Modeling of particle imaging through shock waves

摘要

In compressible flows particle imaging, as done in Particle Image Velocimetry (PIV), is far from trivial. The inhomogeneous refractive index field can cause aero-optical aberrations including blurring of the image, especially near optical interfaces such as shock waves. The understanding of the process causing particle image blur (or blurring of the point spread function of the imaging system) is important in order to assess the measurement accuracy of optical measurement systems, such as PIV. A model for imaging through a shock wave is presented to determine the characteristic shape of blurred particle images when imaged across shock waves. The conjectured model is validated through a PIV experiment, where particle image recordings of the flow across a steady oblique shock wave are obtained in a supersonic wind tunnel. The parametric study focuses on two dominating parameters: 1) the angle between the viewing axis and the shock wave; 2) the numerical aperture of the imaging optics.