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    SimScale DocumentationValidation CasesValidation Case: Choked Flow Due to Cavitation

    Validation Case: Choked Flow Due to Cavitation

    This validation case belongs to computational fluid dynamics and aims to validate the following parameters:

    Simulation results were compared to experimental results available in the article “Characterization of high-pressure cavitating flow through a thick orifice plate in a pipe of constant cross-section“\(^1\), by Ebrahimi et al.

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    Geometry

    This validation case uses a simple straight pipe section with an orifice plate, where the arrows indicate the flow direction:

    cavitation pipe geometry
    Figure 1: Pipe geometry based on the experimental setup

    The dimensions of the pipe are listed below:

    DimensionValue \([mm]\)
    Inlet diameter28.5
    Inlet section length12.7
    Orifice plate diameter6.35
    Orifice plate length12.7
    Outlet diameter28.5
    Outlet section length44.45
    Table 1: Geometry dimensions

    The reference study tackles multiple scenarios, with various combinations of pressures at the inlet and outlet. This validation case focuses on the harshest scenario explored by the reference study, with an inlet pressure of 5000 \(psi\).

    Analysis Type and Mesh

    Analysis Type: Steady-state, Multi-purpose with k-epsilon and Cavitation model

    Mesh and Element Types:

    The mesh was created with SimScale’s Multi-purpose mesh type, which is a body-fitted structured mesh. A manual sizing definition relative to the CAD was used.

    Mesh TypeMinimum Cell SizeMaximum Cell SizeCell Size on SurfacesNumber of cellsElement Type
    Manual1e-5 (relative)0.005 (relative)0.0025 (relative)11379163D Hexahedral
    Table 2: Mesh data for the choked flow due to cavitation validation case
    cavitating choked flow pipe mesh
    Figure 2: Multi-purpose meshing performed on the valve with refinement around the edge of the valve

    Simulation Setup

    Material

    Fluid:

    • Water
      • Kinematic viscosity \((\nu)\): 5.5668e-7 \(m^2/s\)
      • Density \((\rho)\): 988 \(kg/m^3\)
      • Vapor molecular weight: 18 \(kg/kmol\)
      • Liquid bulk modulus: 2.15e9 \(Pa\)
      • Liquid bulk modulus coefficient: 0
      • Liquid reference pressure: 1.01325e5 \(Pa\)
      • Saturation pressure: 1.234162e4 \(Pa\)
      • Liquid temperature: 48.9 \(°C\)

    Boundary Conditions

    Using Figure 1 as a base, the table below provides the boundary conditions used in the setup:

    Boundary ConditionValue
    Pressure inlet \([psi]\)5000 (total pressure)
    Pressure outlet \([psi]\)345; 506; 1101; 2052; 2502; 2813 (fixed gauge pressure)
    No-slip wallPipe walls and orifice plate
    Table 3: Boundary conditions for pipe and valve

    Result Comparison

    As the delta pressure between the inlet and outlet increases, a low-pressure region in the orifice causes bubbles to arise. These bubbles will occupy a portion of the orifice’s cross-section, limiting the amount of water that can go through, which causes a choked flow phenomenon.

    Therefore, the main parameter of interest is the volumetric flow rate through the system, using the inlet as a reference. The table below summarizes the results:

    Outlet Pressure \([psi]\)Volumetric Flow Rate – Reference \([GPM]\)Volumetric Flow Rate – Simulation \([GPM]\)Error
    34577.081.85.9%
    50677.181.85.7%
    110177.181.85.7%
    205277.081.04.9%
    250275.272.4-3.9%
    281370.767.9-4.1%
    Table 4: Result comparison between the reference study and the simulation results

    Overall, the Multi-purpose solver was able to predict the flow behavior over a wide range of pressures, including choked flow behavior for outlet pressures of around 2050 \(psi\) or less.

    In the post-processor, cavitation is observed by monitoring density and gas volume fractions. The images below show the behavior for the case with the outlet pressure equal to 345 \(psi\).

    cavitating flow density choked
    Figure 3: Low-pressure regions (blue) indicate the formation of bubbles, causing the density to greatly decrease

    The bubbles close to the wall limit the cross-section area that water can flow through, choking the flow. The gas volume fraction shows this behavior more clearly:

    cavitating flow gas volume fraction water
    Figure 4: Bubbles (red) in the orifice plate region

    References

    Note

    If you still encounter problems validating your simulation, then please post the issue on our forum or contact us.

    Last updated: September 11th, 2024

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