CFD Online Logo CFD Online URL
www.cfd-online.com
[Sponsors]
Home > Forums > Special Topics > Mesh Generation & Pre-Processing

NACA4415 Airfoil / Y+ Value Lift'n'Drag

Register Blogs Members List Search Today's Posts Mark Forums Read

Like Tree1Likes
  • 1 Post By CFD Germany

Reply
 
LinkBack Thread Tools Search this Thread Display Modes
Old   June 5, 2017, 16:34
Question NACA4415 Airfoil / Y+ Value Lift'n'Drag
  #1
New Member
 
Join Date: Jun 2017
Posts: 6
Rep Power: 8
CFD Germany is on a distinguished road
Hello everyone,

I do a student research project at the moment. The topic is to calculate the lift and drag-coefficients of a NACA4415 Airfoil with/without winglet and to create the polar-diagramms. I use the k-w model, the freestream velocity is 95 km/h the length of the airfoil 1.5m.

I asked a prof of mine in which way the Y+ Value is important to calculate the coefficients. He meant its ok to have a Y+ between 30-70 or 30-100. We have had a training course where i was said to use a Y+ less than 1. This would be very important.

On the internet I found out that a Y+ less than 1 would be important at heat transfer and the drag-coefficient. Is it really necessary to have such a low Y+ for right results?

Thank You
CFD Germany is offline   Reply With Quote

Old   June 12, 2017, 03:22
Default
  #2
Senior Member
 
Colinda
Join Date: May 2012
Location: Brussels
Posts: 150
Rep Power: 13
colinda1 is on a distinguished road
Indeed for a correct drag prediction it is important to have low y+ values IF you use a turbulence model without wall functions. But be careful; it is not the only thing that is important. Very often the focus is so much on Y+ that the rest is forgotten. E.g. the expansion ratio should not be too high either.
Also it would be important to have a sufficiently fine mesh in the wake. It would be wise to perform a mesh dependency study.
colinda1 is offline   Reply With Quote

Old   June 12, 2017, 05:23
Default
  #3
New Member
 
Join Date: Jun 2017
Posts: 6
Rep Power: 8
CFD Germany is on a distinguished road
Thank you for the fast answer. I'm using a turbulence model with wall condition.

I will try to use a Wall function 1 or 2 mm (or should it be less for example 0,5?) thick with 5 Layer. I would choose a lowest thickness round about 0.05mm. That gives me a Y+ < 1 on the Wing Surface.

I have big Expansion ratios from the Wall. I made 3 areas. The inner with 50mm, middle 250 and outher 1250mm, for reasons of better Performance. I could also use more areas to get a lower ratio.

The Flow room is 10 times the lenght of the Wing. Thats important for the Lift Report.

Sent from my D5803 using CFD Online Forum mobile app
CFD Germany is offline   Reply With Quote

Old   June 12, 2017, 05:51
Default
  #4
Senior Member
 
Colinda
Join Date: May 2012
Location: Brussels
Posts: 150
Rep Power: 13
colinda1 is on a distinguished road
When you write "wall condition" do you mean wall boundary condition?

A wall function is different: in the viscous sublayer it allows to approximate the boundary layer by a function instead of solving the Navier-Stokes equations inside it. It allows to work with higher Y+ values at the wall outside of the viscous sub-layer. Expansion ratios should be really small in the boundary layer (approx. 1.2 to 1.5 would be good)
colinda1 is offline   Reply With Quote

Old   June 12, 2017, 06:11
Default
  #5
New Member
 
Join Date: Jun 2017
Posts: 6
Rep Power: 8
CFD Germany is on a distinguished road
Yes thats what i meant. I understood it wrong because I was so focused on the mesh.

I will look it up if a wall function is used i'm not sure yet.

So to get a lower ratio i should create a continous change in the mesh size, getting fine at the Wing Surface?

Sent from my D5803 using CFD Online Forum mobile app
CFD Germany is offline   Reply With Quote

Old   June 18, 2017, 14:31
Default
  #6
New Member
 
Join Date: Jun 2017
Posts: 6
Rep Power: 8
CFD Germany is on a distinguished road
Ok i looked it up, i'm using a wall function. Also the graphs of Lift and drag follow the right pattern, so i think its correct, thank you now i understand it better!

Sent from my D5803 using CFD Online Forum mobile app
colinda1 likes this.
CFD Germany is offline   Reply With Quote

Reply

Tags
y+;lift;drag;airfoil;naca

Thread Tools Search this Thread
Search this Thread:

Advanced Search
Display Modes

Posting Rules
You may not post new threads
You may not post replies
You may not post attachments
You may not edit your posts

BB code is On
Smilies are On
[IMG] code is On
HTML code is Off
Trackbacks are Off
Pingbacks are On
Refbacks are On


Similar Threads
Thread Thread Starter Forum Replies Last Post
SU2 AOA optimization 454514566@qq.com SU2 9 March 7, 2022 17:17
Ffd_control_point_2d feiyi SU2 4 September 30, 2019 13:42
High drag for airfoil compared to XFOIL and wind tunnel data Ry10 SU2 15 October 30, 2016 18:27
2D FFD Optimization RLangtry SU2 2 August 5, 2014 10:48
Problem with restart solution in shape_optimization.py robyTKD SU2 Shape Design 21 May 29, 2013 10:26


All times are GMT -4. The time now is 10:17.