Application of UVP within Porous Beds

Standard measurement devices do not normally provide detailed information about flows in porous media because either they are too intrusive (e.g., hot/film wire anemometers) or because the solid phase impedes their physical access to the flow as in the case of laser Doppler anemometers or particle image velocimetry (PIV). In this study, a Metflow ultrasonic velocity profiler (UVP) is used to measure instantaneous velocity fields within porous media composed of plastic balls packed in a cubic pattern. Simple considerations of the ultrasound beam properties and propagation, plus a comparison with measurements performed by a PIV system, demonstrate that UVP devices are suitable for such a purpose.     

MICROMIXING AND FAST REACTION IN THE CORE OF TURBULENT PIPE FLOW

Most work on micromixing within the last decade has considered stirred tank reactors. Here the core region of turbulent flow in a pipe is studied experimentally and theoretically. A neutralization as well as the azo coupling between 1-naphthol and diazotised sulphanilic acid were conducted in the core and, combined with a micromixing model, led to local rates of turbulent energy dissipation. These were compared with values available in the literature and determined from physical measurements. The chemically determined values were somewhat greater, possibly due to the radial movement of the reagents from the centre line and additional turbulence generated by the feed pipe. Nevertheless Eq. (11) should apply to micromixing in the core. Total average rates of energy dissipation greatly exceeded the turbulent rates in the core.     

A computational study of annular cascade flows using aq-ω turbulence model with a wall function

A computational code has been developed for steady viscous flows in three dimensional annular cascades. This code solves a special form of the thin-layer Navier-Stokes equations with a two-equationq-ω turbulence model in curvilinear coordinates using a time asymptotic method for steady state solutions. It employs a scalar implicit approximate factorization in time and a finite volume formulation with second-order upwind-differencing in space. A wall function treatment is implemented at solid boundaries for turbulence equations instead of integration to the wall to relieve gridding requirements. In order to validate the effectiveness of this code, computational studies have been made to access modeling capability for complex turbulent flow fields in three dimensional annular cascade geometries which typically include laminar-turbulent boundary layer transition. The results have been compared with both the computational studies with integration to the wall and the experimental studies. The wall function treatment was found to be reliable by predicting secondary flows and loss contours reasonably well.     

Mean-field/PDF numerical approach for polydispersed turbulent two-phase flows

The purpose of this paper is to give an overview in the realm of numerical computations of polydispersed turbulent two-phase flows, using a mean-field/PDF approach. In this approach, the numerical solution is obtained by resorting to a hybrid method, where the mean fluid properties are computed by solving mean-field (RANS) equations with a classical finite volume procedure whereas the local instantaneous properties of the particles are determined by solving stochastic differential equations (SDEs). The fundamentals of the general formalism are recalled and particular attention is focused on a specific theoretical issue: the treatment of the multiscale character of the dynamics of the discrete particles, i.e. the consistency of the system of SDEs in asymptotic cases. Then, the main lines of the particle/mesh algorithm are given and some specific problems, related to the integration of the SDEs, are discussed, for example, issues related to the specificity of the treatment of the averaging and projection operators, the time integration of the SDEs (weak numerical schemes consistent with all asymptotic cases), and the computation of the source terms. Practical simulations, for three different flows, are performed in order to demonstrate the ability of both the models and the numericals to cope with the stringent specificities of polydispersed turbulent two-phase flows.     

确定高速速度系数β的方法及其相关经验公式

针对高速流动的气进达西流动的问题，提出确定高速速度系数和方法。方法利用青海气田气井单层测试的不稳定与稳定试井资料，建立高速速度系数与有效渗透率的相关经验公式，并进行了相关公式的推导。结论：与国外普遍采用的公式相比，该公式具有更好的代表性和可靠性。     

气吹电弧介质恢复强度的数值计算

本文在电弧轴对称及局部热力学平衡条件下,建立了气吹电弧二维(r,z)非定常电弧数学模型。在考虑紊流效应时,选用3K-ε双方程紊流模型。计算结果给出电流过零后0～300μ3时间内电弧温度的恢复特性,并由此计算出电流过零后弧隙间介质强度的恢复特性。此计算结果与实验测量结果基本吻合。     

Analysis and approximation of a fractional Laplacian-based closure model for turbulent flows and its connection to Richardson pair dispersion

We study a turbulence closure model in which the fractional Laplacian ${(?\Delta )}^{\alpha }$ of the velocity field represents the turbulence diffusivity. We investigate the energy spectrum of the model by applying Pao’s energy transfer theory. For the case $\alpha =1∕3$, the corresponding power law of the energy spectrum in the inertial range has a correction exponent on the regular Kolmogorov $?5∕3$ scaling exponent. For this case, this model represents Richardson’s particle pair-distance superdiffusion of a fully developed homogeneous turbulent flow as well as Lévy jumps that lead to the superdiffusion. For other values of $\alpha$, the power law of the energy spectrum is consistent with the regular Kolmogorov $?5∕3$ scaling exponent. We also propose and study a modular time-stepping algorithm in semi-discretized form. The algorithm is minimally intrusive to a given legacy code for solving Navier–Stokes equations by decoupling the local part and nonlocal part of the equations for the unknowns. We prove the algorithm is first-order accurate and unconditionally stable. We also derive error estimates for full discretizations of the model which, in addition to the time stepping algorithm, involves a finite element spatial discretization and a domain truncation approximation to the range of the fractional Laplacian.     

Investigation of Turbulence Effects on the Aeroelastic Properties of a Truss Bridge Deck Section

This paper presents the flutter derivatives (FDs) extracted from a stochastic system identification (SSI) method under different turbulent flows. The objective of the study is to investigate the effects of oncoming turbulence on the flutter of suspended long-span bridges using a section model wind-tunnel test. Several wind-tunnel tests were performed on a truss bridge deck section with different oncoming turbulent properties involving reduced turbulence intensities and turbulent scales. This study includes an investigation of the effect of oncoming flows on modal dynamic responses. The transient and buffeting response data from the wind-tunnel test are analyzed using the system identification technique in extracting FDs, and the difficulties involved in this method are discussed. The time-domain SSI is applied to extract all FDs simultaneously from one and two degree-of-freedom (1DOF and 2DOF) systems. Finally, the results under different conditions are discussed and conclusions are formed.     

电控盒防水与导风结构优化的仿真研究

空调室外机,尤其是变频空调,其电控盒的结构上往往存在要解决腔体发热以及防止淋雨破坏的双重难题.本文采用仿真软件对不同结构的电控盒进行建模和数值模拟计算,分析并对电控盒的结构进行优化设计改进方向.     

Quality of CFD models for jet flow analysis for the design of burners and boilers

CFD models are increasingly used for the design and optimisation of boiler combustion chambers. Numerous commercial codes are available, and the user is confronted with making a proper choice for a particular application. In this paper, the accuracy and effectiveness of the popular code FLUENT™ is investigated in terms of the different turbulence models and numerical schemes that are bundled in the software. The tests are performed for different simple experiments, involving classical hydrodynamic conditions with no combustion. The conclusion of these tests involves also the additional criterion of the computational time required for achieving a reasonable accuracy.