Investigation on test modeling criteria for multistage turbine
For the improvement of the flow field similarity in multi-stage turbine modeling tests operating at medium temperature level,a three-dimensional numerical model of a two-stage turbine was constructed and validated.The influence of the test modeling criteria selection on the flow field similarity was quantitatively studied and a new method for adjusting the specific heat ratio of working fluid was proposed.Results indicated that,the specific heat ratio of working fluid under medium temperature modeling conditions was not equal to the design value,resulting in a gradual decrease of the flow field similarity along the flow direction in the multi-stage turbine;When ensuring the similarity criterion of expansion ratio,the aerodynamic load coefficient of the last stage turbine blade was reduced by 4.78％,and the blade outlet flow angle deviated by 3°-5°;When ensuring the similarity criterion of corrected power,the corrected speed of the last turbine stage is 1.29％higher,and the back pressure for the film cooling flow of the blade decreased by 2.5％-6.5％;The test working fluid generated by combusting air into a gas and mixing with vapor had the same values of specific heat ratio to the real gas used in the different classes of heavy duty gas turbine.As this working fluid was used in the test condition at medium temperature level,the three modeling criteria including the corrected speed,the corrected power and the expansion ratio were satisfied together,and the deviation of aerodynamic parameters from the design values were within the range of-0.54％to 0.52％.
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