Automated Aerodynamic Optimization of an Aggressive S-Shaped Intermediate Compressor Duct

Abstract

As bypass-ratio in modern aero engines is continuously increasing over the last decades, the radial offset between low pressure compressor (LPC) and high pressure compressor (HPC), which needs to be overcome by the connecting s-shaped intermediate compressor duct (ICD), is getting higher. Due to performance and weight saving aspects the design of shorter and therefore more aggressive ducts has become an important research topic. In this paper an already aggressive design (with respect to current aero engines) of an ICD with integrated outlet guide vane (OGV) is used as a baseline for an aerodynamic optimization. The aim is to shorten the duct even further while maintaining it separation free. The optimization is broken down into two steps. In the first optimization-step the baseline design is shortened to a feasible extent while keeping weak aerodynamic restrictions. The resulting highly aggressive duct (intermediate design), which is shortened by 19 % in axial length with respect to the baseline, shows separation tendencies of low momentum fluid in the strut/hub region. For the second step, the length of the optimized duct design is frozen. By implementing new design features in the process of the optimizer, this optimization-step aims to eliminate separation and to reduce separation tendencies caused by the aggressive shortening. In particular, these features are: a nonaxisymmetric endwall contouring and parametrization of the strut and the OGV to allow for changes in lift and turning in both blade designs. By comparison of the three designs: Baseline, intermediate (separating flow) and final design, it can be shown, that it is possible to decrease length of the already aggressive baseline design even further, when adding a nonaxisymmetric endwall contouring and changes in blade shape of the strut and OGV. Flow separation can be eliminated while losses are kept low. With a more aggressive and therefore shorter duct the engine length and weight can be reduced. This in turn leads to lighter aircrafts, less fuel consumption and lower CO2 and NOx emissions.

Super Aggressive S-Ducts for Air Breathing Rocket Engines

“…The new design was tested experimentally and shown to completely remove the corner separation. A similar approach is adopted by Stürzebecher et al [11] where a computational optimisation combines non-axisymmetric endwall profiling, OGVs integrated into the duct and a turning strut which builds on the work of Walker et al [12] and Wallin et al [13]. The resulting design is 19% shorter than an already aggressive baseline with no predicted increase in loss.…”

Review on the aerodynamics of intermediate compressor duct

“…-This method found the applications in the field of isoenergetic inviscid incompressible flow, isoenergetic isentropic compressible flow, as well as for viscous compressible flow. Sturzebecher et al [75] AutoOpti algorithm and End wall contouring -The duct was shortened up by 42% length while keeping the loss as much as low. -Implementing non-axisymmetric end wall contouring on hub and shroud wall, a 19% length reduction of the baseline duct could be further possible along with a 2% reduction in loss.…”

On the effect of inter compressor duct length on compressor performance

“…Oil-streak paint showed for rig (B) severe flow separation in the ICD hub region. In an aerodynamic optimisation by Stürzebecher et al [17] this separated ICD (B) has been stabilised with a hub endwall contouring supported by a locally bowed strut trailing edge that leads to suppression of hub-strut corner separation. To the authors knowledge this ICD is the most aggressive duct still separation free and therefore defines the current separation limit (compare Fig.…”