Session: 36-03 MDO & Multi-Fidelity

Submission Number: 175529

A Multi-Disciplinary Mission-Oriented Pre-Design Process for Turbine Blade Cooling Systems 

High-pressure turbines (HPT) of aero-engines are exposed to extreme temperatures due to the demand for high thrust and efficiency. However, the benefits to be gained from higher combustion temperatures can be constrained by the coolant needed in the turbine. Estimating coolant requirements based only on an aerothermal analysis at take-off conditions can be an oversimplification that must then be compensated for with high safety factors to avoid component failure or low lifetime. By optimizing the cooling system instead for both aerothermal and structural performance in the context of a specific mission, we can reduce uncertainties and thus safety factors which ultimately leads to less coolant and a lower TSFC. The goal of this paper is to propose and discuss a holistic and mission-oriented pre-design process for a more accurate dimensioning of a turbine cooling system. This serves not only as a stepping stone for future technology studies at the DLR, but also as a contribution to public cooling system design guidelines in the turbo-machinery community.

 

This pre-design workflow spans the engine, turbine, and airfoil scales, each validated over time against various data sets such as those from the NASA Energy Efficient Engine program. A 0D engine model provides the boundary conditions for the meanline and through-flow turbine models for design and off-design calculation. At this level, a semi-empirical model provides a reliable initial estimate for the cooling system requirements. Each cooled row is then modelled in further detail. It is split into a hub, mid and tip radial section to model first the external flow field and second the cooling system. In this second step, metal temperature and stress distribution fields are calculated at each radial section and for each operating point, in an aerothermal-structural optimization that includes either the complete flight envelope or is directed at a specific mission. The turbine and airfoil modelling levels are coupled in both directions and the system is automatically iterated until convergence is achieved, at which point the engine model is updated. This approach yields higher confidence in the resulting design when compared against the single-point one-directional cooling design approach previously used at the DLR.

 

The proposed process is applied to a turbofan HPT configuration with a focus on the rotor cooling system. When comparing the resulting design to a previous single-point optimized cooling system, we see that, without a mission-oriented approach, the cooling system may be under dimensioned, which can lead to component failure or reduced lifetime. After demonstrating this pre-design process, we take advantage of its automated and iterative nature to study the effect of different material properties at airfoil, turbine and engine level. This provides a foundation for future studies on turbine technologies such as ceramic matrix composites and additive manufacturing, where the fuel savings gained from using novel material technologies can be combined with those from a mission-oriented design to achieve a maximum benefit.

Presenting Author: Francisco Carvalho German Aerospace Center (DLR)

Presenting Author Biography: Mr. Francisco Carvalho is a PhD candidate at the DLR Institute for Propulsion Technology in the Turbine department. His work as a scientific researcher is focused on turbine preliminary design with a focus turbine cooling.

Authors:

Francisco Carvalho German Aerospace Center (DLR)
Patrick Wehrel German Aerospace Center (DLR)
Meiken Patzer German Aerospace Center (DLR)
Robin Schöffler German Aerospace Center (DLR)
Clemens Grunwitz German Aerospace Center (DLR)
Julie Frank German Aerospace Center (DLR)
Robin Brakmann German Aerospace Center (DLR)
Florian Herbst German Aerospace Center (DLR)