An experimental study on the effects of two-dimensional positive surface defects on the laminar–turbulent transition of a sucked boundary layer

Abstract

To cite this version:Jeanne Methel, Maxime Forte, Olivier Vermeersch, Grégoire Casalis. An experimental study on the effects of two-dimensional positive surface defects on the laminar-turbulent transition of a sucked boundary layer. Abstract Laminar-turbulent transition can be e↵ectively delayed using Laminar Flow Control (LFC) by boundary layer suction. However, major obstacles to the industrial implementation of this technique are related to practical limitations such as proper integration of the suction system or unreliability of current design tools. The influence of surface discontinuities that can arise from installing an LFC system (and that can potentially cancel or deteriorate its stabilizing effect on the boundary layer) is scarcely documented in the open literature, adding to the complexity of improving numerical models. The present investigation therefore focuses on experimentally characterizing the e↵ects of surface defects on the laminar-turbulent tran-J. Methel Jeanne Methel et al. ural Tollmien-Schlichting instabilities. For these critical cases, the mechanisms of transition therefore seem mainly governed by the presence of the positive surface defects rather than by instabilities altered by wall suction.

Experimental investigation of hybrid laminar flow control by a modular flat plate model in the DNW-NWB

“…To rule out the possibility of additional porous wall roughness, causing this effect, Methel et al sealed the suction surface on the lower side by adhesive tape. In this way the transition was shifted downstream, almost to the position where it was located without the porous wall [13]. This is the same tendency, found in the present experiments.…”

“…4. In [13] Methel et al applied an alternative design goal, to reduce the suction peak, and also obtained an asymmetric nose geometry. The design of a symmetric nose was demonstrated by Grappadelli et al in [14], which is not appropriate for these experiments at the given model thickness, due to the required half-axis ratio of the windward nose part.…”

“…Results from former experiments suggested an interaction between TS waves and the plenum flow below the porous wall with a resulting influence on the process of transition as well. In [13], Methel et al describe how the transition on a flat plate is shifted upstream as the porosity of the surface increases. To rule out the possibility of additional porous wall roughness, causing this effect, Methel et al sealed the suction surface on the lower side by adhesive tape.…”

Direct numerical simulation of TS-waves over suction panel steps from manufacturing tolerances

“…Comparisons with existing empirical ∆N-correlations from Crouch [25] and Perraud [16] at small step Reynolds numbers are shown in Table 2 for different FFS and BFS. The empirical correlations in [25] and [16] were formally validated in comparison with experimental data by Methel in [26]. Comparisons were carried out for DNS results at 2230 Hz, since the other TS-modes show comparable n-factor shifting and consequently ∆N is expected in the same range as ∆n.…”

Influence of Surface Irregularities on the Expected Boundary-Layer Transition Location on Hybrid Laminar Flow Control Wings

“…backward/forward-facing steps (BFS/FFS), gaps, etc.) that might enhance the spatial development of those flow instabilities and, therefore, reduce the potential benefit of the suction system [3]. For this reason, it is crucial during the design process to quantify the influence of such surface irregularities in terms of BL instability.…”