Shock interaction mechanisms on a double wedge at Mach 7
Present computational study investigates formation andinteraction mechanisms of shocks and boundary layer for lowenthalpyMach 7flows of nitrogen over double wedges, which have fixed fore and various aft angles of 30 ° and 45°–60°, respectively. We use a density based finite-volume Navier-Stokes solver to simulate lowenthalpyMach 7flows of nitrogen over double wedges. The solver is first and second order accurate in time and space, respectively. The meshes used in simulations of two-dimensional laminarflows consist of multiple blocks of structured mesh. Depending on the intensity, impingement angle, and impingement loc...
Source: Physics of Fluids - September 2, 2016 Category: Physics Authors: Ahmet Selim Durna, Mohamad El Hajj Ali Barada and Bayram Celik Source Type: research
Investigation of the viscous reconnection phenomenon of two vortex tubes through spectral simulations
This paper aims to shed further light on theviscous reconnection phenomenon. To this end, we propose a robust and efficient method in order to quantify the degree of reconnection of twovortex tubes. This method is used to compare the evolutions of two simple initialvortex configurations: orthogonal and antiparallel. For the antiparallel configuration, the proposed method is compared with alternative estimators and it is found to improve accuracy since it can account properly for the formation of looping structures inside the domain. This observation being new, the physical mechanism for the formation of those looping struc...
Source: Physics of Fluids - September 2, 2016 Category: Physics Authors: Guillaume Beardsell, Louis Dufresne and Guy Dumas Source Type: research
Transient motion of and heat transfer in a rarefied gas between plane
parallel walls with different surface properties
Transient motion of and heat transfer in a rarefied gas between plane parallel walls
with different surface properties are studied based on kinetic theory. It is assumed
that one wall is a diffuse reflection boundary and the other wall is a Maxwell-type
boundary, and the transient behavior of the gas caused by a sudden heating of one of
the walls is studied. The linearized Boltzmann equation for a hard-sphere molecular
gas is numerically studied using the modified hybrid scheme of the characteristic
coordinate and finite difference methods, to correctly describe the discontin...
Source: Physics of Fluids - September 2, 2016 Category: Physics Authors: Toshiyuki Doi Source Type: research
Lifting a large object from an anisotropic porous bed
An analytical study of two dimensional problem of lifting an object from the top of a fully saturated rigid porous bed is discussed. It is assumed that the porous bed isanisotropic in nature. Theflow within the gap region between the object and the porous bed is assumed to be governed by Stokesequation while theflow within the porous bed is governed by Brinkmanequation. The breakout phenomenon for different kinds ofsoil is reported. The effect of mechanical properties likeanisotropic permeability, grain diameter size, and porosity on streamlines, velocity, and force is analyzed. Relevant comparison with C. C. Mei, R. W. Ye...
Source: Physics of Fluids - September 2, 2016 Category: Physics Authors: Timir Karmakar and G. P. Raja Sekhar Source Type: research
Boundedness of the mixed velocity-temperature derivative skewness in homogeneous isotropic turbulence
Thetransport equation for the mean scalar dissipation rateϵ¯θ is derived by applying the limit at small separations to the generalized form of Yaglom ’s equation in two types offlows, those dominated mainly by a decay of energy in the streamwise direction and those which are forced, through a continuous injection of energy at large scales. In gridturbulence, the imbalance between the production ofϵ¯θ due to stretching of the temperature field and the destruction ofϵ¯θ by the thermal diffusivity is governed by the streamwise advection ofϵ¯θ by the mean velocity. This imbalance is intrinsically different from t...
Source: Physics of Fluids - September 1, 2016 Category: Physics Authors: S. L. Tang, R. A. Antonia, L. Djenidi, L. Danaila and Y. Zhou Source Type: research
Dynamic unified RANS-LES simulations of high Reynolds number separated flows
The development of hybrid RANS-LES methods is seen to be a very promising approach to enable efficient simulations of highReynolds number turbulent flows involvingflow separation. To contribute to further advances, we present a new, theoretically well based, dynamic hybrid RANS-LES method, referred to as DLUM. It is applied to a highReynolds numberflow involving both attached andseparated flow regimes: a periodic hillflow is simulated at aReynolds number of 37 000. Its performance is compared to pureLES, pureRANS, other hybrid RANS-LES (given by DLUM modifications), and experimental observations. It is shown that the us...
Source: Physics of Fluids - September 1, 2016 Category: Physics Authors: Reza Mokhtarpoor, Stefan Heinz and Michael Stoellinger Source Type: research
The correlation between wake transition and propulsive efficiency of a flapping foil: A numerical study
We study numerically the propulsive wakes produced by a flapping foil. Both pure pitching and pure heaving motions are considered, respectively, at a fixedReynolds number ofRe = 1700. As the major innovation of this paper, we find an interesting coincidence that the efficiency maximum agrees well with the 2D-3D transition boundary, by plotting the contours of propulsive efficiency in the frequency-amplitude parametric space and comparing to the transition boundaries. Although there is a lack of direct 3D simulations, it is reasonable to conjecture that the propulsive efficiency increases with Strouhal number until the wake...
Source: Physics of Fluids - September 1, 2016 Category: Physics Authors: Jian Deng, Liping Sun, Lubao Teng, Dingyi Pan and Xueming Shao Source Type: research
Rise of an argon bubble in liquid steel in the presence of a transverse magnetic field
The rise of gaseousbubbles in viscousliquids is a fundamental problem in fluid physics, and it is also a common phenomenon in many industrial applications such as materials processing, food processing, and fusion reactor cooling. In this work, the motion of a single argon gasbubble rising in quiescentliquid steel under an externalmagnetic field is studied numerically using a Volume-of-Fluid method. To mitigate spuriousvelocities normally generated during numerical simulation of multiphase flows with large density differences, an improved algorithm forsurface tension modeling, originally proposed by Wang and Tong [ “Defor...
Source: Physics of Fluids - September 1, 2016 Category: Physics Authors: K. Jin, P. Kumar, S. P. Vanka and B. G. Thomas Source Type: research
Viscous slip coefficients for binary gas mixtures measured from mass flow rates through a single microtube
Theviscous slip coefficient for helium-argon binary gas mixture is extracted from the experimental values of the massflow rate through a microtube. The massflow rate ismeasured by the constant-volume method. Theviscous slip coefficient was obtained by identifying themeasured massflow rate through a microtube with the corresponding analytical expression, which is a function of the Knudsen number. Themeasurements were carried out in theslip flow regime where the first-order slipboundary condition can be applied. Themeasuredviscous slip coefficients of binary gas mixtures exhibit a concave function of the molar ratio of the m...
Source: Physics of Fluids - September 1, 2016 Category: Physics Authors: H. Yamaguchi, K. Takamori, P. Perrier, I. Graur, Y. Matsuda and T. Niimi Source Type: research
Numerical analysis of contact line dynamics passing over a single wettable defect on a wall
In this study, thedynamics of a contact line passing a single defect, which was represented by a locally wettable part (whose static contact angle is less than the other part, namely, chemically heterogeneous and physically flat part), was analyzed using numerical simulations employing the front-tracking method and the generalized Navierboundary condition. We observed that the contact line was distorted with a logarithmic shape far from the defect; however, the distortion was dependent on the wall velocity. The apparent (averaged)dynamic contact angle of the wall with a defect was evaluated using a macroscopicenergy balanc...
Source: Physics of Fluids - August 31, 2016 Category: Physics Authors: Yasufumi Yamamoto, Shohei Higashida, Hiroyuki Tanaka, Tatsuro Wakimoto, Takahiro Ito and Kenji Katoh Source Type: research
Passive nanofluidic diode using non-uniform nanochannels
In this work, we propose a nanofluidic diode for simple fluids using non-uniform nanochannels. Molecular dynamics simulations show that the fluidic diode allowswaterflows in the forward direction and blocksflows in the backward direction in a wide range ofpressuredrops. The unidirectionalwaterflows are owing to the distinct activationpressures in different directions. In the forward (converging) direction, the activationpressure is small because of the relatively low capillarypressure and thewater coalescence at the exit. In the backward direction, the activationpressure is high due to the highinfiltrationpressure. Thepres...
Source: Physics of Fluids - August 31, 2016 Category: Physics Authors: Jingwen Mo, Chu Li, Long Li, Jun Wang and Zhigang Li Source Type: research
An experimental study of the elastic theory for granular flows
This paper reports annular shear cell measurementsgranular flows with an eye towards experimentally confirming theflow regimes laid out in the elastictheory ofgranular flow. Tests were carried out on four different kinds of plastic spherical particles under both constant volumeflows and constant applied stressflows. In particular, observations were made of the new regime in thatmodel, the elastic-inertial regime, and the predicted transitions between the elastic-inertial and both the elastic-quasistatic and pure inertial regimes. (Source: Physics of Fluids)
Source: Physics of Fluids - August 30, 2016 Category: Physics Authors: Tongtong Guo and Charles S. Campbell Source Type: research
Hydrodynamic effects on phase separation morphologies in evaporating thin films of polymer solutions
We examine effects ofhydrodynamics onphase separation morphologies developed during drying ofthin films containing a volatilesolvent and two dissolvedpolymers. Cahn-Hilliard and Flory-Huggins theories are used to describe thefree energy of the phase separating systems. Thethin films, considered as Newtonian fluids, flow in response to Korteweg stresses arising due to concentration non-uniformities that develop duringsolvent evaporation. Numerical simulations are employed to investigate the effects of a Peclet number, defined in terms of system physical properties, as well as the effects of parameters characterizing the spe...
Source: Physics of Fluids - August 29, 2016 Category: Physics Authors: Garyfalia A. Zoumpouli and Stergios G. Yiantsios Source Type: research
Coupled effect of viscosity and density gradients on fingering instabilities of a miscible slice in porous media
Miscible displacements inporous media exhibit interesting spatio-temporal patterns. A deeper understanding of the physical mechanisms of these emergent patterns is relevant in a number of physicochemical processes. Here, we have numerically investigated the instabilities in amiscible slice in verticalporous media. Depending on theviscosity and density gradients at the twointerfaces, four distinct flow configurations are obtained, which are partitioned into two different groups, each containing a pair of equivalent flows until the interaction between the twointerfaces. Ananalysis of the pressure drop around the respective u...
Source: Physics of Fluids - August 26, 2016 Category: Physics Authors: Satyajit Pramanik and Manoranjan Mishra Source Type: research
Mixed-derivative skewness for high Prandtl and Reynolds numbers in homogeneous isotropic turbulence
The mixed-derivative skewnessSu θ of a passivescalar field in high Reynolds and Prandtl numbers decaying homogeneousisotropic turbulence is studied numerically using eddy-damped quasi-normalMarkovian closure, forReλ≥ 103 up toPr = 105. A convergence ofSu θ forPr≥ 103 is observed for any high enoughReynolds number. This asymptotic highPr regime can be interpreted as a saturation of the mixingproperties of theflow at small scales. The decay of the derivative skewnesses from high to lowReynolds numbers and the influence of large scales initial conditions are investigated as well. (Source: Physics of Fluids)
Source: Physics of Fluids - August 25, 2016 Category: Physics Authors: Antoine Briard and Thomas Gomez Source Type: research
