Aspect ratio effect on particle transport in turbulent duct flows
The dynamics of dilute micron-sized spherical inertial particles inturbulentduct flows is studied by means of direct numerical simulations of the carrier phaseturbulence with one-way coupled Lagrangian particles. The geometries are a square and a rectangular duct with width-to-height aspect ratioAR of 3 operating atReτ,c = 360 (based on the centerplane frictionvelocity and duct half-height). The present study is designed to determine theeffect ofturbulence-driven secondarymotion on the particle dynamics. Our results show that a weak cross-flow secondarymotion significantly changes the cross-sectional map of the particle c...
Source: Physics of Fluids - November 8, 2016 Category: Physics Authors: A. Noorani, R. Vinuesa, L. Brandt and P. Schlatter Source Type: research
On the accuracy of RANS simulations with DNS data
Simulation results conducted for incompressible planar wall-bounded turbulent flows with the Reynolds-Averaged Navier-Stokes(RANS)equations with nomodeling involved are presented. Instead, all terms but the moleculardiffusion are represented by the data from direct numerical simulation (DNS). In simulations, the transportequations for velocity moments through the second order (and the fourth order where the data are available) are solved in a zero-pressure gradient boundary layer over a flat plate and in a fully developedchannel flow in a wide range ofReynolds numbers using DNS data from Silleroet al., Lee and Moser, and J...
Source: Physics of Fluids - November 8, 2016 Category: Physics Authors: Svetlana V. Poroseva, Juan D. Colmenares F. and Scott M. Murman Source Type: research
Weakly nonlinear instabilities of a liquid ring
The weakly nonlinear instability of a liquid ring is investigated by perturbation method and illustrates several important features at the early stage of evolution after destabilization. When the centerline maintains circular, the ring would transform into a droplet chain during its shrinkage, but tends to possess some local pinching during the expansion. If there is an additional distortion of the centerline, an evident tendency to protrude spikes, on each of which a droplet may be formed, is predicted. The analysis concentrates on inviscid cases, because the viscosity of ring liquid is proven to merely affect the base st...
Source: Physics of Fluids - November 8, 2016 Category: Physics Authors: Sicheng Zhao and Jianjun Tao Source Type: research
Flows induced by exponential stretching and shearing plate motions
Boundary-layersolutions for theflow induced by an exponentially stretching surface also sheared in its own plane are given. Prior to this study no similaritysolutions have been reported forflows generated by exponentially sheared surfaces concomitant with surface stretching in any form. The method ofsolution is self-similarity. The results found here are intimately related to those of Magyari and Keller [ “Heat and mass transfer in the boundary layers on an exponentially stretching continuous surface,” J. Phys. D: Appl. Phys.32, 577 –585 (1999)] who studied themotion andheat transfer induced by an exponentially stret...
Source: Physics of Fluids - November 8, 2016 Category: Physics Authors: Patrick Weidman Source Type: research
Vortex ring formation in starting forced plumes with negative and positive buoyancy
The limiting process ofvortex ring formation in starting forced plumes, with Richardson number in the range of −0.06 ≤Ri≤ 0.06, was studied numerically under the Boussinesq approximation. The examination of the dynamics of the startingflow evolution reveals that the plume-ambient density difference affects thevortex ring pinch-off mainly through three mechanisms, i.e., the baroclinic production of vorticity, the buoyancyacceleration (or deceleration) on the vortical structures, and its effect on the trailing shear layerinstability. AsRi increases from negative to positive values, three regimes can be identified in te...
Source: Physics of Fluids - November 8, 2016 Category: Physics Authors: L. Gao and S. C. M. Yu Source Type: research
An accelerated stochastic vortex structure method for particle collision and agglomeration in homogeneous turbulence
Modeling the response of interacting particles, droplets, or bubbles to subgrid-scale fluctuations in turbulent flows is a long-standing challenge in multiphase flow simulations using the Reynolds-Averaged Navier-Stokes approach. The problem also arises for large-eddy simulation for sufficiently small values of the Kolmogorov-scale particle Stokes number. This paper expands on a recently proposed stochasticvortex structure(SVS) method formodeling of turbulence fluctuations for colliding or otherwise interacting particles. Anaccelerated version of theSVS method was developed using the fast multipole expansion and local Tayl...
Source: Physics of Fluids - November 8, 2016 Category: Physics Authors: Farzad F. Dizaji and Jeffrey S. Marshall Source Type: research
Dynamics of immiscible liquids in a rotating horizontal cylinder
Thedynamics of aninterface between two immiscibleliquids of different density is studied experimentally in a horizontal cylinder at rotation in the gravity field. Twoliquids entirely fill thecavity volume, and the container is rotated sufficiently fast so that theliquids are centrifuged. The lightliquid forms a column extended along the rotation axis, and the heavyliquid forms an annular layer. Under the action of gravity, the lightliquid column displaces steadily along the radius, downwards in the laboratory frame. As a result,fluid oscillations in thecavity frame are excited at theinterface, which lead to the generation ...
Source: Physics of Fluids - November 8, 2016 Category: Physics Authors: N. V. Kozlov, A. N. Kozlova and D. A. Shuvalova Source Type: research
Self-propelled flexible fin in the wake of a circular cylinder
The behavior of a self-propelled flexible fin behind a circular cylinder in a uniformflow was explored using the immersed boundary method. The transverse heaving motion of the leading edge of the fin was prescribed, whereas the lateral behavior was spontaneously determined by thehydrodynamicinteractions between the fin and the fluid environment. Three different behaviors were observed: propulsion upstream, drift downstream, and holding stationary at an equilibrium position. In a uniformflow, the fin could not overcome the positive netdrag, and it drifted downstream. By contrast, a fin in the wake of a cylinder was propelle...
Source: Physics of Fluids - November 8, 2016 Category: Physics Authors: Sung Goon Park, Boyoung Kim and Hyung Jin Sung Source Type: research
On the separation of multicomponent mixtures in a cylindrical thermogravitational column
This work studies the stationary separation of a multicomponent mixture in a thermogravitational column(TGC). The existing theory for a flat-plate column is extended to the case of a cylindrical column. The equations of motion and heat/mass transfer are written in cylindrical coordinates to take into account the impact of the cylinders curvature and the ratio of their radii on the separation process. To characterize the impact of each component on convective motion induced bythermal diffusion, the dimensionless separation ratios are used. A multicomponent system as a whole is described by the net separation ratio. The appr...
Source: Physics of Fluids - November 7, 2016 Category: Physics Authors: Sofia V. Kozlova and Ilya I. Ryzhkov Source Type: research
Three-dimensional flow field over a trailing-edge serration and implications on broadband noise
The three-dimensionalflow field over the suction side of a NACA 0018 airfoil with trailing-edge serrations was studied by means of time-resolved tomographic particle imagevelocimetry. Meanflow results show that the boundary layer thickness decreases along the streamwise direction with a corresponding reduction of the size of theturbulent structures developing over the suction side of the serrations. At a positive angle of attack, streamwise-oriented and counter-rotatingvortices aligned with the edge of the serrations are found to be the main features of the meanflow field. Their formation is attributed to thepressure imbal...
Source: Physics of Fluids - November 4, 2016 Category: Physics Authors: F. Avallone, S. Pr öbsting and D. Ragni Source Type: research
Linear stability of buoyant convective flow in a vertical channel with internal heat sources and a transverse magnetic field
Linear stability of buoyant convectiveflow of an electrically conductingfluid in a vertical channel owing to internal heat sources has been studied. Theflow takes place in a transverse, horizontalmagnetic field. The results show that up to four different local minima may be present in the neural stability curve. Up to two of these modes may be the most unstable depending, critically, on the value of the Hartmann number. Over a wide range of moderate to high Hartmann numbers, thermal waves dominate theinstability. As the Hartmann number increases, however, this mode is strongly damped. Then the so-called Hartmann mode takes...
Source: Physics of Fluids - November 4, 2016 Category: Physics Authors: A. Hudoba and S. Molokov Source Type: research
Numerical investigation of 3D effects on a 2D-dominated shocked mixing layer
In this study, a 2D perturbation with small-scale, 3D fluctuations is modeled using the hydrodynamics codeMiranda. AMach 1.95 shockwave accelerates a helium-over-SF6interface, similar to the experiments of Motlet al. [ “Experimental validation of a Richtmyer-Meshkov scaling law over large density ratio and shock strength ranges,” Phys. Fluids21(12), 126102 (2009)], to explore the regime where a 2D dominatedflow will experience 3Deffects. We report on thestructure, growth, and mixing of the post-shockedinterface in 2D and 3D. (Source: Physics of Fluids)
Source: Physics of Fluids - November 3, 2016 Category: Physics Authors: Daniel Reese and Christopher Weber Source Type: research
Effects of wing shape, aspect ratio and deviation angle on aerodynamic performance of flapping wings in hover
Thisnumerical study is focused on assessing the effect on theaerodynamic hovering performance of wing shapes defined by the radius of the first moment of the wing area (r1¯) and aspect ratio (AR). In addition, the effect of introducing a deviation angle in thekinematics is examined. The performance ofr1¯=0.43, 0.53, and 0.63 wings with AR of 1.5, 2.96, 4.5, and 6.0 is investigated atReynolds numbers (Re) = 12, 400, and 13 500. The performance trends of the wing shapes have been observed to be independent of Re for both 2-angle and 3-anglekinematics. This is because high suctionpressures associated with the leading-edgevo...
Source: Physics of Fluids - November 2, 2016 Category: Physics Authors: Aamer Shahzad, Fang-Bao Tian, John Young and Joseph C. S. Lai Source Type: research
Turbulence modulation by micro-particles in smooth and rough channels
Inertial micro-particles, dispersed inturbulent flows, are affected by the local dynamics of the carrierflow field. The presence of a relative dilute loading of particles entails some relevant changes in the meanvelocity field. Moreover, the roughness of the solid boundary affects both the carrier and the carried phase dynamics and their mutual interaction. The underlying physics has been exhaustively tackled in the so-called one-way coupling regime, i.e., negligible action of particles onto the fluid, whereas many aspects of the particle back-reaction have been much less investigated and are still poorly understood. Thus ...
Source: Physics of Fluids - November 1, 2016 Category: Physics Authors: M. De Marchis and B. Milici Source Type: research
Formula for growth rate of mixing width applied to Richtmyer-Meshkov instability
This study shows that the derived formula is not only an approach for modeling of the mixing zone width but also a quantitative tool for the study of an RMI-inducedmixing process. This formula is expected to be useful in the analysis of turbulent mixing in the later stages of theRMI process. (Source: Physics of Fluids)
Source: Physics of Fluids - November 1, 2016 Category: Physics Authors: Fujie Gao, Yousheng Zhang, Zhiwei He and Baolin Tian Source Type: research
