Flow-Control Effectiveness of Convergent Surface Indentations on an Aerofoil at Low Reynolds Numbers

Shah, N. K. and Kontis, K. (2017) Flow-Control Effectiveness of Convergent Surface Indentations on an Aerofoil at Low Reynolds Numbers. In: 2017 AIAA Aviation Forum, Denver, CO, USA, 05-09 Jun 2017, ISBN 9781624105012 (doi: 10.2514/6.2017-3568)

Abstract

Passive flow control on aerofoils has largely been achieved through the use of protrusions such as vane-type vortex generators. Consequently, innovative flow-control concepts should be explored in an effort to improve current component performance. Therefore, experimental research has been performed at The University of Manchester to evaluate the flow-control effectiveness of a novel type of vortex generator made in the form of a surface indentation. The surface indentation has a trapezoidal planform. A spanwise array of indentations has been applied in a convergent orientation around the maximum-thickness location of the upper surface of a NACA-0015 aerofoil. The aerofoil has been tested in a twodimensional set-up in a low-speed wind tunnel at an angle of attack (AoA) of 3° and a chordbased blockage-corrected Reynolds number (Recorr) of ~2.70 x 105 . The baseline model has been found to suffer from a long laminar separation bubble (LSB) at low AoA. The application of the indentations at low AoA has considerably shortened the separation bubble. The indentations achieve this by shedding up-flow pairs of streamwise vortices. Despite the considerable reduction in bubble length, the increase in leading-edge suction due to the shorter bubble is limited by the removal of surface curvature and blockage (increase in surface pressure) caused locally by the convergent indentations. Furthermore, the up-flow region of the vortices, which locally weakens the pressure recovery around the trailing edge of the aerofoil by thickening the boundary layer, also contributes to this limitation. Due to the conflicting effects of the indentations, the changes in the pressure-lift and pressure-drag coefficients, i.e., cl,p and cd,p, respectively, are small. Nevertheless, the indentations have improved cl,p and cd,p beyond the uncertainty range, i.e., by ~1.3% and ~0.3%, respectively, at 3° AoA. The wake measurements show that turbulence intensity and Reynolds stresses have considerably increased in the indented case, thus implying that the indentations increase the viscous drag on the model. In summary, the convergent indentations are able to reduce the size of the LSB, but conversely, they are not highly effective in enhancing cl,p and cd,p at the tested Re.

• Item Type: Conference Proceedings
• Status: Published
• Refereed: Yes
• Glasgow Author(s) Enlighten ID: Kontis, Professor Konstantinos
• Authors: Shah, N. K., and Kontis, K.
• College/School: College of Science and Engineering > School of Engineering > Autonomous Systems and Connectivity
• ISBN: 9781624105012
• Copyright Holders: Copyright © 2017 American Institute of Aeronautics and Astronautics, Inc.
• First Published: First published in 2017 AIAA Aviation Forum
• Publisher Policy: Reproduced in accordance with the publisher copyright policy