{
  "abstract": "Turbulent boundary layers characterised by friction Reynolds numbers in the range $Re_τ = 880 - 1460$ and flowing over flush-mounted passively rotating discs are investigated in a wind tunnel with the purpose of reducing the skin-friction drag. The test surface is composed of thirty-two rotating discs arranged in a staggered configuration and supported by bearings mounted in cylindrical cavities. As the discs are half covered by thin rigid plates, a steady rotation of the discs is sustained via the asymmetric distribution of the wall-shear stress exerted by the wall turbulence on the exposed halves of the discs. Direct force measurements reveal that the drag increases with respect to a flat-plate case because of the flow interaction with the disc housings and the covering plates. The effect of the disc motion is isolated and a 3\\% drag reduction is measured with respect to the flow over stationary discs. The skin-friction identity by \\cite{Elnahhas_Johnson_2022} (\\emph{J. Fluid Mech.}, vol. 940, 2022), extended herein to include the disc-flow effects, is utilised for the first time to analyse experimental data. This direct slip effect, quantified by using the measured disc angular velocities in the Elnahhas-Johnson identity, is negligible. Measurements obtained by particle image velocimetry disclose that a roughness mean-flow effect occurs between adjacent discs because of the clearance gaps around the discs and that a downwash secondary flow exists near the covering plates, analogous to flows over streamwise-elongated rectangular roughness elements. This downwash velocity is streamwise modulated because of the spanwise disc motion and alters the wall-normal transport term in the Elnahhas-Johnson identity, thus reducing the drag locally.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2607.13496",
  "author_total": 2,
  "authors": [
    {
      "name": "Max W. Knoop"
    },
    {
      "name": "Pierre Ricco"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/cmcz0g676hkme.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2607.13496",
  "fulltext_url": null,
  "id": "cmcz0g676hkme",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2607.13496",
  "language": null,
  "licence": "CC-BY-4.0",
  "licence_label": "CC BY 4.0",
  "licence_source": "article",
  "licence_url": "http://creativecommons.org/licenses/by/4.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "physics.flu-dyn"
    ]
  ],
  "openalex": null,
  "pdf_url": "https://arxiv.org/pdf/2607.13496",
  "pmcid": null,
  "pmid": null,
  "published": "2026-07-15",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/cmcz0g676hkme.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:25:48Z",
      "native_id": "2607.13496",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2607.13496"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:physics.flu-dyn",
      "subfield": "fluid-dynamics"
    }
  ],
  "title": "Turbulent boundary layers altered by passively rotating discs",
  "title_text": "Turbulent boundary layers altered by passively rotating discs",
  "type": "preprint",
  "updated_at": "2026-10-30T12:25:48Z",
  "url": "https://research.draconitic.com/paper/cmcz0g676hkme",
  "venue": "arXiv",
  "versions": [
    {
      "doi": "10.1017/jfm.2026.11917",
      "pid": null,
      "relation": "published-as",
      "title": null,
      "venue": null
    }
  ]
}