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| Author | : Lee Braiden |
| Publisher | : |
| Total Pages | : |
| Release | : 2016 |
| Genre | : |
| ISBN | : |
| Author | : Krasnov, D. |
| Publisher | : KIT Scientific Publishing |
| Total Pages | : 42 |
| Release | : 2016-10-26 |
| Genre | : |
| ISBN | : 3731505622 |
| Author | : Bayode Owolabi |
| Publisher | : Springer |
| Total Pages | : 141 |
| Release | : 2019-05-31 |
| Genre | : Science |
| ISBN | : 303019745X |
This book presents several new findings in the field of turbulent duct flows, which are important for a range of industrial applications. It presents both high-quality experiments and cutting-edge numerical simulations, providing a level of insight and rigour rarely found in PhD theses. The scientific advancements concern the effect of the Earth’s rotation on large duct flows, the experimental confirmation of marginal turbulence in a pressure-driven square duct flow (previously only predicted in simulations), the identification of similar marginal turbulence in wall-driven flows using simulations (for the first time by any means) and, on a separate but related topic, a comprehensive experimental study on the phenomenon of drag reduction via polymer additives in turbulent duct flows. In turn, the work on drag reduction resulted in a correlation that provides a quantitative prediction of drag reduction based on a single, measurable material property of the polymer solution, regardless of the flow geometry or concentration. The first correlation of its kind, it represents an important advancement from both a scientific and practical perspective.
| Author | : O. Pironneau |
| Publisher | : Cambridge University Press |
| Total Pages | : 536 |
| Release | : 1992-07-31 |
| Genre | : Mathematics |
| ISBN | : 9780521416184 |
The workshop concentrated on the following turbulence test cases: T1 Boundary layer in an S-shaped duct; T2 Periodic array of cylinders in a channel; T3 Transition in a boundary layer under the influence of free-stream turbulence; T4 & T5: Axisymmetric confined jet flows.
| Author | : A. Sterl |
| Publisher | : |
| Total Pages | : |
| Release | : 1989 |
| Genre | : |
| ISBN | : |
| Author | : Jiaxin Yan |
| Publisher | : |
| Total Pages | : 0 |
| Release | : 2018 |
| Genre | : |
| ISBN | : |
Direct numerical simulations are performed to investigate turbulent flows in a rectangular duct of aspect ratio varying from 1.0 to 3.0 at a fixed low Reynolds number 150. Persistent secondary flows of Prandtl's second kind are observed in the corners of the ducts. As the aspect ratio increases, streamwise vortices near the top and bottom walls extend towards to the central vertical plane of ducts. Particularly, the displacement of vortex cores near the top/bottom wall can be described as a function of the distance to the sidewall. Detailed analyses of turbulence statistics including the mean flow, turbulent kinetic energy, turbulent intensities, Reynolds stress budgets, and pre-multiplied one-dimensional energy spectrum are conducted to understand the aspect ratio effects on the flow physics. In the duct of aspect ratio 3.0, hairpin flow structures are present in the central regions of the duct, and their characteristics are similar to those exhibited in the plane channel flows. Furthermore, as indicated by the energy spectra, a spanwise quasi-homogeneous region spans over approximately 270 wall units in the central region of the rectangular duct.
| Author | : Herman Branover |
| Publisher | : Halsted Press |
| Total Pages | : 312 |
| Release | : 1978 |
| Genre | : Science |
| ISBN | : |
| Author | : M. Piller |
| Publisher | : |
| Total Pages | : 8 |
| Release | : 2001 |
| Genre | : |
| ISBN | : |
In this paper, we present the results from Direct Numerical Simulations of turbulent, incompressible flow through a square duct, with an imposed temperature difference between two opposite walls, while the other two walls are assumed perfectly insulated. The mean flow is sustained by an imposed, mean pressure gradient. The most interesting feature, characterizing this geometry, consists in the presence of turbulence-sustained mean secondary motions in the cross-flow plane. In this study, we focus on weak turbulence, in that the Reynolds number, based on bulk velocity and hydraulic diameter, is about 4450. Our results indicate that secondary motions do not affect dramatically the global parameters, like friction factor and Nusselt number, in comparison with the plane-channel flow. This issue is investigated by looking at the distribution of the various contributions to the total heat flux, with particular attention to the mean convective term, which does not appear in the plane channel flow.
| Author | : Asmund Huser |
| Publisher | : |
| Total Pages | : 462 |
| Release | : 1992 |
| Genre | : Turbulence |
| ISBN | : |
| Author | : Amar KC |
| Publisher | : |
| Total Pages | : 90 |
| Release | : 2014 |
| Genre | : Darcy's law |
| ISBN | : |
Magnetohydrodynamic (MHD) natural convection in a porous medium with low-magnetic Reynolds number (Re[subscript m]) is investigated in a rectangular cavity with isothermal walls on the left and right and adiabatic walls on the top and bottom. The validity of Darcy's law is addressed for high-Rayleigh number (Ra) flows with high permeability, where the velocity-pressure gradient relationship transitions from linear (i.e. the Darcy law) to nonlinear, due to the fact that the form drag due to solid obstacles is now comparable with the surface drag due to friction, which in turn results in the Darcy-Forchheimer law. In addition, the effect of different magnetic field strengths in terms of Hartmann numbers (Ha) is also investigated for cavities for varying aspect ratios to analyze how the flow and thermal characteristics in a porous medium are influenced by the applied magnetic field. Here, the interaction between the fluid velocity and the electromagnetic forces gives rise to different flow scenarios. In particular, the influence of magnetic field under the varying conditions of convective currents (through Ra) and length scales (through aspect ratios) on quantities such as stream function, temperature and Nusselt number, Nu is studied. Assessment of three regularization-based models and two eddy-viscosity-based subgrid-scale (SGS) turbulence models for large eddy simulations (LES) are carried out for MHD decaying homogeneous turbulence (DHT) and MHD transition to turbulence for the Taylor-Green vortex (TGV) through comparisons to direct numerical simulations (DNS). Simulations are conducted using the low-magnetic Reynolds number approximation (Re[subscript m] “ 1) and the initially-isotropic turbulence problem has a Taylor scale Reynolds number (Re[subscript lambda]) of 120. LES predictions using the Leray-[alpha], LANS-[alpha], and Clark-[alpha] regularization-based SGS models are compared to the classic non-dynamic Smagorinsky and the dynamic Smagorinsky models. Regarding the regularization models, this work represents their first application to MHD decaying turbulence or transition-to-turbulence problems. Analyses of turbulent kinetic energy decay rates, energy spectra, and vorticity fields are made between the varying magnetic field cases. Overall, the regularization models did poorly compared to the eddy-viscosity models for all MHD cases, but the comparisons improved as the magnetic field increase in magnitude.
