#### Turbomachinery

Design for non-synchronous vibration (NSV) in turbomachinery

This research presents the detailed investigation of coupled-mode flutter and non-synchronous vibration in turbomachinery. Coupled-mode flutter and non-synchronous vibration are two aeromechanical challenges in designing turbomachinery that, when present, can cause engine blade failure.

Non-synchronous vibration (NSV) study of a NACA0012

This project seeks to bring some light into the physical flow mechanisms behind non-synchronous vibrations (NSV). A better understanding of the parameters that drive NSV is needed to establish guidelines to design NSV-free engines.

“GUIde” stands for Government Agencies, Universities, and Industry working together on a common goal. Through cooperation, the organizations within the Consortium develop an enhanced view of how to achieve their objective.

#### Fixed Wing Aircraft

The interaction between a cantilevered elastic plate and a uniform axial flow is a canonical fluid-structure interaction problem. If the flow is aligned normal to the clamped edge then the system is referred to as flag-like. It is well-known that this system exhibits a flutter instability when the flow velocity is increased above a critical velocity.

The aeroelastic stability of rectangular plates are well-documented in literature for certain sets of boundary conditions. Specifically, wing flutter, panel flutter, and divergence of a plate that is clamped on all sides are well-understood. However, the ongoing push for lighter structures and novel designs have led to a need to understand the aeroelastic behavior of elastic plates for other boundary conditions.

Folding Wing

This project focuses on analyzing the aeroelastic behavior of folding wings, a concept describing a wing that consists of multiple segments that are connected by hinges and can rotate relative to each other.

Limit Cycle Oscillations

#### Rotary Wing Aircraft

Rotary Wing Aerodynamics and Planform Optimization

For this project, we are researching the optimal aerodynamic rotor design for conventional and compound helicopters. This includes determining the blade twist, chord, and root inputs that produce the most efficient flight.

Rotor Vibration Reduction Using Multi-Element Multi-Path Design

Rotor blade vibration reduction has become an important consideration in aerospace engineering, turbomachinery, automobile engineering, etc. In the design of rotorcraft and wind turbines there is always a need to reduce the rotor blade vibration to maintain the stability and operational life of the whole structure. The approach to be explored in this research to solve vibration problem is the multi-element multi-path (MEMP) structures that inherently suppress vibration. The following figures show the evolution of this concept on helicopter rotor blades.

#### Solar Sail Spacecraft

Developing solar sail capabilities requires effective means of designing, analyzing and testing solar sail technologies. Because of the cost prohibitive nature of testin the systems and subsystems in space, accurate analysis and response predictions are vital to the future development of the technology

##### Acoustics

In acoustics, the group is lead by Dr. Bliss whoose primary effort is in the application of ANM to structural acoustics, particularly to acoustic scattering from submerged elastic bodies with structural discontinuities. He has also developed a method called Alternate Resonance Tuning (ART) to prevent low frequency sound transmission into flexible wall enclosures, with applications to aircraft interior noise. He also conducts research on mathematical homogenization applied to structural acoustic systems, and on general boundary conditions for bulk-reacting sound absorbing surfaces.

#### Reduced Order Modeling in Turbulence and Aerodynamics

Model Order Reduction for High Reynolds Number Flows

Turbulence is a phenomenon characterized by chaotic, multi-scale dynamics, both, in space and time. At high Reynolds numbers, the dynamics of turbulence exhibit an energy cascade: large scale eddies are broken down into smaller and smaller eddies until the scales are fine enough so that viscous forces can dissipate their energy. We generalize the POD-based Galerkin model order reduction approach by incorporating Navier-Stokes equation constraints.

POD Decomposition for Vortex Induced Vibrations Around a Cylinder

For a certain range of Reynolds numbers, flow passing by a cylinder will lead to a fluid dynamic instability, often referred to as von Karman vortices. These alternating, shedding vortices cause unsteady forces on the surface of the cylinder, which tend to make the cylinder oscillate; a phenomenon called 'vortex-induced vibrations'.

Extrapolative Potential of Turbulent ROMs

An investigation to develop a model-order reduction strategy robust enough to be applied accurately to turbulent flow regimes outside of the data set used to generate the model.

#### Nonlinear Aeroelasticity and Dynamics

Nonlinear Asymptotic Modal Analysis

Quickly and accurately describing the behavior of complicated and intricate dynamical systems opens the door to revolutionary design possibilities, including sensing technology in extreme environments, reliable failure predictions, and electromagnetic field control of plasmas. Time-marching simulations and Classical Modal Analysis (CMA) are often too computationally demanding to offer solutions to practical problems, but methods such as Statistical Energy Analysis (SEA) and Asymptotic Modal Analysis (AMA) can offer the quick insight necessary to appropriately develop design criteria.

System Identification of Nonlinear Aeroelastic Systems

We explore a novel, sparse representation of the Volterra series whose identification costs are significantly lower than the identification costs of the full Volterra series. We demonstrate that sparse Volterra reduced-order models are capable of efficiently modeling aerodynamically induced limit cycle oscillations of the prototypical NACA 0012 benchmark model.

Sensitivities to Initial Conditions of a Dynamic Snap-Through Buckling Structure

A nonlinear, dynamic snap-through buckling apparatus was constructed. Its vast bifurcation tendencies were explored experimentally and numerically, basins of attractions were created, and pathological behavior was identified and validated via numerical modeling.

Recent Advances in Nonlinear Aeroelasticity at Duke

Nonlinear Dynamics of the Lid-Driven Cavity

Development of ROM methods in the context of a canonical flow regime.

Aeroelastic Evaluation of the NASA HIAD

The NASA HIAD is an inflatable spacecraft that is currently being developed by NASA as a new method for transporting large payloads to the surfaces of planets. An aeroelastic evaluation will characterize any unstable behavior that may occur due to the interaction between the structure and the aerodynamic forces during entry, descent, and landing.