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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.
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 orthogonal decomposition (POD) modes. Furthermore, OMD is shown to provide an approximation to the Koopman modes and eigenvalues of the underlying system. A comparison between OMD and DMD is made using both a synthetic waveform and an experimental data set. The OMD technique is shown to have lower residual errors than DMD and is shown on a synthetic waveform to provide more accurate estimates of the system eigenvalues. This new method can be used with experimental and numerical data to calculate the ‘optimal’ low-order model with a user-defined rank that best captures the system dynamics of unsteady and turbulent flows.
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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 (February 1, 2019): 51–61. http://dx.doi.org/10.4197/eng.30-1.4.
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 investigation of the unsteady flow field was carried out using dynamic mode decomposition. The analysis identified two distinct unsteady modes; high-frequency mode and low-frequency mode. At angle of attack 45◦ the high-frequency mode is dominant in the frontal part of the body and the low-frequency mode is dominant at the rear part. At α = 55◦ , the highfrequency mode is dominant downstream of vortex breakdown. At α = 65◦ , the spectrum shows a wide range of modes. Reconstruction of the dynamical modes shows that the low-frequency mode is associated with the unsteady wake and the high-frequency mode is associated with unsteady shear layer.
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Vabishchevich, Petr N. "Fundamental mode exact schemes for unsteady problems." Numerical Methods for Partial Differential Equations 34, no. 6 (June 19, 2018): 2301–15. http://dx.doi.org/10.1002/num.22292.
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.
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-rate condition. The research shows that the first-order average flow mode extracted by DMD is the dominant flow structure in the flow field of the volute. The second-order and third-order modes are the most important oscillation modes causing unsteady flow in the volute, and the characteristic frequency of the two modes is consistent with the blade passing frequency and the 2x blade passing frequency obtained by the fast Fourier transform (FFT). By reconstructing the internal flow field of the volute with the blade passing frequency for the nominal flow-rate condition, the periodic variation of the unsteady flow structure in the volute under this frequency is visually reproduced, which provides some ideas for the study of the unsteady structure in the internal flow field of centrifugal pumps.
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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 (December 24, 2020): 4. http://dx.doi.org/10.3390/fluids6010004.
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 two steady and two unsteady modes. The results obtained have been connected with the changes in the topology of the flow. Finally, higher-order dynamic mode decomposition has been applied to identify the main flow structures in the unsteady flow inside the FDA nozzle. The highest-amplitude dynamic mode decomposition (DMD) modes identified by the method model the vortex street in the expansion of the geometry.
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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 (January 1, 1997): 85–93. http://dx.doi.org/10.1115/1.2841014.
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 aerodynamic response due to so-called spinning modes (pressure and vorticity waves), with each mode corresponding to a different circumferential wave number and frequency. Then, for each mode, we compute the reflection and transmission coefficients for each blade row. These coefficients can be obtained from any of the currently available unsteady linearized aerodynamic models of isolated cascades. A set of linear equations is then constructed that couples together the various spinning modes, and the linear equations are solved via LU decomposition. Numerical results are presented for both the gust response and blade vibration problems. To validate our model, we compare our results to other analytical models, and to a multistage vortex lattice model. We show that the effect of neighboring blade rows on the aerodynamic damping of vibrating cascades is significant, but nevertheless can be modeled with a small number of modes.
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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.
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 displays similarities to the flow behind an isolated sphere in a free stream. As the Reynolds number of the flow increases, hairpin vortices form and are shed over the surface of the sphere. However, for cases with reversed rotation, the wake takes the form of two distinct streamwise vortices that form around the sides of the body. These streamwise structures in the wake undergo a transition to a new unsteady mode as the Reynolds number increases. During the evolution of this unsteady mode, the streamwise vortices form an out-of-phase spiral pair. Four primary wake modes are identified and a very good qualitative agreement is observed between the numerical and experimental results. The numerical simulations also reveal the existence of an additional unsteady mode that is found to be unstable to small perturbations in the flow.
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Chiang, H. W. D., and S. Fleeter. "Passive Control of Flow-Induced Vibrations by Splitter Blades." Journal of Turbomachinery 116, no. 3 (July 1, 1994): 489–500. http://dx.doi.org/10.1115/1.2929438.
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 determined by developing a complete first-order unsteady aerodynamic analysis together with an unsteady aerodynamic influence coefficient technique. The torsion mode flow induced vibrational response of both uniformly spaced tuned rotors and detuned rotors are then predicted by incorporating the unsteady aerodynamic influence coefficients into a single-degree-of-freedom aero-elastic model. This model is then utilized to demonstrate that incorporating splitters into axial flow rotor designs is beneficial with regard to flow induced vibrations.
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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 (July 21, 2009): 677–86. http://dx.doi.org/10.1243/09576509jpe841.
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 channel with ink injection for flow visualization. Unsteady CFD analyses have been made with some success in prediction of the unsteady flow structures. In particular, the pre-instability behaviour of the passage vortex in the experiments matches the results of the numerical investigations.
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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 (May 27, 2019): 175–84. http://dx.doi.org/10.1515/tjj-2017-0031.
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 structures and the ordering of modal evolution characteristics. The best control effect will be achieved when the total energy ratio of the first mode is the highest and the excitation frequency reaches the separation vortex frequency at the same time. In order to quantitatively analyze the order degree of the unsteady flow field, the maximum Lyapunov exponent was introduced. The results showed that with the energy in higher modes transferred to the lower modes, the flow field transfers from a disordered pattern to an ordered one.
Dissertations / Theses on the topic "Unsteady mode":
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McCombes, Tom Ruaridh. "An unsteady hydrodynamic model for tidal current turbines." Thesis, University of Strathclyde, 2014. http://oleg.lib.strath.ac.uk:80/R/?func=dbin-jump-full&object_id=25495.
Due to concerns about the impacts of carbon emissions on the environment, the security of supply of electricity and the likelihood of achieving "peak-oil" in the near future, governments have legislated to reduce reliance on fossil fuels. An attractive alternative is power obtained from tidal currents, and the coast of the British Isles is especially hydraulically active. Tidal energy converters typically resemble wind turbines however, unlike wind turbines, they are expected to operate in an environment which is singularly hostile, and will also be expected to generate power in non-ideal operating conditions. This thesis is concerned with the ability to model individual and groups of tidal devices including their mutual interactions. The ability to capture unsteady inflow conditions at realistic array spacing requires preservation of turbine wakes over a sufficiently large range at spatial resolutions and over time durations which are not feasible using standard computational fluid dynamics software. This thesis has combined methodologies developed for helicopter wake modelling with techniques used in naval architecture for modelling thick maritime propellers into a computational tool. The particular formulation of the Navier-Stokes equations employed allows the determination of the unsteady pressure and force distributions on a turbine rotor due to the effects of a neighbouring device, even if it is operating some significant distance upstream. The constituents of the method of this thesis are developed and applied to "proof-of-principle" studies. These include flow past static and oscillating 2-D aerofoils and past a 3-D wing, wind turbine and tidal turbine configuration. The results from these studies demonstrate that the model is convergent and capable of capturing the time dependant forces on these devices, and by comparison with analytical or experimental results, or via inter-model comparison begins the process of calibration and validation of the model. The method is then applied to flow past groups of turbines in various array configurations, and a coaxial, contra-rotating device. The outcome of this work is a decision making tool which can be used to improve success and reduce risk in tidal power array planning, optimise device configurations and is translatable back into rotorcraft or naval architecture usage.
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Strganac, Thomas W. "A numerical model of unsteady, subsonic aeroelastic behavior." Diss., Virginia Polytechnic Institute and State University, 1987. http://hdl.handle.net/10919/74775.
A method for predicting unsteady, subsonic aeroelastic responses has been developed. The technique accounts for aerodynamic nonlinearities associated with angles of attack, vortex-dominated flow, static deformations, and unsteady behavior. The angle of attack is limited only by the occurrence of stall or vortex bursting near the wing. The fluid and the wing together are treated as a single dynamical system, and the equations of motion for the structure and flowfield are integrated simultaneously and interactively in the time domain. The method employs an iterative scheme based on a predictor-corrector technique. The aerodynamic loads are computed by the general unsteady vortex-lattice method and are determined simultaneously with the motion of the wing. Because the unsteady vortex-lattice method predicts the wake as part of the solution, the history of the motion is taken into account; hysteresis is predicted. Two models are used to demonstrate the technique: a rigid wing on an elastic support experiencing plunge and pitch about the elastic axis, and an elastic wing rigidly supported at the root chord experiencing spanwise bending and twisting. The method can be readily extended to account for structural nonlinearities and/or substitute aerodynamic load models. The time domain solution coupled with the unsteady vortex-lattice method provides the capability of graphically depicting wing and wake motion. Ph. D.
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Janowski, Michael David. "Analysis of a simplified nonlinear ground resonance model." Thesis, Georgia Institute of Technology, 1986. http://hdl.handle.net/1853/16084.
This study is concerned with the recovery of fluid mechanical modes that can be used to describe the physical properties of unsteady separated flows. The flow configuration of interest is a spanwise homogeneous NACA 0015 airfoil with leading edge laminar separation and turbulent recirculation. An in-depth understanding of the unsteady flow dynamics and fluid mechanical stability properties, can assist in the future development of more efficient separation control strategies. In order to provide a richer understanding of the physics, the flow fields are numerically generated, and characterised at various key Reynolds numbers leading up to the target turbulent case. Proper Orthogonal Decomposition modes are recovered to most efficiently represent the unsteady scales of motion, and linear stability modes are sought to identify how a perturbation will evolve in this unsteady environment. The generation of the Proper Orthogonal Decomposition modes can require very large amounts of data, and the current study presents a means of recovering these modes using parallel computation. To enable the stability analysis, a means of performing the calculation in steady two-dimensional flows of semi-complex geometry has been developed. The corrections required to perform the stability analysis in unsteady turbulent flows has also been identified by using a non-linear eddy viscosity model to close the triple decomposition stability equations. It is intended that the means of recovering these fluid mechanical modes can assist in the future development of reduced order models necessary for the control of unsteady separated flows Cette étude s’intéresse à la détermination de modes pouvant être utilisés en mécanique des fluides pour décrire les propriétés physiques d'écoulements instationnaires décollés. La configuration d'écoulement qui nous intéresse est un profil d'aile NACA 0015 transversalement homogène caractérisé par un décollement laminaire au bord d'attaque et une zone de recirculation turbulente. Comprendre en profondeur la dynamique instationnaire de l'écoulement et ses propriétés de stabilité peut aider à améliorer l'efficacité de futures stratégies de contrôle de décollement. Afin de mieux appréhender la physique, l'écoulement est d’abord simulé puis caractérisé pour plusieurs valeurs du nombre de Reynolds allant jusqu’au régime turbulent. On retrouve alors que les modes obtenus par décomposition orthogonale aux valeurs propres (Proper Orthogonal Decomposition) représentent de manière efficace les échelles instationnaires du mouvement. Par ailleurs, les modes de stabilité linéaire sont recherchés afin d'identifier comment une perturbation évolue dans un environnement instationnaire. La détermination des modes de Proper Orthogonal Decomposition pouvant nécessiter une grande quantité de données, cette étude présente un moyen de les évaluer par calcul parallèle. Pour permettre l'analyse de stabilité, il a fallu développer des programmes permettant de réaliser les calculs pour un écoulement stationnaire bidimensionnel en géométrie semi-complexe. Les corrections nécessaires pour effectuer l'analyse de stabilité dans des écoulements turbulents instationnaires ont aussi été identifiés en utilisant un modèle de viscosité tourbillonnaire non linéaire pour fermer les équations de stabilité en décomposition triple. La détermination de ces modes en mécanique des fluides doit aider le développement futur de modèles réduits nécessaires au contrôle d'écoulement instationnaire décollé
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Boyd, David Douglas Jr. "Rotor/Fuselage Unsteady Interactional Aerodynamics: A New Computational Model." Diss., Virginia Tech, 1999. http://hdl.handle.net/10919/28591.
A new unsteady rotor/fuselage interactional aerodynamics model has been developed. This model loosely couples a Generalized Dynamic Wake Theory (GDWT) to a Navier-Stokes solution procedure. This coupling is achieved using a newly developed unsteady pressure jump boundary condition in the Navier-Stokes model. The new unsteady pressure jump boundary condition models each rotor blade as a moving pressure jump which travels around the rotor azimuth =and is applied between two adjacent planes in a cylindrical, non-rotating grid. Comparisons are made between predictions using this new model and experiments for an isolated rotor and for a coupled rotor/fuselage configuration. Ph. D.
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Chua, Weng Heng. "Flow visualization studies over a UCAV 1303 model." Thesis, Monterey, Calif. : Naval Postgraduate School, 2009. http://edocs.nps.edu/npspubs/scholarly/theses/2009/Jun/09Jun%5FChua.pdf.
Thesis (M.S. in Mechanical Engineering)--Naval Postgraduate School, June 2009. Thesis Advisor(s): Chandrasekhara, M. S. "June 2009." Description based on title screen as viewed on July 10, 2009. Author(s) subject terms: Unsteady Aerodynamics, UCAV Maneuvers, 2D-unsteady flows. Includes bibliographical references (p. 43-44). Also available in print.
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Ghimire, Ganesh Raj. "Developing Sediment Transport and Deposition Prediction Model of Lower Ohio River near the Olmsted Locks and Dam Area." OpenSIUC, 2016. https://opensiuc.lib.siu.edu/theses/1967.
The present study focuses on the sediment deposition and consequent dredging issues in Lower Ohio River at the Olmsted Locks and Dam area-River mile (RM)-964.4 during the ongoing in-the-wet construction methodology. The study reach is between Locks and Dam 53 (RM 962.6) at upstream, and RM 970 at downstream. One dimensional (1-D) HEC-RAS numerical modeling in conjunction with Arc-GIS was employed. Stream flow measurements, velocity, incoming sediment concentration, bed gradation, and annual hydrographic survey data acquired from public archives of USGS and USACE Louisville District were used as inputs. The model was subjected to the 1-D quasi-unsteady and completely unsteady sediment transport module, available in the latest HEC-RAS 5.0 Beta release. Calibration and validation of the hydrodynamic and sediment models were performed using measured water surface elevation, velocity, and sediment loads at measured sections. Post-model calibration and validation, deposition to excavated cross-sections for future dam shells at Olmsted was predicted, which warrants dredging. The study attempted to analyze the sediment transport trend with the focus on depositionat Olmsted Locks and Dam area using the sensitivity analysis approach of transport capacity functions. Moreover, the capability of 1-D HEC-RAS quasi-unsteady and completely unsteady models were assessed in prediction of sediment deposition in the construction area (dam shells excavation area). A temporal deposition prediction model was developed that can potentially replace the current ad-hoc approach used to determine the dredging schedule. Likewise, a representative environmental risk associated with sedimentation in the study area was examined. The model can potentially be used as a decision support tool to analyze the long term impact of sedimentation in the vicinity of Olmsted Locks and Dam if further updates on the river bathymetry, and specific field data are supplemented to the model.
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Ghommem, Mehdi. "Modeling and Analysis for Optimization of Unsteady Aeroelastic Systems." Diss., Virginia Tech, 2011. http://hdl.handle.net/10919/29604.
Simulating the complex physics and dynamics associated with unsteady aeroelastic systems is often attempted with high-fidelity numerical models. While these high-fidelity approaches are powerful in terms of capturing the main physical features, they may not discern the role of underlying phenomena that are interrelated in a complex manner. This often makes it difficult to characterize the relevant causal mechanisms of the observed features. Besides, the extensive computational resources and time associated with the use these tools could limit the capability of assessing different configurations for design purposes. These shortcomings present the need for the development of simplified and reduced-order models that embody relevant physical aspects and elucidate the underlying phenomena that help in characterizing these aspects. In this work, different fluid and aeroelastic systems are considered and reduced-order models governing their behavior are developed.
In the first part of the dissertation, a methodology, based on the method of multiple scales, is implemented to show its usefulness and effectiveness in the characterization of the physics underlying the system, the implementation of control strategies, and the identification of high-impact system parameters. In the second part, the unsteady aerodynamic aspects of flapping micro air vehicles (MAVs) are modeled. This modeling is required for evaluation of performance requirements associated with flapping flight. The extensive computational resources and time associated with the implementation of high-fidelity simulations limit the ability to perform optimization and sensitivity analyses in the early stages of MAV design. To overcome this and enable rapid and reasonably accurate exploration of a large design space, a medium-fidelity aerodynamic tool (the unsteady vortex lattice method) is implemented to simulate flapping wing flight. This model is then combined with uncertainty quantification and optimization tools to test and analyze the performance of flapping wing MAVs under varying conditions. This analysis can be used to provide guidance and baseline for assessment of MAVs performance in the early stages of decision making on flapping kinematics, flight mechanics, and control strategies. Ph. D.
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Romano, Federico. "Q1D unsteady ballistic model for solid rocket motors performance prediction." Master's thesis, Alma Mater Studiorum - Università di Bologna, 2021.
The simulation tool ROBOOST, in use at the Alma Propulsion Lab of the University of Bologna – Forlì Campus, exploits a hybrid ballistic model 0D-1D. The need of a complete Q1D model for the entire combustion time, from motor start-up to burn out arised. The present work is devoted to the development and test of a Q1D unsteady ballistic model for solid rocket motors performance prediction. The newly developed code, called SOL1D, is written in Matlab environment and is capable of predicting the time and space evolution of all the main thermodynamic variables during the solid rocket motor combustion process. The model has been tested and validated on a BARIA motor, thus demonstrating its adherence to experimental data. SOL1D paves the way for future works aimed at simulating performances of actual launchers.
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Hosder, Serhat. "Unsteady Skin-Friction Measurements on a Maneuvering Darpa2 Suboff Model." Thesis, Virginia Tech, 2001. http://hdl.handle.net/10919/33582.
Steady and unsteady flow over a generic Suboff submarine model is studied. The skin-friction magnitudes are measured by using hot-film sensors each connected to a constant temperature anemometer. The local minima in the skin-friction magnitudes are used to obtain the separation locations. Steady static pressure measurements on the model surface are performed at 10° and 20° angles of attack. Steady and unsteady results are presented for two model configurations: barebody and sail-on-side case. The dynamic plunge-pitch-roll model mount (DyPPiR) is used to simulate the pitchup maneuvers. The pitchup maneuver is a linear ramp from 1° to 27° in 0.33 seconds. All the tests are conducted at ReL=5,500,000 with a nominal wind tunnel speed of 42.7±1 m/s. Steady results show that the flow structure on the leeward side of the barebody can be characterized by the crossflow separation. In the sail-on-side case, the separation pattern of the non-sail region follow the barebody separation trend closely. The flow on the sail side is strongly affected by the presence of the sail and the separation pattern is different from the crossflow separation. The flow in the vicinity of the sail-body junction is dominated by the horseshoe type separation. Unsteady results of the barebody and the non-sail region of the sail-on-side case show significant time lags between unsteady and steady crossflow separation locations. These effects produce the difference in separation topology between the unsteady and steady flowfields. A first-order time lag model approximates the unsteady separation locations reasonably well and time lags are obtained by fitting the model equation with the experimental data. The unsteady separation pattern of the sail side does not follow the quasi-steady data with a time lag and the unsteady separation structure is different from the unsteady crossflow separation topology observed for the barebody and the non-sail region of the sail-on-side case. Master of Science
Webb, J. C. On the nonlinear stability of viscous modes within the Rayleigh problem of an infinite flat plate. Hampton, Va: Institute for Computer Applications in Science and Engineering, 1994.
Winfield, James Frederick. A three-dimensional unsteady aerodynamic model with applications to flapping-wing propulsion. [Downsview, Ont.]: University of Toronto, Department of Aerospace Science and Engineering, 1990.
Winfield, James Frederick. A three-dimensional unsteady aerodynamic model with applications to flapping-wing propulsion. Ottawa: National Library of Canada, 1990.
DeLong, Lewis L. Computer program HYDRAUX: A model for simulating one-dimensional, unsteady, open-channel flow. Reston, Va: Dept. of the Interior, U.S. Geological Survey, 1989.
Berry, John D. Unsteady velocity measurements taken behind a model helicopter rotor hub in forward flight. Hampton, Va: National Aeronautics and Space Administration, Langley Research Center, 1997.
Isomura, Kousuke. "The Effect of Blade Vibration Mode on a Flutter in a Transonic Fan." In Unsteady Aerodynamics and Aeroelasticity of Turbomachines, 725–32. Dordrecht: Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-5040-8_47.
Bell, D. L., and L. He. "Three Dimensional Unsteady Flow Around a Turbine Blade Oscillating in Bending Mode — An Experimental and Computational Study." In Unsteady Aerodynamics and Aeroelasticity of Turbomachines, 53–65. Dordrecht: Springer Netherlands, 1998. http://dx.doi.org/10.1007/978-94-011-5040-8_4.
Baaijens, Frank P. T. "Numerical Analysis of Unsteady Viscoelastic Contraction Flows of Multi-Mode Fluids." In Topics in Applied Mechanics, 181–88. Dordrecht: Springer Netherlands, 1993. http://dx.doi.org/10.1007/978-94-011-2090-6_19.
Statnikov, V., T. Sayadi, M. Meinke, P. Schmid, and W. Schröder. "Investigations of Unsteady Transonic and Supersonic Wake Flow of Generic Space Launcher Configurations Using Zonal RANS/LES and Dynamic Mode Decomposition." In High Performance Computing in Science and Engineering ‘14, 379–401. Cham: Springer International Publishing, 2014. http://dx.doi.org/10.1007/978-3-319-10810-0_26.
Nishioka, T., and K. Kondo. "A Unified Derivation of Explicit Expressions for Transient Asymptotic Solutions of Dynamically Propagating Cracks under the Mode I, II and III Unsteady State Conditions." In Contemporary Research in Engineering Science, 393–417. Berlin, Heidelberg: Springer Berlin Heidelberg, 1995. http://dx.doi.org/10.1007/978-3-642-80001-6_23.
Branlard, Emmanuel. "Model of a Wind Turbine with Unsteady Circulation or Unsteady Inflow." In Research Topics in Wind Energy, 339–44. Cham: Springer International Publishing, 2017. http://dx.doi.org/10.1007/978-3-319-55164-7_26.
Freymuth, P. "An Unsteady Model of Animal Hovering." In Lecture Notes in Engineering, 231–45. Berlin, Heidelberg: Springer Berlin Heidelberg, 1989. http://dx.doi.org/10.1007/978-3-642-84010-4_18.
Pascarella, Gaetano, and Marco Fossati. "Model-Based Adaptive MOR Framework for Unsteady Flows Around Lifting Bodies." In Model Reduction of Complex Dynamical Systems, 283–305. Cham: Springer International Publishing, 2021. http://dx.doi.org/10.1007/978-3-030-72983-7_13.
Kamliya Jawahar, Hasan, Kabilan Baskaran, and Mahdi Azarpeyvand. "Unsteady Characteristics of Mode Oscillation for\\ Screeching Jets." In AIAA AVIATION 2021 FORUM. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2021. http://dx.doi.org/10.2514/6.2021-2279.
Schmidt, David, and Frank Chavez. "Significance of unsteady aerodynamics and structural mode shape on predicting model variation." In AIAA Guidance, Navigation, and Control Conference and Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2001. http://dx.doi.org/10.2514/6.2001-4336.
Silkowski, Peter D., and Kenneth C. Hall. "A Coupled Mode Analysis of Unsteady Multistage Flows in Turbomachinery." In ASME 1997 International Gas Turbine and Aeroengine Congress and Exhibition. American Society of Mechanical Engineers, 1997. http://dx.doi.org/10.1115/97-gt-186.
A computational method is presented for predicting the unsteady aerodynamic response of a vibrating blade row which 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 modelling neighboring blade row effects. Using this approach, the coupling between blade rows is modelled using a subset of the so-called spinning modes, i.e. pressure, vorticity, and entropy waves which propagate between the blade rows. The blade rows themselves are represented by reflection and transmission coefficients. These coefficients describe how spinning modes interact with, and are scattered by, a given blade row. The coefficients can be calculated using any standard isolated blade row model; here we use a linearized full potential flow model together with rapid distortion theory to account for incident vortical gusts. The isolated blade row reflection and transmission coefficients, inter-row coupling relationships, and appropriate boundary conditions are all assembled into a small sparse linear system of equations which describes the unsteady multistage flow. A number of numerical examples are presented to validate the method and to demonstrate the profound influence of neighboring blade rows on the aerodynamic damping of a cascade of vibrating airfoils.
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Luetke, Nathan, Taj Mohieldin, and Surrendra Tiwari. "Unsteady Numerical Analysis of Hydrogen Combustion in a Dual Mode Engine." In 43rd AIAA/ASME/SAE/ASEE Joint Propulsion Conference & Exhibit. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2007. http://dx.doi.org/10.2514/6.2007-5425.
Tonti, Federica, Justin Hardi, Sebastian Karl, and Michael Oschwald. "Unsteady Modelling of LOx/GH2 Flame Response to Longitudinal Chamber Mode Forcing." In 2018 Joint Propulsion Conference. Reston, Virginia: American Institute of Aeronautics and Astronautics, 2018. http://dx.doi.org/10.2514/6.2018-4949.
Partridge, J. M., and N. A. Gatsonis. "A Current-Mode Triple Langmuir Probe methodology for the investigation of unsteady, small." In 2009 IEEE 36th International Conference on Plasma Science (ICOPS). IEEE, 2009. http://dx.doi.org/10.1109/plasma.2009.5227604.
Asada, Kengo, and Kozo Fujii. "Computational Analysis of Unsteady Flow-Field Induced by Plasma Actuator in Burst Mode." In 5th Flow Control Conference. Reston, Virigina: American Institute of Aeronautics and Astronautics, 2010. http://dx.doi.org/10.2514/6.2010-5090.
Lengani, Davide, Berardo Paradiso, Andreas Marn, and Emil Go¨ttlich. "Identification of Spinning Mode in the Unsteady Flow Field of a LP Turbine." In ASME 2011 Turbo Expo: Turbine Technical Conference and Exposition. ASMEDC, 2011. http://dx.doi.org/10.1115/gt2011-46226.
This paper presents an experimental investigation of the vane-blade unsteady interaction in an unshrouded LP turbine research rig with uneven blade/vane count (72 blades and 96 vanes). The rig was designed in cooperation with MTU Aero Engines and considerable efforts were put on the adjustment of all relevant model parameters. In particular blade count ratio, airfoil aspect ratio, reduced massflow, reduced speed, Mach and Reynolds numbers were chosen to reproduce the full scale LP turbine at take off condition. Measurements by means of a fast-response pressure probe were performed adopting a phase-locked acquisition technique in order to provide the time resolved flow field downstream of the turbine rotor. The probe has been fully traversed both in circumferential and radial traverses. The rotor exit is characterized by strong perturbations due to the tip leakage vortex and the rotor blade wake. Circumferential non uniformities due to the upstream vane wake and to the downstream exit guide vane potential effects are also identified. Furthermore in the present configuration with an uneven blade/vane count the non-uniformities due to the stator and rotor row are misaligned along the whole turbine circumference and create a spinning mode that rotates in direction opposite to the rotor at a high frequency. The aeroacoustic theory is employed to explain such further unsteady pattern. The variations of the exit flow angle within a cycle of such pattern are not negligible and almost comparable to the ones within the blade passing period.
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Berg, I. A., S. V. Porshnev, and B. K. Asamoah. "On testing the feasibility of infrared studies of torch burning in unsteady mode." In CENTRAL EUROPEAN SYMPOSIUM ON THERMOPHYSICS 2019 (CEST). AIP Publishing, 2019. http://dx.doi.org/10.1063/1.5114455.
Kiewat, Marco, Lukas Haag, Thomas Indinger, and Vincent Zander. "Low-Memory Reduced-Order Modelling With Dynamic Mode Decomposition Applied on Unsteady Wheel Aerodynamics." In ASME 2017 Fluids Engineering Division Summer Meeting. American Society of Mechanical Engineers, 2017. http://dx.doi.org/10.1115/fedsm2017-69299.
Wheel aerodynamics has a major impact on the overall aerodynamic performance of a vehicle. Different vortex excitation mechanisms are responsible for the induced forces on the geometry. Due to the high degree of complexity, it is difficult to gain further insight into the vortex structures at the rotating wheel. Therefore, wheel aerodynamics is usually investigated using temporally averaged flow fields. This work presents an approach to apply a recently introduced low-memory variant of Dynamic Mode Decomposition (DMD), namely Streaming Total DMD (STDMD), to investigate temporally resolved simulations in greater detail. The performance of STDMD is shown to be comparable to conventional DMD for a rotating generic closed wheel simulation test case. By creating a Reduced-Order Model (ROM) using a comparably small amount of DMD modes, the amount of complexity in the flow field can be drastically reduced. Orthonormal basis compression, amplitude ordering and a newly introduced amplitude weighting method are analyzed for creating a suitable ROM of DMD modes. A combination of compression and ordering by eigenvalue-weighted amplitude is concluded to be best suited and applied to the Delayed Detached Eddy Simulation (DDES) of the rotating generic closed wheel and a production vehicle rim wheel. The most dominant flow structures are captured at frequencies between 18Hz and 176Hz. Leading modes for both geometries are found close to the wheel rotation frequency and multiples of that frequency. The modes are identified as recirculation modes and vortex shedding.
Reports on the topic "Unsteady mode":
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Tseng, Ming T., and D. M. Gee. Unsteady Flow Model for Forecasting Missouri and Mississippi Rivers. Fort Belvoir, VA: Defense Technical Information Center, February 1997. http://dx.doi.org/10.21236/ada393969.
Hosder, Serhat, and Roger L. Simpson. Unsteady Skin-Friction Measurements on a Maneuvering DARPA2 Suboff Model. Fort Belvoir, VA: Defense Technical Information Center, June 2001. http://dx.doi.org/10.21236/ada390663.
Kokes, Joseph, Mark Costello, and Jubaraj Sahu. Generating an Aerodynamic Model for Projectile Flight Simulation Using Unsteady, Time Accurate Computational Fluid Dynamic Results. Fort Belvoir, VA: Defense Technical Information Center, September 2006. http://dx.doi.org/10.21236/ada457421.
Carver, C., N. A. Chipman, and T. E. Carleson. Modelling the unsteady growth state population balance for a nonlinear growth model in an MSMPR crystallizer. Office of Scientific and Technical Information (OSTI), March 1994. http://dx.doi.org/10.2172/164923.
Dahl, Travis, Ronald Heath, Stanford Gibson, and Christopher Nygaard. HEC-RAS unsteady flow and sediment model of the Mississippi River : Tarbert Landing to the Gulf. Engineer Research and Development Center (U.S.), January 2019. http://dx.doi.org/10.21079/11681/31782.
Wissink, Andrew, Jude Dylan, Buvana Jayaraman, Beatrice Roget, Vinod Lakshminarayan, Jayanarayanan Sitaraman, Andrew Bauer, James Forsythe, Robert Trigg, and Nicholas Peters. New capabilities in CREATE™-AV Helios Version 11. Engineer Research and Development Center (U.S.), June 2021. http://dx.doi.org/10.21079/11681/40883.
CREATE™-AV Helios is a high-fidelity coupled CFD/CSD infrastructure developed by the U.S. Dept. of Defense for aeromechanics predictions of rotorcraft. This paper discusses new capabilities added to Helios version 11.0. A new fast-running reduced order aerodynamics option called ROAM has been added to enable faster-turnaround analysis. ROAM is Cartesian-based, employing an actuator line model for the rotor and an immersed boundary model for the fuselage. No near-body grid generation is required and simulations are significantly faster through a combination of larger timesteps and reduced cost per step. ROAM calculations of the JVX tiltrotor configuration give a comparably accurate download prediction to traditional body-fitted calculations with Helios, at 50X less computational cost. The unsteady wake in ROAM is not as well resolved, but wake interactions may be a less critical issue for many design considerations. The second capability discussed is the addition of six-degree-of-freedom capability to model store separation. Helios calculations of a generic wing/store/pylon case with the new 6-DOF capability are found to match identically to calculations with CREATE™-AV Kestrel, a code which has been extensively validated for store separation calculations over the past decade.
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Rahai, Hamid, and Jeremy Bonifacio. Numerical Investigations of Virus Transport Aboard a Commuter Bus. Mineta Transportation Institute, April 2021. http://dx.doi.org/10.31979/mti.2021.2048.
The authors performed unsteady numerical simulations of virus/particle transport released from a hypothetical passenger aboard a commuter bus. The bus model was sized according to a typical city bus used to transport passengers within the city of Long Beach in California. The simulations were performed for the bus in transit and when the bus was at a bus stop opening the middle doors for 30 seconds for passenger boarding and drop off. The infected passenger was sitting in an aisle seat in the middle of the bus, releasing 1267 particles (viruses)/min. The bus ventilation system released air from two linear slots in the ceiling at 2097 cubic feet per minute (CFM) and the air was exhausted at the back of the bus. Results indicated high exposure for passengers sitting behind the infectious during the bus transit. With air exchange outside during the bus stop, particles were spread to seats in front of the infectious passenger, thus increasing the risk of infection for the passengers sitting in front of the infectious person. With higher exposure time, the risk of infection is increased. One of the most important factors in assessing infection risk of respiratory diseases is the spatial distribution of the airborne pathogens. The deposition of the particles/viruses within the human respiratory system depends on the size, shape, and weight of the virus, the morphology of the respiratory tract, as well as the subject’s breathing pattern. For the current investigation, the viruses are modeled as solid particles of fixed size. While the results provide details of particles transport within a bus along with the probable risk of infection for a short duration, however, these results should be taken as preliminary as there are other significant factors such as the virus’s survival rate, the size distribution of the virus, and the space ventilation rate and mixing that contribute to the risk of infection and have not been taken into account in this investigation.
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Computer program HYDRAUX: a model for simulating one- dimensional, unsteady, open-channel flow. US Geological Survey, 1989. http://dx.doi.org/10.3133/wri884226.
The computer program FourPt (Version 95.01), a model for simulating one-dimensional, unsteady, open-channel flow. US Geological Survey, 1997. http://dx.doi.org/10.3133/wri974016.
