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LDA system for in-flight local velocity measurements on airplane wings

The development of laminar wing technology requires wind tunnel studies with numerical flow simulations and in-flight measurements. A strategy for in-flight flow measurements is outlined. It is shown that laser Doppler anemometry (LDA) is well suited for providing the desired local velocity information, but must be specifically adapted for the various spatial, geometrical, and power constraints imposed by the test aircraft. This program yielded two optical units suitable for in-flight velocity measurements on airplane wings. Laboratory and free flight measurements studying boundary layer transition on an airplane wing downstream of an excitation source were successfully carried out and a summary of results is presented. Finally, suggestions for further advancements of LDA systems are proposed.