Fluid-solid-thermal Multifield Analysis And Optimization Design Of Thermal Protection And Drag Reduction For Labyrinth Seals

Seal structures between rotors and stators of rotating machines are important components of pumps and compressors,among other turbomachinery devices.With the high-end trendings of turbomachinery to higher temperature,higher speed and higher pressure,the leakage of fluid medium in seal structures becomes more and more serious.In order to prevent leakage of sealing fluid,labyrinth seals have been widely used in turbomachinery.In high parametrical environment,the turbulent flow in the clearance circulation of the labyrinth seal will increase the friction resistance between the stator-and the rotor walls.The heat generated by the frictional resistance causes rising fluid temperature.Meanwhile,the operations of the machine will also the heat up the seal structure.There is a strong heat exchange between the labyrinth seal and the leakage flow.If the heat transfer characteristics of the labyrinth seal are ignored in the design process,the annular flow will transmit the heat to the seal structure quickly,and hence affect the normal operation of the device.The large fluid resistance not only produces heat,but also increases the power consumption which reduces the efficiency of operation of the device.It can be seen that the analysis and optimization design of drag reduction and heat insulation for the sealed structure are urgently needed,which will provide effective guarantee for the normal operation of the structure.Therefore,the fluid solid thermal multi-field analysis of labyrinth seal structure was carried out.A optimal design of drag reduction and heat insulation is proposed for the grooved parameters of the seal structure.Based on bionics,the optimal design of bearing and heat insulation of seal is carried out.In this dissertation,the fluid control equation and energy equation of the annular flow are derived using the bulk-flow theory and the three-control-volume theory for labyrinth seals.The perturbation method,harmonic expansion,Newton-Raphson iteration method and finite difference method are used to solve the fluid control equations and energy equations.Then,the distributions of the flow field(i.e.pressure field,velocity field and temperature field)are obtained.The results of the perturbation method are verified by CFD simulation.The flow field of labyrinth seal structure with different structural parameters was analyzed.The influence of structural parameters on flow field,drag reduction and heat insulation performance of labyrinth seal was found,and reasonable explanation was made from the energy point of view.Finally,three grooved parameters were selected as design variables.Based on the method of moving asymptotes algorithm,the optimal designs of the resistance reduction and heat insulation of labyrinth seal are carried out.In order to improve the efficiency of optimization,the radial basis function(RBF)method is used to generate the explicit response surface of the maximum temperature and resistance of the fluid with respect to the grooved parameters prior to the optimization,which provides favorable pre-conditions for the optimization design and improves the efficiency of sensitivity analysis of the optimization iteration.Inspired by the structural layout of a bionic snail shell,a new type of multi-layer sandwich structure composed of thermal insulation material layer and load-bearing material layer is proposed.Through genetic algorithm optimization design,the topology structure consistent with the bionic prototype material arrangement is obtained,that is,the multi-layer sandwich structure with bearing material on both upper and lower surfaces and thermal insulation material in the middle is obtained.Based on ANSYS simulation analysis,it is verified that the layer arrangement order and layer thickness ratio of the bionic structure have the optimal comprehensive performance of bearing and heat insulation under the specific material thickness.With changing material layer arrangement order and layer thickness ratio of the structure,the comprehensive performance of bearing and heat insulation is obviously weakened.In conclusion,the bionic multilayer sandwich structure can be applied to labyrinth seal structures to achieve the optimal comprehensive performance of bearing and heat insulation.