Diffuser effect on circumferential gas pressure non-uniformity in the exhaust manifold of a steam turbine

Exhaust manifold is an important part of steam and gas turbines, and it affects the efficiency of both the turbine and the turbo-installation. Currently, axial-to-radial type of the exhaust manifold is used in steam turbines, which causes circumferential gas pressure nonuniformity in the area after the last row of blades due to the gas flow turn. It worsens the vibration condition of the last row of blades and causes forced vibrations and ageing of the blade material. The decrease of circumferential pressure non-uniformity is a way to protect the blades from vibration. Therefore, it is essential to consider the effect of diffuser parts on the non-uniformity. However, there is insufficient published information about the diffuser effect on the entrance circumferential non-uniformity. The authors of this work show analytically the decrease of circumferential pressure non-uniformity by the diffuser using pressure recovery factor. The validity of the conclusions was proved by numerical experiments. For this purpose three similar exhaust manifold models were created in SolidWorks. The only difference between them was that the first model did not have a diffuser, the second one had a completely circular diffuser and the third model had a shoe-noise circular diffuser. The aerodynamic analysis was carried out using the SolidWorks module of the Flow-Works software. Calculations were performed for two working substance (water steam and air) for each model. The results of these calculations, shown in diagrams, confirmed the analytical conclusions. The findings can be used in turbine design and estimation of vibration reliability of the last row of blades.

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