Thermodynamic Analysis of Distributed Propulsion

Abstract The ability of propulsion Sources (Sources) to increase the L/D-efficiency of aircraft is highly dependent on the Sources’ locations, surrounding surface morphologies, and lost work associated with Sources’ operating points. Computational fluid dynamics (CFD) calculations were performed on airfoils (i.e., 2D CFD) to provide guidelines for identifying base case specifications of these variables. Trailing-edge upper-surface Source locations provided the greatest direct impact on L/D-efficiency, but mid-chord Sources provided the ability to minimize the interference of sequential thin-plate wing sections. Optimal surrounding surface morphologies depend on the mode of operation, being different for descent and cruising; and so, morphing surfaces are needed to maximize the effectiveness of distributed propulsion. Relative to free stream conditions, Sources have lower pressures at intakes and higher pressures at discharges; the optimal positioning of these pressure differences to generate lift has a significant impact on L/D-efficiency. Metrics were identified to maximize the gain-loss ratio of increased L/D-efficiency versus lost thrust. Distributed-propulsion approaches have particular utility toward designing high-L/D low-AR airframes.