FLUID DYNAMICS PROFESSIONAL ENGLISH IN USE FOR ENGINEERING

 

PROFESSIONAL ENGLISH IN USE FOR ENGINEERING UNIT 39. FLUID DYNAMICS

 

A Fluid dynamics and aerodynamics Fluid dynamics is the study of how gases and liquids flow around objects. The branch of fluid dynamics concerned with airflow – called aerodynamics – is relevant to the design of aircraft, vehicles and structures. Aerodynamics tests can be done in wind tunnels – tunnels through which air is blown at high velocity. Analysis can also be done using computational fluid dynamics(CFD) – computers with complex simulation software. B Drag Aerodynamic drag (or drag) is the resistance of an object to an airflow. It is measured by the drag coefficient. Objects with a low drag coefficient have little force exerted on them by an airflow. We say they are streamlined. There are different types of drag: ·      Form drag is due to the shape of the object. C Laminar flow and turbulent flow In aerodynamics, engineers focus on the airflow in the boundary layer – the air close to the surface of an object. If the object is streamlined, the airflow in the boundary layer will be laminar, following a direct, clean path. With a less streamlined object, the airflow will be turbulent, D Aerofoils Aerofoils are components designed to make air flow in specific ways. They include: ·      aircraft wings, which generate lift – that is, upward aerodynamic 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. EXERCISES 39.1 Sort the terms in the box into categories (1-5). Look at A, B, C and D opposite to help you. CFD form drag rotor slipstream wind tunnel downforce lift skin friction wake wing 1. Types of aerodynamic resistance: __________ and __________. 2. Aerodynamic forces acting in specific directions: __________ and __________. 39.2 Use one term from each category in 39.1 to complete the sentences below. Look at A, B and C opposite to help you. 1. The widening zone of turbulent air behind a fast-moving vehicle is called the ______________. 2. In very strong winds, the low pressure generated just above the sheltered sides of the roofs of buildings generates ______________, which can cause the roof to ‘explode’ outwards due to the higher-pressure air inside the building. 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. aerofoil angle boundary drag laminar leading trailing airflow attack downforce flow layer pitch turbulent In aerodynamic-speak, the term ‘spoiler’ is slightly confusing, as it has two different meanings. In automotive engineering, 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. While this may seem strange by turning what would otherwise be a smooth, (5)________ _________ into a messy (6)________ _________, the car’s (7)________ coefficient can be reduced, and the vehicle’s handling can be made more stable at higher speeds.

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