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Physics of Fluids Collection


 
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Physics of Fluids : Characteristics of cylindrical flame accelerat...

By: Kuo-Long Pan and Roman Fursenko

Description: We have studied the outward propagation of a cylindrical flame by means of a flame-tracking numerical method and direct computation of the Sivashinsky equation. The flame speed is modified by the local curvature, via a Markstein length ℓ, that somehow groups the complicated physiochemical effects and can be monotonically relevant to the system pressure. The flame is found to accelerate in a universal profile as a function of time, which is insensitive to ini...

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Physics of Fluids : The controlled relaminarization of low velocit...

By: G. M. G. Watson and L. W. Sigurdson

Description: The controlled suppression of instabilities, or “relaminarization,” in low velocity ratio and Reynolds number elevated jets-in-crossflow (JICFs) is discussed for jet-to-crossflow velocity ratios (R) less than 1.5 and jet Reynolds numbers (Red) less than 2000. The principal control method is via a synthetic jet from an annular slit coaxially surrounding the jet flow. Effects of forcing the JICF jet shear layer are studied using photographs obtained by smoke f...

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Physics of Fluids : Weakly nonlinear stability analysis of a flow ...

By: Paresh Chokshi and V. Kumaran

Description: The finite amplitude stability of a plane Couette flow over a deformable solid medium is analyzed with emphasis on the class of high Reynolds number (Re) modes, referred to as the wall modes, for which the viscous stresses are confined to a thin layer adjacent to the fluid-solid interface with thickness O(Re−1/3) times the channel width in the limit Re⪢1. Here, the Reynolds number is defined in terms of the top plate velocity V and the channel width R. Previ...

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Physics of Fluids : High-order large-eddy simulation of flow over ...

By: M. Minguez, R. Pasquetti, and E. Serre

Description: The structure of the turbulent flow over a simplified automotive model, the Ahmed body ( S. R. Ahmed and G. Ramm, SAE Paper No. 8403001, 1984 ) with a 25° slanted back face, is investigated using high-order large-eddy simulations (LESs) at Reynolds number Re = 768 000. The numerical approach is carried out with a multidomain spectral Chebyshev–Fourier solver and the bluff body is modeled with a pseudopenalization method. The LES capability is implemented tha...

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Physics of Fluids : Experimental investigation of turbulent diffus...

By: Balaji Gopalan, Edwin Malkiel, and Joseph Katz

Description: High-speed inline digital holographic cinematography is used for studying turbulent diffusion of slightly buoyant 0.5–1.2 mm diameter diesel droplets and 50 μm diameter neutral density particles. Experiments are performed in a 50×50×70 mm3 sample volume in a controlled, nearly isotropic turbulence facility, which is characterized by two dimensional particle image velocimetry. An automated tracking program has been used for measuring velocity time history of ...

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Physics of Fluids : Favorable pressure gradient turbulent flow ove...

By: Mark F. Tachie and Mohammad K. Shah

Description: This paper reports on experimental study of turbulent flows over straight and inclined transverse ribs of square and triangular cross sections attached to the bottom and top walls of an asymmetric converging channel. The pitch-to-height ratio of the ribs was 10. A particle image velocimetry technique was used to conduct extensive velocity measurements at channel midspan and in planes close to the leading and trailing edges of the inclined ribs. From these me...

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Physics of Fluids : Modeling inertial particle acceleration statis...

By: S. Ayyalasomayajula, Z. Warhaft, and L. R. Collins

Description: Our objective is to explain recent Lagrangian acceleration measurements of inertial particles in decaying, nearly isotropic turbulence [ Ayyalasomayajula et al., Phys. Rev. Lett. 97, 144507 (2006) ]. These experiments showed that as particle inertial effects increased, the variance in the particle acceleration fluctuations was reduced, and the tails of the normalized particle acceleration probability density function (PDF) became systematically attenuated. W...

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Physics of Fluids : Magnetohydrodynamic turbulence in a channel wi...

By: Dmitry Krasnov, Oleg Zikanov, Jörg Schumacher, and Thomas Boeck

Description: The effect of a uniform spanwise magnetic field on a turbulent channel flow is investigated for the case of a low magnetic Reynolds number. Direct numerical simulation (DNS) and large eddy simulation (LES) computations are performed for two values of the hydrodynamic Reynolds number (104 and 2×104) and with the Hartmann number varying in a wide range. It is shown that the main effect of the magnetic field is the suppression of turbulent velocity fluctuations...

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Physics of Fluids : Direct numerical simulation and Lagrangian mod...

By: Brian L. Sawford and Stephen M. de Bruyn Kops

Description: Direct numerical simulation (DNS) results are presented for the joint statistics of two inhomogeneous scalar fields, one due to a mixing layer source and the other due to a contiguous top-hat source. These two sources form the basis for all scalar mixing across three streams. The results are used to assess the performance of a Lagrangian stochastic modeling system incorporating the interaction with the conditional mean mixing model at two different times: A ...

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Physics of Fluids : Numerical study of an original device to gener...

By: J. Giordano, J. D. Parisse, and P. Perrier

Description: This study is devoted to the design of an experimental device to generate shock waves in a micropipe. Indeed, the recent advances in the microfluidics of gas lead the scientific community to the question of scaling law in supersonic regime. Thus, in this paper, we simulate the flow induced by the opening of a small solenoid valve to know if it is able to generate a minishock wave. This shock wave moving in an intermediate pipe could be transmitted into a mic...

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Physics of Fluids : Large amplitude internal solitary waves in a t...

By: Arnaud Goullet and Wooyoung Choi

Description: We study large amplitude internal solitary waves in a two-layer system where each layer has a constant buoyancy frequency (or Brunt–Väisälä frequency). The strongly nonlinear model originally derived by Voronovich [J. Fluid Mech. 474, 85 (2003) ] under the long wave assumption for a density profile discontinuous across the interface is modified for continuous density stratification. For a wide range of depth and buoyancy frequency ratios, the solitary wave s...

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Physics of Fluids : The Rossby-inertia-buoyancy instability in bar...

By: Daniel Hodyss and David S. Nolan

Description: The behavior of vortex Rossby (VR) waves undergoing inertia-buoyancy (IB) wave emission on vortices with baroclinic vertical structures is studied. We consider monotonic vortices, where the potential vorticity (PV) decays monotonically with radial distance from the vortex center, and “single-peak” vortices, where the PV reaches a single radial maximum off the vortex center. A linear anelastic model is numerically solved as an eigenvalue problem. The differen...

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Physics of Fluids : Unsteady flow separation on slip boundaries

By: Francois Lekien and George Haller

Description: We derive analytic criteria for the location and angle of unsteady particle separation and reattachment in two-dimensional flows with free-slip boundary conditions. Our wall-based criteria show that, in general, fluid breakaway from the boundary takes place at locations different from either instantaneous or averaged stagnation points. Indeed, for time-varying flows, separation does not occur along a free streamline or along an average free streamline. We ap...

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Physics of Fluids : Numerical study of the Guderley and Vasilev re...

By: Andrea Defina, Francesca Maria Susin, and Daniele Pietro Viero

Description: We present high-resolution numerical solutions of the depth-averaged two-dimensional inviscid shallow water equations which provide new information on shock reflection configuration within the von Neumann paradox conditions. The computed flow field and shock wave patterns close to the triple point for the Guderley and the Vasilev reflections confirm the four-wave theory. We suggest that the most likely Guderley reflection model is a four-wave pattern with a ...

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Physics of Fluids : Elastic molecular collision models for quantum...

By: Hiroaki Matsumoto

Description: Elastic molecular collision models for Monte Carlo simulation of rarefied gas flow, such as the variable hard sphere (VHS), variable soft sphere (VSS), and variable sphere (VS) molecular models, were extended to quantum mechanical scattering, and then applied to the simulation of spherical expansion of 4He. The profiles of number density, flow velocity, and parallel and perpendicular kinetic temperatures obtained with the VHS, VSS, and VS models were in good...

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Physics of Fluids : Natural convection in enclosures with partiall...

By: P. Kandaswamy, N. Nithyadevi, and C. O. Ng

Description: Unsteady laminar natural convection in an enclosure with partially thermally active side walls and internal heat generation is studied numerically. Thermally inactive parts of the side walls and horizontal walls are thermally insulated. The governing equations are solved using the control volume method with a power law scheme. Nine different combinations of the hot and cold thermally active zones are considered. The effects of heat generations, aspect ratios...

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