Session: 07-01: Education

Paper Number: 153845

Teaching Aero-Engine Performance: Performance Analysis of Single-Spool and Two-Spool Engines 

In this paper we present an approach for teaching aircraft engine performance analysis, which progressively leads from the analytical description of the single-spool engine to the operating behavior of two-spool engines, which can only be calculated numerically. This approach allows students to gain a deeper understanding of how engine performance software works and how engine design and control parameters affect performance under various operating conditions. As such, this paper extends and complements our approach to teaching engine cycle design at RWTH Aachen University presented in a previous publication [1].

We start with giving a brief overview of the assumptions and the steps involved in deriving analytic equations for the single-spool turbojet operating line and discuss the effect of changing turbine and exhaust nozzle areas on the operating lines. In addition to the derivation of the steady-state operating line, we also briefly discuss how the shaft power balance is extended to account for transient performance. We then proceed with the analysis of two-spool turbojet engine operating behavior, which requires an easily solved iterative scheme to account for the shift of the LP compressor operating line as the HP compressor operating point changes. Solving the iteration with pen and paper, as our students do in a homework assignment, is possible but of course is time consuming and impractical. We thus arrive at the conclusion that describing the operating behavior of two-spool turbojets, and all other two- and three-spool engines, requires the use of numerical performance software.

With this conclusion, in the second part of the paper we move from theory to practice, starting with a brief overview of how performance software works. Our focus is on the numerical solver, which is based on iteration schemes. These schemes are adapted depending on the task and differ from our earlier simple analysis, among other things, because performance software uses maps to describe the operating behavior of compressors and turbines instead of working with the assumption of constant component efficiencies. Therefore, performance analysis results obtained from simplified analytics are different from those obtained with performance software. We let the students explore several such real-world effects. In the paper, we will describe and discuss the student homework assignments in detail. This spans from simplified numerical calculation of two-spool engine operating points to modeling real engine performance – we use the Rolls-Royce Olympus as an example – and also touches on transient performance, i.e., acceleration and deceleration.

In summary, our experience at RWTH Aachen university shows that teaching engine performance analysis by combining analytical work with practical exercises using performance software is successful and students gain a profound understanding of turbojet operational behavior. We recommend calculating single and two-spool engine operating lines as an introduction to engine performance analysis as described in this paper, and thereby bridging the gap from analytics to real-world tasks. In a future publication, we will present the extension of this approach to turbofan engines.

 

 

[1] Jeschke, P., Koschel, W., Klumpp, C., and Weintraub, D. (September 19, 2024). "Teaching Aero-Engine Performance: From Analytics to Hands-On Exercises Using Gas Turbine Performance Software." ASME. J. Eng. Gas Turbines Power. January 2025; 147(1): 011015. https://doi.org/10.1115/1.4066244

Presenting Author: Peter Jeschke RWTH Aachen - Institute of Jet Propulsion and Turbomachinery

Presenting Author Biography: 1988 – 1993: General Mechanical Engineering, TU Darmstadt (Technical University)
1991 – 1992: Master Aerospace Engineering, Cornell University, USA
1993 – 1998: Ph.D., Technical Thermodynamics, TU Darmstadt
1998 – 2000: Siemens AG, Power Generation (KWU), steam turbines, Mülheim, Germany, Process development for designing steam turbine blading
2000 – 2005: MTU Aero Engines, Munich, Director of development for the PW6000 high-pressure compressor
2005 – 2007: LEISTRITZ AG, Nuremberg, Director central development and innovation
2007 – today: RWTH Aachen University, Head of the Institute of Jet Propulsion and Turbomachinery (IST), University Professor

Authors:

Daniel Weintraub RWTH Aachen - Institute of Jet Propulsion and Turbomachinery
Christian Klumpp RWTH Aachen - Institute of Jet Propulsion and Turbomachinery
Peter Jeschke RWTH Aachen - Institute of Jet Propulsion and Turbomachinery