{
  "id": "2309.13929",
  "version": "v1",
  "published": "2023-09-25T07:58:37.000Z",
  "updated": "2023-09-25T07:58:37.000Z",
  "title": "Opposition flow control for reducing skin-friction drag of a turbulent boundary layer",
  "authors": [
    "Giulio Dacome",
    "Robin Mörsch",
    "Marios Kotsonis",
    "Woutijn J. Baars"
  ],
  "categories": [
    "physics.flu-dyn"
  ],
  "abstract": "This work explores the dynamic response of a turbulent boundary layer to large-scale reactive opposition control, at a friction Reynolds number of $Re_\\tau \\approx 2\\,240$. A hot-film is employed as the input sensor, capturing large-scale fluctuations in the wall-shear stress, and actuation is performed with a single on/off wall-normal blowing jet positioned $2.4\\delta$ downstream of the input sensor, operating with an exit velocity of $v_{\\rm j} = 0.4U_\\infty$. Our control efforts follow the work by Abbassi et al. [Int. J. Heat Fluid Fl. 67, 2017], but includes a control-calibration experiment and a performance assessment using PIV- and PTV-based flow field analyses. The controller targets large-scale high-speed zones when operating in ``opposing\" mode and low-speed zones in the ``reinforcing\" mode. An energy-attenuation of about 40% is observed for the opposing control mode in the frequency band corresponding to the passage of large-scale motions. This proves the effectiveness of the control in targeting large-scale motions, since an energy-intensification of roughly 45% occurs for the reinforcing control mode instead. Skin friction coefficients are inferred from PTV data to yield a direct measurement of the wall-shear stress. Results indicate that the opposing control logic can lower the wall-shear stress by about 3% with respect to a desynchronised control strategy, and by roughly 10% with respect to the uncontrolled flow. A FIK-decomposition of the skin-friction coefficient was performed, revealing that the off-the-wall turbulence follows a consistent trend with the PTV-based wall-shear stress measurements, although biased by an increased shear in the wake of the boundary layer given the formation of a plume due to the jet-in-crossflow actuation.",
  "revisions": [
    {
      "version": "v1",
      "updated": "2023-09-25T07:58:37.000Z"
    }
  ],
  "analyses": {
    "keywords": [
      "turbulent boundary layer",
      "opposition flow control",
      "reducing skin-friction drag",
      "wall-shear stress",
      "targets large-scale high-speed zones"
    ],
    "note": {
      "typesetting": "TeX",
      "pages": 0,
      "language": "en",
      "license": "arXiv",
      "status": "editable"
    }
  }
}