78 Pages

Unit 3 Fluid dynamics

Fluids (the generic name given to both liquids and gases) are all around us – the air we breathe, the water in lakes, rivers and the sea, the liquids we drink. They are a familiar part of everyday life and the way in which fluids behave is understood by everyday experiences. For instance, liquids have a defined volume but take the shape of the container they are in; a kilogram of water generally has a fixed volume but it can be confined inside a bottle or spread out over a large area if spilled on the floor. Some fluids flow more easily than others: water is easy to pour, but syrup moves more slowly. Fluids that are moving create forces on solid objects: the umbrella blows inside out on a windy day! In engineering it is important to understand the behaviour of fluids in a scientific way, to be able to quantify the effects so that calculations can be undertaken to design systems involving fluids and to predict their performance. For instance, if water needs to be pumped 25 metres uphill at a rate of 10 litres per second, how big does the pump have to be and how much energy is needed to pump the water? Could the system be designed to be more sustainable and use less energy? If an oil storage tank needs to be built, how thick will the walls need to be? How much force does the oil exert on the walls? In this chapter the behaviour of fluids will be explained in a mathematical way and tools will be introduced to enable design calculations to be performed. These will be related to some of the everyday experiences that we have of fluids to help understanding.