Fluid flows can be classified based on viscosity, compressibility, and flow regime. These factors determine how fluids behave under different conditions, affecting their motion and properties.
Understanding flow types is crucial for engineering applications. Laminar vs turbulent, steady vs unsteady, and internal vs external flows all have distinct characteristics that impact fluid behavior and system design.
Classification of Fluid Flows
Classification of fluid flows
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Top images from around the web for Classification of fluid flows
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Fluid Dynamics – University Physics Volume 1 View original
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Laminar and turbulent steady flow in an S-Bend - The Answer is 27 View original
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Viscosity describes a fluid's internal resistance to flow
Viscous flows have significant internal resistance (honey, oil, syrup)
Viscous forces dominate over inertial forces
Inviscid flows have negligible internal resistance (water, air at low speeds)
Inertial forces dominate over viscous forces
Compressibility relates to how fluid density changes with pressure
Compressible flows have fluid density that varies significantly with pressure changes (high-speed gas flows, supersonic flows)
Mach number (ratio of flow speed to speed of sound) > 0.3
Incompressible flows have fluid density that remains nearly constant with pressure changes (liquids, low-speed gas flows)
Mach number < 0.3
Flow regime categorizes flows based on their behavior and characteristics
Laminar flows have fluid particles moving in smooth, parallel layers
Turbulent flows have fluid particles moving in a chaotic and irregular manner
Laminar vs turbulent flows
Laminar flows exhibit smooth, parallel layers of fluid motion
No mixing occurs between layers
Low Reynolds number (Re<2300 for pipe flows)
Velocity profile is parabolic in fully developed pipe flows (slow-moving fluids, small pipes, high-viscosity fluids)
Turbulent flows display chaotic and irregular fluid motion
Mixing occurs between layers
High Reynolds number (Re>4000 for pipe flows)
Velocity profile is flatter compared to laminar flows (fast-moving fluids, large pipes, low-viscosity fluids)
Steady vs unsteady flows
Steady flows have flow properties that do not change with time at any point
Velocity, pressure, and density remain constant
Mathematically represented as ∂t∂=0
Examples include fully developed pipe flows and constant flow rate from a tank
Unsteady flows have flow properties that change with time at any point
Velocity, pressure, and density vary over time
Mathematically represented as ∂t∂=0
Examples include starting or stopping of a flow, pulsating flows, and waves
Internal and external flows
Internal flows are confined by boundaries on all sides
Examples include pipe flows, duct flows, and flow through a nozzle
Applications involve piping systems, HVAC ducts, and hydraulic systems
External flows occur over a surface or body, with at least one side not confined by a boundary
Examples include flow over an airfoil (wings), flow around a car (vehicle aerodynamics), and flow past a building (wind engineering)
Applications involve aerodynamics, wind engineering, and hydrodynamics