# Source-Doublets panel methods MatLAB

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May 4, 2022, 12:47
Source-Doublets panel methods MatLAB
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Sebastiano Vianello
Join Date: Mar 2021
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Good evening everyone.
I'm developing a 3D panel method in MatLAB for aerodynamic analysis of a generic wing. This will be later on coupled with a structural solver to conduct some aeroelasic analysis.
The problem setup follows the method proposed by Katz and Plotkin in the well known 'Low Speed Aerodynamics'.
The geometry is discretized using a constant source-doublets distribution on each panel: the former provides the thickness contribution, the latter the vorticity contribution.
The analyzed airfoil is a NACA0006 straight wing, with chord = 1m and span = 10m. There are 10 spanwise sections and 100 panels per section.
For , the pressure distribution (Cp), is close to the one computed using XFOIL (albeit the Cp variation is not as abrupt as though close to the leading edge).
When imposing an angle to the profile( in this case , however, the situation is much different, with the pressure distribution being much different.
You can find attached the doublets and sources intensities distributed on the airfoil, which seems reasonable to me.
I've tried to look at other implementations of the method but from that I couldn't find what was wrong with my code.
Did anyone had a similar experience? Or is willing to help me with the solution of the problem?
Attached Images
 0006_0deg_Cp.png (13.0 KB, 14 views) 0006_0deg_doublet.png (40.1 KB, 19 views) 0006_5deg_Cp.png (24.9 KB, 14 views) 0006_5deg_doublet.png (37.1 KB, 18 views)

 May 13, 2022, 12:50 #2 Member   james nathman Join Date: May 2011 Posts: 60 Rep Power: 14 The trailing-edge pressure at 5 degrees indicates your method has no wake. What are the lift coefficients at the centerline of the wing for 0 & 5 degrees?

 May 17, 2022, 12:43 #3 Senior Member   Will Kernkamp Join Date: Jun 2014 Posts: 261 Rep Power: 12 Blackjack is correct. You need to create wake panels with a constant doublet strength equal to the sum of the doublet strength of the trailing edge panels of upper and lower surface. In that way, you ensure that there is no vortex at the trailing edge. This is the so called Kutta condition at the trailing edge. It causes the flow to smoothly leave the trailing edge. This is necessary for lift to occur. The wake panels should be in the direction of the flow, but it doesn't have to be very precise for a decent result. A good start would be to extend the edges from the trailing edge straight in the flow direction. The length should be a several times the span of the wing to ensure that the vortex at the end of your wake panels does not influence the flow at the wing.

 Tags doublets, matlab, panel, source