FLUID MECHANICS

The main objective of the course is to provide the basic knowledge of Fluid Mechanics. After a preliminary part in which the physical characteristics of fluids are described, with particular emphasis on those that distinguish them from solids, the course introduces the fundamental topics of Fluid Mechanics, accompanied by the necessary theoretical framework. The course also includes lessons to be dedicated to carrying out exercises in the classroom, relating to the application of the principles of Fluid Mechanics to the solution of engineering problems.

The teaching will be carried out through lectures and classroom exercises.

Should teaching be carried out in mixed mode or remotely, it may be necessary to introduce changes with respect to previous statements, in line with the programme planned and outlined in the syllabus.

Introduction to the course

Definition of fluid substance. The continuum hypothesis. Dimensions and measurement units. Mass forces and surface forces. Stress tensor and its properties. Fluid properties: compressibility, thermal elasticity, surface tension, viscosity. Non-Newtonian fluids. Gas absorption.

Fluid statics
Stress in fluids at rest. Equations of fluid statics in differential form. Equation of fluid statics in global form. Statics of incompressible fluids under the action of gravity force. Stevin's law. Pressure measurements. Hydrostatic thrusts on plane surfaces. Hydrostatic thrusts on curved surfaces. Hydrostatic thrusts on immersed body. Fluids of low specific weight.

Fluid kinematics

Generalities on fluid kinematics. Material volume and control volume. Lagrangian and Eulerian approaches. Local derivative and material derivative. Velocity and acceleration. The Reynolds transport theorem. Trajectories. Streamlines. Smoke lines. Flux tube. Steady flow. Unsteady flow. Uniform flow. Two-dimensional flow. Continuity equation in differential form. Continuity equation in global form. Continuity equation for currents. Rotation and deformation of fluid elements. Irrotational flows.

Fluid dynamics

Momentum equation in differential form. Euler equation. Boundary conditions. Momentum equation in global form. Example of application.
Euler equation in the intrinsic coordinate system. Pressure distribution in gradually varied currents. Bernoulli's theorem. Geometric representation of Bernoulli’s theorem. Energy implications of Bernoulli's theorem. Mechanical energy equation. Outflow phenomena. Extension of Bernoulli theorem to a current. Exchange of energy between a current and a machine. Venturimeter. Pitot tube. Extension of Bernoulli's theorem to real fluids. Continuous head losses. Localized head losses.
Constitutive relationship of viscous fluids. The Navier-Stokes equations. Momentum equation of viscous fluids in global form.

Confined flows
Reynolds experiment. Flow regimes. Laminar regime. Turbulent regime. The Reynolds number. Tangential stresses in uniform flow. Laminar flow in a pipe. Poiseuille formula. Laminar flow between parallel plates. Turbulent flow. The mean flow equation. Viscous and turbulent shear stresses. Application of the Buckingham theorem to the determination of the resistance law formula. Darcy-Weisbach formula. Friction factor. Flow in smooth pipes. Friction factor in smooth pipes. Mean velocity distribution of a turbulent flow in a smooth pipe. Flows in rough pipes. Nikuradse's experiments. Friction factor in rough pipes. Velocity distribution in turbulent flow in a rough pipe. Commercial pipes. Colebrook and White formula. Moody chart. Empirical formulas for the calculation of the head losses. Localized head losses. Head loss due to abrupt enlargement, sharp-edged inlet and outlet in a reservoir. Flows subject to negative pressure.

1) Y. A. Cengel, J. M. Cimbala "Fluid Mechanics - Fundamentals and Applications" Fourth Edition, McGraw-Hill

2) G. Alfonsi, E. Orsi "Problemi di Idraulica e Meccanica dei Fluidi" CEA Milano, 1984.

3) G. Pezzinga "Esercizi di Meccanica dei Fluidi" Aracne editrice, 2008.

4) Notes provided by the teacher available during the course on the Studium Platform.