Experimental investigations on boundary layer transition over a flat plate with suction and comparison with linear stability theory
M. Corelli Grappadelli (Technical University of Braunschweig)
S. Asaro (TU Delft - Flight Performance and Propulsion)
Rolf Radespiel (Technical University of Braunschweig)
Camli Badrya (University of California)
More Info
expand_more
Other than for strictly personal use, it is not permitted to download, forward or distribute the text or part of it, without the consent of the author(s) and/or copyright holder(s), unless the work is under an open content license such as Creative Commons.
Abstract
Laminar boundary layer suction has significant potential for reducing aircraft drag, thereby diminishing its environmental impact. This study presents wind tunnel experiments conducted on a flat plate to examine the effectiveness of laminar boundary layer suction in delaying the transition and compares the measured data with the en method based on linear stability theory (LST). The experiments, performed over a range of freestream velocities from 15 to 50 m/s, comprised infrared thermography, pressure measurements, and hot-wire anemometry. The boundary layer suction is implemented through interchangeable suction boxes mounted on the flat plate, with two types of suction surfaces tested, featuring hole diameters of 120 and 60μm and a constant porosity of 0.9%. The study examines the influence of various parameters on transition, as the intensity of the suction coefficient, particularly at elevated values, as well as the impact of the micro-holes diameter, the chordwise distribution of the suction velocity and the freestream Reynolds number. A discrepancy between the experimentally measured transition location and the predictions from LST is observed. To identify the origin of this deviation, boundary layer measurements are taken on the porous surface while varying both the suction coefficient and its spatial distribution. A particular flow disturbance near the porous surface, amplified by the suction intensity, is identified, leading to increased velocity fluctuations in the near-wall measurement points. The difference depends on both the suction coefficient and the suction velocity distribution. For this reason, a configuration is investigated in which only the first and last of the four suction chambers are used to aspirate the boundary layer. It is observed that the flow disturbances are significantly reduced, and the boundary layer predictions align more closely with the experimental data.
help_outline