Numerical Study On Gas-thermal Coupling Of Medium-pressure Rotor Cooling Under Unsteady Flow Condition

The operation practice of thermal power generating units shows that the use of supercritical and ultra-supercritical units can reduce heat consumption and reduce nitrogen oxide emissions,which is an effective measure to achieve energy saving and emission reduction in power production.The development of supercritical and ultra-supercritical units is in urgent need of better high temperature resistant materials.Due to the difficulty in the production of 12%Cr rotor steel with high temperature resistance to 566 °C,the process is poor.Both domestic and foreign manufacturers agree to tap the potential of Cr-Mo-V steel and choose this material to manufacture high and medium pressure rotors.In order to enhance the heat resistance of the high and medium pressure rotors without changing the material,it is necessary to adopt a steam cooling technique for the medium pressure rotor with the highest operating temperature.It can be seen that the medium-pressure rotor steam cooling technology is the key technology for the development of supercritical and ultra-supercritical steam turbines.For medium-pressure rotor cooling under steady flow conditions,detailed gas-thermal coupling numerical simulation studies have been carried out at home and abroad.However,in the actual flow of the steam turbine,the relative position of the moving and stationary blades changes periodically due to the high-speed rotation of the moving blades,causing the main steam and cooling steam parameters to fluctuate with time,thereby causing the temperature field and flow field of the cooled components under the same cooling conditions.Significantly different from steady flow.Evaluating the effects of unsteady flow of main steam and cooling steam on the first stage of the cooled medium pressure,especially the temperature field and flow field of the moving vane,providing a reference for pre-considering problems that may arise from unsteady flow characteristics when designing the cooling unit.In the domestic 600 MW ultra-supercritical steam turbine,the cooling of the medium-pressure rotor is implemented by using Mitsubishi's steam cooling structure.In order to evaluate the cooling effect of the cooling structure and the influence of the introduction of cooling steam on the mainstream flow performance,this paper applies the commercial software ANSYS CFX to the steady and unsteady gas-heat coupling values of the medium-pressure first stage using medium-pressure rotor cooling.the study.The results show that under the condition of constant cooling steam inlet conditions,the relative position of static and moving blades changes with time,causing the flow of cold steam to change with time,so the temperature field of the blade roots also changes with time.The cycle changes.The unsteadiness of the main steam flow has negligible effect on the first-stage flow field and temperature field of the medium-pressure.Compared with cooling without cooling,the temperature fluctuation range is about ten times larger in one cycle,which needs to be considered when designing the cooling device,and safety measures are taken in advance.