Development of a Phase-Lagged approach for unsteady turbomachinery analysis

This PhD thesis is aimed at developing a computational method which allows to solve blade row interactions by using a reduced computational domain. In this model (named \Phase-lagged") the traditional assumption of circumferential direct-periodicity is replaced by one of phase-shifted periodicity, resulting in an impressive reduction of the computational costs. This model was implemented in the Q3D as well as in the 3D releases of the TRAF code, a CFD solver previously developed at the \S. Stecco" Department of Energy Engineering of the University of Florence by the research group of Prof. Arnone. The Phase-lagged model was developed for single stage problems and then generalized in order to handle multi-stage environment. The currently implemented formulation can solve both single-passage and multi-passage computational domains. The latter have been introduced to assure greater stability to the numerical scheme. The validation of the implemented model was carried out for single and multi-stage test-cases for both Q3D and 3D approach. The validation was mainly performed comparing Phase-lagged results with the time accurate results of the Full Annulus approach. For a single 3D test-case the comparisons with some experimental data will be presented as well. Finally, the results of an unsteady analysis of a whole LPT module are shown: these results conrm the robustness and accuracy of the model and can be seen as a feasible method for the introduction of the unsteady simulations in the aerodynamic design.