Investigation On Calculational Method Of Maneuver Loads For Flexible Aircraft In Transonic Flow

Flight loads acting on the aircraft structure are the basis for the design concerning structural strength of the aircraft.For the modern aircraft,the critical flight loads often present in the different maneuvers in transonic flows,in which the nonlinear aerodynamic characteristics become prominent due to the present of the shock wave and flow separation.However,the applicable method solving aerodynamics of the maneuvering aircraft is the linear method which might not provide accurate solutions for strong transonic shock cases.In addition,the effects of the aeroelastic deformation on maneuver loads are much more evident due to the larger structure flexibility of the modern aircraft.Simultaneously,the flight control system is applied to the aircraft design widely.Actually,the calculation of maneuver loads for flexible aircraft is a typical multidisciplinary problem relating to aerodynamics structure and flight control.Consequently,tremendous challenges present in calculating accurately the critical flight loads acting on the flexible aircraft.We intend to account for technology difficulties in calculating flight loads for maneuvering aircraft through developing the high precision and efficiency aerodynamic calculation method and establishing the coupling solver model for maneuver loads analysis.The present works mainly include the following sections:(1)The high precision and efficiency aerodynamic calculation method is developed for calculating unsteady aerodynamics in transonic flows based on the fine flow field from CFD code and the overset field-panel method,in which steady flow solution based on RANS solver code are imported into transonic small disturbance equations,thus,the unsteady shock location is dominated by the steady shock location in the small amplitude sense.A block-tridiagonal approximation technology is used to improve the computational efficiency and save the memory,and the overset field panel scheme is developed to minimize the volume cell generation effort for complex configuration.Taking F5 wing,LANN wing,CRM WBH and SDM configuration as examples,the ability of the overset field-panel method in calculating transonic unsteady aerodynamics is verified.(2)The code calculating dynamic derivative in transonic flow is developed using unsteady aerodynamics from overset field-panel method.Comparing with the CFD method,the present method improves greatly the computational efficiency.Longitudinal and directional derivatives are computed for SDM configuration at various flight conditions in terms of Mach numbers and angles of attack.The results show that the nonlinear characteristics of dynamic derivatives appear at high angles of attack as well as in the transonic region.Furthermore,the models for pitch,roll and yaw are established based on MATLAB/Simulink,and corresponding maneuver simulations are accomplished.(3)Formulation of the static aeroelastic/trim analysis is investigated with aerodynamics obtained from overset field-panel method.The capability of static aeroelastic/trim analysis is improved for flight conditions of transonic flow and high angles of attack,comparing with DLM method.The improvement bring that it is possible to provide accurate trim results for maneuver loads analysis in transonic flow.(4)In order to cast the dynamic aeroelastic equation of motion in a state space form,least square fits is used to construct CLS arithmetic.The generalized aerodynamic force matrixes for F5 wing and AGARD 445.6 wing are approximately solved using CLS arithmetic.The effects of the approximation root values as well as the number of roots on the approximate error are analyzed,and a general rule with regard to approximation root is obtained for CLS arithmetic.(5)A time-domain state-space form aeroelastic model for maneuver loads analysis is proposed.The effects of time step as well as initial trim conditions on maneuver loads analysis are studied.The response results of airframe states and loads are compared for different aerodynamics from DLM method and OFPM method respectively.Comparing the response results from aeroelastic model for maneuver loads analysis and that from traditional maneuver simulation,the validity and reliability of aeroelastic model for maneuver loads analysis are verified.(6)Based on state-space aeroelastic model for maneuver loads analysis,maneuver loads analysis for a large airplane and a propeller-driven aircraft are carried out.Pitch,roll and yaw maneuver are analyzed respectively to investigate the response of the airframe states and loads acting on component of the aircraft.Critical loads cases of wing,horizontal tail,vertical tail,elevator,aileron and rudder in different maneuver flight condition are obtained,and the effect of flexible deformation on component loads is also investigated.The results show that the effect of structural deformation on loads must be considered in the design concerning structural strength of modern aircraft.