Rinku Mukherjee

This paper uses a numerical post-stall predictive tool based on ‘decambering’ approach to study the aerodynamic characteristics of a lead-trail formation in pre and post-stall flow conditions. A basic lead-trail formation consisting of 2 wings and an extended formation consisting of 5 wings are studied with a view to the possibility of fuel savings, increase in range of operation, delayed flow separation and efficient positioning of the wings with respect to each other. Whether increasing the number of wings in a configuration is more useful is also looked into. The optimum operational angles of attack for maximum advantage in terms of fuel efficiency of all wings is studied including post-stall angles of attack. Numerical results for CL, CDi, section Cl distribution and their dependence on vertical offsets and angle of attack are reported.

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.

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.