Measurements of turbulent flow in a duct with repeated ribs applied to two opposite walls

Abstract

Laser‐Doppler velocimetry measurements were made for turbulent flows past repeated ribs applied to two opposite walls of a rectangular duct. The rib pitch‐to‐height, rib width‐to‐height, and rib height‐to‐duct height ratios were 10, 5, and 0.13, respectively. The Reynolds number based on the hydraulic diameter and the bulk velocity was varied between 6×10³ and 1×10⁵. The complicated flow field was characterized in terms of mean‐velocity and turbulence intensity as well as pressure distribution and flow visualization. Additionally the periodic fully developed length was determined. This length is important for numerical modeling. Furthermore, the degree of turbulence enhancement of ribbed walls over the smooth ducts was documented.     

Rotating-disk-type flow over loose boundaries

Rotating-disk-type flow of a liquid over a loose boundary, such as a layer of sand, is investigated. For this flow the formation of a new large-scale spiral pattern has been discovered. The new pattern is reminiscent of the Type-I spiral-vortex structures which characterize the laminar–turbulent transition region of boundary layers over rigid rotating disks. Flow visualizations reveal that the new pattern and the Type-I spiral vortices co-exist in the loose-boundary flow. The research investigating the origin of the new large-scale pattern is reviewed. Then photographs from flow visualizations are analysed to obtain estimates for the critical Reynolds number for which Type-I spiral vortices first appear for the loose-boundary flow and for the critical Reynolds numbers for the laminar–turbulent transition of the boundary layer. The results suggest that Type-I vortices appear at much lower Reynolds numbers over loose boundaries in comparison with flow over rigid rotating disks and that transition also appears to be advanced to much lower Reynolds numbers. The discussion of the results suggests that advanced transition arises from disturbances introduced into the flow after the loose boundary has been mobilized and not from disturbances associated with the roughness that the surfaces of the granular layer represents to the flow while grains are at rest.     

A perturbation solution for compressible viscous channel flows

The two-dimensional compressible Navier-Stokes equations are solved by a perturbation expansion in the parameter (Mach number)²/Reynolds number. A fortieth-order solution is generated by a computer algorithm. These series are then summed as convergent series of diagonal Padé approximants. Effectively-exact solutions have been found for Reynolds numbers between zero and 1000 and a range of subsonic Mach numbers in the case of fully-developed isothermal flow between parallel side walls. Choking of the flow is shown to occur for a moderate value of channel Reynolds number. The two-dimensional velocity and pressure fields are obtained. The engineering assumption that friction factor is sensibly independent of Mach number may lead to significant underprediction of head loss in the laminar flow regime.     

TDD — A method for on-line determination of short half-lives

The two detector delay (TDD) method for the determination of half-lives of nuclides continuously transported in a liquid stream through a tube has been tested with nuclides covering the half-life range 0.8–27 s. The sensitivity of the method to Reynolds number, a parameter associated with the velocity profile of the liquid flow within the tube, has been studied. The method has also been used to determine the previously not well-known half-life of ³⁶P to be (5.2 ± 1.2) s, and the cross section for the ³⁶S(n,p)³⁶P reaction at 14 MeV to be (6.1_−0.9^+1.8) mb.     

Simulation of Non-Isothermal Turbulent Flows Through Circular Rings of Steel

This article is intended to examine the fluid flow patterns and heat transfer in a rectangular channel embedded with three semi-circular cylinders comprised of steel at the boundaries. Such an organization is used to generate the heat exchangers with tube and shell because of the production of more turbulence due to zigzag path which is in favor of rapid heat transformation. Because of little maintenance, the heat exchanger of such type is extensively used. Here, we generate simulation of flow and heat transfer using non-isothermal flow interface in the Comsol multiphysics 5.4 which executes the Reynolds averaged Navier stokes equation (RANS) model of the turbulent flow together with heat equation. Simulation is tested with Prandtl number (Pr = 0.7) with inlet velocity magnitude in the range from 1 to 2 m/sec which generates the Reynolds number in the range of 2.2 × 10⁵ to 4.4 × 10⁵ with turbulence kinetic energy and the dissipation rate in ranges (3.75 × 10⁻³ to 1.5 × 10⁻²) and (3.73 × 10⁻³−3 × 10⁻²) respectively. Two correlations available in the literature are used in order to check validity. The results are displayed through streamlines, surface plots, contour plots, isothermal lines, and graphs. It is concluded that by retaining such an arrangement a quick distribution of the temperature over the domain can be seen and also the velocity magnitude is increasing from 333.15% to a maximum of 514%. The temperature at the middle shows the consistency in value but declines immediately at the end. This process becomes faster with the decrease in inlet velocity magnitude.     

Effect of rotation of the inner cylinder on the equilibrium condition of spherical particles in a turbulent ascending flow in an annular channel

The equilibrium condition of a solid spherical particle in a turbulent flow is considered. A relation between the rotational velocity of the inner cylinder and the critical velocity of the ascending flow in an annular channel is obtained for the range of Reynolds numbers 10³ –5 · · 10⁴.     

The influence of inlet velocity profile on three-dimensional three-generation bifurcating flows

 The influence of inlet velocity profile on the three-dimensional three-generation bifurcating flow has been numerically studied using a CFD code based on finite volume method. The bifurcating airways simulated the branches of human lung. The axial length and cross-sectional diameter of the three-generation airway are taken from the anatomic data of the 5th–7th generation airway of an averaged height man. The curvature and bifurcating angle of each junction are taken as 2.265 diameter of the next generation and 70^∘, respectively, from physiological consideration. Computations are carried out for eight Reynolds numbers ranging from 200 to 1600, each under uniform and parabolic inlet velocity profiles, to consider the relations between the entry flow patterns and the overall flow characteristics including mainstream flow pattern, secondary flow vortices, asymmetrical flow partition and pressure drop. The mass flow ratio between the medial and lateral branch, and the total pressure drop are closely related to the entry flow patterns for larger Reynolds numbers. Received: 1 October 2001 / Accepted: 12 July 2002 Support given by the Research Grants Council of the Government of the HKSAR under Grant No. PolyU 5166/01E and by the Hong Kong Polytechnic University under Central Research Grant No. A-PD75 is gratefully acknowledged.     

Velocity profile of the turbulent flow of weak polymer solutions in a tube

Experimental data relatingto the velocity profiles of the turbulent flow of polyox, guar resin, and polyacrylamide solutions (10^?6 to 6.10^?4 g/cm³) in a 35-mm diameter tube are presented. Analytical relationships obtained by expressingthese profiles in the form of a three-layer model enable us to relate the form of the velocity profiles to the resistance coefficient and the Reynolds number of the flow.     

An investigation of the Prandtl number effect on turbulent heat transfer in channel flows by large eddy simulation

Summary Fully developed turbulent channel flow with passive heat transfer has been calculated to investigate the turbulent heat transfer by use of the large eddy simulation (LES) approach coupled with dynamic subgrid-scale (SGS) models. The objectives of this study are to examine the effectiveness of the LES technique for predicting the turbulent heat transfer at high Prandtl numbers and the effects of the Prandtl number on the turbulent heat transfer in a fully developed turbulent channel flow. In the present study, the Prandtl number is chosen as 0.1 to 200, and the Reynolds number, based on the central mean velocity and the half-width of the channel, is 10⁴. Some typical cases are computed and compared with available data obtained by direct numerical simulation (DNS), theoretical analysis and experimental measurement, respectively, which confirm that the present approach can be used to predict the heat transfer satisfactorily, even at high Prandtl numbers. To depict the effect of the Prandtl number on turbulent heat transfer, the distributions of mean value and fluctuation of resolved flow temperatures, the heat transfer coefficient, turbulent heat fluxes, and some instantaneous iso-thermal sketches are analyzed.     

Numerical and experimental studies on laminar forced convective heat transfer in a channel with surface‐mounted heated blocks

Abstract

The steady separated flow due to heated blocks mounted on one principal wall of a two‐dimensional channel has been numerically and experimentally studied. Numerical solutions of the Navier‐Stokes equations using the finite‐difference and the power‐law techniques have been obtained up to a Reynolds number of 2600. The effects of the Reynolds number and the block spacing on the fluid flow and heat transfer are investigated in detail. Results show that there exists two different types of flow between blocks, the D‐type and the K‐type flows. Furthermore, the Nusselt number monotonously increases or decreases along every face of the blocks. The calculated results of the reattachment length behind the second block and the local Nusselt number distribution compare well with the results obtained by the LDV and the naphthalene sublimation measurements, respectively. Heat transfer correlating equations are presented in terms of the Reynolds number and the block spacing.     

Friction factor correlation and pressure loss of single-phase flow inside herringbone microfin tubes

Pressure drop of single-phase turbulent flow inside herringbone microfin tubes of different fin dimensions has been measured experimentally to develop a general correlation of single-phase friction factor for the herringbone tubes. Water has been used as a working fluid and the mass flow rate has been varied from 0.03 to 0.2 kg/s, where the Reynolds number range is 10⁴ to 6.5 × 10⁴. Comparison of experimental data of the herringbone microfin tubes with those of helical microfin and smooth tubes shows that pressure drop of the herringbone tube is significantly higher than the helical and smooth tubes depending on the fin geometric parameters and mass velocity of the working fluid. Through semi-analytical approach and using the present experimental data, a new correlation of single-phase friction factor for the herringbone microfin tubes has been proposed incorporating the effects of fin geometric parameters. The proposed correlation can predict the experimental data within ±10%.     

Simulating sedimentation of liquid drops

This work was carried out to investigate the effect of fluid properties on the flow pattern and on the sedimentation velocity of an axisymmetric steady flow of a Newtonian fluid past a liquid drop in an unbounded region. The governing equations of motion were solved by the finite element method. The results show that the flow pattern of a liquid drop depends strongly both on the Reynolds number and on the ratio of the viscosity between the drop and the surrounding flowing fluids. The viscosity ratio in the range 0.02<μ^*<50 has appreciable effect on the drag coefficient. Finally, a correlation for the sedimentation velocity is presented. Copyright © 2004 John Wiley & Sons, Ltd.     

Typical flow between enclosed corotating disks and its dependence on Reynolds number

Abstract

The flow in an enclosed co‐rotating disk pair is investigated by Laser Doppler Velocimetry (LDV) measurements and flow visualizations. First, the typical flow structure at Re = 5.25 × 10⁵ and S = 0.09 is clarified. The flow fields in the r – θ and the r – z planes are both investigated and then divided into several flow regions based on the distinct flow types observed. The flow regions found in the two different planes are also compared and integrated. Second, with S fixed, the dependence of the flow field structure upon the Reynolds number is discussed. Three regimes of the r – θ plane flow with different Reynolds numbers are identified based on the measured mean velocity and spectral intensity. When Re < 1.6 × 10⁵, no solid body region is found and the flow is in a laminar regime. In the range 1.6 × 10⁵ ≤ Re ≤ 2.0 × 10⁶, the solid body region and the outer region vortices coexist, and an empirical equation is developed to estimate the number of vortices. When Re > 2.0 × 10⁶, the flow becomes turbulent. As Re increases from 9.3 × 104 to 5.25 × 10⁵, the spectral intensity initially increases and then decreases before increasing again to an even higher level, resulting in an increasing sawtooth pattern.     

不同雷诺数条件下静止管道车环状缝隙流场数值模拟

为了探究雷诺数对于静边界环状缝隙流场的影响,采用Fluent软件对雷诺数为115 513、154 018、192 522三种工况下静止管道车环状缝隙流场进行了数值模拟,并通过物理试验进行验证,结果表明:同一雷诺数条件下,在环状缝隙入口处流速最大,之后沿管道车车身方向,环状缝隙流流速呈现先减小后增大的变化趋势,且环状缝隙流流速大于管道内水流的平均流速;各横断面环状缝隙流场均以管道中心呈同心圆分布,即半径相同的各点环状缝隙流流速值大致相同,且从管道车壁面到管壁面方向环状缝隙流流速呈现二次抛物线的变化形式;不同雷诺数条件下,管道内压强值沿程变化趋势大致相同,管道车上游位置处压强沿程呈现逐渐降低的变化趋势,环状缝隙内部和管道车下游位置处的压强值沿程呈现先升高后降低的变化趋势;随着雷诺数的增加,环状缝隙流流速值与压强值和涡量值均呈现出逐渐增大的变化趋势;数值模拟结果同试验结果基本吻合,两者所得环状缝隙流流速最大相对误差不超过7%,表明通过数值模拟来研究管道车环状缝隙流场的方法是可行的。     

Heat transfer on the inlet section of a tube at increased levels of initial flow turbulence

The authors report the results of an experimental study of heat transfer on the initial section of a tube with uniform velocity profile at the inlet and a degree of flow turbulence up to 20% in the range of Reynolds numbers from 10⁴ to 10⁵.     

Hydrodynamics and Heat Transfer Analysis of Airflow in a Sinusoidally Curved Channel

For heat transfer enhancement in heat exchangers, different types of channels are often tested. The performance of heat exchangers can be made better by considering geometry composed of sinusoidally curved walls. This research studies the modeling and simulation of airflow through a units long sinusoidally curved wavy channel. For the purpose, two-dimensional Navier Stokes equations along with heat equations are under consideration. To simulate the fluid flow problem, the finite element-based software COMSOL Multiphysics is used. The parametric study for Reynolds number from to and the period of vibration P from to are observed. The surface plots, streamline patterns, contours, and graphs are presented for the velocity field magnitude, temperature, and pressure against the Reynolds number as well as period of vibration. The results are compared with various literature. It is found that due to the creation of periodic contraction regions the velocity magnitude of the flow is continuously increasing with the increase of Reynolds number, on the contrary the pressure is decreasing from inlet to outlet of the channel. Also, a periodic variation in the pressure distribution along the vibrating boundaries has been found with an average increase of for the high Reynolds number. A novel work was done by expressing the rotation rate per second in terms of local Reynolds number for the recirculating regions found due to the periodic oscillation of the boundaries. The average temperature near the outlet where a fixed temperature is imposed initially is decreasing with an increase in Reynolds number. The convection process is weakened due to an increase of periodic vibration of boundaries.     

Buckling Analysis of Non-cementing Casing String in Borehole

This article is from the cooperation projects of Tarim Oilfield—the sidetracking feasibility analysis of lateral drilling. It analyzed the buckling behavior of non-cementing casing string in the borehole by means of theoretical analysis and modeling analysis. When free section of casing string occurs buckling, casing string bends along the sidewall, leads to additional force and additional bending moment. If casing string’s deformation is too large, it reduces the ability to resist broken of casing string. The study of non-cementing casing string buckling is important to the feasibility of lateral drilling. The free section of casing string is the research objective of this paper. Considering the factors such as self weight of casing string, fluid pressure inside and outside casing, downhole temperature and contact frictional force between casing and shaft lining, the differential equation of buckling is derived by the energy method. The solution of the buckling differential equation has been solved, and the analytical solution of the sinusoidal and spiral buckling of the casing string along the tube column has been obtained. This article analyzed the buckling behavior of non-cementing casing string in the borehole by means of theoretical analysis and finite element analysis. The results show that the difference of the analytical solution and simulation results of the buckling differential equation is <15%.     

时差法超声波流量计流速修正系数的数值模拟

文章利用了计算机数值模拟的方法得出了超声波流量计流速测量的修正系数，这种数值模拟的方法是基于计算流体力学（CFD）软件Fluent上实现的。通过计算在不同的超声波波束直径和不同雷诺系数下流速测量的修正系数，与利用数学分析计算方法得出的结果进行了相应的比较，结果表明，两种方法得出的修正系数具有很好的一致性。因此，对于在更为复杂的测量环境中，流速的修正系数用数值模拟的方法具有很好的辅助作用。     

卫星式柔印机中心压印滚筒螺旋流道冷却性能研究

目的 探究卫星式柔印机在印刷过程中,中心压印滚筒内部冷却水流道结构对其冷却效果的影响。方法 以双层中心压印滚筒为研究对象,采用数值模拟方法分析螺旋流道内冷却水的速度场和外滚筒的温度场,并与无螺旋流道的中心压印滚筒进行对比;探究流道截面形状对滚筒表面轴向温差的影响规律。结果 有螺旋流道的滚筒的表面温度整体较低,且轴向温差(4.2 ℃)更小。在相同的入口流速条件下,横截面高宽比大的螺旋流道滚筒表面轴向温差更小。在入口冷却水流速为2.5 m/s的条件下,横截面高宽比为0.6的螺旋流道对应的滚筒表面轴向温差为2.46 ℃。结论 采用高宽比较大的矩形截面螺旋流道,有利于缩小中心压印滚筒表面的轴向温差,从而改善滚筒的冷却效果。     

竖直管路内流动液氢条件中弹状氢气泡运动速度

低温加注系统中的弹状流可能引发各种非稳现象,造成低温液氢传输管路的破坏.针对垂直管路内气液两相流实验化困难的问题,运用建模仿真的方法建立了竖直管路中弹状流气泡的运动模型,模拟了弹状氢气泡在流动液氢中的上升过程,并对其运动速度进行了研究.仿真结果表明:弹状氢气泡在流动液氢中运动时,其速度模型中的速度系数与流体的速度有关,...