Cierpka Christian, Scharnowski Sven, Kähler Christian J
Institute of Fluidmechanics and Aerodynamics, Bundeswehr University Munich, Neubiberg, Germany.
Appl Opt. 2013 Apr 20;52(12):2923-31. doi: 10.1364/AO.52.002923.
For the basic understanding of turbulence generation in wall-bounded flows, precise measurements of the mean velocity profile and the mean velocity fluctuations very close to the wall are essential. Therefore, three techniques are established for high-resolution velocity profile measurements close to solid surfaces: (1) the nanoprobe sensor developed at Princeton University, which is a miniaturization of a classical hot-wire probe [Exp. Fluids 51, 1521 (2011)]; (2) the laser Doppler velocimetry (LDV) profile sensor, which allows measurement of the location of the particles inside the probe volume using a superposition of two fringe systems [Exp. Fluids 40, 473 (2006)]; and (3) the combination of particle image velocimetry and tracking techniques (PIV/PTV), which identify the location and velocity of submicrometer particles within the flow with digital imaging techniques [Exp. Fluids 52, 1641 (2006)]. The last technique is usually considered less accurate and precise than the other two. However, in addition to the measurement precision, the effect of the probe size, the position error, and errors due to vibrations of the model, test facility, or measurement equipment have to be considered. Taking these into account, the overall accuracy of the PTV technique can be superior, as all these effects can be compensated for. However, for very accurate PTV measurements close to walls, it is necessary to compensate the perspective error, which occurs for particles not located on the optical axis. In this paper, we outline a detailed analysis for this bias error and procedures for its compensation. To demonstrate the capability of the approach, we measured a turbulent boundary layer at Re(δ)=0.4×10(6) and applied the proposed methods.
为了基本了解壁面流动中湍流的产生，精确测量靠近壁面的平均速度剖面和平均速度脉动至关重要。因此，已建立了三种用于在靠近固体表面处进行高分辨率速度剖面测量的技术：（1）普林斯顿大学开发的纳米探针传感器，它是经典热线探针的小型化[《实验流体》51, 1521 (2011)]；（2）激光多普勒测速剖面传感器，它利用两个条纹系统的叠加来测量探针体积内粒子的位置[《实验流体》40, 473 (2006)]；以及（3）粒子图像测速和跟踪技术（PIV/PTV）的组合，它通过数字成像技术识别流场中亚微米级粒子的位置和速度[《实验流体》52, 1641 (2006)]。通常认为最后一种技术不如其他两种技术精确。然而，除了测量精度外，还必须考虑探针尺寸的影响、位置误差以及模型、测试设备或测量设备振动引起的误差。考虑到这些因素，PTV技术的整体精度可能更高，因为所有这些影响都可以得到补偿。然而，对于靠近壁面的非常精确的PTV测量，有必要补偿因粒子不在光轴上而产生的透视误差。在本文中，我们概述了对这种偏差误差的详细分析及其补偿程序。为了证明该方法的能力，我们测量了雷诺数Re(δ)=0.4×10(6)下的湍流边界层并应用了所提出的方法。
