Loading the Starting Simulation File

For this tutorial, you are provided with an input file that contains the mesh around the pipe bounded by the spherical pressure outlet boundary.

Due to the large number of cells, and the time it takes the solver to run, you are advised to launch this tutorial on at least 4 cores.
To load the starting simulation file:
  1. Start a double-precision version of Simcenter STAR-CCM+ and select File > Open.
  2. In the Load a File dialog:
    1. Select an appropriate parallel option and set Compute Processes to at least 4.
      For more information on parallel options, see Process Options.
    2. Click Browse.
    3. In the Open dialog, navigate to the aeroacoustics folder of the downloaded tutorial files and select SL_tailpipe_start.sim.
    4. Click Open, then OK.
  3. Expand the following nodes and review some of the pre-defined settings:
    Scenes


    The Mesh scene displays the imported volume mesh:


    The cylindrical pipe is in the center of the computational domain. The mesh uses trimmed cells with embedded refinement and two prism layers around the jet nozzle geometry. For a sponge layer model simulation, you are advised to place the surrounding outflow boundary, here the pressure outlet boundary, at a sufficient distance from the noise sources to reproduce the acoustic behavior of the far-field, that is, far enough away from the source of the acoustic waves. To save cells, an outer ring of cells that coarsens towards the pressure outlet is extruded from an internal interface.

    For aeroacoustics simulations, you bear in mind two main requirements when generating a high-quality mesh:

    • The mesh must resolve the sound-generating turbulence scales
    • The mesh must resolve the propagating acoustic waves up to the desired frequency.

    Usually, to address the large disparity between the length scales of the turbulent structures and the length scales of the sound waves, the mesh that you create consists of two different areas with different mesh densities.

    The cell size in the acoustic propagation area is chosen such as to resolve the acoustic waves up to an upper frequency limit, which is f = 500 ⁢   Hz for this tutorial. To ensure a mesh resolution of 20 cells per wavelength (points per wavelength—PPW), you estimate the cell size as:

    Δ ⁢ x = λ 20 = c f 20 = 347 ⁢   m/ s 500 ⁢     1 / s 20 = 0.0347 ⁢ m

    where λ is the wavelength and c is the speed of sound of air.

    At the pressure probe, the mesh must properly resolve the acoustic waves. This requirement translates to the acoustic waves having to propagate from the source of noise, the jet nozzle, to the probes with minimal numerical dissipation. The decay in amplitude due to numerical dissipation is proportional to the propagation distance, measured in number of wavelengths. For this tutorial mesh, in the space separating the noise source from the pressure probe, the cell size is around 0.045 m, which is close to the estimated value of 0.0347 m.

    You can verify if the cell size is sufficient to resolve the turbulent structures from a precursor steady RANS simulation by using the Mesh Frequency Cutoff field function. For more information, see Visualizing the Mesh Frequency Cutoff Hz Contour.

    Regions


    Region_1 represents the fluid domain including the internal volume of the tailpipe and the environment. The following boundaries are available:
    • Interface - Inner, Interface - Outer—the two sides of the internal interface that connects the trimmed mesh with the outer ring of extruded cells.
    • Pipe Inlet—a mass flow inlet boundary.
    • Pipe Walls—a wall boundary with non-slip condition
    • Pressure Outlet—a pressure outlet boundary
    Derived Parts


    The starting file contains two derived parts:
    • Plane Section—a plane section that cuts through the center of the simulation domain.
    • Pressure Probe—a point probe that is placed 0.75 m above the jet nozzle.
    Plots


    The Pressure Monitor Plot is set up to display the pressure at the point probe over time.
    Tools > Tables


    The table noSL_pressureProbe lists the pressure over time at the point probe for a simulation of this tutorial without using the Sponge Layer model. After the simulation run of this tutorial you compare the results with the tabulated values.
  4. Save the simulation as SL_tailpipe_run.sim.