Introduction

Computational Fluid Dynamics (CFD) has become an integral part of the aircraft design process [1]. Over the past 15 years, research efforts concentrated on the accurate and reliable computation of aerodynamic flows with significant viscous effects. This includes high-lift flows featuring pressure-induced separation, viscous wake interaction and confluent boundary layers as well as cruise-flight conditions incorporating shock-boundary-layer interaction and shock-induced separation. As turbulent effects play a significant role in these flows, an adequate representation is crucial for successful aerodynamic performance prediction.

Owing to the currently prohibitive demand with respect to computer resources, any approach other than solving the Reynolds-Averaged Navier-Stokes (RANS) equations will not be feasible for practical problems in the near future [2]. A variety of RANS methods exist, ranging from simple algebraic models up to Reynolds-Stress Transport Models (RSTM). While the former have to be considered outdated, the use of the latter is still prohibitive in complex applications, mainly due to convergence and stability problems as well as their computational expenses. For that reason, transport-equation Eddy-Viscosity Models (EVM) remain the backbone of turbulent viscous computations in the industrial design process.

This motivates the work on improved EVM, linear and non-linear, performed within the MEGAFLOW framework and subsequent projects. By devising, implementing and validating such approaches based on a physically sounder representation of turbulence, a more accurate simulation quality is aspired.