11-pt12-turb_comp matching 30 [compatibility mode]
TRANSCRIPT
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PEMP
RMD510
Session delivered by:Session delivered by:
. . .. . .
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PEMP
RMD510
Session Objectives
• To discuss the operating
and turbines• To understand the basic
conditions for compressor and
turbine matching
• in a single shaft gas turbine
• To discuss the matching of gas
generator with free powerturbine and nozzle
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PEMP
RMD510Introduction
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, e range o
possible operating conditions is considerably reduced.
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 plottedto on the compressor characteristics and joined up to form an
equilibrium running line or equilibrium running diagram.
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PEMP
RMD510Introduction
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
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maximum compressor efficiency.
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PEMP
RMD510Test Cases
Three cases are discussed here:
A single shaft gas turbine delivering shaft power
A free turbine engine where the gas generator turbine drivesthe 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 theree 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 arethermodynamically similar and differ only in the manner in which
the output is utilised.
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PEMP
RMD510Test Cases
6© M.S.Ramaiah School of Advanced Studies, Bengaluru15Brayton cycle for case (b) and (c)
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PEMP
RMD510Component Characteristics
Compressor characteristics Turbine characteristics
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PEMP
RMD510Assumptions
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 non-dimensional speed.
Inlet and exhaust losses are considered negligible.
of the compressor delivery pressure.
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PEMP
RMD510Single 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 oint is as follows:
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PEMP
RMD510Single Shaft Gas Turbine
Compressor and turbine are directly coupled, hence
Speed compatibility (1)
Flow compatibility
From combustor pressure loss:
Assuming m1 = m3 = m(2)
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PEMP
RMD510Single Shaft Gas TurbineIf 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)
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PEMP
RMD510Single Shaft Gas Turbine
If the engine is coupled to a dynamometer on the test bed, then the load could beset 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
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.
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PEMP
RMD510Single Shaft Gas Turbine
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.
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oa c arac er s c
of a propeller
qu r um runn ng nes
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PEMP
RMD510Equilibrium Running of a Gas Generator
A gas generator performs the same function for the free turbine engine and the jetengine. 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.
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ssuming t at t e tur ine non- imensiona ow is in epen ent o t e non-
dimensional speed , the procedure is as follows:
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PEMP
RMD510Equilibrium Running of a Gas Generator
(4)
(2)
(1)
(6)(3)
(2)
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PEMP
RMD510Equilibrium Running of a Gas Generator
(2) (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 ofconstant 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 ecompressor characteristic.
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PEMP
RMD510Equilibrium Running of a Gas Generator
Note:
(1) (2)
(3) (6)
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PEMP
RMD510Equilibrium Running of a Gas Generator
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PEMP
RMD510Matching of Gas Generator with Free Turbine
The mass flow leaving the gas generator is equal to that entering the powerturbine.
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)
where (8)
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PEMP
RMD510Matching 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 andthe power turbine outlet pressure is also pa.
(7)
in slide 21.
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PEMP
RMD510
Generator with Free
(a) Iteration for gas generator
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for free power turbine
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PEMP
RMD510Matching of Gas Generator with Free Turbine
in Slide 18.
in Slide 13.
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PEMP
RMD510Matching of Gas Generator with Nozzle
The propelling nozzle area for a jet engine is fixed from design point calculations.
Propelling Nozzle Characteristics
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)
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PEMP
RMD510Matching of Gas Generator with Nozzle
Propelling Nozzle Characteristics
(14)(15)
in Slide 25
(14)
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(16)
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PEMP
RMD510Matching of Gas Generator with Nozzle
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
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PEMP
RMD510Matching of Gas Generator with Nozzle
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
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uniquely determined by the fixed turbine operating point and will be independent of
the flight speed.
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PEMP
RMD510Matching of Gas Generator with Nozzle
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
The ram pressure ratio is given by
(19)
(20)
Now the procedure of flow chart (slide 21) can be followed with eqn. 19 substitutedfor 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.
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PEMP
RMD510Matching of Gas Generator with Nozzle
The result is a fan of
equilibrium running lines of
constant M a, merging into a
single running line at higher
compressor speeds when thenozzle is choked.
Increasing the Mach number
pushes the equilibrium running
line away from the surge line atlow 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.
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PEMP
RMD510Session Summary
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.
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PEMP
RMD510
T an you
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