Safe merging aircraft flows in multi-route schemes

Nowadays, the problem of creating an optimal safe schedule for arrival of aircraft coming in several flows to a checkpoint, where these flows join into one, is very important for air-traffic management. Safety of the resultant queue is present if there is a safe interval between neighbor arrivals to the merge point. Change of an arrival instant of an aircraft is provided by changing its velocity and/or usage of fragments of the air-routes scheme, which elongate or shorten the aircraft path. Optimality of the resultant queue is considered from the point of some additional demands: minimization of the deviation of the actual aircraft arrival instant from the nominal one, minimization of order changes in the resultant queue in comparison with the original one, minimization of fuel expenditures, etc. The optimality criterion to be minimized, which reflects these demands, is often taken as a sum of penalties for deviations of the assigned arrival instants from the nominal ones. Each individual penalty is considered in almost all papers as either the absolute value of the difference between the assigned and nominal arrival instants or a similar function with asymmetric branches (which punishes delays and accelerations of an aircraft in different ways). The problem can be divided into two subproblems: one is a search for an optimal order of aircraft in the resultant queue, and the other is a search for optimal arrival instants for a given order. The second problem is quite simple since it can be formalized in the framework of linear programming and solved quite efficiently. However, the first one is very difficult and now is solved by various methods. The paper suggests sufficient conditions for the problem, which guarantee that the order of the optimal assigned instants is the same as the order of the nominal ones and, therefore, exclude the first subproblem.

Flight safety is the most important operational and technical characteristic of the air transport system, which is influenced by many factors, unstable and random in nature, which, as a rule, are interconnected with each other. The management of any property of a complex dynamic system, including the safety property of an operated air transport system, provides, as a mandatory procedure, a quantitative assessment (measurement) of the current value of the parameters by which control is carried out, since, in accordance with the basic postulate of management, to control is possible only by what is measurable. During the operation of the aircraft, information is accumulated about the state of the automatic exchange, as about the object of study. In this case, to some extent, the uncertainty in the knowledge about the object is eliminated. The main reason for uncertainty is the randomness of phenomena and processes. Obviously, there are no phenomena or events in which there are no elements of chance. No matter how accurately and carefully the operating conditions of the aircraft are recorded, it is impossible to ensure that with repeated (continued) observations, the results completely and exactly coincide. Random deviations inevitably accompany any natural phenomenon. Unlike common practice random elements cannot be neglected, especially since the result of operation depends on a large number of factors and even more combinations of them. It is necessary to study random phenomena, investigate patterns and find out the causes of random occurrences in a regular phenomenon. Finding any stable patterns is usually very difficult. However, if we consider a sequence of a large number of observations, then some rather interesting properties are revealed: individual (separate) observations are unpredictable, and the average results show stability or a pronounced trend of change (pattern of change) characteristic of dynamic systems.

Online Estimation of Aircraft Flow Angles in Turbulent Atmosphere

Flight accuracy in the airspace is becoming an increasingly difficult issue due to the expanding number of aircraft operating in it. In order to meet the needs of all airspace users, aircraft flows are being increased, and different aircraft systems that minimise the risk of aircraft accidents are being developed to ensure flight safety. However, statistically, the impact of the human factor on aviation accidents and incidents remains high. This article focuses on the assessment of pilot flight accuracy during route flights and presents a methodology based on automated assessment tunnels for accurately assessing pilot flight deviations from a pre-set flight trajectory axis both on the horizontal and vertical plane.

Shock wave and turbulent boundary layer interaction widely exists in the internal and external flow of high-speed aircraft. The aerodynamic performance and flight safety of aircraft are seriously affected by the strong pressure fluctuation in the interaction region. To investigate statistical characteristics of fluctuating pressure, the interaction between an incident shock of 33.2° and a spatially developed Mach 2.25 turbulent boundary layer is analyzed by means of direct numerical simulation (DNS). The numerical results have been carefully validated against with previous experiment and DNS at similar flow conditions in terms of mean velocity profile, turbulence intensity and wall pressure distribution. Statistics at the wall and in the outer layer, including fluctuation intensity, power spectral density, two-point correlation and space-time correlation, are quantitatively compared. The differences between them are analyzed in detail. It is found that the effect of the shock interaction on the wall-pressure fluctuation and the fluctuating pressure in the outer layer are utterly different. Based on the analysis of the power spectra density, the fluctuations in the separated region are both characterized by the low-frequency content, but in the reattachment region, the peak frequency of outer pressure fluctuations quickly shifts to higher frequency, with the low-frequency energy of wall-pressure fluctuation still being predominant. It is identified that the two-point correlations of pressure fluctuation at the wall and in the outer layer are both more elongated in the spanwise direction than that in the streamwise direction. The integral scale at the wall is generally increased, while the one in the outer layer increases sharply after passing the shock and then gradually decreases. The analysis of space-time correlation indicates that the iso-correlation contours are similar to the elliptical distribution and the convection velocity deduced by the correlation is dramatically decreased. Downstream of the interaction, the convection velocity in the outer layer is higher than that of wall-pressure fluctuation.

The aircraft wake vortex is an important factor affecting flight safety; as an important part of the aircraft, the powered nacelle will inevitably have an important impact on the aircraft wake vortex, so it is of great practical significance to research it. The present study focused on the numerical simulation of the wake flow of large aircraft (as the front aircraft) and the comparative analysis of the influence of engine jets on the wake flow. In order to meet the accuracy requirements and control the consumption of computing resources, LES and RANS methods were compared, and the RANS method was finally selected for subsequent calculation. The dynamic effect of jet flow was simulated by simplifying the boundary conditions of the inlet fan and outlet bypass as the mass flow boundary condition. The simulation results showed that the engine nacelle will have a significant impact on the morphology of the aircraft wake flow (position and strength of the main vortex in the wake flow system), which is caused by the vortices formed under the shear flow and separated flow of the nacelle. However, the nacelle will not significantly change the total strength of the wake vortex (half-plane circulation). The engine jet intensity causes additional turbulent mixing, which will accelerate the fusion of the nacelle vortex and ultimately change the intensity ratio of the inner wing vortex and the wingtip vortex, affecting the trajectory of the wake of the mean vortex. The study provides a corresponding reference for the following research on a wake vortex by a powered nacelle.

The paper considers issues of interaction between aviation and avifauna, relevant in terms of flight safety and safety of habitats for birds living in the impact area of ​​ airports. A number of parameters of aircraft and air traffic flow significantly affect the behavior and diversity of birds living in the respective areas. The analysis showed that species composition of avifauna at airports includes very few fully synanthropic species, while semi-synanthropes, such as members of the family Corvidae, are often found in airport areas and, due to their size and behavior, are of major hazard to aircrafts. A variety of methods for assessing the level of ornithological hazard are proposed by researchers and used in some countries. The authors presented a matrix method for assessing the risk of collisions between birds and aircraft, adapted to the conditions of Ukrainian airports. In particular, this method takes into account the peculiarities of avifauna monitoring carried out at the airports of Ukraine and the range of data on birds that may be available at these enterprises. The proposed analytical approach to ornithological risk assessment and ornithological management was tested on the example of Boryspil Airport, for which the attractiveness of the territory for birds, focal species of birds that need the most attention during ornithological observations by the airport staff, and the risk level were determined. It is necessary to expand the list of indicators according to which data should be collected during routine ornithological monitoring of airports.

The Federal Aviation Administration’s NextGen program aims to increase the capacity of the national airspace, while ensuring the safety of aircraft. This paper provides a distributed merging and spacing algorithm that maximizes the throughput at the terminal phase of flight, using information communicated between neighboring aircraft through the ADS-B framework. Aircraft belonging to a mixed fleet negotiate with each other and use dual decomposition to reach an agreement on optimal merging times, with respect to a pairwise cost, while ensuring proper interaircraft spacing for the respective aircraft types. A set of sufficient conditions on the geometry and operating conditions of merging forks is provided to identify when proper interaircraft spacing can always be achieved using the proposed algorithm for any combination of merging aircraft. Also, optimal decentralized controllers are derived for merging air traffic when operating under such conditions. The performance of the presented algorithm is verified through computer simulations.

The NextGen program is the FAA's response to the ever increasing air traffic, that provides tools to increase the capacity of national airspace, while ensuring the safety of aircraft. In support of this vision, this paper provides a decentralized algorithm based on dual decomposition for safe merging and spacing of aircraft at the terminal phase of the flight. Aircraft negotiate optimal merging times that ensure safety, while penalizing deviations from the nominal path. We provide feasibility conditions for the safe merging of all incoming legs of flight and put the viability of the proposed algorithm to the test through simulations.

Detection of flow fields constitutes a critical role in the advancement and innovation of hypersonic aircraft. Under hypersonic conditions, aircraft aerodynamics manifest a multitude of complex phenomena, including intense turbulence and fluctuations, transitions within the boundary layer, interactions between shock waves and boundary layers, as well as the effects of high-temperature gas. Thus, the surveillance of hypersonic aircraft flow fields is imperative not only for flight safety but also for the progression of hypersonic technologies. Given the practical limitations that restrict sensors installed to only key areas for detection, we propose a GNN-based method for hypersonic aircraft flow field reconstruction from limited sensors. Moreover, we have introduced a novel graph modeling technique for enhancing the reconstruction motivated by that solely the most significant edges within the graph are efficacious for field reconstruction. The methodology encompasses the following steps, modeling graphs from diverse perspectives, and transforming them into minimum spanning trees. These sparse graphs are then integrated with learnable weights optimized by automatic differentiation. Our method has been tested on an open-source turbulence dataset, the two components of graph pruning and weight optimization bring about 34% and 10% improvements on average. Furthermore, our approach has been validated in the reconstruction of hypersonic aircraft flow fields for at least 10% error reduction among all the situations.

Air data system of aircraft measures flow variables, primarily to monitor flight safety. The computational fluid dynamics approach to the problems for evaluating air data in a typical combat aircraft flow field is to find suitable sensor locations, to determine residual pressure correction and to compute local flow angularity at the proposed locations of sensors. The functional relationship between local flow angles and free-stream parameters being linear, it can be displayed as charts or nomograms.

The safety of an aircraft depends on the wing flow process, therefore, the study of air flow in various flight conditions is one of the most important parts of the design and operation of an aircraft. A hydrodynamic tube is one of the most effective means for studying the processes of aircraft flow in aerodynamics. It allows you to simulate special conditions and study flow characteristics that cannot be studied in real flight. Standard flow visualization methods, such as colored jets or fine particles, allow us to obtain qualitative data on the flow behavior. But it is more important to have quantitative flow characteristics that allow you to predict the development of the process and develop recommendations on flight safety measures. In this paper, the possibility of conducting non-contact three-dimensional measurements in hydrodynamic tubes by photogrammetric methods is considered. The article presents the development of a system of remote three-dimensional measurements based on images to obtain an accurate three-dimensional visualization of the flow used to quantify the parameters of the flow of aerodynamic elements in a hydrodynamic tube. The results of experimental studies on the calibration of a three-dimensional measurement system for the case of shooting an object through two boundaries of optical media are presented. The developed method of calibration of a photogrammetric system for three-dimensional measurements in an aqueous medium has demonstrated its applicability to the problem of spatial analysis of flow flows in a hydrodynamic tube.

Nowadays, the problem of safe aircraft flows merging is considered usually as one-stage. However, real air-route schemes assume often a tree-like structure when primary flows are merged at some points and the resultant flows are merged further. In this case, the safety of merging should be controlled not only at the final point, but also at some intermediate ones. With that, aircraft can change their order between these merge points by means of usage of holding areas and/or path alignments. In this paper, the authors suggest a mixed integer linear programming formalization of such a problem. The suggested procedure is realized as a computational program with the optimization Gurobi library. Results of numerical simulations are presented.