Vibration Study On The Radial Inflow Turbine For ORC Low Temperature Waste Heat Recovery System

The vibration simulation analysis of the radial inflow turbine which is applied in Organic Rankine Cycle (ORC)waste heat recovery system is researched in this thesis. The load setting is derived from experimental data, then the Fluid-solid Coupling Analysis and the Harmonic Response Analysis are carried out by simulation platform-ANSYS Workbench. The chief research results are as follows:1. The experimental data of radial inflow turbine suffered torque is analyzed. Flow at 60% rated quality, the radial inflow turbine rotates in the vicinity of the 53000rpm using organic working fluid R123. In this condition, the radial inflow turbine suffered the maximum torque is 1.59N-m, the minimum torque is 1.27 N-m, the average torque is 1.46 N-m. Torque fluctuation of the reason is that organic working medium pump is Hydraulic diaphragm type pump, which is belong to the centrifugal pump.2. The Fluid-solid Coupling Analysis is carried out on the radial inflow turbine. The results show that:along the radial direction, as the radius increases, the equivalent stress decreases and the amount of deformation increases. At the rated speed, the maximum equivalent stress is 34.32MPa, which is far less than the yield strength of material, occurred at the root of the blade. The maximum deformation is 0.00314mm, which is far less than the impeller tip clearance of 0.5mm, occurred at the impeller inlet.3. The modal analysis is carried out on the radial inflow turbine and axis. The results show that:Within the rated speed, there are 6 order natural frequency, that is 3858Hz、3860Hz、4498Hz、7505Hz、9268Hz、9272Hz. The modal vibration mode is mainly axial vibration and bending vibration. The 7th～12th order natural frequency of the corresponding rotational speed area is 67373～67987 rpm, both of vibration form are bending torsional vibration of the blade. This speed region is a strong resonance region.4. The External load that the radial inflow turbine suffered is simplified harmonic load, then the Harmonic Response Analysis is carried out on the radial inflow turbine and axis. The results show that:at the remote bearing mounting surface (the surface of connecting coupling), the phenomenon of excessive vibration amplitude will happen and the coupling will cause damage at the speed of 15975 rpm, which the maximum amplitude of vibration is 0.927mm, but the equivalent stress will not be excessive. At the near bearing mounting surface, the phenomenon of excessive equivalent stress amplitude will happen at the speed of 26488rpm, which is 260.8MPa second only to the material yield strength. If the radial inflow turbine turn under this speed for a long time, the fatigue fracture phenomenon will be occurred on axis. At the suction surface and pressure surface, the phenomenon of excessive axial vibration amplitude will happen at the speed of 26488rpm, which is 0.603mm. In this speed, the blade is likely to collide the volute. For the sake of the safety of the equipment, the radial inflow turbine operation should be avoided in the vicinity of rotating speed is 15975 rpm and 26488 rpm for a long time.