2019/08/19 14:47
阅读:195
分享:方案摘要:
产品配置单:
三维立体PIV
型号: FlowMaster® 3D
产地: 德国
品牌: LaVision GmbH
¥100万 - 120万
参考报价
联系电话
LaVision DaVis 智能成像软件平台
型号: DaVis
产地: 德国
品牌: LaVision GmbH
¥10万 - 30万
参考报价
联系电话
方案详情:
Bileaflet mechanical heart valves (BMHVs), though a life-saving tool in treating heart valve disease, are often associated with serious complications, including a high risk of hemolysis, platelet activation, and thromboembolism. One likely cause of this hyper-coagulative state is the nonphysiologic levels of stress experienced by the erythrocytes and platelets flowing through the BMHVs. Research has shown that the combination of shear stress magnitude and exposure time found in the highly transient leakage jet emanating from the b-datum gap during valve closure is sufficient to cause hemolysis and platelet activation. Regions of flow stasis in the valve vicinity may also allow activated platelets to aggregate and form thrombus.
This thesis addresses the hypothesis that passive flow control may have the potential to reduce flow-induced thrombogenicity by altering the fluid mechanics of bileaflet mechanical heart valves. To test this hypothesis, a steady model of the regurgitant b-datum line jet was developed and studied. This model served as a test bed for various vortex generator array designs. The fluid mechanics of the b-datum line jet model was investigated with flow visualization and particle image velocimetry. In vitro tests with whole human blood were performed with and without the vortex generators in order to determine how the presence of the passive flow control affected the propensity of the blood to form thrombus. An effort was then made to correlate the fluid mechanics of the jet model with the procoagulant potential results from the blood experiments. The effect of the vortex generators on the fluid mechanics of the valve under physiologic pulsatile conditions was also investigated via flow visualization in the Georgia Tech Left Heart Simulator.
By studying a steady model of the regurgitant b-datum line jet, it was found, using an in vitro system with whole human blood, that the presence of vortex generators significantly decreased the blood’s propensity for thrombus formation. The potential of applying passive flow control to cardiovascular hardware in order to mitigate the injurious effects of shear-induced platelet activation is thus demonstrated.
The investigation into the effect of vortex generators on the fluid mechanics of the b-datum line jet showed that the jet oscillated aperiodically and that the effect of the applied flow control was played out at both the scale of the chamber (large-scale) and on the scale of the vortex generator fins (small-scale). On the large scale, the presence of vortex generators appeared to decrease the magnitude or frequency of jet oscillation, thereby stabilizing the jet. After removing the effect of the large-scale oscillations via phase averaging, the effect of the vortex generators on the small scale was examined. On the small scale, the jet without flow control was found to have higher levels of velocity RMS, particularly on the jet periphery, and higher levels of Reynolds shear stress. It is proposed that the vortex generators effect this change by generating vorticity in the plane of the jet. This vorticity is theorized to stabilize the jet, delaying roll-up of the jet shear layer which occurs via the Kelvin-Helmholtz instability.
The method by which the vortex generators acted on the fluid mechanics of the steady jet system to decrease the blood’s procoagulant potential was investigated via flow visualization and DPIV. The results from these studies implicate two possible mechanisms by which the vortex generators may act. First, the peak turbulent shear stresses in the jet were reduced by 10-20% with the application of vortex generators. Even if only a few platelets were activated in each passage through the valve, the cumulative effect of this difference in peak stresses after many passes would be greatly magnified. Thus, this reduction in turbulent shear stresses may be sufficient to explain the change seen in the blood’s procoagulant potential with the application of passive flow control. It is suspected, though, that the second mechanism is dominant. The flow fields revealed that the presence of the vortex generators delayed or prevented the roll-up of the Kelvin-Helmholtz instability in the b-datum jet’s shear layers into discrete vortices. By doing so, it is thought that opportunities for the interaction of activated and unactivated platelets entrained in these vortices were prevented, thereby inhibiting further propagation of the coagulation cascade. Even if the rate at which platelets were activated was similar for cases with and without flow control, it seems that the flow fields experienced by the platelets subsequent to activation can determine the level of procoagulant potential. Under the steady conditions observed in this experiment, the jet influenced by vortex generators was thus shown to induce significantly lower levels of procoagulant potential.
下载本篇解决方案:
更多
在一个双稳湍流涡旋火焰中,对间歇性动态的时间-频率定位
本研究考察了一个双稳湍流旋转火焰中的复杂流场,其中火焰不规则地在离开的M形和附着的V形之间交替。流场由于火焰形状转换在不同的时间尺度上出现各种类型的间歇性动力学。为了正确识别、分离和时间上解析这些动态组分,通过将多维数据序列的最大重叠离散小波包变换(MODWPT)与常规瞬态POD相结合,开发了一种新的多分辨率proper orthogonal decomposition(MRPOD)方法。特别注意选择小波滤波器、分解水平和重构带宽以实现可变的频谱通带和足够的时间分辨率。当应用于双稳旋流火焰中高速三分量速度场测量的数据序列时,MRPOD能够隔离通常被合并为单个POD模式的频率组分,对于即使是弱的和高度间歇性的动力学,增强了空间/时间的一致性。由于改进的频谱纯度,一系列先前未知的动态被揭示出来,其中包括预旋涡核(PVC)和热声(TA)不稳定性等已被描述的不稳定性。特别是,在火焰形状转换期间,发现非周期切换模式只与先前确定的转移模式相耦合,在倒流和燃烧器进口附近产生显著的修改,这是一个已知会影响PVC增长率的区域。在M-V转换期间,TA振荡驱动反复的火焰再附着,最终稳定为V火焰。但是,持续高的TA振幅似乎并不一定预示着这种转换的开始。发现了PVC的更高阶谐波以及TA调制PVC动力学的证据,它们也表现出双峰行为:虽然保持其特征频率,但这些不稳定性在V-或M火焰期间才能发挥作用,且只能具有单螺旋或双螺旋结构。
能源/新能源
2023/04/10
Particle-laden Taylor-Couette流:高阶转变和径向局部波浪涡旋的证据
我们扩展了在中性浮力颗粒悬浮的Taylor-Couette流中已知的流动转换,通过在半径比η = 0.917和长径比Γ = 21.67的几何形状中访问更高的悬浮雷诺数(Resusp ∼ O(103))。通过流体可视化实验研究了几种颗粒体积分数(0 ≤ φ ≤ 0.40)下的流动转换,这些实验中流体由旋转的内缸驱动。尽管有效斜率更高,但我们观察到存在非对称的图案,例如旋涡,存在颗粒的情况下。我们实验的一项新发现是方位局部化的波动涡流,其特征在一些本来是轴对称的Taylor涡旋中存在波状。这种流动状态的存在表明,除了已经被确认的颗粒不稳定性效应外,它们还可以抑制不稳定性的增长。颗粒悬浮液中对应于高阶转换的流动拓扑似乎与单相流中观察到的拓扑相似。然而,一个关键区别是在更高颗粒负载下出现的第二个不协调频率的出现减少了,这可能对混沌的发生有影响。同时进行的扭矩测量使我们能够估计努塞尔数(Nuω)、Taylor数(Ta)和相对粘度(χe)之间的经验比例关系:Nuω∝Ta0.24χe 0.41。Ta的比例指数与颗粒负载无关。显然,颗粒不会触发在内外缸之间的角动量传递的性质上的定性变化。
航空航天
2023/04/10
7根杆束的流体-结构相互作用:用实验数据对比数值模拟
液体通过棒束中流动在许多核能应用中被观察到,例如在第四代液态金属快中子繁殖核反应堆(LMFBR)的堆芯中。该结构的一个主要特征是由于棒间子通道中速度差异而出现的棒间间隙中流动脉动。一方面,这些脉动是有益的,因为它们增强了棒和流体之间的热交换。另一方面,流体脉动可能引起柔性燃料棒的振动,这种机制通常称为流致振动(FIV)。随着时间的推移,这可能导致棒的机械疲劳和振动损伤,最终可能危及其结构完整性。在SESAME框架下,荷兰代尔夫特理工大学(TU Delft)、根特大学(UGent)和NRG合作开展了一项工作,旨在对7根棒束中的FIV进行实验测量,并将数值模拟与所获得的实验数据进行验证。由TU Delft进行的实验是通过一个P/D=1.11的七边形棒束进行重力驱动流动,其中200mm的中心棒段由硅胶制成,其中100mm是柔性的。采用激光多普勒测速仪(LDA)进行流量测量,而高速摄像机则测量了硅胶棒上诱导的振动。数值模拟采用了非稳态雷诺平均Navier-Stokes方程(URANS)方法进行湍流建模,并采用强耦合算法解决了流固耦合(FSI)问题。测得的流脉动频率以及平均棒位移和振动频率被用于进行基准测试。
能源/新能源
2023/04/10
使用高速激光诊断技术对旋流喷雾火焰中心涡核的实验研究。
中心级旋流燃烧可以有效地降低NOx排放。但是,这种复杂的燃烧场容易产生大规模的相干结构,例如旋转涡核和中心涡核(CVC)。本研究主要利用10 kHz高速CH化学发光(CL)、20 kHz颗粒图像测速仪(PIV)和CH2O平面激光诱导荧光(PLIF),在高温高压下研究中心级旋流喷雾燃烧器中CVC对流场和火焰的影响。对于试验火焰,CH CL和CH2O PLIF火焰都是三叉形状的,并且火焰动力学的中心部分表明了CVC结构。对于分层火焰,在燃烧器中心线附近的一个强旋涡带区域内存在CVC结构。适当正交分解(POD)模式的分析表明,CVC的运动主要是摆动,其次是进动。同时诊断表明,CVC的吸入导致CH2O从剪切层输送到燃烧器的中心区域。总体而言,CH2O信号主要分布在两个正的速度区域,即主燃气和中心涡核周围。利用CVC对自由基输运的作用是改善燃烧器混合,例如温度分布的潜在方法。
能源/新能源
2023/04/10