Influence of stage design parameters on ventilation power produced by steam turbine last stage blades during low load operation

The ventilation power and the temperature increase experienced by steam turbine last stages operating at low load are strongly influenced by some design parameters such as radial clearances, degree of reaction and pitch to chord ratio. This paper presents a detailed numerical analysis about the role of these different design parameters. A series of temperature and flow field measurements performed on a steam turbine last stage blades are used for the validation of the numerical results. For the considered test cases, it seems that the size of the radial clearances of the rotating blades does not a play a significant role on the ventilation phenomenon. The impact of the pitch to chord ratio on ventilation power can be divided into two components such as number of moving blades and chord size. The increase on the number of blades is more significant than the increase in the chord. The degree of reaction at design influences the ventilation power since it drives the inception of flow separation, affecting the reverse flow height downstream the last stage moving blades (LSMB).