Highly loaded HPT blading in KTH test turbine - An attempt to reduce the number of blades in the first stage in a high pressure turbine

Abstract: The main goal with this thesis was to investigate the possibility to reduce the number of blades in a high pressure gas turbine row. The reason for this study was the interest to reduce the amount of cooling air needed within the blade row by reducing the wetted area, hopefully without losing efficiency. Another reason for reducing the number of blades was to reduce the costs. A new design of an uncooled scaled model blade for a first stage blade row in a modern industrial gas turbine was developed. The design process mixed a combination of new ideas and more proven design principles of Siemens Industrial Turbomachinery AB. The new blade row was designed so it would fit in the existing test turbine at the Royal Institute of Technology in Stockholm. This new blade row containing 50 blades was then compared to the existing BC7M blade row which has 60 blades. By the use of Siemens in-house codes beta2, MAC1, Multall and Cato such parameters as efficiency, Zweifel coefficient, degree of reaction and losses were studied. The final design of the new blade resulted in a reduction of the blades combined wetted area by 9320 mm2 or 9.7 %, this without losing more than 0.12 percentage efficiency from 92.02 % to 91.90 % according to the Multall results. According to the beta2 results the efficiency increased with 0.16 percentage from 92.03 % to 92.19 %. The profile hub-section area has though decreased by 1276 mm2 or 20.4 % which means that this extra uncovered platform wetted area on the rotor may need cooling. Even though these numbers appear to be good, some problem has to be solved before being able to manufacture this new blade row, e.g. the stagnation point at the leading edge, especially at the tip-section occurs on the pressure side. This will not be a problem for this uncooled model. However in case of a cooled full scale design, the shower head cooling at the leading edge will end up on the suction side, which may result in an overheated pressure side. Of course a structural analysis should be done as well.