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Persistence of inlet conditions in the near-grid region of active-grid turbulence

Mohd. Hanzla, Christopher Ruhl, and Arindam Banerjee*

  • Atlantic Marine Energy Center (AMEC), Department of Mechanical Engineering and Mechanics, Lehigh University, Bethlehem, Pennsylvania 18015, USA

  • *Contact author: arb612@lehigh.edu
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Phys. Rev. Fluids 11, 064617 – Published 30 June, 2026

DOI: https://doi.org/10.1103/wbd1-hp6s

Abstract

Active grids enable the controlled generation of high Reynolds number turbulence; however, the influence of inlet conditions in the near-grid region remains poorly understood. Here we present a physics-focused experimental study of active-grid-generated turbulence in a water tunnel, focusing on the near-grid region (x/M<20), where the flow remains approximately homogeneous but strongly anisotropic. Inlet conditions are varied by independently controlling the operating protocol, the global blockage ratio (25%–74%), the mesh Reynolds number (ReM), and the Rossby number (Ro). At the highest global blockage (74%), trends in large-scale statistics with ReM and Ro are consistent with measurements reported farther downstream in the literature. In contrast, at substantially lower blockages (≲40.2%), qualitatively different behavior emerges: turbulence intensity decreases monotonically with increasing ReM and exhibits little sensitivity to Ro. These results demonstrate that global blockage acts as a contributing parameter for the persistence of inlet-condition effects, whereas ReM and Ro modulate the redistribution of energy across scales. While large-scale quantities differ at lower global blockage relative to the far-grid region, the dissipative length scale exhibits consistent trend with ReM and Ro across all blockages. Despite persistence of inlet condition in the near-grid region, streamwise velocity spectra exhibit collapse at low and high wave numbers when scaled by the integral and Kolmogorov length scales, respectively, indicating that two distinct length scales are required to describe the near grid. Together, these findings provide insight into how forcing geometry and timescales influence the transition from forcing-dominated toward more universal turbulence behavior, and establish global blockage as an important parameter controlling near-grid active-grid turbulence.

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Phys. Rev. Fluids 11, 064617– Published 30 June, 2026
  • Received 9 February 2026
  • Accepted 3 June 2026
Article part of CHORUS
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