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1.
在预应力钢筋上连续包裹一层缓凝砂浆是新型缓粘结预应力混凝土体系得以工程应用的关键。为了弄清包覆过程,了解物料性能、加工条件和螺杆参数等输入变量对包覆输出结果的影响,基于缓凝预应力筋包覆试验,运用Polyflow软件,对宾汉姆体的缓凝砂浆在螺旋槽内流动和变形情况进行CFD(computational fluid dynamics)模拟。得到了可视化的速度场和剪切速率场,模拟了分析螺杆转速、螺杆几何参数对物料流变特性的影响。模拟结果可视,且直观地验证了包覆试验现象,揭示了包覆机理,为包覆装置可靠作业和结构优化提供了理论依据。 相似文献
2.
This study is conducted to investigate the Bingham—Papanastasiou fluid flow driven by a rotating infinite disk. The Bingham—Papanastasiou model is a modification of the Bingham plastic model, which is developed by introducing a continuation parameter to overcome its discontinuity. The von K´armán similarity solution is used to transform the flow equations from ordinary differential equations to a nonlinear system of partial differential equations, which is solved numerically. The effect of the Bingham flow parameters on the radial, tangential, and axial velocities, pressure, and radial and tangential skin friction coefficients is discussed. 相似文献
3.
P. Balakumar 《Theoretical and Computational Fluid Dynamics》1997,9(2):103-119
Two-dimensional nonlinear equilibrium solutions for the plane Poiseuille–Couette flow are computed by directly solving the
full Navier–Stokes equations as a nonlinear eigenvalue problem. The equations are solved using the two-point fourth-order
compact scheme and the Newton–Raphson iteration technique. The linear eigenvalue computations show that the combined Poiseuille–Couette
flow is stable at all Reynolds numbers when the Couette velocity component σ2 exceeds 0.34552. Starting with the neutral solution for the plane Poiseuille flow, the nonlinear neutral surfaces for the
combined Poiseuille–Couette flow were mapped out by gradually increasing the velocity component σ2. It is found that, for small σ2, the neutral surfaces stay in the same family as that for the plane Poiseuille flow, and the nonlinear critical Reynolds
number gradually increases with increasing σ2. When the Couette velocity component is increased further, the neutral curve deviates from that for the Poiseuille flow with
an appearance of a new loop at low wave numbers and at very low energy. By gradually increasing the σ2 values at a constant Reynolds number, the nonlinear critical Reynolds numbers were determined as a function of σ2. The results show that the nonlinear neutral curve is similar in shape to a linear case. The critical Reynolds number increases
slowly up to σ2∼ 0.2 and remains constant until σ2∼ 0.58. Beyond σ2 > 0.59, the critical Reynolds number increases sharply. From the computed results it is concluded that two-dimensional nonlinear
equilibrium solutions do not exist beyond a critical σ2 value of about 0.59.
Received: 26 November 1996 and accepted 12 May 1997 相似文献
4.
离心泵叶轮内宾汉流体湍流流场的数值计算 总被引:8,自引:0,他引:8
考虑宾汉流体本构关系特点,建立了任意曲线坐标系(ζ,η)下宾汉流体湍流流动的基本方程,应用压力加权校正算法,实现了速度场和压力场的关联,采用交错网格技术,解决了非物理压力振荡问题,在此基础上,对离心泵叶轮内回转面上宾汉流体湍流流动进行了数值模拟,并分析探讨了离心泵叶轮内宾汉流体湍流流动机理。 相似文献
5.
Large-eddy simulation (LES) results for laminar-to-turbulent transition in a spatially developing boundary layer are presented.
The disturbances are ingested into a laminar flow through an unsteady suction-and-blowing strip. The filtered, three-dimensional
time-dependent Navier–Stokes equations are integrated numerically using spectral, high-order finite-differences, and a three-stage
low-storage Runge–Kutta/Crank–Nicolson time-advancement method. The buffer-domain technique is used for the outflow boundary
condition. The localized dynamic model used to parametrize the subgrid-scale (SGS) stresses begins to have a significant impact
at the beginning of the nonlinear transition (or intermittency) region. The flow structures commonly found in experiments
are also observed in the present simulation; the computed linear instability modes and secondary instability $\Lambda$-vortex
structures are in agreement with the experiments, and the streak-like structures and turbulent statistics compare with both
the experiments and the theory. The physics captured in the present LES are consistent with the experiments and the full Navier–Stokes
simulation (DNS), at a significant fraction of the DNS cost. A comparison of the results obtained with several SGS models
shows that the localized model gives accurate results both in a statistical sense and in terms of predicting the dynamics
of the energy-carrying eddies, while requiring fewer ad hoc adjustments than the other models.
Received: 5 April 1996 and accepted 27 March 相似文献
6.
We present an analytical solution of axisymmetric motion for a Bingham fluid initially at rest subjected to a constant pressure gradient applied suddenly. Using the Laplace transform, we obtain expressions which allow the calculation of the instantaneous velocity, plug radius and rate of flow as a function of time. We also give a relation for the shear stress in the plug and in the region where the behaviour of the fluid is Newtonian. 相似文献
7.
在交错网格中用MAC方法求解二维不可压N S方程 ,对圆截面液柱与固壁、液面斜撞击问题进行了数值模拟 ,得到了自由面随时间演化的图像。主要考察了 :(1)固壁和液面 ;(2 )牛顿、非牛顿流体 ;(3)碰撞入射角 ;(4 )Bingham流体近似本构式中参数q0 、K对计算结果的影响。结果表明 :液柱与液面碰撞形成的自由面更复杂。碰撞初期 ,Bingham流体和水的自由面相似 ;但碰撞后期 ,Bingham流体的自由面相对简单。对液柱与液面碰撞自由面的影响较大。本文条件下 ,当K 2 0时 ,K对自由面的影响不大 ;当q0 增大时 ,自由面变得相对简单。 相似文献
8.
9.
The issue of turbine lifetime is an important one, particularly for modern turbines operating at high temperature regimes. A cooling design such as ribs may achieve an improved lifetime and complex mechanisms of heat transfer need to be well studied. In this paper, a Direct Numerical Simulation (DNS) is presented for a 3-D channel flow with two square ribs on the lower wall. The full unsteady compressible Navier-Stokes equations are solved with an original hybrid finite difference/finite element scheme. The Reynolds number of the simulation is 7 000 based on the bulk velocity at the inlet and the channel height. The present study is mainly devoted to understand the mechanism of heat transfer at the wall through the topological analysis of the flow and the temperature flux. Results show that the large-scale structures generated by obstacles splash onto the lower surface and induce longitudinal vortices which enhance heat transfer at the wall. A comprehensive data base including 56 correlations was set up for testing and improving turbulence models for this complex, separated flow. 相似文献
10.
Counter-current flow occurs in many reservoir processes and it is important to understand and model these processes in order to operate them effectively. Both drainage and imbibition processes exist simultaneously during counter-current flow. It has thus proven difficult to model this type of flow using conventional techniques because of the impossibility of assigning a single capillary pressure curve applicable over the entire sample. In the current paper, a new saturation-history-dependent approach has been developed to simulate a counter-current flow experiment done with an X-ray CT scanner. Hysteresis in both capillary pressure and relative permeabilities is considered during simulation. Capillary hysteresis loop and relative permeabilities are extracted through history matching and a family of scanning curves is constructed connecting the two branches of the capillary hysteresis loop. Each gridblock of the sample is assigned a different scanning curve according to the local saturation history. History-dependent modeling of the experiment reproduced two-dimensional saturation distributions over time with good accuracy, which cannot be obtained with traditional simulation using only one capillary pressure curve. 相似文献
11.
12.
A direct numerical simulation (DNS) of a recirculating, swirling flow is performed at a Reynolds number of 5000. Detailed
one and two point statistics are presented in this paper. Flow visualization and frequency analysis are used to identify a
precessing vortex core and to characterize its position, extent and influence on the flow field. The results are compared
with laser Doppler velocimetry (LDV) measurements as well as large eddy simulation (LES) data reported in the literature.
The present work constitutes a first step in setting up a DNS data base for complex flows. 相似文献
13.
Georgios C. Florides Andreas N. Alexandrou Georgios C. Georgiou 《ournal of non Newtonian Fluid Mechanics》2007
The flow and shape evolution during the compression of a finite amount of a Bingham plastic is investigated by means of numerical simulations. The problem relates to the popular compression test used for the rheological characterization of non-Newtonian fluids. The flow is modelled in Lagrangian coordinates using the Papanastasiou regularization for the Bingham plastic and a mixed-Galerkin finite element method. Simulations have been performed for compression under both constant load and constant velocity. Results for various Reynolds and Bingham numbers are presented and discussed. 相似文献
14.
把界面捕捉等效方程、Level-Set方程和欧拉方程组耦合,在Stiffened状态方程下,采用高分辨率NND格式求解流体力学方程组并用Level-Set函数捕捉界面的位置。对二维情况下激波和气泡相互作用的问题进行数值模拟,并与波传算法的模拟结果进行比较。计算结果表明该方法能有效的抑制间断附近的非物理振荡,有很强的捕捉界面的能力。 相似文献
15.
16.
In this paper we consider a fully developed turbulent flow in a round pipe with a small inner annulus. The diameter of the
inner annulus is less than 10% of the diameter of the outer pipe. As a consequence, the surface area of the inner pipe compared
to the outer pipe is small. The friction exerted by the wall on the flow is proportional to the surface area and the wall
shear stress. Due to the small surface area of the inner annulus the additional stress on the flow due to the presence of
the annulus may expected to be negligible. However, it will be shown that the inner annulus drastically changes the flow patterns
and gives rise to unexpected scaling properties. In previous studies (Chung et al., Int J Heat Fluid Flow 23:426–440, 2002; Churchill and Chan, AIChE J 41:2513–2521, 1995) it was argued that radial position of the point of zero shear stress does not coincide with the radial location of the point
of maximum axial velocity. In our direct numerical simulations we observe a coincidence of these points within the numerical
accuracy of our model. It is shown that the velocity profile close to the inner annulus is logarithmic. 相似文献
17.
18.
In this paper we report on a fourth-order, spectro-consistent simulation of a complex turbulent flow. A spatial discretization of a convection-diffusion equation is termed spectro-consistent if the spectral properties of the convective and diffusive operators are preserved, i.e. convection skew-symmetric; diffusion symmetric positive definite. We consider a fully developed flow in a channel, where a matrix of cubes is placed at a wall of the channel. The Reynolds number (based on the channel width and the mean bulk velocity) is equal to Re = 13,000. The three-dimensional flow around the surface mounted cubes has served at a test case at the 6th ERCOFTAC/IAHR/COST workshop on refined flow modeling (Delft, June 1997). Here, mean velocity profiles as well as Reynolds stresses at various locations in the channel have been computed without using any turbulence models. The results agree well with the available experimental data. 相似文献
19.
Numerical Simulation of Ferrofluid Flow for Subsurface Environmental Engineering Applications 总被引:3,自引:0,他引:3
Oldenburg Curtis M. Borglin Sharon E. Moridis George J. 《Transport in Porous Media》2000,38(3):319-344
Ferrofluids are suspensions of magnetic particles of diameter approximately 10nm stabilized by surfactants in carrier liquids. The large magnetic susceptibility of ferrofluids allows the mobilization of ferrofluid through permeable rock and soil by the application of strong external magnetic fields. We have developed simulation capabilities for both miscible and immiscible conceptualizations of ferrofluid flow through porous media in response to magnetic forces arising from the magnetic field of a rectangular permanent magnet. The flow of ferrofluid is caused by the magnetization of the particles and their attraction toward a magnet, regardless of the orientation of the magnet. The steps involved in calculating the flow of ferrofluid are (1) calculation of the external magnetic field, (2) calculation of the gradient of the external magnetic field, (3) calculation of the magnetization of the ferrofluid, and (4) assembly of the magnetic body force term and addition of this term to the standard pressure gradient and gravity force terms. We compare numerical simulations to laboratory measurements of the magnetic field, fluid pressures, and the twodimensional flow of ferrofluid to demonstrate the applicability of the methods coded in the numerical simulators. We present an example of the use of the simulator for a fieldscale application of ferrofluids for barrier verification. 相似文献
20.
The transitional turbulent regime in confined flow between a rotating and a stationary disc is studied using direct numerical
simulation. Besides its fundamental importance as a three-dimensional prototype flow, such flows frequently arise in many
industrial devices, especially in turbomachinary applications. The present contribution extends the DNS simulation into the
turbulent flow regime, to a rotational Reynolds number Re =3 × 105. An annular rotor-stator cavity of radial extension ΔR and height H, is considered with L = 4.72(L = ΔR/H) and Rm = 2.33 (Rm = (R
1+ R
0)/ΔR). The direct numerical simulation is performed by integrating the time-dependent Navier–Stokes equations until a statistically
steady state is reached. A three-dimensional spectral method is used with the aim of providing both very accurate instantaneous
fields and reliable statistical data. The instantaneous quantities are analysed in order to enhance our knowledge of the physics
of turbulent rotating flows. Also, the results have been averaged so as to provide target turbulence data for any subsequent
modelling attempts at reproducing the flow.
This revised version was published online in July 2006 with corrections to the Cover Date. 相似文献