Validation case
Expansion chamber against the exact 1-D solution
Against exact one-dimensional solutions, for the straight duct, expansion chamber, SpectraSim gives: duct: |T| = 1.0000; chamber: within 0.36 dB below 0.4 of the first cross-mode cut-on, the rest is the known limit of the 1-D theory.
0.36 dB below 0.4 of the first cross-mode cut-on
Results
How close is SpectraSim?
Duct: |T| = 1.0000; chamber: within 0.36 dB below 0.4 of the first cross-mode cut-on, the rest is the known limit of the 1-D theory.
Model and set-up
- Reference
- Exact one-dimensional solutions
- Pipes of 30 mm, chamber of 90 mm and 500 mm long: an area ratio of 9.
- Air at 20 °C, anechoic ends, 146 frequencies from 50 Hz to 1.5 kHz.
- A straight duct is checked the same way: its transmission coefficient comes out exactly 1.
How to read the result
- The 1-D solution is exact only for plane waves. Towards the chamber’s first cross-mode (2235 Hz) the real 3-D field departs from it, so the small differences above 0.4 of that cut-on are the limit of the theory, not of the solver.
Selected cases
Other validation cases
-
Measured Concentric-tube resonators ≈ 2 dB peak levels against measured -
Measured Parallel-baffle (splitter) silencer 1.37 dB TL rms difference, 50 Hz to 4 kHz -
Analytical Pod silencer with absorbing pod and lining 1.3 dB TL rms difference below the 1.7 kHz cut-on -
Code-to-code Muffler with an extended-tube chamber 0.12 dB TL rms difference, 20 Hz to 1 kHz -
Code-to-code Exhaust muffler with three absorbing packings 0.16 dB TL rms difference, 20 to 500 Hz
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.