Transition Prediction Method And Application On Aircraft Complex Geometry

Transition prediction of boundary layer flow around aircraft complex geometry is an active research area in fluid dynamics and has considerable engineering value in aerospace field.A reliable and practical automatic transition prediction method that can offer an accurate and robust analysis tool for drag reduction design of aircraft complex configuration with high performance laminar flow wing,is necessary and important.Therefore,research on transition prediction method and application on aircraft complex geometry is carried out in this dissertation.Dual e^N transition prediction method based on linear stability theory is developed and improved.Based on the developed method,the studies of the transition prediction method of boundary layer around backward swept wing for laminar flow control,and the boundary layer transition prediction of new concept natural laminar supercritical forward swept wing（FSW）are carried out.Study on transition prediction application to wing-body complex configuration is carried out and influence of fuselage on boundary layer instability and transition of wing is analysed.The works and conclusions of this dissertation are summarized as:（1）A dual e^N transition prediction method based on linear stability theory is developed and improved.The corresponding transition prediciton program module is developed and integrated into"RANS solver coupled with automatical boundary layer transition prediction,PMNS3D",the independent intellectual property in-house code of research group.By comparison of e^N transition prediction methods based on different integral strategies of perturbation amplification factor,a problem of original dual e^N method is found and solved.The improvement is as follows:the original dual e^N method employs envelope method to calculate the integration of perturbation amplification factor for Tollmien-Schlichting（TS）wave,N_TS.But when a cross-flow（CF）instability disturbance is quite strong,it may be wrongly integrated into the N_TS.The improved dual e^N method employs fixed wave angle method instead of envelope method to ensure that none of CF instability（CFI）disturbances will be mixed into N_TS,thereby,the situation where N_TS first reaches its threshold value in transition dominated by CFI is avoided.By comparison with the experimental transition position,it is verified that the improved method is reliable.（2）Aiming at the difficulty of the design of natural laminar flow（NLF）backward swept wing（BSW）on large-scale civil transport aircraft,the study of the transition prediction method of boundary layer around BSW for laminar flow control is carried out.A laminar flow control method through changing the pressure distribution at leading edge by a small bulge is proposed.Based on the analysis of CFI characteristics,the traditional natural laminar supercritical airfoil pressure distribution is improved with a designed bulge at the leading edge area on the upper surface.So a small adverse pressure gradient is created to suppress the three-dimensional CFI disturbance which usually develops rapidly in the leading edge acceleration zone.As a result,the leading edge transition of BSW induced by CFI can be avoided.Then,the maintained favorable pressure gradient after the bulge of traditional natural laminar supercritical airfoil can suppress TS instability（TSI）.The proposed method can suppress both TSI and CFI simultaneously,and extensive NLF region can be sustained on BSW,which is verified through the swept wings with infinite and finite wingspan.（3）Study on transition prediction method of boundary layer around swept wing for laminar flow control is carried out.With an example of 40°swept infinite wing,the feasibility of hybrid laminar flow control by the leading edge suction is verified.Detailed study on influence of different suction intensity and suction range distribution on CFI shows that,the more forward the suction area is located,the more obvious the hybrid laminar flow control effect on suppression of CFI disturbance.When the total suction intensity is the same,a stronger suction at leading edge acceleration zone,where rapid growth of CFI exists,has a more effective suppression on CFI disturbance.And boundary layer transition of the swept wing can be delayed.（4）For short-and medium-range civil transport aircraft,study on transition prediction for NLF FSW is carried out.A comparison study on transition characteristics,boundary layer stability and aerodynamic performances of a NLF FSW and a BSW is also carried out.The results show that:FSW has more advantages in NLF supercritical wing design.In addition,the CFI of FSW and influence of the leading edge sweep angle on transition of FSW are studied.（5）The developed dual e^N transition prediction method is applied to three-dimensional aircraft complex geometry.PMNS3D,the independent intellectual property in-house code of research group is improved from simulation of flow around wing to simulation of flow around aircraft complex geometry.A study on transition prediction for wing-body configuration is carried out.The developed method is verified by the DLR-F4 wing-body configuration model.Results show that,the automatic transition prediction method developed for flow around three-dimensional aircraft complex geometry can not only predict transition location accurately,but also explain the mechanism of transition.The influence of fuselage on boundary layer CFI and location of transition of BSW and FSW is investigated.Then,with the propeller slipstream,simulation of free transition flow around an aircraft complex geometry,including wing,fuselage,horizontal tail,vertical tail and propeller,is carried out.It is concluded that,the developed transition prediction method can be used for transition flow of aircraft complex geometry.