A venturi is a a convergent – divergent duct. When placed in a steady stream of air it enables a given volume of air entering it over any given time span to accelerate smoothly and pass through the restriction at the throat in the same
amount of time Once it has passed the throat, the air then decelerates to pass out through the exit at the same speed it entered ‘++diagram++
(b) . the pressure distribution around an aerofoil which is producing lift.
A streamline airflow around an aerofoil behaves in the same way as the flow through a venturi Air moving over the aerofoil shape must accelerate to pass over the top surface. it therefore gains dynamic energy and the static pressure
in that area is decreased At the same time air passing below the aerofoil is not deviated from its path – there is no change in velocity and static pressure remains the same In this pressure distribution a small force is generated
which tends to move the aerofoil towards the lower pressure area (image)
12.6.10. Describe streamline airflow around an aerofoil.
Streamline airflow: If succeeding molecules in the airstream follow the same steady and predictable path this can be represented as a streamline No flow is across the streamlines only along them – – (image)
12.6.8. Explain Bernoullis Theorem in simple terms.
Bernoullis Theorem States that.. In the streamline flow of an ideal fluid the sum of the
energy of position
plus the energy of motion
plus the pressure energy
will remain constant
Energy of position will not change significantly for aviation proposes. Leaving us with : Dynamic energy + static pressure = a constant.
increased the dynamic energy of motion
dynamic pressure
Increase
[vfr_Pic p1=”bernoulli_StaticMinus.png” p2=”200″]
static pressure
Decrease
total constant
to equal the Same
Decreased the dynamic energy of motion
dynamic pressure
Decrease
[vfr_Pic p1=”bernoulli_StaticPlus.png” p2=”200″]
static pressure
Increase
total constant
to equal the Same
Therefore, when the speed of the airflow is increased the dynamic energy of motion is increased and the static pressure will reduce to keep the total constant.(image)
Is the curvature of an aerofoil surface. The curvature of a line drawn equidistant between the upper and lower surfaces of the aerofoil is the mean camber of the aerofoil. (image)