Yap correction - Revision history

Kett: Elaboration on calculating $y_n$ needed for the Yap correction

2010-11-09T18:55:55Z

Elaboration on calculating <math>y_n</math> needed for the Yap correction

← Older revision		Revision as of 18:55, 9 November 2010
Line 34:		Line 34:
	==Implementation issues==		==Implementation issues==

-	The Yap source term contains the explicit distance to the nearest wall, <math>y_n</math>. ~~In an unstructured 3D solver this~~ distance is ~~usually not available and it can be ambiguous how~~ to ~~compute it~~ in ~~more~~ complex topologies. This makes the Yap correction most suitable for use in a structured code where ~~the~~ normal wall distance is readily available. There are several alternative formulations that can be used instead though ''(anyone have the references??)''.	+	The Yap source term contains the explicit distance to the nearest wall, <math>y_n</math>. This distance is sometimes difficult to efficiently calculate in complex geometries. In structured grids, the coordinate distance to the nearest wall can be used as an approximation. Otherwise, a brute force calculation must be used which greatly benefits from a multi grid approach. In topologies with domain boundaries that are not walls the problem becomes more complex, because the non-wall boundaries will block the direct path to the wall boundaries. A simple loop over length must now be accompanied by topological path checking. This makes the Yap correction most suitable for use in a structured code where some normal wall distance is readily available. There are several alternative formulations that can be used instead though ''(anyone have the references??)''.

	When implementing the Yap correction it is common to use it only if the source term is positive. Hence:		When implementing the Yap correction it is common to use it only if the source term is positive. Hence:

DavidF at 12:41, 2 October 2008

2008-10-02T12:41:21Z

← Older revision		Revision as of 12:41, 2 October 2008
Line 1:		Line 1:
	{{Turbulence modeling}}		{{Turbulence modeling}}
-	The Yap correction [[#References\|[Yap. C. J. (1987)]]] consists of a ~~modifification~~ of the epsilon equation in the form of an extra source term, <math>S_\epsilon</math>, added to the right hand side of the epsilon equation. The source term can be written as:	+	The Yap correction [[#References\|[Yap. C. J. (1987)]]] consists of a modification of the epsilon equation in the form of an extra source term, <math>S_\epsilon</math>, added to the right hand side of the epsilon equation. The source term can be written as:

	:<math>\rho S_\epsilon \equiv 0.83 \, \rho \, \frac{\epsilon^2}{k} \, \left(\frac{k^{1.5}}{\epsilon \, l_e} - 1 \right) \, \left(\frac{k^{1.5}}{\epsilon \, l_e} \right)^2</math>		:<math>\rho S_\epsilon \equiv 0.83 \, \rho \, \frac{\epsilon^2}{k} \, \left(\frac{k^{1.5}}{\epsilon \, l_e} - 1 \right) \, \left(\frac{k^{1.5}}{\epsilon \, l_e} \right)^2</math>

Jola at 09:13, 12 June 2007

2007-06-12T09:13:46Z

← Older revision		Revision as of 09:13, 12 June 2007
Line 1:		Line 1:
		+	{{Turbulence modeling}}
	The Yap correction [[#References\|[Yap. C. J. (1987)]]] consists of a modifification of the epsilon equation in the form of an extra source term, <math>S_\epsilon</math>, added to the right hand side of the epsilon equation. The source term can be written as:		The Yap correction [[#References\|[Yap. C. J. (1987)]]] consists of a modifification of the epsilon equation in the form of an extra source term, <math>S_\epsilon</math>, added to the right hand side of the epsilon equation. The source term can be written as:

Jola at 16:21, 18 October 2006

2006-10-18T16:21:23Z

← Older revision		Revision as of 16:21, 18 October 2006
Line 29:		Line 29:
	The Yap correction is active in nonequilibrium flows and tends to reduce the departure of the turbulence length scale from its local equilibrium level. It is an ad-hoc fix which seldom causes any problems and often improves the predictions.		The Yap correction is active in nonequilibrium flows and tends to reduce the departure of the turbulence length scale from its local equilibrium level. It is an ad-hoc fix which seldom causes any problems and often improves the predictions.

-	Yap showed strongly improved results with the k-epsilon model in separated flows when using this extra source term. The Yap correction has also been shown to improve ~~the~~ results in stagnation region. Launder [[#References\|[Launder, B. E. (1993)]]] recommends that the Yap correction should always be used with the epsilon equation.	+	Yap showed strongly improved results with the k-epsilon model in separated flows when using this extra source term. The Yap correction has also been shown to improve results in a stagnation region. Launder [[#References\|[Launder, B. E. (1993)]]] recommends that the Yap correction should always be used with the epsilon equation.

	==Implementation issues==		==Implementation issues==

Jola: minro error fix

2006-10-18T16:20:00Z

minro error fix

← Older revision		Revision as of 16:20, 18 October 2006
Line 25:		Line 25:
	</math>		</math>

-	Where the epsilon equation has been written in the same way is in the CFD-Wiki article on [[low-Re k-epsilon models]].	+	Where the epsilon equation has been written in the same way as is in the CFD-Wiki article on [[low-Re k-epsilon models]].

	The Yap correction is active in nonequilibrium flows and tends to reduce the departure of the turbulence length scale from its local equilibrium level. It is an ad-hoc fix which seldom causes any problems and often improves the predictions.		The Yap correction is active in nonequilibrium flows and tends to reduce the departure of the turbulence length scale from its local equilibrium level. It is an ad-hoc fix which seldom causes any problems and often improves the predictions.

Jola at 14:40, 25 May 2006

2006-05-25T14:40:26Z

← Older revision		Revision as of 14:40, 25 May 2006
Line 1:		Line 1:
-	The Yap correction consists of a modifification of the epsilon equation in the form of an extra source term, <math>S_\epsilon</math>, added to the right hand side of the epsilon equation. The source term can be written as:	+	The Yap correction [[#References\|[Yap. C. J. (1987)]]] consists of a modifification of the epsilon equation in the form of an extra source term, <math>S_\epsilon</math>, added to the right hand side of the epsilon equation. The source term can be written as:

	:<math>\rho S_\epsilon \equiv 0.83 \, \rho \, \frac{\epsilon^2}{k} \, \left(\frac{k^{1.5}}{\epsilon \, l_e} - 1 \right) \, \left(\frac{k^{1.5}}{\epsilon \, l_e} \right)^2</math>		:<math>\rho S_\epsilon \equiv 0.83 \, \rho \, \frac{\epsilon^2}{k} \, \left(\frac{k^{1.5}}{\epsilon \, l_e} - 1 \right) \, \left(\frac{k^{1.5}}{\epsilon \, l_e} \right)^2</math>

Jola at 14:39, 25 May 2006

2006-05-25T14:39:41Z

← Older revision		Revision as of 14:39, 25 May 2006
Line 29:		Line 29:
	The Yap correction is active in nonequilibrium flows and tends to reduce the departure of the turbulence length scale from its local equilibrium level. It is an ad-hoc fix which seldom causes any problems and often improves the predictions.		The Yap correction is active in nonequilibrium flows and tends to reduce the departure of the turbulence length scale from its local equilibrium level. It is an ad-hoc fix which seldom causes any problems and often improves the predictions.

-	Yap showed strongly improved results with the k-epsilon model in separated flows when using this extra source term. The ~~Yep~~ correction has also been shown to improve the results in stagnation region. Launder [[#References\|[Launder, B. E. (1993)]]] recommends that the Yap correction should always be used with the epsilon equation.	+	Yap showed strongly improved results with the k-epsilon model in separated flows when using this extra source term. The Yap correction has also been shown to improve the results in stagnation region. Launder [[#References\|[Launder, B. E. (1993)]]] recommends that the Yap correction should always be used with the epsilon equation.

	==Implementation issues==		==Implementation issues==

-	The Yap source term contains the explicit distance to the nearest wall, <math>y_n</math>. In an unstructured 3D solver this distance is usually not available and it can be ambiguous how to compute it in more complex topologies. This makes the Yap correction most suitable for use in a structured code where the normal wall distance is readily available.	+	The Yap source term contains the explicit distance to the nearest wall, <math>y_n</math>. In an unstructured 3D solver this distance is usually not available and it can be ambiguous how to compute it in more complex topologies. This makes the Yap correction most suitable for use in a structured code where the normal wall distance is readily available. There are several alternative formulations that can be used instead though ''(anyone have the references??)''.

	When implementing the Yap correction it is common to use it only if the source term is positive. Hence:		When implementing the Yap correction it is common to use it only if the source term is positive. Hence:

Jola at 14:31, 25 May 2006

2006-05-25T14:31:27Z

← Older revision		Revision as of 14:31, 25 May 2006
Line 6:		Line 6:

	:<math>l_e \equiv c_\mu^{-0.75} \, \kappa \, y_n</math>		:<math>l_e \equiv c_\mu^{-0.75} \, \kappa \, y_n</math>
		+
		+	<math>y_n</math> is the normal distance to the nearest wall.

	This source term should be added to the epsilon equation in the following way:		This source term should be added to the epsilon equation in the following way:

Jola at 14:30, 25 May 2006

2006-05-25T14:30:39Z

← Older revision		Revision as of 14:30, 25 May 2006
Line 1:		Line 1:
	The Yap correction consists of a modifification of the epsilon equation in the form of an extra source term, <math>S_\epsilon</math>, added to the right hand side of the epsilon equation. The source term can be written as:		The Yap correction consists of a modifification of the epsilon equation in the form of an extra source term, <math>S_\epsilon</math>, added to the right hand side of the epsilon equation. The source term can be written as:

-	:<math>\rho S_\epsilon = 0.83 \, \rho \, \frac{\epsilon^2}{k} \, \left(\frac{k^{1.5}}{\epsilon \, l_e} - 1 \right) \, \left(\frac{k^{1.5}}{\epsilon \, l_e} \right)^2</math>	+	:<math>\rho S_\epsilon \equiv 0.83 \, \rho \, \frac{\epsilon^2}{k} \, \left(\frac{k^{1.5}}{\epsilon \, l_e} - 1 \right) \, \left(\frac{k^{1.5}}{\epsilon \, l_e} \right)^2</math>

	Where		Where

Jola at 14:30, 25 May 2006

2006-05-25T14:30:06Z

← Older revision		Revision as of 14:30, 25 May 2006
Line 25:		Line 25:
	Where the epsilon equation has been written in the same way is in the CFD-Wiki article on [[low-Re k-epsilon models]].		Where the epsilon equation has been written in the same way is in the CFD-Wiki article on [[low-Re k-epsilon models]].

-	The Yap correction is active in nonequilibrium flows and tends to reduce the departure of the turbulence length scale from its local equilibrium level.	+	The Yap correction is active in nonequilibrium flows and tends to reduce the departure of the turbulence length scale from its local equilibrium level. It is an ad-hoc fix which seldom causes any problems and often improves the predictions.

-	Yap showed strongly improved results with the k-epsilon model in separated flows when using this extra source term. It has also been shown to improve the results in stagnation region. Launder [[#References\|[Launder, B. E. (1993)]]] ~~also~~ recommends that ~~this term~~ should always be used with the epsilon equation.	+	Yap showed strongly improved results with the k-epsilon model in separated flows when using this extra source term. The Yep correction has also been shown to improve the results in stagnation region. Launder [[#References\|[Launder, B. E. (1993)]]] recommends that the Yap correction should always be used with the epsilon equation.

	==Implementation issues==		==Implementation issues==

Yap correction - Revision history

Kett: Elaboration on calculating y_n needed for the Yap correction

DavidF at 12:41, 2 October 2008

Jola at 09:13, 12 June 2007

Jola at 16:21, 18 October 2006

Jola: minro error fix

Jola at 14:40, 25 May 2006

Jola at 14:39, 25 May 2006

Jola at 14:31, 25 May 2006

Jola at 14:30, 25 May 2006

Jola at 14:30, 25 May 2006

Kett: Elaboration on calculating $y_n$ needed for the Yap correction