Unit 41 Fluid Mechanics

Unit 41:

Fluid Mechanics

Unit code:

QCF level:

Credit value:


The aim of this unit is to extend learners’ knowledge of the principles of fluid mechanics and the techniques used to predict the behaviour of fluids in engineering applications.

Unit abstract

This unit will begin by looking at the forces exerted by a static fluid on immersed surfaces and the concept of centre of pressure. It also examines a range of hydraulic devices and systems that incorporate the transmission of hydraulic pressure. Learners will then examine viscosity in fluids, its measurement and the characteristics of Newtonian and non-Newtonian fluids.

The unit then examines fluid flow phenomena. These include the estimation of head loss in pipes, viscous drag around streamlined and bluff bodies and the concept of Reynolds’ number. It also introduces learners to the techniques and applications of dimensional analysis. Finally, learners will examine the operational characteristics of hydraulic machines, in particular the operating principles of water turbines and pumps.

Learning outcomes

On successful completion of this unit a learner will:

1     Be able to determine the behavioural characteristics and parameters of static fluid systems

2       Understand the effects of viscosity in fluids

3     Be able to determine the behavioural characteristics and parameters of real fluid flow

4       Understand the operating principles of hydraulic machines.

Unit content

1      Be able to determine the behavioural characteristics and parameters of static fluid systems

Immersed surfaces: rectangular and circular surfaces eg retaining walls, tank sides, sluice gates, inspection covers, valve flanges

Centre of pressure: use of parallel axis theorem for immersed rectangular and circular immersed surfaces

Devices: hydraulic presses; hydraulic jacks; hydraulic accumulators; braking systems; determine outputs for given inputs

2      Understand the effects of viscosity in fluids

Viscosity: shear stress; shear rate; dynamic viscosity; kinematic viscosity

Viscosity measurement: operating principles and limitations of viscosity measuring devices eg falling sphere, capillary tube, rotational and orifice viscometers

Real fluids: Newtonian fluids; non-Newtonian fluids including pseudoplastic, Bingham plastic, Casson plastic and dilatent fluids

3      Be able to determine the behavioural characteristics and parameters of real fluid flow

Head losses: head loss in pipes by Darcy’s formula; Moody diagram; head loss due to sudden enlargement and contraction of pipe diameter; head loss at entrance to a pipe; head loss in valves; flow between reservoirs due to gravity; hydraulic gradient; siphons; hammerblow in pipes

Reynolds’ number: inertia and viscous resistance forces; laminar and turbulent flow; critical velocities

Viscous drag: dynamic pressure; form drag; skin friction drag; drag coefficient

Dimensional analysis: checking validity of equations such as those for pressure at depth; thrust on immersed surfaces and impact of a jet; forecasting the form of possible equations such as those for Darcy’s formula and critical velocity in pipes

4      Understand the operating principles of hydraulic machines

Impact of a jet: power of a jet; normal thrust on a moving flat vane; thrust on a moving hemispherical cup; velocity diagrams to determine thrust on moving curved vanes; fluid friction losses; system efficiency

Operating principles of turbines: operating principles, applications and typical system efficiencies of common turbo-machines including the Pelton wheel, Francis turbine and Kaplan turbine

Operating principles of pumps: operating principles and applications of reciprocating and centrifugal pumps; head losses; pumping power; power transmitted; system efficiency

Learning outcomes and assessment criteria

Learning outcomes
Assessment criteria for pass

On successful completion of
The learner can:

this unit a learner will:

LO1 Be able to determine the

determine the hydrostatic pressure and thrust on

behavioural characteristics

immersed surfaces

and parameters of static fluid

determine the centre of pressure on immersed



determine the parameters of devices in which a fluid

is used to transmit force

LO2 Understand the effects of

explain the characteristics of and parameters of

viscosity in fluids

viscosity in fluids

describe viscosity measurement techniques

describe the effects of shear force on Newtonian

and non-Newtonian fluids

LO3 Be able to determine the

determine head losses in pipeline flow

behavioural characteristics

determine Reynolds’ number for a flow system and

and parameters of real fluid

assess its significance


determine viscous drag of bluff and streamlined


apply dimensional analysis to fluid flow

LO4 Understand the operating

evaluate the impact of a jet of fluid on a moving vane

principles of hydraulic

identify and explain the operating principles of water


turbines and pumps.



This unit has links with Unit 2: Engineering Science and Unit 61: Engineering Thermodynamics.

Essential requirements

Learners will need access to laboratory facilities suitable for the investigation of viscosity, Reynolds’ number for pipeline flow and the measurement of drag forces on bluff and streamlined bodies.

Employer engagement and vocational contexts

Liaison with industry can help centres provide access to relevant industrial facilities and related plant. Where possible work-based experience should be used to provide practical examples of fluid systems.

A visit to a utilities water treatment plant, pumping station or hydro-electric generating installation will enhance delivery of the unit.