Examination of flow field and force predictions for closely coupled wings using a lifting line approach

Abstract The effectiveness of a lifting line-based continuous vortex sheet methodology to quantify and qualitatively capture the behaviour of multiple lifting surfaces in close proximity at various Reynolds numbers is examined. This is done through the implementation and testing of an iterative non-linear modified lifting line theory method. A key feature is the desingularisation of the wake to ensure accurate predictions of the trailing wake. The results of this analysis are rigorously examined initially through a verification study, followed by a comparison to Reynolds-averaged Navier-Stokes simulations and various experiments involving wingtip vortex interactions found in the literature. While similar approaches have been proposed in the literature, no past work has rigorously examined the effectiveness of the method. In this work, experiments from the literature are used to provide an assessment of accuracy for both the computational fluid dynamics (CFD) simulations and the lifting line analysis at different flight conditions. The results show that the lifting line-based analysis employed is reasonably accurate even at low Reynolds numbers, providing accurate estimates of overall and sectional lift and drag values for both leading and follower wings, as well as over a wide range of Reynolds numbers, angles of attack and wing aspect ratios. Furthermore, flow interaction between multiple flying surfaces is qualitatively compared for each test case, highlighting key differences between LLT and CFD predictions.