Centrifugal Compressors

UNIVERSITY OF WEST BOHEMIA

FACULTY OF MECHANICAL ENGINEERING

DEPARTMENT OF POWER SYSTEM ENGINEERING

Inovace předmětu „TEORIE PROUDOVÝCH STROJŮ “ v rámci projektu CZ.1.07/2.2.00/15.0006

JET ENGINESJET ENGINES

Centrifugal flow compressorsCentrifugal flow compressors

INTRODUCTION

PURPOSE OF COMPRESSORS● Compressor is a device which provide a compression

of air and its transport to combustion chamber in a required amount to ensure continuous process of combustion.

● Compression in centrifugal flow compressor is achieved by centrifugal velocities

● The air in outlet from blade canal is upright to axis of rotation

● Velocity of outlet air depends by diameter of blades and rotor's RPM

INTRODUCTION

Requirements ● Continual supply of required amount of air to

combustion chamber● High values pressure ratio● Stable work in each conditions where engine works● High values of efficiency● Low price● Minimal weight and dimensions● Simple construction and maintenance

INTRODUCTION

Advanteges● Higher pressure ratio in one stage (π=10)● Low length in axial direction● Good efficiency

Disadvatages● High frontal drag● Its necessary to use on outlet a diffuser and

manifold

COMPRESSOR TYPES

TYPES DEVIDED BY DIRECTION OF INLET● Axial inlet● Radial inlet● Diagonal inlet● Single-entry inlet● Dual-entry inlet

TYPES DEVIDED BY NUMBER OF STAGES● Single stage compressors● Dual stage compressors

EXAMPLES

Fig. 2 Centrifugal flow compressor with single axial inlet

EXAMPLES

Fig. 3 Centrifugal flow compressor with dual-entry radial inlet

EXAMPLES

Fig. 4 Centrifugal compressor with single diagonal inlet

COMPRESSOR TYPES

TYPES DEVIDED BY TYPE OF IMPELLER● Single-entry impeller● Dual-entry impeller● Impeller with straight blades● Impeller with curved blades forward● Impeller with curved blades backward● Closed impeller case● Semi-open impeller case● Open impeller case

EXAMPLES

Fig. 5 Single and dual entry impeller

EXAMPLES

Fig. 6 Impellers shape and cases

Straight Curved forward Curved backward

Opened Semi-opened Closed

COMPRESSOR TYPES

TYPES DEVIDED BY NUMBER OF STAGES● Single stage compressors● Dual stage compressors

TYPES DEVIDED BY ARRANGEMENT OF SPOOL

● Bladed diffuser● Non-bladed diffuser

EXAMPLE

Fig. Dual stage centrifugal flow compressor

EXAMPLES

Fig. Various types of dual stage centrifugal compressors

MAIN PARTS

Fig. Main parts of centrifugal flow compressor

MAIN PARTS

Fig. Impeller

MAIN PARTS

Fig. Particle move through the non-blade diffuser

MAIN PARTS

Fig. Particle move through the blade diffuser

MAIN PARTS

Fig. Bladed diffuser

MAIN PARTS

Fig. Output manifold and its loads

MAIN LAYERS

Fig. Layers through the compressor

PARAMETERS TROUGH THE COMPRESSOR

Fig. 7 Ideal and real process of compression in T-S diagram

PARAMETERS THROUGH THE COMPRESSOR

Fig. Evolution of parameters through the compressor

PARAMETERS THROUGH THE COMPRESSOR

Fig. Evolution of velocity parameters through the impeller

BASIC PARAMETERS

ABSOLUTE PRESSURE RATIO

Is non-dimensioned parameter. It is a ratio of outlet an inlet absolute pressure in compressor.

p1a

– absolute pressure value before compressor [Pa]

p5a

– absolute pressure value behind compressor [Pa]

Ca=p5a

p1a

BASIC PARAMETERS

ABSOLUTE COMPRESSOR EFFICIENCY

Is a ratio of adiabatic work and effective work of compression in compressor.

Ca=W ad ,Ca

W e ,Ca

=c p.T 5ad ,a−T 1a

c p. T 5a−T 1a [1]≈0.78−0.82

BASIC PARAMETERS

ηCa

– absolute compressor efficiency[1]

Wad,Ca

– absolute adiabatic compress work [J.kg-1]

We,Ca

– absolute polytropic compress work [J.kg-1]

cp – heat capacity at constant pressure [J.kg-1.K-1]

T5ad,a

– absolute adiabatic gas temperature on the end of compression [K]

T5a

– absolute polytropic gas temperature on the end of compression [K]

T1a

– absolute temperature on the beginning of compression [K]

BASIC PARAMETERS

AIR FLOW RATE

Define mass flow rate of air by one second, which flows trough the compressor.

Q a=ϱ . c1. A1[ kg.s−1]

BASIC PARAMETERS

Qa – Air flow rate through the compressor [kg.s -1]

Qa≈ 25 kg.s-1 (single-entry impeller)

Qa≈ 50 kg.s-1 (single-entry impeller)

ρ – Density [kg.m-3]

c1 – Absolute velocity of the air in the inlet [m.s -1]

A1 – Inlet flow area [m2]

REFERENCES

● Otis, Vosbury: Aircraft gas turbine powerplants – Jeppesen: 2002

● Rolls royce – The jet engine, 1996● Hanus D., Maršálek J, : Studijní modul 15,

Turbínový motor, CERM, s.r.o. Brno 2004● Kadrnožka J.: Tepelné turbíny a

turbokompresory, CERM, s.r.o. Brno 2004

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