- Practice · 3+3 marks
Turbomachine: definition, parts and classification
Short answer
A turbomachine transfers energy continuously between a rotating blade row and a flowing fluid. Its main parts are rotor, stator, shaft, casing. Turbines are power-producing, classified by flow direction (axial, radial, mixed) and blade action: impulse (entire pressure drop in nozzle, constant pressure across rotor) and reaction (pressure drop in stator and rotor).
Define a turbomachine. Name its main parts and classify turbomachines (turbines in particular) on the basis of energy transfer, flow direction, and action of the fluid on the blades.
A turbomachine is a device in which energy is transferred continuously between a rotating element (rotor, fitted with blades) and a flowing fluid, through the dynamic action of the blades on the fluid. Pumps, fans, compressors, steam turbines, gas turbines and hydraulic turbines are examples.
Main parts
- Rotor (runner/impeller) with blades - the element that exchanges energy with the fluid.
- Stator - fixed casing with guide vanes or nozzles that direct the fluid onto the rotor.
- Shaft and bearings - carry the torque and support the rotor.
- Casing - encloses the flow path and contains the pressure.
- Inlet and outlet passages - volute, diffuser, draft tube, exhaust duct.
inlet --> [ Stator | Rotor ] --> outlet
nozzle blades
| |
+--shaft-+--> to load
Classification
| Basis | Classes |
|---|---|
| Direction of energy transfer | Power-producing (turbines: fluid gives energy to rotor); power-absorbing (pumps, fans, compressors, blowers) |
| Fluid used | Incompressible (hydraulic turbines, pumps); compressible (steam and gas turbines, compressors) |
| Direction of flow in rotor | Axial; radial (inward or outward); mixed flow |
| Action of fluid on blades | Impulse - whole pressure drop in the nozzle, rotor blades only change the direction of velocity, pressure is constant across the rotor (Pelton, De Laval). Reaction - pressure falls in both stator and rotor, so the blades also act as nozzles (Parsons, Francis, Kaplan) |
| Number of stages | Single stage; multistage |
| Admission | Full admission; partial admission |
The ratio of the pressure (enthalpy) drop in the rotor to the drop in the whole stage is the degree of reaction: zero for a pure impulse stage and 0.5 for a 50% reaction stage.
✓ Answer checked by Claude Opus 5.5 (high effort)
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