OVERVIEW

The course explores in depth the architecture and operating principles of power-absorbing turbomachines and positive displacement machines, providing a strong theoretical foundation for their choice, installation, and operation.
 

AIMS AND CONTENT

LEARNING OUTCOMES

The course aims at providing the basic information about the functioning of compressors, fans, and pumps. The effects of the kind of fluid, and of structural and economic issues on the machine architecture are also considered. On such a basis, choice and installation criteria are derived, and information are provided about the machine operation, also considering the system in which the machine is installed. Preliminarily, physical properties of technical fluids are recalled, together with thermodynamic and fluid dynamic equations relevant to fluid machinery

AIMS AND LEARNING OUTCOMES

Through active participation in lectures and problem-solving sessions, together with independent study, students will acquire:

• an operational knowledge of the physical properties of the fluids commonly processed by fluid machines, the thermodynamic transformations involved, the conservation equations used for flow analysis, similarity theory, and statistical methods;

• a basic understanding of the architecture of the main types of power-absorbing turbomachines, the functions of their components, and the variations of the principal fluid-dynamic and thermodynamic quantities within them;

• with specific reference to axial power-absorbing turbomachines, an operational knowledge of one-dimensional and two-dimensional flow models in the meridional plane and on the blade-to-blade surface;

• with specific reference to multistage axial compressors, a basic understanding of the variation of the principal fluid-dynamic and thermodynamic quantities along the machine, as well as of the characteristic curves;

• with specific reference to radial power-absorbing turbomachines, an operational knowledge of one-dimensional flow models in the meridional plane and on the blade-to-blade surface;

• a basic understanding of the fluid-dynamic and structural constraints governing the design and operation of axial and radial power-absorbing turbomachines;

• an understanding of compressor off-design operating phenomena, including stall, surge, and choking;

• with reference to reciprocating and rotary positive displacement pumps and compressors, a basic knowledge of the functioning and of the causes of deviation from the ideal behavior.

PREREQUISITES

Students are expected to have a basic knowledge of Fluid Dynamics, Thermodynamics, and Fluid Machinery.

TEACHING METHODS

Theoretical lectures and applied sessions.

Students who hold valid certification for Specific Learning Disorders (SLD; DSA in Italian), disabilities, or other special educational needs are invited to contact both the instructor and the Polytechnic School's disability liaison, Professor Federico Scarpa (federico.scarpa@unige.it), at the beginning of the course to discuss any appropriate accommodations for teaching activities and examinations, consistent with the learning objectives of the course and the student's individual learning needs.

SYLLABUS/CONTENT

1. Review of Fluid Dynamics and Thermodynamics

1.1. Fundamental physical properties of fluids and fluid models

Vapour pressure; constitutive equation and viscosity; state equation of perfect gases, internal energy and enthalpy, specific heats, polytropic transformations; bulk modulus of compressibility and speed of sound. Limits of applicability of the various models and the effect of temperature. Recurrent integrals in the work exchange computation.

1.2. One-dimensional balance equations for fluid machines

Continuity equation (for compressible and incompressible flow), energy equation (for compressible and incompressible flow, in mechanical and thermal form, in the absolute and relative frame), equations of linear and angular momentum, Euler equation. Head and increments of total pressure, total temperature, and total enthalpy. Basic assumptions and limits of applicability. Design and performance-analysis problems and features of the related algorithms.

1.3. Theory of similarity

Non-dimensionalization of solutions of the Navier–Stokes equations (for compressible and incompressible flow) and choice of the reference dimensional parameters. Fundamental non-dimensional parameters for airfoils and fluid machines: Mach and Reynolds numbers; pressure coefficient, lift and drag coefficients, incidence, adverse pressure gradient, boundary-layer separation, and stall; flow and head coefficients, non-dimensionalization of pump and fan characteristic curves, interpretation of their trends and stall; corrected flow rate, corrected rotational speed, compression ratio, and their relationship with the Mach number; non-dimensionalization of axial-compressor characteristic curves, interpretation of their trends, stall, and choking; compressor–turbine matching and gas-turbine operation.

1.4. Statistical methods and empirical correlations in the study of fluid machines

Specific speed and specific diameter, empirical correlations, relation with design constraints and their influence on machine geometry. Limits of applicability.

2. Typical Applications of the Balance Equations

2.1. Incompressible-flow applications

Pump operation in a hydraulic circuit between reservoirs. Fan efficiency chain. Applications of the linear-momentum equation to nozzles and propulsion systems. Thrust and propulsive efficiency.

2.2. Compressible-flow applications

Reheat effect in compression. Adiabatic, polytropic, and isothermal efficiencies. De Saint Venant and Hugoniot equations, characteristic curve of a nozzle. Rayleigh flow: effect of heat transfer on the main fluid dynamic and thermodynamic variables and applications to combustors.

3. Turbomachines (Compressors, Blowers, Fans, and Pumps, Axial and Radial)

3.1. Architecture and operation of axial-flow turbomachines

Geometrical representation of axial turbomachines: meridional and cylindrical blade-to-blade views. Representation of blade sections and velocity triangles. Function of the rotor and stator in single- and multistage machines. Cascade aerodynamics: non-dimensional parameters, velocity triangles, blade thrust, work exchange, and pressure rise. Multistage axial compressors: typical architectures, distribution of work exchange, compression ratio, and degree of reaction. Two-dimensional flow in the annuli: radial equilibrium equation and common vortex laws. Maximum blade loading: de Haller criterion and Diffusion Factor. Aerodynamic and structural constraints on blade span.

3.2. Architecture and operation of mixed-flow and radial-flow turbomachines

Geometrical representation of mixed-flow and radial turbomachines: meridional view and blade-to-blade flow surface. Representation of blade sections and velocity triangles. Effect of radius variation on work exchange and compression. Function of the radial rotor: velocity triangles and variation of pressure, velocity, and enthalpy; typical blade geometries and characteristic curve; outlet blade angle, slip effect, and related correlations. Function of the stator and volute: bladed and unbladed diffuser, velocity triangles and variation of pressure, velocity, and enthalpy; volute design. Flow on the blade-to-blade flow surface: blade loading and blade design. Aerodynamic and structural constraints on blade curvature and thickness.

4. Positive-Displacement Machines

4.1. Generalities

Reciprocating and rotary machines, classification, compression and pumping work, ports and valves.

4.2. Reciprocating positive-displacement pumps

Indicator diagram, work exchange, flow rate, and average and instantaneous power.

4.3. Reciprocating positive-displacement compressors

Causes of deviation from ideal behaviour: clearance volume and its consequences on the operation of reciprocating compressors. Volumetric efficiency and its dependence on operating conditions and compression ratio.

4.4. Multistage compression and intercooling

Distribution of the compression ratio among stages. Intercooling and its effects on compression work, fluid temperature, and overall efficiency. Conditions for minimum work.

4.5. Valves, flow rate control, and characteristic curves

Operation of automatic and actuated valves. Effect of valve opening and closing advance and delay on the indicator diagram and machine performance. Main methods for flow rate control in reciprocating compressors and their energy implications. Characteristic curves of positive-displacement pumps and compressors and operating limits.

RECOMMENDED READING/BIBLIOGRAPHY

For examination preparation:

• Course notes prepared by the instructor and other teaching materials available on the AulaWeb course website for the relevant academic year.

For further study of specific topics:

• R. I. Lewis, Turbomachinery Performance Analysis, Arnold.
• L.A. Catalano, M. Napolitano, Elementi di Macchine operatrici a fluido. Pitagora Editrice.

TEACHERS AND EXAM BOARD

LESSONS

LESSONS START

https://corsi.unige.it/en/corsi/11959/studenti-orario

Class schedule

The timetable for this course is available here: Portale EasyAcademy

EXAMS

EXAM DESCRIPTION

Oral exam at the end of the course, normally every Tuesday. Please contact the lecturer by e-mail at Andrea.Cattanei@unige.it at least one week in advance.

Students with a certified learning disability (DSA), a disability, or other special educational needs are invited to contact the instructor at the beginning of the course to discuss teaching and examination arrangements that, while respecting the learning objectives of the course, take individual learning needs into account and provide appropriate accommodations.

Please also note that requests for exam accommodations or exemptions must be submitted using the form available at this link

https://modulionline.unige.it/richiesta-adattamenti#no-back, to the course professor, the DIME contact person (federico.scarpa@unige.it), and the relevant office (inclusione.studenti@info.unige.it) at least seven working days before the examination, in accordance with the guidelines available at this link

https://unige.it/disabilita-dsa/richiesta-servizi

ASSESSMENT METHODS

Discussion of topics covered during the course based on two questions. The examination is intended to assess the student's understanding of the physical meaning and engineering relevance of the subjects discussed.

FURTHER INFORMATION

Ask the professor for other information not included in the teaching schedule.