Validation case

Pod silencer with absorbing pod and lining

Against the paper’s own plane-wave theory (Munjal, 2003), solved again with the same inputs, for the pod silencer with absorbing pod and lining (Munjal, 2003), 20–5000 Hz, SpectraSim gives: absorbing section rms 1.3 dB, largest 2.3 dB below the 1.7 kHz cut-on; the paper's printed curve is matched below 1 kHz (rms 2.9 dB) and lies 7–13 dB lower above it, most likely an unreported protective perforate.

SpectraSim 0.6.0a1 · Analytical · Row in the validation table

1.3 dB TL rms difference below the 1.7 kHz cut-on

Cutaway of a pod silencer: inlet pipe and expansion cone, a central absorbing pod with bullet nose and tail inside an absorbing lining, then a contraction cone to the outlet pipe; arrows show the flow through the annular passage. — Pod silencer with absorbing pod and lining (Munjal, 2003), 20–5000 Hz. Cut away to show the inside.

Results

How close is SpectraSim?

Absorbing section rms 1.3 dB, largest 2.3 dB below the 1.7 kHz cut-on; the paper's printed curve is matched below 1 kHz (rms 2.9 dB) and lies 7–13 dB lower above it, most likely an unreported protective perforate.

Transmission loss 0 to 5000 Hz of the pod section alone and of the full pod silencer: SpectraSim, the re-solved Munjal theory and the paper’s printed curve. — Left: the absorbing section alone. Right: the full silencer with its cones. SpectraSim, the re-solved theory and the paper’s printed curve.

Model and set-up

Reference: The paper's bulk-reacting plane-wave theory, solved again with the same inputs

Pod radius 50 mm, flow passage to 100 mm, lining to 150 mm, 500 mm long; cones of 150 mm to pipes of 50 mm radius.
Pod and lining: 15 kPa·s/m² packing with Mechel’s Delany–Bazley constants, entered as user constants; no protective perforate (the paper gives none).
Air at 24.6 °C; a 30° sector with symmetry planes, exact for plane-wave excitation; 229 frequencies from 20 Hz to 5 kHz.

How to read the result

The reference is the paper’s own bulk-reacting plane-wave theory, solved again with the same inputs, so both sides use exactly the same data.
Full silencer at low frequency: the 80 Hz peak (9.3 against 9.5 dB), the 150 Hz dip and the 250 Hz shoulder are reproduced.
Above about 1.2 kHz the paper’s printed curve lies 7–13 dB below both SpectraSim and the re-solved theory: the gap is in the paper’s inputs, most likely an unreported protective perforate. Its figure is a check below 1 kHz only.

Selected cases

Other validation cases

All validation results

Check it on your own muffler.

Download SpectraSim and run your geometry, or let our engineers run the study and compare it with your test.

Request a quote Download Request a design study