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Title: The automatic control of boundary layer transition
Author: Rioual, Jean-Luc
ISNI:       0000 0001 3519 6208
Awarding Body: University of Southampton
Current Institution: University of Southampton
Date of Award: 1994
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In the attempt to reduce the skin friction drag of modern civil aircraft, Hybrid Laminar Flow Control (HLFC) is receiving most attention. This method applied to wings, engine nacelles or fins uses wall suction and wall shaping for the maintenance of laminarity. Among the uncertainties associated with this technology are the monitoring of laminarity during operation, and more importantly, the attainment of the optimum suction distribution which yields the required transition delay with minimum suction effort. Automatic feedback systems seem to be the ideal candidates to maintain laminarity by regulating the suction rate of a number of independent strips. Such systems must firstly avoid excessive power penalties due to suction, secondly avoid instabilities due to inappropriate suction and thirdly, but not least, shorten wind tunnel and flight tests by replacing time consuming and uncertain manual adjustments. Microphones and polyvinylidenefluoride (PVDF) films seem to be most appropriate to locate transition without ambiguity and without disturbing the flow. Experimental investigations show very good performance of microphones used to measure the transition process. A simple signal processing method is developed in order to obtain a normalised pressure signal analogous to the turbulent intermittency factor. A strategy using a set of such normalised pressures enables the production, at regular short time intervals, of a signal corresponding to the transition location. This signal is then used in a single channel feedback control system. The controller regulates the suction rate at the surface of a porous surface in order to maintain transition at a specified location whatever the flow conditions. The same monitoring strategy is used in a multiple channel control system which regulates transition using the optimum suction distribution of an arbitrary number of independent suction panels.
Supervisor: Not available Sponsor: Not available
Qualification Name: Thesis (Ph.D.) Qualification Level: Doctoral
EThOS ID:  DOI: Not available
Keywords: Drag reduction