Back to basics: Vortex lattice method for stability derivative estimation

The Vortex Lattice Method (VLM) roots back to the principles of lifting line theory and is thus also limited by the incompressible, inviscid and irrotational flow field assumption.

Basically the method works on splitting the geometry to a number of panels and calculating the contribution of all panels in terms of velocity potential (φ) on a control point in each panel. The resulting velocity, in combination with the free stream speed (Vinf) and the Kutta condition provide a solution for the vortices’ strength (γ) and through the integration of those, lift and induced drag forces are calculated. An output of the VLM is the stability derivative estimation used for an initial assessment of the aircraft stability and flying qualities.

As with many other subjects, while this method is taught during standard aerospace courses, students most often lack deeper understanding due to not going through the method’s application principles by writing a part of the computational code required to solve a panel method problem.

Below some images of applying the VLM for a B737 model using the AVL program.




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