Adjustable window for 2D PIV estimation based on local Lagrangian coherency

Authors

  • Ali Rahimi Khojasteh French National Institute for Agriculture, Food, and Environment (INRAE), France
  • Dominique Heitz French National Institute for Agriculture, Food, and Environment (INRAE), France
  • Yin Yang French National Institute for Agriculture, Food, and Environment (INRAE), France

DOI:

https://doi.org/10.18409/ispiv.v1i1.136

Keywords:

Adjustable window, optical flow, Lagrangian Coherent Structures (LCS)

Abstract

We present a novel approach to adjust shapes of the interrogation windows (IW) in Particle Image Velocimetry (PIV) measurements as a function of temporal and spatial local coherent motions. Lagrangian Coherent Structures (LCS) has been widely utilized to determine local flow boundaries. We propose using Finite-Time Lyapunov Exponent (FTLE) to quantify LCS separatrix boundaries (i.e. ridges) and adjust the interrogation window. We integrated the proposed method with a local optical flow PIV algorithm. The evaluation was performed using synthetic particle images of 2D homogeneous isotropic turbulence obtained from Direct Numerical Simulation (DNS). The results showed significant improvements in regions with complex flow behaviours, particularly shear, vortex and hyperbolic motions. We studied improvements of the velocity estimation in a real experiment of the wake flow behind a cylinder at Reynolds number equal to 3900. It was found that optical flow featured by coherency based interrogation window (coherent optical flow) reveals detailed vector field estimations in regions with complex behaviours inside the wake flow.

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Published

2021-08-01

Issue

Section

Algorithms and Techniques