M. Ibbotson - Professional english in use engineering (794233), страница 23
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Look at A opposite to help you.at a higher pressureat a lower pressureatmospheric pressuregauge pressureone atmospherepressure differentialcompressed airexert pressure onexplodepressurizedoutside airpressurized aircraft cabins?It's a well-known fact that the cabins of commercial aircraft are (l) ................................. This is an obviousrequirement, given that at high altitude the air is (2) ................................ than (3) ................................
at groundlevel. If passengers were exposed to these conditions while ftying at altitude, they would suffer numeroushealth problems. Hence the need, at high altitude, to maintain the air inside the fuselage(4) ................................ than the (5) ................................. But how is this achieved and controlled?At the moment an aircraft's doors are closed at the airport, the cabin pressure is clearly equivalent to(6) ................................ , meaning the (7) ................................ of the cabin is zero.
Once the aircraft takes off andbegins to climb, the pressure of the outside air will begin to decrease, while air pressure inside the aircraftremains the same thanks to the airtight fuselage.However, maintaining the air pressure simply by keeping the same air inside the aircraft for the durationof a ftight would be problematic- firstly because the air needs to be continually renewed for thecomfort of passengers, and secondly because at very high altitude the significant (8) ..............................
..between the inside and outside of the cabin would (9) ................................ the inside of the fuselage toan unacceptably high degree. Although the resulting stresses would not be high enough to cause thefuselage to (l 0) ................................
,they would result in a high rate of metal fatigue. Consequently, as theaircraft climbs, air is released through valves in the fuselage until a slightly lower pressure is attainedequivalent to the pressure of the outside air at an altitude of between 5,000 and 8,000 feet. Air is thenconstantly renewed during the ftight by releasing it through the valves, and replacing the equivalentvolume with (ll) ................................ pressurized to the same level by the aircraft's engines.38.3Match the two parts to make correct sentences. Look at B opposite and Appendix X onpage 112 to help you.1 Header tanks are designed to2 To prime means to3 Siphonic action is able to4 Water towers are large tanks designed toOve,r .f-o tjotcabcdmake liquid flow upwards from its surface.generate hydrostatic pressure in a building.supply large numbers of buildings.fill a pipe or hose to its full bore, removing the air.·~Think about a system you're familiar with which contains fluid that is at a higher or lowerpressure than atmospheric pressure.
What is the reason for having a positive or negativepressure? How great is the pressure differential, relatiw to atmospheric pressure? How is thepressure differential generated and maintained?Professional English in Use Engineering83~lllliiililFluid dynamics-Fluid dynamics and aerodynamicsFluid dynamics is the study of how gases and liquids flow around objects. The branch of fluiddynamics concerned with airflow- called aerodynamics - is relevant to the design of aircraft,vehicles and structures. Aerodynamic tests can be done in wind tunnels - tunnels throughwhich air is blown at high velocity. Analysis can also be done using computational fluiddynamics (CFD) -computers with complex simulation software.-DragAerodynamic drag (or drag) is the resistance of an object to an airflow.
It is measured by thedrag coefficient. Objects with a low drag coefficient have little force exerted on them by anairflow. We say they are streamlined . There are different types of drag:-•Form drag is due to the shape of the object.•Skin friction is the drag caused by air flowing over the surface of the object.•Pressure drag is the pressure differential between the air upstream of the object (flowingtowards it) and the air downstream of it (flowing away behind it). The lower-pressurezone close behind a moving object is often called the slipstream.•Interference drag depends on the amount of turbulence around the object.Laminar flow and turbulent flowIn aerodynamics, engineers focus on the airflow in the boundary layer- the air close to thesurface of an object.
If the object is streamlined, the airflow in the boundary layer will belaminar, following a direct, clean path. With a less streamlined object, the airflow will beturbulent, flowing in a disturbed, messy fashion. A turbulent flow produces more drag than alaminar flow, and generates a bigger wake- that is, the V-shaped zone of turbulent air behindthe object. Wakes contain vortices. A vortex is a twisting flow - like water going down theplughole in a bath.-AerofoilsAerofoils are components designed to make air flow in specificways. They include:•aircraft wings, which generate lift- that is, upwardaerodynamic force•the blades of plane propellers, and helicopter rotor blades,which generate thrust to propel aircraft through the air•wings on racing cars, which generate downforce downward aerodynamic force.An aircraft propeller with twobladesAerofoils have specially designed profiles (cross-sectional shapes), often with their leadingedge- the front edge, relative to the airflow- shaped differently to their trailing edge, at therear.
The behaviour of air around an aerofoil depends on the velocity of the airflow, and alsoon the angle of attack (or pitch) of the aerofoil - its angle relative to the airflow.leading edgeairflowangle of attack,or pitchtrailing edge-----------------------------------------------------------------L:: _:::.-:.-~84Professional English in Use EngineeringBrE: aerofoi l;AmE: airfoilThe section of an aircraft wing an example of an aerofoil39.1Sort the terms in the box into categories (1-5).
Look at A, B, C and D opposite to help you.CFDdownforceform dragliftrotorskin frictionslipstreamwakewind tunnelwmgTypes of aerodynamic resistance: ................................................ and ................................................2 Aerodynamic forces acting in specific directions: ................................................ and3 Aerodynamic effects downstream of an object: ................................................ and ...............................................
.4 Types of aerofoil: a ................................................ and a ............................................... .5 Aerodynamic analysis tools: ................................................ and a ............................................... .39.2Use one term from each category in 39.1 to complete the sentences below. Look at A, BandC opposite to help you.1 The widening zone of turbulent air behind a fast-moving vehicle is called the2 In very strong winds, the low pressure generated just above the sheltered sides of the roofsof buildings generates ................................................, which can cause the roof to 'explode' outwardsdue to the higher-pressure air inside the building.3 The aerodynamic effectiveness of designs can be tested in a ................................................
.4 On an aircraft fuselage, the heads of rivets are designed to be as flat as possible in order tolimit ................................................ .5 Most helicopters have either two or three main ................................................ .39.3 Use the words in the box to complete the article, taken from a popular science magazine.You will need to use some words twice. Look at B, C and D opposite to help you.aerofoilairflowangleattackboundarydownforcedragflowlaminarlayerleadingpitchtrailingturbulentIn aerodynamic-speak, the term 'spoiler' is slightly confusing, as it has two different meanings.
In automotiveengineering, a spoiler is a wing-like (1) ................................ on the back of a car. Unlike the wings on racing cars,the purpose of spoilers on road cars is not to generate (2) ..... ............... ............ ,but to 'spoil' or disrupt the (3) ................................ within the (4) .............................. ..................................
-the air close to the surface of the car's body. Whilethis may seem strange, by turning what would otherwise be a smooth,(5) ................................................................ into a messy, (6) .............................. .................................. ,the car's (7) ................................ coefficient can be reduced, andthe vehicle's handling can be made more stable at higher speedsIn aeronautical engineering, spoilers- also called airbrakes- are aerofoils mounted on the tops of anaircraft's wings. When deployed- most often at the moment a plane lands- they rotate in an angularmotion, with their (8) ................................
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