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CAMRYN BURLEY
DEMONSTRATING LAMINAR FLOW
WHAT IS LAMINAR FLOW?
• Lamina means layer
• When there are two plates, one of which is moving, there is one layer (lamina)
that moves with the plate and another that remains essentially still next to the
stationary plate
VELOCITY GRADIENT
• In a tube, the velocity is greatest at the center and slowest near the walls
TYPES OF FLOW
• Laminar flow- the particles in the fluid move in a straight line with parallel
velocity vectors
• Turbulent flow- once the fluid in the pipe achieves a critical speed, the
particles flow irregularly and create whirlpool-like regions
• Transient flow- the velocity and pressure of the liquid change over time
THE REYNOLD’S NUMBER
• The Reynold’s Number (Re) is non-dimensional velocity and can be used to
determine if flow is laminar, transient, or turbulent
• Laminar- Re < 2300
• Transient- 2300 < Re < 4000
• Turbulent- Re > 4000
CALCULATING THE REYNOLD’S NUMBER
• 𝑅𝑒 =
• 𝑅𝑒 =
• 𝑅𝑒 =
(𝜌𝑢2 )
𝜇𝑢
𝜌𝑢𝐿
𝜇
𝑢𝐿
𝑣
𝐿
Where:
• 𝜌 = density
• 𝑢 = velocity of the cross
section of the pipe
• 𝜇 = dynamic viscosity
• 𝐿 = length
• 𝑣 = kinematic viscosity
STOKES FLOW
• Stokes flow is an extreme form of laminar flow
• Occurs when Re<<1
• Examples of Stokes flow in the real world
LAMINAR FLOW IN THE REAL WORLD
• Airfoils
LAMINAR VS. TURBULENT FLOW
• Which is more efficient over an airfoil?
LAMINAR VS. TURBULENT FLOW
Laminar Flow
Pros
• Minimizes drag, which
improves efficiency and
reduces fuel costs
Cons
• At the speeds aircrafts reach,
maintaining laminar flow is
difficult, as it is sensitive to
bugs and dirt on the leading
edge of the airfoil
• Can easily transition to
turbulence, which leads to
sudden changes in handling
LAMINAR VS. TURBULENT FLOW
Turbulent Flow
Pros
• More predictable
performance (laminar flow
can break down)
Cons
• Increased drag, which
decreases efficiency
LAMINAR VS. TURBULENT FLOW
LAMINAR VS. TURBULENT FLOW
LAMINAR VS. TURBULENT FLOW
• If laminar flow could be easily maintained, that would be much preferred in
order to increase efficiency
• Since that does not occur in the real world, designers optimize turbulent wing
flow
• Boeing leading-edge suction method attempts to maintain laminar flow
SOURCES
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http://www.education.com/science-fair/article/laminar-flow/
http://hyperphysics.phy-astr.gsu.edu/hbase/pfric.html#vel
http://www.engineeringtoolbox.com/reynolds-number-d_237.html
http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/ROBERT_CASEY/typeofluid.htm
http://www.fluidmechanic.co.uk/transient.htm
http://www.engineeringtoolbox.com/dynamic-absolute-kinematic-viscosity-d_412.html
http://www.math.nyu.edu/faculty/childres/chpseven.PDF
https://uqu.edu.sa/files2/tiny_mce/plugins/filemanager/files/4282164/Stokes%20flow.pdf
http://www.symscape.com/blog/laminar-vs-turbulent-flow-over-airfoils