Related Experiment Video
Updated: May 24, 2026
09:17
Experimental Investigation of the Flow Structure over a Delta Wing Via Flow Visualization Methods
Published on: April 23, 2018
Leading edge vortex in a slow-flying passerine.
Florian T Muijres1, L Christoffer Johansson, Anders Hedenström
1Department of Biology, Lund University, Sölvegatan 37, 223 62 Lund, Sweden. fmuijres@uw.edu
Biology Letters
|March 16, 2012
Summary
Hovering passerine birds, like the pied flycatcher, generate significant lift using leading edge vortices (LEVs) during their downstroke. This mechanism compensates for their less active upstroke, with LEVs contributing substantially to weight support.
Area of Science:
- Aviation Biology
- Biomechanics
- Animal Flight
Background:
- Most hovering animals, including insects and hummingbirds, utilize both wing strokes and leading edge vortices (LEVs) for lift.
- Hovering passerine birds typically rely more heavily on their downstroke for lift generation, with a less active upstroke.
Purpose of the Study:
- To investigate whether passerine birds, specifically the pied flycatcher, employ LEVs during the downstroke to enhance lift.
- To compare the contribution of LEVs to weight support in passerines versus hummingbirds.
Main Methods:
- Airflow dynamics around the wing of a freely flying pied flycatcher were captured.
- Quantitative analysis of leading edge vortex (LEV) contribution to lift and weight support was performed.
Main Results:
- Leading edge vortices (LEVs) contribute up to 49% of weight support in the pied flycatcher during the downstroke.
- This contribution is approximately three times higher than that observed in hummingbirds.
- LEV strength was found to be lowest near the wingtip, correlating with a reduced angle-of-attack and upward feather bending.
Conclusions:
- Passerine birds may compensate for their less active upstroke by generating exceptionally strong leading edge vortices (LEVs) during the downstroke.
- The unique distribution of LEV strength in passerines, with reduced strength at the wingtip, may serve to delay vortex shedding and maintain lift.
- This study highlights a distinct aerodynamic strategy employed by avian hoverers for efficient flight.
Related Concept Videos
01:28Irrotational Flow
Irrotational flow is characterized by fluid motion where particles do not rotate around their axes, resulting in zero vorticity. For a flow to be irrotational, the curl of the velocity field must be zero. This imposes specific conditions on velocity gradients. For instance, to maintain zero rotation about the z-axis, the gradient condition:
01:18Boundary Layer Characteristics
When a fluid encounters a solid surface, a boundary layer forms due to the interaction between the fluid's motion and the stationary surface. This phenomenon is characterized by a thin region adjacent to the surface where viscous forces dominate, influencing the fluid's velocity profile. The development of the boundary layer begins at the leading edge of the surface and evolves as the fluid moves downstream.As the fluid flows over the surface, friction between the fluid and the wall slows down...
01:24Turbulent Flow
Turbulent flow is characterized by unpredictable fluctuations in velocity and pressure, which result in a chaotic fluid movement distinct from the orderly patterns of laminar flow. While laminar flow is governed by smooth, parallel layers with minimal mixing, turbulent flow exhibits highly irregular, three-dimensional patterns. This behavior arises due to instabilities in the fluid's velocity profile, and amplifies as the flow velocity increases. Minor disturbances, known as turbulent spots,...
01:17Steady, Laminar Flow Between Parallel Plates
Understanding steady, laminar flow between parallel plates is essential for analyzing and designing flow in narrow rectangular channels, commonly found in various water conveyance and drainage systems. The Navier-Stokes equations govern fluid motion and are generally challenging to solve due to their nonlinearity. However, simplifications are possible in certain cases, like the steady laminar flow between parallel plates. For this scenario, we assume steady, incompressible, laminar flow.
01:26General External Flow Characteristics
The study of external flow is essential for creating structures and objects that interact efficiently and safely with moving fluids, such as air or water. When a body is immersed in a flowing fluid, it experiences two primary forces: drag, which opposes motion along the flow direction, and lift, which acts perpendicular to the flow. The shape, size, and orientation of the object influence these forces.Streamlined and Blunt Bodies in External FlowObjects in fluid flow are classified as...
01:30Bernoulli's Equation for Flow Along a Streamline
Bernoulli's equation relates the energy conservation in a fluid moving along a streamline. The equation applies to incompressible and inviscid fluids under steady flow. For such a flow, Newton's second law is applied to a small fluid element, which experiences forces due to pressure differences, gravity, and velocity variations. The force balance leads to the following form of Bernoulli's equation: