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Effect of centerline separation on a vortex dominated wake

Rhylan A. Huss* and Farrukh S. Alvi

  • Department of Mechanical and Aerospace Engineering, FAMU-FSU College of Engineering, Florida State University, Tallahassee, Florida 32310, USA

  • *Contact author: rhylanhuss@gmail.com
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Phys. Rev. Fluids 11, 074702 – Published 28 July, 2026

DOI: https://doi.org/10.1103/bn64-wtlz

Abstract

An experimental investigation was conducted on the wake of a rounded-edge slanted afterbody over a Reynolds number range of ReD=40K to ReD=200K. High-speed particle image velocimetry (PIV), surface pressure measurements, and high-accuracy drag measurements provided substantial insight into this complex flow. In particular, they revealed an undocumented wake-state transition from a previously observed centerline-separated (CS) vortex state to a new centerline-attached (CA) vortex state between ReD≈130K and 180K. This wake transition was accompanied by a significant drag reduction and the transition of the upstream boundary layer from laminar to turbulent. The CS vortex state shared characteristics with laminar separation bubbles and produced spatially diffuse vortices that exhibited two distinct instabilities: a low-frequency flapping instability that governed the vortex dynamics and a high-frequency short-wave instability that drove shear layer breakdown and reattachment. The reduction in recirculation length was attributed to diminished viscous damping at higher Reynolds numbers, enabling earlier shear layer transition. In contrast, the CA state exhibited neither frequency signature and lacked a separated region, indicating a fundamentally different underlying dynamical mechanism. The vortices in the CA state were highly structured and spatially coherent, further distinguishing them from the diffuse and unsteady vortices observed in the CS state. These results provide new physical insight into the interplay between upstream boundary-layer transition, separated shear layer dynamics, wake topology, and their collective effect on global aerodynamics in terms of drag. Together, they provide a more comprehensive and unified understanding of the wake states and their transition between CS and CA for bluff body wakes.

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Phys. Rev. Fluids 11, 074702– Published 28 July, 2026
  • Received 11 October 2025
  • Accepted 22 May 2026
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