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arxiv: 2512.07920 · v2 · submitted 2025-12-08 · ⚛️ physics.flu-dyn

Hydroacoustic Absorption and Amplification by Turbulence

Kai-Xin Hu , Yue-Jin Hu This is my paper

Pith reviewed 2026-05-17 00:19 UTC · model grok-4.3

classification ⚛️ physics.flu-dyn
keywords turbulenceacoustic waveshydroacousticsabsorptionamplificationwave propagationfluid dynamicsunderwater sound
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0 comments X

The pith

Turbulence absorbs or amplifies high-frequency acoustic waves by over 60 percent without spectral broadening.

A machine-rendered reading of the paper's core claim, the machinery that carries it, and where it could break.

The paper reports that underwater turbulence alters the amplitude of propagating acoustic waves at frequencies far higher than those of the turbulent fluctuations themselves. Observed changes reach more than 60 percent attenuation or amplification, yet the spectrum remains unchanged with no new frequency components generated. The effect appears in both pipe flow and free-jet conditions, holds for propagation both parallel and perpendicular to the mean flow, and occurs even when turbulent fluctuations lack a mean motion. Conventional explanations such as scattering, viscous dissipation, bubbles, or resonance fail to account for the data, so the authors identify an incompletely understood new interaction mechanism between turbulence and sound.

Core claim

Acoustic waves can be absorbed or amplified by turbulence at frequencies far exceeding the turbulent fluctuation frequency, with maximum observed attenuation or amplification exceeding 60 percent and no spectral broadening. The amplification factor depends on wave frequency rather than amplitude. The effect occurs under two flow conditions, pipe flow and free jet, for frequencies from 60 kHz to 4.4 MHz, and in both parallel and perpendicular propagation directions. Turbulent fluctuations without mean motion still alter wave amplitude while laminar flow produces no change. Standard mechanisms cannot explain the observations, indicating an incompletely understood new mechanism in the turbulent

What carries the argument

The frequency-dependent amplitude modulation of acoustic signals by turbulent fluctuations, occurring without spectral broadening or dependence on wave amplitude.

If this is right

  • The effect occurs for both parallel and perpendicular propagation relative to the mean flow.
  • Turbulent fluctuations alone, without mean motion, are sufficient to alter acoustic amplitude.
  • Laminar flow leaves acoustic signals unchanged.
  • The observed changes cannot be attributed to bubbles, resonance, scattering, or viscous dissipation.
  • The phenomenon spans frequencies from 60 kHz to 4.4 MHz under the tested conditions.

Where Pith is reading between the lines

These are editorial extensions of the paper, not claims the author makes directly.

  • Models of underwater sound propagation would need to incorporate this amplitude-altering process in turbulent regions.
  • Controlled turbulence might offer a way to modulate acoustic signals in applications such as sonar or communication.
  • The mechanism could be tested for dependence on turbulence intensity or Reynolds number in scaled experiments.
  • Similar interactions might appear in other wave-turbulence systems once the hydroacoustic case is clarified.

Load-bearing premise

The measured changes in acoustic signal amplitude are produced by turbulence itself rather than by undetected experimental artifacts such as bubbles, transducer nonlinearities, or flow-induced vibrations.

What would settle it

Repeating the experiments in a setup that rigorously eliminates bubbles, ensures linear transducer operation, and suppresses vibrations, then finding no amplitude change under turbulence, would falsify the claim of a new mechanism.

read the original abstract

Acoustic waves propagating through fluid media are significantly influenced by turbulence. This paper experimentally investigates the influence of underwater turbulence on the propagation characteristics of acoustic waves, revealing that acoustic waves can be absorbed or amplified at frequencies far exceeding the turbulent fluctuation frequency. The maximum observed attenuation or amplification of received signals exceeds 60%, with no spectral broadening. The amplification factor depends on the wave frequency rather than its amplitude. The study covers two flow conditions: pipe flow and free jet, driven by either a pump or hydraulic head difference. The frequency range generated by the hydroacoustic transducers covers 60 kHz to 4.4 MHz, while the wave propagation directions both parallel and perpendicular to the mean flow are considered. For each case, the amplitudes of all frequency components simultaneously decreases or increases under turbulence, with no new spectral components appearing. Turbulent fluctuations without mean motion can still alter the wave amplitude, while laminar flow has no effect on acoustic signals. Comparison with conventional theories and experiments indicates that mechanisms such as bubbles, resonance, scattering, or viscous dissipation cannot explain the observed phenomena. This indicates that there exists an incompletely understood new mechanism in the interaction between turbulence and acoustic waves.

Editorial analysis

A structured set of objections, weighed in public.

Desk editor's note, referee report, simulated authors' rebuttal, and a circularity audit. Tearing a paper down is the easy half of reading it; the pith above is the substance, this is the friction.

Referee Report

2 major / 2 minor

Summary. The manuscript reports experimental observations that underwater turbulence absorbs or amplifies acoustic waves at frequencies (60 kHz–4.4 MHz) far above turbulent fluctuation scales, producing amplitude changes exceeding 60% with no spectral broadening. The effect occurs in both pipe-flow and free-jet geometries, persists under pure turbulent fluctuations without mean flow, is absent in laminar flow, depends on frequency rather than amplitude, and is claimed to be unexplained by bubbles, resonance, scattering, or viscous dissipation after comparison with conventional theories.

Significance. If the observations prove free of artifacts, the result would identify a previously unrecognized turbulence–acoustic interaction at high frequencies, with potential relevance to underwater propagation, sonar, and flow diagnostics. The reported absence of spectral broadening and the persistence without mean flow are distinctive features that would challenge standard scattering and dissipation models.

major comments (2)
  1. [Experimental methods and results] The central claim that conventional mechanisms are ruled out rests on qualitative comparisons rather than quantitative bounds. No measurements of bubble void fraction, transducer linearity under matched flow conditions, or vibration spectra of the mounting hardware are reported, leaving open the possibility that undetected artifacts scaling with fluctuation intensity could produce the observed amplitude changes.
  2. [Results] The abstract and text state that amplitude changes exceed 60% and that all frequency components change simultaneously, yet no numerical values, error bars, statistical tests, or raw time-series examples are supplied. This absence makes it impossible to assess the reproducibility or magnitude of the claimed effect.
minor comments (2)
  1. [Abstract and results] The frequency range 60 kHz–4.4 MHz is stated, but the manuscript would benefit from an explicit table or list of the discrete frequencies tested together with the corresponding attenuation/amplification percentages.
  2. [Experimental setup] Notation for the two flow configurations (pipe flow versus free jet) and the two driving methods (pump versus hydraulic head) should be introduced once and used consistently when presenting the data.

Simulated Author's Rebuttal

2 responses · 0 unresolved

We thank the referee for their careful and constructive review. We address each major comment below and have revised the manuscript to strengthen the quantitative support for our claims while preserving the core observations.

read point-by-point responses

  1. Referee: The central claim that conventional mechanisms are ruled out rests on qualitative comparisons rather than quantitative bounds. No measurements of bubble void fraction, transducer linearity under matched flow conditions, or vibration spectra of the mounting hardware are reported, leaving open the possibility that undetected artifacts scaling with fluctuation intensity could produce the observed amplitude changes.

    Authors: We agree that more quantitative bounds would improve the exclusion of conventional mechanisms. In the revised manuscript we add order-of-magnitude estimates of bubble void fraction based on the experimental conditions and published values for similar water flows, together with transducer linearity data obtained under matched flow conditions. Direct vibration spectra of the mounting hardware were not recorded; however, the effect appears identically in two geometrically distinct setups, vanishes in laminar flow, and is independent of acoustic amplitude, all of which are inconsistent with vibration-induced artifacts. We include a brief quantitative discussion of expected vibration levels and why they cannot account for the observed frequency-dependent amplitude changes. revision: partial

  2. Referee: The abstract and text state that amplitude changes exceed 60% and that all frequency components change simultaneously, yet no numerical values, error bars, statistical tests, or raw time-series examples are supplied. This absence makes it impossible to assess the reproducibility or magnitude of the claimed effect.

    Authors: We accept that the presentation of results requires additional quantitative detail. The revised manuscript now reports specific peak amplitude changes (with standard deviations from repeated trials), includes error bars on all plotted data, and adds a statistical test confirming that the observed shifts are significant. Representative raw time-series segments and their spectra are provided in a new figure to illustrate the simultaneous, broadband amplitude change without spectral broadening or new components. revision: yes

Circularity Check

0 steps flagged

No circularity: purely observational claims with no derivations or self-referential reductions

full rationale

The paper reports experimental measurements of acoustic amplitude changes (up to 60%) in turbulent pipe and jet flows across 60 kHz–4.4 MHz, with and without mean flow. It states that laminar flow has no effect, fluctuations without mean motion do alter amplitude, and conventional mechanisms (bubbles, resonance, scattering, viscous dissipation) are ruled out by comparison with prior theories and experiments. No equations, fitted parameters, predictions, or derivations appear in the provided text. The conclusion of an 'incompletely understood new mechanism' follows directly from the reported observations and external comparisons rather than reducing to any internal definition, self-citation chain, or renamed input. This is a standard observational structure with no load-bearing circular steps.

Axiom & Free-Parameter Ledger

0 free parameters · 1 axioms · 0 invented entities

The central claim rests on the experimental observation that turbulence alters acoustic amplitude independently of mean flow and that conventional mechanisms are insufficient.

axioms (1)
  • domain assumption Turbulent fluctuations without mean motion can still alter acoustic wave amplitude while laminar flow does not.
    Stated as a key experimental finding used to support the new-mechanism conclusion.

pith-pipeline@v0.9.0 · 5501 in / 1016 out tokens · 64966 ms · 2026-05-17T00:19:07.006588+00:00 · methodology

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Lean theorems connected to this paper

Citations machine-checked in the Pith Canon. Every link opens the source theorem in the public Lean library.

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Reference graph

Works this paper leans on

18 extracted references · 18 canonical work pages

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