Aerodynamic Performance and Flow Control in Low Reynolds Number Flows

Aerodynamic performance at low Reynolds numbers is dominated by laminar–turbulent transition phenomena within boundary layers and the formation of laminar separation bubbles. In these regimes, viscous forces are comparable with inertial forces, leading to early flow separation, reduced lift generation and increased drag. This behaviour is critical for micro-air vehicles, near-space aircraft and unmanned systems operating at Reynolds numbers below 500 000. Advances in experimental and numerical methods have elucidated the role of instabilities such as Kelvin–Helmholtz vortices and Tollmien–Schlichting waves in triggering transition and vortex shedding. Flow-control techniques—including periodic surface morphing, acoustic excitation and active air-jet actuation—are under investigation to delay separation, manipulate coherent structures and enhance aerodynamic efficiency. Computationally, the development of transition models coupled to Reynolds-averaged Navier–Stokes solvers and high-fidelity direct or large-eddy simulations has improved predictive capabilities, guiding the design of low-Reynolds-number airfoils with optimised performance under varying turbulence intensities. The global significance of this work lies in the potential for quieter, more efficient small-scale aircraft and space-exploration vehicles, where reliable lift, stability and energy efficiency at low Reynolds numbers are paramount.

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Aerodynamic Performance and Flow Control in Low Reynolds Number Flows publication trend

The graph below shows the total number of articles in aerodynamic performance and flow control in low reynolds number flows across all publications each year (not limited to Nature Index journals).

Technical terms

Reynolds number (Re): Dimensionless ratio of inertial to viscous forces in a flow, governing the onset of turbulence.

Boundary layer: Thin region of fluid adjacent to a solid surface where viscous effects are significant and velocity gradients are large.

Laminar separation bubble: Region of reversed flow and recirculation that forms when a laminar boundary layer separates from a surface and subsequently reattaches downstream.

Kelvin–Helmholtz instability: Shear-layer instability mechanism that generates vortex rollers in regions of strong velocity gradient.

Tollmien–Schlichting waves: Instability waves within the boundary layer that amplify to trigger laminar–turbulent transition.

References

1. Control of low Reynolds number flow around an airfoil using periodic surface morphing: A numerical study. Journal of Fluids and Structures (2018).
2. Transition in a separation bubble under tonal and broadband acoustic excitation. Journal of Fluid Mechanics (2018).
3. Validation of the γ-Reθ Transition Model for Airfoils Operating in the Very Low Reynolds Number Regime. Flow, Turbulence and Combustion (2022).
4. Investigation on flow structure and aerodynamic characteristics over an airfoil at low Reynolds number—A review. AIP Advances (2021).
5. Aerodynamic Characteristics of Different Airfoils under Varied Turbulence Intensities at Low Reynolds Numbers. Applied Sciences (2020).