Influence studyof flow separation on the nozzle vibration response

In the present paper,the vibration response difference of the upper stage nozzlewith higher expansion ratio between ground and altitude simulation hot-firing test is analyzed.lt indicates that the acceleration response of the nozzle under ground hot-firing test is muchhigher than that of the altitude condition.In order to find the essential reason,the experimentaland numerical simulation studies of the flow separation are developed by using the test enginenozzle.The experimental data show that the nozzle intemal flow occurred flow separation andthe divergence cone intemal wall pressure pulsation increased significantly downstream fromthe separation location.The numerical simulation and experimental results indicate that theincrease of internal wall pressure and turbulence pulsating pressure are the substantial reason ofvibration response increasing aggravatingly during the ground firing test.

Thermal-structural response and low-cycle fatigue damage of channel wall nozzle

To investigate the thermo-mechanical response of channel wall nozzle under cyclic working loads,the fnite volume fluid-thermal coupling calculation method and the fnite element thermal-structural coupling analysis technique are applied.In combination with the material lowcycle fatigue behavior,the modifed continuous damage model on the basics of local strain approach is adopted to analyze the fatigue damage distribution and accumulation with increasing nozzle work cycles.Simulation results have shown that the variation of the non-uniform temperature distribution of channel wall nozzle during cyclic work plays a signifcant role in the thermal-structural response by altering the material properties;the thermal-mechanical loads interaction results in serious deformation mainly in the front region of slotted liner.In particular,the maximal cyclic strains appear in the intersecting regions of liner gas side wall and symmetric planes of channel and rib,where the fatigue failure takes place initially;with the increase in nozzle work cycles,the residual plastic strain accumulates linearly,and the strain amplitude and increment in each work cycle are separately equal,but the fatigue damage grows up nonlinearly.As a result,a simplifed nonlinear damage accumulation approach has been suggested to estimate the fatigue service life of channel wall nozzle.The predicted node life is obviously conservative to the Miner＇s life.In addition,several workable methods have also been proposed to improve the channel wall nozzle durability.