Mobile system for acoustical measurement techniques (SAG)

Figure 1 shows the DLR microphone array in the low-speed test facility of Airbus Bremen (B-LSWT). By means of this microphone array sound sources can be localized and quantified on aircraft half models in the closed test section of this industrial wind tunnel (see also: Measuring principle of the Microphone array). The application of the high-speed PIV system to measure the sound velocity non-intrusively is shown in Figure 2
 

General data

• Site at DLR Göttingen
• Opening in 2008
• Operation vear-around

Technical Data

• anechoic room 7,4 m x 6,75 m x 4,3 m (following DIN EN ISO 3745:2012-07, Appendix A) with optional flow test stand (nozzle dimensions 0,4 m x 0,4 m, up to 50 m/s)
• 9 time-synchronized data acquisition systems of
  type VIPER with a total of 496 channels at a sampling rate of up to 250 kHz
• 2 data acquisition systems of type Oros
  with a total of 56 channels
• 60 ¼-inch condenser microphones
• 20 ½-inch condenser microphones
• 80 ¼-inch multifield condenser microphone
• 100 ¼-inch cryogenic condenser microphones
• 250 pre-polarized electret microphones
• 40 uniaxial accelerometers
• 30 triaxial accelerometers
• 60 piezo-resistive pressure transducers
• 18 sound intensity probes (p-p and p-u)
• 1 three-dimensional intensity probe
• Microphone arrays for various applications
• Measurements in closed test sections (up to 288 microphones)
• Measurements in open test sections (up to 250 microphones)
• Measurements in cryogenic environments (144 microphones)
• Measurements in pressurized cryogenic environments (96 microphones)
• Cabin microphone array (60 microphones, flight-test approved)
• Near-field holography
• Miscellaneous: filters, artificial head, signal generators, exterior microphones, noise sources, pistonphone, 1-point laser vibrometer

Applications

• Lokalisierung und Quantifizierung von Schallquellen
• Localization and quantification of noise sources
• Identification of source mechanisms
• Mobile operation in flight testing
• Investigation of boundary layer excitation
• Measurement and reduction of noise in the aircraft cabin
• Mobile operation in industrial wind tunnels
• Open measurement sections
• Closed measurement sections
• Wind tunnels with cryogenic and pressurized measurement section

Project highlights

• SIMKAB (Simplifizierte Kabine, LuFo IV-2)
  Objective: technical survey of source locations, main transmission routes, and noise emission in the cabin in a flight test with the DLR’s Airbus model A320 research aircraft ATRA
• ALSA (Akustische Lokalisation von Strömungsablösung im ETW, LuFo IV-3)
• Objective: Survey of aeroacoustic noise sources on downscaled models at flight reynolds numbers and investigation of relation between near-field and acoustic far-field.
• PROTEG (Production Optimising Technologies, Lufo IV-3)
  Objective: experimental survea of the boundary layer exciation of a light-weight plate at M =0.8
• NEMO (Noise Source Evaluation using In-flight Data and Modal Characterization of CRAFD Demonstrator, LuFo IV-4)
  Objective: detailed analysis of SIMKAB flight test data retrieved from the A320-ATRA and derivation of an empirical model for the boundary layer exciation.
• FlightLab (optical vibration measurement techniques and efficient analysis tools, Lufo V-1)
  Objective: Development of a physical modell for prediction of noise emission of a light-weight plate under boundary layer excitation.
• InScan (accurate and time-optimized in-flight intensitätsscanning, Lufo V-2)
  Objective: Development of an array-based measurement concept for swift and precise determination of cabin noise
• MAAM-course (Mikrophone Arrays for Aeroacoustic Measurements, 2014, 2016)
• Research support (Daimler, VW, Porsche, Audi, Hübner, DNW-LLF, KRRI - Korean Railroad Research Institute

Cooperations

• German-Dutch Windtunnels (DNW)
• European Transonic Windtunnel (ETW)
• TU Cottbus, TU Berlin, NASA, Trinity College Dublin,
• Airbus, RUAG

Literature