A low shear rate turbulent flow apparatus

This paper describes some experiments on a turbulent flow viscometer consisting of a continuous pipe loop of transparent material mounted on a circular wheel. The wheel is partially filled with fluid and rotated at a constant speed. The results show that the apparatus gives sensible results and although only a limited range of Reynolds numbers is possible it can be used as a useful qualitative apparatus to test dilute fluids which have abnormal turbulent flow properties.     

Stochastic calibration of sensors in turbulent flow fields

The calibration of high-bandwidth sensors is typically carried out in an steady environment or at least a well-controlled unsteady flow. A simple technique for calibration of sensors in flow fields with arbitrary unsteadiness (such as a turbulent field) is described. Although the method requires a DC reference measurement at each calibration point, the resulting calibration is accurate for both average and unsteady measurements up to the full bandwidth of the sensor. Applications and limitations of the technique are also discussed.This work is supported by AFOSR grant F49620-93-1-0194, monitored by Dr. J. McMichael and ONR grant N00014-92-J-1918, monitored by Dr. L.P. Purtel. The author gratefully acknowledges helpful discussions with Olivier Piepsz, Ruben Rathnasingham and Bill George.     

An apparatus for studying periodic plasma

Summary The apparatus described permits Langmuir probe theory to be applied to the plasma of any periodic gas discharge. Examples of applications to the study of mercury arc rectifiers are given.     

An upwind compact mpact approach with group velocity control for compressible flow fields

In this paper we construct an upwind compact finite difference scheme with group velocity control for better simulation of compressible flow fields. Compared with traditional difference schemes, compact schemes have higher accuracy for the same stencil width. By means of the characteristic analysis of the operators, the group velocity of wave packets will be controlled to suppress the non‐physical oscillations in numerical solutions. In numerical simulation of the 3D compressible flow fields the third‐order accurate upwind compact operator is used to approximate the derivatives in the convection terms of the compressible N–S equations, the traditional finite difference scheme is used to approximate the viscous terms. Numerical solutions indicate that the method is satisfactory. Copyright © 2004 John Wiley & Sons, Ltd.     

Local convective heat transfer for laminar and turbulent flow in a rotor-stator system

Abstract The aim of this work is to show a better comprehension of the flow structure and thermal transfer in a rotor-stator system with a central opening in the stator and without an airflow imposed. The experimental technique uses infrared thermography to measure the surface temperatures of the rotor and the numerical solution of the steady-state heat equation to determine the local heat transfer coefficients. Analysis of the flow structure between the rotor and the stator is conducted by PIV. Tests are carried out for rotational Reynolds numbers ranging from 5.87×10⁴ to 1.4×10⁶ and for gap ratios ranging from 0.01 to 0.17. Analysis of the experimental results has determined the influence of the rotational Reynolds number, the gap ratio and systems geometry on the flow structure, and the convective exchanges in the gap between the rotor and the stator. Some correlations expressing the local Nusselt number as a function of the rotational Reynolds number and the gap ratio are proposed.     

Evaluation of transient turbulent flow fields using digital cinematographic particle image velocimetry

This paper describes an experimental development for temporal and spatial reconstruction of continuously varying flow fields by means of digital cinematographic particle image velocimetry (PIV). The system uses a copper-vapor laser illumination synchronized with a high-speed camera, and continuously samples at 250 fps to measure transient and non-periodic turbulent flows with relatively low frequencies, i.e., the surf zone turbulence produced by depth-limited wave break in a long laboratory flume. The use of the developed PIV system comprehensively records the temporal development of both phase-averaged and instantaneous turbulent vortex flows descended from the breaking waves to the bottom. Also, the measured power spectra show harmonic frequencies, ranging from the orbital frequency of 0.5 Hz up to the order of 5 Hz, and the well-known −5/3 dependence upon the turbulence fluctuation frequencies thereafter. Received: 2 December 1999/Accepted: 6 September 2000     

Comparison of the Eulerian and Lagrangian approaches in studying the flow pattern and heat transfer in a separated axisymmetric turbulent gas-droplet flow

The Eulerian and Lagrangian approaches are used to perform a numerical study of the disperse phase dynamics, turbulence, and heat transfer in a turbulent gas-droplet flow in a tube with sudden expansion with the following ranges of two-phase flow parameters: initial droplet size d ₁ = 0–200 µm and mass fraction of droplets M _L1 = 0–0.1. The main difference between the Eulerian and Lagrangian approaches is the difference in the predictions of the droplet mass fraction: the Eulerian approach predicts a smaller value of M _L both in the recirculation region and in the flow core (the difference reaches 15–20%). It is demonstrated that the disperse phase mass fraction calculated by the Lagrangian approach agrees better with measured data than the corresponding value predicted by the Eulerian approach.     

A new apparatus for studying mechanical behavior under pressure

Using a servohydraulic intensifier, a servohydraulic universal test machine and a novel test chamber, pressures of 750 MPa and axial stresses of almost any magnitude are simultaneously generated and applied to the gage section of a solid, cylindrical specimen. Under combined axial-stress/external-pressure loadings, a solid specimen experiences a truly three-dimensional, homogeneous stress state in which the axial stress equals σ₁ and the radial and circumferential stresses equal the negative of the pressure, —P. Through independent computer control of the pressure and axial stress, amterial behavior under monotonically and cyclically applied multiaxial stresses are investigated. This paper describes the experimental details of the test chamber design, high-pressure fluid production and sealing, load and strain measurement under high pressure, computer control and data acquisition. Experimental results obtained from triaxial monotonic tests on low alloy steel and triaxial cyclic tests on a Ni-Ti alloy using this unique apparatus are presented.     

Particle collisions in a turbulent flow

An equation for the two-point probability density function of the two-particle the coordinate and velocity distribution is obtained. A closed system of equations for the first and second two-point moments of the velocity fluctuations of a pair of particles with allowance for the turbulent flow inhomogeneity is given. Boundary conditions for the equations of the particle concentration and the intensity of the relative random velocity during particle collision are obtained. A unified formula describing the interparticle collision process as a result of turbulent motion and the average relative particle velocity slip is obtained for the kernel of the coagulation equation. The effect of the average velocity slip of the particles and the carrier phase on the parameters of motion of the dispersed admixture and its coagulation is investigated on the basis of a two-point two-time velocity fluctuation autocorrelation function with two time and space scales representing the energy-bearing and small-scale motion of the fluid phase.Moscow. Translated from Izvestiya Rossiiskoi Akademii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, pp. 104–116, March–April, 1996.     

Modelling a recirculating density-driven turbulent flow

A mathematical model of turbulent density-driven flows is presented and is solved numerically. A form of the k–? turbulence model is used to characterize the turbulent transport, and both this non-linear model and a sediment transport equation are coupled with the mean-flow fluid motion equations. A partitioned, Newton–Raphson-based solution scheme is used to effect a solution. The model is applied to the study of flow through a circular secondary sedimentation basin.     

Particle deposition from a turbulent flow

The diffusion equations and boundary condition for particle deposition from a turbulent flow are obtained on the basis of the kinetic equation for the probability density of the particle distribution. This approach makes it possible to calculate the deposition fairly simply without introducing additional empirical information relating to the particles (empirical constants are needed only for calculating the characteristics of the turbulent carrier flow). Moscow. Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 5, pp. 96–104, September–October, 1988.     

Spectral and instantaneous flow field characteristics of the laminar to turbulent transition in a cone and plate apparatus

Fluid-surface interaction, is very much influenced by the flow distribution and the flow spectra. For biological surfaces, cell functions such as mytosis and cell turnover, can be triggered by the instantaneous flow fluctuations which induce augmented shear stress levels inside the wall surface boundary layer. The objective of this work is to study the flow field along a cellular surface and to understand the interaction process. For that purpose, a cone and plate apparatus was built in which the transitional and turbulent instantaneous flow field characteristics, especially near the plate surface, were investigated using spatial hot wire anemometry, concentrating on time domain and spectral analysis. The frequency spectrum of velocity fluctuations near the plate is influenced by the plate roughness. We found that there is a linear relation between wall roughness and the preferred frequencies of the spectra. In addition a universal law exists for mean velocities, similar to the logarithmic law of the wall, when normalized by R˜ ^1/2, the apparatus Reynolds number. Received: 31 March 1998/Accepted: 11 January 1999     

Effect of system rotating on turbulent boundary layer flow

This paper experimentally investigated the effect of rotating on the turbulent boundary layer flow using hot-wire. The experiments were completed in a rotating rig with a vertical axis and four measured positions along the streamwise direction in channel, which focuses on the flow flied in the rotating channel. The rotating effects on velocity profile, wall shear stress and semi-logarithmic mean velocity profile are discussed in this paper. The results indicated that: due to the Coriolis force induced by rotating, the phenomenon of velocity deficit happens near the leading side. The velocity deficit near the leading side, do not increase monotonically with the increase of Ro. The trend of the velocity deficit near the leading side is also affected by the normal component of pressure gradient, which is another important force in the cross-section of the rotating channel. The wall shear stress near the trailing side is larger than that on the leading side, and the semi-logarithmic mean velocity profile is also different under rotating effects. The phenomenon reveals that the effect of rotation penetrates into the logarithm region, and the flow near the leading side tends to turn into laminar under the effect of rotation. The rotation correction of logarithmic law is performed in current work, which can be used in the wall function of CFD to increase the simulating accuracy at rotating conditions.     

Application of a line implicit method to fully coupled system of equations for turbulent flow problems

For unstructured finite volume methods, we present a line implicit Runge–Kutta method applied as smoother in an agglomerated multigrid algorithm to significantly improve the reliability and convergence rate to approximate steady-state solutions of the Reynolds-averaged Navier–Stokes equations. To describe turbulence, we consider a one-equation Spalart–Allmaras turbulence model. The line implicit Runge–Kutta method extends a basic explicit Runge–Kutta method by a preconditioner given by an approximate derivative of the residual function. The approximate derivative is only constructed along predetermined lines which resolve anisotropies in the given grid. Therefore, the method is a canonical generalisation of point implicit methods. Numerical examples demonstrate the improvements of the line implicit Runge–Kutta when compared with explicit Runge–Kutta methods accelerated with local time stepping.     

Calibration ofX-probes for turbulent flow measurements

We compare two methods of calibrating the yaw response of hot-wire probes: (i) the assumption that an effective angle, independent of the flow speed, can be deduced; (ii) the more general approach of determining the yaw response at a number of different speeds. The first, simpler, approach is shown to give surprisingly reasonable results for the usual turbulence statistics, even in high turbulence intensity flows. Some differences in the distribution of the inclination of the instantaneous velocity vector are observed. There is no advantage in using thek ² factor to allow for longitudinal cooling.     

Circulatory flow in the inter-jet zone of a system of free turbulent jets

Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, No. 4, pp. 97–99, July–August, 1993.     

床面上直立圆柱的三维湍流数值模拟

从数值预报桥墩等结构物床面局部冲刷的角度发展绕直立圆柱的三维湍流的数值模拟技术. 基于Wilcox的k-ω两方程湍流模式，采用基于有限体积法的压力修正SIMPLE算法, 计算了绕床面直立圆柱的三维湍流流场，分析了光滑和粗糙床面两种情况下的流动情况. 通过系列的验证计算，表明该计算模型能够比较准确地反映不同外来流条件下绕直立圆柱的流场. 计算结果揭示了床面粗糙度对绕圆柱的湍流流动的影响.