# Aeroacoustic

This document describes how to perform aeroacoustic signal processing in Flow360.

# 📊 Analysis Interface

The Analysis interface provides comprehensive tools for analyzing acoustic data through various representations and processing methods.

# 📋 Available Plots

View Type Description
Spectra Frequency-domain representation of acoustic signals.
OASPL Overall Sound Pressure Level analysis across frequency spectrum. To download the OASPL file, click on three dots next to plot type.
Pressure-time history Temporal evolution of pressure fluctuations at the location of the observer.
Harmonic content SPL values at the harmonic frequency and its associates. To download the tonal OASPL file, click on three dots next to plot type when Harmonic content is selected.
Thickness and loading component Thickness, loading and total pressure components.

# 🔧 Processing Options

# Observers

List of selectable observers based on their group for which the analysis will be performed.

# Boundaries

List of selectable boundaries for which the analysis will be performed. Total is selected by default and refers to the aggregate of all boundaries.

# Frequency Range

Parameter Description Default Range Unit
Frequency range Range of frequencies to perform the analysis 10 - 10000 Hz

# Averaging Settings

Option Description
Number of segments Number of segments used for averaging
Segmentation method Method for dividing the signal into multiple segments for averaging: RPM-based or Time interval-based

# Signal Processing Options

Option Description
Use 1/3 octave band Apply 1/3 octave band filtering for frequency analysis
Use A-weighting Apply A-weighting curve to better represent human hearing perception
Welch method Apply Welch method for calculating spectra

# Welch Method Parameters

Parameter Description Options
Segment length Length of segments for Welch's method analysis None or user-specified value
Scaling Scaling method for power spectrum calculation Spectrum, Density
Average Statistical method for averaging across segments Mean, Median

# 🔍 Detailed Descriptions

# Frequency Range Configuration

The frequency range setting determines the span of frequencies included in the acoustic analysis:

  • Default range: 10 Hz to 10000 Hz

Note: This range is used for the analysis, not just the display.

# Averaging Configuration

The averaging system allows for detailed control over how the acoustic data is processed:

  • Default segments: 1
  • Segmentation options:
    • RPM-based: Suitable for rotating machinery analysis
    • Time interval-based: General purpose, with configurable time step

# Welch Method Settings

It can be used for calculating spectra.

  • Segment length options:
    • None: Automatic segment length determination (default)
    • Value: User-specified custom segment length
  • Scaling options:
    • Spectrum: Power spectrum scaling (default)
    • Density: Power spectral density scaling
  • Averaging methods:
    • Mean: Arithmetic mean across segments (default)
    • Median: Median value across segments

💡 Tips
  • Use A-weighting to reflect how humans perceive noise.
  • Use options to improve comparison between observers and to validate results against experimental data.
  • Use different types of analysis for comparison to identify potential sources of noise.
  • Compare different types of analysis to qualitatively differentiate between deterministic and non-deterministic types of noise.

❓ Frequently Asked Questions

  • What is the recommended number of segments for averaging?

    The default value of 1 segment calculates the average across all segments. The number of segments for averaging should be chosen to ensure each segment contains sufficient data to resolve the highest frequency of interest for a representative, continuously averaged signal. As a guideline, the total number of data after averaging should contain at least twice the frequency of interest.

  • When should I use A-weighting?

    Apply A-weighting when comparing results to human perception or when meeting certification requirements that specify A-weighted sound levels.

  • What is the difference between RPM and Time interval segmentation?

    RPM-based segmentation is useful for rotating machinery analysis, where one revolution is used to segment unsteady data. Time-interval segmentation is more general and applicable to all unsteady simulations. Note that when using time-interval segmentation, the interval must NOT be smaller than the simulation time step.

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