Session: 36-01 Preliminary Design and Structural Optimisation

Paper Number: 151307

Pre-Design and Analysis of a Military Hybrid High-Pressure Turbine 

The high-pressure turbine (HPT) of a military aero-engine is exposed to extreme temperatures due to the demand for high thrust and efficiency. At the same time, there is a noticeable plateau in Ni-based superalloys in terms of operating temperatures. Reducing cooling requirements is essential to minimize energy waste, and it can be approached from two fronts: material or cooling technologies. Combining the two is challenging. New materials like ceramic matrix composites (CMC) perform well at high temperatures but are restricted to geometrically less complex shapes, such as vanes with an outer shell and an impingement insert. Additive manufacturing (AM) enables more complex cooling configurations for both vanes and blades but at the expense of high-temperature mechanical performance. From this dilemma, a hybrid HPT concept is developed with a combination of different material technologies per turbine row.

This analysis is based on a DLR in-house pre-design toolkit, consisting of a 0D engine model and 1D-2D turbine models derived from meanline and throughflow programs. The HPT vane is modelled in greater detail. The external airfoil design is optimised for aerodynamic performance, and the internal cooling system is optimised for thermal performance. The output is fed back to the turbine model until convergence is achieved. For the first design iteration, a semi-empirical turbine level cooling model provides reliable initial estimates, accelerating convergence. Finally, the turbine is coupled with the engine for a system level analysis. This workflow and the toolkit are discussed with a particular focus on the cooling system. Both have been adapted or extended to deal with challenges related to a military use case. Aspects such as combustor hot streaks and radiation, core and coating material properties, as well as the full flight envelope, are part of the cooling system modelling and are discussed in detail.

A reference turbine featuring state-of-the-art technology is initially modelled, followed by a series of hybrid turbine configurations. Promising configurations are identified and discussed between component, turbine, and engine levels. At the component level, radiation, hot streaks, and their effect on the HPT reference and CMC vane are discussed. Results show that impingement cooling alone is insufficient for the CMC vane, and film cooling is required, posing a challenge for component structural integrity. At the turbine level, results show that applying CMC to the HPT vane row can lead to a reduction in stage cooling requirements of up to 34% and an increase in stage isentropic efficiency of up to 0.75%. At the same time, preliminary data show that an HPT AM blade row leads to an increase in cooling requirements and a drop in isentropic efficiency. Coolant-related pressure loss is shown to be crucial for turbine performance evaluation. Its effect on the Brayton cycle and efficiency of each turbine configuration is discussed in detail.

Finally, the effect of material properties, pre-design parameters, and operating conditions on the cooling system is discussed based on parametric studies between engine, turbine, and component levels. From these data, guidelines for pre-design processes and material research goals are discussed.

Presenting Author: Francisco Carvalho DLR e.V.

Presenting Author Biography: Francisco Carvalho is a doctoral candidate at the DLR Institute of Propulsion Technology in the Turbine Department. His work as a research associate focuses primarily on the preliminary design of turbines and secondarily on the cooling of turbine blades. He completed his Master's degree in Aerospace Engineering in Portugal in 2019.

Authors:

Francisco Carvalho DLR e.V.
Patrick Wehrel DLR e.V.
Tomasz Matuschek German Aerospace Center (DLR)
Robin Schöffler DLR e.V.
Robin G. Brakmann DLR e.V.
Thomas Behrendt DLR e.V.
Paul-Benjamin Ebel DLR e.V.
Uwe Schulz DLR e.V.
Florian Herbst DLR e.V.