Research On Bypass Dual Throat Nozzle With Parallelogram Cross-section And The Transition Section

Thrust vectoring is a key technology necessary for the new generation fighter jets.Compared with traditional mechanical vector nozzles,fluidic vector nozzles have obvious advantages in structure and weight,and become currently a popular research direction.In addition,the use of hereotype nozzle outlets will be a new trend in aircraft design that emphasizes high stealth and aerodynamic configuration integration.This paper combines the special-shaped outlet design with the fixed-geometry fluidic vector nozzle,and proposes a bypass dual-throat nozzle(BDTN)with a parallelogram cross-section,in order to further increase the blending efficiency of the outlet jet flow on the basis of ensuring the thrust vector,which is expected to further improve the low detectability of the aircrafts.Firstly,the flow field structure and aerodynamic performance of the parallelogram cross-section BDTN with different geometrical conditions were calculated and analyzed by three-dimensional numerical calculation.The calculation shows that the parallelogram configuration and rectangular configuration follow the same change regularity of aerodynamic parameters.In the vector state,the pitch vector angle and thrust coefficient of the parallelogram BDTN decrease compared to the rectangular configuration,and the smaller the wall inclination angle α,the more the vector angle decreases;in the non-vector state,the thrust coefficient and flow coefficient of the parallelogram BDTN are basically consistent with those of the rectangular configuration.Within the full range of NPR = 1.5-10,a parallelogram cross-section BDTN withα≥60 can obtain a pitch vector angle of not less than 10 °and a maximum of more than 15 °.The outlet jet blending characteristics of the BDTN with a parallelogram cross-section were further studied.The results show that compared with the rectangular configuration,the outlet jet of the parallelogram configuration BDTN has a greater magnitude of flow vortices and spanwise vortices,and is more vigorously mixed with the external ambient air.The jet center is disturbed faster,which makes the centerline velocity decay faster.Thus,the jet blending efficiency greatly increases with a small thrust loss and the length of the jet core area is effectively shortened.Under the condition of the same total inlet temperature,the length and area of the high-temperature core region of the jet at the outlet of α = 60 ° parallelogram nozzle is much smaller than that of the rectangular configuration,and the centerline velocity and temperature decay of the jet are also faster.The cold flow wind tunnel experiment was carried out to verify the numerical calculation method in this paper.The experiment results show that the parallelogram BDTN can produce effective vector deflection,and has a good valve regulating linerity,which shows a promising engineering practicability.Under the different conditions of the bypass valve opening degree and NPR,the experimentally measured pressure distribution of the cavity wall of the nozzle is in good agreement with the numerical calculation results.The wave structure and vector deflection variation reflected by the schlieren system are consistent with the calculation results.Finally,three design schemes of transition section are proposed for the flow channel matching requirement between BDTN inlet and turbine outlet.Calculations show that the circular-to-rectangular transition section can maintain or even exceed the original the nozzle performance level while shortening the axial length.Appropriately reducing the inlet diameter of the transition section can improve the nozzle performance comprehensively.For the truncated circular-to-rectangular transition section,compared with the geometric fusion design,the pattern of area change in the first-rush and then-decline mode can increase the nozzle vector angle by1.68 °,the thrust coefficient by 0.52%,and the overall total pressure recovery coefficient by 1.3%.For the circular-to-parallelogram transition section,as the length of the transition section is reduced,the nozzle performance parameters are gradually increased in the vector state,while the nozzle performance in the non-vector state changes little.Compared with the geometric fusion design,the three kinds of cross-sectional area change regulations have no gains on the performance of parallelogram BDTN,but a reasonable segmented discrete method can further improve the thrust vector performance of the nozzle.