The influence of the wing-tip vortex of leading aircraft on energy savings,quantified by formation aerodynamic force fraction of the following aircraft,is studied at transonic speed for a matrix of leading aircraft’s vortex locations.The research model adopts the hybrid formation of medium and large aircraft.The leading aircraft is scaled by 2.1%,and the following aircraft is scaled by 1.4%.An aerodynamic benefit "map"is developed to determine the optimum location of the following aircraft relative to the leading aircraft wake and to compare with experimental results,thus validating the use of CFD for the formation flight at cruising speed.The response surface model of aerodynamic gain effect relative to formation parameters is established via numerical calculation and wind tunnel test.The optimal formation parameters and the setting criteria of the study model are optimized.Results show that the wing-tip vortex of large aircraft significantly increases lift and reduces drag on the medium-sized aircraft following it.Reduced drag slightly increases with the flow direction position.With the increase of flow direction distance,the peak area moves from 15%of wing-tip overlap to 20%of overlap.In addition,the maximum drag decreases about 16%,and the maximum lift increases about 12%.The lift drag ratio of the optimal position is increased by 27%,which is twice as large as that of the same scale ratio aircraft formation.Results show that the increase of lift is mainly caused by the increase of suction peak and suction range.
Yang TAONeng XIONGXiaobing WANGJun LINZhiyong LIUShang MAJunqiang WU
Numerical simulation of wing stall of a blended flying wing configuration at transonic speed was conducted using both delayed detached eddy simulation(DDES) and unsteady Reynolds-averaged Navier-Stokes(URANS) equations methods based on the shear stress transport(SST) turbulence model for a free-stream Mach number 0.9 and a Reynolds number 9.6 × 106. A joint time step/grid density study is performed based on power spectrum density(PSD) analysis of the frequency content of forces or moments, and medium mesh and the normalized time scale0.010 were suggested for this simulation. The simulation results show that the DDES methods perform more precisely than the URANS method and the aerodynamic coefficient results from DDES method compare very well with the experiment data. The angle of attack of nonlinear vortex lift and abrupt wing stall of DDES results compare well with the experimental data. The flow structure of the DDES computation shows that the wing stall is caused mainly by the leeward vortex breakdown which occurred at x/xcr= 0.6 at angle of attack of 14°. The DDES methods show advantage in the simulation problem with separation flow. The computed result shows that a shock/vortex interaction is responsible for the wing stall caused by the vortex breakdown. The balance of the vortex strength and axial flow, and the shock strength, is examined to provide an explanation of the sensitivity of the breakdown location. Wing body thickness has a great influence on shock and shock/vortex interactions, which can make a significant difference to the vortex breakdown behavior and stall characteristic of the blended flying wing configuration.
Tao YangLi YonghongZhang ZhaoZhao ZhongliangLiu Zhiyong
