fluid mechanics Flashcards
when an aerofoil is travelling what is the difference in velocity between the 2 directions the air will take
the air that travels over the top of the aerofoil will travel with higher velocity and underneath will have lower velocity
when an aerofoil is travelling what is the difference in pressure between the 2 directions the air will take
the air travelling over the top with greater velocity will create an area with lower pressure and underneath where the air is travelling with lower velocity there will be higher pressure
air that travels quickly gains dynamic pressure and looses static pressure creating a pressure difference
how does a discuss get upwards lift
because of the bernoulli principle the higher pressure underneath will cause the discuss to lift because the air will want to move to the lower pressure area
what is lift
causes the object to move perpendicular to the direction of travel
enabling objects to stay in the air for longer increasing their horizontal displacement
what is the angle of attack
this is the tilt of a projectile relative to air flow, it creates a difference between the airflow.
this alters the velocity of the airflow and therefore the pressure creating upward or downward lift force
explain how a high angle of attack will affect the distance travelled by the discus (3)
AO1: the discus doesnt travel as far, it is stalled.
AO3: a high aoa will mean the discus produces less lift/more drag (1) as a result air begins to flow less smoothly over the top of the discus (1) meaning that air flow over the top becomes more and more separated (1)
reference to downwards lift and a switch in the air pressure gradient
definition of drag force
it is the resistance force experienced when travelling through a fluid environment and acts in the opposite direction
has a negative effect on velocity
it is a combination of air resistance and friction
what are the two types of drag
surface and form
what is surface drag and what is it also known as
relates to the friction between the surface of of the object and the fluid environment
skin drag
what is a fluid environment
liquid or gas, water or air
how can swimmers and cyclists reduce their surface drag
by wearing skin tight clothing and shaving their body hair
what is form drag
refers to the impact of the fluid environment on the object, relating to how streamlined the object is
how do cyclists reduce their form drag
drafting which is changing the leader, Belgian tourniquets
how do swimmers and cyclist reduce their form drag
by creating the smallest possible cross sectional front area
how can sprinters reduce their form drag
by keeping their arms close to their body and keeping their hands flat
what is laminar flow
when there is no turbulence behind the object
what is vortex flow
when there is turbulence behind an object which acts to pull back the performer
which type of flow is good which is bad
laminar flow is good and vortex flow is bad
how do cyclists reduce their form drag
tuck in, specialised helmet and bike, reduce front cross-sectional area
what is streamlining
involving shaping a body so that it can move as effectively and quickly through a fluid as possible, this creates less turbulence (vortex flow) reducing form drag and increasing speed (laminar flow)
reduces friction for a cyclist
analyse how laura kenny has maximised her speed in the photograph (IP), use bernouliis principle of lift and knowledge of the factors that influence drag (15)
AO1:
BP is to do with lift force and downward force created when air flows over an aerofoil, where there is an increase in the velocity of air there is a decrease in the pressure, where flow is fast, pressure is low, where flow is slow pressure is high.
lift force is a force that acts perpendicular to the direction of travel
drag acts in the opposite direction of motion and so will slow something down.
2 types: surface and form
factors that affect drag: velocity of body or air, cross sectional area, shape of body, type of surface
analyse how laura kenny has maximised her speed in the photograph (IP), use bernouliis principle of lift and knowledge of the factors that influence drag (15)
AO2:
streamline position>air over the top has shorter dist than underneath, so it travels slower = high pressure = downwards lift force with tyres applying more force to the track
drag opposite direction so slows laura down.
minimise: streamlined helmet, tight clothing, streamlined position ie back is parallel to the track, arms tucked into the body (reduce form drag)
to reduce surface drag the tyres are very thin and suit is smooth.
analyse how laura kenny has maximised her speed in the photograph (IP), use bernouliis principle of lift and knowledge of the factors that influence drag (15)
AO3:
streamlining with the helmet allows air to pass quicker over the top reducing drag created = cycle faster
other factors as well as like clothing and body position ensure cycles as fast as she can so wont reduce speed in order to reduce drag
explain how a lift force is imparted to a discus and explain its effects on the flight path of the discus (5)
discus is a aerofoil shape
takes on an appropriate AOA to direction of motion.
air has to travel further over the top of the discus.
air travels faster over the top of the dicus.
this creates low pressure on top called the bernoulli principle.
air moves from high to low creating lift force.
makes flight path nonparabolic.
lengthens flight path so discus is in the air for longer.
how does the bernoulli principle work for a cyclist
body forms an aerofoil shape creating an AOA
air travels further and faster under cyclist.
creates low pressure under cyclist.
air forced from high to low pressure.
forces bike down increasing tyre friction with the floor.
friction between wheels and track for a cyclist acts…
and comment on drag for a cyclist
against the cyclist
air resistance/fluid friction acts against cyclist
increases as their speed increases
acts in opposite direction to them
by cyclists using high pressure tyres what benefit does this have
reduces friction so can achieve higher velocity
