Vanes of low-pressure turbines (LPT) run under boundary conditions generated by a preceding high-pressure turbine (HPT). HP stages are generally cooled with significant cooling air mass flow; moreover, they are transonic due to large pressure gradients necessary to cool the gas further in 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 boundary conditions can result in enhanced level of losses due to large incidence angles of LPT vanes and other unpredictable effects. 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 losses. In this case the special meridional contouring of the vanes’ outer and inner surfaces allows a decrease in the flare angle in the rear part of the vane.

One way to increase aerodynamic effectiveness of such vanes is to enlarge the axial chord, which on one hand reduces the flare angle gradient along the flow path, on the other, results in the decrease of the vane aspect ratio. The low aspect ratio can lead to an increase in secondary losses as well. In this case it is necessary to find a balance between axial chord increase and aspect ratio reduction. Moreover, taking cooling into account, the enlargement should be accompanied by a reduction in the number of vanes to avoid increasing the surface area and cooling air mass flow through the vanes significantly. This, in turn, causes the loading on a single vane to go up, leading to an increase in secondary losses.

In this work, in order to compensate the negative effect of the 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 “lean”, a “reverse bow” and a “bowed” 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.


Improving Characteristics of a Cooled Transonic Vane of Low Pressure Turbine Under Nonuniform Inlet Conditions

Division / Sponsor:
International Gas Turbine Institute (IGTI)

Paper Proceedings: https://asmedigitalcollection.asme.org/GT/GT2020/volume/84058

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