Experimental and numerical investigations of solidity effects on compressor performance and stability

The solidity in compressors is defined as the ratio between the chord and the peripheral distance between two adjacent blades, the pitch. The solidity is therefore directly linked to the number of blades and the weight of the engine. The selection of this parameter occurs at the earliest stage of the aerodynamic design of axial compressors and it represents a crucial choice in the whole design process. To improve the current design practices and in view of reducing the number of blades, the present work, supported by Techspace Aero, investigates the solidity effects on the performance of a controlled diffusion blade that is representative of a state-of-the-art low pressure compressor airfoil. By means of both numerical and experimental investigations conducted at the von Karman Institute, new correlation rules are derived in order to update the existing low-speed correlations for both deviation angle and loss predictions at design and off-design incidence angles. The optimization of the solidity at the level of the meridional design is addressed by coupling the VKI throughflow solver ACPreDesign to the VKI optimizer CADO. Uncertainty quantification techniques such as Monte-Carlo sampling or stochastic collocation are then introduced to model the uncertainties inherently present in any empirical correlation. The optimization under uncertainty, also known as the problem of robust optimization, is the final issue approached in this thesis. The study highlights the importance of epistemic uncertainties and their impact on the performance requirements during the throughflow design.