Document
9x15 Low Speed Wind Tunnel
Acoustic Improvements
Wind Tunnel Facility Manager: David Stark Acoustics Branch Point - of - Contact: David Stephens
Executive Summary
The 9 - by 15 - Foot Low Speed Wind Tunnel (9x15 LSWT) at NASA Glenn Research Center was built in 1969 in the return leg of the 8 - by 6 - Foot Supersonic Wind Tunnel (8x6 SWT). The 8x6 SWT was completed in 1949 and acoustically treated to mitigate community noise issues in 1950. This treatment included the addition of a large muffler downstream of the 8x6 SWT test section and diffuser.
The 9x15 LSWT was designed for performance testing of V/STOL aircraft models, but with the addition of the current acoustic treatment in 1986 the tunnel been used principally for acoustic and performance testing of aircraft propulsions systems. The present document describes an anticipated acoustic upgrade to be completed in 2017.
Unique facility for testing propulsors
9x15 LSWT 8x6 SWT Mach 0 to 0.23 0 to 0.1 Number 0.25 to 2.0 Simulated Sea Level 1000 to 35,000 ft Altitude
Fan/Propulsor Testing in 9x15 Tunnel
• The GRC 9x15 Low Speed Wind Tunnel has Honeywell Turbofan with Acoustic Liners been extensively used to study and acoustically characterize nearly all of the NASA/Industry propulsor concepts over the past 20 years.
• Except for maintenance, the acoustic treatment has remained essentially unchanged in 20+ years.
NASA/GE Open Rotor P&W Geared Turbofan P&W Advanced Ducted Propulsor
Testing quiet fans requires
a quiet wind tunnel
• Historically this has been done by testing a Mach 0.1, which is below true take - off and landing speeds.
Empty 9x15 vs Low Power ADP with Liners Empty 9x15 vs Low Power ADP with Liners Empty 9x15 vs Low Power ADP with Liners • Future fans may be even 90 90 quieter 80 80 80 • Low tip speed • Low pressure ratio 70 70 70 • Acoustic liners • Open rotors and other 60 60 60 ADP Aft (126º emitted) Third Octave SPL, dB concept fans require Third Octave SPL, dB Third Octave SPL, dB ADP Aft (126º emitted) - - ADP Aft (126º emitted) - ADP Broadside (89º emitted) testing at higher tunnel ADP Broadside (89º emitted) ADP Broadside (89º emitted) One 50 One 50 One 50 ADP Forward (23º emitted) speeds than Mach 0.1 ADP Forward (23º emitted) Current Empty 9x15, Mach 0.10 ADP Forward (23º emitted) Current Empty 9x15, Mach 0.10 40 40 Current Empty 9x15, Mach 0.20 100 1000 10000 100000 100 1000 10000 100000 100 1000 10000 100000 Frequency, Hz Frequency, Hz Frequency, Hz
Support from NASA Agency and Center Levels
• Preliminary assessment by Jacobs Technology, Inc performed in 2012 • Funded by Environmentally Responsible Aviation • Initial FY15 NASA funding resulted in initiation of 9x15 Design contract that resulted in completion of a 30% design review.
• Additional funding in FY15 from NASA GRC, NASA AETC project and NASA Augmentation funded a 9x15 Design/Build contract which began in September 2015 from the 30% design point. The FY15 funding provided 60% of the total project Design/Build cost.
• FY16 funding from NASA GRC and NASA AETC is currently being approved by Congress through the FY16 NASA Operating Plan and this funding will provide the remaining 9x15 Design/Build funding .
Anticipated Schedule
• December 2015 – Final pre - construction aerodynamic calibration of 8x6 and 9x15 test sections • January 2016 – Final pre - construction background noise measurement of 9x15 test section • September 30, 2016 – Boundary layer ingestion test in 8x6 tunnel ends • October 31, 2016 – Wind Tunnel Shutdown for Start of Site Work • Both 8x6 and 9x15 shut down • September 4, 2017 – Acceptance Testing Begins • Acceptance testing for 8x6 and 9x15 test sections • September 29, 2017 – Tunnel Ready for Testing
Planned Wind Tunnel Renovation
Complementary but discrete improvements
1. Add fairings and turning vanes to turn 2
2. Add acoustic baffles downstream of doors 1 & 2
3. Replace test section flow surfaces, remove slots
4. Reshape diffuser and add acoustic treatment
5. Add turning vanes to turn 3
1 2 5
Flow 9x15 Tunnel, Top View
Current 9x15
Test Section
• The test section surface is perforated steel over a bulk Kevlar absorber • Facing plate is 16 ga , 1/8” holes, 40 percent open • The acoustic treatment is built as dozens of individual boxes • There are slots in both walls, and many seams throughout the tunnel • The 2012 study by Jacobs concluded that the majority of the noise in the 9x15 test section above 2 kHz is due to boundary layer flow over perforated steel surface Test Section Perforated Metal (Current)
Test Section Acoustic Treatment Replacement
The most significant improvement comes from replacing the flow Roughness Noise Facility at Virginia Tech surface with a micronic wire cloth Two dozen candidates panels screened dB #6 PSD, -10 9x15 Baseline Mic -20 Solid Plate 5/32 63% 200x600 -30 For more information, see AIAA - 2015 - 3261 0 5000 10000 15000 20000 Frequency, Hz
Minimal impact to anechoic quality
• Impact of wire cloth over perforate has been investigated at LaRC Normal Incidence Tube, LaRC Curved Duct Test Rig and Glenn Acoustical Testing Laboratory 0.98 0.96 0.94 0.92 0.9 ATL 9x15 Baseline ATL 63% 5/32 200x600 0.88 NIT 9x15 Baseline NIT 63% 5/32 200x600 Absorption Coefficient 0.86 0 1000 2000 3000 4000 5000 6000 Frequency, Hz • Anechoic quality of test section to be assessed by external contractor according to ISO 26101
Anticipated Improvement to 9x15 noise levels
after all 5 upgrades
90.0 Empty Tunnel, Jacobs 80.0 Frequency (2012) Prediction 630 81.2 65.6 794 80.6 69.3 1000 80.5 71.9 70.0 1260 82.2 73.3 1587 80.6 73.7 2000 78.5 73.9 60.0 2520 79.4 73.1 Third Octave SPL, dB - 3175 81.0 73.5 4000 82.8 73.3 One 5040 84.3 72.7 Current Empty 9x15, Mach 0.20 50.0 6350 84.2 72.4 8000 83.1 70.5 Predicted Empty 9x15, Mach 0.20 10079 81.2 68.3 12699 79.3 64.7 40.0 16000 77.8 63.0 100 1000 10000 100000 20159 76.2 61.3 Frequency, Hz 25398 75.6 58.5 32000 72.6 55.7 Acceptance criteria: No less 40317 66.3 52.6 50797 62.4 49.9 than 3 dB from prediction
Relative to P&W Advanced Ducted Propulsor (ADP)
Model Fan Measurements
Empty 9x15 vs Low Power ADP with Liners Third Octave SPL, dB - ADP Aft (126º emitted) One ADP Broadside (89º emitted) ADP Forward (23º emitted) Current Empty 9x15, Mach 0.20 Predicted Empty 9x15, Mach 0.20 100 1000 10000 100000 Frequency, Hz
A - Weighted Noise Levels
Expected Quiet Improvement: 9.3 dB(A) Fast Figure from: AIAA 2002 - 2503 - Recent Advances in Large - Scale Aeroacoustic Wind Tunnels Edward Duell , Joel Walter, Steve Arnette , Joseph Yen. Sverdrup Technology, Inc.
Test Section to be lengthened 5 - feet into diffuser
Red Lines denote limits of measurements in upstream and downstream directions. First or last measurement repeated as needed to complete analysis.
• Current test section length restricts aft measurement angles • Floor mounted microphones are a marginal solution • This can have a significant impact on EPNL calculations • The addition of a 5 - foot straight extension into the current diffuser will enable measurement to 150º geometric from upstream
Turn 2 Turning Vanes
Heat Exchanger Muffler Exit
Velocity Field in Turn 2
Heat Muffler Exchanger Exit Case 1: Existing design Case 2 : Proposed C - 2 design Proposed designs provides much more uniform airflow into cooler.
This should result in more uniform temperature in the test section.