Fluid chapter 1

• Fluid mechanics


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


  Fluid mechanics is also referred to as fluid dynamics by considering fluids at rest as a special case of motion with zero velocity
• Hydrodynamics


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


  A subcategory of hydrodynamics, which deals with liquid flows in pipes and open channels
• Gas dynamics


  Deals with the flow of fluids that undergo significant density changes, such as the flow of gases through nozzles at high speeds
• Aerodynamics


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


  A substance in the liquid or gas phase
• Stress


  Force per unit area
• Normal stress


  The normal component of a force acting on a surface per unit area

  
• Shear stress


  The tangential component of a force acting on a surface per unit area

  
• Pressure


  The normal stress in a fluid at rest
• A fluid deforms continuously under the influence of a shear stress, no matter how small
• A solid can resist an applied shear stress by deforming
• Liquids


  • Groups of molecules can move relative to each other, but the volume remains relatively constant because of the strong cohesive forces between the molecules
  • Take the shape of the container they are in, and they form a free surface in a larger container in a gravitational field
• Gases


  • Expand until they encounter the walls of the container and fill the entire available space
  • The gas molecules are widely spaced, and the cohesive forces between them are very small
  • Cannot form a free surface in an open container
• Phases of matter


  • Solid
  • Liquid
  • Gas
• Intermolecular bonds are strongest in solids and weakest in gases
• Solid


  The molecules are arranged in a pattern that is repeated throughout
• Liquid


  Molecules can rotate and translate freely
• Gas


  The molecules are far apart from each other, and molecular ordering is nonexistent
• Application areas of fluid mechanics

  • Design of artificial hearts
  • Aerodynamics of vehicles
  • Meteorology, oceanography, and hydrology
• No-slip condition


  A fluid flowing over a stationary surface comes to a complete stop at the surface
• Boundary layer


  The flow region adjacent to the wall in which the viscous effects (and thus the velocity gradients) are significant
• Flow separation can occur during flow over a curved surface
• Viscous flows


  Flows in which the frictional effects are significant
• Inviscid flow regions


  Regions (typically regions not close to solid surfaces) where viscous forces are negligibly small compared to inertial or pressure forces
• External flow


  The flow of an unbounded fluid over a surface such as a plate, a wire, or a pipe
• Internal flow


  The flow in a pipe or duct if the fluid is completely bounded by solid surfaces
• Open-channel flow


  The flow of liquids in a duct that is only partially filled with the liquid and has a free surface
• Incompressible flow


  If the density of flowing fluid remains nearly constant throughout (e.g., liquid flow)
• Compressible flow


  If the density of fluid changes during flow (e.g., high-speed gas flow)
• Mach number


  Expresses the flow speed relative to the speed of sound

  
• Mach number ranges


  • Ma = 1 Sonic flow
  • Ma < 1 Subsonic flow
  • Ma > 1 Supersonic flow
  • Ma >> 1 Hypersonic flow

  
• Laminar flow


  The highly ordered fluid motion characterized by smooth layers of fluid

  
• Turbulent flow


  The highly disordered fluid motion that typically occurs at high velocities and is characterized by velocity fluctuations
• Transitional flow


  A flow that alternates between being laminar and turbulent
• Forced flow


  A fluid is forced to flow over a surface or in a pipe by external means such as a pump or a fan
• Natural flow


  Fluid motion is due to natural means such as the buoyancy effect
• Steady flow


  No change at a point with time
• Unsteady flow


  The opposite of steady