Rinku Mukherjee

This paper investigates an improvement of the aerodynamic performance of a rectangular wing by re-designing its camberline to control the laminar separation of its boundary layer. This is experimentally implemented using an Aluminium secondary skin on the wing surface, which aligns itself to the separated boundary layer, such that the flow remains attached to it, which otherwise would have separated on the baseline configuration. The shape of the skin, which is now regarded as the effective flow surface, is essentially a decambered version of the baseline shape of the wing and is predicted numerically using an in-house code based on two linear functions that account for the local deviation of camber by accounting for the difference in coefficients of lift and pitching moments. Aerodynamic characteristics of the effective decambered configurations using numerical analysis, CFD, and wind tunnel experiments are reported. Results indicate that significant improvement in aerodynamic performance can be achieved for laminar separation control through this active flow surface.

The surface of a rectangular wing is morphed numerically at high angles of attack such that it still operates at the reduced coefficient of lift at which the baseline wing operates but while the flow is separated on the baseline wing, it remains attached on the morphed wing. The aerodynamic characteristics of the baseline wing are obtained experimentally and that of the morphed wing is obtained numerically. The morphed surface at high angles of attack is obtained using a novel ‘decambering’ technique, which accounts for the deviation of the coefficients of lift and pitching moment from that predicted by the potential flow. Two wings with different airfoil sections, N ACA0012 and N ACA4415 are tested and compared at high α. Numerical morphing of wing surface for design coefficient of lift (CL ) (in terms of percentage increment) is presented at angles of attack 50 and 150 . This concept of design CL of a morphing wing is one of the possible solutions to fly at different flight conditions with corresponding targets and maneuvering requirements. A significant addition to the present numerical approach is to provide some comparison of the flow separation behavior with CFD at the root section of both the wing sections. The effects of morphed surfaces on drag penalty, coefficient of lift and post-stall angles of attack are studied and compared in terms of aerodynamic performance.

This paper identifies the laminar separation bubble at the root or span-wise midsection of a rectangular wing using direct surface pressure measurements and analyses their behavior. The locations of separation, transition, and reattachment are identified from surface pressure measurements and oil flow visualizations. Surface oil flow visualization results also clarified the wing-tip and separation bubble interactions near the leading edge of the wing. The transition structure and turbulence characteristics in the separated shear layer locations are studied using Laser Doppler Velocimetry. Time series analysis is carried out to distinguish the flow patterns of transition and later transition locations along with chordwise locations of the root section of the wing.

The surface of a rectangular wing is morphed at high angles of attack such that it continues to operate at the reduced coefficient of lift (Cl) at which the baseline wing operates, but unlike the baseline wing, where the flow is separated, the flow remains attached on the morphed wing. A morphed surface is also generated to operate at a local design 2D (two-dimensional) Cl, which is obtained by incrementing the baseline Cl by a percentage at pre and post-stall angles of attack. The morphed surface is generated numerically using a novel ‘decambering’ technique, which accounts for the deviation of the coefficients of lift and pitching moment from that predicted by potential flow, analytically, using CFD and implemented experimentally by attaching an external Aluminium skin to the leading edge of the wing. Two different wing sections, NACA0012 and NACA4415, are tested on a rectangular planform. The effect of morphing on the aerodynamic performance is discussed, and aerodynamic characteristics are reported. Results indicate that significant improvement in aerodynamic performance is achieved at high angles of attack, especially at post-stall through this active morphed flow surface.

Experimental investigation on two rectangular wings with NACA0012 and NACA4415 profiles is performed at different Reynolds numbers to understand their aerodynamic behaviours at a high α regime. In-house developed numerical code VLM3D is validated using this experimental result in predicting the aerodynamic characteristics of a rectangular wing with cambered and symmetrical wing profile. The sectional coefficient of lift ((Formula presented.)) obtained from the numerical approach is used to study the variation in spanwise lift distribution. The lift and moment characteristics obtained from wind tunnel experiments are plotted, and change in the maximum coefficient of lift ((Formula presented.)) and stall angle (α stall) are studied for both of the wing sections. A significant addition to the novelty of the present experiments is to provide some comparison of the numerical induced drag coefficient, (Formula presented.) with experimentally fitted model coefficients using least square technique. A novel method is used to examine the aerodynamic hysteresis at high angles of attack. The area included in the lift- Re curve loop is a measure of aerodynamic efficiency, and its variation with angle of attack and wing plan forms is studied.

This paper investigates an improvement of the aerodynamic performance of a wing at high, including post-stall angles of attack by re-designing its camber line to control the separation of its boundary layer. This is experimentally implemented using an Aluminum secondary skin on the wing surface, which aligns itself to the separated boundary layer at high angles to attack, such that the flow remains attached to it, which otherwise would have separated on the baseline configuration. The shape of the skin, which is now regarded as the active flow surface, is essentially a morphed version of the baseline shape of the wing and is predicted numerically using an in-house code based on a ‘decambering’ technique that accounts for the local deviation of camber by accounting for the difference in the coefficients of lift and pitching moment predicted by viscous and potential flows. This technique is tested on a rectangular planform using different wing sections, NACA0012, NACA4415, and NRELS809. The effective morphed flow surface is also used for the baseline wing to operate at a design local 2D Cl, which is obtained by incrementing the baseline Cl by a user defined percentage at design pre and post-stall angles of attack. Aerodynamic characteristics of the effective morphed configurations using numerical analysis, CFD, and wind tunnel experiments are reported.

This paper reports an investigation into the effects of the transient flow behavior on a rectangular wing at high angles of attack. In-house developed numerical code Unsteady Vortex Lattice Method (UVLM) coupled with decambering technique is used to understand the aerodynamic behaviors of a rectangular wing with different airfoil sections. The spectral density of the transient coefficient of lift data is calculated for both wing sections, and a low-frequency oscillation is identified near the static stall. The transient sectional coefficient of lift (Clsec) is utilized to study the variation in span-wise lift distribution at different time steps numerically. Transitional behavior of decambered surfaces for different wing sections is also discussed to provide insight into the unsteady separated boundary layer characteristics.