Windtunnel/Boundary Conditions - Revision history

Lothar.brendel: major tidying, focus on a manual for the user_defined_parameters, 2 new pages for the problems

2025-05-23T15:56:23Z

major tidying, focus on a manual for the user_defined_parameters, 2 new pages for the problems

← Older revision		Revision as of 17:56, 23 May 2025
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	[[Windtunnel online\|up]]		[[Windtunnel online\|up]]

	= New ~~Keywords~~ =		= New user_defined_parameters in pluto.ini =

	== in ~~pluto~~.~~ini ==~~		* <code>KinematicViscosity_m2_per_s</code>, <code>DynamicViscosity_Pa_s</code>: read in ''visc_nu.c''

	* <code>ObjectType_int</code>: 0=~~nothing, 1~~=~~cylinder/sphere, 2~~=~~square/cube of size <code>ObjectDiameter_cm</code>~~		== for Domain Boundaries ==
	* <code>WindPressure_Pa</code>, <code>WindPressure_mbar</code> (mutually exclusive): pressure at entry (left)
	* <code>PressureGradient_mbar_per_cm</code> positive (even though pressure drops from left to right)
	* Wind velocity is ramped up to <code>WindVelocity_m_per_s</code> over time <code>InjectionTime_s</code>
	* <code>WindTemperature_C</code>
	* <code>KinematicViscosity_m2_per_s</code>, <code>DynamicViscosity_Pa_s</code>,
	* <code>Wall_BoundaryCondition</code> for tangential walls, value from {0,1,2,3}

	~~(ignored if given values <0)~~		* <code>Wall_BoundaryCondition</code> for tangential walls (X2_BEG, X2_END), value from {0,1,2,3}:
			{\| class="wikitable"
	~~== in init.c ==~~		! value \|\| [[:File:WT- Boundary Condition Skizze.jpg\|meaning]] \|\| VX1 \|\| VX2

	* ~~macro~~ <code>~~SOLID~~</code> ~~to enable an object~~
	* array <code>solid</code> containing value 1 ~~or 0 for object matter being present/absent~~

	= ~~Walls =~~
	[[File:WT- Boundary Condition Skizze.jpg\|~~thumb~~]]

	~~== tangential ==~~

	~~{\| class="wikitable" id="ganz_oben"~~
	~~\|+ id="Ü-id" \|~~
	~~\|- id="K-id"~~
	~~!colspan="3"\| Boundary condition for the wall~~
	~~\|- id="Sprungziel1"~~
	\| \|\| ~~vx1~~ \|\| ~~vx2~~
	\|-		\|-
	\| no-shear \|\| zero-gradient \|\| reflective		\| 0 \|\| no-shear \|\| zero-gradient \|\| reflective
	\|-		\|-
	\| no-slip \|\| reflective \|\| reflective		\| 1 \|\| no-slip \|\| reflective \|\| reflective
	\|-		\|-
	\| no-wall \|\| zero-gradient \|\| zero-gradient		\| 2 \|\| no-wall \|\| zero-gradient \|\| zero-gradient
	\|-		\|-
	\| one-way wall \|\| zero-gradient \|\| zero-gradient & no-inflow		\| 3 \|\| one-way wall \|\| zero-gradient \|\| zero-gradient & no-inflow
	\|}		\|}

	== entry/~~exit ==~~		* <code>WindPressure_Pa</code>, <code>WindPressure_mbar</code> (mutually exclusive): pressure at entry (X1_BEG)
			* <code>PressureGradient_mbar_per_cm</code>:
			** driving the flow if positive<sup>1</sup>
			** ignored if negative, then ''WindVelocity'' is driving the flow.
			* <code>WindVelocity_m_per_s</code>, <code>InjectionTime_s</code>: Wind velocity at entry (X1_BEG) is ramped up from 0 to the given value over the given time (if pressure gradient < 0 is specified).
			* <code>WindTemperature_C</code>: determines density (via pressure) at entry (X1_BEG)

	~~=== prescribed velocity at entry (~~left~~) ===~~		<sup>1</sup>: even though pressure ''drops'' from left to right

	==~~= prescribe pressure drop (left to right) =~~==		== for Solid Object ==

	* current simulation result: $~~v_x$-profile slightly asymmetric and $v_x~~<0$ ~~at one wall~~		(needs <code>SOLID = YES</code> in ''makefile_user_machinedefs'')

			* <code>ObjectType_int</code>:
			** 0 = nothing
			** 1 = cylinder/sphere of diameter <code>ObjectDiameter_cm</code> centered on the origin
			** 2 = square/cube of edge length <code>ObjectDiameter_cm</code> centered on the origin
			** $-n$ = File ''solid.txt'' contains (at most) $n$ voxels (lines of $x~y~z$). Voxels outside the origin-centered sphere of radius 0.6·<code>ObjectDiameter_cm</code> are discarded.

	= ~~Object~~ =		* <code>Obj_BoundaryCondition</code>:
			** -1 = no-slip
			** <s>1 = no-shear</s> (unavailable due to an [[Windtunnel/Boundary_Conditions/on_Object\|unresolved issue]])

	* Strong asymmetry when driven by pressure gradient. Bug!		= Analytical Solutions =
	~~[[File:Asymmetry.png\|thumb\|center\|500px\|$v_y$ is not symmetric to the $x$-axis.]]~~
	* At the boundary of a region which has <code>FLAG_INTERNAL_BOUNDARY</code> set, '''no''' boundary conditions are specified. Ghostcells are frozen.
	* Rolfs proposition for the object boundary: Set the mass ''flux'' at the boundary to zero after the Riemann solver has computed it.

	~~= Open Questions =~~		(for comparisons)

	~~== Reflective cells ==~~

	~~Setting the vector \~~(~~\vec v_g\~~) in a ghost cell as $\vec v_g=-\vec v$, with $\vec v$ being the value in the adjacent real cell, yields $\vec 0$ as interpolation right at the boundary. This works for plane walls. What to do in cases where a ghost cell has more than one real cell as nearest neighbor? This calls for [[Talk:Windtunnel/Boundary_Conditions\|discussion]]!

	~~= Analytical Solutions =~~

	== empty 2D channel ==		== empty 2D channel ==

Lothar.brendel: /* Object */ flux 0

2024-10-29T13:48:48Z

Object: flux 0

← Older revision		Revision as of 15:48, 29 October 2024
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	[[File:Asymmetry.png\|thumb\|center\|500px\|$v_y$ is not symmetric to the $x$-axis.]]		[[File:Asymmetry.png\|thumb\|center\|500px\|$v_y$ is not symmetric to the $x$-axis.]]
	* At the boundary of a region which has <code>FLAG_INTERNAL_BOUNDARY</code> set, '''no''' boundary conditions are specified. Ghostcells are frozen.		* At the boundary of a region which has <code>FLAG_INTERNAL_BOUNDARY</code> set, '''no''' boundary conditions are specified. Ghostcells are frozen.
			* Rolfs proposition for the object boundary: Set the mass ''flux'' at the boundary to zero after the Riemann solver has computed it.

	= Open Questions =		= Open Questions =

Lothar.brendel: /* Object */ polished thumb

2024-10-22T15:48:04Z

Object: polished thumb

← Older revision		Revision as of 17:48, 22 October 2024
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	* Strong asymmetry when driven by pressure gradient. Bug!		* Strong asymmetry when driven by pressure gradient. Bug!
	[[File:Asymmetry.png\|thumb\|~~It shows that vx2~~ is not symmetric to the ~~y=0~~ axis.]]		[[File:Asymmetry.png\|thumb\|center\|500px\|$v_y$ is not symmetric to the $x$-axis.]]
	* At the boundary of a region which has <code>FLAG_INTERNAL_BOUNDARY</code> set, '''no''' boundary conditions are specified.		* At the boundary of a region which has <code>FLAG_INTERNAL_BOUNDARY</code> set, '''no''' boundary conditions are specified. Ghostcells are frozen.

	= Open Questions =		= Open Questions =

Shaghie: /* Object */

2024-10-22T13:51:29Z

Object

← Older revision		Revision as of 15:51, 22 October 2024
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	* current simulation result: $v_x$-profile slightly asymmetric and $v_x<0$ at one wall		* current simulation result: $v_x$-profile slightly asymmetric and $v_x<0$ at one wall


	= Object =		= Object =

	* Strong asymmetry when driven by pressure gradient. Bug!		* Strong asymmetry when driven by pressure gradient. Bug!
			[[File:Asymmetry.png\|thumb\|It shows that vx2 is not symmetric to the y=0 axis.]]
	* At the boundary of a region which has <code>FLAG_INTERNAL_BOUNDARY</code> set, '''no''' boundary conditions are specified.		* At the boundary of a region which has <code>FLAG_INTERNAL_BOUNDARY</code> set, '''no''' boundary conditions are specified.

Lothar.brendel: /* Object */ asymmetry, no BCs

2024-10-22T12:53:15Z

Object: asymmetry, no BCs

← Older revision		Revision as of 14:53, 22 October 2024
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	= Object =		= Object =

			* Strong asymmetry when driven by pressure gradient. Bug!
			* At the boundary of a region which has <code>FLAG_INTERNAL_BOUNDARY</code> set, '''no''' boundary conditions are specified.

	= Open Questions =		= Open Questions =

Lothar.brendel: /* empty circular tube */ z

2024-10-10T19:53:26Z

empty circular tube: z

← Older revision		Revision as of 21:53, 10 October 2024
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	$$		$$
	v(r) = \frac{\Delta p}{L}\frac{R^2-r^2}{4\mu}		v_z(r) = \frac{\Delta p}{L}\frac{R^2-r^2}{4\mu}
	$$		$$

	with $\mu$=dynamical viscosity		with $\mu$=dynamical viscosity

Lothar.brendel: /* empty 2D channel */ xy

2024-10-10T19:53:06Z

empty 2D channel: xy

← Older revision		Revision as of 21:53, 10 October 2024
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	$$		$$
	v(r) = \frac{\Delta p}{L}\frac{D^2/4-r^2}{2\mu}		v_x(y) = \frac{\Delta p}{L}\frac{D^2/4-y^2}{2\mu}
	$$		$$

Lothar.brendel: /* empty 2D channel */ 1/2

2024-10-02T09:05:18Z

empty 2D channel: 1/2

← Older revision		Revision as of 11:05, 2 October 2024
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	== empty 2D channel ==		== empty 2D channel ==

			$$
			v(r) = \frac{\Delta p}{L}\frac{D^2/4-r^2}{2\mu}
			$$

	== empty circular tube ==		== empty circular tube ==

Lothar.brendel: /* empty circular tube */ dp/L

2024-10-02T08:53:48Z

empty circular tube: dp/L

← Older revision		Revision as of 10:53, 2 October 2024
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	$$		$$
	v(r) = \frac{\~~text dp~~}{~~\text dx~~}\frac{R^2-r^2}{4\mu}		v(r) = \frac{\Delta p}{L}\frac{R^2-r^2}{4\mu}
	$$		$$

	with $\mu$=dynamical viscosity		with $\mu$=dynamical viscosity

Lothar.brendel: HG_3D

2024-10-02T08:51:50Z

HG_3D

← Older revision		Revision as of 10:51, 2 October 2024
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	Setting the vector $\vec v_g$ in a ghost cell as $\vec v_g=-\vec v$, with $\vec v$ being the value in the adjacent real cell, yields $\vec 0$ as interpolation right at the boundary. This works for plane walls. What to do in cases where a ghost cell has more than one real cell as nearest neighbor? This calls for [[Talk:Windtunnel/Boundary_Conditions\|discussion]]!		Setting the vector $\vec v_g$ in a ghost cell as $\vec v_g=-\vec v$, with $\vec v$ being the value in the adjacent real cell, yields $\vec 0$ as interpolation right at the boundary. This works for plane walls. What to do in cases where a ghost cell has more than one real cell as nearest neighbor? This calls for [[Talk:Windtunnel/Boundary_Conditions\|discussion]]!

			= Analytical Solutions =

			== empty 2D channel ==



			== empty circular tube ==

			$$
			v(r) = \frac{\text dp}{\text dx}\frac{R^2-r^2}{4\mu}
			$$

			with $\mu$=dynamical viscosity