粒子图像测速(PIV)技术的发展

在流场显示测量技术中，粒子图像测速(PIV)技术占有相当重要的地位，本文重点介绍了PIV的测试原理及应用要求，并以TSI公司开发的PIV系统为例对DPIV系统的构成作了概括，同时指出了PIV技术的未来发展方向。     

An alternative illumination source based on LEDs for PIV measurements on human swimmers—A feasibility study

Methods for flow visualization help to investigate the motion of fluids that are normally invisible. Especially, Particle Image Velocimetry (PIV) – with a laser as light source – has been established in the field of engineering and partly in biology. Since the standard measuring equipment applying a laser system is very sensitive with respect to transport, temperature, humidity as well as laser safety requirements have to be adhered, the observation and classification of flow pattern around human swimmers in swimming pools has been rarely applied. There is a need for a simple, powerful, affordable, robust, and portable illumination source which shall not harm the swimmer by exceeding the permitted maximum radiation for human skin and eyes. As a result, this technical note demonstrates an alternative light source system based on LEDs which enables PIV measurements around human swimmers similar to experiments with a (traditional) laser system. As an example, the flow fields of two different swimmers with a similar movement and phase are compared using both illumination methods laser and LED. Furthermore, a series of sequential velocity fields, produced by the motion of a monofin swimmer, generate a vortex pair with an inverse Karman vortex street which is typically seen in fish and marine mammal locomotion. Consequently, this LED illumination source is show to provide a sufficient suitable light intensity as well as light quality enabling the measurement of the flow field around swimmers.     

Fluid flow characteristics in the aquaculture tank for a breeding fish

The aquaculture tank is used for breeding fish in sea water which was pumped up to land. The flow characteristics in the aquaculture were investigated with varying the tank geometry and flow rate. The numerical analysis has been employed for calculating the velocity and temperature distributions in a water tank of rectangular type. The finite volume method and SIMPLE algorithm with 3-dimensional standard k-ε turbulence model were used for the numerical analysis. For comparison with experimental results, the PIV system was applied to visualize the flow patterns quantitatively. The numerical results showed good agreements with the experimental results. The mean velocity and temperature versus aquarium depth were represented for various circulating flow rates. Especially, the aquaculture environment is recommended that the aquarium depth has to be d=0.5 m, and this case is the condition of higher velocity and temperature in winter season.     

Behaviour of weak soils reinforced with soil cement columns formed by the deep mixing method: Rigid and flexible footings

This paper presents a comparison of the failure behaviour of the Deep Mixing (DM) method under models of rigid and flexible foundations. A series of physical model tests at 1 g were performed in this study consisting of unreinforced and fully and partially penetrated soil–cement columns. For the improvement case, the columns of 23.5 mm diameter and lengths of 200 and 100 mm were installed in the ground model with an improvement area ratio, a_p, of 26.0%. The failure mechanism was measured using close range photogrammetry and Particle Image Velocimetry (PIV). For verification, the bearing capacity performance and failure mechanisms were then compared with the Ultimate Limit State numerical analysis and the existing analytical solution proposed by Boussida. The results show a good agreement between the bearing capacity value obtained from the experiment and the numerical software.     

Effects of a swirling and recirculating flow on the combustion characteristics in non-premixed flat flames

The effects of swirl intensity on non-reacting and reacting flow characteristics in a flat flame burner (FFB) with four types of swirlers were investigated. Experiments using the PIV method were conducted for several flow conditions with four swirl numbers of 0, 0.26, 0.6 and 1.24 in non-reacting flow. The results show that the strong swirling flow causes a recirculation, which has the toroidal structures, and spreads above the burner exit plane. Reacting flow characteristics such as temperature and the NO concentrations were also investigated in comparison with non-reacting flow characteristics. The mean flame temperature was measured as the function of radial distance, and the results show that the strong swirl intensity causes the mean temperature distributions to be uniform. However the mean temperature distributions at the swirl number of 0 show the typical distribution of long flames. NO concentration measurements show that the central toroidal recirculation zone caused by the strong swirl intensity results in much greater reduction in NO emissions, compared to the non-swirl condition. For classification into the flame structure interiorly, the turbulence Reynolds number and the Damkohler number have been examined at each condition. The interrelation between reacting and non-reacting flows shows that flame structures with swirl intensity belong to a wrinkled laminar-flame regime.     

Swirl effect on the spray characteristics of a twin-fluid jet

In the liquid fuel combustion chamber, employed fuel must be atomized before being injected into the combustion zone. Therefore, the complete fuel atomization is the most important condition for the combustion efficiency. The atomization quality strongly affects the combustion performance, exhaust pollutant emissions, and flame stability. Therefore, the whole process of spray atomization is of fundamental significance. During past decades many experimental and theoretical studies in this field have been carried out and some improved results have been obtained. Two-phase atomizers, having a variety of advantages such as spray uniformity, appreciable atomization, and smaller SMD with an increase of ambient gas, are considered to be applied in various industrial processes. The purpose of present study is to investigate the mean velocity, turbulence shear stress, turbulence intensity, mean drop size distribution, and droplet data rate in a two-phase swirling jet using PDPA systems.