While the VLM results are in good agreement with the experiment, this is only true in the linear range. Experimental lift curve compared to two computational techniques.įirst, inviscid computational methods such as the vortex-lattice method (VLM) do not predict flow separation.
Inverse methods were responsible for significant advances in airfoil design in the 1950s, when enough computational power was available to allow integral boundary-layer methods to be coupled with potential-flow solutions. Airfoil design is a field of specialization that requires multiple airfoils to be evaluated to help the designer build an experience-based understanding of airfoil behavior. The knowledgeable designer understands the consequences, including regions of laminar flow or early separation. This is used to calculate a geometry that will generate such a distribution. It allows the airfoil designer to specify a desired velocity distribution along the surface.
The inverse airfoil design method is a better approach to design an airfoil with a desired pressure distribution. This is a mandatory step and requires the predicted results to be compared with reliable wind tunnel tests. The above software is capable of such predictions, although the accuracy must be validated by the user. Accurate prediction of flow separation growth with AOA, subsequent stall, and width and depth of the drag bucket at lower AOA is vital for this work. The airfoil ordinates are entered into the software to predict lift, drag, and pitching moment at the specified AOA. Direct analysis evaluates the pressure field around an already defined airfoil.
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