Experimental investigation of tornado-like vortex dynamics with swirl ratio: The mean and turbulent flow fields

An experimental simulation of tornado-like vortices is conducted in a small tornado vortex simulator in order to study the effect of swirl ratio on flow characteristics. Particle Image Velocimetry (PIV) method is employed to quantitatively determine the tornado-vortex velocity field for swirl ratios ranging from 0.08 to 1. The radial and tangential components of velocity as well as the core radius of the tornado increase with increase in swirl ratio. The location of the maximum radial and tangential velocities is adjacent to the ground where the tornado vortex interacts with the surface. The values of normal and shear turbulent stresses indicate the existence of a laminar core for small swirl. As expected the shear stresses increase with swirl ratio as the vortex becomes turbulent. The highest turbulent production corresponds to the critical case of vortex touchdown.     

实验用离心泵叶轮内流场的PIV测量

离心泵叶轮内流场的流动规律直接影响泵的扬程、效率等外特性指标,利用PIV测试技术可以在不干扰流场的情况下,进行高精度的测量。在实验中,使用PIV测量技术测量了离心泵内部流场,得到了离心泵内的速度分布,初步掌握了离心泵在不同工作条件下内部的流动特性。     

EXPERIMENTAL AND NUMERICAL STUDY FOR HYDRODYNAMIC CHARACTERISTICS OF AN OSCILLATING HYDROFOIL

The present article reports the experimental Particle Image Velocimetry （PIV） investigation and the corresponding numerical simulation results about the water flow over the oscillating hydrofoil and its unsteady dynamic characters. The experimental study focuses on the effect of mean angles of attack. The comparison between the PIV results and numerical prediction about the flow field using Fluent well demonstrates the capability of CFD on the simulation of the water flow around the pitching hydrofoil. The numerical results indicate that the forced oscillating frequencies have evident effects on the flow separation and vortex shedding. The simulations about the hydrodynamic drag and lift coefficients were also performed.     

利用PIV技术对淹没冲击水射流动力学特性的研究

根据二维PIV技术的要求。建立了淹没射流流场研究的实验台架,并对井眼中流动的淹没射流的动力学流动进行了系统的测量。在射流瞬时流场中,射流边界处由于受速度梯度引起的涡运动的影响,流体速度表现出波动性,射流的时均流场比较均匀。实验证明了先进的PIV流场测量技术用于淹没射流的动力学流场特点和速度结构研究的可行性。     

内插螺旋立式上行管流场及传热性能的实验研究

通过粒子图像测速流场实验与传热实验相结合,研究了内插螺旋立式上行管的螺旋节距、丝径、中径比等结构参数在不同Re下对流场、阻力及传热性能的影响。结果表明,内插螺旋能够有效扰动和混合管内流体,使管内形成多个纵向旋涡的流体结构、增大管壁附近液体涡量,有利于强化传热。当Re相同时,管内平均流速v、Nu和综合换热性能PEC均随丝径增大而增大,随中径比减小而增大;随节距增大,3种参数均出现增大的趋势,节距大于20 mm后开始减小。管内流体的阻力f随丝径和节距增大而减小,随中径比增大而增大。综合比较,在较低Re时,节距p=20 mm、丝径e=1.6 mm、中径比D/d=0.75时综合传热效果最好。     

Experimental determination of the discharge flow coefficient at a doorway for fire induced flow in natural and mixed convection

The study is an experimental investigation of the discharge flow coefficient at a doorway‐type opening in the case of a fire in an enclosure open to atmosphere. Natural and mixed convection flows are considered with the use of mechanical ventilation. The discharge coefficient is defined as the ratio between the effective flow rate determined experimentally and a theoretical flow rate based on a Bernoulli approach. The effective mass flow rate is obtained from velocity field measured with stereoscopic particle image velocimetry technique. The theoretical flow rate is calculated from vertical temperature profiles measured from both sides of the doorway. Only inflow rate is considered for the calculation of the discharge coefficient. In natural convection mode, a C_D value of 0.54 ± 0.5 is obtained on a reduced‐scale opening (to be compared with 0.68 at large scale). In a mixed convection case, the discharge coefficient is much lower and reaches 0.26 ± 0.06. This study shows that the discharge coefficient C_D may vary significantly regarding the dimension of the opening and the flow conditions (natural and mixed convection). It illustrates the limits of considering a constant discharge coefficient when dealing with doorway flows in a confined and mechanically ventilated compartment. Copyright © 2014 John Wiley & Sons, Ltd.     

二维矩形突起物绕流流动特性的实验分析

利用PIV技术，对在均匀来流条件下无压流流道内底壁矩形突起物流动的二维瞬时流速场进行了测量，得到了湍流情况下，两种台阶比（h1／h=2、4），相同流量（Q=40L／s）情况下突起物绕流流动特性及流场中旋涡生成发展与演化的一般规律．同时还对两种工况下流场结构的时均特点和突起物附近水面线的变化情况进行了分析．     

PIV系统测量误差的评价方法研究

通过解决高速高精度的转速控制、安全性控制等技术问题研制了PIV基准速度场系统,最高速度达200m/s,且达到了可用于对PIV系统标定的误差要求;介绍了利用基准速度系统对PIV测量误差评价的实验方法,解决了示踪粒子模拟、体激光投射的PIV测量方法等关键技术问题,并完整的介绍了实验的流程;通过PIV系统误差来源分析、速度基准系统不确定度分析以及PIV测量结果分析等完整的介绍了数据分析的方法与流程,得到了1套PIV设备的误差标定结果。     

Blood flow interpretation in femoral pseudoaneurysm

A femoral artery pseudoaneurysm is one complication of vascular intervention, and the incidence is increasing. Early management is then needed to avoid potential dangers from it. It differs from a true aneurysm in that it doesn＇t include any component of the vascular wall, and is not studied as much as a true aneurysm. Here, a model of a femoral pseudoaneurysm was made and a Computational Fluid Dynamics（CFD） simulation was verified with PIV experiment. Afterwards, a CFD simulation with two different models was performed to look for any findings which may help in developing new treatment methods.     

正弦波纹挡板式沉降器内流动特性

采用VOF模型对正弦波纹式入口挡板的重力非均相沉降器内流场进行数值模拟研究。对比了正弦波纹挡板与平挡板的平均流场分布情况,分析了沉降器的轴向流速均一程度(λ₁)随时间演化特性,探究了λ₁和面积加权平均湍流强度(I_a)在沉降器内空间分布特性;引入流场均稳指标USC,研究了冲击间距(L_b/D)对USC的影响。结果表明:正弦波纹挡板作为入口构件可以有效降低返混。在0.84b/D减小,平挡板沉降器内流场的λ₁基本不变,但正弦波纹挡板沉降器内流场的λ₁降低,且对I_a的影响不明显。对比平挡板,正弦波纹挡板可以有效降低轴向速度的梯度,使返混区面积减小,流场稳定性提高。随着L_b/D增加,USC值呈现多峰值趋势,L_b/D=2.17时正弦波纹板沉降器的USC取得极大值为14.68,较平挡板提高了...