Estimation of lack of knowledge about initial data influence on the numerical simulation results of work flow of axial turbine blade row
Aerospace propulsion engineering
Аuthors*, **, ***
Samara National Research University named after Academician S.P. Korolev, 34, Moskovskoye shosse, Samara, 443086, Russia
Comparison of the turbomachinery numerical modeling results with experimental data shows that designers cannot achieve quantitative agreement while having qualitative agreement of the results. Uncertainty of modeling initial data is one of the reasons. The researcher must specify the particular channel geometric dimensions to create computational model. The actual dimension value is unknown — it is known only the range of possible values, defined by measuring instrument error or technological tolerance value
Similarly designer does not have reliable information about the workflow parameters, measured directly or indirectly with error. Also, usually the flow parameters distribution has complex nature, simplifying in the simulation.
Thus, there is only a rough idea of the tested channel actual sizes and flow parameters taken as boundary conditions for the numerical simulation carrying out. This leads to significant calculation quantitative errors.
Currently, there is little number of publications on this subject. And algorithms and software implementation taking into account initial data uncertainty are at early stage.
Therefore, research aimed at quantification of initial data uncertainty impact on turbomachines calculated performances was conducted.
Analysis of industry standards and turbomachinery workshop drawings from various companies was conducted at the preparatory stage. The most important turbomachinery geometric dimensions and bogey value of tolerances for it were identified in the analysis. Error values for the flow physical parameters were taken according to technical literature.
The quantification of geometric and physical variables uncertainty impact on turbomachinery row workflow was conducted using untwisted airfoil cascade of axial turbine nozzle assembly (NA) with uniform cross-section throughout the channel height.
Channel capacity, loss factor and NA outlet flow angle were accepted as controlled performance criteria. The NA base variant calculation results and experimental data comparison demonstrated that created model adequately described the processes occurring in the cascade, but not well predicted the losses numerical value.
The series of computational calculations were carried out for this cascade. The first group of calculations was aimed at the impact of geometric parameters uncertainty on NA parameters identifying. The second group — at identifying the studied parameters depending on the flow parameters changes that are used as boundary conditions in the simulation.
The obtained results showed that initial data uncertainty in CFD calculations has a significant impact on the obtained quantitative estimates. The difference between calculated data modified in accordance with the technological tolerances and accuracy of the measured values of the geometry and process parameters may exceed 5% by value of the considered criteria.
Keywords:turbine, the initial data, characteristic, airfoil, throughput, loss ratio, boundary conditions, finite element mesh, computational model, tolerances, errors
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