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!