Fluid Dynamics Flashcards
Define fluid dynamics.
study of the effect of the forces that are created when an object travels through a fluid
What is considered a fluid?
gases, vapours, and liquids and fluids (sometimes even grains or fine powders)
The 2 fluids that concern us the most are:
- air
- water
Name 3 forces that concern us in fluid dynamics.
- buoyancy
- drag
- lift
What is buoyancy?
the tendency of an object to float or rise in a liquid or a gas
What is Archimedes principle?
any body in a fluid will experience a buoyant force equal to the weight of the volume of the fluid it displaces
Buoyancy is an indicator of ______.
density
Density =
mass/volume
What is the centre of buoyancy?
the point at which the buoyant forces are said to act
Where is the centre of buoyancy in a homogenous body?
same as the centre of mass
Where is the centre of buoyancy in a human body?
- mid-chest
- superior to CoG
- determines how a body “sits” in water
…..
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Name the characteristics of a fluid.
- laminar flow
- turbulent flow
What does laminar flow consist of?
- layered
- closest layer hugs the surface
- more movement further out
- bonds between layers = viscosity
What does turbulent flow consist of?
layering breaks down to a significant level
What is drag?
- the opposing force acting on an object travelling through a fluid
- acts in a direction which is opposite to the propelling force
What are the 3 kinds of drag?
- surface or friction drag
- form or pressure drag
- wave drag
What is surface drag?
- similar to friction in that it is reduced by smoothing the surface on which it acts
- layer of fluid right next to surface is slowed
What are 4 factors that affect surface drag?
- relative velocity of fluid flow
- surface area of body
- viscosity of the fluid
- roughness of the body surface
What is form drag?
- affected by the area
- caused by pocket of turbulence behind moving body (the faster the relative motion, the greater the turbulence
How does form drag create pressure differential?
- positive at leading surface, negative behind
- force directed from high to low
How do golf ball dimples relate to form drag?
- creates layer of turbulent flow
- this layer is carried with the ball
- flow of the rest of the fluid is laminar = less pressure differential
What is theoretical square law?
- all other factors being equal, friction/form drag increases with the square of the relative velocity of motion
- except for with wave drag, which increases with the cube of the relative velocity of motion
Drag has a greater impact for _____ speed sports such as…
- high speed
- downhill skiing, bobsled, luge
What is wave drag?
- “wall” of water created in front
- builds up high pressure
- greater the velocity, greater the pressure
- greater impact on swimmer (increases according to the cube of the velocity)
- effects only felt in water
What is lift?
- right angles to the relative flow
- different pressures on opposing sides of the object (from high to low)
- up or down
- Newton’s 3rd law: reaction forces of fluid against object resulting from object’s force applied to fluid
What is Bernoulli’s principle?
the total energy in steady flowing fluid system is a constant along the flow path. An increase in the fluid’s speed must therefore be matched by a decrease in its pressure
What is the Magnus effect?
- spin on a ball causes the path of the ball to be curved
- ball curves a certain way because it is deflected from a high pressure to a low pressure
- curve occurs in direction of spin (low pressure)
- see diagram
Give an example of theoretical square law.
cyclist crouching low can create a ten-fold reduction in drag
