Transonic High Reynolds Number Transition Experiments in the ETW Cryogenic Wind Tunnel

Abstract

With the goal of studying Natural Laminar Flow (NLF) wings for future ‘green’ transport aircraft, the aim of the European Research Project TELFONA is to develop and demonstrate the possibility of testing full aircraft models at large Reynolds numbers in the cryogenic Wind Tunnel ETW, with direct measurements of total drag. Two main steps were defined, first the design and test of a ‘calibration’ model, to be followed by a realistic transport aircraft model. This paper is dedicated to the first one, which was especially designed in order to allow a calibration of the Wind Tunnel transition N-factors at large values of the chord Reynolds number typical of testing in ETW. In order to do so, the wing shape was optimized so that TS and CF N-factors would show a monotonous growth over the longest possible distance. Apart from classical aerodynamic forces, two lines of pressure taps, as well as four patches of a two components cryogenic Temperature- Sensitive Paint (cryoTSP), were installed on both sides of each wing. Model surface temperatures were recorded by several CCD cameras as the intensity of light emission from the TSP, which has to be excited by suitable light sources. After the tests, stability analysis was applied in order to ‘calibrate’ the various models currently used by research labs in Europe, involving a wide range of approaches, including simplified database, local linear and non local linear stability approaches. The paper will describe these different phases of the activities, from design, testing and numerical validation, with a focus on the validation and calibration of transition prediction tools. Examples of numerical results obtained by the project partners will be confronted to the experiments.