三维立体PIV

采用LaVision的时间分辨激光诱导荧光火焰分析系统FlameMaster-TR和2D3C时间分辨立体PIV测速系统，对应变速率、局部熄灭和流体力学不稳定性对附着和上升涡流火焰过渡的影响进行了实验测量研究。

以寒鸦为测试对象。在风洞中，采用LaVision公司的时间分辨2D3C立体PIV测量系统，对开槽翼尖的多核漩涡对鸟类滑翔和扑翼飞行的支撑作用进行了研究。实验装置包括一台英国Litron公司的LDY304PIV高重复频率激光器，两台Imager pro HS 4M型高速相机，和DaVis8.4软件平台构成。

Ship laboratory has specific components for underwater measurements 􀁺 system used for phase-locked measurements behind the propeller for a twin-screw vessel 􀁺 the purpose of the study has been to − gain information on the interaction of the propeller and the rudder − explore the capabilities of the measurement system

The far wake trajectory of the tumbling tip vortex effect of a reduced-scale, 1 m diame- ter, four-bladed rotor during hover is studied using vortex methods combined with a center of mass analysis approach. Measurements of all three components of the velocity field are acquired using a stereo PIV system synchronized to capture up to 800 wake age of the vortex with 10 offsets during hover conditions. The nominal operating condition of the rotor is at a rotational speed of 1520RPM, corresponding to Rec = 248,000 with a chord length of 58.5mm. The rotor was operated with a pitch of 7.2± 0.5 and a CT / of 0.029. The far wake vortex tumbling phenomenon is captured and described. It is shown that tip vortices from two blades tumble through approximately 180 of rotation before they coalesce. It is seen that the parent vortices are stronger than the daughter vortex, but due to vortex stretching the daughter vortex has a smaller radius with greater swirl strength. An accurate characterization and prediction of the trajectory of the far wake vortex tum- bling can enhance the ability to predict and alleviate the resuspension of particles during brownout as well as provide a database for far wake validation of CFD codes.

Forces on flapping or rotating wings, like flapping wings of micro air vehicles or blades of wind turbines are of great interest to engineers. To investigate the ways birds and insects fly, forces created by flapping wings are of importance to biologists. The pressure field, combined with the velocity field, gives a complete description of the (incompressible) flow dynamics. Furthermore the pressure field is the main contributor to the aerodynamic loading of bodies immersed in the fluid. Traditional techniques to determine pressure and forces rely on the determination of surface pressure and integral loads by point pressure and force balance measurements. In situations where it is difficult (or impossible) to instrument the body, using particle image velocimetry (PIV) velocity data to determine forces and pressure poses an interesting alternative to the existing approaches to determine sectional loading.

Experimental velocity measurements of a low-speed jet, performed using time-resolved tomographic PIV, are used to study the dynamics of large-scale structures and their sound radiation. The experimental results show the roll-up of axisymmetric vortices that pair downstream, and subsequently lose their azimuthal coherence. Models of linear instability waves using both steady laminar and mean-field base flows flow are applied. While good agreement can be obtained for the vortex roll-up frequency in the near-nozzle region using the laminar base flow, non-linear effects must be included, via the mean field, in order to capture the downstream evolution of both the fundamental and subharmonic (vortex pairing). The velocity fluctuations for both frequencies have a wave-packet structure with some jitter in the form of modulations of the spatial extent and amplitude of the envelope. The sound radiation is modelled using a jittering wave-packet model, an shows agreement with the exponential directivity shape of Laufer and Yen (J. Fluid Mech. 134, 1983).

Energy supply is one of the primary building blocks of our society. Worldwide, and especially in rapidly developing countries, e.g. China and India, the demands of energy for housing, industry, transportation and communication are constantly increasing [83]. The global energy supply is currently dominated by combustion of fossil fuels. In 2008, 85.1% of the global primary energy supply was produced from the combustion of oil (34.6%), coal (28.4%) and natural gas (22.1%). From the 12.4% of renewable energy sources, 82% (in total 10.2%) was bioenergy based on burning renewable rescources [45]. Recent reports confirm that a dramatic shift towards CO2 neutral energy supply is required to stop the current trend of global warming [135]. Nevertheless, the slow developement of renewable energies over the last decades as well as the absence of large technological advancements in nuclear fusion technology indicate that this structure will not substantially change in the coming decades. Besides emissions of CO2, further pollutants are formed during the combustion of fossil or biofuels. From these emissions, nitric oxides (NOx) have been identified as a major problem of practical combustion processes [214]. In the recent decades nitric oxides became a significant contributor to photochemical smog and ozone in urban air [180]. It further participates in the chain reaction removing ozone form the stratosphere with the consequence of increased ultraviolet radiation reaching earth’s surface [90]. NOx is generally formed during the oxidation process of nitrogen containing fuels such as coal and oil. However, the gross NOx emissions are created at high combustion temperatures from nitrogen in the air. These are typical for hard coal plants, internal combustion engines and gas turbines. Hence, it is essential to understand the physico-chemical processes of NOx formation and concepts to reduce or even eliminate NOx emissions.

The flow at Reynolds number 100k around an inflexible, two-dimensional flapping airfoil is investigated using the stereoscopic Particle Image Velocimetry (PIV) technique. The typical phenomenon of a moving laminar separation bubble during one flapping cycle is identified. The measurement data is compared with URANS computations.

The wake behind a simpli¯ed model of a generic aircraft (the SWIM model) is measured in the Low Speed Low turbulence wind tunnel (LSL) at Delft University of Technology. Two measurement techniques have been used in order to qualitatively and quantitatively measure the wake, i.e. stereoscopic particle image velocimetry (Stereo PIV) and a 5 hole probe (5HP). Furthermore balance measurements have been carried out over a range of con¯gurations for later comparison purposes. The goal of the wake measurements is to give a comparison between the two measurement techniques. The 5HP measurements are processed using a windows based program called Pressure Field Visualisation. This program calculates vector ¯elds from the input pressure data and has several exporting options. The Stereo PIV measurements are correlated using DaVis 7.3 using a window size of 16 x 16 pixels with 50% overlap.

We report particle image velocimetry measurements of the collision of a vortex ring with a heated wall kept at constant temperature. We consider the case when both the vortex ring and the thermal boundary layer generated by the vertical heated wall are stable and laminar prior to any interaction. The impingement process can be divided into two parts. sid A ring-driven stage, where the vortex ring grows in diameter while approaching the wall and therefore it sweeps progressively an increased surface on the wall. siid A boundary layer-driven stage, where the vortex ring moves upward due to the thermal convective motion generated by the heated wall. In some cases, the head-on collision triggers the ring’s azimuthal instability as revealed by the formation of vortical structures arranged on a wavy starlike pattern and confirmed by flow visualizations. A single collision generates important velocity gradients and shear stresses along the wall accompanied with the creation of local vorticity normal to the vertical heated wall. Peak wall shear stresses occur near the point of impact of the vortex ring core.

采用LaVision公司的DaVis7.0.11图像数据采集和分析处理软件平台，两台 imager Pro CCD 相机，可编程时间控制单元PTU构成一套2D3C立体粒子成像测速系统，并利用该系统研究了被动流量控制在双瓣尖机械心脏瓣膜泄漏射流中的应用。

Embolic coiling is the most popular endovascular treatment available for cerebral aneurysms. Nevertheless, the embolic coiling of wide-neck aneurysms is challenging and, in many cases, ineffective. Use of highly porous stents to support coiling of wide-neck aneurysms has become a common procedure in recent years. Several studies have also demonstrated that high porosity stents alone can significantly alter aneurysmal hemodynamics, but differences among different stent configurations have not been fully characterized. As a result, it is usually unclear which stent configuration is optimal for treatment. In this paper, we present a flow study that elucidates the influence of stent configuration on cerebral aneurysm fluid dynamics in an idealized wide-neck basilar tip aneurysm model. Aneurysmal fluid dynamics for three different stent configurations (half-Y, Y and, cross-bar) were first quantified using particle image velocimetry and then compared. Computational fluid dynamics (CFD) simulations were also conducted for selected stent configurations to facilitate validation and provide more detailed characterizations of the fluid dynamics promoted by different stent configurations. In vitro results showed that the Y stent configuration reduced cross-neck flow most significantly, while the cross-bar configuration reduced velocity magnitudes within the aneurysmal sac most significantly. The half-Y configuration led to increased velocity magnitudes within the aneurysmal sac at high parent-vessel flow rates. Experimental results were in strong agreement with CFD simulations. Simulated results indicated that differences in fluid dynamic performance among the different stent configurations can be attributed primarily to protruding struts within the bifurcation region.