Unsteady Aerodynamic Methods

Animal flight represents a great challenge and model for biomimetic design efforts. Powered flight at low speeds requires not only appropriate lifting surfaces (wings) and actuator (engine), but also an advanced sensory control system to allow maneuvering in confined spaces, and take-off and landing. Millions of years of evolutionary tinkering has resulted in modern birds and bats, which are achieve controlled maneuvering flight as well as hovering and cruising flight with trans-continental non-stop migratory flights enduring several days in some bird species. Unsteady aerodynamic mechanisms allows for hovering and slow flight in insects, birds and bats, such as for example the delayed stall with a leading edge vortex used to enhance lift at slows speeds. By studying animal flight with the aim of mimicking key adaptations allowing flight as found in animals, engineers will be able to design micro air vehicles of similar capacities.

Download Full-text

Aerodynamic Asymmetry Analysis of Unsteady Flows in Turbomachinery

Journal of Turbomachinery ◽

10.1115/1.3103922 ◽

2009 ◽

Vol 132 (1) ◽

Cited By ~ 13

Author(s):

Kivanc Ekici ◽

Robert E. Kielb ◽

Kenneth C. Hall

Keyword(s):

Harmonic Balance ◽

Coupling Effect ◽

Unsteady Flows ◽

Unsteady Aerodynamic ◽

Blade Row ◽

Balance Technique ◽

Turbomachinery Blades ◽

Aerodynamic Asymmetry ◽

Frequency Domain Approach ◽

Harmonic Balance Technique

A nonlinear harmonic balance technique for the analysis of aerodynamic asymmetry of unsteady flows in turbomachinery is presented. The present method uses a mixed time-domain/frequency-domain approach that allows one to compute the unsteady aerodynamic response of turbomachinery blades to self-excited vibrations. Traditionally, researchers have investigated the unsteady response of a blade row with the assumption that all the blades in the row are identical. With this assumption the entire wheel can be modeled using complex periodic boundary conditions and a computational grid spanning a single blade passage. In this study, the steady/unsteady aerodynamic asymmetry is modeled using multiple passages. Specifically, the method has been applied to aerodynamically asymmetric flutter problems for a rotor with a symmetry group of 2. The effect of geometric asymmetries on the unsteady aerodynamic response of a blade row is illustrated. For the cases investigated in this paper, the change in the diagonal terms (blade on itself) dominated the change in stability. Very little mode coupling effect caused by the off-diagonal terms was found.

Download Full-text

FLAPPING WING DEVICES FOR MARS EXPLORATION

Proceedings of the Canadian Engineering Education Association (CEEA) ◽

10.24908/pceea.v0i0.4035 ◽

2011 ◽

Author(s):

Asier Ania ◽

Dominique Poirel ◽

Marie-Josée Potvin ◽

Steeve Montminy

Keyword(s):

Reynolds Number ◽

Insect Flight ◽

Low Reynolds Number ◽

Flapping Wing ◽

Low Density ◽

Mars Exploration ◽

Unsteady Aerodynamic ◽

Aerial Vehicle ◽

Low Reynolds

The use of an aerial vehicle would greatly enhance the domain of exploration on Mars. The main constraint in such a design would be the extreme Martian environment. The low-density atmosphere suggests the use of a low Reynolds number flight regime modeled after flapping wing insect flight. This flapping wing flight employs several unsteady aerodynamic mechanisms; delayed stall, wake capture, and rotational mechanisms. Two prototypes, a flapping wing and a rotary-flapping wing hybrid, have been built and will be tested in order to quantify the 'overall lift' generated and allow us to evaluate the efficacy of flapping wing flight on Mars.

Download Full-text