A comparative analysis of the uncertainty of astigmatism-μPTV, stereo-μPIV, and μPIV

Astigmatism or wavefront deformation, microscopic particle tracking velocimetry (A-mu PTV) (Chen et al. in Exp Fluids 47:849-863, 2009; Cierpka et al. in Meas Sci Technol 21:045401, 2010b) is a method to determine the complete 3D3C velocity field in micro-fluidic devices with a single camera. By using an intrinsic calibration procedure that enables a robust and precise calibration on the basis of the measured data itself (Cierpka et al. in Meas Sci Technol 22:015401, doi:10.1088/0957-0233/22/1/015401"10.1088/0957-0233/22/1/015401, 2011), accurate results without errors due to spatial averaging or bias due to the depth of correlation can be obtained. This method takes all image aberrations into account, allows for the use of the whole CCD sensor, and is easy to apply without expert knowledge. In this paper, a comparative study is presented to assess the uncertainties of two state-of-the-art methods for 3C3D velocity field measurements in microscopic flows: stereoscopic micro-particle image velocimetry (S-mu PIV) and astigmatism micro-particle tracking velocimetry (A-mu PTV). First, the main parameters affecting all methods' measurement uncertainty are identified, described, and quantified. Second, the test case of the flow over a backward-facing step is analyzed using all methods. For comparison, standard 2D2C mu PIV measurements and numerical flow simulations are shown as well. Advantages and disadvantages of both methods are discussed.