Fluid mechanics

• Fluid Mechanics


  The science that deals with the behaviour of fluids at rest (fluid statics) or in motion (fluid dynamics), and the interaction of fluids with solids or other fluids at the boundaries
• Branches of fluid mechanics


  • Fluid Statics
  • Fluid Dynamics
• Fluid Statics


  The study of the behaviour of fluids at rest
• Branches of fluid statics


  • Hydrostatics
  • Aerostatics
• Hydrostatics


  Deals with the study of incompressible fluids (i.e. fluids that do not undergo significant density changes with pressure such as liquids, especially water) at rest
• Aerostatics


  Deals with the study of compressible fluids (i.e. fluids that undergo significant density changes with pressure) at rest
• Fluid Dynamics


  The study of the behaviour of fluids in motion
• Branches of fluid dynamics


  • Hydrodynamics
  • Aerodynamics
  • Hydraulics
  • Gas dynamics
• Hydrodynamics


  The study of the motion of fluids that can be approximated as incompressible (such as liquids, especially water, and gases at low speeds)
• Aerodynamics


  Deals with the flow of gases (especially air) over bodies such as aircraft, rockets, and automobiles at high or low speeds
• Hydraulics


  A branch of hydrodynamics that deals with liquid flows in pipes and open channels
• Gas dynamics


  A branch of fluid dynamics which deals with the flow of fluids that undergo significant density changes, such as the flow of gases through nozzles at high speeds
• Deformation caused by shearing forces on an element of fluid

  
• For fluids at rest, the shear stress is zero and pressure is the only normal stress
• The fluid in contact with the boundary adheres to it and will, therefore, have the same velocity as the boundary
• Shear strain


  Increases with a constant applied shear force
• Rate of shear strain

  Proportional to applied shear force
• Newton's law of viscosity

  Shear stress is proportional to the rate of shear strain

  
• Differences between solids and fluids


  • Strain is a function of the applied stress, provided that the elastic limit is not exceeded (Solids)
  • The rate of strain is proportional to the applied stress (Fluids)
  • Strain (deformation) is independent of the time over which the force is applied and, disappears when the force is removed, provided the elastic limit is not exceeded (Solids)
  • A fluid continues to flow for as long as the force is applied and will not recover its original form when the force is removed (Fluids)
• Criteria for fluid classification


  • Response to externally applied pressure
  • Response to shear stress

  
• Compressible fluids


  Fluids whose densities change with pressure
• Incompressible fluids


  Fluids whose densities are independent of pressure
• Types of fluids based on response to shear stress


  • Newtonian fluids
  • Non-Newtonian fluids

  
• Newtonian fluids


  Fluids where the ratio of the shear stress to rate of shear is constant and is equal to the viscosity of the fluid

  
• Non-Newtonian fluids


  Fluids where the ratio of shear stress to rate of shear is not constant and the apparent viscosity of the fluid is a function of the rate of shear

  
• Ideal fluid


  An incompressible fluid with zero viscosity (or in other words shear stress is always zero regardless of the motion of the fluid)
• Characteristics of an ideal fluid


  • No viscosity
  • No surface tension
  • Incompressible
• In reality, an ideal fluid does not exist
• Continuum concept of a fluid


  A hypothetical continuous, homogeneous matter with no holes
• Despite the relatively large gaps between molecules, a gas can usually be treated as a continuum because of the very large number of molecules even in an extremely small volume
• Point function


  A function whose value depends on the final and initial states of the thermodynamic process, irrespective of the path followed by the process
• Applications of fluid mechanics


  • Piping systems
  • Aeronautic systems
  • Automobile engineering
  • Civil engineering
• Fluid mechanics plays a major part in the design and analysis of aircraft, rockets, jet engines
• The sleek streamlined shape of recent model cars is the result of effort to minimize drag by using extensive analysis of flow over surfaces
• Fluid mechanics is also considered in the design of buildings and bridges to make sure that the structures can withstand wind loading
• Property


  Any characteristic of a system
• Types of properties


  • Intensive
  • Extensive
  • Specific
• Intensive property


  Independent on mass of system
• Extensive property


  Dependent on mass of system
• Specific property


  Extensive properties per unit mass (intensive properties)