<title>Vortex wake control via smart structures technology</title>

The NRC has undertaken re-instrumentation of the NRC CT-133 ruggedised research aeroplane, for high altitude atmospheric research. In the process, a new air data system has been designed, and optimized for high data acquisition rates, in particular matching the capability of the aircraft’s FRL inertial reference and navigation system, to derive and acquire wind vector data at 600 Hz. The platform has been used to conduct transport aircraft wake vortex (WV) surveys, and acquire instability wake vortex flowfield data, most recently in comparative straight flight and turning flight manoeuvres, using a Falcon 20 wake generator, to 3 nm distance. Vortex core traverse analysis has highlighted a greater frequency of small-scale vortex segments with high (>150% exceedance of the primary vortex) tangential velocities in turning flight; also, a greater bandwidth in short-wave instability wavelengths, and higher amplitude in long-wave instability, also multi-wavelength, but centred at 3 to 5 generator wingspans, whether in straight or turning flight. Such observations and general considerations of possible tactical jet aircraft wake vortex flowfields suggests the need to establish from flight data, wake vortex flowfield environmental design requirements, in order that contemporary and new tactical aircraft types may be developed with robust flight control systems, able to handle the [frequency amplitude] environments experienced during wake vortex encounters.

Along with the rapid development of the air transportation industry, the impact of aircraft wake vortices on flight safety and airport capacity has become increasingly prominent. In this paper, we propose a transformer-based model to solve the problem of multiple LIDAR wake vortex detection and recognition in airports. By setting up multiple Doppler LIDARs in the near-Earth flight areas of different runways of Shenzhen Baoan Airport (SZX), a large amount of accurate wind field data is captured for wake vortex data collection. In the deep learning framework, the radial velocity sequence obtained from the LIDAR is used as the input of the transformer. Meanwhile, local meteorological information and LIDAR operating parameters are introduced into the model, providing prior knowledge at different observation points. The experimental results show that the model has unified modeling for different LIDAR wake vortex detection, and has obtained excellent recognition results.

Black box design is a constraint driven design approach that distills essential elements of a physical process into inputs and outputs. This paper details the black box design implementation and validation of shape memory alloy (SMA) coil actuators as active members in a Watt I six bar avian-inspired wearable morphing angel wing mechanism. SMA coil actuators leverage the unique characteristics of high energy density SMA wire by providing a compact structural platform for large actuation displacement applications. The moderate force and displacement performance of low spring index coil actuators paired with their virtually silent actuation performance made them an attractive actuator solution to an avian-inspired wearable morphing wing mechanism for the University of Minnesota Department of Theatre Arts and Dance production of ‘Marisol’. The wing design constraints (extended span of 7.5 ft, a closed span of 3 ft) required a tailorable actuator system with capacity to perform at particular target force and strain metrics cyclically. A low spring index parameter study was conducted to facilitate an accelerated phase of design prototyping. The parameter study featured six SMA coil actuator prototypes made with 0.012” diameter Dynalloy Flexinol® wire of varying spring indexes (C = 2.5–4.9). The coil actuators were manufactured through a CNC winding process, shape set in a furnace at 450 °C for 10 minutes, and water quenched for hardening. A series of thermomechanical actuation tests were conducted to experimentally characterize the low spring index actuation performances. The coil actuation characterizations demonstrated increased force and decreased actuator displacement corresponding to decreased spring indexes. Scaling these results aided an accelerated design of an actuator system. The actuator system consisted of four C = 3.05 coil actuators wound with 0.02” diameter SMA that were integrated into each Watt I mechanism. The characterization of the force-displacement profiles for low index SMA coil actuators provides an effective empirical design strategy for scaling actuator performance to mechanical systems requiring moderate force, moderate displacement actuators.

Enhancement of wake vortex decay by air blowing from the ground

Vortex wakes of conventional aircraft and their propagating nature close to the ground have a great impact on the safety and efficiency of the traffic flow on an airport. The development of a measurement technique which helps detecting e.g. the density gradients in the air due to the wake vortices and understanding the nature of such a flow structure in its natural environment can improve the predictability of this hazardous phenomenon. Therefore, the practical aspects of the implementation of an advanced Schlieren technique on an airport are described in this chapter. Two experiments based on slightly different setups and locations relatively to the runway were conducted in order to assess the feasibility of the Background Oriented Schlieren method (BOS) for the detection and investigation of aircraft wake vortices. The evaluation of the obtained data indicated a sufficient ability of this technique to detect strong density gradient but on the other hand, turned out to be less efficient when dealing with the peculiarities of a large scale outdoor experiment.

An aircraft wake vortex retrieval method that estimates the horizontal and vertical positions and radii-averaged circulations of wake vortices from lidar-measured Doppler spectra on a lateral range–height indicator is proposed. The method formulates relationships between state variables and measured Doppler spectra for each individual wake vortex and iteratively optimizes the state variables so as to match the measured Doppler spectra. Because the state variables consist of a position, the parameters of an assumed two-dimensional vortex model, and a local background wind, high retrieval accuracy is achieved without adverse influences from errors in the preestimation of position or background wind. The separate formulation of each wake vortex enables the method to flexibly handle nonideal cases, for example where only one wake vortex of a pair remains or a long-persistent wake vortex and a newly generated pair of wake vortices coexist on a single range–height indicator. The retrieval results were evaluated against reference flight data from 864 flights collected during a wake vortex observation campaign conducted by the Japan Aerospace Exploration Agency at Narita International airport. The evaluation was performed by an approach using self- and cross-evaluation models, which allowed the evaluation of a large number of retrievals considering time variation of the wake vortex parameters. As a result, the proposed method was found to retrieve horizontal position with a bias error of and a standard error of 4.8 m; vertical position with bias and standard errors of and 3.5 m, respectively; and radii-averaged circulation with bias and standard errors of and , respectively.

Nickel-Titanium (NiTi)-based shape memory alloys (SMAs) enable new sustainable and environmentally friendly solid-state heating and cooling technologies. Elastocaloric (EC) heat pump systems exploit superelastic SMAs as a non-volatile, inflammable, and non-global-warming refrigerant, in contrast to the well-established vapor compression technology. The high specific latent heat released or absorbed during mechanical loading or unloading of the SMA material leads to a high temperature change in the material. As a result of the small required work input to induce the phase transformation, a high coefficient of performance (COP) can be achieved by this technology. The potential of these alloys can be exploited through an adequate thermodynamic cycle, efficient mechanical system design, and choice of suited EC materials. A fully functional continuous operating EC heat pump system based on SMA was developed and realized recently. The EC heat pump system comprises 24 thin wire bundles of 30 wire segments in one bundle. To assist the design process of an optimized device with given performance and efficiency requirements, the air-cooling behavior of single wires and simple bundle arrangement has been analyzed, and intensive parameter studies on different airflow rates have been performed. Regarding validating the EC heat pump system, a reproducible manufacturing process is presented for the first time, which supports the installation of at least 720 SMA segments in the same thermo-mechanical state. This work introduces the bundle fabrication process for the first time and validates it by comparing the key thermo-mechanical values of 135 SMA bundles.

The design of the Wake Vortex Prediction and Monitoring System WSVBS is described with all its components and their interaction. The WSVBS was developed to tactically increase airport capacity for approach and landing on closely-spaced parallel runways. The WSVBS supports dynamic adjustment of aircraft wake vortex separations dependent on weather conditions and the resulting wake vortex behavior without compromising safety. Dedicated meteorological instrumentation and short-term numerical terminal weather prediction provide the input to the prediction of wake-vortex behavior and respective safety areas. The prediction tools employ a number of conservative aircraft parameter combinations that represent the medium and heavy aircraft weight categories. Safe aircraft separations correspond to times when the predicted safety areas associated with wake vortices generated by leading heavy aircraft cannot overlap the arrival flight corridor. A LIDAR monitors the correctness of WSVBS predictions in the most critical regions at low altitude.

Aircraft wake vortices, evolving close to the ground in a cross wind, are a potential hazard to aircraft landing or taking off on the same or parallel runways. The objective of this work has been to study, by means of numerical simulation, the effect of aerodynamic and environmental conditions on the generation and transport of these vortices. The approach has been to use a computer code which solves the two-dimensional, timedependent, incompressible Navier-Stokes equations expressed in stream function-vorticity form, to study wake vortices in ground effect with crosswind. The code permits the specification of arbitrary atmospheric stability and wind profiles. A mixed no-slip/free-slip lower boundary condtion has been invoked to model the interaction of the vortices with the ground. Comparisons of code output with laboratory and field data have been used to validate the code. Simulation results have shown that, even after evolution times and cross-runway transport distances on the order of 3 min and 500 m, vortices generated by large aircraft close to the ground in a crosswind can carry sufficient average circulation to be a potential hazard to smaller aircraft. Additional full-scale data need to be acquired and additional numerical comparisons need to be performed to assess the significance of these new results.

This contribution presents the kinetostatic analysis of a spatial compliant mechanism actuated by three Shape Memory Alloy (SMA) wire actuators. This mechanism exploits both shape memory and superelastic effects of SMA actuators. The moving platform of the mechanism is mounted on a pillar made of superelastic SMA and its mobility is obtained from the large deflection of the pillar by the selective actuation of any one or two wires in differential manner. The deflection expressions obtained are basically force-displacement kinematic relationships, derived after incorporating follower forces and variable moments developed by the actuators. Two sets of geometric parameters, related to deflected and undeflected conditions, have been utilized to solve the coupled relationship between the force developed by the SMA actuation and the force required for the elastica deflection. The deflection expressions are solved using Romberg integration method and the numerical results obtained have been validated by comparing them with those obtained from FEM simulation. The results show that, for the design of compliant mechanisms exhibiting large displacements the force-displacement relationships in linear form, as applicable to small deflections, are no longer valid.

The paper is devoted to the problem of safe flight in vortex hazard conditions. A vortex wake is always produced behind flying aircraft. This vortex wake is invisible to other aircraft following it. Therefore, getting into a vortex wake from a preceding aircraft often becomes unexpected and quite often leads to flight incidents. This is confirmed by the statistics of flight accidents. With the introduction of aircraft weighing more than 500 tons, the problem of vortex safety has only sharpened. The fact is that the old standards that define safe intervals between flying aircraft are still active. These standards are given in this paper. It is also shown that even if these standards are observed, the flight of a medium-class aircraft at the same level as a heavy-class aircraft is unsafe. To study the effect of the vortex wake from the preceding aircraft, a special computational software complex based on the discrete vortex method was developed. This complex has passed the necessary testing and state registration. A number of measures were carried out to validate and verify the developed complex, confirming the operability of the programs included in it and the reliability of the results obtained. On the basis of this computational and software complex studies on the effect of the A380 aircraft vortex wake on MS-21 class aircraft were performed. The studies were undertaken for various altitudes and speeds of the A380 aircraft and for its various flight configurations. As a criterion for the MS-21 aircraft safe flight, the roll moment that occurs due to falling into the vortex wave, in particular, its coefficient was chosen. If the coefficient of the MS-21 aircraft roll moment when it hits the vortex wake exceeds that from the ailerons, such a flight is considered dangerous. The distances behind the A380 that are unsafe for the MS-21 aircraft flight are given.

Aircraft wake is a pair of counter-rotating vortices generated behind the aircraft, which can greatly impact the safety of fast takeoff and landing of aircraft and limit the improvement of airport capacity. The current wake parameter retrieval methods cannot locate the wake vortex's position and estimate its strength level in real time. To deal with this issue, a novel algorithm based on YOLOv5s deep learning network is proposed. The new algorithm establishes single vortex locating concept to adapt the wake vortex's evolution at complicate background wind field conditions, and proposes strength-based classification standard which can represent the real-time hazard of wake vortex to shorten the takeoff and landing intervals. Meanwhile, EIOU loss function is introduced to improve the precision of YOLOv5s network. Compared with the state-of-the-art object detection approaches, such as Cascade R-CNN, FCOS, and YOLOv5l, the superiority of new method is demonstrated in terms of accuracy and robustness by using the field detection data from Hong Kong International Airport.

Dynamic recrystallization (DRX) takes place when FeMnSiCrNi shape memory alloy (SMA) is subjected to compression deformation at high temperatures. Cellular automaton (CA) simulation was used for revealing the DRX mechanism of FeMnSiCrNi SMA by predicting microstructures, grain size, flow stress, and dislocation density. The DRX of FeMnSiCrNi SMA has a characteristic of repeated nucleation and finite growth. The size of recrystallized grains increases with increasing deformation temperatures, but it decreases with increasing strain rates. The increase of deformation temperature leads to the decrease of the flow stress, whereas the increase in strain rate results in the increase of the flow stress. The dislocation density exhibits the same situation as the flow stress. The simulated results were supported by the experimental ones very well. Dislocation density is a crucial factor during DRX of FeMnSiCrNi SMA. It affects not only the nucleation but also the growth of the recrystallized grains. Occurrence of DRX depends on a critical dislocation density. The difference between the dislocation densities of the recrystallized and original grains becomes the driving force for the growth of the recrystallized grains, which lays a solid foundation for the recrystallized grains growing repeatedly.

This paper presents the design, control and evaluation of a novel robotic finger actuated by shape memory alloy (SMA) tubes which intrinsically afford an internal conduit for fluidic cooling. The SMA tubes are thermomechanically programmed to flex the robotic finger when Joule heated. A superelastic SMA plate provides a spring return motion to extend the finger when cooling liquid is pumped through the internal channel of the SMA tube actuators. The mechanical design and nonlinear force controller are presented for this unique robotic finger. Sinusoidal and step response experiments demonstrate excellent error minimization when operated below the bandwidth which was empirically determined to be 6 rad s−1. Disturbance rejection experiments are also performed to demonstrate the potential to minimize externally applied forces. This method of internal liquid cooling of Joule heated SMA tubes simultaneously increases the system bandwidth and expands the potential uses of SMA actuators for robotic applications. The results show that this novel robotic finger is capable of precise force control and has a high strength to weight ratio. The finger can apply a force of 4.35 N and has a mass of 30 g. Implementing this design into wearable prosthetic devices could enable lightweight, high strength applications previously not achievable.

The work presented herein examines the interaction of aircraft wake vortices with nonuniform ambient shear in close proximity of the ground. The investigation is based on two- and three-dimensional numerical simulations using a grid-based Reynolds-averaged Navier-Stokes solver. The simulations are tailored to establish the extent of simplifications in mathematical modeling that can be realized while maintaining acceptable accuracy. The results are intended to provide the ground work for the development of real-time algorithms that may be used at airports in dynamic spacing of aircraft during landing and take-off. Through comparison with field data as well as simulations based on a one-equation turbulence model, the assumption of a constant eddy viscosity is shown to be adequate for modeling the turbulent diffusion of wake vortices in low-turbulence ambient conditions. Nonlinear interactions are demonstrated in the instance of simultaneous influence of ambient shear and ground proximity on the wake-vortex dynamics. Furthermore, neither axial motion within the core of the wake vortices nor nonuniform headwind shear are shown to have significant influence on the kinematics of the wake / crosswind-shear interaction, lending support for twodimensional modeling of this flow if three-dimensional instability effects are accounted for separately. Finally, the results help to establish the levels of accuracy and resolution of wind measurements that are required for reliable prediction of wake-vortex dynamics in nonunifonnly sheared ambient conditions. .M4