---
title: "Turbomachines: definition and classification"
subject: "Fluid Machines"
chapter: 1
key: "semester_5/fluid_machines:turbomachine-definition-classification"
source: https://www.bctengineer.com/q/semester_5/fluid_machines/turbomachine-definition-classification
site: BCT Engineering
---

# Turbomachines: definition and classification

Fluid Machines · Chapter 1: Introduction of Turbomachime and Dynamic Action of Fluid

- Asked in: year not given, 5 marks
- Video: [Introduction and classification of Turbomachines  |  Lecture no:01](https://www.youtube.com/watch?v=sdRQYw8sd-U) — EasyMechLearn
- Answer checked by Claude Sonnet 5.5 on 2026-10-14
- Page: https://www.bctengineer.com/q/semester_5/fluid_machines/turbomachine-definition-classification
- Whole chapter: https://www.bctengineer.com/md/semester_5/fluid_machines/chapter-1

## Question

Define a turbomachine. Classify turbomachines with suitable examples.

## Short answer

A turbomachine transfers energy continuously between a rotating element and a fluid via dynamic blade action. Classification: by energy direction (turbines like Pelton, pumps like centrifugal), fluid type (hydraulic, thermal), action (impulse e.g. Pelton, reaction e.g. Francis), flow direction (axial, radial, mixed, tangential), number of stages, and shaft position.

## Answer

A **turbomachine** is a device in which energy is transferred continuously between a rotating element (rotor or runner) and a flowing fluid, through the dynamic action of the fluid on the blades. The change in the fluid's angular momentum gives the torque on the shaft.

#### Classification

**1. By direction of energy transfer**

- *Power-producing (turbines):* fluid gives energy to the rotor. Examples: water turbine, steam turbine, gas turbine, wind turbine.
- *Power-absorbing (pumps, fans, blowers, compressors):* the rotor gives energy to the fluid.

**2. By the fluid handled**

- Hydraulic (incompressible fluid, mainly water): water turbines, centrifugal pumps.
- Thermal (compressible fluid): steam and gas turbines, compressors, fans.

**3. By the action of the fluid in the rotor**

- *Impulse type:* the whole pressure drop occurs in the nozzle; the rotor works at constant (atmospheric) pressure. Example: Pelton wheel, De Laval steam turbine.
- *Reaction type:* pressure drops also in the rotor, so the rotor is full of fluid. Example: Francis and Kaplan turbines, Parsons turbine.

**4. By the direction of flow through the rotor**

| Type | Flow direction | Example |
|---|---|---|
| Axial | Parallel to shaft | Kaplan turbine, axial pump |
| Radial (inward or outward) | Perpendicular to shaft | Centrifugal pump, old Francis |
| Mixed | Both components | Modern Francis, mixed-flow pump |
| Tangential | Jet along tangent to wheel | Pelton wheel |

```text
  Axial            Radial           Tangential
  ||| -> |||       -> O <-          jet
                                      \  (  )
                                       -> (Pelton)
```

**5. By the number of stages:** single-stage and multistage (e.g. multistage boiler feed pump).

**6. By shaft position:** horizontal, vertical, inclined.

## Check yourself

The answer's key points as multiple-choice questions, with the correct option and why.

1. What produces the torque on the shaft of a turbomachine?
   A. Static pressure acting on a fixed wall
   B. Change of volume of a trapped fluid
   C. Reciprocating motion of a piston
   D. Change in the fluid's angular momentum through dynamic action on blades
   Answer: D. A turbomachine exchanges energy continuously through the dynamic action of fluid on rotating blades; the angular momentum change gives the torque. (Key point: Definition)

2. In an impulse turbine such as the Pelton wheel, where does the pressure drop occur?
   A. In the draft tube only
   B. Entirely in the rotor
   C. Entirely in the nozzle, the rotor runs at atmospheric pressure
   D. Equally in nozzle and rotor
   Answer: C. In impulse machines the whole pressure drop is in the nozzle; the rotor works at constant (atmospheric) pressure. (Key point: Impulse vs reaction)

3. Which group of machines gives energy to the fluid (power-absorbing)?
   A. Water turbine, steam turbine
   B. Pelton wheel, Kaplan turbine
   C. Pumps, fans, blowers, compressors
   D. Wind turbine, gas turbine
   Answer: C. Pumps, fans, blowers and compressors have the rotor giving energy to the fluid; turbines are power-producing. (Key point: Energy transfer direction)

4. A Kaplan turbine is classified by flow direction through the rotor as:
   A. Axial
   B. Mixed
   C. Radial
   D. Tangential
   Answer: A. In a Kaplan turbine the flow is parallel to the shaft, i.e. axial. Pelton is tangential. (Key point: Flow direction)

## Related in Fluid Machines

- [Classification of hydroelectric plants](https://www.bctengineer.com/question.md?key=semester_5%2Ffluid_machines%3Ahydroelectric-plant-classification) — Fluid Machines, chapter 2

## Related in other subjects

- [Turbomachine: definition, parts and classification](https://www.bctengineer.com/question.md?key=semester_7%2Fturbo_machines%3Aturbomachine-definition-classification) — Turbo Machines, chapter 1
- [Hazardous waste: definition and classification](https://www.bctengineer.com/question.md?key=semester_7%2Fenvironment_and_pollution_control%3Ahazardous-waste-definition-classification) — Environment and Pollution Control, chapter 5