{
  "abstract": "Recent indoor experiments on small-scale hovering rotors have reported mid-frequency quasi-tonal peaks of uncertain origin in the residual (aperiodic) far-field sound spectrum, even without wake recirculation. This study investigates their physical origin using hybrid Reynolds-averaged Navier-Stokes/large-eddy simulations coupled with a Ffowcs Williams-Hawkings acoustic analogy, applied to a four-bladed ideally twisted rotor in hover. The high-resolution simulation reproduces the measured higher-harmonic blade-passage-frequency tones, confirming that they arise from the rotor flow itself and not from the enclosed-chamber test environment. Flow-field analysis attributes the tones to blade secondary vortex interaction (BSVI): the outboard blade sections, between approximately r/R = 0.88 and 0.96, are repeatedly impinged upon by coherent, S-shaped secondary vortex worms formed by entrainment of the wake shear layer into the primary tip vortices of preceding blades. These aperiodic secondary vortices produce blade-to-blade correlated loading, yielding a quasi-tonal signature distinct from both purely periodic blade-vortex interaction and mostly stochastic blade-wake interaction noise. Spectral proper orthogonal decomposition of the zero-mean upwash confirms that the mid-frequency (3-10 kHz) content is dominated by a single, low-rank, spatially coherent mode associated with the braids, whereas a lower-frequency mode near 1 kHz is linked to the primary tip vortex core. BSVI is thus identified as a distinct and previously uncharacterized source of aperiodic tonal noise in hovering rotors, with direct implications for the acoustic design of small- to medium-scale rotorcraft and electric vertical take-off and landing propulsors.",
  "abstract_shown": true,
  "affiliations": [],
  "article_type": null,
  "arxiv": "2609.27137",
  "author_total": 2,
  "authors": [
    {
      "name": "Jordon Won"
    },
    {
      "name": "Seongkyu Lee"
    }
  ],
  "bibtex": "https://research.draconitic.com/paper/39wwnsfcjq2bg.bib",
  "cited_by": 0,
  "doi": "10.48550/arxiv.2609.27137",
  "fulltext_url": null,
  "id": "39wwnsfcjq2bg",
  "issns": [],
  "landing_url": "https://arxiv.org/abs/2609.27137",
  "language": null,
  "licence": "LicenseRef-arXiv-nonexclusive-1.0",
  "licence_label": "arXiv licence",
  "licence_source": "article",
  "licence_url": "http://arxiv.org/licenses/nonexclusive-distrib/1.0/",
  "metadata_licence": "CC0-1.0",
  "native_subjects": [
    [
      "arxiv",
      "physics.flu-dyn"
    ],
    [
      "openalex",
      "2202|Aerodynamics and Acoustics in Jet Flows"
    ]
  ],
  "openalex": "W7214227924",
  "pdf_url": "https://arxiv.org/pdf/2609.27137",
  "pmcid": null,
  "pmid": null,
  "published": "2026-09-22",
  "publisher": null,
  "ris": "https://research.draconitic.com/paper/39wwnsfcjq2bg.ris",
  "sources": [
    {
      "first_seen": "2026-10-30T12:23:56Z",
      "native_id": "2609.27137",
      "source": "arxiv",
      "url": "https://arxiv.org/abs/2609.27137"
    }
  ],
  "subjects": [
    {
      "field": "physics",
      "origin": "arxiv:physics.flu-dyn",
      "subfield": "fluid-dynamics"
    }
  ],
  "title": "Blade secondary vortex interaction noise in hovering rotors",
  "title_text": "Blade secondary vortex interaction noise in hovering rotors",
  "type": "preprint",
  "updated_at": "2026-10-30T12:23:56Z",
  "url": "https://research.draconitic.com/paper/39wwnsfcjq2bg",
  "venue": "arXiv",
  "versions": []
}