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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Thu, 13 Jun 2024 11:32:12 GMT2024-06-13T11:32:12ZGlobal stability, sensitivity and passive control of low-Reynolds-number flows around NACA 4412 swept wings
http://hdl.handle.net/10985/23404
Global stability, sensitivity and passive control of low-Reynolds-number flows around NACA 4412 swept wings
NASTRO, Gabriele; ROBINET, Jean-Christophe; LOISEAU, Jean-Christophe; PASSAGGIA, Pierre-Yves; MAZELLIER, Nicolas
The stability and sensitivity of two- and three-dimensional global modes developing on steady spanwise-homogeneous laminar separated flows around NACA 4412 swept wings are numerically investigated for different Reynolds numbers Re and angles of
attack α. The wake dynamics is driven by the two-dimensional von Kármán mode whose emergence threshold in the α–Re plane is computed with that of the three-dimensional centrifugal mode. At the critical Reynolds number, the Strouhal number, the streamwise wavenumber of the von Kármán mode and the spanwise wavenumber of the leading three-dimensional centrifugal mode scale as a power law of α. The introduction of a sweep angle attenuates the growth of all unstable modes and entails a Doppler effect in the leading modes’ dynamics and a shift towards non-zero frequencies of the three-dimensional centrifugal modes. These are found to be non-dispersive as opposed to the von Kármán modes. The sensitivity of the leading global modes is investigated in the vicinity of the critical conditions through adjoint-based methods. The growth-rate sensitivity map displays a region on the suction side of the wing, wherein a streamwise-oriented force has a net stabilising effect, comparable to what could have been obtained inside the recirculation bubble. In agreement with the predictions of the sensitivity analysis, a spanwise-homogeneous force suppresses the Hopf bifurcation and stabilises the entire branch of von Kármán modes. In the limit of small amplitudes, passive control via spanwise-wavy forcing produces a stabilising effect similar to that of a
spanwise-homogeneous control and is more effective than localised spherical forces.
Sun, 01 Jan 2023 00:00:00 GMThttp://hdl.handle.net/10985/234042023-01-01T00:00:00ZNASTRO, GabrieleROBINET, Jean-ChristopheLOISEAU, Jean-ChristophePASSAGGIA, Pierre-YvesMAZELLIER, NicolasThe stability and sensitivity of two- and three-dimensional global modes developing on steady spanwise-homogeneous laminar separated flows around NACA 4412 swept wings are numerically investigated for different Reynolds numbers Re and angles of
attack α. The wake dynamics is driven by the two-dimensional von Kármán mode whose emergence threshold in the α–Re plane is computed with that of the three-dimensional centrifugal mode. At the critical Reynolds number, the Strouhal number, the streamwise wavenumber of the von Kármán mode and the spanwise wavenumber of the leading three-dimensional centrifugal mode scale as a power law of α. The introduction of a sweep angle attenuates the growth of all unstable modes and entails a Doppler effect in the leading modes’ dynamics and a shift towards non-zero frequencies of the three-dimensional centrifugal modes. These are found to be non-dispersive as opposed to the von Kármán modes. The sensitivity of the leading global modes is investigated in the vicinity of the critical conditions through adjoint-based methods. The growth-rate sensitivity map displays a region on the suction side of the wing, wherein a streamwise-oriented force has a net stabilising effect, comparable to what could have been obtained inside the recirculation bubble. In agreement with the predictions of the sensitivity analysis, a spanwise-homogeneous force suppresses the Hopf bifurcation and stabilises the entire branch of von Kármán modes. In the limit of small amplitudes, passive control via spanwise-wavy forcing produces a stabilising effect similar to that of a
spanwise-homogeneous control and is more effective than localised spherical forces.