Performance analysis of a heaving wing using DNS and LES

Abstract

The weight and structure of civil transport aircraft are mainly dictated by the loads they experience at the limit of the design envelope (e.g. turbulence, gusts and manoeuvres). During the design process aircraft loading is often predicted using simplified models. However, under extreme operating conditions aircraft experience erratic unsteady loads that are not well understood, and hence difficult to predict using state of the art reduced models. Achieving a more profound understanding of the flow structures dictating the aerodynamic loads under extreme conditions will be crucial for the design of efficient aircraft. An example of such conditions occurs when a wing starts heaving or encounters a gust near its stall angle (e.g. during landing); unsteady flows and transient effects, including flow instabilities and vortex shedding, take place, making the aerodynamic loads highly unpredictable (see for example Von Ellenrieder et al, J Fluid Mech, 490:129–138, 2003, [1]). These complex physical mechanisms can only be fully captured by experiments and accurate numerical simulations, both of which are currently expensive to be used during the design stages, but can provide useful insight. Direct numerical simulations (DNS), being free from simplified modelling assumptions, have the advantage of including all the relevant flow physics. On the other hand, the large eddy simulation (LES) technique can be used to simulate realistic flow conditions, but its accuracy in predicting complex flow phenomena including flow instability and vortex shedding is not clear. This work focuses on assessing the performance of OpenFoam’s LES solver for the prediction of the aerodynamic loads acting on a heaving wing at incidence through comparisons with DNS and experimental results.