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Averaged inflow velocity #833

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Averaged inflow velocity #833

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@LasNikas LasNikas commented Jun 15, 2025 •
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The animation below shows a pulse wave propagation scenario (with reference_pressure_in = 5000 and reference_pressure_out = 0). In the upper part, the simulation is performed without averaging the extrapolated inflow velocity. In the lower part, the same simulation is shown, but with the inflow velocity averaged, leading to a more stable simulation.

When no velocity is prescribed at the inflow, the velocity is extrapolated from the fluid domain.
Thus, turbulent flows near the inflow can lead to non-uniform buffer-particles distribution, resulting in a potential numerical instability. Averaging mitigates these effects.

# Without averaged inflow velocity
trixi_include(@__MODULE__, joinpath(examples_dir(), "fluid", "pipe_flow_2d.jl");
              open_boundary_layers=14, domain_size=(2.0, 0.4), tspan=(0.0, 2.0),
              open_boundary_model=BoundaryModelTafuni(),
              pressure=0.0, wcsph=true, particle_spacing=0.02,
              saving_callback=SolutionSavingCallback(dt=5e-3, prefix=""),
              particle_shifting=ParticleShiftingCallback(),
              average_inflow_velocity=false,
              reference_velocity_in=nothing, reference_density_in=nothing,
              reference_velocity_out=nothing, reference_density_out=nothing,
              reference_pressure_in=5000, reference_pressure_out=0)

# With averaged inflow velocity
trixi_include(@__MODULE__, joinpath(examples_dir(), "fluid", "pipe_flow_2d.jl");
              open_boundary_layers=14, domain_size=(2.0, 0.4), tspan=(0.0, 2.0),
              open_boundary_model=BoundaryModelTafuni(),
              pressure=0.0, wcsph=true, particle_spacing=0.02,
              saving_callback=SolutionSavingCallback(dt=5e-3, prefix="averaged"),
              particle_shifting=ParticleShiftingCallback(),
              average_inflow_velocity=true,
              reference_velocity_in=nothing, reference_density_in=nothing,
              reference_velocity_out=nothing, reference_density_out=nothing,
              reference_pressure_in=5000, reference_pressure_out=0)
averaged_velocity_.mp4

Snapshot after 1.5 sec: highlighting more stable simulation even with no-slip BC
(the simulation without averaged inflow velocity fails at 0.11 sec).
image

LasNikas added 18 commits June 11, 2025 16:46
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codecov bot commented Jun 17, 2025 •
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Codecov Report

Attention: Patch coverage is 88.88889% with 2 lines in your changes missing coverage. Please review.

Project coverage is 70.49%. Comparing base (785ade6) to head (5eaa528).

Files with missing lines Patch % Lines
src/schemes/boundary/open_boundary/mirroring.jl 86.66% 2 Missing ⚠️
Additional details and impacted files 
@@            Coverage Diff             @@
##             main     #833      +/-   ##
==========================================
+ Coverage   70.43%   70.49%   +0.05%     
==========================================
  Files         106      106              
  Lines        6867     6884      +17     
==========================================
+ Hits         4837     4853      +16     
- Misses       2030     2031       +1
Flag Coverage Δ
unit 70.49% <88.88%> (+0.05%) ⬆️

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@LasNikas LasNikas marked this pull request as ready for review June 17, 2025 19:24
@LasNikas LasNikas requested review from efaulhaber and svchb June 17, 2025 19:24
@LasNikas LasNikas self-assigned this Jun 18, 2025
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/run-gpu-tests

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