Tnvestigation On The Deformation And The Tip Clearance Control Of The High Pressure Rotor Blade Of A Vaneless Counter-rotating Turbine

The blades of vaneless counter-rotating turbines are deformed inevitably due to the centrifugal,aerodynamic and thermal loads under running conditions.Differing from conventional turbines,the relative Mach number at the outlet of the high-pressure rotor of vaneless counter-rotating turbines must be high enough because the low-pressure rotor needs enough pre-swirl without the low-pressure vane,so that the flow in the high pressure rotor of a vaneless counter-rotating turbine is transonic and choked.The choked flow results in that the variation of the back pressure cannot affect the flow field upstream of the throat at choked conditions,leading to that the temperature variations of the front and rear parts of the blade are different from each other.Thus the deformation of the high pressure rotor blade at leading edge and trailing edge differs from each other particularly.The radial deformation of the blade has a direct impact on the blade tip clearance height,further influencing the turbine performance and the working safety.Therefore,it is necessary to analyze the blade deformation and the tip clearance variation of a vaneless counter-rotating turbine,and then to optimize the active tip clearance control method.The deformation and the tip clearance control method of the high-pressure rotor blade of a vaneless counter-rotating turbine are investigated in the thesis.The main contents of the thesis are as follows.1)The deformation of the high pressure rotor blade of a vaneless counter-rotating turbine is calculated with thermal-fluid-structural interaction simulation,and the influence of transonic flow on the blade deformation is illustrated by analyzing the variation of the flow field at off-design conditions.Aero-thermal two-way interaction simulation is adopted to simulate the heat transfer between the flow field and the solid blade,so that the temperature distributions of the blades are captured.Then,the blade deformation is obtained by aero-elastic and thermal-elastic one-way interaction simulation based on the temperature distributions.At conditions ranging more than 60%design rotating speed and more than 85%design expansion ratio,as the expansion ratio decreases,the blade height at leading edge remains unchanged,but that at trailing edge increases obviously,differing from the blade deformation of a conventional subsonic turbine in such conditions.The reason is that the flow of the high pressure rotor is transonic and choked at those conditions,leading to that the fluid and solid temperature upstream of the throat is not affected by the varied expansion ratios,but that downstream of the throat increases as the expansion ratio decreases.As a result,the blade height at leading edge keeps constant,but that at trailing edge rises on account of thermal expansion.2)A method of dimension conversion of turbine blades from high temperature to low temperature is proposed based on thermal-fluid-structural interaction simulation.The dimension of the high pressure rotor blade of a vaneless counter-rotating turbine at cold condition is gained by subtracting the nodal displacements of the blade calculated by thermal-fluid-structural interaction simulation from the coordinate values of the control lines of the designing blade profile.Afterwards,the blade dimension under the operating condition is calculated according to the blade dimension at cold condition,and is compared with the dimension of the original designing blade.The result shows that the dimensions of the two blades match well,and the errors are in reasonable ranges.3)The tip clearance variation of the high pressure rotor blade of a vaneless counter-rotating turbine is analyzed,and then an optimized method to cool casing for tip clearance control system is presented.The increased blade height at trailing edge of the high pressure rotor of a vaneless counter-rotating turbine leads to an obvious decrease in the blade tip clearance height and a hidden accident that blade tip would crash the casing.The blade tip clearance height at trailing edge is enlarged at design condition to account for the blade nonuniform deformation by diminishing the blade height.However,the increasing blade tip clearance height in axial direction results in larger outflow velocity of the tip clearance leakage flow downstream of 30%axial chord and the stronger shear strength of the tip clearance flow near the blade tip,leading to that the intensity of the tip clearance leakage vortex is enhanced.In addition,more tip clearance leakage flow is generated,and the influence of that on the main stream is stronger,resulting in more flow losses and worse turbine performance.In order to guarantee good turbine performance with safety,three adjustable and independent cooling air flows are guided to cool three locations on the casing.The three locations respectively correspond with the blade leading edge of the high-pressure rotor,duct and the blade trailing edge of the low-pressure rotor.The heights of the blade tip clearances at leading edge and trailing edge are controlled by adjusting the thermal expansions at different axial locations of the casing.The deformations of the casing cooled by different cooling air flows are calculated with thermal-fluid-structural interaction simulation,and the results show that the difference of the blade tip clearance height between at leading edge and at trailing edge is diminished by distributing these cool air flows appropriately.The reasonable blade tip clearance heights are guaranteed.