sphere wake." Journal of Fluid Mechanics 643 (January 15, 2010): 137–62. http://dx.doi.org/10.1017/s0022112009992072.

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A numerical and experimental investigation is reported for the flow around a rolling sphere when moving adjacent to a plane wall. The dimensionless rotation rate of the sphere is varied from forward to reversed rolling and the resulting wake modes are found to be strongly dependent on the value of this parameter. Results are reported for the Reynolds number range 100 < Re < 350, which has been shown to capture the unsteady transitions in the wake. Over this range of Reynolds number, both steady and unsteady wake modes are observed. As the sphere undergoes forward rolling, the wake displa

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8

Chiang, H. W. D., and S. Fleeter. "Passive Control of Flow-Induced Vibrations by Splitter Blades." Journal of Turbomachinery 116, no. 3 (1994): 489–500. http://dx.doi.org/10.1115/1.2929438.

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Splitter blades as a passive control technique for flow-induced vibrations are investigated by developing an unsteady aerodynamic model to predict the effect of incorporating splitter blades into the design of an axial flow blade row operating in an incompressible flow field. The splitter blades, positioned circumferentially in the flow passage between two principal blades, introduce aerodynamic and/or combined aerodynamic-structural detuning into the rotor. The unsteady aerodynamic gust response and resulting oscillating cascade unsteady aerodynamics, including steady loading effects, are det

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9

Vabishchevich, Petr N. "Fundamental mode exact schemes for unsteady problems." Numerical Methods for Partial Differential Equations 34, no. 6 (2018): 2301–15. http://dx.doi.org/10.1002/num.22292.

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10

Aurahs, L., C. Kasper, M. Kürner, M. G. Rose, S. Staudacher, and J. Gier. "Water flow model turbine flow visualization study of the unsteady interaction of secondary flow vortices with the downstream rotor." Proceedings of the Institution of Mechanical Engineers, Part A: Journal of Power and Energy 223, no. 6 (2009): 677–86. http://dx.doi.org/10.1243/09576509jpe841.

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This article presents detailed flow visualization photographs, root mean square processed photography, and computational fluid dynamics (CFD) results of the interaction of the vane passage vortex and horseshoe vortex with the rotor of an axial flow turbine model. Different modes of vortex breakdown behaviour have been experimentally observed inside the rotating passage of the turbine blade. These are spiral vortex mode and bubble mode breakdown. The breakdown mode changes as the vortices are influenced by the periodic pressure field of the rotor. The measurements were taken in a vertical water

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11

Wang, Jin-Chun, Xin Fu, Guo-Ping Huang, Shu-Li Hong, and Yuan-Chi Zou. "Application of the Proper Orthogonal Decomposition Method in Analyzing Active Separation Control With Periodic Vibration Wall." International Journal of Turbo & Jet-Engines 36, no. 2 (2019): 175–84. http://dx.doi.org/10.1515/tjj-2017-0031.

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AbstractThe proper orthogonal decomposition (POD) method is employed to analyze the unsteady flow control mechanism because it is a good approach to decouple the spatial and temporal structures of unsteady flow fields. The results showed that the main effect of the periodic excitation is reallocating the energy of each mode, and selectively strengthening or weakening certain modes. Under proper amplitude and frequency of periodic excitation, the energy in higher modes will be transferred to the first mode and the translation of the modal energy is coming from the reconstructing of spatial flow

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12

Gerolymos, G. A. "Coupled Three-Dimensional Aeroelastic Stability Analysis of Bladed Disks." Journal of Turbomachinery 115, no. 4 (1993): 791–99. http://dx.doi.org/10.1115/1.2929317.

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Анотація:

In the present work an algorithm for the coupled aeromechanical computation of three-dimensional compressor cascades vibrating in a traveling-wave mode is presented and applied to the determination of aeroelastic stability of a transonic fan rotor. The initial vibratory modes are computed using a finite-element structural analysis code. The unsteady flow field response to blade vibration is estimated by numerical integration of the three-dimensional unsteady Euler equations. Coupling relations are formulated in the frequency domain, using a mode-modification technique, based on modal projectio

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13

Chen, Hao. "Numerical Calculations on the Unsteady Aerodynamic Force of the Tilt-Rotor Aircraft in Conversion Mode." International Journal of Aerospace Engineering 2019 (December 7, 2019): 1–15. http://dx.doi.org/10.1155/2019/2147068.

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Анотація:

A computational method is developed in order to predict the unsteady aerodynamic characteristics of the tilt-rotor aircraft in conversion mode. In this approach, the rotor is modeled as an actuator disk so that the effect of individual blades can be ignored. A novel predictor-corrector-based dynamic mesh method is presented for dealing with extremely large mesh deformation during a conversion process. The dual time-stepping approach and the finite volume scheme are applied to solve the unsteady N-S equation. A parallel algorithm is utilized in this work to improve the computational efficiency.

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14

Ma, Wei. "Discontinuous Growth Mechanisms of Mode II Crack under High-Speed Impact Conditions." Advanced Materials Research 41-42 (April 2008): 169–73. http://dx.doi.org/10.4028/www.scientific.net/amr.41-42.169.

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Анотація:

A recoverable plate impact testing technology has been used for studying the growth mechanisms of mode II crack. The results show that interactions of microcracks ahead of a crack tip cause the crack growth unsteadily. Failure mode transitions of materials were observed. Based on the observations, a discontinuous crack growth model was established. Analysis shows that the shear crack grows unsteady as the growth speed is between the Rayleigh wave speed cR and the shear wave speed cs; however, when the growth speed approaches 2cs, the crack grows steadily. The transient microcrack growth makes

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15

Hochet, Antoine, Alain Colin de Verdière, and Robert Scott. "The Vertical Structure of Large-Scale Unsteady Currents." Journal of Physical Oceanography 45, no. 3 (2015): 755–77. http://dx.doi.org/10.1175/jpo-d-14-0077.1.

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AbstractA linear model based on the quasigeostrophic equations is constructed in order to predict the vertical structure of Rossby waves and, more broadly, of anomalies resolved by altimeter data, roughly with periods longer than 20 days and with wavelengths larger than 100 km. The subsurface field is reconstructed from sea surface height and climatological stratification. The solution is calculated in periodic rectangular regions with a 3D discrete Fourier transform. The effect of the mean flow on Rossby waves is neglected, which the authors believe is a reasonable approximation for low latit

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16

Buffum, D. H., and S. Fleeter. "Effect of Wind Tunnel Acoustic Modes on Linear Oscillating Cascade Aerodynamics." Journal of Turbomachinery 116, no. 3 (1994): 513–24. http://dx.doi.org/10.1115/1.2929440.

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The aerodynamics of a biconvex airfoil cascade oscillating in torsion is investigated using the unsteady aerodynamic influence coefficient technique. For subsonic flow and reduced frequencies as large as 0.9, airfoil surface unsteady pressures resulting from oscillation of one of the airfoils are measured using flush-mounted high-frequency-response pressure transducers. The influence coefficient data are examined in detail and then used to predict the unsteady aerodynamics of a cascade oscillating at various interblade phase angles. These results are correlated with experimental data obtained

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17

Wei, Xindi, Yumeng Tang, Jiexuan Hou, and Yangwei Liu. "Analysis of unsteady tip leakage flow in an axial compressor rotor using dynamic mode decomposition." Journal of the Global Power and Propulsion Society 8 (October 24, 2024): 405–20. http://dx.doi.org/10.33737/jgpps/191168.

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Tip leakage flow (TLF) is an important flow structure in the compressor, and it has a significant effect on the efficiency and stability of the compressor. In this study, dynamic mode decomposition (DMD) is used to study the spatiotemporal flow structure of the tip leakage flow in a compressor rotor. The high-fidelity flow field calculated via the delayed-detached eddy simulation (DDES) of an axial compressor rotor is used as the input dataset for the DMD algorithm. The results show that the unsteady motion of the tip leakage vortex (TLV) is quite different at its generation, development, and

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18

Palies, Paul, Milos Ilak, and Robert Cheng. "Transient and limit cycle combustion dynamics analysis of turbulent premixed swirling flames." Journal of Fluid Mechanics 830 (October 5, 2017): 681–707. http://dx.doi.org/10.1017/jfm.2017.575.

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Premixed low swirling flames (methane–air and hydrogen–methane–air) are experimentally investigated for three different regimes. Stable, local transient to instability and limit cycle regimes corresponding to three distinct equivalence ratios are considered. Dynamic mode decomposition is applied to the hydrogen–air–methane flame to retrieve the modes frequencies, growth rates and spatial distributions for each regime. The results indicate that a vortical wave propagating along the flame front is associated with the transition from stability to instability. In addition, it is shown that a key e

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19

Buffum, D. H., and S. Fleeter. "The Aerodynamics of an Oscillating Cascade in a Compressible Flow Field." Journal of Turbomachinery 112, no. 4 (1990): 759–67. http://dx.doi.org/10.1115/1.2927719.

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Fundamental experiments are performed in the NASA Lewis Research Center Transonic Oscillating Cascade Facility to investigate and quantify the aerodynamics of a cascade of bioconvex airfoils executing torsion mode oscillations at realistic reduced frequency values. Both steady and unsteady airfoil surface pressures are measured at two inlet Mach numbers, 0.65 and 0.80. and two incidence angles, 0 and 7 deg, with the harmonic torsional airfoil cascade oscillations at realistic high reduced frequency and unsteady data obtained at several interbladephase angle values. The time-variant pressures a

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20

CHEN, LONG, YIZHAO WU, and JIAN XIA. "AEROELASTIC ANALYSIS OF ROTOR BLADES USING CFD/CSD COUPLING IN HOVER MODE." Modern Physics Letters B 24, no. 13 (2010): 1307–10. http://dx.doi.org/10.1142/s0217984910023499.

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A computational fluid dynamics (CFD) is coupled with a computational structural dynamics (CSD) to simulate the unsteady rotor flow with aeroelasticity effects. An unstructured upwind Navier-Stokes solver was developed for this simulation, with 2nd order time-accurate dual-time stepping method for temporal discretization and low Mach number preconditioning method. For turbulent flows, both the Spalart-Allmaras and Menter's SST model are available. Mesh deformation is achieved through a fast dynamic grid method called Delaunay graph map method for unsteady flow simulation. The rotor blades are m

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21

Pilkington, D. J., and N. J. Wood. "Unsteady aerodynamic effects of trailing edge controls on delta wings." Aeronautical Journal 99, no. 983 (1995): 99–108. http://dx.doi.org/10.1017/s000192400002827x.

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AbstractEffective control of combat aircraft at high angles of attack requires the flight control system to operate to higher frequencies and gains. This increases the possibility of excitation of the structural modes by altering the aeroservoelastic stability of the complete system. This paper details the results of tests carried out on a rigid, 55° leading edge sweep delta wing, half model fitted with a half span elevon operated through a closed loop control system. The effects of steady elevon deflections up to 40° angle of attack are described. The unsteady pressures resulting from elevon

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22

Savenkov, N. V., and O. O. Zolotarev. "Determination of fuel consumption of an ice with electromechanical injectors and a deadlock type ramp on transients." Nauchno-tekhnicheskiy vestnik Bryanskogo gosudarstvennogo universiteta 10, no. 4 (2024): 316–27. https://doi.org/10.22281/2413-9920-2024-10-04-316-327.

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The internal combustion engine operates in unsteady modes for a significant part of the time when the vehicles is moving. This is unavoidable for vehicles with traditional power plants for the following reasons: 1) the need to regulate the power on the driving wheels, 2) the effective performance and environmental qualities of the engine in unsteady modes are often worse in relation to those in steady-state modes of operation; this is due to the influence of many factors and has been studied in many well-known scientific papers. Experimental studies of current fuel consumption, effective torqu

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23

Crouch, J. D., A. Garbaruk, and M. Strelets. "Global instability in the onset of transonic-wing buffet." Journal of Fluid Mechanics 881 (October 24, 2019): 3–22. http://dx.doi.org/10.1017/jfm.2019.748.

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Global stability analysis is used to analyse the onset of transonic buffet on infinite swept and unswept wings. This high-Reynolds-number flow is governed by the unsteady Reynolds averaged Navier–Stokes equations. The analysis generalizes earlier studies focused on two-dimensional airfoils. For the unswept wing, results show spanwise-periodic stationary modes in addition to the earlier-observed oscillatory mode. The oscillatory mode is nominally two-dimensional with a spanwise wavelength greater than ten wing chords. The stationary modes of instability exist over two bands of spanwise waveleng

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24

Li, Z., and P. Xia. "Aeroelastic modelling and stability analysis of tiltrotor aircraft in conversion flight." Aeronautical Journal 122, no. 1256 (2018): 1606–29. http://dx.doi.org/10.1017/aer.2018.93.

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ABSTRACTIn conversion flight, the aeroelastic modelling of tiltrotor aircraft needs to consider the unsteady effect of the rotor wake bending due to the rotor tilting. In this paper, the unsteady models of the rotor wake bending and dynamic inflow have been introduced into the aeroelastic modelling of the tiltrotor aircraft in conversion flight by using Hamilton’s generalized principle. The method for solving the aeroelastic stability of tiltrotor aircraft in conversion flight has been established by using the small perturbation theory and the Floquet theory. The influences of unsteady dynamic

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25

Makoveeva, Eugenya V., Dmitri V. Alexandrov, and Alexander A. Ivanov. "On the Theory of Unsteady-State Operation of Bulk Continuous Crystallization." Crystals 12, no. 11 (2022): 1634. http://dx.doi.org/10.3390/cryst12111634.

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Motivated by an important application in the chemical and pharmaceutical industries, we consider the non-stationary growth of a polydisperse ensemble of crystals in a continuous crystallizer. The mathematical model includes the effects of crystal nucleation and growth, fines dissolution, mass influx and withdrawal of product crystals. The steady- and unsteady-state solutions of kinetic and balance equations are analytically derived. The steady-state solution is found in an explicit form and describes the stationary operation mode maintained by the aforementioned effects. An approximate unstead

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26

Silkowski, P. D., and K. C. Hall. "1997 Best Paper Award—Structures and Dynamics Committee: A Coupled Mode Analysis of Unsteady Multistage Flows in Turbomachinery." Journal of Turbomachinery 120, no. 3 (1998): 410–21. http://dx.doi.org/10.1115/1.2841732.

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A computational method is presented for predicting the unsteady aerodynamic response of a vibrating blade row that is part of a multistage turbomachine. Most current unsteady aerodynamic theories model a single blade row isolated in an infinitely long duct. This assumption neglects the potentially important influence of neighboring blade rows. The present “coupled mode” analysis is an elegant and computationally efficient method for modeling neighboring blade row effects. Using this approach, the coupling between blade rows is modeled using a subset of the so-called spinning modes, i.e., press

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27

Berman, V., E. Bournaski, V. Fadeichev, I. Skorokhod, and L. Orlova. "Numerical simulation of the unsteady fluid motion in pipelines in the pump unit start-up mode." Hydrodynamics and Acoustics 3(93), no. 1 (2024): 5–15. https://doi.org/10.15407/jha2024.01.005.

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From the experience of operating pipeline transport systems of various incompressible and compressible viscous flows, it is known that transportation conditions are constantly changing during their operation. In turn, this causes sharp fluctuations in the characteristics of such flows, which can be dangerous to pipeline equipment and personnel. In this regard, starting from the design stage, it is necessary to have convenient methods for calculating transient (unsteady) modes of flow movement, which allow determining possible pressure and flow fluctuations in different modes of operation of tr

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28

Zhao, Dan. "Nonlinear Self-Excited Combustion Oscillations of a Premixed Laminar Flame." Applied Mechanics and Materials 110-116 (October 2011): 1150–54. http://dx.doi.org/10.4028/www.scientific.net/amm.110-116.1150.

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Self-excited combustion oscillations are caused by a coupling between acoustic waves and unsteady heat release. A premixed laminar flame in a Rijke tube, anchored to a metal gauze, is considered in this work. The flame response to flow disturbances is investigated by developing a nonlinear kinematic model based on the classical-equation, with the assumption of a time-invariant laminar flame speed. Unsteady heat release from the flame is assumed to be caused by its surface variations, which results from the fluctuations of the oncoming flow velocity. The flame is acoustically compact, and its p

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29

Gong, Ziqiao. "Unsteady Simulation and Mode Analysis of Disturbed Cylinder Flow." Journal of Physics: Conference Series 2565, no. 1 (2023): 012015. http://dx.doi.org/10.1088/1742-6596/2565/1/012015.

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Abstract The unsteady simulation of cylinder flow with inlet velocity disturbance is simulated and compared with that without disturbance. POD is adopted to analyze and capture the dominant modes of the vortex street in the cylinder wake. The results show that the POD method is efficient in reconstructing the flow field. When the inlet velocity disturbance exists, the number of modes required to reconstruct the flow field accurately is almost unchanged, but the energy proportion of each mode changes. The larger the disturbance frequency is, the smaller the shape and vorticity magnitude of the

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30

Levin, Lev, Mikhail Semin, Stanislav Maltsev, Roman Luzin, and Andrey Sukhanov. "Numerical Analysis of the Impact of Variable Borer Miner Operating Modes on the Microclimate in Potash Mine Working Areas." Computation 13, no. 4 (2025): 85. https://doi.org/10.3390/computation13040085.

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Анотація:

This paper addresses the numerical simulation of unsteady, non-isothermal ventilation in a dead-end mine working of a potash mine excavated using a borer miner. During its operations, airflow can become unsteady due to the variable operating modes of the borer miner, the switching on and off of its motor cooling fans, and the movement of a shuttle car transporting ore. While steady ventilation in a dead-end working with a borer miner has been previously studied, the specific features of air microclimate parameter distribution in more complex and realistic unsteady scenarios remain unexplored.

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31

SCHRADER, LARS-UVE, LUCA BRANDT, and DAN S. HENNINGSON. "Receptivity mechanisms in three-dimensional boundary-layer flows." Journal of Fluid Mechanics 618 (January 10, 2009): 209–41. http://dx.doi.org/10.1017/s0022112008004345.

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Receptivity in three-dimensional boundary-layer flow to localized surface roughness and free-stream vorticity is studied. A boundary layer of Falkner–Skan–Cooke type with favourable pressure gradient is considered to model the flow slightly downstream of a swept-wing leading edge. In this region, stationary and travelling crossflow instability dominates over other instability types. Three scenarios are investigated: the presence of low-amplitude chordwise localized, spanwise periodic roughness elements on the plate, the impingement of a weak vortical free-stream mode on the boundary layer and

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32

Long, Yuexiao, Huaxing Li, Xuanshi Meng, Jia Li, and Zhengchao Xiang. "Structure optimization of the AC-SDBD plasma actuator under duty-cycle mode." Modern Physics Letters B 32, no. 26 (2018): 1850315. http://dx.doi.org/10.1142/s0217984918503153.

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Alternating current dielectric barrier discharge plasma actuators driven by steady and unsteady mode were experimentally optimized in a static atmosphere. The purpose of this optimization is to enhance the effective controllability of flow control. Electrical properties were evaluated using the measured voltage, current and power consumption data. The dielectric barrier with different materials was tested and the aerodynamic characteristics were identified by particle image velocimetry and electronic force balance. Meanwhile, the duty-cycle technique was applied to operate the actuator in unst

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33

Qiu, Jiahui, Yunhong Zhong, Yang Liu, Yijia Zhao, Min Zhang, and Juan Du. "Analysis on stall mechanism of axial flow compressor with rotating inlet distortion by dynamic mode decomposition." Journal of the Global Power and Propulsion Society 8 (October 8, 2024): 390–404. http://dx.doi.org/10.33737/jgpps/191166.

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Анотація:

To study the impact of rotating inlet distortion on stall mechanism of an axial compressor, the full-annulus unsteady simulation results are analysed using dynamic mode decomposition (DMD). Firstly, the frequency and energy ratio of each mode at near stall condition for the compressor with uniform inflow are obtained. A dominating frequency band 0.3–0.6 BPF regarded as the characteristic frequency of unsteady tip leakage flow is observed. The distribution of eigenvalues further confirms that there are a few critical unstable modes in the flow field. With further throttling, four large-scale di

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34

Zhang, Kai, and AJ Wang. "Analysis of dynamic stall flow field of high bypass fan rotor based on airworthiness certification." Proceedings of the Institution of Mechanical Engineers, Part G: Journal of Aerospace Engineering 234, no. 11 (2020): 1757–69. http://dx.doi.org/10.1177/0954410020919281.

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Анотація:

In order to ensure flight safety, the stall test is one of the most important steps in the airworthiness certification phase of civil aircraft. The twisted-swept fan is one of the most important components of the high bypass ratio engine. The unsteady flow field of the fan rotor stall condition is obtained by numerical simulation. At the same time, the time series flow field data of the stall condition flow field is acquired. The modal analysis of the unsteady flow field at stall condition was performed using the dynamic mode decomposition and proper orthogonal decomposition methods. Through m

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35

Kishore, V. Ratna, S. Minaev, M. Akram, and Sudarshan Kumar. "Dynamics of premixed methane/air mixtures in a heated microchannel with different wall temperature gradients." RSC Advances 7, no. 4 (2017): 2066–73. http://dx.doi.org/10.1039/c6ra27582f.

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The unsteady flame propagation mode (FREI) is affected by the wall temperature gradient. As the temperature gradient approaches zero, the mixture ignites at its auto-ignition temperature, frequency decreases and this leads to extinction of FREI mode.

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36

Guo, Zhengfei, and Markus J. Kloker. "Control of crossflow-vortex-induced transition by unsteady control vortices." Journal of Fluid Mechanics 871 (May 22, 2019): 427–49. http://dx.doi.org/10.1017/jfm.2019.288.

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The fundamental mechanisms of a hitherto unstudied approach to control the crossflow-induced transition in a three-dimensional boundary layer employing unsteady control vortices are investigated by means of direct numerical simulations. Using a spanwise row of blowing/suction or volume-force actuators, subcritical travelling crossflow vortex modes are excited to impose a stabilizing (upstream) flow deformation (UFD). Volume forcing mimics the effects of alternating current plasma actuators driven by a low-frequency sinusoidal signal. In this case the axes of the actuators are aligned with the

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37

Chen, Guanbin, and Wenli Chen. "Experimental Investigation and Validation on Suppressing the Unsteady Aerodynamic Force and Flow Structure of Single Box Girder by Trailing Edge Jets." Applied Sciences 12, no. 3 (2022): 967. http://dx.doi.org/10.3390/app12030967.

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In the present investigation, a wind tunnel experiment was performed to evaluate the effectiveness of the trailing edge jets control scheme to mitigate the unsteady aerodynamic force and flow structure of a single box girder (SBG) model. The flow control scheme uses four isolated circular holes for forming the jet flow to modify the periodic vortex shedding behind the SBG model and then alleviate the fluctuation of the aerodynamic force acting on the test model. The Reynolds number is calculated as 2.08 × 104 based on the incoming velocity and the height of the test model. A digital pressure m

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38

Krishnappan, B. G. "Modelling of settling and flocculation of fine sediments in still water." Canadian Journal of Civil Engineering 17, no. 5 (1990): 763–70. http://dx.doi.org/10.1139/l90-089.

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A numerical model to predict settling behaviour of fine sediment mixtures in a stagnant water column is described. Both single-grain settling mode and the floc settling mode are considered. The single-grain settling mode is analyzed by solving the unsteady, one-dimensional diffusion–advection equation numerically and the floc settling mode is examined by solving a coagulation equation expressed as a discrete equation in logarithmic radius space considering the differential settling as the only collision mechanism. The model results are compared with the laboratory experimental data of K. Kranc

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39

Li, Yangxi, Yiqun Hou, Ben Zhang, et al. "The Kinematics and Dynamics of Schizopygopsis malacanthus Swimming during Ucrit Testing." Animals 12, no. 20 (2022): 2844. http://dx.doi.org/10.3390/ani12202844.

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The swimming kinematics (how fish move) and dynamics (how forces effect movement) of Schizopygopsis malacanthus were investigated during the determination of by stepped velocity testing. A video tracking program was used to record and analyze the motion of five test fish in a Brett-type flume during each velocity step. The findings fell into three groups: (1) Even when flow was uniform, fish did not swim steadily, with speeds fluctuating by 2.2% to 8.4% during steady swimming. The proportion of unsteady swimming time increased with water velocity, and defining steady and unsteady swimming stat

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40

Kolodiazhna, Liubov V., and Yurii A. Bykov. "Aeroelastic Characteristics of Rotor Blades of Last Stage of a Powerful Steam Turbine." Journal of Mechanical Engineering 26, no. 1 (2023): 6–14. http://dx.doi.org/10.15407/pmach2023.01.006.

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Blades of powerful steam turbines are subjected to significant unsteady loads, which, in some cases, can lead to the appearance of self-excited oscillations or auto-oscillations. These fluctuations are extremely dangerous and negatively affect the life time of the blading. When developing new or upgrading existing turbine stages, it is necessary to carry out research on the aeroelastic behavior of the rotor blades. As a result of the modernization of a low-pressure cylinder of a 1000 MW steam turbine, the length of the rotor blades of the last stage increased to 1650 mm. In this regard, a nume

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41

Yentsch, Robert J., and Datta V. Gaitonde. "Unsteady Three-Dimensional Mode Transition Phenomena in a Scramjet Flowpath." Journal of Propulsion and Power 31, no. 1 (2015): 104–22. http://dx.doi.org/10.2514/1.b35205.

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42

Liu, Yong, Hongjuan Ran, and Dezhong Wang. "Research on Unsteady Characteristics of Pump Turbine in Pumping Mode." IOP Conference Series: Earth and Environmental Science 627 (January 7, 2021): 012028. http://dx.doi.org/10.1088/1755-1315/627/1/012028.

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43

Bardin, Alexey, Vyacheslav Ignatjev, Andrey Orlov, and Sergey Perchenko. "Verifying of reciprocal relations for nonlinear quadripole in unsteady mode." Results in Physics 7 (2017): 665–66. http://dx.doi.org/10.1016/j.rinp.2017.01.029.

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44

MORSE, T. L., and C. H. K. WILLIAMSON. "Steady, unsteady and transient vortex-induced vibration predicted using controlled motion data." Journal of Fluid Mechanics 649 (April 13, 2010): 429–51. http://dx.doi.org/10.1017/s002211200999379x.

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In this study, we represent transient and unsteady dynamics of a cylinder undergoing vortex-induced vibration, by employing measurements of the fluid forces for a body controlled to vibrate sinusoidally, transverse to a free stream. We generate very high-resolution contour plots of fluid force in the plane of normalized amplitude and wavelength of controlled oscillation. These contours have been used with an equation of motion to predict the steady-state response of an elastically mounted body. The principal motivation with the present study is to extend this approach to the case where a freel

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45

Wu, Xiaoxiong, and Yuming Du. "Unsteady Flow Field Analysis of a Compressor Cascade Based on Dynamic Mode Decomposition." Aerospace 11, no. 12 (2024): 1019. https://doi.org/10.3390/aerospace11121019.

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Traditional flow field modeling methods are limited by high computational complexity, making them difficult to apply in practical engineering. This study applies the Dynamic Mode Decomposition (DMD) method to perform reduced-order modeling of unsteady flow fields over an airfoil and a compressor cascade. As a data-driven modal decomposition technique, DMD extracts low-dimensional modes from high-dimensional spatiotemporal data, preserving key dynamic characteristics and significantly reducing computational costs. Numerical simulations were conducted to generate time snapshots, forming matrices

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46

Gan, Yanlin, and Xiangming Li. "Global Instability of Rod Eutectic Growth in Directional Solidification." Crystals 13, no. 3 (2023): 548. http://dx.doi.org/10.3390/cryst13030548.

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In our previous work, we obtained the uniformly valid asymptotic solution of a cylindrical rod eutectic. In order to further study the critical point of the stable growth of a rod eutectic, we have considered the unsteady growth of a rod eutectic on the basis of the steady solution of the rod eutectic. Based on the experimental system of rod eutectic growth, combined with solidification thermodynamics and kinetics, the unsteady mathematical model of the rod eutectic was established. We used the asymptotic analysis method to seek the analytical solution of the mathematical model and used the no

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47

Ryzhova, Elena L., and Vladislav Yu Osipov. "The use of technical means for diagnosing traction engines rolling stock." Modern Transportation Systems and Technologies 10, no. 4 (2024): 556–76. https://doi.org/10.17816/transsyst635142.

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Aim. Demonstrate the practical significance of assessing the technical condition of traction electric locomotives during unsteady operating modes by analyzing the nature and causes of an emergency increase in the armature current of the NB–520V traction motor in traction mode. This study uses comparative analysis of trip file fragments from EP1 series electric locomotives at a locomotive depot. Methods. A review was conducted on innovative methods for studying the unsteady operating modes of traction electric motors in locomotives. These methods help determine the causes of emergency armature

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48

Kobayashi, H. "Annular Cascade Study of Low Back-Pressure Supersonic Fan Blade Flutter." Journal of Turbomachinery 112, no. 4 (1990): 768–77. http://dx.doi.org/10.1115/1.2927720.

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Анотація:

Low back-pressure supersonic fan blade flutter in the torsional mode was examined using a controlled-oscillating annular cascade test facility. Precise data of unsteady aerodynamic forces generated by shock wave movement, due to blade oscillation, and the previously measured data of chordwise distributions of unsteady aerodynamic forces acting on an oscillating blade, were joined and, then, the nature of cascade flutter was evaluated. These unsteady aerodynamic forces were measured by direct and indirect pressure measuring methods. Our experiments covered a range of reduced frequencies based o

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49

Sun, Tiezhi, Qingmo Xie, Li Zou, Hao Wang, and Chang Xu. "Numerical Investigation of Unsteady Cavitation Dynamics over a NACA66 Hydrofoil near a Free Surface." Journal of Marine Science and Engineering 8, no. 5 (2020): 341. http://dx.doi.org/10.3390/jmse8050341.

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Cavitation is a typical and unavoidable phenomenon for small waterline ships and high-speed vehicles. It creates a highly complex multiphase flow near the free surface and is primarily represented by the free surface-cavitation interaction. In this paper, the large-eddy method and Schnerr-Sauer cavitation model are combined to address the effects of a free surface on the cavitation dynamics of a NACA66 hydrofoil. The numerical method is validated by comparing the cavitation morphology and pressure with available experimental data. The results show that the presence of a free surface affects th

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50

Kielb, R. E., and J. K. Ramsey. "Flutter of a Fan Blade in Supersonic Axial Flow." Journal of Turbomachinery 111, no. 4 (1989): 462–67. http://dx.doi.org/10.1115/1.3262294.

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Анотація:

An application of a simple aeroelastic model to an advanced supersonic axial flow fan is presented. Lane’s cascade theory is used to determine the unsteady aerodynamic loads. Parametric studies are performed to determine the effects of mode coupling, Mach number, damping, pitching axis location, solidity, stagger angle, and mistuning. The results show that supersonic axial flow fan and compressor blades are susceptible to a strong torsional mode flutter having critical reduced velocities that can be less than one.

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