Part 4: Boundary Layer Concepts and Flow over Immersed Bodies Flashcards
What is an External Flow?
a flow field for which the object is completely surrounded by the fluid. Ex. Submarine, plane, building
A body interacts with the surrounding fluid through..
pressure and shear stresses
What is Drag?
the resultant force acting on a body due to the pressure and/or shear stresses acting in the direction of the approach velocity
What is Lift?
the resultant force acting on a body due to pressure and/or shear stresses acting perpendicular to the direction of the approach velocity.
T or F: Both Re and body shape have significant effect on the Cd?
True
What plays a dominant factor on the lift coefficient?
Body Shape
What is the Boundary Layer?
The region adjacent to the surface of a body in which viscous effects are important.
T or F: Flow within the boundary layer is only laminar?
False, flow within the boundary layer can be turbulent or laminar.
How low must the Re be so that a boundary layer does not occur?
Re<1000
What is the Transitional Range of Re?
2x10^5 to 3x10^6
True or False: Outside the boundary layer the flow behaves as it were inviscid?
True
The boundary layer is response to…
fluid viscosity
Where does the no-slip condition occur?
at a solid boundary
How is the edge of the boundary layer defined?
By velocity, once U reaches 99%U
The flow outside of the boundary layer is classified as the “ “
free stream
T or F: Flow posses vorticity inside the boundary layer?
True
T or F: Flow posses vorticity outside the boundary layer?
False, only within the boundary layer
What type of mixing/rotation occurs in the laminar layer?
simple mixing`
What type of mixing/rotation occurs in the turbulent layer?
random mixing
What is the displacement thickness?
It is used to describe the “outward shift” from edge of body to account for velocity deficit relative to free stream.
True or False: Shear stress decreases as x increases
True, as you move further down the pipe you have less shear stress
True or False: The drag on a flat plate is not related to the momentum deficit within the boundary layer?
False, it is
” “ is the dimensionless wall shear stress
local friction coefficient
Laminar Flow is characterized by
-Viscous, flowing in layers, random motion is on a molecular level, velocity at a point is constant
Turbulent flow is characterized by
-Non-viscous, eddies, mixing, random motion occurs at a macroscopic scale, velocity at a point is fluctuating
