Fluid Mechanics-ISpring 2010 Lecture # 01
Course Outline • Introduction to Fluids and Fluid Properties • Fluid Statics • Integral Relations for fluid flow • Dimensional Analysis and Similarity • Differential Relations for fluid flow • Pipe Flows & Potential Flow
Books FLUID MECHANICS BY Frank M. White Yunus A. Cengel Reference Book: Fluid Mechanics by Munson & Young
Why Study Fluid Mechanics? • Fluid Mechanics is omnipresent • Aerodynamics • Bioengineering and biological systems • Combustion • Energy generation • Geology • Hydraulics and Hydrology • Hydrodynamics • Meteorology • Ocean and Coastal Engineering • …numerous other examples… • Fluid Mechanics is beautiful
States of Matter Fluid
Microscopic Difference Fixed Position Molecules in Solids Molecules move about each other in Liquids Molecules are in random motion in Gases
What is a Fluid? Fluid Able to flow or alter shape freely Solid Firm and stable in shape
Relatively strong cohesive forces in molecules. Retain its volume and make a free surface if unconfined from top. Molecules are widely spaced. Does not retain its volume if unconfined from top. No gravitational effects except buoyancy. Difference between a Liquid & a Gas Liquid Gas
Stress The internal resistance of a material to the applied force is called Stress.
Shear force on a Solid & Fluid Solid (Stress is proportional to strain) Fluid (Stress is proportional to strain rate)
Definition of a Fluid Any substance that is continuously deformed when subjected to shear stress is called a fluid.
Fluid Mechanics Mechanics is the branch of physics that is concerned with the analysis of the action of forces on matter. Fluid Mechanics is the analysis of action of forces on fluids.
Branches of Fluid Mechanics Fluid Statics: The analysis of action of forces on fluids at rest e.g. Water stored in a tank Fluid Dynamics: The analysis of action of forces on moving fluids e.g. water flowing in a river or a pipe flow
Basic laws of Mechanics • Conservation of Mass • Conservation of Momentum • Conservation of Energy • Laws of Thermodynamics
Properties of the Fluid • The analysis of the fluid flow is the determination of fluid properties as a function of position and time. Outlet Inlet Y Throat X
Fluid Flow Variables • Pressure • Velocity • Temperature • Density All flow variables are functions of space (x,y,z) & time (t)
Types of Properties • Extensive Properties Depends upon the size of the system or amount of the material e.g. mass, length, volume etc • Intensive Properties Independent of the size of the system or amount of the material e.g. Temperature, pressure, velocity, viscosity, density etc
Specific Properties • Extensive properties per unit mass are called specific properties. Examples include specific volume v= V/m and specific total energy e=E/m.
Specific gravity • The ratio of the density of a substance to the density of some standard substance at a specified temperature (usually water at 4°C), i.e., SG=ρ/ρwater
Specific weight • The weight per unit volume.
Why it is? • Easier to move in air at rest. • Difficult to move in Water at rest. • More difficult to move in Oil at rest. • Honey flows slowly than water • Always difficult to move in a running fluid towards you.
Viscosity • Relationship between the local stresses to strain rate of the fluid element. A quantitative measure of fluid’s resistance to flow • Order of viscosity of different fluids is e.g. Air<Water<SAE30<glycerin <blackstrap molasses
Drag Force • The force a flowing fluid exerts on a body in the flow direction is called the drag force, and the magnitude of this force depends, in part, on viscosity.
Coefficient of Viscosity Units: Kg/(m.s) or Pa.s Also known as absolute or dynamic viscosity
Kinematic Viscosity • The ratio of absolute viscosity to the density is known as Kinematic Viscosity. Units: m2/s