Design of a low-solidity stator inner endwall by optimization based on 3D RANS flow simulations

Aircraft are incontestably an important way of transportation in our society, for both commercial and passenger transport. Since the number of flights operated each day has drastically increased in the last decades, it is now time to reduce their fuel consumption and at the same time to limit their environmental impact. To equip more efficient aircraft, Safran Aero Boosters develops cutting-edge Low-Pressure compressors with improved performances. Gaining both in efficiency and in operating range requires a smart combination of mostly three-dimensional technologies. One way to increase the efficiency is to reduce the number of blades in order to reduce the skin friction losses at the blade wall. However, this affects the operating range in a negative way; secondary flows occur more rapidly in the blade passage. To counter this, a new technology called contouring 3D, or non-axisymmetric endwall, can be applied. By adding bumps and/or valleys to the endwall, we try to reduce the secondary flows on the low-solidity stator. The objective of this study was to get back the operability that was lost due to the reduction of solidity of 20\% on the stator. Starting with a parametrization of the shape, optimization was performed based on 3D RANS (Reynolds-averaged Navier-Stokes) flow simulations. Using Design of Experiments methods, a set of geometries was selected and analyzed numerically. From there, a Surface Response Model could be built, to try predicting the performances of other shapes. This model was then the basis for the evolutionary optimization algorithms, which allowed to determine optimal shapes to gain in operating range. The most interesting geometries present a bump at the center of the blade from the leading edge to the trailing edge, with a peak near the leading edge or the trailing edge. Thanks to a modification of the pressure field, the recirculation area could be concentrated near the blade.