01 Fluid Concepts Flashcards
What is uniform flow?
Fluid flow in which velocity and cross section do not change from point to point.
(Ie non uniform flow: If cross section contracts in incompressible fluid; flow will accelerate and it’s velocity will increase)
What is steady flow?
Fluid flow in which velocity and pressure, at a point, don’t change with time.
What is viscosity?
The resistance of fluid to deformation or changing shape, or resistance to flow.
What is absolute (dynamic) viscosity?
The tangential force per unit area (shear stress T), required to move one horizontal plane of fluid wrt another plane.
What is kinematic viscosity and why is it used?
Absolute viscosity normalised by the fluids density. (Ie Just divided through by its density)
This makes it easier to compare different fluids viscosities with each other.
Difference between compressible and incompressible flow.
Compressible: fluid density notably changed in the considered system.
Incompressible: changes in the fluids density within a system are negligible
Reynolds number typical threshold values in fully developed pipe flow
LAMINAR <~ 2000
TURBULENT >~ 4000
Boundary conditions applied in analytical solutions
- no slip
- fluid interface
Boundary conditions which arise within CFD
Inflow and Outflow
Symmetry and periodic
What is the no slip boundary condition
For a fluid in contact with a solid wall, the velocity of the fluid equals that of the wall. (Ie stationary fluid if a stationary wall)
What is the fluid interface BC
When two fluids meet at an interface, the velocity (u) must be the same on both sides and the shear stress (tau) must be the same on both sides
Ie uA = uB and tauA = tauB
How does the viscosity of air differ from viscosity of water
Viscosity of air «_space;viscosity of water
TRUE OR FALSE: With pipe flow, the transition from laminar to turbulent will always occur between Reynolds numbers of 2000 and 4000
False.
The transition to turbulent flow can occur at higher Reynolds numbers if the conditions are smooth and steady.
