Transonic buffet characteristics under conditions of free and forced transition

TL;DR

This study uses large-eddy simulations and stability analyses to compare laminar and turbulent transonic buffet phenomena, revealing that both types share the same fundamental mechanism despite different boundary layer states.

Contribution

First direct comparison of free- and forced-transition transonic buffet using large-eddy simulations and stability analysis, linking findings across modeling approaches.

Findings

Both buffet types share the same fundamental mechanism.

Dynamic features are consistent across boundary layer states.

Reynolds-averaged and scale-resolving methods produce comparable results.

Abstract

Transonic buffet is commonly associated with self-sustained flow unsteadiness involving shock-wave/boundary-layer interaction over aerofoils and wings. The phenomenon has been classified as either laminar or turbulent based on the state of the boundary layer immediately upstream of the shock foot and distinct mechanisms for the two types have been suggested. The turbulent case is known to be associated with a global linear instability. Herein, large-eddy simulations are used for the first time to make direct comparisons of the two types by examining free- and forced-transition conditions. Corresponding simulations based on the Reynolds-averaged Navier--Stokes equations for the forced-transition case are also performed for comparison with the scale-resolving approach and for linking the findings with existing literature. Coherent flow features are scrutinised using both data-based spectral proper orthogonal decomposition of the time-marched results and operator-based global linear stability and resolvent analyses within the Reynolds-averaged Navier--Stokes framework. It is demonstrated that the essential dynamic features remain the same for the two buffet types (and for the two levels of the aerodynamic modelling hierarchy), suggesting that both types arise due to the same fundamental mechanism.