Abstract

The instantaneous volumetric pressure in the near-wake of a truncated cylinder is measured by use of tomographic particle tracking velocimetry (PTV) using helium-filled soap bubbles (HFSB) as tracers. The measurement volume is several orders of magnitude larger than that reported in tomographic experiments dealing with pressure from particle image velocimetry (PIV). The near-wake of a truncated cylinder installed on a flat plate (Re D = 3.5 × 104) features both wall-bounded turbulence and large-scale unsteady flow separation. The instantaneous pressure is calculated from the time-resolved 3D velocity distribution by invoking the momentum equation. The experiments are conducted simultaneously with surface pressure measurements intended for validation of the technique. The study shows that time-averaged pressure and root-mean-squared pressure fluctuations can be accurately measured both in the fluid domain and at the solid surface by large-scale tomographic PTV with HFSB as tracers, with significant reduction in manufacturing complexity for the wind-tunnel model and circumventing the need to install pressure taps or transducers. The measurement over a large volume eases the extension toward the free-stream regime, providing a reliable boundary condition for the solution of the Poisson equation for pressure. The work demonstrates, in the case of the flow past a truncated cylinder, the use of HFSB tracer particles for pressure measurement in air flows in a measurement volume that is two orders of magnitude larger than that of conventional tomographic PIV.

Highlights

  • Volumetric and surface pressure measurements have become possible from tomographic particle image velocimetry (PIV) measurements as reviewed in van Oudheusden (2013)

  • Despite the use of this system by Ghaemi and Scarano (2013) for pressure extraction from time-resolved tomographic PIV, only a 1.6 × 0.6 × 2.4 cm3 measurement volume was achieved in a turbulent boundary layer at 10 m/s

  • Very few time-resolved tomographic PIV experiments, mainly in water, are reported in the literature where both the region of interest and an irrotational region are included in the measurement volume (e.g. Jeon et al 2016)

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Summary

Introduction

Volumetric and surface pressure measurements have become possible from tomographic particle image velocimetry (PIV) measurements as reviewed in van Oudheusden (2013). Despite the use of this system by Ghaemi and Scarano (2013) for pressure extraction from time-resolved tomographic PIV, only a 1.6 × 0.6 × 2.4 cm3 measurement volume was achieved in a turbulent boundary layer at 10 m/s.

Results
Conclusion

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