Boundary layer suction configurations with minimal pump requirements for multi-element airfoils

Abstract

High lift systems are indispensable but complex and heavy systems so new methods to allow lighter and simpler high lift systems are actively sought after. One of the methods that have already proven to be able to increase high lift performance is boundary layer suction. In practice however the application of it is uncommon mainly due to the often high power requirements. The objective of the presented project is studying possible BLS systems with minimal requirements, which may then be driven by ‘naturally occurring’ low pressure zones. Influencing the wake with suction was identified as most promising in this respect, more particularly preventing the phenomenon ‘wake burst’ where the wake rapidly expands and dominates the flowfield in such way that it leads to a loss of lift. Simulations were performed with the inviscid-viscid interaction flow solver MSES, adapted for suction. The results showed that the application of suction was very successful to bring the expansion rate of displacement thickness of the wake below 0.23, which was identified as the critical value above which wake burst is likely. On selected geometries (NLR7301 and MFFS026) this leads to an increase in lift of up to 4.5%. This is not a significantly better than earlier investigated BLS configurations, but the requirements imposed on the eventual BLS system are much lower, especially when considering the required under pressure.