There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

A review of shape memory alloy research, applications and opportunities

To improve the performance of particle image velocimetry in measuring instantaneous velocity fields, direct cross-correlation of image fields can be used in place of auto-correlation methods of interrogation of double- or multiple-exposure recordings. With improved speed of photographic recording and increased resolution of video array detectors, cross-correlation methods of interrogation of successive single-exposure frames can be used to measure the separation of pairs of particle images between successive frames. By knowing the extent of image shifting used in a multiple-exposure and by a priori knowledge of the mean flow-field, the cross-correlation of different sized interrogation spots with known separation can be optimized in terms of spatial resolution, detection rate, accuracy and reliability.

Theory of cross-correlation analysis of PIV images : Image analysis as measuring technique in flows

Aircraft wings are a compromise that allows the aircraft to fly at a range of flight conditions, but the performance at each condition is sub-optimal. The ability of a wing surface to change its geometry during flight has interested researchers and designers over the years as this reduces the design compromises required. Morphing is the short form for metamorphose; however, there is neither an exact definition nor an agreement between the researchers about the type or the extent of the geometrical changes necessary to qualify an aircraft for the title ‘shape morphing.’ Geometrical parameters that can be affected by morphing solutions can be categorized into: planform alteration (span, sweep, and chord), out-of-plane transformation (twist, dihedral/gull, and span-wise bending), and airfoil adjustment (camber and thickness). Changing the wing shape or geometry is not new. Historically, morphing solutions always led to penalties in terms of cost, complexity, or weight, although in certain circumstances, thes...

A Review of Morphing Aircraft

Originally introduced in the fluid mechanics community, dynamic mode decomposition (DMD) has emerged as a powerful tool for analyzing the dynamics of nonlinear systems. However, existing DMD theory deals primarily with sequential time series for which the measurement dimension is much larger than the number of measurements taken. We present a theoretical framework in which we define DMD as the eigendecomposition of an approximating linear operator. This generalizes DMD to a larger class of datasets, including nonsequential time series. We demonstrate the utility of this approach by presenting novel sampling strategies that increase computational efficiency and mitigate the effects of noise, respectively. We also introduce the concept of linear consistency, which helps explain the potential pitfalls of applying DMD to rank-deficient datasets, illustrating with examples. Such computations are not considered in the existing literature, but can be understood using our more general framework. In addition, we show that our theory strengthens the connections between DMD and Koopman operator theory. It also establishes connections between DMD and other techniques, including the eigensystem realization algorithm (ERA), a system identification method, and linear inverse modeling (LIM), a method from climate science. We show that under certain conditions, DMD is equivalent to LIM.

On Dynamic Mode Decomposition: Theory and Applications

Rotating stall and surge are flow instabilities that have plagued jet engines since the early days of their development. With the growing need for higher efficiencies, compressors are required to operate closer to the surge line. The breakdown of the flow into either rotating stall or surge is undesirable due to the effects it has on the jet engines performance and reliability. The traditional methods only partially protect against rotating stall or reduce compressor efficiency. This paper presents a single-stage axial compressor design that will be used to test a stall suppression system which introduces oscillatory blowing through one of the rotor blades.

Single-Stage Axial Compressor for the Study of Rotating Stall Suppression

View of a breakdown - Scientific visual analysis of vortex breakdown over a delta wing

This work discusses the development of a simulation of fish locomotion and its corresponding control. The simulation is based on unsteady panel methods and can calculate the loads on a general 2-D deformable hydrofoil (simplification of an aquatic animal) and then integrate them to produce the motion history. The code receives as input a specified body geometry history and outputs its loading and path. In order to achieve the reverse the simulation is used in conjunction with a neural network controller that predicts the needed body deflections (body geometry history) necessary to perform a specified maneuver. Validation results are presented that show the accuracy of the present simulation and several uncontrolled test cases are presented to show the capabilities of the controller.

Simulation of Fish Locomotion and Control

A comprehensive effort to study techniques aimed at rotorcraft blade-vortex interaction (BVI) reduction and the alleviation of the associated impulsive noise was recently initiated in the Aerospace Engineering Department at Texas A & M University. This is a multidisciplinary effort that seeks to exploit advances in the areas of aerodynamics, active materials, instrumentation, and conventional, as well as knowledge-based, aerodynamic system identification and control to benefit an application of high aerodynamic complexity and top importance in rotorcraft. This work reports to the community our progress to date, scientific findings, proposed designs and their implementations, and how all these pieces fit together in our ongoing effort of implementing a reduced BVI rotor. (Author)

Progress toward a reduced blade-vortex-interaction rotor

This paper presents results of an on-going effort to develop a new rotating stall suppression system. This system uses oscillatory blowing along the blade span on one or more airfoils in a row. The results presented herein focus on the flow characteristics of the internal plenum, and the performance of the oscillatory blowing system. A numerical simulation and an experimental investigation are being used to study the internal flow characteristics. The numerical simulation uses a Reynolds-averaged Navier-Stokes flow solver where the turbulence was modeled with the Shear Stress Transport model. The experimental setup developed for validating the oscillatory flow was developed to determine the relationship between the geometric configurations of the internal plenum and the resultant unsteady flow characteristics. The numerical simulations will be validated by data obtained from the experimental setup.

Othon K. Rediniotis

Papers

Single-Stage Axial Compressor for the Study of Rotating Stall Suppression

View of a breakdown - Scientific visual analysis of vortex breakdown over a delta wing

Simulation of Fish Locomotion and Control

Progress toward a reduced blade-vortex-interaction rotor

Internal Plenum Design and Testing for an Oscillatory Blowing Rotating Stall Suppression System