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KHPRDECOM TR 18-D-76 U.S. ARMY RESEARCH, DEVELOPMENT &
ENGINEERING COMMAND TITLE: Advanced Variable Speed Power Turbine AUTHOR(s) Michael Bonacum and Paul Vitt COMPANY NAME: General Electric COMPANY ADDRESS: One Neumann Way, Cincinnati, OH 45215 DATE (MONTH YEAR): August 01, 2019 FINAL REPORT: W911W6-12-2-0012
DISTRIBUTION: UNLIMITED
FORT EUSTIS, VA 23604-5577
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1. REPORT DATE (DD-MM-YYYY)
01-08-2019 2. REPORT TYPE
FINAL REPORT 3. DATES COVERED (From - To) January 2012-August 2019
4. TITLE AND SUBTITLE
5a. CONTRACT NUMBER
General Electric One Neumann Way Cincinnati, OH 45215
8. PERFORMING ORGANIZATION REPORT NUMBER
9. SPONSORING / MONITORING AGENCY NAME(S) AND ADDRESS(ES) 10. SPONSOR/MONITOR’S ACRONYM(S)
U.S. Army Research, Development and Engineering Command (RDECOM) Aviation and Missile Research, Development and Engineering Center (AMRDEC) Aviation Development Directorate-Aviation Applied Technology Directorate (ADD- AATD) Fort Eustis, VA 23604-5577
ADD-AATD
13. SUPPLEMENTARY NOTES
UL Note: No proprietary/limited information may be included in the abstract.
14. ABSTRACT Current and future US Army rotorcraft will rely on significant technological advancements to
deliver improved performance capabilities to the future warfighter of tomorrow. One critical
needed technology is an advanced variable speed power turbine (AVSPOT) design. A robust power
turbine (PT) design, capable of high-efficiency operation between 55-105% speed provides a
versatile power system that is compatible with the types of future rotorcraft configurations
that are currently being studied for Future Vertical Lift (FVL) applications. The AVSPOT
Program successfully matured incidence tolerant airfoil design methodologies required for
efficient wide speed PT operation. This report details the aerodynamic and mechanical design
of the variable speed PT concept and the aerodynamic rig design and test results. Overall,
the design efforts and the data collected on test will form the foundation for continued
development of additional technologies to enable successful turbine designs for the stringent
requirements of FVL applications.
test
a. REPORT
code) 757-878-1907
Standard Form 298 (Rev. 8-98) Prescribed by ANSI Std. Z39.18
AVSPOT Final Report – Unlimited Rights TIA: W911W6-12-2-0012
Document #: RDECOM TR 18-D-76 Date: 01 August 2019
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Revision History
AVSPOT Final Report – Unlimited Rights TIA: W911W6-12-2-0012
Document #: RDECOM TR 18-D-76 Date: 01 August 2019
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Table of Contents
1 Summary ............................................................................................................................................... 1 2 Conclusions, Key Learnings, and Recommendations ........................................................................... 5 3 Aerodynamic Design ............................................................................................................................ 6
3.1 Design Procedure ......................................................................................................................... 7 3.2 Baseline Design Space Evaluation .............................................................................................. 7 3.3 Final Advanced Design ............................................................................................................. 10
3.3.1 1D Design.............................................................................................................................. 10 3.3.2 2D Design.............................................................................................................................. 11 3.3.3 3D Design.............................................................................................................................. 12
4 Engine Design ..................................................................................................................................... 13 4.1 Cycle Design ............................................................................................................................. 14 4.2 Component Design .................................................................................................................... 14
4.2.1 Airfoils .................................................................................................................................. 14 4.2.2 Rotor Structure ...................................................................................................................... 15 4.2.3 Static Structure ...................................................................................................................... 15 4.2.4 Advanced Material Technology ............................................................................................ 15 4.2.5 Component Durability ........................................................................................................... 16
4.3 System Design ........................................................................................................................... 17 5 Rig Design and Predictions ................................................................................................................. 19
5.1 Rig Mechanical Design ............................................................................................................. 19 5.2 Rig Pre-Test Predictions ............................................................................................................ 20
6 Rig Test ............................................................................................................................................... 20 6.1 Set-up ......................................................................................................................................... 21 6.2 Test Operations .......................................................................................................................... 23 6.3 Summary of Completed Testing ................................................................................................ 24
7 Rig Test Results .................................................................................................................................. 26 7.1 Key Mechanical Results ............................................................................................................ 26 7.2 Aerodynamic Data Summary .................................................................................................... 27 7.3 Rig Aerodynamic Validation ..................................................................................................... 28
7.3.1 Inlet condition characterization and stability for Aero Design Point .................................... 28 7.3.2 Exit Contours and Profiles .................................................................................................... 29 7.3.3 Airfoil Loading Measurement ............................................................................................... 31 7.3.4 Flow Visualization ................................................................................................................ 31
7.4 Derivatives and Reynolds Effects .............................................................................................. 32 7.4.1 Clearance Derivatives ........................................................................................................... 32 7.4.2 Purge Derivatives .................................................................................................................. 32 7.4.3 Reynolds Effects ................................................................................................................... 33
7.5 Turbine Aerodynamic Design Validation .................................................................................. 33 7.5.1 Aero Design Point Performance ............................................................................................ 33 7.5.2 Prediction Models Comparison to Test Data for the Design PR Speedline .......................... 34
7.6 Turbine Maps ............................................................................................................................. 35 7.7 Rig Test Results Conclusion...................................................................................................... 36
8 Performance vs Program Goals ........................................................................................................... 36 9 References & Definitions .................................................................................................................... 39
9.1 References ................................................................................................................................. 39 9.2 Acronyms and Definitions ......................................................................................................... 39
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Figures
Figure 1-1: AVSPOT technology enables next-gen rotorcraft concepts to meet FVL goals. ........ 1
Figure 1-2: AVSPOT PT rig installed at NDTL ............................................................................. 2 Figure 1-3: AVSPOT altitude performance map of efficiency plotted as a function of turbine
speed from 55%-105% .................................................................................................................... 3 Figure 1-4: Product design incorporates learnings from AVSPOT rig test and other relevant GE
development efforts. ....................................................................................................................... 4
Figure 3-1: Vector diagrams and the definition of incidence on the airfoil (left), and the loss
bucket as a function of incidence angle (right) ............................................................................... 7 Figure 3-2: Comparison of %Delta Efficiency as a Function of Speed (%N) for 1D (solid, blue
circles) and 3D CFD Models (dashed, red squares) ....................................................................... 8 Figure 3-3: Comparison of %Delta Flow Function as a Function of Speed (%N) for 1D (solid,
blue circles) and 3D CFD Models (dashed, red squares) ................................................................ 9 Figure 3-4: NASA research shows the impact of incidence loss on one type of airfoil design
considered for variable speed operation (Reference 2)................................................................. 10
Figure 3-5: Flowpath with 2D through-flow solution streamlines used to complete airfoil design
(Bottom) ........................................................................................................................................ 11 Figure 3-6: Example of multipoint optimization on a simple airfoil. ........................................... 12
Figure 3-7: Multistage CFD Efficiency Contour Comparison to Baseline................................... 13 Figure 4-1: Additive manufacturing process. .............................................................................. 16
Figure 5-1: Rig Test Vehicle ......................................................................................................... 19 Figure 6-1: NDTL facility overview ............................................................................................. 21 Figure 6-2: AVSPOT PT Rig installed at NDTL.......................................................................... 22
Figure 7-1: AVSPOT test data validates intended performance improvements at low speed
relative to the base design ............................................................................................................. 28
Figure 7-2: PL45 5-hole vs. CFD Swirl Match behind Pre-Swirler ............................................. 29 Figure 7-3: Absolute Total Pressure (psia) measurements show good agreement with CFD
predictions. .................................................................................................................................... 30
Figure 7-4: Absolute Total Temperature (°R) measurements agree with CFD predictions ......... 30
Figure 7-5: Swirl (°) measurements show very good agreement with CFD predictions .............. 31
Figure 7-6: Measured delta efficiency vs. average clearance closure. ......................................... 32
Figure 7-7: AVSPOT design speed line efficiency lapse test data compared to CFD and 1D
model predictions. ......................................................................................................................... 34 Figure 7-8: AVSPOT performance map. Lines of constant Pressure Ratio. ................................ 35 Figure 7-9: AVSPOT flow function map. Lines of Constant Speed. ........................................... 36 Figure 8-1: Product design incorporates learnings from AVSPOT rig test and other relevant GE
development efforts. ..................................................................................................................... 38
Table 9-2: Turbine Descriptive Parameters .................................................................................. 41
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1 Summary
Current and future US Army rotorcraft will rely on significant technological advancements to
deliver improved performance capabilities to the future warfighter of tomorrow. One critical
needed technology is an advanced variable speed power turbine (AVSPOT) design. A robust
power turbine (PT) design, capable of high-efficiency operation between 55-105% speed
provides a versatile power system that is compatible with the types of future rotorcraft
configurations, shown in Figure 1-1, that are currently being studied for Future Vertical Lift
(FVL) applications.
Figure 1-1: AVSPOT technology enables next-gen rotorcraft concepts to meet FVL goals.
To conduct system-level research on the technologies required to enable this capability, the U.S.
Army Aviation Development Directorate (ADD), in conjunction with NASA, issued a broad
agency announcement (BAA) to industry. The goal of this BAA was to identify and mature
technologies for ADD and NASA to provide to both future warfighter and civil aviation
applications.GE Aviation entered into a Technology Investment Agreement (TIA No. W911W6-
12-2-0012) in 2012 and provided the personnel, supplies, services, and facilities necessary to
conduct research and development efforts into the design, fabrication, and validation testing of
an AVSPOT rig. The research executed under this TIA builds on the research conducted with
ADD in 2005 on the Advanced Power Turbine (APT) program. That program successfully
advanced the state of the art in conventional PT design in a similar size class.
The performance objective of the AVSPOT Program is the development of a PT with:
• Output speed range: 55% ≤ NPT ≤ 105%
• Adiabatic efficiency at engine conditions:
o η ≥ 90% at Cruise at 25,000 ft., Max Continuous Power, 55% NPT
o η ≥ 92% at Takeoff/Hover, Max Rated Power, 100% NPT
• Life/Durability as stated in the BAA at 4K/95F operating conditions
o 6,000-hour mission life
15,000 cold start double hump (CSDH) cycles
7,500 CSDH cycles for turbine blades
• Minimal system weight and complexity
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The final AVSPOT design is a simple, compact configuration incorporating advanced airfoil
technology coupled with an optimal primary aero design point (ADP). This design approach
accommodates the blade incidence angle and other aerodynamic changes across the speed range
and delivers significant performance improvement at 55% speed relative to a baseline
conventional design. The notional application (vision system) for this technology is an engine
with a state of the art (SOA) conventional PT developed by GE using Advanced Affordable
Turbine Engine (AATE) Program learnings. This is used as the baseline for all comparisons to
the AVSPOT results.
A component test rig was designed for the aerodynamic equivalent full-scale size of the final
AVSPOT design. The rig configuration and instrumentation package were defined to collect
steady state data across the operating range to generate a performance map, as well as steady
traverse data at the stage exit locations, and unsteady traverse data at the turbine exit to better
understand the complex flow physics both on and off design.
The aero validation testing was completed at the Notre Dame Turbomachinery Laboratory
(NDTL) in South Bend, Indiana from March through May of 2018 and all primary test points
and objectives were achieved successfully. The rig is pictured in the cell in Figure 1-2. Data from
the rig test validates the aerodynamic technology employed in the turbine.
Figure 1-2: AVSPOT PT rig installed at NDTL
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The AVSPOT power turbine aero rig test successfully achieved all main objectives:
Understood key performance derivatives, including Reynolds number, purge flows, and
tip clearances Measured PT performance trends vs. speed at multiple pressure ratios (PR) to produce
PT map and validate analytical trends. Measured airfoil static pressures on two vanes to validate airfoil design and analytical
tools.
Completed flow visualization.
A complete turbine map, shown in Figure 1-3 was collected. This map will enable future system-
level studies of FVL-relevant propulsion systems, ensuring all operational performance
requirements can be met with an optimized AVSPOT design. In addition, high fidelity traverse
data was also collected at three key speeds, providing flow field insights at far off-design
operating conditions for use in further design refinement studies. The data shown in Figure 1-3 is
as measured rig data and is therefore not directly comparable to the AVSPOT engine condition
program goals.
Figure 1-3: AVSPOT altitude performance map of efficiency plotted as a function of
turbine speed from 55%-105%
The demonstrated AVSPOT configuration delivers performance improvements relative to a
conventional design across the entire 55%-105% speed range. In order to meet the full AVSPOT
performance goals, GE has developed a path to further improve performance and meet program
goals in the future. Incorporating the AVSPOT rig learnings and leveraging the validation of
additional advanced technologies on adjacent GE development programs results in a final
AVSPOT product configuration. Figure 1-4 shows the demonstrated performance of the
AVSPOT as tested configuration, as well as the projected performance of a future design that
incorporates technologies in excess of the incidence tolerant advanced airfoils tested in this TIA.
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Figure 1-4: Product design incorporates learnings from AVSPOT rig test and other
relevant GE development efforts.
This report details the aerodynamic and mechanical design of the variable speed PT concept and
the aerodynamic rig design and test results. Overall, the design efforts and the data collected on
test will form the foundation for continued development of additional technologies to enable
successful turbine designs that maximize performance for FVL applications.
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2 Conclusions, Key Learnings, and Recommendations
The AVSPOT design achieved the program goal of advancing the state of the art in wide speed
turbine design. The program scorecard is shown in Table 2-1.
Table 2-1: AVSPOT Program Scorecard
Criteria BAA Goal Demonstration Future Product
Engine Size class 2,000-10,000 SHP
Operational Speed
Efficiency at Takeoff,
LCF (cycles) – Turbine
representative rig
efficient wide speed PT operation. GE believes these technologies are sufficiently mature to
proceed into a development program as a result of the design and testing activities completed to
date. A number of other conclusions, learnings, and recommendations for future development
activities are a direct outcome of the AVSPOT Program. These include:
Design Technology:
• Initial design efforts were directed towards a solution which did not meet the program
goals without further technology improvements. To focus the design efforts on a
lightweight, engine-relevant package, the activity reverted to a design that fit within a
similar installation envelope as the baseline turbine.
• Airfoil technology was applied to the first turbine blade through the last stage vane. The
last stage blade design was highly constrained, so the technology was not applied there.
Additional benefits are likely when the technology can be expanded to the last blade.
• Multi-point airfoil profile optimization – minimizing loss across a range of operating
points while minimizing thickness – for the advanced airfoil designs provided a
significant reduction in the airfoil max thickness relative to prior profiles designed for
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wide speed operation. Minimizing weight while optimizing performance is a key factor
for a product relevant design.
• The ADP was set to balance the off-design performance characteristic between cruise
condition and sea level takeoff condition.
• Future engine system evaluations with a variable speed power turbine need to consider
the flow function change with shaft speed.
Test Design:
• Use of “stabbed and brazed” rig vane designs results in excessive manufacturing
complexities.
• Designing “engine-like” seals and rotors on the rig eliminates the need for complex
corrections back to the engine configuration, since leakages and associated windage
losses are consistent from rig to engine.
• Incorporating a rigorous balance plan leveraging successful engine experience into the rig
design results in very low levels of imbalance on test.
• Designing the instrumentation package and associated routing features in parallel with
the rest of the rig reduces costly and risky part re-work and ensures that there are no
unexpected clashes during assembly.
Test:
• The area traverse data collected were very high quality and compared well with the more
traditional exit rake measurements.
conditions on the critical surfaces.
• Losses in the rig exhaust scroll need to be modeled more effectively.
Tools:
• Rig data indicated that the design was less sensitive than expected based on the 1D
models. 3D CFD was more effective at capturing the measured trends, but still
underpredicted the performance. The rig captured the complete interaction of all the loss
mechanisms.
• Reynolds lapse was measured at a range of incidence angles – this data is not currently
available in literature, so it will provide a key calibration dataset for the design tools.
3 Aerodynamic Design
The three main aerodynamic challenges in designing a variable speed PT optimized for high
altitude flight are off-design incidence effects, Reynolds number losses, and stage loading
impacts. Airfoil incidence angle swings across a wide range, from negative at high speed to
positive at low speed. Reynolds numbers are low at very high altitudes on small turbomachines
such as those designed for AVSPOT and begin to approach the transitional flow range. Stage
loading, a function of work extraction and pitchline speed, increases as the PT slows down,
increasing secondary flow and profile losses. The AVSPOT design incorporates aerodynamic
technologies focused on minimizing these effects. Below is a brief summary of the aerodynamic
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tools and methods used in the program, the trade studies completed, and the final aerodynamic
design of the turbine.
The design procedure consisted of the following steps:
1. Preliminary Design: A 1-D meanline code was used to develop the preliminary turbine
flowpath and free-vortex vector diagram.
2. Flowpath and Vector Diagram: An axisymmetric streamline curvature solver was used
to develop the 2-D vector diagram.
3. Detailed Airfoil Geometry: The airfoils were designed on surfaces defined by the 2-D
code streamlines using a parametric airfoil design tool.
4. Flow Field and Performance Evaluation: Multi-row CFD models were used to evaluate
the advanced design.
Several aerodynamic design iterations were completed early in the program. First, a
configuration utilizing conventional airfoil technologies was designed in order to establish a
performance baseline for a concept that used existing technologies to address PT operational
efficiency across a wide speed range. These studies were completed early in the program to
better understand the design space for the AVSPOT technologies. The 1-D model was used to
evaluate trades on stage count, flowpath geometry, design speed, worksplit, airfoil counts, and
overall PT performance. The AVSPOT inlet was constrained to align with the APT to allow
reuse of the existing rig inlet section. The exit case radius was constrained by the max allowable
tip speed and the AN2 constraint then set the hub radius.
The primary performance challenges for a constant-power, variable speed turbine operating from
55% to 105% speed are the incidence and the stage loading impacts. To balance the off-design
loss due to incidence, the range of angles the blade experiences must be biased to the negative
side, as shown by the fundamental incidence loss characteristic in Figure 3-1.
Figure 3-1: Vector diagrams and the definition of incidence on the airfoil (left), and the loss
bucket as a function of incidence angle (right)
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The stage loading variation with speed shows that at 55% speed the stage loading increases by
more than 3x compared to 100% speed. The impact of the stage loading level on performance
can be shown on the industry standard Smith chart, which clearly shows the performance
challenge operating at the 55% speed condition.
After completing the 1D design space evaluation, the design proceeded through the normal
process outlined above, culminating with multi-bladerow steady CFD model runs for the
baseline design at the MCP operating condition with PT speeds of 55%, 65%, 75%, 85%,100%
and at MRP 100%N. The CFD highlighted that the impact of operating slower than design speed
is captured by the…