Research On Transient Thermal Coupling Characteristics Of High Speed Rotating Blade-casing Structure

When the aero-engine runs to lightweight,high speed,heavy load and continuous operation,the structure is more compact,the gap between rotor and stator requires a smaller,so the problem of rotor/stator rub-impact fault has now become a major technological bottleneck.At present,the research on rub-impact fault of aero-engine is mainly concentrated in nonlinear dynamic response,thermal shock and contact stiffness,whilst the effect of thermal coupling has been lack of system and deep investigations.With the theory of rotor dynamics,heat transfer and vibration analysis,a further study on vibration characteristics of high speed rotating blades under thermal coupling,thermal buckling response of restrained blades and transient rub-impact of blade-casing structure have been made to improve rubbing state,control system energy diffusion and provide reference for optimization of structural design parameters in the paper.The main contents include:(1)Based on the Hamilton's principle,the vibration balance equation of high speed rotating blades under thermal-structure coupling is derived.The effects of temperature field,spin softening and centrifugal force are considered to establish dynamic model of multi-fields coupling.And then the modal analysis of thermal-structure coupling of blades is carried out by FEM.The results demonstrate that rotating blades have obvious bending-torsional due to the coupling effects of temperature field,spin softening and centrifugal force.Radial deformation of blades increases with rising temperature and rotating velocity,which could affect the gap between tip and casing directly and intensify the possibility of rubbing.(2)The linear and nonlinear thermal buckling dynamic models of restrained blades are established on the basis of thermal buckling theory.And then the geometric mode,buckling stress and critical buckling load are studied to determine thermal stability and instability form.The results show that the nonlinear analysis results are closer to actual situation.And blade tip endure more stress under thermal shock.Moreover,the blade torsional deformation could further reduce the gap between tip and casing.(3)In terms of the thermal coupling bending-torsional vibration form of constrained blades,an impact-contact model of cantilever beam-spring between blade and casing is established.Meanwhile,the rubbing stress,contact temperature and energy changing of blade-casing are analyzed comprehensively by using transient pulse force.The results indicate that blade and casing cause different types of local rubbing and full rubbing with the increase from 0 to rated speed(1323.7rad/s)of rotating speed.The surface energy of rubbing contact area gathers rapidly,which leads to the increase of temperature and thermal stress.With that,the heat distortion would be generated on the tip and root of blade.It could cause a great hidden danger to the service life of blade-casing and operation safety of engine.Systematical studies on the transient thermal coupling characteristics of high speed rotating blade-casing have not only important theoretical significance,but also practical value for rub-impact fault of rotating machinery.