Abstract
The aim of this paper is to study the physics related to lift generation on an airfoil. A new hypothesis [1] of physical mechanism of flight relies on existence of streamwise vortical structures above the wing and inside the wake. The vortices origin as a consequence of flow instability inside the boundary layer developed under adverse pressure gradient. These structures are highly dynamical in nature, they change position and size very rapidly. A simple airfoil in the form of a flat plate with moderate angle of attack is considered in the presented research that generates suitable flow at rather low Reynolds number. Stereo PIV time resolved measurement technique is used to capture high-dynamic data in several planes which are located in the wake and are perpendicular to freestream or parallel to the airfoil. The overall image of the flow field dynamics will be created using POD decomposition. Distinct flow patterns with associated kinetic energy are to be described as well as their role in the studied case. Existence of streamwise vorticity is proved, topology and other parameters are estimated in the paper; however related pressures and forces are not evaluated.
Highlights
In more than hundred years, we have witnessed very fast development of aeronautics
The simple Newton mechanics suggest the origin of the lift of a tilted flat plate by redirecting a horizontal stream of fluid particles, but indicated a disappointingly small value, proportional to the square of the angle of attack
The color with color bar represents the distribution of scalar quantities
Summary
In more than hundred years, we have witnessed very fast development of aeronautics. The ability to fly an apparatus with wings is proved by many experiments and without any doubts. Classical mathematical fluid mechanics could not give satisfactory explanation of the mystery of gliding flight. The simple Newton mechanics suggest the origin of the lift of a tilted flat plate by redirecting a horizontal stream of fluid particles, but indicated a disappointingly small value, proportional to the square of the angle of attack. D’Alembert followed up in 1752 by formulating his paradox about zero lift and drag of inviscid incompressible irrotational steady flow. This kind of hypothetical potential flow seemed to describe the airflow around a wing since the viscosity of air is very small. D’Alembert’s paradox had to be resolved, but nobody could figure out how and it was still an open problem when
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