Research On The Performance Of Flexible Variable Structure Nozzle Based On Fluid Solid And Thermo Solid Coupling Method

Rocket motor has become the main power device in space,and Laval nozzle is an important part of it.Due to the traditional nozzles do not have high compensation ability,the performance loss is large,so many different high compensation nozzles were born.However,the height compensation capability of these nozzles is limited,and the height compensation capability varies greatly under different working conditions,so the real-time height compensation cannot be realized.As a new type of high compensation nozzle,the extension section of flexible variable structure nozzle can be spread and extended with the reduction of atmospheric pressure in the external environment,so that the gas can be expanded more fully.The static pressure at the nozzle outlet is almost equal to the external atmospheric pressure,which is close to the state of complete expansion,so its high compensation ability is very excellent.However,under the action of flow field wall pressure,the extension section will deform and deviate from the design surface,so it causes performance loss.At present,the research work of flexible variable structure nozzle is still in the initial stage,and the research results are few.Therefore,it is of great significance to study the performance loss caused by the deformation of the extended section of flexible variable structure nozzle,the distribution law of deformation and stress of the extended section and the performance of thrust vector.In this paper,the influence of wall deformation on thrust performance of flexible variable structure nozzle is taken as the entry point.The fluid-structure coupling and thermo-structure coupling methods are used to calculate the total deformation and stress distribution of the extension section under different loads and constraints.By comparing the first six order modal frequencies of the extended segment with different constraints and different types of prestress,the effects of constraints and types of prestress on modal frequencies of the extended segment are studied.In order to investigate the thrust vector performance of flexible variable structure nozzle,the validity of two thrust vector generation methods was evaluated.The main research contents of this paper are as follows:(1)A simulation model of flexible variable structure nozzle is established,and one-way directional and two-way directional fluid-structure interaction calculations is carried out for flexible variable structure nozzle with circumferential constraints in the extended section.The results show that the performance loss of nozzle caused by wall deformation in the extended section is small.The thermal deformation and thermal stress of the extension segment caused by gas thermal load are studied by thermal-structure coupling calculation.It is found that the deformation and stress of the extension segment caused by wall pressure in the flow field are in the same order of magnitude.It is found that the deformation and stress distribution of the extension section are different from that of the fluid-structure coupling study.(2)The effects of circumferential and axial fixed constraints on the first six modal frequencies of flexible variable structure nozzle extension are studied.It is found that circumferential constraints are more effective than axial constraints in improving modal frequencies;The effects of different prestress types on the modal frequency of the extension section are studied.It is found that the effects of stress caused by flow field wall pressure and thermal stress on the modal frequency of the extension section are opposite whether it is one circumferential constraint or two circumferential constraints.(3)The thrust vector performance of the flexible variable structure nozzle with asymmetric constraints in the extension section and the flexible variable structure nozzle with concave wall is studied.The results show that the thrust vector generated by the flexible variable structure nozzle with asymmetric constraints in the extension section is very small and the thrust vector performance is poor;The flexible variable structure nozzle with concave wall can produce large thrust vector,and the thrust vector performance is good.