[FMDenaro]

if you need to evaluate heat transfer at the wall how can you say that you are not interested in the physics near the wall? Heat transfer at the wall depends on both the thermal and dynamical boundary layer

[srv1406]

Thanks for the quick reply. Yes you are right. I misframed my statement. I do have to get proper behaviour of the momentum boundary layer as well in order to capture the thermal boundary layer. It is just that momentum B.L is not directly of my interest. Actually i am carrying out a heat transfer problem in a combustion furnace, which is near rectangular in shape, with air-fuel mixture coming into the furnace from small circular burners. And my purpose is to find the resutant heat transfer at some of the surfaces. Can you plese let me know about my query now ?

[FMDenaro]

Originally Posted by srv1406

Thanks for the quick reply. Yes you are right. I misframed my statement. I do have to get proper behaviour of the momentum boundary layer as well in order to capture the thermal boundary layer. It is just that momentum B.L is not directly of my interest. Actually i am carrying out a heat transfer problem in a combustion furnace, which is near rectangular in shape, with air-fuel mixture coming into the furnace from small circular burners. And my purpose is to find the resutant heat transfer at some of the surfaces. Can you plese let me know about my query now ?

Honestly, I doubt you can accurately solve a heat transfer problem at walls without a necessary grid resolution for the boundary layers...Assume you have a decoupled problem, after you solve first the velocity field how can you accurately predict the heat transfer without any information for the velocity near the wall?
In other words, if you disregard the physics near the wall for the momentum, I consider you should simply disregard the details of the heat transfer at the wall (in some sense you have the counterpart of the wall model for the heat transfer)

[srv1406]

Yes, the standard wall function also takes care for the solution of thermal boundary layer in the log-law region , just like for the momentum boundary layer. So that seems to work fine to help reduce grid resolution. But what I am worried about is that there must be some higher limit of yplus to which the wall function works. I want to know this limit of yplus.

[FMDenaro]

Originally Posted by srv1406

Yes, the standard wall function also takes care for the solution of thermal boundary layer in the log-law region , just like for the momentum boundary layer. So that seems to work fine to help reduce grid resolution. But what I am worried about is that there must be some higher limit of yplus to which the wall function works. I want to know this limit of yplus.

I would only consider the model for y+<100

https://upload.wikimedia.org/wikiped...glish).svg.png

[srv1406]

Yes, from that figure it does look like it would not be good to consider yplus more than 100, because wall function models upto the log law layer. Actually the departure from log layer and beginning of the outer layer depends on Re or more precisely the adverse pressure gradient. Higher it is, the outer layer begins sooner. It can be seen from a plot in the source mentioned below as well. For zero gradient (flat plate) or favourable pressure gradient, the log layer extends upto yplus of 1000, and the outer layer starts beyond that. But again, yes, a maximum value of 100 would be in the safer side.

https://www.euhit.org/infrastructure...nel/facilities

[Avr.Tomer]

Y+, Y* and Law of the Wall: https://cfdisraelblog.wordpress.com/...w-of-the-wall/

[medguedem]

I am a doctoral student at the university. currently I imply CFD modeling in fluent. I spent a year in the mesh , could you help me to choose the best mesh for (y plus) and (dy first cell no mesh) for a turbulent simulation with number of Re = 6000 to 100000 to calculate the constant (B) of the log law logaritmic profile.
Vx / (V *) = 2.5Ln (y / k) + B.
with roughness effect artificial
1. Please explain to me how chosen y +, how chosen turbulence model (k epsilon , k-w, scalable or enhanced RNG or standart ....)
2. Can i use the same mesh to calculate the shear stress and the logarithmic profile and constant B.

[FMDenaro]

Originally Posted by medguedem

I am a doctoral student at the university. currently I imply CFD modeling in fluent. I spent a year in the mesh , could you help me to choose the best mesh for (y plus) and (dy first cell no mesh) for a turbulent simulation with number of Re = 6000 to 100000 to calculate the constant (B) of the log law logaritmic profile.
Vx / (V *) = 2.5Ln (y / k) + B.
with roughness effect artificial
1. Please explain to me how chosen y +, how chosen turbulence model (k epsilon , k-w, scalable or enhanced RNG or standart ....)
2. Can i use the same mesh to calculate the shear stress and the logarithmic profile and constant B.

Why do you not discuss these issues with your tutor(s)? You need to learn not simply to do ...

[medguedem]

if you have an answer tell me if not i don't need any recommendations

[FMDenaro]

Originally Posted by medguedem

if you have an answer tell me if not i don't need any recommendations

The answer is to study. This forum cannot substitute the role of the tutor of a PhD student. A lot of people think that they can write private email for any kind of help as well as they ask for somehow homework.
You do not need recomendation? Well, the answers is that I have some answers but I do not teach here.

[sbaffini]

Originally Posted by medguedem

if you have an answer tell me if not i don't need any recommendations

Wow, Captain Politeness here, you are going to have a lot of help, especially considering that you also hijacked the thread

[e.smigelskis]

Hello everyone,

I am trying to model two-phase upstream flow inside the tube with condensation (film flowing down).

For my understanding there are two regions of shear stress that are of interest: wall - liquid and liquid film surface - 2ph flow.

In this case should I calculate two boundary layers, one considering liquid film velocity and another one considering 2ph flow velocity? Also, the thickens of the liquid film is to be evaluated during simulations, so second boundary layer (l. film surface - 2ph flow) location is not known.

What kind of approach would you suggest? Also, any references to helpful material would be appreciated.

(I am relative new in CFD and planning of using ANSYS CFX)

Thank you in advance.