How to select certains faces to calculate lift coefficient?

xuankushuocai · October 12, 2017, 16:20

Hi guys,

I want to calculate the lift coefficient of a model with a fan patch created in OpenFOAM. The problem is that I don't want to calculate the lift force on the fan patch. Who knows how to recognize different types of surfaces or select surfaces to do the calculation? Thanks.

kandelabr · October 13, 2017, 04:18

If you calculate forces using the forces function object you can choose over which patches to integrate:

https://cpp.openfoam.org/v4/classFoa...s.html#details

jpeter3 · October 15, 2017, 10:43

You can code it into the solver as follows:

You can access the boundary field using .boundaryField().

That returns an array of fields, one for each patch.

You can identify patchID of your patch by using .findPatchID("nameOfThePatch") that Will be used to acces the one you need.

Looping through boundary field of selected patch you can access data on the faces on that patch to calculate what you want.

Like this:

//Find patch ID for your patch:
label patchID = mesh.boundaryMesh().findPatchID("yourPatchName");

//Store face IDs of your patch:
const polyPatch& cPatch = mesh.boundaryMesh()[patchID];

//Field you want to extract values from:
const someFieldType& yourFieldRef = yourField

//Loop over face IDs of faces that are located on your patch:
forAll(cPatch, facei)
{
//Data you seek:
scalar/vector... data = yourFieldRef.boundaryField()[patchID][facei];
}

xuankushuocai · October 16, 2017, 13:49

Hi, Nejc and Jaka, thanks a lot. I have figured it out.

October 12, 2017, 16:20	How to select certains faces to calculate lift coefficient?	#1
xuankushuocai New Member Xiaojie Wang Join Date: Aug 2017 Posts: 9 Rep Power: 9	Hi guys, I want to calculate the lift coefficient of a model with a fan patch created in OpenFOAM. The problem is that I don't want to calculate the lift force on the fan patch. Who knows how to recognize different types of surfaces or select surfaces to do the calculation? Thanks.

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October 13, 2017, 04:18		#2
kandelabr Senior Member Nejc Join Date: Feb 2017 Location: Slovenia Posts: 196 Rep Power: 9	If you calculate forces using the forces function object you can choose over which patches to integrate: https://cpp.openfoam.org/v4/classFoa...s.html#details

October 15, 2017, 10:43		#3
jpeter3 New Member JPeternel Join Date: Oct 2014 Posts: 19 Rep Power: 12	You can code it into the solver as follows: You can access the boundary field using .boundaryField(). That returns an array of fields, one for each patch. You can identify patchID of your patch by using .findPatchID("nameOfThePatch") that Will be used to acces the one you need. Looping through boundary field of selected patch you can access data on the faces on that patch to calculate what you want. Like this: //Find patch ID for your patch: label patchID = mesh.boundaryMesh().findPatchID("yourPatchName"); //Store face IDs of your patch: const polyPatch& cPatch = mesh.boundaryMesh()[patchID]; //Field you want to extract values from: const someFieldType& yourFieldRef = yourField //Loop over face IDs of faces that are located on your patch: forAll(cPatch, facei) { //Data you seek: scalar/vector... data = yourFieldRef.boundaryField()[patchID][facei]; }

October 16, 2017, 13:49		#4
xuankushuocai New Member Xiaojie Wang Join Date: Aug 2017 Posts: 9 Rep Power: 9	Hi, Nejc and Jaka, thanks a lot. I have figured it out.