Research On Wake Surfing Of Formation Flight Based On CFD Simulation

The wake vortex retained by the wing when it generates lift.Encountering the wake vortex retained by the aircraft and the preceding aircraft may cause accident signs and even accidents threatening flight safety.In recent years,the focus of research is often placed on the distance or time to separate the space between the front and rear aircraft to avoid the wake of the front aircraft.The concept of wake surfing was born abroad and has just come into the view of domestic scholars.Instead of having spacers to avoid obstacles,the concept takes into account the use of its characteristics to gain extra lift.In this paper,the numerical simulation method commonly used in the aerospace field is used to simulate the wake generation of the forward aircraft,calculate and analyze the position of the formation available for the rear aircraft under the wake surfing technology,and reduce the extra lift and fuel consumption of the rear aircraft while avoiding risks.According to the applicable scenario of wake surfing,A330-200 aircraft is selected to fly at high altitude with its applicable cruising speed as the background,and the ring volume,radius and subsidence motion of its wake vortex are simulated.Nine sets of longitudinal intervals were selected according to the wake dissipation law,and the vortex induced velocity was calculated using the H-B vortex model.The rolling moment generated by a single vortex at different positions relative to the vortex core was modeled and analyzed by strip method,and the rolling moment coefficient at each position was obtained.According to the correlation range published by ICAO in the wake interval study,the feasibility screening of the surf position is carried out in the combination of three vertical distances and five horizontal distances from the vortex core.The source of the extra lift of the rear plane in wake surfing is that the wings are generally subjected to upwashing currents in the turbulent flow during wake surfing.After the pilot obtains longitudinal balance in the wake region,the vector difference in induced velocity of the upwash airflow is compensated,and the aircrafts gains additional vertical separation.According to this law,an equivalent induced velocity transformation method is proposed in this paper.The induced velocity of eddy current at a certain position is used to equivalent represent the turbulence uniformly acting on the rear machine in the upwash airflow of different sizes and directions.This method can be used to calculate the extra lift gained by the rear machine in wake surfing.The simplified formula can still be used to complete the calculation when the rear machine is at the same height as the vortex.Finally,according to the lift change of the rear engine and the relevant data of the model,the fuel saving efficiency of the rear engine in several groups of available positions is calculated,and finally the optimal formation combination form under this working condition is proposed,and the specific form is discussed.Taking the vertical and horizontal interval of0.5 times wingspan with vortex core as an example,the saving rate of aviation fuel consumption generally reaches more than 8% in the available positions,and the highest can reach 11.43%.In the previous wake surfing research,the rear aircraft are often placed above the outside slope of the front aircraft wake.Through the study of this paper,the formation mode of the rear aircraft located below the outside slope is proposed,which not only ensures the similar fuel saving efficiency,but also obtains more vertical spacing for the front and rear aircraft.According to the different induced roll directions of the two positions,the fault tolerance of the rear machine located at the lower Angle is better.Finally,the concept of wake suspension is proposed to describe the formation.