Muffler For Large Guns - Cervus · 2017. 10. 9. · The IfL-Muffler I MAN: construction, tanks, mechanics RHEINMETALL: ballistic, safety, firing: acoustics, measurements IfL-muffler

Baltimore 2001

Institutfür Lärmschutz

InstituteforNoise Control

A Muffler For Large Guns

Edmund Buchta

Karl-Wilhelm Hirsch

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Baltimore 2001, Buchta, Hirsch, muffler for 120 mm gun

Overview

� Introduction

� The Idea

� The Construction

� Acoustical Measurements

� Why it Works

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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.

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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