Choosing the Rational Radius Value for the Fillet in the Rotor Blade Root Zone

Abstract

The root zone of rotor blades is the less studied element of the flow section of steam turbine. This problem is especially vital for the long blades in the low pressure section. The design of this zone is related to two aspects embracing aerodynamic and strength properties. The investigations were carried out using the models that were constructed based on the real rotor blade of the last stage of a turbine operated by the PJSC Turboatom with the working section length of 1030 mm. These investigations enabled the establishment of the rational shape for the blade zone in question for the first time. To reduce the stress concentration the passage from the blade surface to the shank seat was made using the fillets. When the data on the stressed state character of a transient zone are unavailable the fillet radius is selected based on the conceptions of appropriateness of the selection of the feasibly highest value of it. The available radius of 45 mm was selected arbitrary enough for the given fillet. The investigations carried out showed the possibility of an increase in the aerodynamic efficiency with the retention of strength indices. Consideration was given to the problems of formation of active and root zones of the blade and the influence of different geometric factors was analyzed. It has been established that it is quite possible to reduce the root fillet radius from 45 to 25 or 30 mm.