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<p>Hi,</p>
<p>It is known that at least some hydro schemes used in Flash can
produce anomalies near the symmetry axis for specific flows:
Blondin & Lufkin
<a class="moz-txt-link-freetext" href="https://ui.adsabs.harvard.edu/abs/1993ApJS...88..589B/abstract">https://ui.adsabs.harvard.edu/abs/1993ApJS...88..589B/abstract</a></p>
<p>Basically it turns out that treating the symmetry axis as a
reflecting boundary is not quite good enough.<br>
</p>
<p>I'm pretty sure that the "fix" discussed in that paper is not
implemented for the split solver in flash but I'm less sure of the
unsplit solver.</p>
<p>Or what you are seeing could be something else, but I figured it
might be useful to mention this known issue.</p>
<p>Dean<br>
</p>
<p><br>
</p>
<div class="moz-cite-prefix">On 2/22/21 3:53 AM, Thibault Goudal
wrote:<br>
</div>
<blockquote type="cite"
cite="mid:704272321.4366485.1613987607656.JavaMail.zimbra@u-bordeaux.fr">
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12pt; color: #000000">
<div>Hi everyone,</div>
<div><br>
</div>
<div>I've been runing 2D cylindrical FLASH simulations based on
the LaserSlab setup.</div>
<div>I would like to study the evolution of hydrodynamic
instabilities at the ablation front.</div>
<div><br>
</div>
<div>I attached bellow an illustration of the density map
results. I only run the right side. The left part is built by
the symmetry with the white axis at x=0.</div>
<div>In white color, I circled what is my concern. This bubbly
structure seems to show that the boundary symmetry at the left
edge of the numerical box isn't what I expected to be a flat
laser irradiation.<br>
</div>
<div>It seems that at x=0, the laser deposition is lower. At
late times, this impacts the instability growth on the axis.<br
data-mce-bogus="1">
</div>
<div><br data-mce-bogus="1">
</div>
<div>I used the "reflect" or "axisymmetric" hydro boundary on
the axis. <br data-mce-bogus="1">
</div>
<div>I also attached some parameters from the flash.par which
could be relevant to fix my issue.<br data-mce-bogus="1">
</div>
<div><br data-mce-bogus="1">
</div>
<div>I guess this is kind of a typical problem when you deal
with such geometry.<br data-mce-bogus="1">
</div>
<div>If you have any idea, I'll be glad to discuss about all of
this.<br data-mce-bogus="1">
</div>
<div><br data-mce-bogus="1">
</div>
<div>Thank you!<br data-mce-bogus="1">
</div>
<div><br>
</div>
<div><br>
</div>
<div><br>
# RADIATION/OPACITY BOUNDARIES<br>
<br>
rt_mgdXlBoundaryType = "reflecting"<br>
rt_mgdXrBoundaryType = "vacuum"<br>
rt_mgdYlBoundaryType = "vacuum"<br>
rt_mgdYrBoundaryType = "vacuum"<br>
rt_mgdZlBoundaryType = "reflecting"<br>
rt_mgdZrBoundaryType = "reflecting"</div>
<div><br>
</div>
<div><!--StartFragment-->#CONDUCTION
<!--StartFragment-->BOUNDARIES<!--EndFragment--> <br>
<br>
diff_eleXlBoundaryType = "neumann"<br>
diff_eleXrBoundaryType = "neumann"<br>
diff_eleYlBoundaryType = "neumann"<br>
diff_eleYrBoundaryType = "neumann"<br>
diff_eleZlBoundaryType = "neumann"<br>
diff_eleZrBoundaryType = "neumann"<br>
<br>
#HYDRO
<!--StartFragment-->BOUNDARIES<!--EndFragment--><br>
<br>
# Hydro boundary conditions:<br>
xl_boundary_type = "reflect"<br>
xr_boundary_type = "outflow"<br>
yl_boundary_type = "outflow"<br>
yr_boundary_type = "outflow"<br>
zl_boundary_type = "reflect"<br>
zr_boundary_type = "reflect"<br>
<!--EndFragment--> <br>
# LASER PARAMETERS <br>
<br>
ed_laser3Din2D = .true.<br>
ed_laser3Din2DwedgeAngle = 0.1<br>
<br>
ed_lensX_1 = 1000.0e-04<br>
ed_lensY_1 = 0.0e-04<br>
ed_lensZ_1 = -1000.0e-04<br>
ed_lensSemiAxisMajor_1 = 1000.0e-04<br>
ed_lensSemiAxisMinor_1 = 1000.0e-04<br>
ed_targetX_1 = 0.0e-04<br>
ed_targetY_1 = 0.0e-04<br>
ed_targetZ_1 = 1400.0e-04<br>
ed_targetSemiAxisMajor_1 = 1000.0e-04<br>
ed_targetSemiAxisMinor_1 = 1000.0e-04<br>
ed_pulseNumber_1 = 1<br>
ed_wavelength_1 = 0.351<br>
ed_crossSectionFunctionType_1 = "gaussian2D"<br>
ed_gaussianExponent_1 = 4.0<br>
ed_gaussianRadiusMajor_1 = 900e-04<br>
ed_gaussianRadiusMinor_1 = 900e-04<br>
ed_numberOfRays_1 = 16384<br>
ed_gridType_1 = "radial2D"<br>
ed_gridnRadialTics_1 = 512<br>
ed_semiAxisMajorTorsionAngle_1 = 0.0<br>
ed_semiAxisMajorTorsionAxis_1 = "x"<br>
<br>
<br>
<br>
<br>
</div>
<div><br>
</div>
<div data-marker="__SIG_POST__">--</div>
<div>
<div style="text-align: left;" data-mce-style="text-align:
left;"><span style="color: #000000;" data-mce-style="color:
#000000;">Thibault Goudal</span></div>
<div style="text-align: left;" data-mce-style="text-align:
left;"><span style="color: #000000;" data-mce-style="color:
#000000;">PhD Student CEA</span></div>
<div style="text-align: left;" data-mce-style="text-align:
left;"><span style="color: #000000;" data-mce-style="color:
#000000;">CELIA CNRS UMR5107 laboratory</span></div>
<div style="text-align: left;" data-mce-style="text-align:
left;"><span style="color: #000000;" data-mce-style="color:
#000000;">+33664160842</span></div>
<div style="text-align: left;" data-mce-style="text-align:
left;"><span style="color: #000000;" data-mce-style="color:
#000000;"><a class="moz-txt-link-abbreviated" href="mailto:thibault.goudal@u-bordeaux.fr">thibault.goudal@u-bordeaux.fr</a><br>
</span></div>
</div>
</div>
</blockquote>
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