Ansys Acoustic Tutorial Pdf
Acoustic Simulation of a SilencerPosted inWhen building an HVAC system, people must often consider the noise that is generated by the flow in the ducts. To help prevent from too much noise propagation, silencers or mufflers need to be designed. This design is critical, as the result is often a trade-off between various criteria (geometry, pressure loss in the flow, transmission loss)ANSYS R18 has new out-of-the box capabilities to help engineers run multiple simulations to understand the acoustic behavior of silencers.This article showcases the process of setting up an acoustic harmonic analysis by giving you tips and tricks on how to proceed to get quick and accurate results.
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Geometry preparationAt first sight, geometry may appear complex, since both fluid and structural parts must be considered. The porous medium: here the user has to specify the properties of the equivalent fluid of the porous material. Depending on the material properties that are provided, different physical models can be used:. Johnson-Champoux-Allard (JCA):. The world of divergent the path to allegiant pdf free download. Fluid Resistivity σ,. Porosity φ,.
Tortuosity α ∞,. Viscous Characteristic Length Λ,.
Thermal Characteristic Length Λ’. Delany-Bazley (DLB):. Fluid Resistivity σ. Used when 0.01. The perforated plate: the plate is simplified by using a 2x2 transfer admittance matrix to trim the complicated perforated structure, instead of meshing it with its holes. Depending on the hole pattern, 3 models are available for the transfer matrix:. Hexagonal grid plate (HGYM).
Square grid plate (SGYM). General transfer admittance matrix (YMAT)For the first two models of grid plates, the following parameters have to be defined:.
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Holes Radius. Grid Period. Plate Thickness. For cylindrical structures, ratio of inner and outer structure (value of 1 can be taken for flat plates)If those parameters match the actual design, results will be the same as the case where the actual holes are considered.
Acoustic Exterior PortsPorts are used to locate specific acoustic regions to:. Define Transfer Admittance Matrix between two ports. Calculate Sound Power Results (input power for one port or transmission loss between two ports)Therefore, 6 acoustic exterior ports will need to be defined:. At the inlet and the outlet for transmission loss calculation (Port 1 and 2). It is advised to use Port Number 1 and 2 for Power Result Plots. At the vertical boundaries of the two perforated plates to define the transfer admittance matrixRadiation BoundaryTo avoid waves to be reflected at the inlet and the outlet, an acoustic radiation boundary is defined at the locations shown on the following figure. This condition is called the Robin condition.
Loading Normal Surface VelocityAs an excitation, a normal velocity can be applied on the inlet to simulate the sound generated by the vibration of a surface.Usually, this kind of analysis is made to get the transmission loss result (see results), which is a rate of incident of energy versus the transmitted one. The magnitude of the excitation at the inlet is thus not critical. It is however important to understand that this value is not the value of the flow speed.
MeshingMeshing is critical in this type of analysis, especially as far as the element size is concerned.The element size must be tightly related to the wavelength:To capture the sound propagation with accuracy, here are the rules to be followed:. If linear elements (no mid-side nodes) are used, at least 12 elements per wavelength are needed. If quadratic elements are used, only 6 elements per wavelength are required.Note for the meshing of the perforated plates: Trim element for transfer admittance matrix is only available for hexahedral and prism elements. For hexahedral elements, only a pair of opposite element faces can be defined as the ports.
In case of prism elements, only two triangular element faces are used for the ports. A pair of ports of the 2×2 transfer admittance matrix must be defined in the same element.
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There is no limitation on the trim element mesh size between two ports. Analysis SettingsA few steps are required:. The frequency range needs to be defined. The ‘Full Method’ must be specified. The MAPDL database needs to be saved. The ‘General Miscellaneous’ results must be calculatedSeveral options are possible to define the analysis frequency range.
The most convenient way may be to use the User Defined Frequency options and to specify the frequencies at which data are usually given for acoustic absorbers i.e. The center frequencies of octave bands (63 Hz, 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 4000 Hz, 8000 Hz). ResultsThe acoustic pressure at each analysis frequency can be plotted and animated. Figure 1: Acoustic Pressure @2000HzThe most common requested result is the transmission loss curve. The Transmission Loss (TL in dB) is the rate of incident sound power which is transmitted through the system:To define this result, simply ask for an ‘Acoustic Power Result Plot’ using the acoustic exterior ports 1 and 2 which are associated to inlet and outlet (respectively) defined in the boundary conditions.Or in a logarithmic scale (as it is usually provided): ConclusionThe solution took less than one minute to solve with 2 cores.
It would be very easy and fast to optimize the design of a silencer using DesignXplorer. One would simply need to define parameters such as geometrical dimensions and/or material properties like porous medium resistivity, maximum transmission loss, etc. Adopting simulation driven product development would be beneficial in this case since evaluating multiple virtual prototypes would be much better than the classical process of making real prototypes and testing them.
No one is providing the download link for the above tutorial. What is the use of this discussion? No one is getting the benefit of this discussion forum.The number of the tutorials are provided in the ANSYS FLUENT Tutorial Guide pdf for practicing but we are unable to find the link of resources file for downloading and practicing. How one can do the practice without the resource files.Please provide the downloading link of the above tutorial not only for the above tutorial but also for the remaining tutorial as well which are described in the ANSYS FLUENT Tutorial Guide pdf.