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This study examines how permeability affects the aerodynamic behavior of two-dimensional porous rectangular plates at various angles of attack. At low Reynolds numbers (30-90), researchers found that increasing porosity (measured by Darcy number) weakens vortex formation behind the plate and reduces lift, drag, and torque forces. The flow patterns transition from vortex dipoles at low porosity to simpler recirculation regions at higher porosity, with the specific transition behavior depending on both porosity level and incidence angle.
Why it matters
The findings provide fundamental insights into how porosity affects aerodynamic forces on small wings, which could inform the design of micro air vehicles, passive flow control devices, and bio-inspired flying systems that utilize porous surfaces for lift modulation and drag reduction.
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⚠️ Preprint – Noch nicht peer-reviewed
Dieser Artikel wurde noch nicht von unabhängigen Experten begutachtet. Die Ergebnisse sind vorläufig und sollten mit Vorsicht interpretiert werden.
Abstract: This paper investigates the effect of permeability on two-dimensional rectangular plates at incidences. The flow topology is investigated for Reynolds number ($Re$) values between 30 and 90, and the forces on the plate are discussed for $Re=30$, where the wake is found to be steady for any value of the Darcy number ($Da$) and the flow incidence ($alpha$). At $Re=30$, for a plate normal to the stream and vanishing $Da$, the wake shows a vortex dipole with a stagnation point on the plate surface. With increasing $Da$, the separation between the vortex dipole and the plate increases; the vortex dipole shortens and is eventually annihilated at a critical $Da$. For any value of $Da$ below the critical one, the vortex dipole disappears with decreasing $alpha$. However, at low $Da$, the two saddle-node pairs merge at the same $alpha$, annihilating the dipole; while at high $Da$, they merge at different $alpha$, resulting in a single recirculating region for intermediate incidences. The magnitudes of lift, drag, and torque decrease with $Da$. Nevertheless, there exists a range of $Da$ and $alpha$, where the magnitude of the plate-wise force component increases with $Da$, driven by the shear on the plate’s pressure side. Finally, the analysis of the fluid impulse suggests that the lift and drag reduction with $Da$ are associated with the weakening of the leading and trailing edge shear layer, respectively. The present findings will be directly beneficial in understanding the role of permeability on small porous wings.
Source: Porous plates at incidence