08081 - Turbomachinery

Learning outcomes

The objective is to give to students the information required to understand the behavior of all the turbomachineries employed in the aeronautical and aerospace field.

Course contents

Fundamentals (10 hours, 1 ECTS)

• Classification of fluid machines.
• Principles of mass and energy conservation.
• First law of thermodynamics for closed and open systems (mechanical and thermal forms).
• Entropy and enthalpy.
• Perfect and ideal gases: definition, main thermodynamic processes, and their representation on thermodynamic diagrams.
• Actual, polytropic, and isentropic work and efficiency in compression and expansion processes.
• Introduction to the Brayton cycle: layout of the simple gas turbine plant, representation on the T-s diagram, and conditions for cycle representation.

Centrifugal Pumps (10 hours, 1 ECTS)

• Operating principle and machine layout.
• Head calculation and characteristic performance curves.
• Operating issues: priming, cavitation, and surging.
• Similarity criteria and sizing of centrifugal pumps.
• Operation of pumps connected in series and in parallel.

Turbines (20 hours, 2 ECTS)

• Impulse turbines: velocity triangles, stage work, and stage efficiency.
• Pressure-stage turbines: velocity triangles, stage work, stage efficiency, and work recovery.
• Reaction turbines: velocity triangles, stage work, stage efficiency, and work recovery.
• Cooling of the first-stage turbine blades.
• Selection of blade materials and cooling technologies.
• Methods for estimating cooling air flow rates.
• Cooled expansion.

Compressors (15 hours, 1.5 ECTS)

• Centrifugal compressors: operating principle, specific work, and stage efficiency.
• Compressor and turbine performance.
• Buckingham Pi theorem and similarity criteria.
• Characteristic performance maps of compressors and turbines.
• Axial compressors: velocity triangles, specific work, and stage efficiency.
• Abnormal operating conditions: choking, stall, and rotating stall.
• Use of the inducer.
• Start-up issues in gas turbines.

Volumetric Machines (3 hours, 0.25 ECTS)

• Rotary and reciprocating volumetric pumps (single-acting and double-acting).
• Rotary and reciprocating volumetric compressors.
• Operating principles and main performance characteristics.

Compression Refrigeration Cycles (5 hours, 0.25 ECTS)

• Definition of the Coefficient of Performance (COP).
• Two-phase compression refrigeration cycle with two evaporation temperature levels.

Readings/Bibliography

Le turbomacchine motrici e operatrici, S. Sandrolini, G. Naldi, Pitagora Editrice, Bologna

Sistemi energetici e Macchine a Fluido, M. Bianchi, A. Peretto, G. Negri di Montenegro, Bonomo Editore

Teaching methods

Teaching is organized in class lectures and numerical exercises.

Attendance is strongly recommended for an improved learning of concepts and notions, but does not affect the final evaluation process.

Assessment methods

The assessment consists of an oral examination lasting approximately one hour, during which students are required to answer three questions covering the topics included in the course syllabus.

The examination is designed to assess the achievement of the intended learning outcomes, with particular reference to the Dublin Descriptors.

In particular, the following aspects will be evaluated:

• knowledge and understanding of the operating principles of turbomachinery, thermodynamic processes, design criteria, and the main performance characteristics of pumps, turbines, compressors, positive displacement machines, and refrigeration cycles (Dublin Descriptor 1 – Knowledge and Understanding);
• ability to apply knowledge and understanding to analyze the operation and performance of turbomachinery and to interpret the behavior of the different machine types under various operating conditions (Dublin Descriptor 2 – Applying Knowledge and Understanding);
• ability to develop independent judgments by integrating concepts from different topics of the course and justifying engineering solutions and design choices (Dublin Descriptor 3 – Making Judgements);
• communication skills, including the use of appropriate technical terminology and the ability to clearly explain concepts and accurately sketch the operating principles and layouts of turbomachines and related systems (Dublin Descriptor 4 – Communication Skills).

The final grade is based on the following assessment criteria:

• Knowledge and understanding of the course topics: 30%;
• Ability to apply knowledge and integrate concepts: 30%;
• Critical analysis and independent reasoning: 20%;
• Technical communication skills and accuracy of graphical representations: 20%.

The examination is graded on a 30-point scale, with 18/30 being the minimum passing grade.

The course Turbomachinery T (6 ECTS) is one of the two modules that, together with Aeronautical and Space Propulsion T (6 ECTS), constitute the integrated course Aerospace Propulsion T (12 ECTS). The final recorded grade is the arithmetic average of the grades obtained in the two modules. If the average results in a decimal value of 0.5, it is rounded up to the next whole number.

The distinction 30 cum laude may be awarded only in one of the following cases:

• the student has obtained 30 cum laude in both modules;
• the student has obtained 30 cum laude in one module and 30/30 in the other.

The examination schedule is published well in advance on the University's AlmaEsami platform. Students are required to present a valid identification document on the day of the examination.

Teaching tools

The slides used by the teacher are available on the VirtuaLe platform.
Practical examples and engines are shown in the lab facilities.

Office hours

See the website of Vittorio Ravaglioli