| Popis: |
Vanes of low-pressure turbines (LPT) run under inlet conditions generated by a preceding high-pressure turbine (HPT). HP stages are generally cooled and transonic as well due to the large pressure ratio necessary to reduce the gas temperature upstream of the downstream stages. Therefore radial distributions of inlet flow angle, total pressure and total temperature at the boundary upstream of the LPT are highly non–uniform. Such non-uniform inlet conditions can result in enhanced level of the total losses including the secondary losses. Moreover, vanes of LPT have meridional openings along inner and outer boundaries of the flow path, which causes intensification of the secondary flows leading to an increase in secondary losses. In this case the special meridional contouring of the vanes’ outer and inner surfaces allows a decrease in the flare angle namely meridional opening in the rear part of the vane. In this work, in order to compensate the negative effect of non-uniform inlet conditions, meridional opening and low aspect ratio, 3D profiling of the vane row is used as a way of reducing secondary losses. Some variants of LPT vanes with various complex 3D shapes are investigated. In particular, vane variants with a “reversed bow”, a “bowed” and a “lean” in the circumferential direction have been examined. Significant modification of the vane row is limited by cooling system design, which has to incorporate a deflector in the inner hollow of the vane to improve cooling effectiveness. A compromise between aerodynamic quality and cooling limitations has been achieved. |
