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Baltimore 2001
Institutfür Lärmschutz
InstituteforNoise Control
A Muffler For Large Guns
Edmund Buchta
Karl-Wilhelm Hirsch
2
Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
Overview
� Introduction
� The Idea
� The Construction
� Acoustical Measurements
� Why it Works
3
Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
Introduction� In co-operation with Rheinmetall and MAN the IfL
did the acoustical measurements and developed a muffler for the 120 mm gun of the Leopard 2.
� The goal of this investigation was to reduce the noise load from shots with large guns� in the vicinity of military testing facilities� and other facilities where shooting is done from defined
positions.
� A similar approach was tested earlier by USA CERL at Aberdeen proofing ground using foam in a large muffler for howitzer shots.
� In parallel to the IfL muffler, Rheinmetall developed its own concept for the inner part of the muffler.
4
Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
The Idea� The general idea of this type of muffler is to expand the
propellant gases into an appropriate tank and store the gas there until pressure and motion are low enough that they can leave the tank in a steady subsonic flow into the surrounding air.
� We must let the projectile out. (No question about that.)
� We cannot close the tank quick enough behind the projectile. (At least, we were not able to.)
� The gases in the tank will start a pipe-like periodic motion.(that is our view on what happens.)
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
The Approach� Try to build a dynamic ‚door‘ in the tank so that the gases
can go in easily but when they try to leave make it as difficult as possible for them.
� We tried a system of wedges and use them as‚non-reciprocal‘ flow resistors.
barrel
ø 120 mm
non-reciprocalflow resistor tank
outlet
ø 130 mm
gas flowfrom barrel
gas flowto outlet
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
The Construction
front back
projectileprojectile
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
The IfL-Muffler I
MAN: construction, tanks, mechanicsMAN: construction, tanks, mechanicsMAN: construction, tanks, mechanics
RRRHEINMETALLHEINMETALLHEINMETALL: ballistic, safety, firing: ballistic, safety, firing: ballistic, safety, firing
IfLIfLIfL: acoustics, measurements: acoustics, measurements: acoustics, measurements
IfL-muffler and Leopard 2at Rheinmetall proofing ground
frontback
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
The IfL-Muffler IIinner construction
projectile
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
The IfL-Muffler III‘the front door‘
projectile
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
The IfL-Muffler IVfront part
projectile
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
The IfL-Muffler V‘the closed door‘
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
Acoustical Measurements
on a circleradius 250 m
on a circleradius 1000 m
on a line 135°
behind the barrel
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
Results Ione-third octave spectra at 180°, 250 m
with muffler
without muffler
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
Results IICSEL along the line 135° behind the muzzle
dB
km
without muffler
with muffler
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
Results IIIthe effect of the flow resistors
** 90°
80 90 110 120
0°
45°
dB
135°
180°
225°
270°
315°*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
*
100
empty tank
with resistors
directivity pattern
at 250 m
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
Results IVpressure time history at 135°, 1000 m
one clear blast multiple blasts
±15 Pa ±0.8 Pa
1 s1 s
with mufflerwithout muffler
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
1
2
3
4
5
6
7
8
firstblast
secondblast
continuous flow
High Speed PhotographyRheinmetall
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
There is evidence that ...� the muffler works because it splits the gas into two main
blasts and a steady flow that is vibrating internally.
� the muffler does not ‚absorb‘ acoustical energy but modifies the radiation of sound by changing the geometry.
� with a muffler there are multiple sourcessmaller in size compared to a big one without a muffler.
� due to smaller sources and their different radiation impedance compared to a big one these sources cannot radiate the low frequencies efficiently.
� the change in radiation impedance is the key to understand the muffler.
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
Conclusion
� The ‚non-reciprocal‘ muffler reduces the
total radiated energy by round about 8 dB.
� The level reduction in some selected
one-third octave bands can exceed 30 dB.
� The muffler works well in particular in the
low frequency range.
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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun
Enhanced Muffler