# area on reference value

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

 November 26, 2010, 06:35 area on reference value #1 New Member   satriya Join Date: Jun 2010 Posts: 6 Rep Power: 8 when i scale airfoil geometry on the scale factor from 1 to 0,0823 should i change the value of area to 0,0823 m^2 on the reference value to get appropriate cl an cd??

 November 26, 2010, 08:36 #2 Member     Burak Join Date: May 2009 Posts: 90 Rep Power: 9 is it 2d or 3d? if 2d, 0,0823 is ok, but if 3d, you must square it.

 November 27, 2010, 04:54 #3 New Member   satriya Join Date: Jun 2010 Posts: 6 Rep Power: 8 it is 2d airfoil but i still confused about pressure coefficient CP why it's always same altough i've scale the geometry?? (same velocity and AoA) i use inviscid model

 November 27, 2010, 06:33 #4 Member     Burak Join Date: May 2009 Posts: 90 Rep Power: 9 cp is a dimensionless value and is related with geometry(airfoil). if you dont change your geometry, cp will be same. this is due to inviscid flow. and since Cl and Cd are integrals of Cp, they will not change, either. BUT: In real life, the flow is viscous and cp slightly changes with velocity (Reynolds number). This is because laminar and turbulent flow characteristics over the surface. You should study boudary layer, laminar-turbulent seperation to understand what I mean.

 November 28, 2010, 08:03 #5 New Member   satriya Join Date: Jun 2010 Posts: 6 Rep Power: 8 i've scale airfoil geometry from 1 m to 0,083 m, cp result doesn't change but cl & cd change

 November 28, 2010, 08:09 #6 Member     Burak Join Date: May 2009 Posts: 90 Rep Power: 9 cl and cd are x and y components of cp. do you confuse center of pressure with coefficient of pressure?

 December 9, 2010, 04:35 #7 New Member   satriya Join Date: Jun 2010 Posts: 6 Rep Power: 8 here we are. i following this tutorial (https://confluence.cornell.edu/displ...ecificationand) then i try for different velocity also i scale the geometry from 1m to 0,0823m but the xyplot on pressure coefficient always same for the same AoA why altough i change the velocity..

 December 9, 2010, 05:36 #8 Member     Burak Join Date: May 2009 Posts: 90 Rep Power: 9 because you are using inviscid model. use laminar or turbulent models.

 December 10, 2010, 03:12 #9 New Member   satriya Join Date: Jun 2010 Posts: 6 Rep Power: 8 inviscid = viscosity is negliable (myu=0) cp= (p-pfs)/0,5.rho.v^2 there is no myu on the cp formula.. so why it's because of the inviscid model??

 Thread Tools Display Modes Linear Mode

 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 OffTrackbacks are On Pingbacks are On Refbacks are On Forum Rules

 Similar Threads Thread Thread Starter Forum Replies Last Post skabilan OpenFOAM Installation 3 July 28, 2009 00:35 allenzhao OpenFOAM Installation 127 January 30, 2009 20:08 mike CFX 1 March 19, 2008 08:22 Bruno Main CFD Forum 1 January 30, 2007 01:34 anne OpenFOAM Installation 8 June 15, 2006 09:27

All times are GMT -4. The time now is 10:02.