Turbomachinery

For more details on this topic, see Centrifugal compressor.

Mounting of a steam turbine produced by Siemens, Germany

Turbomachinery, in mechanical engineering, describes machines that transfer energy between a rotor and a fluid, including both turbines and compressors. While a turbine transfers energy from a fluid to a rotor, a compressor transfers energy from a rotor to a fluid. The two types of machines are governed by the same basic relationships including Newton's second Law of Motion and Euler's energy equation for compressible fluids. Centrifugal pumps are also turbomachines that transfer energy from a rotor to a fluid, usually a liquid, while turbines and compressors usually work with a gas.

Classification

A steam turbine from MAN SE subdidiary MAN Turbo

In general, the two kinds of turbomachines encountered in practice are open and closed turbomachines. Open machines such as propellers, windmills, and unshrouded fans act on an infinite extent of fluid, whereas, closed machines operate on a finite quantity of fluid as it passes through a housing or casing.

Turbomachines are also categorized according to the type of flow. When the flow is parallel to the axis of rotation, they are called axial flow machines, and when flow is perpendicular to the axis of rotation, they are referred to as radial (or centrifugal) flow machines. There is also a third category, called mixed flow machines, where both radial and axial flow velocity components are present.

Turbomachines may be further classified into two additional categories: those that absorb energy to increase the fluid pressure, i.e. pumps, fans, and compressors, and those that produce energy such as turbines by expanding flow to lower pressures. Of particular interest are applications which contain pumps, fans, compressors and turbines. These components are essential in almost all mechanical equipment systems, such as power and refrigeration cycles.

Classification of fluid machinery in species and groups

machine type → group ↓	machinery	combinations of power and machinery	engines
open turbomachine	propeller		wind turbines
hydraulic fluid machinery (≈ incompressible fluids)	centrifugal pumps turbopumps and fans	Fluid couplings and clutches (hydrodynamic gearbox); Voith Turbo-Transmissions; pump-turbines (in pumped-storage hydroelectricity)	water turbines
thermal turbomachinery (compressible fluid)	compressors	gas turbines (inlet of GT consists of a compressor)	steam turbines ← turbine jet engines

Dimensionless ratios to describe turbomachinery

A pelton wheel turbine wheel being installed into power generation equipment

The following dimensionless ratios are often used for the characterisation of fluid machines. They allow a comparison of flow machines with different dimensions and boundary conditions.

1. Pressure range ψ
2. Flow number φ (including delivery or volume number called)
3. Performance numbers λ
4. Run number σ
5. Diameter Number δ

See also

• Secondary flow in turbomachinery
• Exoskeletal engine - an inside-out turbine
• Turbocharger

Sources

• Sydney Lawrence Dixon, Fluid mechanics and thermodynamics of turbomachinery, 1998
• Earl Logan (1993). Turbomachinery: basic theory and applications. CRC Press. ISBN 9780824791384. http://books.google.com/books?id=s4Qfa1AWGGkC&printsec=frontcover&dq=turbomachinery&source=bl&ots=U_mTFto9da&sig=8zz82kSRJZT6uYdBpqKxcNwNNik&hl=en&ei=ND23TMudHMSclgfGpqi9DA&sa=X&oi=book_result&ct=result&resnum=4&sqi=2&ved=0CCgQ6AEwAw#v=onepage&q&f=false. 
• Erian A. Baskharone (2006). Principles of turbomachinery in air-breathing engines. Cambridge University Press. ISBN 9780521858106. http://books.google.com/books?id=dY6a4bZg-LsC&pg=PA10&lpg=PA10&dq=Turbomachinery+classification&source=bl&ots=YcpNwn4tO-&sig=Lz-l5x3cLfhmvVPLT-BbbCoiDWU&hl=en&ei=LkO3TLOhCIOglAf17a27DA&sa=X&oi=book_result&ct=result&resnum=1&ved=0CBIQ6AEwAA#v=onepage&q&f=false. 

External links

• Hydrodynamics of Pumps