Enstrophy-based proper orthogonal decomposition of flow past rotating cylinder at super-critical rotating rate
Spinning cylinder rotating about its axis experiences a transverse force/lift, an account of this basic aerodynamic phenomenon is known as the Robins-Magnus effect in text books. Prandtl studied thisflow by an inviscid irrotational model and postulated an upper limit of the lift experienced by the cylinder for a critical rotation rate. This non-dimensional rate is the ratio of oncoming free stream speed and the surface speed due to rotation. Prandtl predicted a maximum lift coefficient asCLmax = 4π for the critical rotation rate of two. In recent times, evidences show the violation of this upper limit, as in the experimen...
Source: Physics of Fluids - November 23, 2016 Category: Physics Authors: Tapan K. Sengupta and Atchyut Gullapalli Source Type: research
Lagrangian filtered density function for LES-based stochastic modelling of turbulent particle-laden flows
The Eulerian-Lagrangian approach based on Large-Eddy Simulation (LES) is one of the most promising and viable numerical tools to study particle-laden turbulent flows, when the computational cost of Direct Numerical Simulation (DNS) becomes too expensive. The applicability of this approach is however limited if the effects of the Sub-Grid Scales (SGSs) of the flow on particle dynamics are neglected. In this paper, we propose to take these effects into account by means of a Lagrangian stochastic SGS model for the equations of particle motion. The model extends to particle-laden flows the velocity-filtered density function me...
Source: Physics of Fluids - November 22, 2016 Category: Physics Authors: Alessio Innocenti, Cristian Marchioli and Sergio Chibbaro Source Type: research
On the evolution of flow topology in turbulent Rayleigh-B énard convection
Small-scale dynamics is the spirit ofturbulence physics. It implicates many attributes offlowtopology evolution, coherent structures, hairpin vorticity dynamics, and mechanism of the kinetic energy cascade. In this work, several dynamical aspects of the small-scale motions have been numerically studied in a framework of Rayleigh-B énard convection (RBC). To do so, direct numerical simulations have been carried out at two Rayleigh numbersRa = 108 and 1010, inside an air-filled rectangular cell of aspect ratio unity andπ span-wise open-ended distance. As a main feature, the average rate of the invariants of the velocity gr...
Source: Physics of Fluids - November 22, 2016 Category: Physics Authors: F. Dabbagh, F. X. Trias, A. Gorobets and A. Oliva Source Type: research
Lock-in in forced vibration of a circular cylinder
The phenomenon of lock-in/synchronization in uniformflow past anoscillating cylinder is investigated via a stabilizedfinite element method atRe = 100. Computations are carried out for various amplitudes and frequencies of cylinderoscillation to accurately obtain the boundary of the lock-in regime. Results from earlier studies show a significant scatter in the lock-in boundary. The scatter might be an outcome of the difference in data collection or the use of a different criterion for identifying lock-in. A new criterion for lock-in is proposed, wherein the following two conditions are to be satisfied. (i) The most dominant...
Source: Physics of Fluids - November 21, 2016 Category: Physics Authors: Samvit Kumar, Navrose and Sanjay Mittal Source Type: research
Experimental investigation of interface deformation in free surface flow of concentrated suspensions
We report detailed experiments on quantitativemeasurement of thesurface deformation of concentratedsuspension of non-colloidal particles in openchannel flow. The motion and location of theinterface and the velocity field of the bulkflow beneath thefree surface weremeasured using the particleimagevelocimetry technique. Experiments were performed to study the effect of particle size, particle concentration, andviscosity of suspending fluid on the corrugation. Theinterfacefluctuation was found to increase linearly with theflow rate. The deformation of theinterface increased with increase in particle concentration until an opt...
Source: Physics of Fluids - November 21, 2016 Category: Physics Authors: A. Ashok Kumar, Bhaskar Jyoti Medhi and Anugrah Singh Source Type: research
Small-charge underwater explosion bubble experiments under various boundary conditions
Small-chargeunderwater explosion experiments were performed to investigatebubbles subjected to gravity and variousboundary conditions, including single boundary(free surface and rigid wall boundary), combined boundaries offree surface and solid wall, solid wall boundaries with a circular opening, and resilient wall boundaries. With high speed camera andpressure sensors, the behavior ofexplosionbubbles was studied and features of associatedpressure pulses were analyzed. Detailed image analysis on the final stages ofbubble collapse was carried out and revealed a possible explanation for the weakening ofpressure waves atbubbl...
Source: Physics of Fluids - November 17, 2016 Category: Physics Authors: P. Cui, A. M. Zhang and S. P. Wang Source Type: research
Effects of Taylor-G örtler vortices on turbulent flows in a spanwise-rotating channel
Fully developed turbulent channel flow with system rotation in the spanwise direction has been studied by direct numerical simulation atRem = 2800 and 7000 with 0 ≤Rom≤ 0.5. The width of the computational domain is adjusted for each case to contain two pairs of Taylor-Görtler (TG)vortices. Under a relatively low rotation rate, the turbulent vortical structures are strongly influenced by the TGvortices. A conditional average method is employed to investigate theeffects of these TGvortices on turbulence. In the upwash region where the fluid is pumped away from the pressure wall by the TGvortices, turbulence is found to ...
Source: Physics of Fluids - November 16, 2016 Category: Physics Authors: Yi-Jun Dai, Wei-Xi Huang and Chun-Xiao Xu Source Type: research
The linear stability of swirling vortex rings
Thestability ofvortex rings with an azimuthal component of velocity is investigated numerically for various combinations of ring wavenumber and swirl magnitude. Thevortex rings are equilibrated from an initially Gaussian distribution of azimuthal vorticity and azimuthal velocity, at a circulation-basedReynolds number of 10 000, to a state in which thevortex core is qualitatively identical to that of the piston generatedvortex rings. Theinstability modes of these rings can be characterised as Kelvininstability modes, analogous toinstability modes observed for Gaussian and Batchelorvortex pairs. The shape of an amplified mod...
Source: Physics of Fluids - November 16, 2016 Category: Physics Authors: C. Gargan-Shingles, M. Rudman and K. Ryan Source Type: research
Transition to turbulence by interaction of free-stream and discrete mode perturbations
Mixed mode transition is studied by direct numerical simulation. Low frequency streaks are induced within the boundary layer by free-streamturbulence and an Orr-Sommerfeld discrete mode eigenfunction is introduced at the inlet. Amplitudes are selected such that the interaction of these modes can cause transition. Aside from the highest amplitude of free-streamturbulence, neither disturbance alone is sufficient to cause transition within theflow domain. Results are classified into three routes to transition, depending upon the 2D Tollmien-Schlichting (TS) mode strength and free-streamturbulence intensity. (1) At lowturbulen...
Source: Physics of Fluids - November 16, 2016 Category: Physics Authors: Rikhi Bose and Paul A. Durbin Source Type: research
Extrema of the dynamic pressure in an irrotational regular wave train
We prove that in a regularwave train, which propagates at thesurface of water in irrotational flow over a flat bed, the maximum and minimum of the dynamicpressure occur at thewave crest and at thewave trough, respectively. This result is valid without any restrictions on thewave amplitude. (Source: Physics of Fluids)
Source: Physics of Fluids - November 14, 2016 Category: Physics Authors: A. Constantin Source Type: research
Unsteady solute dispersion in Herschel-Bulkley fluid in a tube with wall absorption
The axial dispersion of solute in a pulsatile flow of Herschel-Bulkley fluid through a straight circular tube is investigated considering absorption/reaction at the tube wall. The solute dispersion process is described by adopting the generalized dispersion model suggested by Sankarasubramanian and Gill [ “Unsteady convective diffusion with interphase mass transfer,” Proc. R. Soc. A333, 115 –132 (1973)]. Firstly the exchange, convection, and dispersion coefficients are determined for small and large time, and then the axial mean concentration of a solute in the tube is determined. The effect of power-law indexl, yiel...
Source: Physics of Fluids - November 14, 2016 Category: Physics Authors: Jyotirmoy Rana and P. V. S. N. Murthy Source Type: research
Internal breather-like wave generation by the second mode solitary wave interaction with a step
The transformation of an internal second mode solitarywave over a bottom step in a computational tank filled with a three-layer stratifiedfluid was studied. The convex waveforms were generated by a collapse mechanism for stratification with a thin mid-layer. Thewave transformation depends on the blocking parameterB which is a ratio of the amplitude of the incidentwave to the thickness of the lower water layer over the step. Three regimes of second modewave transformation over the step are identified. In regime I (2 (Source: Physics of Fluids)
Source: Physics of Fluids - November 11, 2016 Category: Physics Authors: Kateryna Terletska, Kyung Tae Jung, Tatiana Talipova, Vladimir Maderich, Igor Brovchenko and Roger Grimshaw Source Type: research
Effects of Prandtl number on the laminar cross flow past a heated cylinder
Flow past a heated cylinder at constant surface temperature is computationally simulated and analyzed in the laminar regime at moderate buoyancy. The parameters governing theflow dynamics are theReynolds number,Re, the Richardson number,Ri, and the Prandtl number,Pr. We perform our computations in the range 10 ≤Re≤ 35, for which theflow past an unheated cylinder results in a steady separation bubble, and vary the other two parameters in the range 0 ≤Ri≤ 2, 0.25 ≤Pr≤ 100. The heat transfer from the entire cylinder surface, quantified by the average Nusselt numberNuavg, is shown to obeyNuavg = 0.7435Re0.44Pr0.346...
Source: Physics of Fluids - November 11, 2016 Category: Physics Authors: S. Ajith Kumar, Manikandan Mathur, A. Sameen and S. Anil Lal Source Type: research
Linear and nonlinear dynamics of an insoluble surfactant-laden liquid bridge
This paper deals with the linear and nonlineardynamics of an axisymmetric liquid bridge whosefree surface is covered with an insolublesurfactant. In particular, we focus on theeffect of the Marangoni elasticity andsurfaceviscosities, both shear and dilatational. For linear oscillations, both the frequencies and damping rates are calculated and their dependence on thesurfactant properties are elucidated. Nonlineardynamics are considered in the breakage process, taking into account theeffect of thesurfactant properties on the formation of satellitedroplets and thedynamics near pinch-off. In particular, it is seen that Marang...
Source: Physics of Fluids - November 10, 2016 Category: Physics Authors: Alberto Ponce-Torres, Miguel A. Herrada, Jos é M. Montanero and José M. Vega Source Type: research
Numerical studies on the dynamics of two-layer Rayleigh-B énard convection with an infinite Prandtl number and large viscosity contrasts
In this study, theheat transport efficiency of two-layerconvection was evaluated, and the coupling modes between the two layers were directly analyzed using the temperature anomaly and deviatoric stress fields near the interface. Results show that the mechanical coupling mode is dominant in two-layerconvection when the absoluteviscosity contrast between the two layers is sufficiently small, and it weakens, becoming closer to the thermal coupling mode, as the LVLviscosity decreases. This transition from the mechanical coupling to the thermal coupling modes is quantitatively detected even when theviscosity contrast between t...
Source: Physics of Fluids - November 8, 2016 Category: Physics Authors: Masaki Yoshida and Yozo Hamano Source Type: research
