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.

In this paper, numerical analysis is conducted using a local camber correction approach called “decambering” to predict pre and post-stall aerodynamic characteristics of multiple lifting surfaces operating in formation. A three wings Chevron formation and five and nine wings V-formation are studied. NACA2412 wing section is used and experimental validation is provided with Cessna 172 aircrafts flying in Chevron formation. Effect of wing incidence and shifting of stall angles is looked at along with changes in geometric offsets between the wings in formation. The spanwise distribution of coefficients of lift and induced drag at different angles of attack, including high and post-stall angles of attack is studied for all the wings. The span efficiency factor, which represents the correction in drag due to change in lift as compared to that of an ideal wing of the same aspect ratio but with elliptical lift distribution is calculated. The maximum possible efficiency is then used to estimate the maximum reduction in drag possible for individual wings in different formations. The change in efficiency with number of lifting surfaces in a formation is also estimated.

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.