Turbine and Compressor Design

7/29/2019 Turbine and Compressor Design

1/57

Turbine and Compressor

Design

Team:

Kevin Garvey

Alex von Oetinger


2/57

Major Topics

Compressor and Turbine Design Cooling

Dynamic Surge Stall Propagation


3/57

BackgroundHistory: First gas turbine was developed in 1872 by Dr. F. Stolze.

Gas Turbine EngineWhat does it do? Generates thrust by mixing compressed ambient air with

fuel and combusting the mixture through a nozzle topropel an object forward or to produce shaft work.


4/57

How Does it Work? Newtons third law

For every action, there is an equal andopposite reaction.

As the working fluid is exhausted out the nozzleof the gas turbine engine, the object that theengine is attached to is pushed forward. In the

case of generating shaft work, the shaft turns agenerator which produces electrical power.


5/57

How Does it Work? Cont.

Shaft

ExhaustGas

AmbientAir In


6/57

Operation

Compressor is connected to the turbine via ashaft. The turbine provides the turning momentto turn the compressor.

The turning turbine rotates the compressor fanblades which compresses the incoming air.

Compression occurs through rotors and statorswithin the compression region. Rotors (Rotate with shaft)

Stators (Stationary to shaft)


7/57

Types of Gas Turbines

Centrifugal Compressed air output is around the outer perimeter

of engine

Axial Compressed air output is directed along the centerline

of the engine

Combination of Both Compressed air output is initially directed along

center shaft of engine and then is compressed

against the perimeter of engine by a later stage.


8/57

Example of Centrifugal

Flow

Intake airflow is being forced around theoutside perimeter of the engine.

CentrifugalCompressor

Airflow beingforced aroundbody of engine


9/57

Example of Axial Flow

Intake airflow is forced down the center shaftof the engine.

MultistageAxial

Compressor

CenterShaft


10/57

Example of Combination

Flow

Intake AirFlow

Axial Compressor

CentrifugalCompressor

Intake air flow is forced down the centershaft initially by axially compressor stages,and then forced against engine perimeter

by the centrifugal compressor.


11/57

Major Components of

Interest Compressor

Axial

Centrifugal

TurbineAxial

Radial

Axial Compressor Centrifugal Compressor


12/57

Axial Compressor Operation

A&P Technician Powerplant Textbook published by Jeppesen Sanderson Inc., 1997

Axial compressors are designed in a divergentshape which allows the air velocity to remainalmost constant, while pressure graduallyincreases.

Average Velocity
http://ffden-2.phys.uaf.edu/212_fall2003.web.dir/Oliver_Fleshman/3-15l.jpg


13/57

Axial Compressor Operation

cont. The airflow comes in through the inlet andfirst comes to the compressor rotor. Rotor is rotating and is what draws the airflow

into the engine.After the rotor is the stator which does not move

and it redirects the flow into the next stage ofthe compressor.

Air flows into second stage. Process continues and each stage gradually

increases the pressure throughout the

compressor.


14/57

Axial Compressor Staging

An axial compressor stage consists of a rotorand a stator.

The rotor is installed in front of the stator

and air flows through accordingly. (See Fig.)

www.stanford.edu/ group/cits/simulation/
http://www.stanford.edu/group/cits/simulation/http://www.stanford.edu/group/cits/simulation/


15/57

Centrifugal Compressor

Operation

Centrifugal compressors rotate ambient air about animpeller. The impeller blades guide the airflow towardthe outer perimeter of the compressor assembly. The airvelocity is then increased as the rotational speed of the

impeller increases.


16/57

Axial Turbine OperationHot combustion gasesexpand, airflowpressure andtemperature drops. This

drop over the turbineblades creates shaftwork which rotates thecompressor assembly.

Axial Turbine with airflow Airflow around rotor

Airflow through

stator
http://www.ucmr.com/galerii/imagepages/image-cap11.html


17/57

Radial Turbine Operation

Same operationcharacteristics as axial flowturbine.

Radial turbines are simplerin design and lessexpensive to manufacture.

They are designed muchlike centrifugalcompressors.

Airflow is essentiallyexpanded outward fromthe center of the turbine.

Radial Flow Turbine


18/57

Gas Turbine Issues

Gas Turbine Engines Suffer from anumber of problematic issues:

Thermal Issues Blade (airfoil) Stalls

Dynamic Surge

http://www.turbosolve.com/index.html


19/57

Thermal Issues Gas Turbines are limited

to lower operatingtemperatures due to thematerials available for

the engine itself.

Operating at the lowertemperature will

decrease the efficiencyof the gas turbine so ameans of cooling thecomponents is necessaryto increase temperatures

at which engine is run.


20/57

Cooling Methods

Spray (Liquid) Passage

Transpiration


21/57

Spray Cooling

The method of spraying aliquid coolant onto the

turbine rotor blades andnozzle.

Prevents extreme turbineinlet temperatures from

melting turbine blades bydirect convection betweenthe coolant and theblades.


22/57

Passage Cooling

Hollow turbine bladessuch that a passage isformed for themovement of a coolingfluid.

DOE has relatively newprocess in which excesshigh-pressurecompressor airflow isdirected into turbinepassages.

http://www.eere.energy.gov/inventions/pdfs/fluidtherm.pdf


23/57

Transpiration Cooling

Method of forcing airthrough a porous turbineblade.

Ability to remove heat ata more uniform rate.

Result is an effusing layerof air is produced around

the turbine blade. Thus there is a reduction

in the rate of heattransfer to the turbine

blade.


24/57

Blade (airflow) Stalls When airflow begins

separating from thecompressor blades overwhich it is passing as theangle of attack w.r.t. theblades exceeds thedesign parameters.

The result of a blade stallis that the blade(s) nolonger produce lift andthus no longer produces apressure rise through the

compressor.

Separation Regions


25/57

Dynamic Surge

Occurs when the static (inlet) airpressure rises past the designcharacteristics of thecompressor.

When there is a reversal of

airflow from the compressorcausing a surge to propagate inthe engine.

Essentially, the flow is exhaustedout of the compressor, or front,

of the engine. Result, is the compressor no

longer able to exhaust as quicklyas air is being drawn in and a

bang occurs. http://www.turbosolve.com/index.html

Compressor

Inlet

Turbine Exit


26/57

Dynamic Surge Effects

Cause: Inlet flow is reversed Effect: Mass flow rate is reduced into engine.

Effect: Compressor stages lose pressure.

Result: Pressure drop allows flow to reverse back intoengine.

Result: Mass flow rate increases

Cause: Increased mass flow causes high pressureagain. Effect: Surge occurs again and process continues.

Result: Engine surges until corrective actions are taken.


27/57

Dynamic Surge Process

inm

outm

P

V

Surge Point,Flow

Reverses

No Surge

Conditio

n

CompressorPressure Loss

Occurs

Flow reverses

back intoengine

Corrective

ActionTaken

outm


28/57

Axial Compressor Design

Assumption of Needs Determination of Rotational Speed

Estimation of number of stages General Stage DesignVariation of air angles


29/57

Assumption of Needs

The first step in compressor design in thedetermination of the needs of the system

Assumptions: Standard Atmospheric Conditions

Engine Thrust Required

Pressure Ratio Required

Air Mass Flow Turbine inlet temperature


30/57

Rotational Speed

Determination First Step in Axial Compressor Design Process for this determination is based on

assumptions of the system as a whole

Assumed: Blade tip speed, axial velocity, andhub-tip ratio at inlet to first stage.

Rotational Speed

Equation


31/57

Derivation of Rotational

Speed First Make Assumptions: Standard atmospheric conditions

Axial Velocity:

Tip Speed:

No Intake Losses

Hub-tip ratio 0.4 to 0.6

Ut

350m

s

Ca

150 200m

s


32/57

Compressor Rotational

Speed Somewhat of an iterative process inconjunction with the turbine design.

Derivation Process: First Define the mass flow into the system

is the axial velocity range from the rootof the compressor blades to the tips of theblades.

AUmdot

where U=1aC

1aC


33/57

Axial Velocity Relationship

rr

a

t

ra C

r

rC *1

2

1

Radius to root of

bladerr

tr Radius to tip of blade

tr


34/57

Tip Radius Determination

2

11

2

1

t

r

a

dot

t

r

rC

m

r

By rearranging the mass flow rate equation we canobtain an iterative equation to determine the blade tipradius required for the design.

Now Looking at the energy equation, we can determine theentry temperature of the flow.

p

a

c

CTT

2

2

101

22

2

11

2

00

UTc

UTc pp


35/57

Isentropic Relationships Now employing the isentropic relation between

the temperatures and pressures, then thepressure at the inlet may be obtained.

Now employ the ideal gas law to obtain thedensity of the inlet air.

1

0

1

01

T

TPP

1

1

1

RT

P

Finally Obtaining Rotational


36/57

Finally Obtaining Rotational

Speed Using the equation for tip speed.

Rearranging to obtain rotational speed.

Finally an iterative process is utilized toobtain the table seen here.

NrU tt 2

t

t

r

UN

2

Determining Number of


37/57

Determining Number of

Stages Make keen assumptions Polytropic efficiency of approximately 90%.

Mean Radius of annulus is constant throughall stages.

Use polytropic relation to determine theexit temperature of compressor.

nn

P

PTT

1

01

020102

n = 1.4, Ratio of Specific Heats,Cp/Cv

is the pressure that the compressor

outputs

To1 is ambient temperature

02P


38/57

Determine Temperature

Change Assuming that Ca1=Ca is the work done factor Work done factor is estimate of stage efficiency Determine the mean blade speed.

Geometry allows for determining the rotor bladeangle at the inlet of the compressor.

NrU meanm 2

a

m

C

U

1tan


39/57

Temperature Rise in a Stage

p

ams

c

CUT 210

tantan

1

1

cos

aCV

This will give an estimate of the maximum possible rotordeflection.

Finally obtain the temperature rise through the stage.

2

2cos

V

Ca

Determine the speed of the flow over the blade profile.

Velocity flow

over blade V1.

DeflectionBlade_12


40/57

Number of Stages Required

The number of stages required is dependentupon the ratio of temperature changesthroughout the compressor.

sT

TStages

0

ambTTT 2

is the temperature change within a stage

is the average temperature change over all the stagessT

T

0


41/57

Designing a Stage

Make assumptionsAssume initial temperature change through

first stage.

Assume the work-done factors through each

stage. Ideal Gas at standard conditions

Determine the air angles in each stage.
http://images.google.com/imgres?imgurl=http://fromtheflightdeck.com/Stories/turbofan/index_files/image015.jpg&imgrefurl=http://fromtheflightdeck.com/Stories/turbofan/&h=188&w=264&sz=13&tbnid=3WP8tL-hn0UCMM:&tbnh=76&tbnw=107&hl=en&start=36&prev=/images%3Fq%3DCo


42/57

Stages 1 to 2

Determine the change in the whirl velocity. Whirl Velocity is the tangential component of

the flow velocity around the rotor.


43/57

Stage 1 to 2

Change in whirl velocity through stage.

12 www CCC

m

p

wU

Tc

C

11 tan aw CC Alpha 1 is zero at the first stage.

a

w

a

wm

C

C

C

CU

22

22

tan

tan

Compressor Velocity


44/57

Compressor Velocity

Triangles


45/57

Pressure ratio of the Stage

10

01

03 1

amb

sss

T

T

P

PR

9.0s

The pressure ratio in the stage can be determined throughthe isentropic temperature relationship and the polytropicefficiency assumed at 90%.


46/57

Stage Attributes The analysis shows that the stage can be outlined bythe following attributes:

1.) Pressure at the onset ofthe stage.

2.) Temperature at the onsetof the stage.

3.) The pressure ratio of thestage.

4.) Pressure at the end of the

stage.

5.) Temperature at the end ofthe stage.

6.) Change in pressure

through the stage.Example of a single

sta e

V i i i Ai A l f


47/57

Variation in Air Angles of

Blade Assume the free vortex condition.

Determine stator exit angle.

Then determine the flow velocity.

constrCw 2

13 tantan a

m

C

U

33

cos

mUC


48/57

Air Angle TriangleAlpha 1 is 0 at

the inlet stagebecause there

are no IGVs.

Thus,

Ca1=C1,

and Cw1 is0

Note: This is

the whirl

velocity

componentand not a

blade

spacing!


49/57

Red is

Green is

Blue is

Velocity Triangle

aC

aC

aC

V i i i Ai A l f


50/57


Blade Determine the exit temp., pressure, and density ofstage 1

Determine the blade height at exit.

Finally determine the radii of the blade at stator exit.

p

a

c

CTT

2

2

03 1

03

3033

T

TPP

3

3

3

RT

P

meanr

Ah

2

3

2

hrr meants

2

hrr meanrs

a

dot

C

mA

3

3

V i ti i Ai A l f


51/57


Blade Determine the radii at the rotor exit.

Determine the whirl velocities at the blade root andtip.

2

tstritr

rrr

2

rsrrirr

rrr

Note: That is the radius of the blade at the tip at rotor inlet.trirNote: That is the radius of the blade at the root at rotor inlet.rri

r

rr

meanmwrwr

rCC 22 tr

meanmwtwr

rCC 22

Note: because there is no other whirl velocity component in the

first stage.

22 wmw CC

Fi ll d t i th Ai


52/57

Finally determine the Air

Angles

a

twtrt

a

mwmm

a

rwrrr

a

twt

a

mwm

a

rwr

C

CU

C

CU

C

CU

C

C

C

C

CC

2

2

2

2

2

2

2

2

2

2

2

2

tan

tan

tan

tan

tan

tan

Stator air angle at root ofblade

Stator air angle at middle ofblade

Stator air angle at tip of blade

Deflection air angle at root ofblade

Deflection air angle at middleof blade

Deflection air angle at tip ofblade


53/57

Compressor Design ExampleDesign of a 5 stage axial compressor:

98.0

150

5.452

288

2262.0

2

sm

a

a

t

C

KT

KT

mrGivens:

Use this and chart to get

Rotational speed of engine.

Once rotational speed is found, determine mean blade tip speed.


54/57

Example

s

mNrU

mrr

r

meanm

rtmean

6.2662

1697.02

KTTT amb 5.1642

Determine the total temperature rise through the first stage.

We are designing for more than just one stage, so we

need to define an average temperature rise per stage:

KStages

TTs 9.32

#0

Example (Air Angle


55/57

Example (Air AngleDetermination)

2

0

1

12

1

1

55.126

0

64.60tan

w

m

sp

w

w

www

a

m

Cs

m

U

TcC

s

mC

CCC

CU

E l (Ai A l


56/57

Example (Air Angle

Determination)

smC

V

C

CU

a

a

wm

21.205cos

03.43tan

22

21

2

15.40tan 212a

w

C

C


57/57

Questions???

Turbine and Compressor Design

Documents

Transcript of Turbine and Compressor Design