Bow Wave Effect in Aerial Refueling: Computational Analysis and Modeling

Abstract

Mechanisms contributing to the “bow wave” effect of a receiver on a tanker are investigated, and a modeling method for dynamic simulation is developed. Vortex lattice and Cart3D codes are used to calculate the aerodynamic forces and moments for a C-141B behind a KC-135. The vortex lattice code significantly underpredicts the bow wave effect, whereas the Cart3D code shows good agreement with available flight data. The modeling method uses stream functions for inviscid flow around solid bodies. The flowfield induced by the presence of aircraft bodies is superimposed on the flowfield generated by horseshoe vortices. The resultant flowfield is approximated by the effective uniform translational and rotational velocity components, which are used in the buildup equations for the aerodynamic force and moment coefficients of both tanker and receiver aircraft. This method applied to a flying wing behind a KC135 shows good agreement with Cart3D results. It is concluded that the major contribution to the “bow wave” effect is the effect of the displacement of air due to the volume of the receiver and not upwash from the bound vortex due to the lift of the receiver. This disagrees with earlier studies that did not have the benefit of flight data to use as a benchmark.