Experimental investigation of primary and corner shock boundary layer interactions at mild back pressure ratios
Unstart of rectangular inlets occurs as a result of interactions between shock-induced separation units along the floor/ceiling, corner, and sidewalls. While a significant body of literature exists regarding the individualflow interactions at the inlet floor/ceiling (called primary separation) and sidewalls, limited efforts have focused on the mean and dynamic features of the corner separation. Experiments are conducted to investigate primary and corner shock boundary layer interactions (SBLI) with the objectives of elucidating theflow interactions that occur in the corner, and characterizing the interaction between the co...
Source: Physics of Fluids - August 24, 2016 Category: Physics Authors: M. Funderburk and V. Narayanaswamy Source Type: research
Large eddy simulation of the near-field vortex dynamics in starting square jet transitioning into steady state
Large eddy simulation(LES) is carried out to study thevortex dynamics in the near-field of a starting turbulent squarejet as well as its evolution into a developed steadyjet. Simulations are conducted atReynolds numbers (Re =UjD/υ) of 8000 and 45 000 based on the nozzle hydraulic diameterD andjet velocity (Uj). AReynolds stressmodel was used to simulate the internalflow in the nozzle which provided the inlet conditions for theLES of thejet. To validate the simulations, turbulence statistics are compared with experimental results available for a steady squarejet. Evaluation of the probability density function, skewness, an...
Source: Physics of Fluids - August 23, 2016 Category: Physics Authors: A. Ghasemi, V. Roussinova, R. M. Barron and R. Balachandar Source Type: research
Liquid film flow along a substrate with an asymmetric topography sustained by the thermocapillary effect
We investigateflow in a thinliquid film over a “thick” asymmetric corrugatedsurface in agas-liquid bi-layer system. Using long-wave approximation, we derive a nonlinear evolution equation for the spatiotemporal dynamics of the liquid-gasinterface over the corrugatedtopography. A closed-form expression indicating a non-zero value for aliquidflow rate is derived in a steady state of the system. Through numerical investigations we study the nonlinear dynamics of the liquid-gasinterface with respect to topographical variations of thesolid surface, different thermal properties of theliquid and thesolid, and different values...
Source: Physics of Fluids - August 22, 2016 Category: Physics Authors: Valeri Frumkin and Alexander Oron Source Type: research
Direct numerical simulation of double-diffusive gravity currents
This paper presents three-dimensional direct numerical simulations of laboratory-scale double-diffusive gravitycurrents. Flow is governed by the incompressibleNavier-Stokes equations under the Boussinesq approximation, with salinity and temperature coupled to the equations of motion using a nonlinear approximation to the UNESCO equation of state. The effects of verticalboundary conditions andcurrent volume are examined, with focus on flow pattern development,current propagation speed, three-dimensionalization, dissipation, and stirring and mixing. It was observed that no-slip boundaries cause the gravitycurrent head to tak...
Source: Physics of Fluids - August 19, 2016 Category: Physics Authors: Jared Penney and Marek Stastna Source Type: research
Asymmetric bursting of Taylor bubble in inclined tubes
In the present study, experiments have been reported to explain the phenomenon of approach and collapse of an asymmetric Taylor bubble atfree surface inside an inclined tube. Four different tube inclinations with horizontal (30 °, 45°, 60° and 75°) and two different fluids(water andsilicon oil) are considered for the experiment. Using high speed imaging, we have investigated the approach, puncture, and subsequentliquid drainage for re-establishment of thefree surface. The present study covers all the aspects in the collapse of an asymmetric Taylor bubble through the generation of twofilms, i.e., a capfilm which lies on...
Source: Physics of Fluids - August 19, 2016 Category: Physics Authors: Basanta Kumar Rana, Arup Kumar Das and Prasanta Kumar Das Source Type: research
Studies on dispersive stabilization of porous media flows
Motivated by a need to improve the performance of chemical enhanced oil recovery (EOR) processes, we investigate dispersive effects on the linear stability of three-layerporous mediaflow models of EOR for two different types ofinterfaces: permeable and impermeableinterfaces. Results presented are relevant for the design of smarterinterfaces in the available parameter space of capillary number, Peclet number, longitudinal and transverse dispersion, and theviscous profile of the middle layer. The stabilization capacity of each of these twointerfaces is explored numerically and conditions for complete dispersive stabilization...
Source: Physics of Fluids - August 18, 2016 Category: Physics Authors: Prabir Daripa and Craig Gin Source Type: research
Reflection of cylindrical converging shock wave over a plane wedge
The cylindrical converging shock reflection over a plane wedge is investigated experimentally and numerically in a specially designedshock tube which converts a planar shock into a cylindrical one. When the converging shock is moving along the wedge, both the shock strength and the incident angle are changing, which provides the possibility for the wave transition. The results show that both regular reflection (RR) andMach reflection (MR) are found on the wedge with different initial incident angles. The wave transitions from directMach reflection (DiMR) to inverseMach reflection (InMR) and further to transitioned regular ...
Source: Physics of Fluids - August 18, 2016 Category: Physics Authors: Fu Zhang, Ting Si, Zhigang Zhai, Xisheng Luo, Jiming Yang and Xiyun Lu Source Type: research
Unsteady fluid flow in a slightly curved pipe: A comparative study of a matched asymptotic expansions solution with a single analytical solution
The present work is motivated by the fact that blood flow in the aorta and the main arteries is governed by large finite values of the Womersley numberα and for such values ofα there is not any analytical solution in the literature. The existing numerical solutions, although accurate, give limited information about the factors that affect the flow, whereas an analytical approach has an advantage in that it can provide physical insight to the flow mechanism. Having this in mind, we seek analytical solution to the equations of the fluid flow driven by a sinusoidal pressure gradient in a slightly curved pipe of circular cro...
Source: Physics of Fluids - August 16, 2016 Category: Physics Authors: Gerasimos A. T. Messaris, Maria Hadjinicolaou and George T. Karahalios Source Type: research
Mixing model with multi-particle interactions for Lagrangian simulations of turbulent mixing
We report on the numerical study of the mixing volume model (MVM) for moleculardiffusion inLagrangian simulations of turbulent mixing problems. The MVM is based on the multi-particle interaction in a finite volume (mixing volume).A priori test of the MVM, based on the direct numerical simulations of planarjets, is conducted in the turbulent region and the interfacial layer between the turbulent and non-turbulent fluids. The results show that the MVM predicts well the mean effects of the moleculardiffusion under various numerical and flow parameters. The number of the mixing particles should be large for predicting a value ...
Source: Physics of Fluids - August 16, 2016 Category: Physics Authors: T. Watanabe and K. Nagata Source Type: research
Microscopic origin of self-similarity in granular blast waves
The self-similar expansion of ablast wave, well-studied in air, has peculiar counterparts in dense and dissipative media such as granular gases. Recent results have shown that, while the traditional Taylor-von Neumann-Sedov (TvNS) derivation is not applicable to such granular blasts, they can nevertheless be well understood via a combination of microscopic and hydrodynamic insights. In this article, we provide a detailed analysis of these methods associatingmolecular dynamics simulations and continuum equations, which successfully predict hydrodynamic profiles, scaling properties, and the instability of the self-similar so...
Source: Physics of Fluids - August 16, 2016 Category: Physics Authors: M. Barbier, D. Villamaina and E. Trizac Source Type: research
The Richtmyer-Meshkov instability of a “V” shaped air/helium interface subjected to a weak shock
TheRichtmyer-Meshkov instability of a “V” shaped air/helium gaseousinterface subjected to a weak shock wave is experimentally studied. A soap film technique is adopted to create a “V” shapedinterface with accurate initial conditions. Five kinds of air/helium “V” shapedinterfaces with different vertex angles (60 °, 90°, 120°, 140°, and 160°), i.e., different amplitude-wavelength ratios, are formed to highlight theeffects of initial conditions, especially the initial amplitude, on the flow characteristics. Theinterface morphologies identified by the high-speed schlierenphotography show that a spike is genera...
Source: Physics of Fluids - August 16, 2016 Category: Physics Authors: Zhigang Zhai, Ping Dong, Ting Si and Xisheng Luo Source Type: research
Contribution of velocity-vorticity correlations to the frictional drag in wall-bounded turbulent flows
The relationship between the frictionaldrag and the velocity-vorticity correlations in wall-bounded turbulent flows is derived from the mean vorticity equation. A formula for the skinfriction coefficient is proposed and evaluated with regards to three canonical wall-boundedflows: turbulent boundary layer,turbulent channel flow, andturbulent pipe flow. The frictionaldrag encompasses four terms: advective vorticitytransport,vortex stretching,viscous, and inhomogeneous terms.Drag-reducedchannel flow with the slip condition is used to test the reliability of the formula. The advective vorticitytransport andvortex stretching te...
Source: Physics of Fluids - August 16, 2016 Category: Physics Authors: Min Yoon, Junsun Ahn, Jinyul Hwang and Hyung Jin Sung Source Type: research
Direct numerical simulation of a particle attachment to an immersed bubble
A numerical extension of the “smooth profile method” is presently suggested to simulate the attachment of acolloidal particle to the surface of an immersed bubble. In this approach, the two fluid-particle boundaries and thefluidic boundary are replaced with diffuseinterfaces. The method is tested under various capillary numbers. Upon attachment to a stable bubble, it is found that the method is capable of reproducing the three microprocesses associated with the particle attachment. The change in the trajectory as the particle approaches thefluidicinterface, the collision process, and the sliding down the bubble surface...
Source: Physics of Fluids - August 11, 2016 Category: Physics Authors: Gregory Lecrivain, Ryoichi Yamamoto, Uwe Hampel and Takashi Taniguchi Source Type: research
A law of the wall for turbulent boundary layers with suction: Stevenson ’s formula revisited
Theturbulent velocity field in theviscous sublayer of the boundary layer with suction to a first approximation is homogeneous in any direction parallel to the wall and is determined by only three constant quantities — the wall shear stress, the suction velocity, and the fluidviscosity. This means that there exists a finite algebraic relation between theturbulent shear stress and the longitudinal mean-velocity gradient, using which as a closure condition for theequations of motion, we establish an exact asymptotic behavior of the velocity profile at the outer edge of theviscous sublayer. The obtained relationship provides...
Source: Physics of Fluids - August 10, 2016 Category: Physics Authors: Igor Vigdorovich Source Type: research
Cross-diffusion-driven gravitational instability in a Hele-Shaw cell saturated with a ternary solution
The effect of cross diffusion on the onset of the gravitational instabilities in a Hele-Shaw cell saturated with a ternary solution is analyzed. Based on the linear stability theory, new stability equations are derived in the global domain and then transformed into the similar domain. These stability equations are solved by employing various methods such as an initial value problem approach and quasi-steady state approximations (QSSA ’s). Through the initial growth rate analysis without the QSSA, we prove that initially the system is unconditionally stable. However, the QSSA in the global domain showed that the system ca...
Source: Physics of Fluids - August 9, 2016 Category: Physics Authors: Min Chan Kim and Kwang Ho Song Source Type: research
