ISBN 9783843935647

978-3-8439-3564-7, Reihe Ingenieurwissenschaften

Roberto Ciorciari
Analysis of unsteady secondary flows in linear low-pressure turbine cascades

185 Seiten, Dissertation Universität der Bundeswehr München (2017), Softcover, A5

Zusammenfassung / Abstract

The present thesis deals with the analysis and the evaluation of unsteady effects, generated by periodically incoming wakes, on secondary flows in linear low pressure turbine cascades with a focus on the related development of the aerodynamic losses.

The presented numerical analysis in this thesis provides a new contribution to a better understanding of the primary and secondary loss development characteristics in two linear turbine cascades with steady and unsteady inflow. At constant theoretical exit Mach and Reynolds number, the investigated T106AEIZ cascade with parallel endwalls and the T106Div-EIZ with divergent endwalls have different loading distributions due to the different endwall properties and velocity ratios. The secondary flow development and the related loss development show relevant differences between the two investigated cascades.

The incoming wakes have a higher impact on the flow in the T106Div-EIZ cascade with respect to the flow in the T106A-EIZ cascade. The time averaged loss breakdown of the three-dimensional flow properties downstream of the cascade illustrates the effect of the periodically incoming disturbance on the primary and the secondary losses for different flow coefficients and Strouhal numbers.

The axial development of the entropy generation throughout the cascades and the decrease in intensity of the streamwise vorticity with respect to the undisturbed cases downstream of the cascade indicate that the unsteady incoming disturbances cause a redistribution of the primary and the secondary loss contribution to the passage losses. The influence of a change of the flow coefficient and the Strouhal number of the unsteady disturbance in the investigated configurations turn out to be small in both cases. On the contrary, the properties of the inlet endwall boundary layer and the loading distribution prove to be relevant parameters for the unsteady three-dimensional flow and loss development in the passage.

The predictions are compared to experimental results for the evaluation and the validation of the numerical approach and the applied set-up. The comparison allows to identify the limits of the U-RANS approach with the used k-ω eddy viscosity turbulence model in investigations with relevant anisotropic vortex structures. Nevertheless, the U-RANS approach shows a good qualitative reproduction of the main flow features and allow a useful analysis of the unsteady flow behaviour.