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Spanwise Distribution of Energy Losses in Steam Turbine Last Stage Nozzle
Engineering Education # 06, June 2014
DOI: 10.7463/0614.0712815
Gas-dynamic calculations of the last LPC stage of powerful steam turbine are performed with two alternative shapes of last stage nozzle using the Numeca Fine Turbo software. To compare a nozzle with combined lean (option B) to that of with straight trailing edge (option A) the article offers the method for calculating a distribution of kinetic energy losses in last stage nozzle using the Numeca CFView software package. The method is based on the calculation of loss coefficients for the single streamlines in the meridional plane. The difference between the local coefficients of kinetic energy losses calculated by the proposed method from the experimental results was 0.5 %. The use of the combined lean (option B) led to a change in the distribution of mass flow rate, pressure gradient, and steam flow rotation angles and tilt adjustment in height in the test section, which follows the last stage nozzle. As compared to the option A, for the option B in the zone a reactivity has increased by 20%, the Mach number has decreased from 1.4 to 1.2, a level of kinetic energy losses for the option B was 5.2 % that is lower than for the option A by 1.6% with the same consumption of steam flow. The greatest local decrease of kinetic energy losses for the option B was 2.5 % as compared to the option A due to decreasing intensity of the secondary flows in the shroud region. A relative efficiency of the stage with the guide (nozzle) apparatus B has increased by 1.75 % as compared to the initial option A owing to reducing losses of kinetic energy in the guide apparatus and changing conditions of the flow at the inlet of the bucket.
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