The Investigation Of The Massively Separated Flow And Vortical Flow On The Leeward Side Of Double-Delta Wing By Using Detached-Eddy Simulation

The modern combat aircrafts are designed to meet the demands for increasedspeed and the maneuverability. The double-delta wing or stake/wing configuration hasbeen taken as one of the usual designs of the combat aircrafts and high speed civiltransport for its vortical flow field on leeward side of double-delta wing can providemore stability and maneuverability. But at high Re number and at high angle of attack,the flow on the leeward side has some complicated problems, including massivelyseparated flow and strong nonlinear effects. In present work, the solutions areobtained by using Detached-Eddy Simulation (DES) method. This method proposedby Spalart in1997, is regarded as a numerically feasible approach for predictingmassively separated flows. In my study, the vortical flow on the leeward side ofdouble-delta wing will be investigated.The first chapter has been divided into two parts. Beginning with the comparisonbetween DES and other methods in simulating the turbulent flow, the first partintroduce the construct of DES, some advanced version of DES and the application infundamental researches and the current status in engineering applications. The secondpart introduced the research background and the research status of double-delta wingfrom numerical simulation and experimental study.In the second chapter, the numerical methods using in the DES has beenpresented. In the first part, the structures of two DES methods, i.e., SA-DES based onthe S-A turbulent model and ML-DES based on the mixing length model has beengiven. And then, beginning with the3rd-order and5th-order biased upwind scheme,the developed hybrid3rd-order and4th-order scheme have been presented. Both ofthem can adapt the π dissipation by changing the value of a particular free parameter.At last but not least, a new type3rd-order scheme facing the engineering applicationsproposed by Li Qin has been presented.In the third chapter, the validations of some classic problems have been done,including the laminar cases, steady turbulent cases and unsteady turbulent cases. Thelaminar part contains the flat plane flow, cavity flow and cylinder flow. The steadyturbulent part contains the turbulent flat plane flow. And for the validations of DES,two classic cases have been prepared. The results show that the N-S solver can dealwell with not only the classic steady laminar and turbulent cases, but also thecomplicated cases with massively separated flow like the flow over three-dimensionalcircular cylinder and the flow over the airfoil at high angle of attack.In the fourth chapter, the flow field on the leeward side of double-delta wing hasbeen simulated. The vortical flow field obtained from the simulation has been analyzed. At first, the extreme streamlines on the surface at different angles of attackhave been presented. The extreme streamlines at AOA=10deg and AOA=22.5deghave been compared with the experimental results obtained by Verhaagen. AtAOA=10deg，the positions of vortices on the several streamwise sections fit wellwith the experiment of Verhaagen. And next, the positions where strake vortex andwing vortex breakdown at different AOAs have been presented. The structures ofvortex breakdown at AOA=35deg and the limit circles before and after vortexbreakdown have been analyzed. The analysis about axial velocity and pressuredistribution shows that the strake vortex structure at AOA=35deg is similar to theconical flow. To better understand the structure, the planform of pressure distributionhas been analyzed carefully and the apex of conical flow has been given which is verynear the apex of double-delta wing. At last, the image of the sub-structure resultedfrom the loss of stability of the shear layers on the strake has been obtained andcompared with the experimental pictures of delta wing of similar sweep angle.In fifth chapter, the new type crossflow vortex discovered in the simulations hasbeen analyzed and validated. At the beginning of this chapter, the crossflow vortex onthe ordinary wing has been introduced. The comparison has been carried on betweenthe reasons for the traditional crossflow vortex and the new one. And then the newtype crossflow vortex at different AOAs has been described in quality. In quantitativepart, after the analysis on the crossflow vortex at AoA=20deg,22.5deg and25deg, thevelocity (phase velocity), the wave length, and the reduced frequency have beencomputed. After the transformation of coordinate, the topology of the section flow hasbeen presented, so was the distribution of singular points on it. After that, the detailedanalysis and validation work on the new type crossflow vortex of the double-deltawing have been done from three directions, i.e., the onset of crossflow vortex, theexistence of turning point of the corssflow profile and the relationship between theturning points and the crossflow vortex. According to the analysis, the turning pointstill exists, which shows the reason for the crossflow vortex is inviscid unstability. Forthe onset of crossflow vortex, the effects of the strake and the wing vortex is themajor cause, the pressure gradient is the secondary cause.The sixth chapter is mainly the conclusions of this paper and the plan for the nextstep work.