Turbo Machines

Introduction

• Topic: Turbo Machines
• Focus: Gas turbine engine (a type of turbo engine)

Basics of Turbo Machines

• Term Origin:
  • Turbo has Latin origin: turbinis meaning whirling or spinning top
  • Discusses machines with rotating components (e.g., gas turbine engine)
• Turbo machines involve energy interaction between fluid and rotating components

Open Systems

• Two types:
  • System A: Fluid enters, gives energy to rotor (fluid loses energy). Example: Turbine
  • System B: Fluid enters, takes energy from rotor (fluid gains energy). Example: Compressor/Pump

Classification of Turbo Machines

A. Based on Energy Interaction

1. Power Absorbing Machines

   • Fluid takes energy from rotor
   • Examples: Compressor, Pump

2. Power Producing Machines

   • Fluid loses energy to rotor
   • Examples: Turbine (gas turbine, steam turbine, hydro turbine)

B. Based on Enclosure

1. Extended Turbo Machines: No shroud or cover
   • Examples: Wind turbines, Hydrokinetic turbines

C. Based on Flow Type

1. Compressible Flow Machines: High density variation (Mach number > 0.3)

   • Examples: Compressors, Steam turbines, Gas turbines

2. Incompressible Flow Machines: Low or negligible density variation

   • Examples: Pump, Hydro turbine, Fans, Low-pressure blowers, Wind turbines

D. Based on Medium

1. Hydro Turbo Machines: Deals with liquids

   • Pumps: Axial pump, Centrifugal pump, Mixed pump
   • Turbines: Impulse turbine (Pelton wheel), Reaction turbine (Francis turbine)

2. Thermal Turbo Machines: Deals with gas or steam

   • Compressors: Axial compressor, Centrifugal compressor, Mixed flow compressor
   • Turbines: Steam turbines (impulse type, reaction type), Gas turbines (impulse type)

Positive Displacement Machines (PDM) vs. Non-PDM

Characteristics

1. Positive Displacement Machines

   • Low speed, low volumetric efficiency
   • Example: Reciprocating compressor, pump
   • Mass flow rate is low
   • Achieves isothermal compression with good cooling
   • Insulated PDM shows no change in fluid state upon stopping

2. Non-PDM (Turbo Machines)

   • High speed, close to 100% volumetric efficiency
   • Example: Axial compressor, Centrifugal compressor
   • Mass flow rate is high
   • Generally achieves adiabatic compression
   • Shows change in fluid state upon stopping

Examples of Rotary Machines as PDM

• Two-lobe compressor, Wankel engine

Fan, Blower, and Compressor Differences

• Fans: Small pressure rise (~2 psi or ~14 kPa)
• Blowers: Intermediate pressure rise (~2-10 psi or ~14-69 kPa)
• Compressors: High pressure rise (>10 psi or >69 kPa)

Components of Compressors and Turbines

Compressors

• Parts: Rotor, Stator
• Stage: Combination of Rotor and Stator
• Function
  • Rotor: Supplies kinetic energy to fluid
  • Stator: Converts kinetic energy to pressure rise

Turbines

• Parts: Stator (Nozzle/Guide Vane), Rotor
• Stage: Combination of Nozzle and Rotor
• Function
  • Nozzle: Increases kinetic energy of fluid
  • Rotor: Converts kinetic energy into work

Axial vs. Radial Flow Machines

Axial Flow Machines

• Flow Direction: Along the axis
• Connection: Simple or easier
• Frontal Area: Lesser, less drag
• Flow Characteristics: Less turning, less loss
• Pressure Ratio: Low (Stage: 1.2 - 1.6)
• Thrust Engine Preference: Preferred for large thrust engines due to high mass flow rate
• Mechanical Strength: Requires blade root fixture

Radial Flow Machines

• Flow Direction: Along the radius
• Connection: Complex or difficult
• Frontal Area: Higher, more drag
• Flow Characteristics: Large turning, more loss
• Pressure Ratio: High (Stage: 4 - 8)
• Thrust Engine Preference: Not much preferred
• Mechanical Strength: High, single-piece rotor

Conclusion

• Reviewed definitions, classifications, and differences within turbo machines
• Discussed components and their functions
• Compared axial and radial flow machines

Next class: Further exploration on turbo machines