Aerodynamic Control of Laminar Separation on a Wall-Bounded Airfoil at Transitional Reynolds Numbers
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arXiv
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| Formato: | Preprint |
| Publicado: |
2025
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| _version_ | 1866913801248440320 |
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| author | Klewicki, Charles Schenkman, Ari Spedding, Geoffrey |
| author_facet | Klewicki, Charles Schenkman, Ari Spedding, Geoffrey |
| contents | Experiments were conducted in a low-turbulence wind tunnel to investigate the efficacy of localised acoustic forcing upon the dynamics and stability of the flow on a cambered, wall-bounded airfoil over a range of Reynolds numbers (Re) where the flow state can switch between two limits -- a low-lift state (SI) where separation continues beyond the trailing edge and a high-lift state (SII) where the separated flow is closed off to form a laminar separation bubble. The switching between SI and SII can occur close to a critical angle of attack ($α_{\textrm{crit}}$) which varies with $\textrm{Re}$. The most effective forcing frequencies are found at a constant value of a rescaled Strouhal number, $\textrm{St}^* = \textrm{St}/\textrm{Re}^{1/2}= 0.027$, which indicates that though the primary unstable modes of the separated shear layer are of the inviscid, Kelvin-Helmholtz type, these modes are seeded by length scales that originate in the laminar (viscous) boundary layer. The most effective chordwise forcing location varies with $\textrm{St}/\textrm{Re}^{1/2}$ and incidence angle, $α$, and is always upstream of the separation point. Although the boundary layer flows are far from two-dimensional, forcing at a fixed chord location across all spanwise locations is effective in controlling the SI -- SII transition. Strategies for active and passive feedback control are suggested. |
| format | Preprint |
| id |
arxiv_https___arxiv_org_abs_2504_15191 |
| institution | arXiv |
| publishDate | 2025 |
| record_format | arxiv |
| spellingShingle | Aerodynamic Control of Laminar Separation on a Wall-Bounded Airfoil at Transitional Reynolds Numbers Klewicki, Charles Schenkman, Ari Spedding, Geoffrey Fluid Dynamics Experiments were conducted in a low-turbulence wind tunnel to investigate the efficacy of localised acoustic forcing upon the dynamics and stability of the flow on a cambered, wall-bounded airfoil over a range of Reynolds numbers (Re) where the flow state can switch between two limits -- a low-lift state (SI) where separation continues beyond the trailing edge and a high-lift state (SII) where the separated flow is closed off to form a laminar separation bubble. The switching between SI and SII can occur close to a critical angle of attack ($α_{\textrm{crit}}$) which varies with $\textrm{Re}$. The most effective forcing frequencies are found at a constant value of a rescaled Strouhal number, $\textrm{St}^* = \textrm{St}/\textrm{Re}^{1/2}= 0.027$, which indicates that though the primary unstable modes of the separated shear layer are of the inviscid, Kelvin-Helmholtz type, these modes are seeded by length scales that originate in the laminar (viscous) boundary layer. The most effective chordwise forcing location varies with $\textrm{St}/\textrm{Re}^{1/2}$ and incidence angle, $α$, and is always upstream of the separation point. Although the boundary layer flows are far from two-dimensional, forcing at a fixed chord location across all spanwise locations is effective in controlling the SI -- SII transition. Strategies for active and passive feedback control are suggested. |
| title | Aerodynamic Control of Laminar Separation on a Wall-Bounded Airfoil at Transitional Reynolds Numbers |
| topic | Fluid Dynamics |
| url | https://arxiv.org/abs/2504.15191 |