Time-resolved PIV of a turbulent jet with modal decomposition

Paper · Project 66

This paper reports time-resolved Particle Image Velocimetry measurements of a turbulent jet (Re = 2500), covering the full experimental setup, data processing, and modal analysis of the resulting fields.

Experimental setup

The setup comprised laser sheet illumination and high-speed imaging. Acquisition parameters were optimised at dt = 12.5 ms and 80 Hz based on displacement and confidence criteria, ensuring the measurement is genuinely time-resolved rather than a sequence of uncorrelated snapshots.

Processing

Velocity fields were reconstructed using cross-correlation techniques. The impact of interrogation window size was analysed by comparing DI = 128 px against 32 px, demonstrating improved capture of shear-layer structures and turbulent fluctuations with the refined processing.

Horizontal and vertical velocity fields for both window sizes/assets/img/papers/piv-fields-comparison.png

Fig. 1 — U/U_ref and V/U_ref for D_I = 128 px and 32 px.

Results

Mean flow fields and Reynolds stresses were computed, identifying peak turbulence production in the shear layer and the characteristic jet entrainment behaviour.

Principal Component Analysis via SVD was applied to extract coherent flow structures, identifying the dominant large-scale shear-layer modes, antisymmetric flapping, and higher-frequency turbulent features.

First five spatial modes of the fluctuating velocity field/assets/img/papers/piv-spatial-modes.png

Fig. 2 — Spatial modes of the fluctuating velocity field, U and V components.

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