Investigation into the Aerodynamics of Swashplateless Rotors Using CFD-CSD Analysis

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2012

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Abstract

This study obtains a better understanding of the aerodynamics of integrated

trailing edge flap (TEF) based swashplateless rotors. Both two dimensional (2D)

and three dimensional (3D) analysis/simulations are performed to understand the

behavior of TEF airfoils and integrated TEF based swashplateless rotors.

The 2D aerodynamics of TEF airfoils is explored in detail. A semi-empirical

approach is developed for modeling drag for TEF airfoils in steady flows based

on baseline airfoil drag data alone. Extensive 2D CFD simulations are performed

for a wide range of flow conditions in order to better understand various

aspects of the aerodynamics of TEF airfoils. The trends in the airloads (lift,

drag, pitching moment, hinge moment) for TEF airfoils are obtained. Nonlinear

phenomena such as flow separation, shocks and unsteady vortex shedding are

investigated, and the flow conditions and trends associated with them are

studied.

The effect of airfoil properties such as thickness and overhang are studied.

Various approaches are used to model the effect of gaps at the leading edge of

the flap. An approximate ``gap averaging'' technique is developed, which

provides good predictions of steady airloads at almost the same computational

cost as a simulation where the gap is not modeled. Direct modeling of the gap

is done by using a patched mesh in the gap region. To solve problems (such as

poor grid quality/control and poor convergence) that are associated with the

patched mesh simulations, an alternate approach using overlapping meshes is

used. It is seen that for TEF airfoils, the presence of gaps adversely affects

the effectiveness of the flap. The change in airloads is not negligible,

especially at the relatively higher flap deflections associated with

swashplateless TEF rotors.

Finally, uncoupled and coupled computational fluid/structural dynamics

(CFD-CSD) simulations of conventional (baseline) and swashplateless TEF rotors

is performed in hovering flight. The CFD-CSD code is validated against

experiment and good agreement is observed. It is observed that the baseline

UH-60 rotor performs better than the swashplateless UH-60 rotor. For an

untwisted NACA0012 airfoil based rotor, the performance is similar for the

baseline and swashplateless configurations. The effect of gaps on the

performance of swashplateless TEF rotors is also investigated. It is seen that

the presence of chordwise gaps significantly affects the effectiveness of the

TEF to control the rotor. Spanwise gaps also affect the performance of

swashplateless rotors but their effect is not as significant.

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