External Flow: Boundary Layer theory and thickness

Question 1

what is the velocity of the fluid at the body surface/wall

Answer 1

0

Question 2

how is a boundary layer formed

Answer 2

adjacent layers of the wall are slowered

Question 3

what is the drag force associated with boundary layers determined by

Answer 3

skin friction drag & pressure/form drag

Question 4

what is skin friction drag

Answer 4

shear stress at the wall

Question 5

hat is pressure/form drag

Answer 5

pressure diff between the front face and wake of the body

Question 6

describe the boundary layer over a flat plate for lamiar flow

Answer 6

velocity at the plate is 0
slows fluid adjacent forming a laminar layer of slow fluid
slows more layers and thickens the boundary layers
boundary layer becomes unstable and turbulence develops
turbulent boundary layer thickens at a greater rate

Question 7

what is the difference between laminar and turbulent’s velocity profiles

Answer 7

turbulent is uniform/more evenly distributed

due to mixing fluid particles (still 0 at wall)

Question 8

what is the equation for shear stress at the wall

Answer 8

Mew(du/dy) when y=0 (due it’s higher velocity gradient at the wall, experiences more shear stress)

Question 9

how is the thickness of a boundary layer, delta, determined

Answer 9

distance where u = 0.99U

Question 10

how is the displacement thickness repressented

Answer 10

as a gap of thickness, delta*

Question 11

how is displacement thickness calculated

Answer 11

delta* = int(1+u/U)dy limits[0,delta]

Question 12

what is the momentum thickness and how does it come about

Answer 12

as the boundary layer reduces velocity net momentum of fluid is reduced. represented as momentum thickness, theta

Question 13

how is momentum thickness calculated

Answer 13

theta = int(u/U(1 - u/U)dy limits[0, delta]

Question 14

equation for Reynold’s number over a flat plate

Answer 14

Re = [density * U * x(distance along plate)]/mew