Hydraulic Principles

• Hydraulic engineering


  The study of the flow and conveyance of fluids, especially water
• Mechanics


  The science that deals with static (stationary) and dynamic (moving) bodies under the impact of forces
• Statics


  The science that deals with bodies at rest
• Dynamics


  The science that deals with bodies in motion
• Fluid Mechanics


  The science that deals with fluid behaviours: static fluids (fluids at rest) and dynamic fluids (fluids in motion)
• Hydrodynamics


  The science that deals with the motion of incompressible fluids, e.g. water
• Hydraulics


  A hydrodynamic subcategory, dealing with the flow of liquids in pipes and open channels
• Fluid


  A substance in the liquid or gas phase that deforms continuously under the influence of a shear stress and never stops deforming and approaches a constant rate of strain
• Stress


  Force per area
• Normal Stress


  Perpendicular force acting on a surface

  
• Shear Stress


  Tangential force acting on a surface

  
• Pressure


  Perpendicular stress in static fluids
• The Normal Stress And Shear Stress At Surface Of A Fluid Element
• 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. Molecules can rotate and translate freely.
• Fluid flow classification


  • Viscous flows
  • Inviscid flows
  • Compressible flows
  • Incompressible flows
  • Forced flows
  • Natural flows
  • Internal flows
  • External flows
  • Uniform flows
  • Non-uniform flows
  • Steady flows
  • Unsteady flows
  • Laminar flows
  • Turbulent flows
  • Transitional flows

  
• Reynolds number


  Ratio of inertial forces to viscous forces within a fluid flow
• Re < 2300 is considered laminar flow, 2300 ≤ Re ≤ 4000 is considered transitional flow, Re > 4000 is considered turbulent flow
• Flow combinations


  • Steady uniform flow
  • Steady non-uniform flow
  • Unsteady uniform flow
  • Unsteady non-uniform flow

  
• Flow dimensionality


  The number of spatial coordinates needed to describe all properties of the flow

  
• One-dimensional flows are flows in which the velocity depends on only one space variable, such as flows in pipes and channels
• Two-dimensional flows are flows where the dependent variables depend on only two space variables, such as flows over a wide weir, in the entrance region of a pipe, and around a sphere
• Three-dimensional flows are flows where the flow parameters may vary in space, in the direction of motion, y and z in the plane of the cross-section

  
• Inviscid Flows


  Flows not experiencing significant frictional forces. Negligible frictional forces
• Viscous flows


  Flows experiencing large frictional forces
• Compressible flows


  Density of fluid changes during flow
• Incompressible flows


  Unchanged density in fluid during flow
• Forced flows


  External means such as a pump forces a fluid to flow over a surface or in a pipe.
• Natural flows


  Natural means facilitates flow. E.g. buoyancy, capillary rise
• Internal flows


  Flows where fluid is bounded by surfaces such as pipes
• External flows

  Flow of fluids over surfaces
• Uniform flows


  Flow velocity is the same magnitude and direction at every point in the fluid
• Non-uniform flows


  Flow velocity is not the same at every point the flow.
• Steady flow


  Conditions such as pressure and cross section differ from point to point but NOT with time
• Unsteady flow


  Conditions change with time
• Laminar Flow


  Paths of particles do not obstruct each other

  Viscous forces are prevailing

  Velocity of fluid particles only changes in size

  Lateral component of velocity is zero

  Predictable behaviour
• Turbulent flows

  • Paths intersect each other
  • Inertial forces are prevailing
  • Velocity of fluid particles change in size and direction
  • Lateral components exist
  • Chaotic behavior
• Transitional flows


  Flows that alternate between a laminar flow and a turbulent flow
• Reynolds Number

  Re < 2300 is considered laminar flow

  2300 ≤ Re ≤ 4000 is considered transitional flow

  Re > 4000 is considered turbulent flow
• Unsteady Uniform Flow 


  At a given instant in time, the conditions at every point are the same but will change with time
• Examples of unsteady uniform flow

  • A pipe of constant diameter connected to a pump, pumping at a constant rate then switched off.
  • Flow of water in a pipe of constant diameter at constant velocity.