Turbine_Compressor Matching.pdf

PEMP RMD510

Session delivered by: .

15

.

.

© M.S.Ramaiah School of Advanced Advanced Studies, Bengaluru

1

Session Objectives

PEMP RMD510

ope rating • To discuss the operating and turbines

• To understand the basic conditions for compressor and turbine matching

• in a single shaft gas turbine t he matching of gas • To discuss the generator with free power turbine and nozzle

15


2

Session Objectives

PEMP RMD510

ope rating • To discuss the operating and turbines

• To understand the basic conditions for compressor and turbine matching

• in a single shaft gas turbine t he matching of gas • To discuss the generator with free power turbine and nozzle

15


2

PEMP RMD510

Introduction  The main components of a gas turbine engine are: inlet diffuser, compressor, combustion chamber, turbine, and exhaust nozzle.  The individual components are designed based on established procedures and their performances are obtained from actual tests.

en ese componen s are n egra e n an eng ne, possible operating conditions is considerably reduced.

e range o

 The roblem is to find corres ondin o eratin oints on the characteristics of each component when the engine is running at a steady speed or in equilibrium.  The equilibrium running points for a series of speeds may be plotted to on the compressor characteristics and joined up to form an equilibrium running line or equilibrium running diagram.

15


3

Introduction

PEMP RMD510

 The equilibrium running diagram also shows the proximity of the operating line to the compressor surge line.  If it intersects the surge line, the gas ur ne w no e capa e o being brought up to full speed without some remedial action.  It also shows whether the engine is operating in a region of  Ideally the operating line should lie near the locus of the points of maximum compressor efficiency. 15

© M.S.Ramaiah School of Advanced Studies, Bengaluru

4

Test Cases

PEMP RMD510

 Three cases are discussed here: 

A single shaft gas turbine delivering shaft power

A free turbine engine where the gas generator turbine drives the compressor and the power turbine drives the load 



A simple jet engine with a propelling nozzle

 The gas generator performs exactly the same function for both the ree tur ne eng ne an t e et eng ne.  The flow characteristics of a free turbine and a nozzle are similar.  Hence, the free turbine engine and the jet engine are thermodynamically similar and differ only in the manner in which the output is utilised.

15


5

PEMP RMD510

Test Cases

Brayton cycle for case (b) and (c) 15


6

Component Characteristics

Compressor characteristics

15

PEMP RMD510

Turbine characteristics


7

Assumptions

PEMP RMD510

 Turbine characteristic is represented by a single line,

ecause s oun n prac ce a ur nes o no ex any significant variation in non-dimensional flow with nondimensional speed.  Inlet and exhaust losses are considered negligible.  of the compressor delivery pressure.

15


8

PEMP RMD510

Single Shaft Gas Turbine

 Pressure ratio across the turbine is determined by the compressor pressure ratio and combustor pressure loss.

– Fuel flow.  Procedure for obtainin an e uilibrium runnin

15

oint is as follows:


9


PEMP RMD510

 Compressor and turbine are directly coupled, hence Speed compatibility

(1)

Flow compatibility

 From combustor pressure loss:  Assuming m1 = m3 = m

15


(2)

10

PEMP RMD510

Single Shaft Gas Turbine If T 01 is specified, then obtain T 03 from eqn (2) and

from eqn (1).

Obtain turbine efficiency from turbine characteristics using the known 03 04. Turbine temperature drop

(3)

(4)

(5)

15


11

PEMP RMD510


 If the engine is coupled to a dynamometer on the test bed, then the load could be set independently of the speed and it would be possible to operate at any point on .  If a propeller is the load, then Power

N 3.



 The roblem is to find the sin le oint on each constant s eed line of com ressor characteristic which will give the required net power output at that speed.  This can only be done by trial and error, taking several operating points on the

.

15


12


PEMP RMD510

Generator runs at constant speed with load varied electrically. Each point on this line represents a erent va ue o tur ne n et temperature and power output.

oa c arac er s c of a propeller 15

qu

r um runn ng nes


13

Equilibrium Running of a Gas Generator

PEMP RMD510

 A gas generator performs the same function for the free turbine engine and the jet engine. It generates high pressure, high temperature gas for expansion through the turbine or the nozzle.  Eqns. 1 and 2 are applicable for speed and mass flow compatibility.  The turbine pressure ratio is not known and can be determined by

(6)



. , 03 01 to determine (by trial and error) the turbine inlet temperature required for operation at any arbitrary point on the compressor performance map.  ssuming t at t e tur ine non- imensiona ow is in epen ent o t e nondimensional speed , the procedure is as follows: 15


14


PEMP RMD510

(4)

(2) (1)

(3)

(6)

(2)

15


15

Equilibrium Running of a Gas Generator (2)

PEMP RMD510

(6)

 Calculations can be carried out for a large number of points and the results can be presented on the compressor characteristics by the locus of constant T 03/T 01 (see figure in slide 18).  However, the flow compatibility with the component downstream power ur ne or nozz e w res r c e opera ng zone on e compressor characteristic.

15


16


PEMP RMD510

Note:

(1) (3)

15

(2) (6)


17


15


PEMP RMD510

18

PEMP RMD510

Matching of Gas Generator with Free Turbine  The mass flow leaving the gas generator is equal to that entering the power turbine.  Pressure ratio across the ower turbine is fixed b the ressure ratios across the compressor and gas generator turbine.  The characteristic of the power turbine will have the same form as of the gas ,

 (7)

(8)

where

15


19

PEMP RMD510

Matching of Gas Generator with Free Turbine  The corresponding pressure ratio across the power turbine can be given as

 For stationary gas turbines (ignoring the inlet and exit duct losses), po1 = pa and the power turbine outlet pressure is also pa.

(7)

in slide 21.

15


20

PEMP RMD510

Generator with Free

(a) Iteration for gas generator for free power turbine 15


21

PEMP RMD510

Matching of Gas Generator with Free Turbine

in Slide 18.

in Slide 13.

15


22

Matching of Gas Generator with Nozzle

PEMP RMD510

Propelling Nozzle Characteristics  The propelling nozzle area for a jet engine is fixed from design point calculations.  Once the nozzle size is fixed, it has major influence on off-design operation.  The mass flow parameter is given by (12)

nozzle area

(13)

(14)

15


23


PEMP RMD510

Propelling Nozzle Characteristics

(14)

(15)

in Slide 25

(14)

(16) 15


24


PEMP RMD510

Propelling Nozzle Characteristics Likewise, with the nozzle unchoked, is given by eqn.13; whereas when it is choked, C 5 is the sonic velocity and M 5 is unity. Recallin that

we have the general relation (17)

and when the nozzle is choked, we have

15


25


PEMP RMD510

 The flow characteristics of nozzle and free turbine are similar.  For operation of a jet engine under static conditions, the behaviour of nozzle is same as that of a free turbine.  Hence, the equilibrium running line can be determined according to the flow chart of slide 21, with the nozzle characteristic replacing the power turbine characteristic. 

,

.

 Forward speed produces a ram pressure ratio, which is a function of both flight Mach number and intake efficiency. e compressor e very pressure an nozz e n e pressure ncrease, ea ng o increase in nozzle pressure ratio.  If the nozzle chokes, then the mass flow rate becomes maximum and is independent o nozz e pressure ra o an orwar spee .  Hence, the turbine operating point will also remain unchanged.  Therefore, under choked nozzle condition, the equilibrium running line will be uniquely determined by the fixed turbine operating point and will be independent of the flight speed. 26 © M.S.Ramaiah School of Advanced Studies, Bengaluru 15


PEMP RMD510

 Usually the nozzle is choked during take-off, climb and cruise, and may remain unchoked while preparing to land or taxiing, when the thrust is significantly reduced.  Hence, the running line is affected at low forward speeds when the engine rotational speed is also low and the running line is close to the surge line.  The nozzle pressure ratio p04/ pa is linked to the ram pressure ratio (19)  The ram pressure ratio is given by (20)  Now the procedure of flow chart (slide 21) can be followed with eqn. 19 substituted for eqn. 8, but for each compressor speed line the calculation is repeated for several values of M coverin the desired ran e of fli ht s eed.

15


27


PEMP RMD510

 The result is a fan of equilibrium running lines of constant M a, merging into a single running line at higher compressor speeds when the nozzle is choked.  Increasing the Mach number pushes the equilibrium running line away from the surge line at low compressor speeds, because the ram pressure rise allows the compressor to utilise a ower pressure ra o or pushing the required flow through the nozzle.

15


28

Session Summary  



15

PEMP RMD510

Gas turbine component characteristics have been explained. The procedure for matching of turbine and compressor in a simple single shaft gas turbine is discussed. . The procedures of matching the gas generator to a power turbine and a propelling nozzle are explained.


29

Turbine_Compressor Matching.pdf

Recommend Documents