Pressure-Neutral Acoustic Wind Tunnel
University of Bristol
The Pressure-Neutral Acoustic Wind Tunnel at the University of Bristol is a closed-loop, open-jet facility designed for combined aerodynamic and aeroacoustic testing. It is particularly well suited to the investigation of propellers, rotors, distributed electric propulsion systems and other rotating aerodynamic components across a range of operating and inflow conditions.
The tunnel is equipped with a rectangular nozzle measuring 1.0 m wide by 0.7 m high and provides free-stream velocities from approximately 5 m/s to 35 m/s. A redesigned settling chamber, honeycomb flow conditioner and woven mesh screens provide a uniform flow with a turbulence intensity of approximately 0.2%, making the facility suitable for both aerodynamic performance measurements and detailed flow-field investigations.
The open-jet test section is housed within an acoustically treated chamber approximately 3.8 m long by 4.2 m wide. Foam wedges and acoustic treatment minimise sound reflections, while two sets of large splitter silencers reduce fan and flow noise within the tunnel circuit. These features provide a controlled environment for the measurement of both tonal and broadband noise from rotating and stationary aerodynamic systems.
A defining feature of the facility is its pressure-neutralisation system. Rectangular openings positioned above and below the nozzle and collector allow the pressure within the test chamber to remain balanced during operation. The lower openings are connected to ultra-quiet extraction fans, while the upper openings permit a controlled natural inflow of air. This arrangement prevents the recirculation and ingestion of turbulence generated within the chamber, reducing contamination of aerodynamic and acoustic measurements during propeller and proprotor testing.
The facility supports simultaneous aerodynamic, acoustic and flow-field measurements. Its instrumentation includes far-field microphone arrays, an acoustic beamforming array for noise-source localisation, multi-axis force measurement systems, miniature load cells, pressure scanners, particle-image velocimetry and hot-wire and hot-film anemometry. The measurement systems can be synchronised with propeller rotation, enabling phase-locked investigation of unsteady aerodynamic loading, wake development and noise-generation mechanisms.
The tunnel has been used to investigate isolated and installed propellers, edgewise and forward-flight conditions, turbulence and wake ingestion, rotor–airframe interactions, distributed electric propulsion and the acoustic directivity of single- and multiple-propeller systems.
- Location:
- Bristol
- Owner(s):
- University of Bristol
United Kingdom - Test Section 1 size:
- Anechoic chamber: approximately 3.8 x 4.2 m (L x W) (anechoic down to 160 Hz)
Rectangular nozzle: 1.0 x 0.7 m; maximum speed 35 m/s
- Operational Status:
- Active
- Number and Type of Staff:
- Scientific: 7
Technical Support: 4
- Test support:
- Workshop for wind tunnel model design, manufacture and modification capability.
- Designation:
- Closed-loop, open-section pressure-neutral acoustic wind tunnel
- Performance:
-
Maximum Flow Speed: 5 m/s to 35 m/s
Turbulence intensity: ~ 0.2%
Run Time: Continous
- Testing Capabilities:
-
Outputs: Aeroacoustic measurements
• Near-field and far-field noise measurement
• Acoustic directivity measurements
• Tonal and broadband noise characterisation
• Beamforming and noise-source localisation
• Synchronous and phase-locked acoustic measurements
Aerodynamic measurements
• Thrust, torque and multi-axis force measurement
• Miniature load-cell measurements
• Steady and unsteady surface-pressure measurements
• Propeller and rotor performance characterisation
Flow measurements
• Conventional particle-image velocimetry
• Time-resolved particle-image velocimetry
• Two-dimensional and three-dimensional PIV
• Phase-locked PIV for rotating systems
• Hot-wire and hot-film anemometry
• Wake, turbulence and inflow-distortion characterisation
- Specialist Rigs:
- • Pressure-neutralisation system with ultra-quiet suction fans
• Multiple far-field microphone arrays
• Large beamforming array for noise quantification and localisation
• 6-axis force plate and miniature load-cell systems
• 128-channel pressure-scanning system
• Conventional and time-resolved 2D and 3D PIV, phase-lockable to propeller systems
• Hot-wire and hot-film anemometry systems
- Equipment:
- • Multiple far-field microphone arrays
• Large acoustic beamforming array for noise quantification and source localisation
• More than 60 GRAS free-field microphones available for multi-plane far-field measurements