A Numerical Study of a Rotor Induced Flow Based on a Finite-State Dynamic Wake Model.

A Helicopter rotor undergoes unsteady aerodynamic loads ruled by the aeroelastic coupling between the elastic blades and the dynamic wake induced by rotary wings. Modeling the dynamic interaction between the structural and aerodynamic fields is a key point to understand aeroelastic phenomena associated with rotor stability, flow induced vibration and noise generation, among others. In this study, we address the Generalized Dynamic Wake Model, which describes the inflow velocity field at the rotor disk as a superposition of a finite number of induced flow states. It is a mature model that has been validated based on experimental data and numerically investigated from an eigenvalue problem formulation, whose eigenvalues and eigenvectors provide a deeper insight on the dynamic wake behavior. The paper extends the results presented in the literature to date in order to support physical interpretation of inflow states drawn from the finite-state wake model for flight conditions varying from hover to edgewise flight. The discussion of the wake model mathematical formulation is also oriented towards practical engineering applications to fill a gap in the literature.

Unsteady Aerodynamic Modeling and Prediction of Loads for Rotary Wings in Forward Flight

In this effort, a new approach in aerodynamic modeling that accounts for unsteady wake effects as well as viscous friction drag, Leading edge suction effect and post stall behavior for rotary wings in forward flight is proposed. The adopted approach commingles the unsteadiness with the problem of helicopter rotor blade in forward flight. The results of the local normal force coefficients were compared with experimental results of the 7A rotor case study in high speed test point 312 at five non-dimensional radial positions. A CFD solver, HOST/elsA, results are compared with the obtained results at five radii locations. The results show a good agreement between the experimental results and the proposed model preserving the same pattern of variation along the azimuth angle with a slight discrepancy for amplitude and phase angle. Of particular interest, the presented model showed better agreement with the experimental for higher radii locations.

An Investigation of the Electroaeroelastic Behavior of a Locally Resonant Piezoelectric Metastructure

The literature of aeroelasticity includes the use of smart materials to modify the aeroelastic behavior of fixed or rotary wings. In some cases, they are employed as actuators in active control systems while in others the use of smart materials in passive control schemes is investigated. In this work a different approach is investigated. The aeroelastic behavior of a locally resonant electromechanical metastructure made from flexible substrates with piezoelectric layers connected to resonant shunt circuits is investigated. An electromechanically coupled finite element plate model is employed for predicting the electroelasatic behavior of the wing. The unsteady aerodynamic loads are obtained from the doublet lattice model. By combining the structural and aerodynamic models, the aeroelastic behavior of the metastructure over a range of airflow speeds is studied.