The Basics of Gas Turbine and Aircraft Engine Performance.
ASME GT2024-TOB002

The tutorial begins with the fundamentals of performance calculations and the thermodynamic cycle of the gas turbine. It is explained why further increasing the burner exit temperature will do little to increase thermal efficiency. A reduction of the specific fuel consumption of aircraft engines can essentially only be achieved by improving the propulsion efficiency.
At the beginning of a new engine development, some fundamental decisions must be made: Should the two streams of a turbofan be mixed and expanded in one nozzle or is it better to use two nozzles? When is it better to use a simple convergent nozzle and when is a convergent-divergent nozzle advantageous? Is a two-stage high pressure turbine necessary or is a single-stage turbine sufficient? Is the use of a gearbox between fan and low pressure turbine useful?
The operating behavior of the gas generator of turbofans and turboshafts with more than one spool has much in common with that of a turbojet. It can be explained with a few simple considerations that are very useful for the practice of a gas turbine engineer.

Here you can download  an enhanced version of the material I presented at Turbo Expo 2024.

The Basics of Gas Turbine Off-design Performance.
ASME GT2025-TOB-01-06

The fundamentals of the off-design behavior of gas turbines are explained using the gas generator of the CFM56-3, a turbofan with a high bypass ratio and separate nozzles as example. First, some basic correlations and the nomenclature used are presented. Then the performance behavior of the gas generator components is discussed one after the other. This is followed by a section describing the interaction of these components.

This gas generator can be used as a single-spool turbojet engine for thrust generation. The addition of a power turbine to the gas generator transforms the engine into a turboshaft. The integration of a low-pressure compressor, a gas generator, and a low-pressure turbine constitutes a two-spool turbojet. Finally, the off-design behavior of the CFM56-3 is discussed. This turbofan consists of a fan, a booster, the gas generator and a low-pressure turbine.

The investigation focuses next on the impact of variable compressor geometry on both the gas generator and the single-spool gas turbine as it is utilized for power generation purposes.  Variable turbine inlet guide vanes are a critical component of gas turbines equipped with heat exchangers. They play a crucial role in the efficient operation of these complex systems. Variable nozzles are a key component of low bypass ratio turbofans with afterburners.

The tutorial places significant emphasis on the so-called Mach number similarity.  It is essential to understand this concept to fully comprehend the off-design behavior of gas turbines.

Here you can download the tutorial I presented at Turbo Expo 2025 in Memphis, TN, USA

Simulation of Starting and Windmilling
It is a widespread view that reasonably accurate gas turbine performance calculations are only feasible between idle and max power. However, the common performance programs can calculate the thermodynamic cycle for spool speeds as low as 1% of the design value provided physically sound compressor and turbine maps are available. The 2nd edition of the book “Propulsion and Power” describes how to extend compressor and turbine maps from the idle region down to extremely low spool speeds. With such maps it is feasible to simulate engine starting and windmilling.

This tutorial is intended to support readers of Chapter 17 in "Propulsion and Power" who want to carry out their own calculations on starting and windmilling. The first part of the tutorial describes the steps involved in simulating the start-up of an aircraft engine. Although the specific algorithms in your favorite performance program may differ, the underlying principles remain the same as described here. The presented example simulation is supplemented by sensitivity studies, which illustrate the importance of the various input data.

The second part of this tutorial is dedicated to the simulation of windmilling. It also covers relighting an engine from the windmilling state.

Here you can download the tutorial.

The Basics of Aircraft Engine Thrust Management
ASME GT2026-TOB-01-01

This tutorial describes how aircraft engine thrust is controlled. The approach varies depending on whether the engines are attached to the wings, as in typical commercial airliners, or embedded in the fuselage, as in fighter aircraft.
 
In the first case, it is important that all engines deliver the same amount of thrust to avoid asymmetrical forces on the aircraft, regardless of engine age or deterioration. In the second case, the goal is to use all available thrust when needed. Asymmetry of forces is irrelevant. Since thrust cannot be measured directly on an aircraft, an indirect thrust measurement method must be used. 

This tutorial shows the theoretical background of common thrust rating parameters and how they are scheduled. To protect the engines from excessive mechanical and thermal loads, as well as the aircraft from excessive forces, the engines are “flat-rated.” Deterioration during operation causes a reduction in the exhaust gas temperature (EGT) margin, while thrust remains constant. 

This tutorial also explains the throttle lever layout and provides an overview of the engine display in the cockpit. It specifically references contemporary airliner cockpits, such as those of the Airbus A320 and A350.

Here you can download  the material I presented at Turbo Expo 2026 in Milano, Italy.

All the tutorials are licensed under Attribution 4.0 International (CC BY 4.0) See: https://creativecommons.org/licenses/by/4.0/legalcode