• low-pressure turbine
• secondary flow
• stereoscopic PIV
• turbomachinery
• turbulence
• wind tunnel

Nowadays aerospace decarbonization processes call for a more and more efficient and sustainable technologies. The improvement of the aerothermal efficiency of low-pressure turbine stages has assumed one of the primary role in the ultra high by-pass turbofan architectures; a promising solution that can allow for reducing the fuel consumption, pollution emissions and noise production.
In this context, low-pressure turbine stages operate in specific flow conditions that are challenging in order to attain high efficiency. Numerous studies have been conducted on the impact of different operating conditions (Mach and Reynolds numbers) on the main flow mechanisms that characterize the aerodynamic performance of low-pressure turbine flows. However, still today substantial gaps persist on the effect of freestream turbulence on the fluid dynamics efficiency of low-pressure turbine stages.

The von Karman Institute is performing a study to address the lack of data regarding the effect of freestream turbulence. As a part of this project, this study aims to conduct optical measurements by using the PIV technique to analyze the flow mechanisms of a low-pressure turbine cascade, exposed to different combination of inflow turbulence. In particular, PIV were carried out to analyze the main causes of aerodynamic inefficiency, such as profile losses and secondary flows losses, under different turbulence conditions achieved by using an active turbulence generator.

The PIV technique was chosen because it allows for the instantaneous recording of the whole velocity field on the measurement plane with high spatial resolution and in a non-intrusive manner. This allows the analysis of flow evolution within the blade passage, facilitating the study of boundary layer development as well as wake formation and evolution. The use of stereoscopic PIV measurement technique, in addition to planar PIV, has allowed for visualization of secondary flow structures, resulting from flow interactions with surfaces, as well as the evaluation of the flow angle at the outlet plane.