by Naval Postgraduate School, Available from National Technical Information Service in Monterey, Calif, Springfield, Va .
Written in English
The unsteady aerodynamic forces and moments of an oscillating airfoil for the fixed wing case were determined by Theodorsen along with the development of a lift deficiency function. Loewy subsequently developed an analogous lift deficiency function for the rotary wing case in which there are an infinite number of layers of shed vorticity, or wakes, below the reference airfoil. With the advent of computer panel codes that calculate the time histories of the wakes generated by oscillating airfoils, a theory is developed for the rotary wing case in which there are a finite number of layers of shed vorticity below the reference airfoil. This theory includes a lift deficiency function that is completely analogous to Loewy and Theodorsen. It has long been recognized that an airfoil oscillating in pure plunge produces a propulsive force ( Katzmayr effect ). Garrick used Theodorsen"s work to develop equations for the propulsive force that include the lift deficiency function as a parameter. When either Loewy"s lift deficiency function or the finite wake lift deficiency function is used, the effect of the propulsive force is greatly enhanced with the proper phase relationship of the wakes. The finite wake theory along with Garrick"s work is used to describe the performance characteristics of Higher Harmonic Control. Specifically for the OH-6A, coupled pitch-plunge motion results in a propulsive force that significantly reduces the rotor drag force. Helicopter, Rotary wing, Unsteady aerodynamics, Wake, Propulsive force, Higher harmonic control, Hummingbird.
|Statement||Mark A. Couch|
|The Physical Object|
|Pagination||58 p. ;|
|Number of Pages||58|
Thesis advisor(s): E. R. WoodPages: finite wake lift deficiency function is used, the effect of the propulsive force is greatly enhanced with the proper phase relationship of the wakes. The finite wake theory along with Garrick's work is used to describe the performance characteristics of Higher Harmonic Control. Specifically for the OH-6A,File Size: 1MB. With the advent of computer panel codes that calculate the time histories of the wakes generated by oscillating airfoils, a theory is developed for the rotary wing case in which there are a finite number of layers of shed vorticity below the reference : Mark A. Couch. A Model of the Unsteady Aerodynamics of a Hovering Helicopter Rotor That Includes Variations of the Wake Geometry Journal of the American Helicopter Society, Vol. 40, No. 3 Correlation of unsteady pressure and inflow velocity fields of a pitching rotor blade.
Equations for the 2-D, unsteady, rotary-wing aerodynamic forces and moments with a finite number of wakes, or shed layers of vorticity, beneath the rotor are developed and applied specifically to. Unsteady Lifting Line Theory Using the Wagner Function for the Aerodynamic and Aeroelastic Modeling of 3D Wings 1 September | Aerospace, Vol. 5, No. 3 Nonlinear Aeroelastic Response of Highly Flexible Flying Wing Due to Different Gust Loads. It is interesting to note here that there is also a two-dimensional model of unsteady aerodynamics for rotary wings in which the returning wake is treated by layers of vorticity below the airfoil in a two-dimensional plane. Loewy () used this concept to develop an analog to the Theodorsen function for rotary wings. The modeling of unsteady aerodynamics for rotary-wing applications requires an understanding of the type of aeroelastic phenomena that is of interest. Different regimes require different modeling techniques. This modeling also requires a distinction between the blade-lift model and the induced-flow model.
When it is impossible to treat the motion as simple harmonic, the Theodorsen Function can be replaced with finite-state models that approximate the lift behavior in some frequency range. For rotary-wing problems, the analog to Theodorsen theory is Loewy theory which is a two-dimensional approximation to the effect of the rotor wake. Rotary-wing flow fields are as complex as any in aeronautics. The helicopter rotor in forward flight encounters three-dimensional, unsteady, transonic, viscous aerodynamic phenomena. Rotary-wing problems provide a stimulus for development and opportunities for application of the most advanced computational techniques. The finite wake theory along with Garrick's work is used to describe the performance characteristics of Higher Harmonic Control. The aerodynamic forces and flow structures of a wing of relatively small aspect ratio in some unsteady rotational motions at low Reynolds number (Re=) are studied by numerically solving the Navier-Stokes equations. These motions include a wing in constant-speed rotation after a fast start, wing accelerating and decelerating from one rotational speed to another, and wing rapidly pitching-up.