Begell House Inc.
International Journal of Fluid Mechanics Research
FMR
2152-5102
26
1
1999
Direct Simulation of Low-Reynolds Number Supersonic Wall-Shear Layers I: Mean Flow and One-Point Correlations
1-16
Ferhat F.
Hatay
University of Colorado at Boulder, Boulder, Colorado 80309 ; University of Miami, Coral Gables, FL 33124, USA
Sedat
Biringen
University of Colorado at Boulder, Boulder, Colorado 80309
In the present work, a high-speed, wall-shear layer flow in the low-Reynolds-number regime is investigated using the Direct Numerical Simulation (DNS) approach. For this purpose, the three-dimensional, time-dependent, compressible Navier-Stokes equations are numerically integrated by high-order finite-difference methods; no modeling for turbulence is used because the available resolution is sufficient to capture the relevant scales at this Reynolds number. The DNS approach provides a viable means to probe the physics of low-Reynolds number incipient turbulence in compressible flows especially in the near-wall region where measuring difficulties prohibit a detailed experimental description of the flow.
In this paper, the mean flow, root-mean-square, and Fourier power spectrum distributions are presented and parameters that govern the dynamical and computational aspects of the problem are discussed. The analyses of the higher order turbulence statistics such as Reynolds stress budgets and two-point correlations are presented in a companion paper.
Direct Simulation of Low-Reynolds Number Supersonic Wall-Shear Layers II: Statistical Analysis and Energy Budgets
17-35
Ferhat F.
Hatay
University of Colorado at Boulder, Boulder, Colorado 80309 ; University of Miami, Coral Gables, FL 33124, USA
Sedat
Biringen
University of Colorado at Boulder, Boulder, Colorado 80309
In this paper, one- and two-dimensional two-point (double) correlations from an existing data base for a compressible turbulent shear-layer flow are presented and discussed; computational results are compared with incompressible and compressible turbulent boundary layer experiments. Quantitative comparisons are done by using the one-dimensional correlation tensor whereas two-dimensional correlation data are studied qualitatively to establish the similarities and the differences between compressible and incompressible wall-shear layer flows. A key aspect in the direct numerical simulations of turbulent flows, the adequacy of the extent of the computational domain, is also assessed through the inspection of the correlation distributions.
The focus of this work is to explore the paths of energy transfer through which compressible turbulence is sustained. The structural similarities and differences between the incompressible and compressible turbulence are also investigated. The energy flow patterns or energy cascades are found to be directly related to the evolution of vortical structures which are generated in the near-wall region. Near-wall structures, and mechanisms which are not readily accessible through physical experiments are analyzed and their critical role on the evolution and the behavior of the flow is documented extensively.
Passive Control of Circular Jet Spread-Rates with Axially Splined Nozzles
36-48
A. A. S. Arefin
Kabir
Department of Mechanical Engineering, University of South Carolina, Columbia, SC 29208
Sandip
Dutta
Department of Mechanical Engineering, University of South Carolina Columbia, SC 29208
M. A. Taher
Ali
Mechanical Engineering Department, Bangladesh University of Engineering and Technology, Dhaka-1000, Bangladesh
Experimental measurements for the axial development of streamwise velocity and turbulence distributions in the near field of free circular jets issued from splined nozzles are presented. Results include the axial distribution of mean flow and turbulence related quantities of a free circular jet with different nozzle exit conditions. Hot-wire data reveal interesting characteristics on jet spread-rate, shear layer width, and momentum thickness. Observed jet-characteristics are explained on the basis of the velocity and turbulence profiles measured at the nozzle exit. Axial splines at the circumference of the jet nozzle enhance turbulence at the jet circumference boundary layer without significantly changing the nozzle core flow. The boundary layer at the splined jet nozzle exit, i.e., at the start of the free shear layer, increases in thickness due to an increase in turbulence mixing. The addition of splines reduces the jet spread-rate and the growth of shear layer width. It is also observed that splines cause turbulence suppression at downstream locations and this method can be used as a passive control of jets.
Field Conservation Equations for Polydisperse Suspensions
49-71
Yu. A.
Buyevich
CRSS, University of California, Santa Barbara, USA
A formulation of the field conservation equations for incompressible multiphase disperse systems is developed based on volume averaging. The results differ from generally used previous formulations in the representation of the stress fields. The mean stresses that affect mean flow of the dispersed phase components are shown to be completely independent of stresses that influence the continuous phase mean flow. However, the continuous phase stresses determine the interphase interaction forces that appear in all momentum conservation equations. A consistent account of polydispersivity and collisional effects is provided, thus opening the way for proper constitutive formulations, and extensions to more complex situations including compressibility.
Particulate Pressure in Disperse Flow
72-97
S. K.
Kapbasov
Karaganda State University, Karaganda, 470070 Kazakhstan
Yu. A.
Buyevich
CRSS, University of California, Santa Barbara, USA
We develop a model to describe the velocity variance and particulate pressure in fluidized beds, and also in one-dimensional disperse flows. These quantities involve contributions caused by 1) short-scale pseudoturbulent fluctuations of particles in the dense phase of a fluidized bed, and 2) long-scale fluctuations due to macroscopic flow patterns, such as rising bubbles that are practically devoid of particles. Energy comes to the pseudoturbulent fluctuations from the relative motion of the ambient fluid as it interacts with random fluctuations of the dispersion concentration, and also from gravity working at density fluctuations. Inter-particle exchange by momentum and energy is assumed to be carried out by particle collisions, in which case the particles may be approximately treated as statistically independent, and their fluctuations can be regarded as nearly isotropic. The long-scale contributions to velocity variance and particulate pressure are evaluated on the basis of a simple dimensionality consideration. In some dispersion flows, the gas slip velocity may greatly exceed the particle terminal velocity, and consequently, the pseudoturbulent particulate pressure turns out to be much larger than that in a fluidized bed of the same particles at the same concentration. The theoretical conclusions are proven to be in good keeping with all experimental data for fluidized beds available to date.
To the Theory of Rheological Properties of Magnetic Colloids with Chain-Like Aggregates
98-109
A. Yu.
Zubarev
Ural State University, Ekaterinburg, Russia
L. Yu.
Iskakova
Urals State University, Ekaterinburg, Russia
The model of magnetic fluid with chain-like aggregates is suggested. The distribution function of chains with respect to the number of particles is determined for equilibrium system as well as for system under a weak shear flow. The influence of chains on the effective viscosity of magnetic fluid is estimated.