Aeroacoustics Noise Simulation Setup using Ansys Fluent

Introduction

• This is the second part of the tutorial on calculating aeroacoustics noise using Ansys Fluent.
• Focuses on setting up the simulation.

Model Setup

Initial Steps

• Click on Setup and hit Start.
• Green surface: inlet, black surfaces with arrows: outlets, red walls: no arrows.

Material Properties

• Airflow is compressible.
• Air density: Change from constant to ideal gas.
• Enable Energy as density depends on temperature in the ideal gas model.

Boundary Conditions

Inlet

• Specify velocity: 20 m/s (no mass flow or inlet velocity values).

Outlet

• Default setting: 0 gauge pressure (appropriate, no changes required).

Solver Settings

Methods Section

• Two schemes: Coupled and PISO (use Coupled).
• Disable Pseudo time method due to low air speed.

Controls

• Courant number: Adjust to increase convergence speed (demonstration purpose: initially unchanged).

Initialization

• Use Standard Initialization for internal flows.
• Select inlet and click Initialize.

Running Calculation

• Specify 50 iterations and click Calculate.
• Adjust Courant number to 5 due to non-convergence.
• Run calculation again.

Preparing Aeroacoustics Solution

Viscous Model

• Change to LES or DES (select LES for example).
• Requires highly refined mesh (recommend mesh dependency investigation).
• LES and DES are Transient models.

Methods Section for Aeroacoustics

• Choose between PISO or Coupled (PISO recommended for lower computational cost).
• Change from first order to bounded second order.

Run Aeroacoustics Calculation

• Specify time step size.
• Check solution convergence with 10 time steps.
• Run and converge in one iteration using stationary solution.

Enabling Acoustics

Ffowcs-Williams-Hawkings Model

• Enable acoustics and select model.
• Export acoustic source data.
• Identify permeable surface in internal boundaries.

Adding Microphones

• Specify 4 microphones relative to air muffler (origin).
• Ensure fine mesh and verify mesh independence.

Solving and Extracting Acoustic Signals

• Solve for 200 time steps (0.01 seconds, frequency resolution 100 Hz).
• Extract acoustic signals.
• Use FFT to view sound pressure level versus frequency.
  • Select microphone (e.g., Receiver 2).
  • Plot sound pressure level.
• Increase steps to improve frequency resolution (e.g., additional 300 steps for 40 Hz resolution).

Conclusion

• Continue simulation for better frequency resolution (aim for 10 Hz).
• Tutorial ends, covered aeroacoustics with Ffowcs-Williams-Hawking method.