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Morphological evolution and spreading flow of hollow oil droplet impact on a heated wall Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2021-01-12 De-yu Tu, Qing-min Pan, Jian-hong Zhou, Baohong Tong, Guo-tao Zhang, Wei Wang
A coupled level set and volume–of–fraction method is applied to investigate hollow oil droplet impacts on heated walls. Results show that given the increase in impact velocity, three evolutionary processes of spreading, transition, and central jet occur after the hollow oil droplet impact on a heated wall. The variation in the spreading length of hollow oil droplets is similar in different evolutionary
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Under-resolved and large eddy simulations of a decaying Taylor–Green vortex with the cumulant lattice Boltzmann method Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-11-19 Martin Geier, Stephan Lenz, Martin Schönherr, Manfred Krafczyk
We present a comprehensive analysis of the cumulant lattice Boltzmann model with the three-dimensional Taylor–Green vortex benchmark at Reynolds number 1600. The cumulant model is investigated in several different variants, using regularization, fourth-order convergent diffusion and fourth-order convergent advection with and without limiters. In addition, a cumulant model combined with a WALE sub-grid
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A calculus for flows in periodic domains Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-11-17 Peter J. Baddoo, Lorna J. Ayton
Purpose: We present a constructive procedure for the calculation of 2-D potential flows in periodic domains with multiple boundaries per period window. Methods: The solution requires two steps: (i) a conformal mapping from a canonical circular domain to the physical target domain, and (ii) the construction of the complex potential inside the circular domain. All singly periodic domains may be classified
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On the boundary conditions in the Stokesian flows Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-11-10 Daria Yu. Khanukaeva, Leonid A. Ostrer
The problem of the boundary condition setting is considered for creeping flows over cylindrical and spherical obstacles. The interaction of Newtonian and micropolar liquid with the solid surface is discussed in the context of the Stokes paradox and the cell model technique. Mathematical and mechanical aspects of various types of boundary conditions at the hypothetical liquid surface are considered
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Effect of Mach number on the absolute/convective stability of compressible planar wakes Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-11-05 Shuai Wang, Fengbo Wen, Heng Zhang, Liangjun Su, Xun Zhou
In this paper, the influence of the Mach number on the stability of two-dimensional compressible planar wakes is studied to gain physical insight into the turbine wakes. Two-dimensional instabilities of compressible wakes are studied using local spatiotemporal instability analyses. The absolute/convective boundary of a family of wake profiles is obtained at different Mach numbers. Then, local stability
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Stability of confined vortex sheets Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-11-02 Bartosz Protas
We propose a simple model for the evolution of an inviscid vortex sheet in a potential flow in a channel with parallel walls. This model is obtained by augmenting the Birkhoff–Rott equation with a potential field representing the effect of the solid boundaries. Analysis of the stability of equilibria corresponding to flat sheets demonstrates that in this new model the growth rates of the unstable modes
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Floquet analysis on a viscous cylindrical fluid surface subject to a time-periodic radial acceleration Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-09-14 Dilip Kumar Maity
Parametrically excited standing waves are observed on a cylindrical fluid filament. This is the cylindrical analog of the Faraday instability in a flat surface or spherical droplet. Using Floquet theory, a linear stability analysis is carried out on a viscous cylindrical fluid surface, which is subjected to a time-periodic radial acceleration. Viscosity of the fluid has a significant impact on the
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Numerical simulations of buoyancy-driven flows using adaptive mesh refinement: structure and dynamics of a large-scale helium plume Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-09-01 Nicholas T. Wimer, Marcus S. Day, Caelan Lapointe, Michael A. Meehan, Amanda S. Makowiecki, Jeffrey F. Glusman, John W. Daily, Gregory B. Rieker, Peter E. Hamlington
The physical characteristics and evolution of a large-scale helium plume are examined through a series of numerical simulations with increasing physical resolution using adaptive mesh refinement (AMR). The five simulations each model a 1-m-diameter circular helium plume exiting into a \((4~\hbox {m})^3\) domain and differ solely with respect to the smallest scales resolved using the AMR, spanning resolutions
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Mass transport in electrokinetic microflows with the wall reaction affecting the hydrodynamics Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-08-29 Sourav Mondal, Sirshendu De
The mass transport in electrokinetically actuated microchannel flow is interesting when the wall reactions influence the wall potential, thereby affecting the hydrodynamics. This is the first work where the electro-osmotic flow is impacted by the chemical reactions. Since the wall potential is non-uniform, we have compared the results of the classical Poisson–Boltzmann equations with the generalized
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Investigation of pressure and the Lewis number effects in the context of algebraic flame surface density closure for LES of premixed turbulent combustion Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-08-25 Usman Allauddin, Sai Ranjith Reddy Lomada, Michael Pfitzner
Large scale industrial combustion devices, for example, internal combustion engines, gas turbine combustors, etc., operate under high-pressure conditions and utilize a variety of fuels. Unfortunately, the majority of the current numerical combustion modelling approaches are not fully validated for high-pressure and the non-unity Lewis number (\(\hbox {Le} =\) thermal diffusivity/mass diffusivity) effects
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Flowtaxis in the wakes of oscillating airfoils Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-08-09 Brendan Colvert; Geng Liu; Haibo Dong; Eva Kanso
Many aquatic organisms from copepods to harbor seals are able to detect and respond to flow disturbances. The physiological mechanisms underlying such behavior remain a challenge for current and future research. Here, we propose a simplified flow sensing scenario in which a mobile sensor reorients its heading in response to local flow stimuli, with the goal of tracing the wakes created by oscillating
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Oscillations of a periodically forced slightly eccentric spheroid in an unsteady viscous flow at low Reynolds numbers Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-08-05 Jogender Singh, C. V. Anil Kumar
The equations governing the dynamics of a periodically driven micro-spheroid in an unsteady viscous fluid at low Reynolds number are derived. Its oscillation properties in the presence/absence of memory forces are reported. The core part of the derivation is a perturbation analysis of motion of a sphere. The calculated solutions match with those available in the literature in the limiting case of a
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A priori tests of eddy viscosity models in square duct flow Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-07-31 Davide Modesti
We carry out a priori tests of linear and nonlinear eddy viscosity models using direct numerical simulation (DNS) data of square duct flow up to friction Reynolds number \({\text {Re}}_\tau =1055\). We focus on the ability of eddy viscosity models to reproduce the anisotropic Reynolds stress tensor components \(a_{ij}\) responsible for turbulent secondary flows, namely the normal stress \(a_{22}\)
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Instability of natural convection in a laterally heated cube with perfectly conducting horizontal boundaries Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-07-20 Alexander Yu. Gelfgat
Oscillatory instability of buoyancy convection in a laterally heated cube with perfectly thermally conducting horizontal boundaries is studied. The effect of the spanwise boundaries on the oscillatory instability onset is examined. The problem is treated by Krylov-subspace-iteration-based Newton and Arnoldi methods. The Krylov basis vectors are calculated by a novel approach that involves the SIMPLE
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Phase-field modeling and computer simulation of the coffee-ring effect Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-07-12 Junxiang Yang, Hyundong Kim, Chaeyoung Lee, Sangkwon Kim, Jian Wang, Sungha Yoon, Jintae Park, Junseok Kim
In this study, we propose a novel computational model for simulating the coffee-ring phenomenon. The proposed method is based on a phase-field model and Monte Carlo simulation. We use the Allen–Cahn equation with a pinning boundary condition to model a drying droplet. The coffee particles inside the droplet move according to a random walk function with a truncated standard normal distribution under
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Effects of finite ion size on transport of neutral solute across porous wall of a nanotube Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-07-09 Saikat Bhattacharjee, Morteza Dejam, Sirshendu De
Effect of finite ion size on the transport of a neutral solute across the porous wall of a nanotube is presented in this study. Modified Poisson–Boltzmann equation without the Debye–Huckel approximation is used to determine the potential distribution within the tube. Power law fluid is selected for the study, as its rheology resembles closely to the real-life physiological fluids. The flow within the
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On dispersion of solute in steady flow through a channel with absorption boundary: an application to sewage dispersion Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-07-08 Kajal Kumar Mondal, Subham Dhar, Bijoy Singha Mazumder
The paper describes the longitudinal dispersion of passive tracer materials released into an incompressible viscous fluid, flowing through a channel with walls having first-order reaction. Its model is based on a steady advection–diffusion equation with Dirichlet’s and mixed boundary conditions, and whose solution represents the concentration of the tracers in different downstream stations. For imposing
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Data-driven modeling of the chaotic thermal convection in an annular thermosyphon Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-07-01 Jean-Christophe Loiseau
Identifying accurate and yet interpretable low-order models from data has gained a renewed interest over the past decade. In the present work, we illustrate how the combined use of dimensionality reduction and sparse system identification techniques allows us to obtain an accurate model of the chaotic thermal convection in a two-dimensional annular thermosyphon. Taking as guidelines the derivation
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Toward particle-resolved accuracy in Euler–Lagrange simulations of multiphase flow using machine learning and pairwise interaction extended point-particle (PIEP) approximation Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-06-30 S. Balachandar; W. C. Moore; G. Akiki; K. Liu
This study presents two different machine learning approaches for the modeling of hydrodynamic force on particles in a particle-laden multiphase flow. Results from particle-resolved direct numerical simulations (PR-DNS) of flow over a random array of stationary particles for eight combinations of particle Reynolds number (\({\mathrm {Re}}\)) and volume fraction (\(\phi \)) are used in the development
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Actuator and sensor placement for closed-loop control of convective instabilities Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-06-24 Guilherme A. Freire, André V. G. Cavalieri, Flávio J. Silvestre, A. Hanifi, D. S. Henningson
This work deals with the characterization of the closed-loop control performance aiming at the delay of transition. We focus on convective wavepackets, typical of the initial stages of transition to turbulence, starting with the linearized Kuramoto–Sivashinsky equation as a model problem representative of the transitional 2D boundary layer; its simplified structure and reduced order provide a manageable
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Mixing in three-dimensional cavity by moving cavity walls Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-06-18 Alex Povitsky
The mixing in three-dimensional enclosures is investigated numerically using flow in cubical cavity as a geometrically simple model of various natural and engineering flows. The mixing rate is evaluated for up to the value of Reynolds number \(\hbox {Re}=2000\) for several representative scenarios of moving cavity walls: perpendicular motion of the parallel cavity walls, motion of a wall in its plane
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A systematic study of blockage in three-dimensional branching networks with an application to model human bronchial tree Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-06-12 Kaustav Pradhan; Abhijit Guha
A major aim of the present study is to understand and thoroughly document the fluid dynamics in three-dimensional branching networks when an intermediate branch is partially or completely obstructed. Altogether, 26 different three-dimensional networks each comprising six generations of branches (involving 63 straight portions and 31 bifurcation modules) are constructed and appropriately meshed to conduct
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Compound droplet dynamics of a tumor cell squeezing through conical microfilters Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-06-01 Pengliang Chang; Christopher Landry; Xiaolin Chen; Hua Tan
Circulating tumor cells (CTCs) are regarded as important biomarkers for early cancer detection and treatment. Decades of research have made progress in CTC detection using deformability-based microfilters; however, developing a high-throughput CTC microfilter remains a challenging task due to the lack of the essential understanding of microscopic multiphase flow. To design and optimize a CTC microfilter
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Enhancement of shock-capturing methods via machine learning Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-05-23 Ben Stevens; Tim Colonius
In recent years, machine learning has been used to create data-driven solutions to problems for which an algorithmic solution is intractable, as well as fine-tuning existing algorithms. This research applies machine learning to the development of an improved finite-volume method for simulating PDEs with discontinuous solutions. Shock-capturing methods make use of nonlinear switching functions that
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The exergy concept and compressible turbulence Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-05-19 Andreas Jocksch
Turbulence models facilitated by Kolmogorov’s theory play an important role for compressible flows. Typically the basis of these models is the power spectrum of the velocity \({\mathbf {u}}\) or of the density-weighted velocity \({\mathbf {w}}\equiv \rho ^{1/3}{\mathbf {u}}\). While for incompressible flow the quantity turbulent kinetic energy characterises turbulent motions, from the thermodynamic
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Influences of boattail structures on aerodynamic characteristics of supersonic spinning projectiles Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-05-16 Jie Ma; Zhihua Chen; Dawen Xue; Xiaohui Sun
Previous research studies indicate that the proportion of Magnus force at the spinning projectile tail position is very high. Meanwhile, the large mutations of aerodynamic characteristics are found after adding boattail structures. In order to study the influences of boattail structures on aerodynamics of a spinning projectile, a 6.37-diameter long tangential-ogive-cylinder projectile is selected as
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Large eddy simulation of non-Boussinesq gravity currents with a DG method Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-05-09 Caterina Bassi; Antonella Abbà; Luca Bonaventura; Lorenzo Valdettaro
We present results of three-dimensional direct numerical simulations (DNS) and large eddy simulations (LES) of turbulent gravity currents with a discontinuous Galerkin finite elements method. In particular, we consider the lock-exchange test case as a benchmark for gravity currents. Since, to the best of our knowledge, non-Boussinesq three-dimensional reference DNS are not available in the literature
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Machine-learning-based reduced-order modeling for unsteady flows around bluff bodies of various shapes Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-05-06 Kazuto Hasegawa; Kai Fukami; Takaaki Murata; Koji Fukagata
We propose a method to construct a reduced order model with machine learning for unsteady flows. The present machine-learned reduced order model (ML-ROM) is constructed by combining a convolutional neural network autoencoder (CNN-AE) and a long short-term memory (LSTM), which are trained in a sequential manner. First, the CNN-AE is trained using direct numerical simulation (DNS) data so as to map the
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Dimensionality reduction and reduced-order modeling for traveling wave physics Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-05-02 Ariana Mendible; Steven L. Brunton; Aleksandr Y. Aravkin; Wes Lowrie; J. Nathan Kutz
We develop an unsupervised machine learning algorithm for the automated discovery and identification of traveling waves in spatiotemporal systems governed by partial differential equations (PDEs). Our method uses sparse regression and subspace clustering to robustly identify translational invariances that can be leveraged to build improved reduced-order models (ROMs). Invariances, whether translational
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An ensemble Kalman filter approach to parameter estimation for patient-specific cardiovascular flow modeling Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-04-29 Daniel Canuto; Joe L. Pantoja; Joyce Han; Erik P. Dutson; Jeff D. Eldredge
Many previous studies have shown that the fidelity of three-dimensional cardiovascular flow simulations depends strongly on inflow and outflow boundary conditions that accurately describe the characteristics of the larger vascular network. These boundary conditions are generally based on lower-dimensional models that represent the upstream or downstream flow behavior in some aggregated fashion. However
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Filtration of micropolar liquid through a membrane composed of spherical cells with porous layer Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-04-27 Daria Khanukaeva
This paper considers membranes of globular structure in the framework of the cell model technique. The flow of a micropolar fluid through a spherical cell consisting of a solid core, porous layer and liquid envelope is modeled using coupled micropolar and Brinkman-type equations. The solution is obtained in analytical form. Boundary value problems with different conditions on the hypothetical cell
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Data-driven selection of actuators for optimal control of airfoil separation Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-04-27 Debraj Bhattacharjee; Bjoern Klose; Gustaaf B. Jacobs; Maziar S. Hemati
We present a systematic approach for determining the optimal actuator location for separation control from input–output response data, gathered from numerical simulations or physical experiments. The Eigensystem realization algorithm is used to extract state-space descriptions from the response data associated with a candidate set of actuator locations. These system realizations are then used to determine
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An adaptive mesh refinement approach based on optimal sparse sensing Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-04-10 Daniel Foti; Sven Giorno; Karthik Duraisamy
We introduce a new approach for adaptive mesh refinement in which adaptivity is driven by low rank decomposition and optimal sensing of the dynamically evolving flow field. This method seeks an ordered set of locations for mesh adaptation from the instantaneous data-driven basis of an online proper orthogonal decomposition of the velocity, which organizes features into sparse optimal orthogonal modes
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An inviscid model of unsteady separated vortical flow for a moving plate Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-04-10 Sung-Ik Sohn
An inviscid vortex shedding model for separated vortices from a solid body is studied. The model describes the separated vortices by vortex sheets and the attached flow via conformal mapping. We develop a computational model to simulate the vortex shedding of a moving body, with varying angle. An unsteady Kutta condition is imposed on the edges of the plate to determine the edge circulations and velocities
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Anomalous behavior of fluid flow through thin carbon nanotubes Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-03-16 Mohammad Rezaee; Hojat Ghassemi
Molecular dynamics simulation is used to study flow rate behavior of monoatomic fluid through carbon nanotube (CNT) against the pore diameter. All armchair and zigzag CNTs with diameters below 1.5 nm were considered. Fluid flow rate versus diameter is investigated, and discrepancy was observed in the results. Its non-monotonic behavior is reported and attributed to diameter-dependent potential energy
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Deep model predictive flow control with limited sensor data and online learning Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-03-12 Katharina Bieker; Sebastian Peitz; Steven L. Brunton; J. Nathan Kutz; Michael Dellnitz
The control of complex systems is of critical importance in many branches of science, engineering, and industry, many of which are governed by nonlinear partial differential equations. Controlling an unsteady fluid flow is particularly important, as flow control is a key enabler for technologies in energy (e.g., wind, tidal, and combustion), transportation (e.g., planes, trains, and automobiles), security
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Resolvent analysis in unbounded flows: role of free-stream modes Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-02-27 Petrônio A. S. Nogueira; André V. G. Cavalieri; Ardeshir Hanifi; Dan S. Henningson
The problem of finding optimal forcing and response for unbounded base flows, exemplified by the Blasius boundary layer, is assessed by means of a locally parallel resolvent analysis. A new analysis of previous results in the literature, which stated that a maximum resolvent gain occurs for spanwise wavenumber \(k_z \approx 0.2\), revealed that this result was not domain converged, and larger domains
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Assessment of supervised machine learning methods for fluid flows Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-02-27 Kai Fukami; Koji Fukagata; Kunihiko Taira
We apply supervised machine learning techniques to a number of regression problems in fluid dynamics. Four machine learning architectures are examined in terms of their characteristics, accuracy, computational cost, and robustness for canonical flow problems. We consider the estimation of force coefficients and wakes from a limited number of sensors on the surface for flows over a cylinder and NACA0012
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Effects of contact angle hysteresis on drop manipulation using surface acoustic waves Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-02-24 Mahdi Sheikholeslam Noori; Mohammad Taeibi Rahni; Arash Shams Taleghani
Surface acoustic waves have gained much attention in flow control given the effects arising from acoustic streaming. In this study, the hydrodynamic interference of a drop under surface acoustic waves is comprehensively investigated and the contact angle hysteresis effects are considered, too. This paper reveals the effects of some control parameters such as wave amplitude and wave frequency on the
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A numerical study of a hollow water droplet falling in air Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-02-10 Mounika Balla; Manoj Kumar Tripathi; Kirti Chandra Sahu
We numerically study the dynamics of a hollow water droplet falling in the air under the action of gravity. The focus of our study is to investigate the effects of the difference in radii (thickness) of the hollow droplet, gravity and surface tension at the air–water interface on shape oscillations and the breakup dynamics of the hollow droplet. We found that the oscillations of the inner interface
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A numerical study on heat transfer of a ferrofluid flow in a square cavity under simultaneous gravitational and magnetic convection Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-02-07 Lucas H. P. Cunha; Ivan R. Siqueira; Arthur A. R. Campos; Adriano P. Rosa; Taygoara F. Oliveira
Thermomagnetic convection is based on the use of external magnetic fields to better control heat transfer fluxes in ferrofluids, finding important applications in engineering and many related areas. The improvement of such methods relies on fundamentally understanding the flow of ferrofluids under temperature gradients and external magnetic fields. However, the underlying physics of this phenomenon
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Simulation of collisions of two droplets containing two different liquids using incompressible smoothed particle hydrodynamics method Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-01-22 Yu Nishio; Kohei Komori; Seiichiro Izawa; Yu Fukunishi
The present study aims to simulate a collision of two droplets containing immiscible liquids by employing a three- dimensional incompressible smoothed particle hydrodynamics (SPH) method, with models implemented for the computation. The simulation of a head-on collision of two droplets, both of which contain the same glycerol solution, showed that the droplet behavior agrees very well with that observed
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Numerical study of two-airfoil arrangements by a discrete vortex method Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-01-11 Thierry M. Faure; Laurent Dumas; Olivier Montagnier
The aerodynamic characteristics of two neighboring airfoils are greatly different from those of a single airfoil, for both attached and detached flow conditions. In order to study the features of a two-airfoil arrangement with variations in the angle of attack and distances between the airfoils, and considering possible flow detachments, an adaptation of a discrete-time vortex numerical method is conducted
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Reduced-order model of a reacting, turbulent supersonic jet based on proper orthogonal decomposition Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-01-09 Antoni Alomar; Aurélie Nicole; Denis Sipp; Valérie Rialland; François Vuillot
The present article deals with the spatiotemporal reduction of a reacting, supersonic, turbulent jet. A flowfield dataset is first obtained from a LES simulation including chemical reactions. The spatial reduction is accomplished by performing successively a Fourier transform in the azimuthal direction and a proper orthogonal decomposition (POD), while the temporal reduction is obtained through a selection
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A priori analysis on deep learning of subgrid-scale parameterizations for Kraichnan turbulence Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-01-04 Suraj Pawar; Omer San; Adil Rasheed; Prakash Vedula
In the present study, we investigate different data-driven parameterizations for large eddy simulation of two-dimensional turbulence in the a priori settings. These models utilize resolved flow field variables on the coarser grid to estimate the subgrid-scale stresses. We use data-driven closure models based on localized learning that employs a multilayer feedforward artificial neural network with
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An immersed lifting and dragging line model for the vortex particle-mesh method Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2020-01-04 Denis-Gabriel Caprace; Grégoire Winckelmans; Philippe Chatelain
The numerical study of the wake of full-scale slender devices such as aircraft wings and wind turbine blades requires high-fidelity large eddy simulation tools. The broad spectrum of scales involved entails the use of coarse-grain models for the devices. Actuator disk or line methods have been developed for that purpose, and are to date the most employed in that context. These methods transfer the
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Numerical realization of helical vortices: application to vortex instability Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-11-26 Mattias Brynjell-Rahkola; Dan S. Henningson
The need to numerically represent a free vortex system arises frequently in fundamental and applied research. Many possible techniques for realizing this vortex system exist but most tend to prioritize accuracy either inside or outside of the vortex core, which therefore makes them unsuitable for a stability analysis considering the entire flow field. In this article, a simple method is presented that
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Reduced-order control using low-rank dynamic mode decomposition Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-10-29 Palash Sashittal; Daniel J. Bodony
In this work, we perform full-state LQR feedback control of fluid flows using non-intrusive data-driven reduced-order models. We propose a model reduction method called low-rank dynamic mode decomposition (lrDMD) that solves for a rank-constrained linear representation of the dynamical system. lrDMD is shown to have lower data reconstruction error compared to standard optimal mode decomposition (OMD)
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Analytical and experimental study of the substance transport in the vortex flow Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-10-16 A. V. Kistovich; T. O. Chaplina; E. V. Stepanova
The characteristics of the vortex flow with a free surface formed in a vertical cylindrical container filled with water, where the source of motion is the disk at the bottom endwall, are studied experimentally and analytically. Different types of oils and petroleum are used in experiments as admixtures. The problem of an “oil body” form in a complex vortex flow is considered on the basis of the analysis
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Compressibility effects on the transition to turbulence in a spatially developing plane free shear layer Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-10-16 Dongru Li; Jonathan Komperda; Zia Ghiasi; Ahmad Peyvan; Farzad Mashayek
The compressibility effects on the transition to turbulence in a spatially developing, compressible plane free shear layer are investigated via direct numerical simulation using a high-order discontinuous spectral element method for three different convective Mach numbers of 0.3, 0.5, and 0.7. The location of the laminar–turbulent transition zone is predicted by the analyses of vorticities, Reynolds
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Shock wave structure in a non-ideal gas under temperature and density-dependent viscosity and heat conduction Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-09-21 Manoj Singh; Arvind Patel
The structure of a shock wave is investigated using the continuum hypothesis for steady one-dimensional flow of a viscous non-ideal gas under heat conduction. The coefficients of viscosity and heat conductivity are assumed to be directly proportional to a power of the temperature and density of the gas. The simplified van der Waals equation of state for the non-ideal gas has been assumed in this work
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Initiation of ray tracing models: evolution of small-amplitude gravity wave packets in non-uniform background Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-08-31 Christopher Pütz; Mark Schlutow; Rupert Klein
This study introduces a new computational scheme for the linear evolution of internal gravity wave packets passing over strongly non-uniform stratifications and background flows as found, e.g., near the tropopause. Focusing on linear dispersion, which is dominant at small wave amplitudes, the scheme describes general wave superpositions arising from wave reflections near strong variations of the background
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Investigation of asymmetric flow past a slender body at high angles of attack Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-08-27 Osama Obeid; Ibraheem AlQadi; Jaber AlMutairi
This paper presents an investigation of flow asymmetry around a slender body at high angles of attack. The paper investigated the numerical aspect of simulating such flows. The impact of three simulation parameters, including grid resolution, discretization scheme, and turbulent flow modeling, was assessed. It was shown that insufficient grid density resulted in highly dissipated solution. At high
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Investigation of bubble formation and its detachment in shear-thinning liquids at low capillary and Bond numbers Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-08-21 Mohammad Reza Oshaghi; Hossein Afshin; Bahar Firoozabadi
In the present paper, the formation of an air bubble in a shear-thinning non-Newtonian fluid was investigated numerically. For modeling, an algebraic volume of fluid (VOF) solver of \(\hbox {OpenFOAM}^\circledR \) was improved by applying a Laplacian filter and was evaluated using the experimental results from the literature. The enhanced solver could compute the surface tension force more accurately
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Global thermoacoustic oscillations in a thermally driven pulse tube Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-08-10 Saravana Kumar; Arnab Samanta
We obtain linearized, BiGlobal thermoacoustic solutions in a pulse tube driven via an imposed mean temperature gradient. Here, the pulse tube is treated as a key unit of a thermoacoustic heat engine, in which the conversion of thermal energy to useful acoustic fluctuations occurs. A primary goal of this work is to understand the hydrodynamic efficiency of the energy conversion process and how it depends
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Drag reduction on the 25 $$^{\varvec{\circ }}$$ ∘ Ahmed body using a new zero-net-mass-flux flow control method Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-08-05 Bingxin Wang; Zhigang Yang; Hui Zhu
Periodic-forcing jets are applied to form a zero-net-mass-flux actuator for active flow control study on the \(25^{\circ }\) Ahmed body. Unlike traditional synthetic jet, this new proposed zero-net-mass-flux actuator has managed to divide the blowing phase and suction phase apart on different separation edges on the rear part of the body. Numerical simulation based on the large eddy simulation method
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Layer formation in double-diffusive convection over resting and moving heated plates Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-07-02 Florian Zaussinger; Friedrich Kupka
We present a numerical study of double-diffusive convection characterized by a stratification unstable to thermal convection, while at the same time a mean molecular weight (or solute concentration) difference between top and bottom counteracts this instability. Convective zones can form in this case either by the stratification being locally unstable to the combined action of both temperature and
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A critical assessment of the parabolized stability equations Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-06-13 Aaron Towne; Georgios Rigas; Tim Colonius
The parabolized stability equations (PSE) are a ubiquitous tool for studying the stability and evolution of disturbances in weakly nonparallel, convectively unstable flows. The PSE method was introduced as an alternative to asymptotic approaches to these problems. More recently, PSE has been applied with mixed results to a more diverse set of problems, often involving flows with multiple relevant instability
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Low Mach, compressibility, and finite size effects of localized uniform heat sources in a gas Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-06-01 Swetava Ganguli; Sanjiva K. Lele
The temporal evolution of the initial shock front and the low Mach regime produced behind the front due to the sudden introduction of a spherical, finite-size, low Biot number, uniformly heated energy source in a variable property gas is investigated. While the sphere is of physical interest, analogous problems of a uniformly heated infinitely long cylindrical wire and an infinite plate are also studied
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Large eddy simulations of premixed CH $$_{{\mathbf {4}}}$$ 4 bluff-body flames operating close to the lean limit using quasi-global chemistry and an algebraic chemiluminescence model Theor. Comput. Fluid Dyn. (IF 1.675) Pub Date : 2019-05-27 E. P. Mitsopoulos; I. Lytras; P. Koutmos
The present work describes the numerical study of unconfined turbulent premixed methane/air flames stabilized on an axisymmetric conical baffle under lean and ultra-lean, close to blow-off conditions. A finite-volume-based LES method, using the dynamic Smagorinsky subgrid model in combination with two turbulent combustion methodologies, the thickened flame model and the implicit LES (ILES) laminar