Large Eddy Simulation Research on the Evolution Mechanism of Aircraft Wake Influenced by Cubic Obstacle
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Aircraft wake is a kind of intense air movement, and the study of its generation, development, and dissipation law is of great significance to the flight safety. There are abundant researches on the evolution of aircraft wakes affected by weather and ground effects; however, there are few studies on the influence of a single obstacle on the evolution of aircraft wake. In this article, in order to explore the influence of a single obstacle on the evolution of aircraft wake, firstly, we develop a computational fluid dynamics-based method of simulation of aircraft wake affected by cubic obstacle of different heights in order to obtain the wake intensity changes and position changes before and after being affected by the obstacle. Then, the result data are visualized and analyzed, and we obtain the results of velocity and criterion contours, circulation, and data related to wake vortex structure. CFD simulations are conducted, including the cases of the vertical distance between wake vortex and obstacle which is 20 m, 60 m, 100 m, and no obstacle. The quantitative results indicate that a single obstacle also has a great influence on the evolution of the wake vortex. Obstacle will shorten the time for the wake vortex to enter the fast decay stage, and the smaller the distance the wake vortex is above the obstacle, the faster it enters the fast decay stage. In the same time, the circulation will reduce 20% more under the same calculation time when the wake is 20 m above the obstacle than when the wake is 100 m above the obstacle, and the circulation will reduce 45% more than when there is no obstacle. Single obstacle also leads to the generation of multiple secondary vortices and rotates around the wake vortex, resulting in the increase of wake vortex core radius, wake vortex core spacing, and wake vortex height.Keywords:
Wake turbulence
Large-Eddy Simulation
Circulation (fluid dynamics)
Abstract The current abstract presents selected topics investigated within the wake‐vortex research program of DLR. Two approaches are addressed that both aim at increasing airport capacity without compromising safety. One approach is to directly alleviate wake vortex strength and stability by constructive measures at the aircraft wings. The other approach utilizes the dominant influence of meteorological parameters like turbulence, wind shear, and temperature stratification on wake vortex fate. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)
Wake turbulence
Kármán vortex street
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Today's airport capacity is severely limited by separation of approaching and to a lesser extent departing aircraft to ensure that following aircraft do not encounter the wake vortex generated by the preceding one. The encounter of wake vortices, especially during take-off and landing, can cause critical or even catastrophic flight situations for the succeeding plane. Historically, the wake vortex separation standards are based on a `worst-case-scenario' assuming calm and still air conditions responsible for a relatively long wake vortex lifetime. They have proven sufficiently safe but are unnecessarily limiting capacity in favourable, even in average weather conditions. Thus a capacity increase brought about by any change in separation rules has at least to preserve (or, given the expected traffic growth, even improve) the current level of safety. Accordingly, wake vortex warning systems have been devised to increase airside capacity and are nearing experimental implementation. The current systems contain a forecasting component based on meteorological conditions and on propagating the vortex evolution. Secondly a sensing system is ensuring the required level of safety. Both the model predictions and the sensing systems each have their advantages but also individual drawbacks. This paper presents a novel approach on collaboration of the wake vortex prediction and the sensing part. A general overview on the wake vortex phenomenon is given and an approach of fusing the wake vortex prediction with wake vortex measurement is shown. By means of examples the major advantages of the collaboration approach are presented. A discussion on implementation constraints of the proposed system closes the paper.
Wake turbulence
Separation (statistics)
Limiting
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The presentation shows an approach to alleviate the impact of a wake vortex on an encountering aircraft by means of a special control system. The wake impact alleviation control system presented allows a significant reduction of the wake-induced aircraft response and thus provides the potential to achieve an appreciable safety improvement during wake vortex encounters. This could also support the reduction of wake-vortex-based separation minima for following aircraft equipped with such a controller. The presented wake vortex impact alleviation system is based on an airborne forward-looking Doppler LiDAR sensor. The basic principle of the system is to use this sensor to measure wind remotely ahead of the aircraft. On the basis of these measurements the system estimates whether a wake vortex is located in front of the aircraft. If this is the case, the wake vortex characteristics are identified and the adequate control deflections to countervail the wake-induced aircraft response are computed and applied. An integrated simulation environment comprising a full nonlinear 6-DoF A320 model (with control laws), wake vortex models, and the wake impact alleviation algorithm was developed. The LiDAR sensor subsystem has many design parameters that influence the overall wake impact alleviation performance in a complex way. This makes it particularly difficult to derive adequate requirements. The presented study provides first insights into the role of each parameter as well as some adequate parameter combinations. Based on the results of this study a wake impact alleviation performance of about 60% (in terms of maximum bank angle reduction) seems achievable with the proposed system and various sets of a priori realistic sensor characteristics.
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The mass,velocity and wing shape of the aircraft decide the intensity of wake vortex.The passive conservative model can better depict the movement evolution rule of water vapor and potential temperature in wake vortices.Since parametric studies are computationally expensive to the large amount of CPU time per simulation.In addition,it can't forecast the state distribution characteristic of any aircraft wake vortex in a real-time manner.Therefore,a fast modeling method for aircraft wake vortex was presented.It has solved the problems,such as the high request for computer time,long simulation time and lack of real time simulation.This can provide a theoretical basis to avoid former airplane's wake vortex and reduce the wake accident.
Wake turbulence
Airplane
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Aircraft wake is a kind of intense air movement, and the study of its generation, development, and dissipation law is of great significance to the flight safety. There are abundant researches on the evolution of aircraft wakes affected by weather and ground effects; however, there are few studies on the influence of a single obstacle on the evolution of aircraft wake. In this article, in order to explore the influence of a single obstacle on the evolution of aircraft wake, firstly, we develop a computational fluid dynamics-based method of simulation of aircraft wake affected by cubic obstacle of different heights in order to obtain the wake intensity changes and position changes before and after being affected by the obstacle. Then, the result data are visualized and analyzed, and we obtain the results of velocity and criterion contours, circulation, and data related to wake vortex structure. CFD simulations are conducted, including the cases of the vertical distance between wake vortex and obstacle which is 20 m, 60 m, 100 m, and no obstacle. The quantitative results indicate that a single obstacle also has a great influence on the evolution of the wake vortex. Obstacle will shorten the time for the wake vortex to enter the fast decay stage, and the smaller the distance the wake vortex is above the obstacle, the faster it enters the fast decay stage. In the same time, the circulation will reduce 20% more under the same calculation time when the wake is 20 m above the obstacle than when the wake is 100 m above the obstacle, and the circulation will reduce 45% more than when there is no obstacle. Single obstacle also leads to the generation of multiple secondary vortices and rotates around the wake vortex, resulting in the increase of wake vortex core radius, wake vortex core spacing, and wake vortex height.
Wake turbulence
Large-Eddy Simulation
Circulation (fluid dynamics)
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Wake turbulence
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Abstract As a consequence of its aerodynamic lift, each aircraft is generating wake vortices that can become a serious hazard for the succeeding aircraft and in the worst case lead to loss of control. Separation standards were introduced to prevent dangerous wake encounters that have proven sufficiently safe but also very conservative, thus limiting airspace and airport capacity. The objective of contemporary wake vortex research is regaining capacity in favourable atmospheric conditions, at the same time preserving or even improving the current safety level. The wake vortex advisory systems developed for this purpose are nearing experimental implementation and all include a forecasting component and additional online detection sensors, with both elements having their benefits and limitations. The wake vortex research objectives at the Institute of Flight Guidance (IFF) of the Technische Universitaet Braunschweig focus on a close coupling approach between model predictions and sensor measurements. Using the complementary capabilities of each, the aim of improved performance of the overall system shall be reached. After giving a short overview on the wake vortex phenomenon and current approaches to wake vortex alerting and advisory systems, this paper will introduce the fusion concept. The benefits of this approach will be demonstrated by means of examples. An outlook on further development and envisaged advanced implementation concepts will be given.
Wake turbulence
Separation (statistics)
Limiting
Lift (data mining)
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Based on the constructed wake vortex decaying model,movement model and encountering model,the concept of object-oriented(OO) is applied to develop the Dynamic Calculating tool for the Spacing of Wake Vortex.The tool includes the calculating module of flow field induced by leading aircraft,the encountering and reacting module for the following aircraft,and the module for calculating the spacing of wake vortex.The real-time and efficient calculation of wake vortex spacing can be implemented by using the aircraft parameters,meteorological data,and aerodrome data.And also,the spacing for the pair of B777-200 and B737-800 is calculated by this tool for trialing purpose.
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Kármán vortex street
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The analysis of aircraft wake vortex is of great significance for the improvement of airspace utilization. To overcome the shortcomings of traditional manual methods which are unable to produce satisfactory results on the great number of wake vortex data with high accuracy recognition, a fast automatic method is proposed based on Random Forests (RF). The development of our model is outlined as follows: (1) A wake vortex dataset that consisted of various aircraft measured by Wind3D 6000 LiDAR was collected at Chengdu Shuangliu International Airport from Aug. 16, 2018 to Oct. 10, 2018. (2) The optimal parameters were determined by grid search by visualizing the characteristic values of wake vortices, to get the optimal RF model, allowing high efficiency as well as improved accuracy. In terms of evaluation metrics, the experimental results showed that the method can effectively recognize the wake data in different situations, exhibiting good robustness.
Wake turbulence
Robustness
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Traditional research on static wake-vortex reduction usually considers only the influence of external environmental factors, while ignoring the dynamic change in an aircraft’s flight state. In order to solve this problem, this paper proposes a method to reduce separation using dynamic wake information based on changes in flight velocity. Firstly, relying on the wake-vortex generation and dissipation model, the initial circulations and dissipation parameters of the wake vortex at different aircraft velocities are calculated. Then, the complete evolution process of the wake vortex generated by different types of aircraft at different velocities is analyzed, and the evolution law of a wake vortex with changing velocity is obtained. Afterwards, according to the actual aerodynamic shape of CRJ-900, the aerodynamic model for CRJ-900 when it encounters a wake vortex is established. The situation of an CRJ-900 encountering a wake vortex under TBS is analyzed, which proves that TBS is safe and has a certain reduction potential. Then, taking the rolling moment coefficient as the safety index, the minimum safe separations at different velocities are calculated. Finally, a simulation for the separation reduction based on a dynamic wake vortex is carried out. Compared with the static wake-based separation, the dynamic wake-based separation technology can greatly reduce the aircraft separation requirements while ensuring the operation safety. The final simulation results show that the dynamic separation reduction in CRJ-900 following a medium and heavy aircraft can reach 44.3% and 51.6%, respectively.
Wake turbulence
Separation (statistics)
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