Thrust Performance Study And Profile Optimization Of Annular Throat Expansion Deflection Nozzle

Expansion deflection nozzle is an advanced nozzle with high compensation ability.There are two operating modes:"open"and"closed".When the working height is changed to a certain critical height,the two operating modes will be converted.The expansion deflection nozzle has a certain high compensation ability at low altitude.At the same time,on the premise of satisfying the design of large expansion ratio,the structure of the expansion deflection nozzle is shorter and compact,which can save the space in the engine and increase the payload.Therefore,it is of great significance to carry out the research on the expansion deflection nozzle.There are two types of expansion deflection nozzle,namely annular throat expansion deflection nozzle and discrete throat nozzle.This paper mainly focuses on annular throat expansion deflection nozzle（ATEDN）.In this paper,a two-dimensional axially symmetric ATEDN model was established based on the numerical calculation of ANSYS-Fluent.The SST k-ωturbulence model was used to solve the Navier-Stokes equations,and Wagner cold flow experiment results were taken as a reference to verify the accuracy of the numerical method in this paper.The operation process of ATEDN in the whole airspace under the steady-state condition was numerically simulated,the flow field characteristics of ATEDN under different working modes were described,and the causes of thrust decline under low altitude conditions were analyzed.The influence rules and importance of structural parameters such as the distance from the base of plug cone to the nozzle outlet L,the base radius of plug cone R_H,the central angle of the lower throat circular arcθ_c,the ratio of the upper and lower throat circular arc radius to R_down/R_up,the initial expansion half angleθ_t and the outlet half angleθ_e on the nozzle thrust performance were studied.It was found that the change of L,R_H,R_down/R_up andθ_t had a great effect on the nozzle thrust performance,while the change ofθ_c andθ_e had a small effect on the nozzle thrust performance.The thrust and thrust coefficient of ATEDN increase with the increase of L and R_H,but decrease with the increase of R_down/R_up andθ_t.In order to obtain the largest thrust of ATEDN at the design height,the interaction between four important structural parameters of ATEDN was considered comprehensively,and the ATEDN was optimized based on the proxy model method and CFD numerical calculation.The orthogonal experimental design scheme was used to generate sample points,and the polynomial response surface model（RSM）,elliptic basis neural network model（EBF）and Kriging model were respectively used to fit three proxy models,and the Latin hypercube design was used to generate random test sample points to verify the accuracy of the three proxy models.The R²coefficients corresponding to the above three proxy models are 0.99911,0.99985 and 0.99980respectively,which meet the accuracy requirements.Among them,the determination coefficient of EBF model is the largest,the maximum absolute error,the maximum relative error and the root mean square error are the smallest,and the accuracy is the highest.The adaptive simulated annealing algorithm（ASA）was used to optimize the EBF model,and the optimal solutions were:L=140 mm,R_H=38 mm,R_down/R_up=4/9,θ_t=45°.The thrust result after optimization is 4375N.Compared with the numerical simulation thrust calculation result,the error is 0.63%,which proves the convergence of the optimization result.The optimized simulation results are compared with those of the initial model,and the thrust is greatly improved.