conversion of a turbojet into a turbofan through the use of a ......micro-turbojet engines: simple...
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A Conceptual Performance Study on Integration of a
Continuously Variable Speed Fan into a Micro Turbojet
Asst. Prof. Beni CukurelKobi Kadosh, Michael Palman
Turbo and Jet Engine LaborattoryFaculty of Aerospace Engineering
Technion – Israel Institute of Technology
Operational envelopes of UAVs expand into transonic speed range
Engine design process requires compromises in
□ Thrust □ Weight □ Fuel consumption
□ Development budget □ Manufacturing cost
Compromises are especially noticeable in microjet engine market, suffering
Restrained design costs
Low component efficiencies
Motivation
Lockheed Morphing UAV Concept
Engine requirements for multiple operating points:
□ Low speed loitering □ High speed cruise flight
Impose conflicting design criteria
Micro-turbojet engines:
Simple design
High levels of thrust
Poor fuel consumption - hindering range
Conventional turbofan engines:
Greater propulsive efficiency
Augmented levels of thrust
Not suitable for high speed flight
Motivation
GoalVariable cycle GT engine development which operates via integration of
continuously variable speed fan into an existing micro-turbojet
Continuously Variable Transmission
Continuously Variable Transmission
Non-discretely varies the transmission ratio between 2 boundaries.
Can effectively achieve an infinite number of gear ratios.
In Our Research
Exploring the use of a CVT in turbomachinery applications
CVT Types
Magnetic CVT
( similar to asynchronous generators )
Toroidal CVT
Continuously variable planetary
CVT Turbofan Conversion Advantages
Variable Bypass Ratio Cycle
□ Enhanced performance (thrust) □ Higher efficiency
Independent Fan – Engine Core Operating Lines
□ Easy component matching □ Highest Possible Component Efficiency
Minimal changes to core stream
□ Reduced development time and manufacturing cost
Turbojet Simulation
Component Maps
Compressor:
Turbine:
150020002250250027503000325035003750
1500
2000
2250
25002750
300032503500
3750
44000
55000
66000
77000
88000
99000
110000
0.56
0.62
0.65
0.68
0.7
0.71 0.72
0.73
0.74
PR
mcor
mcor
PR
PR
𝜂𝜂
Code Validation - Turbojet
Operating line (Alt.=0m, Mach=0)
44000
55000
66000
77000
88000
99000
110000
0.56
0.62
0.65
0.68
0.7
0.710.72
0.73
0.74
PR
mcor
Code Validation - Fixed Gear Turbofan
NASA Quiet Fan B Map
0 1 1 2 2 3 3
13068
21780
30492
3484837026
3920441382
435604573847916
0.57
0.67
0.72
0.77
0.790.81
0.82
0.83PR
mcor
CVT Geared Turbofan
Discrete gears + Interpolation CVT model
Gear Ratio Effect
70%
80%
90%
100%
110%
120%
Gear Ratios
(Percent of Nominal)
Thrust (N)
Fuel
Con
sum
ptio
n (k
g/se
c)
For Ma < 0.7 : Nominal Design gear ratio always exhibits the best fuel consumption
CVT only beneficial for Transonic Ma?
CVT Geared TurbofanOperating Lines for Different Gear Ratios
19602
32670
45738
5227255539
5880662073
653406860771874
0.57
0.67
0.72
0.77
0.790.81
0.82
0.8370%
80%
90%
100%
110%
120%
Gear Ratios
(In Percent of Nominal)
11000 2200033000
44000
55000
66000
77000
88000
99000
110000
0.56
0.62
0.65
0.68
0.7
0.710.72
0.73
0.74
70%
80%
90%
100%
110%
120%
Gear Ratios
(In Percent of Nominal)
150020002250250027503000325035003750
70%
80%
90%
100%
110%
120%
Gear Ratios
(In Percent of Nominal)
1500
2000
2250
25002750
30003250
3500
3750
70%
80%
90%
100%
110%
120%
Gear Ratios
(In Percent of Nominal)
70%
80%
90%
100%
110%
120%
Gear Ratios
(In Percent of Nominal)
PR
mcor
PR
mcor
mcor
PRFan Compressor
Turbine Turbine
PR
Spreading Motion Need to further decouple the fan operation from the core
𝜂𝜂
CVT Turbofan with Variable NozzleVariable Bypass Nozzle
Effect on Bypass and Core
1 - Fan
2 – CVT gearbox
3 - Variable bypass nozzle
22000 3300044000
55000
66000
77000
88000
99000
110000
0.56
0.62
0.65
0.68
0.7
0.71 0.72
0.73
0.74
Control mass flow through bypass without affecting core stream
Shift mechanism of fan operating line without effect on core performance
CompressorFan
PR
mcor
PR
mcor
CVT Turbofan with Variable NozzleVariable Bypass Nozzle
Effect on Bypass and Core
1 - Fan
2 – CVT gearbox
3 - Variable bypass nozzle
Control mass flow through bypass without affecting core stream
Shift mechanism of fan operating line without effect on core performance
Fan
150020002250250027503000325035003750
1500
2000
2250
25002750
300032503500
3750
PR
mcor PR
𝜂𝜂
TurbinePR
mcor
CVT Turbofan with Variable NozzleConcept
CVT (Spreading) Var. Bypass (Fanning)
Investigation
Select flight condition
Select a large band of gear ratios, nozzle positions, and core RPMs
Examine Thrust vs. Fuel at each combination
Select gear, nozzle position, RPM with least Fuel per Thrust
19602
32670
45738
5227255539
5880662073
653406860771874
0.57
0.67
0.72
0.77
0.790.81
0.82
0.8370%
80%
90%
100%
110%
120%
Gear Ratios
(In Percent of Nominal)
4791645738
0.67
0.79
0.72
0.57
0.77
43560
0.81
0.82
4138239204
0.83
3702634848
30492
Mach = 0.5, Altitude = 3000 m
21780
13068
Always operating on the most efficient point on the fan map
No operability issues (running out of the map)
Easy to scale and integrate existing fan designs
FanPR
mcor
CVT Turbofan with Variable Nozzle
4791645738
0.67
0.79
0.72
0.57
0.77
43560
0.81
0.82
4138239204
0.83
3702634848
30492
21780
13068
150020002250250027503000325035003750
0 0 0 0 1 0 1 0 2 0 2 0 3 0 3 0 0 0
110000
0.72
99000
0.71
0.73
88000
77000
66000
55000
0.560.65
0.74
4400033000
0.7
0.68
22000
0.62
11000
PR
mcor
CVT Turbofan with Variable Nozzle
Compressor
2500
3500
3750
2750
3250
2000
3000
1500
2250
Turbine
Turbine
PR
mcor
PR
𝜂𝜂
Efficiency of Various Configurations
Fan: ● Stability Issues ● Under matching, thrust increase ~35 % ● Fuel consumption increase ~30%
Variable bypass: ● Good operability thrust increase ~20% ● Poor fuel consumption persists
CVT with variable bypass: ● Reduction in fuel consumption ~20%
Enables operation at Transonic and Supersonic Flight (not modeled here)
Turbojet
Fixed gear turbofanw. fixed bypass
CVT Turbofanw. variable bypass
Fixed gear turbofanw. variable bypass
Fuel
Con
sum
ptio
n
Thrust
For Typical Subsonic Flight Conditions
Conclusions and Future WorkThermodynamic analysis of Variable cycle micro-GT engine development
Integration of continuously variable speed fan and variable bypass nozzle :
□ Enhanced Thrust □ Higher Efficiency □ Augmented Operability
Implications
Cost effective engine that can perform multiple roles.
Make use of readily available turbojet platform
Longer range/More payload
Future Work
Thrust versus weight considerations
Simulation of Operation at Transonic Flight Conditions
Modeling of larger engines
Complete Flight Mission Modeling
Laboratory experimentation
Thank you for your time!
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