Drag loading in a steady flow Flashcards
What is creeping flow?
A flow regime where Reynolds number is very small (Re ≪ 1), often idealised as potential flow.
In creeping flow through a Hele-Shaw cell, the Reynolds number is very ________.
small
True or False: Flow separation begins at Reynolds number around 1.54.
False – symmetry is lost around Re = 1.54, but separation begins around Re ≈ 5.
What forms when flow separates around a cylinder at Re ≈ 9.6?
Re-circulating eddies
As Reynolds number increases, standing eddies become _________.
elongated
What happens to the vortex cores as Re increases?
- Distance to cores increases linearly with Re
- Separation between cores increases as Re
True or False: At Re = 30.2, flow becomes unsteady.
False – flow is still steady but the wake is more than a cylinder diameter long.
Match Re with flow behavior:
Re = 41 →
Re = 105 →
- End of steady flow range (wake begins oscillating)
- Onset of Von Karman vortex shedding
What is a Von Karman vortex street?
A repeating pattern of swirling vortices shed alternately from each side of a bluff body in unsteady flow.
At Re = 2000, flow separates into a turbulent ________.
wake
True or False: Increasing the incident velocity always changes the flow pattern significantly.
False – at high Re, doubling velocity may not significantly affect wake pattern.
What physical forces are produced due to asymmetric wake and vortex shedding?
- Drag force (inline)
- Lift force (transverse)
What is the definition of Drag Coefficient C_D?
C_D = F_D / (½ ρU²A)
What is the definition of Lift Coefficient C_L?
C_L = F_L / (½ ρU²A)
In the drag coefficient equation, the reference area A for a vertical cylinder is A = ___ ⋅length.
diameter
True or False: Drag coefficient remains constant regardless of Reynolds number.
False – it varies with Reynolds number.
