High-speed echographic particle image velocimetry (echo-PIV)

1)一眼 回波-PIV（回波粒子图像测速）限于低帧速率，这降低了流量测量能力。我们将开发和验证高速回波PIV，提供高达100倍的采样率增加。 2)背景：光学与回波PIV 粒子图像测速技术（PIV）是一种非侵入式的光学流动显示技术。PIV拍摄两张时间相近的图像，并估计示踪粒子在这段时间内行进的距离。从已知的时间间隔和测量的位移，瞬时速度场的计算，从中可以推断出几个流动特性。在光学PIV中，用短脉冲激光照射种子粒子以冻结运动。因此，光学PIV仅适用于对光透明的材料。 回波PIV（回波PIV）基于与光学PIV相同的原理。代替激光照射，用超声波对播种颗粒进行声穿透。超声背向散射产生散斑图案，可以跟踪散斑图案以推断从一个图像到下一个图像的位移。超声PIV在血流研究中具有重要的应用价值。然而，回波PIV受到传统超声成像的阻碍，传统超声成像提供的帧速率比光学PIV小得多。实际上，常规超声成像发射连续聚焦波束以完全覆盖感兴趣区域。通常，需要128次发射才能获得一张图像。 该研究项目的目标是使用超快超声产生高速回波PIV，其帧速率高达10，000 fps。高速回波PIV具有扩大流体测量系统家族的潜力。 3)方法 为了测试高速回波PIV，我们将在控制良好的Womersley和涡流中以及在脉冲心脏复制器（ViVitro）中进行速度测量。ViVitro系统与超声和光学PIV兼容。脉动Womersley流将产生在一个圆柱形管道与活塞泵。根据已知的流速（由电磁流量计给出）和管道半径，将使用Womersley方程计算理论速度分布。三维涡流也将在有机玻璃方盒中产生，透明的光和超声波，磁力搅拌器。此外，为了测试具有复杂流动模式的高速回波PIV，我们将研究心脏复制器中的心室内填充。将通过光学三维体积PIV（V3 V-9800，TSI Inc.）测量速度。在不同的实验装置中，将高速回波PIV确定的速度与理论和/或光学PIV给出的地面真实速度进行比较。将在几个平面上针对不同的流动条件进行像素比较。

1) AT A GLANCE Echo-PIV (echographic particle image velocimetry) is limited to low frame rates, which reduces flow measurement capability. We will develop and validate high-speed echo-PIV offering up to a 100-fold increase in sampling rate. 2) CONTEXT: OPTICAL vs. ECHOGRAPHIC PIV Particle image velocimetry (PIV) is a non-intrusive optical technique of flow visualization for experimental fluid dynamics. PIV takes two closely timed images and estimates the distance that tracer particles travelled within this time. From the known time interval and the measured displacements, the instantaneous velocity fields are calculated, from which several flow properties can be deduced. In optical PIV, the seeding particles are illuminated with short-pulse-laser light to freeze the motion. Optical PIV is thus only applicable with materials transparent to light. Echo-PIV (echographic PIV) is based on the same principles as optical PIV. Instead of laser light illumination, the seeding particles are insonified with ultrasound waves. Ultrasound backscattering generates speckle patterns which can be tracked to deduce the displacements from one image to the next one. Echo-PIV has been of high interest in blood flow investigation. Echo-PIV, however, is hampered by conventional ultrasound imaging which offers a frame rate much smaller than optical PIV. Indeed, conventional ultrasound imaging emits successive focused beams to fully cover the region of interest. Typically, 128 emissions are required to obtain one single image. The objective of this research project is to use ultrafast ultrasound to produce high-speed echo-PIV working at frame rates up to 10,000 fps. High-speed echo-PIV has the potential to enlarge the family of fluid measurement systems. 3) METHODS To test high-speed echo-PIV, we will carry out velocity measurements in well-controlled Womersley and vortical flows, as well as in a pulse heart duplicator (ViVitro). The ViVitro system is compatible with both ultrasound and optical PIV. Pulsatile Womersley flows will be generated in a cylindrical pipe with a piston pump. From the known flow rate (given by an electromagnetic flowmeter) and pipe radius, the theoretical velocity profiles will be calculated using the Womersley equation. Three-dimensional vortical flows will be also created in a Plexiglas square box, transparent both to light and ultrasound, with a magnetic stirrer. In addition, to test high-speed echo-PIV with complex flow patterns, we will investigate intraventricular filling in the heart duplicator. The velocities will be measured by optical three-dimensional volumetric PIV (V3V-9800, TSI Inc.). In the different experimental setups, the velocities determined by high-speed echo-PIV will be compared with the ground-truth velocities, given by theory and/or optical PIV. Pixelwise comparisons will be performed on several planes and for different flow conditions.