Information of Acoustic Linear Research Laboratory

The research capabilities of the Acoustic Liner Research Laboratory at UC
The Acoustic Measurement Capabilities
in the Acoustic Linear Research Laboratory
at University of Cincinnati
Asif Syed
Research Professor, School of Aerospace Systems
College of Engineering and Applied Science
University of Cincinnati.
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 1 The research capabilities of the Acoustic Liner Research Laboratory at UC
Test Facilities for Research in Acoustic Liners
1.  Wave Tube of 1.5-inch square cross section
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• 
2. 
Sound attenuation testing up to 4300 Hz.
Normal incidence impedance testing up to 8600 Hz.
New Wave Tube of 2.0-inch square cross section*
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• 
• 
Max frequency of Impedance and Suppression tests - 6700 Hz.
Compatible with Facility at NASA La RC
Capable of conducting tests of transmission loss through materials
3.  The Large Wave Tube (3-inch by 5-inch cross section) for testing 5inch by
12 inch acoustic liner panels.
4.  Acoustic Impedance Measurement System (AIMS)
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• 
1.25 inch diameter impedance tube
Normal incidence impedance testing up to 6000 Hz.
5.  Flow Duct Apparatus*
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Acoustic attenuation in flow using modal measurements
Frequency range: 500 Hz. to 4000 Hz.
Flow speeds up to Mach 0.7
6.  Steady (DC) Flow Resistance Test Stand
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Characterization of flow resistance of porous materials
10 cm (4.0 inch) diameter for flow area.
* The Flow Duct Apparatus and the new wave tube are in the development phase.
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 2 The research capabilities of the Acoustic Liner Research Laboratory at UC
The small wave tube (SWT) of 1.5-inch square cross section
•  The current wave tube is of 1.5-inch square cross section
•  It uses 3 acoustic transducers in the upstream and 3 transducers in the
downstream locations to measure the plane wave amplitudes AU, BU, AD,
and BD.
•  Suppression (dB) testing up to the maximum frequency 4300 Hz.
•  Normalized Impedance testing up to the maximum frequency 8600 Hz.
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 3 The research capabilities of the Acoustic Liner Research Laboratory at UC
Comparison of the Measured Acoustic Suppression data
for Porous versus Impervious Partitions
14
Suppression of the Plane Wave Mode (dB)
12
10
8
6
4
* The baseline configuration had partitions at 3/8 inch spacing.
Baseline configuration with Impervious Partitions*
2
Test configuration with Porous Partitions at 3/8 inch spacing
Test configuration with Porous Partitions at 1/4 inch spacing
Test configuration with Porous Partitions at 3/16 inch spacing.
0
0
1000
2000
3000
4000
5000
6000
Frequency (Hz.)
Examples of measured suppression (dB) data in the
small (1.5-inch square cross section) wave tube (SWT)
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 4 The research capabilities of the Acoustic Liner Research Laboratory at UC
The New Wave Tube
This tube will also be used to test the acoustic transmission loss characteristics of materials.
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 5 The research capabilities of the Acoustic Liner Research Laboratory at UC
Schematic diagram of the large wave tube (LWT)
apparatus for testing acoustic liner panels.
42.00 IN.
A
A
The Acoustic Liner
Panel
12.0 IN.
12.75
Array of 20
acoustic transducers
In two axial planes
The details of the acoustic liner panels need to be worked out so that it may also be tested in the flow duct apparatus.
5.00 IN.
1.50 IN.
Section A-A
The Acoustic Liner
Panel
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 6 The research capabilities of the Acoustic Liner Research Laboratory at UC
The large wave tube (LWT) – transducer distribution.
Distribution of 10 acoustic transducers in one of the two cross-sectional planes
X-ducer #
x (inch)
y (inch)
z (inch)
1
2
3
4
5
6
7
8
9
10
X0
X0
X0
X0
X0
X0
X0
X0
X0
X0
1.5
1.5
1.5
1.5
1.5
0
0
0
0
0
0.25
1.25
2.5
3.75
4.75
4.75
3.75
2.5
1.25
0.25
The locations of the first 10 transducers in the plane: x = x0
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 7 The research capabilities of the Acoustic Liner Research Laboratory at UC
Acoustic Impedance Measurement System (AIMS)
with Circular Tube
PC computer
Measuring Head
NI Data Acquisition System
3/10/13 Asif Syed, Research Professor, University of Cincinna;. Rubber
Gasket
8 The research capabilities of the Acoustic Liner Research Laboratory at UC
Schematic diagrams showing the use of AIMS
in the Impedance Tube and the Plunker modes.
Nondestructive “Plunker” mode
“Impedance Tube” Mode
Acoustic Driver
Acoustic Driver
Brass Tube
Rubber
Gasket
Acoustic Pressure
Transducers
Acoustic Liner
The diameter of the tube in the measuring head is 1.25 inch (3.175 cm)
Two AIMS systems, supplied by UC to MRAS and to P&W Auto-Air, are in constant use since 2005.
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 9 The research capabilities of the Acoustic Liner Research Laboratory at UC
The Flow Duct Facility for Research in Acoustic Liners
Liner Test
Section
Diffuser
Circular to Rectangular
Inlet Nozzle
Provision
For
Acoustic
Liners
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 10 The research capabilities of the Acoustic Liner Research Laboratory at UC
Acoustic transducers
3/10/13 Asif Syed, Research Professor, University of Cincinna;. Liner test section
11 The research capabilities of the Acoustic Liner Research Laboratory at UC
Cross section of the flow duct apparatus
3.0-inch
5.0-inch
  5-inch wide and up to 24-inch long liner test panels on one or two opposite sides
  Designed for mean flow velocities up to Mach 0.7
  Acoustic modal measurements with two arrays of acoustic transducers. Each array
consists of 16 transducers in two planes. One array is located upstream and the
second array is located downstream of the liner test segment of the flow duct.
  Capability to measure boundary layer velocity profiles in the test section and for
controlling the boundary layer thickness.
  Capability to measure the flow resistance of porous materials in the presence of
high speed grazing flow.
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 12 The research capabilities of the Acoustic Liner Research Laboratory at UC
The Flow Resistance Test Stand
(a.k.a the Raylometer) is a stand alone system. It can
test porous test samples which are 4.0 inch (10 cm.) in
diameter.
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 13 The research capabilities of the Acoustic Liner Research Laboratory at UC
Schematic diagram of the steady flow resistance test
stand or the Raylometer
Test Sample
Ta , Pa
ΔPs
Ts , Ps
Pf , Tf
ΔPfm
Laminar Element
Flow Meter
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 14 The research capabilities of the Acoustic Liner Research Laboratory at UC
Resistance, R (cgs Rayl)
An example of test data measured on
the Steady (DC) Flow Test Stand
30
R(U) = A + B U
25
R105 = (A + 105 B)
20
NLF =
15
A
10
B
(A + 200 B)
(A + 20 B)
R (cgs Rayl) = 3.1365 + 0.1149 U
5
0
0
50
100
150
200
250
Flow Velocity, U (cm/s)
R(U) - is the flow resistance (cgs Rayl) at mean flow velocity, U (cm/s)
R105 - is the flow resistance at flow velocity of 105 cm/s
NLF – is the non-linearity factor
A - is the intercept and B is the slope of the straight line fit through the measured test
data. All the flow resistance test data are computed in cgs Rayl units.
3/10/13 Asif Syed, Research Professor, University of Cincinna;. 15