Form, Lift, Drag and Propulsion

Summary

This script delves into the intricacies of fluid dynamics, focusing on flow separation from boundaries and its impact on various applications. It explains how adverse pressure gradients and shear zones in boundary layers lead to separation, affecting flow patterns, drag, and potentially causing structural issues. The video discusses methods to mitigate separation, such as streamlining and controlling boundary layers, and explores the concept of circulation and its role in cross-thrust and lift, particularly in the context of airfoils and propellers. It concludes with insights into the design of propulsive machinery, emphasizing the importance of blade shape and flow dynamics in efficiency.

Takeaways

• 🚫 Separation of flow from a boundary is not just a geometric effect; it requires an adverse pressure gradient and a zone of flow as produced by shear in the boundary layer.
• 🔄 The central streamlines do not separate as pressure rises toward the point of stagnation, but separation occurs when the fluid in contact with a surface is at rest and cannot be further decelerated.
• 📍 Separation points on bodies of appreciable curvature move forward from the zone of maximum pressure rise to where deceleration first occurs.
• 💨 Separation leads to changes in flow patterns, increased boundary drag, energy expenditure, and can cause flow oscillation, pressure fluctuations, noise, and structural damage.
• 🪂 Parachutes and baffles operate on the principle of separation, but in general, separation should be avoided by controlling the boundary layer or the pressure gradient.
• 🔄 The retardation by shear can be offset by moving boundaries, preventing separation, similar to discharging fluid tangentially into the boundary layer region.
• 📉 The drag coefficient indicates the effect of separation and is the ratio of the longitudinal force exerted by the flow to the stagnation pressure.
• 🛠 Streamlining can reduce drag significantly, especially under optimum conditions, by minimizing the separation surface and adverse pressure gradient.
• ⚫ A sphere represents intermediate streamlining, with a pressure distribution indicating separation still occurs, as shown by smoke injection into the wake.
• 🔄 The mathematical concept of circulation is useful in analyzing the cross-thrust exerted on bodies in relative motion, defined as the line integral of the tangential component of velocity around a closed curve.
• 🛫 Lifting veins are designed to take advantage of flow-induced cross-thrust, with a lift coefficient proportional to the relative circulation and the angle of attack.

Q & A

What is the primary cause of flow separation in fluid dynamics as described in the script?

Flow separation primarily occurs due to an adverse pressure gradient, which is common in regions of deceleration, and also requires a zone of already existing flow, such as that produced by shear in the boundary layer.

Why do central streamlines not separate as the pressure rises toward the point of stagnation?

Central streamlines do not separate because the flow between them is not affected by shear, and the fluid in contact with a splitter plate is already at rest and cannot be further decelerated.

What are the three important occurrences that result from flow separation?

The three important occurrences are changes in the anticipated flow pattern, the production of boundary drag which expends energy through the generation of eddies that rapidly transform into turbulence, and the potential for flow oscillation leading to pressure fluctuation, noise generation, and possibly structural damage.

How can separation be avoided in the operation of parachutes and baffles?

Separation can be avoided by controlling the boundary layer or the pressure gradient, or both. For example, if the boundary moves with the flow, the retardation by shear is offset, preventing separation.

What is the purpose of guide vanes in fluid dynamics as mentioned in the script?

Guide vanes are used to change the pressure field as a whole. They can conform to the original boundary and increase the relative radius of curvature locally, or they can be used to redesign the structure to improve flow efficiency.

What is the drag coefficient and how is it related to separation in fluid dynamics?

The drag coefficient is a dimensionless number that indicates the effect of separation. It represents the longitudinal force exerted by the flow per unit projected area in its ratio to the stagnation pressure. It helps in understanding the resistance of a body moving through a fluid.

How does the shape of a body affect its drag in fluid dynamics?

The shape of a body affects its drag by influencing the flow pattern around it. A streamlined shape reduces drag significantly by minimizing the pressure reduction at the rear and the adverse pressure gradient.

What is the significance of circulation in analyzing the cross-thrust exerted on certain bodies in relative motion?

Circulation, defined as the line integral of the tangential component of velocity around a closed curve, is a measure of the fluid's tendency to circulate around the curve. It is crucial in analyzing cross-thrust because it affects the velocity and pressure distribution around bodies, leading to side forces.

How does the angle of attack of a lifting vein affect its lift coefficient?

The lift coefficient of a lifting vein is proportional to the relative circulation, which in turn is proportional to the sine of the angle of attack. As the angle of attack increases, the lift increases until a point called stall is reached, after which the lift decreases.

What is the effect of aspect ratio on the lift-to-drag ratio of a lifting vein?

The lift-to-drag ratio of a lifting vein decreases as the aspect ratio (length over chord) decreases. This is due to a tip effect, where flow occurs around the end of the vein, diminishing the pressure difference and thus reducing efficiency.

How does the design of a propeller blade vary with its radial position?

Each radial section of a propeller blade moves with a different velocity, so the blade must vary continuously in shape from tip to hub. This variation ensures that each element of the blade has a different angle of attack to maintain efficient design.

Outlines

00:00

🚀 Fluid Dynamics and Flow Separation

This paragraph delves into the complexities of fluid dynamics, particularly focusing on the phenomenon of flow separation from boundaries. It explains how separation occurs not only due to an adverse pressure gradient but also requires a zone of flow affected by shear in the boundary layer. The script discusses the effects of separation, such as altered flow patterns, increased boundary drag, and potential flow oscillations, which can lead to structural damage. It also highlights methods to control or prevent separation, such as manipulating the boundary layer or pressure gradient, and introduces the concept of guide veins to improve flow efficiency. The importance of understanding separation is emphasized through its relevance in various applications like parachutes and baffles, and the paragraph concludes with an explanation of the drag coefficient and its significance in assessing the impact of separation on pressure distribution and flow resistance.

05:02

🛰️ Streamlining and the Impact of Shape on Fluid Resistance

The second paragraph examines the influence of an object's shape on the fluid resistance it encounters, illustrating how streamlined forms can significantly reduce drag. It discusses the concept of streamlining and how it can minimize the adverse pressure gradient and separation effects, leading to a reduction in boundary layer drag. The paragraph provides examples of how adding a rounded front or a well-faired tail piece can mitigate separation and reduce drag. It also touches on the relationship between a body's projected area, shape, and the resulting resistance, using the sphere as a reference point for comparison. The discussion extends to the effects of two-dimensional flow and the drag coefficient, explaining how it can be influenced by the body's shape and the presence of other bodies in the flow field. The paragraph concludes with an exploration of the mathematical concept of circulation and its role in analyzing cross-thrust on bodies in relative motion.

10:02

🌀 Vorticity and the Dynamics of Lifting Veins

This paragraph explores the concept of vorticity and its effects on the dynamics of lifting veins. It explains how circulation, a measure of the fluid's tendency to circulate around a curve, can influence the flow pattern and pressure distribution around bodies like cylinders. The paragraph describes the cross-thrust phenomenon, which can cause deflection in spinning objects, and introduces the Karman vortex street, a series of vortices shed alternately from the sides of an oscillating cylinder. It also discusses the instability of certain structural sections, such as the Tacoma Narrows Bridge, and how circulation can be harnessed in lifting veins to generate lift. The paragraph concludes with an analysis of the lift coefficient in relation to the angle of attack and the effects of stall on the flow pattern around an airfoil.

15:05

✈️ Aerodynamics of Propellers and Hydrofoils

The fourth paragraph focuses on the aerodynamics of propellers and hydrofoils, explaining how the principles of lifting veins are applied to these technologies. It discusses the importance of blade shape and angle of attack in determining the lift and drag forces that contribute to the axial thrust and torque of a propeller. The paragraph also touches on the effects of tip vortices and the downwash they create, which can impact the efficiency of lifting surfaces. It further explains how hydrofoils can be used to lift boats out of the water, reducing wave resistance and increasing speed and stability. The discussion extends to the historical use of lifting principles in windmill technology and the modern application of these principles in various types of propellers and turbines.

20:10

🌪️ Advanced Propulsion Systems and Fluid Dynamics

The final paragraph discusses advanced propulsion systems, such as jet engines and torque converters, and their underlying fluid dynamics principles. It explains how stationary guide vanes and moving blades work together to create thrust in a manner similar to lifting veins. The paragraph also addresses the challenges of designing for the compressibility of gases and the importance of matching flow rates, approach directions, and runner speeds to avoid stall and maintain efficiency. It concludes with a look ahead to the next film in the series, which will delve into the effects of compressibility on fluid dynamics.

Keywords

💡Separation of Flow

Separation of flow refers to the phenomenon where a fluid detaches from a solid surface, such as a boundary or plate, due to an adverse pressure gradient. In the context of the video, it is a critical concept explaining how flow patterns change around objects, leading to various effects like drag and turbulence. The script mentions that separation requires not only an adverse pressure gradient but also a zone of already decelerated flow, as seen in the boundary layer.

💡Boundary Layer

A boundary layer is a thin layer of fluid in the immediate vicinity of a bounding surface where the effects of viscosity are dominant. The video script discusses how the boundary layer plays a crucial role in flow separation, affecting the pressure distribution and leading to phenomena like drag. It is also mentioned that manipulating the boundary layer can help control separation, which is vital for the operation of devices like parachutes and baffles.

💡Adverse Pressure Gradient

An adverse pressure gradient is a pressure gradient that acts in the opposite direction to the flow, causing the fluid to decelerate. The script explains that separation of flow generally requires an adverse pressure gradient, which is a common occurrence in regions of flow deceleration. It is a key factor in the development of flow patterns around bodies and the resulting aerodynamic effects.

💡Drag Coefficient

The drag coefficient is a dimensionless quantity that is used to quantify the resistance of an object moving through a fluid. In the script, it is mentioned as an important parameter that indicates the effect of separation on the flow. The drag coefficient is defined as the ratio of the longitudinal force exerted by the flow per unit projected area to the stagnation pressure, and it is used to compare the drag of different shapes, like the yellow disc and a well-faired tail piece.

💡Streamlining

Streamlining is the process of designing the shape of an object to reduce air resistance, thereby minimizing drag. The video script highlights that under optimal conditions, streamlining can reduce drag by as much as 95%. It is an essential concept in the design of efficient vehicles and structures, as it directly impacts their performance and energy consumption.

💡Circulation

Circulation in fluid dynamics is the line integral of the tangential component of velocity around a closed curve, indicating the fluid's tendency to circulate around the curve. The script introduces the concept of circulation to analyze the cross-thrust exerted on bodies in relative motion, such as the deflection of a spinning baseball. It is a fundamental concept in understanding lift and the behavior of fluid around objects.

💡Lift

Lift is the force that opposes the weight of an object and supports it in the air or fluid. The script discusses lift in the context of lifting veins, which are designed to take advantage of flow-induced cross-thrust. Lift is a critical concept in aerodynamics, especially in the design of wings and other airfoils, and is directly related to the circulation around the object.

💡Tip Vortex

A tip vortex is a swirling flow of fluid that forms at the tip of a lifting surface, such as an airfoil or a propeller blade. The script describes the formation of tip vortices and their impact on the flow behind the lifting surface, contributing to phenomena like downwash. Understanding tip vortices is important for predicting the performance and stability of lifting surfaces.

💡Aspect Ratio

The aspect ratio in the context of airfoils and wings is the ratio of the length to the average chord of the airfoil. The script mentions that the aspect ratio affects the lift-to-drag ratio of an airfoil, with higher aspect ratios generally providing better performance. It is a key parameter in the design of wings and other lifting surfaces.

💡Cavitation

Cavitation is the formation of vapor cavities in a liquid due to a rapid decrease in pressure. In the script, cavitation is discussed in relation to ship propellers, where it can cause a reduction in efficiency and potential damage. It is an important consideration in the design of propellers and other marine equipment to ensure smooth operation.

💡Compressibility

Compressibility is a property of a fluid that describes its ability to change volume in response to pressure changes. The script notes that compressibility is an important factor in the design of high-speed propulsion systems, such as jet engines, where it can significantly affect performance. Understanding compressibility is crucial for optimizing the efficiency and operation of such systems.

Highlights

The concept of flow separation from a boundary and its effects on fluid dynamics.

Explanation of how separation reduces the curvature of the limiting streamline until a physically possible pressure field is realized.

The necessity of an adverse pressure gradient and a zone of already decelerated flow for separation to occur.

The behavior of central streamlines in relation to pressure changes and the role of shear in boundary layer separation.

The impact of separation on flow patterns, boundary drag, and the generation of turbulence.

How separation can cause flow oscillation, leading to pressure fluctuations, noise, and potential structural damage.

The importance of controlling boundary layer or pressure gradient to avoid separation in applications like parachutes and baffles.

Techniques to prevent separation, such as moving boundaries and fluid discharge into the boundary layer.

The use of guide veins to alter the pressure field and improve flow efficiency.

Introduction of the drag coefficient as a measure of separation effect and its significance in flow analysis.

The role of streamline form in reducing drag and the concept of streamlining in various applications.

The mathematical concept of circulation and its application in analyzing cross-thrust on bodies in relative motion.

Demonstration of how circulation can be produced by boundary layer shear around a rotating body.

The impact of oscillation of flow pattern on cross-thrust and the resulting oscillatory motion of structures.

The design principles of lifting veins to maximize flow-induced cross-thrust and their application in aircraft wings and hydrofoils.

The relationship between the lift coefficient, circulation theory, and the angle of attack of a lifting vein.

The effects of aspect ratio on the lift-to-drag ratio and the role of tip vortices in reducing efficiency.

The application of lifting vein principles in windmill and propeller design for efficient energy conversion.

The complexity of slipstream and tip vortex effects in ship propellers and their impact on thrust and torque.

The function of stationary guide veins in altering circulation without doing work, as seen in torque converters.

The general principle of using stationary and moving blades in jet engines for propulsive machinery.

Transcripts

[Music]

in our previous films separation of flow

from a boundary was treated as a purely

geometric effect a plate or orifice

diaphragm for example is usually too

thin for the flow to follow without an

impossibly low pressure at the

edge separation simply reduces the

curvature of the limiting stream line

till a physically possible pressure

field is

realized in general however separation

requires not only an adverse pressure

gradient as in any region of

deceleration but also a zone of already

flow as is produced by Shear in

the boundary

layer

here the central stream lines do not

separate as the pressure Rises toward

the point of stagnation because the flow

between them is not otherwise

but the fluid in contact with a

splitter plate is already at rest and

cannot be further decelerated so the

separation must take place if the flow

is to

continue as the boundary layer develops

around any body of appreciable curvature

the point of Separation rapidly moves

forward from the zone of maximum

pressure rise at the rear to the Zone

where deceleration first

occurs as a matter of fact no change in

boundary alignment is really

necessary just so long as there is a

sheer zone of low velocity and an

adverse pressure gradient such as

prevails beneath the front of this Ulus

surge moving slowly against the

flow

separation leads to three important

occurrences first the changes of the

anticipated flow pattern for instance

this channel expansion obviously does

not cause the flow itself to expand as

rapidly as

desired secondly it produces boundary

drags thereby expending energy through

the generation of edes which rapidly

transform to

turbulence finally it can lead to oscill

of the flow with a corresponding

pressure fluctuation boundary vibration

noise generation and perhaps even

structural

damage though separation is very

essential in the operation of parachutes

and baffles it should in general be

avoided by the control of the boundary

layer or the pressure gradient or of

both together if the boundary moves with

the flow for example the retardation by

Shear is offset and separation obviously

is

prevented much the same elimination of

separation is realized if as is now

beginning to occur fluid is discharged

tangentially into the boundary layer

region through boundary

slots even better results will next be

seen to obtain as the boundary layer

fluid is sucked into the slots as

rapidly as it is

a change in the pressure field

as a whole is provided by the

introduction of guide

veins these can be made to conform to

the original boundary and thus increase

the relative radius of curvature locally

or else the whole structure can be

redesigned accordingly as in the case of

this miter bend the flow is obviously

much worse without the veins but much

more efficient once veins have been

installed a type of Oiler number that

indicates the effect of separation is

known as the drag

coefficient the longitudinal force

exerted by the flow per unit projected

area in its ratio to the stagnation

pressure for extreme Degrees of

Separation as must occur at the edges of

this

dis measur of the pressure distribution

at the numbered Pomers on the front and

rear faces will show the cause of the

drag as air now begins to flow from left

to right the front of the dis becomes

subject to positive pressure and the

rear to appreciable

suction the integral of the pressure

distribution will yield the same Force

as that measured on such an air tunnel

Dynam

mometer the high drag of the yellow disc

can be reduced appreciably by adding a

rounded front which minimizes the

curvature of the separation surface and

thus somewhat alleviates the pressure

reduction at the

rear separation is almost completely

eliminated by adding a well fared tail

piece to reduce the adverse pressure

gradient since there can be no

resistance to steady irrotational flow

around the body with without separation

practically the only resistance now is

that of Shear within the boundary

layer under Optimum conditions the

process called streamlining can reduce

the drag some

95% since the resisting Force varies

with the projected area of a body as

well as with its shape at the same

velocity this streamline form would then

produce no more resistance than a dis of

less than a quarter its diameter

a sphere is intermediate between poor

streamlining and good

streamlining as can be seen from the

distribution of pressure measured at the

numbered

Pomers when flow takes place from left

to right the low pressure at the rear

compared with the high pressure at the

front indicates that separation still

occurs as is shown by injecting smoke

into the Wake the line of separation is

even ahead of the

midsection making the boundary layer

turbulent prematurely by a trip wire

tends to reduce the separation tendency

as is evident from the shift of the

separation point to the rear of the

midsection compared with a body

producing two-dimensional flow like this

long plate a more nearly axis symmetric

body Like A square has a much higher

wake pressure and hence a much lower

drag per unit

area the drag coefficient of a square

plate therefore is increased by cutting

it into more nearly two dimensional

strips and slightly separating

them a body that is in the wake of

another being in a zone of reduced

velocity experiences a great reduction

in drag as any cyle who has coasted

along behind a truck is well

aware these Elementary principles also

apply to more complicated structures

such as

buildings roofs should not be designed

for only positive loading since in high

winds they are more likely to be lifted

by suction due to separation than they

are to be blown

in chimneys obviously should not

terminate within zones of separation or

the smoke will fill the region behind

them this has se to be the case almost

regardless of the direction from which

the wind

comes probably the most UNAM line body

is a

parachute but obviously even this can be

designed for maneuverability

moreover even the human body in free

fall can control its turning moment

about three different

axes as this sky diver clearly

shows the mathematical concept of

circulation introduced in connection

with vorticity in our second film is

also useful in analyzing the cross

thrust that is exerted upon certain

bodies in relative

motion the circulation gamma is defined

as the line integral of the tangential

component of the Velocity completely

around a closed

curve it's thus a measure of the

tendency of the fluid to circulate

around the curve either in the One

Direction or in the

other the circular streamlines of an IR

rotational Vortex are all lines of of

constant circulation for the velocity

varies inversely and the circumference

directly with the

radius now if the velocity field of such

a Vortex is superposed upon the velocity

field of ir rotational flow around the

body say a circular

cylinder the velocity on the one side

will be augmented and on the other side

diminished in proportion to the relative

strength of the

circulation and the flow pattern will

change accordingly

where the velocity is increased the

pressure will be reduced and vice versa

so that a side thrust will be exerted

upon the

cylinder such circulation can be

produced in actuality by boundary layer

Shear around a rotating

body this is Illustrated quite

graphically by Rolling a light paper

cylinder down a miniature C

jump because of the rotation of the

cylinder as it leaves the jump the cross

thrust will cause it to deviate quite

markedly from its normal parabolic

trajectory the same effect causes the

deflection of a spinning baseball or a

spinning pingpong ball from its normal

course if a cylinder is not rotating

however oscillation of the float pattern

will cause the circulation to vary first

in One Direction action and thenone in

the other with the result that there is

a rapid oscillation in the cross

thrust this explains the tendency for

telephone wires to sing in a high wind

or it explains the whistling sound that

is given off by this Rod as it swung

rapidly through the

air observation of the flow pattern

behind such a cylinder will reveal the

alternate shedding of vortices either

side of the center line the circulation

around each Vortex being just the

opposite of the momentary circulation

around the cylinder producing the side

thrust the succession of such vortices

is called the Caron Vortex

Trail if the cylinder is free to

oscillate under the side thrust as it is

if suspended from light Springs it will

gradually develop an oscillatory Motion

in the transverse Direction and

eventually move back back and forth over

a distance about equal to its

diameter an elliptical cylinder with

major axis in the direction of the flow

will have a more limited amplitude of

oscillation whereas one with its major

axis normal to the flow will oscillate

much more

marketly some asymmetric forms like

either this semicircular cylinder or ice

encrusted telephone wires are unstable

in the T will tend to oscillate farther

and farther with eventual breakage of

the suspension as a

result a similar sort of instability is

found in various structural sections in

particular the Tacoma Narrows Bridge

here seen oscillating in a high wind

prior to Ultimate

failure

a body that is so designed is to take

maximum advantage of flow induced cross

thrust is known as a lifting vein the

circulation of the starting Vortex seen

here is matched by an equal and opposite

lift producing circulation around the

foil the fact that circulation actually

occurs around the foil is seen from the

vortices that detach as the foil is

stopped

a lift coefficient can be written for a

vein of length L and chord c as the

lifting Force per unit vein

area in its ratio to the stagnation

pressure according to the circulation

theory of lift this coefficient is

proportional to the relative

circulation which in turn is

proportional to the sign of the angle of

attack of the vein

a plot of the measured lift coefficient

against angle of attack shows good

agreement with the circulation Theory at

small angles but a great deviation at

high angles as the phenomenon known as

stall

occurs by means of smoke filaments the

gradual development of stall or Leading

Edge separation is readily seen from the

change in flow pattern around this

symmetrical vein as its angle of attack

is continuously

increased Pomers at the numbered points

around the profile of a vein show that

in a steady crossflow a circulation

induced with growing angle of attack

produces a pressure below and a suction

above the vein the difference increasing

as the angle of attack increases till

stall suddenly

occurs as seen from this polar diagram

of lift versus drag a well-designed

lifting vein will display an efficiency

or racial of lift to drag as high as 25

or

30 this is for an aspect ratio length

over cord that is very

great as the aspect ratio decreases

however the ratio of lift to drag

steadily

diminishes this is because of a tip

effect much like that of the shortened

plate in which flow occurs around the

end and diminishes the pressure

difference near the middle of a vein

smoke filaments show only a

two-dimensional separation

effect near the end however as the vein

is inclined first this way and then that

the pressure on one side and suction on

on the other give rise to an additional

circulation effect an intense tip

Vortex this end view of the same

foreshortened vein shows the growth of

the tip Vortex to

Perfection the resulting flow directly

behind the vein has a downward component

called downwash which necessarily

increases with decreasing aspect

ratio

lifting veins are used not only for the

wings of airplanes but also under modern

hydrofoil boots to lift the holes

completely out of the

water this is an experimental Grumman

craft being tested for the maritime

Administration elimination of wave

resistance obviously leads to much

greater speed and

stability the first use of the lifting

vein principle occurred many centuri

entries ago in connection with the

windmill forerunners of the more recent

airplane propeller shown

here since each radial section of a

propeller moves with a different

velocity for efficient design the blade

as a whole must vary continuously in

shape from tip to

HUB each successive element of the blade

has the same forward speed but a

tangential speed that is proportional to

the

radius hence each will have a different

angle of advance and this in turn makes

necessary a variable angle of the

blade for the single blade element now

shown the forward speed and the

tangential speed determine its direction

of motion relative to the

fluid this and the geometry of the

element then control the angle of attack

the lift and drag measured right

relative to the direction of

motion evidently both contribute to the

axial thrust of the propeller and to the

tangential force that is involved in the

torque a ship propeller usually has

Blades of large cord so that the load is

distributed over a greater

area thus the local pressure drop Will

normally not be great enough to produce

cavitation here however

tests conducted under extreme conditions

in a cavitation tunnel of the Navy's

David Taylor model Basin show by water

vapor formation the decrease in

slipstream diameter that must always

occur as the propeller accelerates the

passing

fluid when the same state of flow is

seen in slow motion the tip Vortex is

found to yield a spiral tube of water

vapor which shows the actual complexity

of the

slipstream

encasing a propeller in a duct as in a

pump or turbine eliminates both a tip

effect and the necking down of the

slipstream the pitch of the blades is

often variable from the breaking limit

to full feather in order to control the

efficiency and other operating

characteristics blowers pumps and turbin

Vary from the axial flow or propeller

type just shown to the radial flow or

centrifugal type of this Alice Charmers

turbine a radial flow unit is shown

schematically in the

laboratory the blue stationary guide

veins give the oncoming flow a

tangential component which ideally is

brought again to Zero by the time the

flow leaves the red veins of the moving

Runner

the work that is done by the fluid on

the runner is proportional to the change

in circulation that is

produced if the camera is now rotated at

the same speed as the runner to show the

flow relative to its

blades these are seen to act as lifting

veins much like those previously

discussed the components of both lift

and drag evidently control the tangent

force on the runner that does the useful

work however if the rate of flow

direction of approach and Runner speed

are not properly related an effect

comparable to stall will occur and the

efficiency will be

reduced a fluid coupling which serves as

a shock-free connection between driving

and driven Mach

Machinery consists of a pump the green

shaft and blades at the left and a

turban the blue shaft and blades at the

right compactly combined in a single

housing if the space is filled with a

fluid of appreciable density turning the

input shaft and Blades will cause the

output blades and shaft to yield the

same torque whether rotating or

stall because the circulation must

increase and decrease by the same amount

as the fluid passes from one side to the

other and Back

Again inclusion of a set of stationary

veins here shown in red permits the

circulation to be changed without doing

work so that the output veins will yield

a higher or lower

torque such a unit is called a torque

converter proper shape of the stationary

veins will even permit the output torque

to be reversed

inside the general principle of using

stationary guide veins visible in the

upper portion of this open model of an

aircraft jet

engine as well as moving blades is the

basis of most propulsive

Machinery though the elements are

carefully shaped and used in many

successive stages they are all basically

lifting veins here however not only the

density and viscosity of the gaseous

fluid must be considered but also its

compressibility a property of which the

effects will be treated in detail in the

next and last film of this

series

[Music]

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