The main objective of the present work is to study the mass extraction in a transonic wind tunnel. The strategy consists in the analysis of the flow in the test section, with special attention devoted to the slots. To this end the results of tests of a NACA 0012 airfoil are presented. Besides, the influence of the returning flaps and forced evacuation compressors upon the results were also assessed. The experimental investigation used both the classical staticpressure taps as well as the ''Pressure Sensitive Paint'' (PSP) techniques. The PSP complete pack includes the devices to apply the special ink, dedicated computer codes, and the electronic equipments necessary in the usage of the technique. This technique permits the measurement of the static pressure along all the surface of the body, and further allowed for the observation of shock waves. To complete the study, the flow inside the test section is also numerically simulated. In overall terms the tunnel stream, the pressure distribution on the airfoil and the flow through the slots are investigated. Values of pressure on the surface of the foil were compared including here the present experimental and numerical results, plus data from the literature what guarantees the proper accuracy of all the investigation performed.

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Transonic wind tunnels (TWT) are sophisticated tools for the investigations of flows with Mach numbers of order one. The most characteristic feature of a facility such as this is, for sure, the openings in the walls of the test section. The openings in the walls permit the proper relief effect, and this, on the other hand, makes possible the experimentation at the transonic range. The results to be presented in this paper correspond to an analysis of the flow in the test section of a TWT containing a NACA 0012 airfoil. Both numerical and experimental investigations were conducted. For the numerical investigation, a threedimensional, finite-difference code, based on the diagonal algorithm, was employed, whereas for the experimentation, the classical static-pressure taps as well as the pressure sensitive paint (PSP) techniques were used. The classical static-pressure tap method is indicated as PSI technique. The pressure distributions were investigated for Mach numbers in the range of 0.6 -0.8 and angles of attack from 0° up to 8°. The relief effect due to the slots, which provides for avoiding choking effects, is clearly demonstrated when one compares the flow along both solid and perforated walls. In the first part of this research report, the main focus will be on the numerical results. Notwithstanding this, and for comparison purposes, some experimental results will be called upon here, together with some literature data.

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