Pressure Distribution on an Aerofoil

8/10/2019 Pressure Distribution on an Aerofoil.

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Apparatus:

The instrument used known as the Cussons P9005 consists of two shaft gas turbines meaning

the compressor and the turbine are mounted on separate shafts independently. There is no

physical link between the two turbines; hence it is a two shaft gas turbine. Our aim of using

this machine is to understand the main facts of a gas turbine and how different parameters

interact with changes.

Parameters:

We will be using a selection of different parameters to measure the output of the gas turbine,

to be able to do this we must first understand what these parameters are. All parameters are

easily obtained by looking at recording instruments on the gas turbine, the only calculable

result was power (Volts x Amps = Power.).

Firstly we have T1-T5:

These are the different temperature sections. T1 and T2 are given as 1x10C and T3,T4&T5

are given as 1x100C

T1: Air inlet (Entry temperature)

T2: Compressor exit

T3: Combustion chamber exit. This will be constant trough out the experiment

T4: Power turbine inlet

T5: power turbine outlet.

Next we have the pressure sections; P2-P4:

All pressured are measured in BAR

P2 is the fuel control.

P3 is the gas generator inlet.

P4 would be the power turbine inlet.

We dont measureP1 and P5 as they are

given as atmospheric pressure.

Ngg (rps): Is the gas generator speed

which was kept at a constant of 100rev/s

N (fpt): is the power turbine speed

which was also kept at the same unit of

100 rev/s

M: Mass flow rate of Qgrams per second.

Also note that the Speed of high pressure turbine is measured in revs per second (100x)

Procedure Raw recorded results and observances during the experiment

During this lab we are asked to complete two different experiments:


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Experiment one we are asked to Fix the speed of the gas generator also known as the HP

(high pressure) turbine from 550 to 250 revs per second decreasing at a rate of 50 revs per

second in seven stages, at each stages we would measure our parameters; t3 is supposed to be

constant but did change a little bit but at the slightest amount so we did not record any change

in exit temperature. Temperature T3 is set to a constant between 700 and 760 degrees Celsiuswe also recorded the Ngg, volts and amps to calculate power; we also took a note of ambient

pressure from the digital display.

Parameter Set 1 Set 2 Set 3 Set 4 Set 5 Set 6 Set 7

N(gg) 11.2 11.6 11.8 12 12 12 12

Power(VxA) 162 364 450 512 512 512 450

N fpt 550 500 450 400 350 300 250

Volts 18 26 30 32 32 32 30

Amps 19 14 15 16 16 16 15

Power 342 364 450 512 512 512 450

Next for the second experiment we changed and fix the speed of the HP (high pressure)

turbine this time from 1400 revs per second to 1000 revs per second at decreasing by a rate of

100rps every set for 5 sets. Once the rps has been set on the HP turbine we measured the

speed of the LP (low pressure) turbine at each stage.

Parameters we needed to look at during this experiment are all of the known temperatures as

well as all known pressure including atmospheric given to us by a digital reader, we also

needed to record the mass flow rate at each stage which we expected to decrease during the

experiment. Finally we needed to record the power by calculating the given amps and volts.

Parameter Set 1 Set 2 Set 3 Set 4 Set 5

N gg 1400 1300 1200 1100 1000

N fpt 0.85 0.65 0.6 0.55 0.65

T1 2 2.2 2 2.2 2.2

T2 8.4 7.2 7 6.2 5.6

T3 7.6 7.25 7.2 7 7

T4 6.6 6.4 6.4 6.25 6.25

T5 6.2 6.0 6.0 6 6

P2 0.6 0.47 0.42 0.34 0.27

P3 0.56 0.44 0.4 0.32 0.26


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P4 0.12 0.09 0.08 0.06 0.04

Volts 25 18 14 12.5 9.5

Amps 12.5 9 7.5 6.5 5

Power 312 162 105 81 47.5- fuel 1.95 1.69 1.65 1.58 1.32

Gas turbine cycles do not like change in speed, they perform much better at a constant

condition and in stable states and this is the main reason why they are not use in more

application where they could potentially be useful such as in cars.

In both experiment we change parameters very slowly. For the 2ndexperiment we were

required to run the turbine with no load but we commenced the experiment with the gas

turbine carrying a full load, the reason for this as our instructor informed us with no load the

turbine can get very loud disallowing us from communicate during the experiment.

We found that from our second experiment things that we would expect to see such as the

mass flow rate decreasing as the experiment proceeded as it is being consumed to produce the

final product of experiment, power.

Other aspects we anticipated is the decrease in temperature, pressure and power as we

reduced the revs per second, simply due to less working being done.

We also found that the temperature at T1 was around 22 degrees constantly and this was

slightly higher than the room temperature which was recorded at around 20 degrees, this wasbecause of heat released by machine. We know that for the gas turbine to work well we need

the inter cooling system as this will lower the entry temperature and we know that the entry

temperature should be as cool as possible as the higher the entry temperature the more energy

the compressor needs and thus the more electricity generation you lose.


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Tabulated results from the experiments carried out.

In this part of the report we shall discuss and tabulate any recorded readings and graphs in

relation to the work being discussed. At the start of the experiment room temperature and

pressure are recorded as show below.

Ambient temperature and pressure

Ambient pressure in (mBar) 1006.44 1.00644 Bars

Ambient temperature in

Celsius

20 293 K

In experiment 1 the following set of results were obtained and tabulated in order to be used

under the instructions given.

EXPERIMENT 1Parameter Set 1 Set 2 Set 3 Set 4 Set 5 Set 6 Set 7

T3 993.15 973.15 973.15 963.15 963.15 963.15 963.15

NGG1120 1160 1180 1200 1200 1200 1200

NGG-Corrected 1110.4026 1150.0598 1169.8884 1189.717 1189.717 1189.717 1189.717

NFPT (RPS) 550 500 450 400 350 300 250

NFPT -Corrected 545.287 495.715 446.144 396.572 347.001 297.429 247.858

NFPT -Corrected

(RPM/1000) 32.717 29.743 26.769 23.794 20.820 17.846 14.871

Volts 18 26 30 32 32 32 30

Amps 19 14 15 16 16 16 15

Power(Volts x

Amps) 342 364 450 512 512 512 450

Powercorrected 341.3772 363.3371 449.1805 511.0676 511.0676 511.0676 449.1805

Powercorrected in

KW 0.341 0.363 0.449 0.511 0.511 0.511 0.449

N:B

In the instructions T3is assumed to be constant but because we are not in the ideal worldthere have been notable temperature changes but these are ignored as we are assuming its

fixed.

All tabulated results will be worked out using the same method for each set as shown below

but with their corresponding values.

Ngg corrected for set 1


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Nfpt corrected for set 1

Power corrected for set 1

Power in KW for set 1

The above graph shows the corrected values of power in KW against the corrected NFPT speed

in (RPM/1000)

Experiment 2&3 HP turbine efficiency & overall plant efficiency

In this experiment we shall have to ensure that the flow is steady and stabilised to the best

before taking any reading. The turbine is set initially at the high and its reduced slowly to the

given reading.

The corrected values will be calculated as shown below using the recorded values. An

example is shown below

0.000

0.100

0.200

0.300

0.400

0.500

0.600

7.000 12.000 17.000 22.000 27.000 32.000

PowerinKW

Nfpt corrected in RPM/1000

Power in KW vs LPT speed in (RPM/1000)

Power in KW vs LPT speed

in (RPM/1000)


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Ngg corrected for set 1

Nfpt corrected for set 1

Power corrected for set 1

fuel correctedin for set 1

HP turbine for set 1

( )

Overall efficiency of the plant for set 1


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The above results are shown in the table below for all sets. All values are worked out

following the above methods.

EXPERIMENT 2 & 3 Hp turbine effeciency

Parameter Set 1 Set 2 Set 3 Set 4 Set 5

NGG 1400 1300 1200 1100 1000

NGGCorrected 1388.003 1288.86 1189.717 1090.574 991.4309

NGG - Corrected (RPM/1000) 83.280 77.332 71.383 65.434 59.486

NFPT (RPS) 85 65 60 55 65

NFPTCorrected 84.2716 64.4430 59.4859 54.5287 64.4430

T1 293 295 293 295 295

T2 357 345 343 335 329

T3 1033 998 993 973 973

T4 933 913 913 898 898T5 893 873 873 873 873

P2 (P2gauge + Pa) 1.6064 1.4764 1.4264 1.3464 1.2764

P3 (P3gauge + Pa) 1.5664 1.4464 1.4064 1.3264 1.2664

P4 (P4gauge + Pa) 1.1264 1.0964 1.0864 1.0664 1.0464

Volts 25 18 14 12.5 9.5

Amps 12.5 9 7.5 6.5 5

Power (Volts x Amps) 312.5 162 105 81.25 9.9408

Powercorrected 311.931 161.705 104.809 81.102 9.923

m fuel 1.95 1.69 1.65 1.5 1.32

m fuelcorrected 1.67395 1.45075 1.41642 1.28765 1.13313

HP turbine 0.929 0.894 0.883 0.784 0.688

0.0036 0.0022 0.0014 0.0012 0.0002

0.400

0.500

0.600

0.700

0.800

0.900

1.000

50.000 55.000 60.000 65.000 70.000 75.000 80.000 85.000 90.000

HPturbineefficiency

Ngg corrected in RPM/1000

HP turbine efficiency VS HP turbine speed in

(RPM/1000)HP turbine efficiency VS HP


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The above graph shows the Hp turbine efficiency against the corrected NGG speed in

(RPM/1000)

Experiment 3

The graph below shows the overall efficiency of the plant against the corrected Ngg values in(RPM/1000).

Q.6

In the final part of the experiment I am required to draw a TS diagram of the full cycle for the

values of set 4 assuming the chamber efficiency is 100%.

In this question we are asked to describe how specific heat (Cp in J/Kg K) of the gas can be

determined.

Cp will be determined by using the equation for the work done by the turbine given below

The time will be taken as one minute but it will be in seconds as its the primary time for time.

The corrected power for set 4 is 81.102 and the time is 60

0.0000

0.0005

0.0010

0.0015

0.0020

0.0025

0.0030

0.0035

0.0040

50.000 55.000 60.000 65.000 70.000 75.000 80.000 85.000

o

fthep

lant

Ngg corrected in RPM/1000

Overall plant effeciency VS corrected Ngg

values in (RPM/1000)

Overall plant effeciency

VS corrected Ngg values

in (RPM/1000)


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The above value is assumed that it will remain constant for this particular set 4 values.

I will use the value for set and the T3and T4values to calculate the Cp.

The values known are , T3= 973K and T4 = 898K

The TS will be after calculating the change in entropy. This will be calculated using the

formula below but the respective temperature must be taken into account.

From the above since temperature is considered at different points we shall instead take the

temperature recorded at each point rather than the change there for the equation will become

Where Q is 4866.12W and Tnis the respective temperature being considered for example for

T1=

The procedure above is followed to produce a table below.

Tn Q Sn in J/K

T1 295 4866.123 16.49533

T2 335 4866.123 14.52574

T3 973 4866.123 5.001154

T4 898 4866.123 5.418845

T5 873 4866.123 5.574023

The above points are plotted to give me the TS diagram shown below for the set 4 results.


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Discussion

In experiment 1it can be noted the speed of the low pressure turbine goes down the power

produced fluctuates from a low value to a maximum value and then back down. This is

mainly because at the start of the experiment the temperature inlet is low and the low pressure

turbine is just warming up and the fuel is at a low temperature even though its being heated

up gradually. This power is increases as the inlet temperature at the low pressure turbine isincreased. It is also notable that this work output starts to drop off after a while and this can

be said that the fuel as been heated up beyond its ideal temperature during the operation. This

loss is affected by many factors not only the temperature but there is also convection and

conduction heat loss by the plant. There is also friction since we do not operate in an ideal

work where parts are cooled to avoid heat loss from the plant. This relates to the real world

where engines cannot continuously work with maximum efficiency for a long time without

being cooled.

In experiment 2 it is seen that the efficiency of the high pressure turbine increases as the

speed of the high pressure turbine. The efficiency is almost 100% but as we are not in theideal world, there are bound to be energy loss, heat loss and the friction. We obtain a value

close to 92% efficiency which is good compared that other gas turbines. In the experiment its

evident that the efficiency drops as the as the Nggspeed is reduced. This case is similar to the

experiment 1in that the power production by the plant is dropping as the speed is reduced

which is a direct result of the (turbine work-compressor work). The compressor has to do a

lot of work which reduces the useful power gained from the plant.

In experiment 3the results obtained for the overall efficiency of the plant are relatively low.

The results are expected as the theory suggests that the overall cycle efficiency and the work

ratio of the basic gas turbine are relatively low. We are happy with the obtained results of the

experiment as they indicate the relationship between the theory and the practical values. The

0

200

400

600

800

1000

1200

0 5 10 15 20

TemperatureinKelvin

Change in entropy in Joules/Kelvin

TS Diagram for set 4 values

TS Diagram for set 4


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graph should have increased gradually but it makes a bend between the Nggcorrected values

of (65.344RPM/1000) and the (71.383RPM/1000). This could be to human error but from

the obtained results are following a pattern so we can only point to the fact that may be the

results were recorded as the turbine was still stabilising giving us the incorrect reading.

For set 4a required TS diagram was plotted but didnt not look like any of the previous TS

diagrams we have plotted in class. The typical TS for the complete cycle efficiency would

look like the one shown below but not like the one plotted for this task.

The obtained TS can be related to the above diagram between stages 3 and 4 in that we are

looking at one set of values of the cycle where the temperature is gradually reducing from T 5

to T1and the entropy is also gradually reducing from T5 to T1. The first few values of T5and

T4the graph appears to be coming from lower entropy and climaxing at temperature T3before

gradually dropping to the temperatures T2and T1with the lowest entropy and making the

same curve. This TS diagram for the one set clearly makes sense and we are happy with it as

it clearly relates to the typical TS diagram for a full gas turbine cycle.

Conclusion

In experiment 1it can be noted the speed of the low pressure turbine goes down the power

produced fluctuates from a low value to a maximum value and then back down. This is

because gas turbines cannot operate at full power all the time otherwise they would not last

long enough. The turbine operates to give maximum power at an ideal temperature of which

is if this is exceeded it will drop off the cliff and the power produced will be low. This is

mainly due to the surfaces of the turbine heating up, the fuel heating up beyond its ideal

operating temperatures without any ideal cooling process. This can be improved by

effectively trying to maintain the ideal operation temperatures for both the fuel and turbine.


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In experiment 2 it is seen that the efficiency of the high pressure turbine increases as the

speed of the high pressure turbine. The efficiency is almost 100% but as we are not in the

ideal world, there are bound to be energy loss, heat loss and the friction. We obtain a value

close to 92% efficiency. This obtained value is in flow with what the theory says that the

efficiency is less than 100% but for the case of the turbine a high degree of efficiency isexpected and this is obtained.

In experiment 3the results obtained for the overall efficiency of the plant are relatively low.

The results are expected as the theory suggests that the overall cycle efficiency and the work

ratio of the basic gas turbine are relatively low. This efficiency can be improved through the

following means.

Better design and manufacture of the blades for the system.

It can also be improved by making improvements through the thermodynamics of the

system.

We found the experiment interesting as we were able to confirm what the theory says in

practical. We believe this has aided in our understanding of the propulsion even further.

References

Wikipedia, the free encyclopedia. (). Gas turbine. Available:

http://en.wikipedia.org/wiki/Gas_turbine. Last accessed 22/11/2012.

Wikipedia, the free encyclopedia. (). Brayton cycle. Available:

http://en.wikipedia.org/wiki/Brayton_cycle. Last accessed 19/11/2012.

John Barbe. (1791). File:John Barber's gas turbine.jpg. Available:

http://en.wikipedia.org/wiki/File:John_Barber%27s_gas_turbine.jpg. Last accessed

22/11/2012.

Sounak Bhattacharjee. (). GAS POWER CYCLES. Available:

http://sounak4u.weebly.com/gas-power-cycle.html. Last accessed 29/12/2012.

Aerodynamics and Propulsion notes GAS TURBINE CYCLES by Dr. Hicham Adjali

Documents

Pressure Distribution on an Aerofoil