Unit Normal Vector and Interface Jump ||.||

mcfdma · May 27, 2021, 14:24

Hi.

Rather than creating two threads, I am going to ask both my questions here since they are related.

I am using interFoam solver for my fluid flow simulation.

I am interested in acquiring the unit normal vector at the interface. I know the equation for normal vector is $\overrightarrow{n} = \nabla\alpha$ which in OF can be written as

Code:

normV = fvc::grad(alpha1);

which compiles properly.

But when I try to compute the unit normal vector given by $\hat n = \frac{\nabla \alpha}{|\nabla \alpha|}$ which I have written using

Code:

unormV = fvc::grad(alpha1)/mag(fvc::grad(alpha1));

that also compiles properly. However, when running a case, my simulation crashes as the unit normal vector divides by 0 in the outer region where $\alpha = 0$ .

I am interested in acquiring unit normal vector to compute a variable which brings me to my second part of the question. The parameter I am measuring qs requires interface knowledge and is given by: $\hat n. || \varepsilon E ||=qs$ .

My questions
1. How can I calculate unit normal vector $\hat n$ at the interface?

2. How can I write the interface jump represented by ||.|| within my solver?

Any help is appreciated.

gyr · February 18, 2023, 16:01

Did you solve the the problem,i am facing the same

überschwupper · February 20, 2023, 06:24

I would do the calculation only for cells where the gradient isnt 0. That means, including an for loop where this condition is met

gyr · February 20, 2023, 09:00

thanks so much

May 27, 2021, 14:24	Unit Normal Vector and Interface Jump \|\|.\|\|	#1
mcfdma Member X Join Date: Jan 2019 Posts: 63 Rep Power: 7	Hi. Rather than creating two threads, I am going to ask both my questions here since they are related. I am using interFoam solver for my fluid flow simulation. I am interested in acquiring the unit normal vector at the interface. I know the equation for normal vector is $\overrightarrow{n} = \nabla\alpha$ which in OF can be written as Code: normV = fvc::grad(alpha1); which compiles properly. But when I try to compute the unit normal vector given by $\hat n = \frac{\nabla \alpha}{\|\nabla \alpha\|}$ which I have written using Code: unormV = fvc::grad(alpha1)/mag(fvc::grad(alpha1)); that also compiles properly. However, when running a case, my simulation crashes as the unit normal vector divides by 0 in the outer region where $\alpha = 0$ . I am interested in acquiring unit normal vector to compute a variable which brings me to my second part of the question. The parameter I am measuring qs requires interface knowledge and is given by: $\hat n. \|\| \varepsilon E \|\|=qs$ . My questions 1. How can I calculate unit normal vector $\hat n$ at the interface? 2. How can I write the interface jump represented by \|\|.\|\| within my solver? Any help is appreciated.

February 18, 2023, 16:01		#2
gyr New Member libya Join Date: Aug 2022 Posts: 15 Rep Power: 3	Did you solve the the problem,i am facing the same

February 20, 2023, 06:24		#3
überschwupper Member Join Date: Jan 2022 Location: Germany Posts: 72 Rep Power: 4	I would do the calculation only for cells where the gradient isnt 0. That means, including an for loop where this condition is met

February 20, 2023, 09:00		#4
gyr New Member libya Join Date: Aug 2022 Posts: 15 Rep Power: 3	thanks so much