Impact of Engine Nacelle Flow on Buffet

TL;DR

This study uses wall-modeled LES to analyze how an ultra-high bypass ratio engine nacelle affects shock dynamics and buffet behavior on a transonic airfoil, revealing a coupling mechanism between nacelle and airfoil shocks.

Contribution

It demonstrates the significant impact of nacelle geometry on shock behavior and buffet characteristics, introducing a dynamic mode analysis of nacelle-airfoil shock coupling.

Findings

Nacelle presence alters flow and shock dynamics significantly.

Nacelle shock influences airfoil shock strength and buffet.

Shared dynamic mode indicates coupling between nacelle and airfoil shocks.

Abstract

The transonic flow around the OAT15A airfoil is computed at buffet conditions, i.e., freestream Mach number $Ma_\infty = 0.73$, chord-based freestream Reynolds number $Re_c = 2\cdot10^6$, and angle of attack $\alpha = 3.5^\circ$ using wall-modeled LES. Two configurations are considered, one which includes a generic ultra-high bypass ratio (UHBR) engine nacelle geometry and one without an engine, which is denoted the baseline case. The introduction of the UHBR-engine nacelle leads to a significant deviation of the flow onto the airfoil from the baseline case and has an essential effect on the occurring shock dynamics. The flow field of the nacelle configuration is characterized by a shock wave on the upper part of the nacelle sharing dynamic features with the shock on the airfoil. This impact of the nacelle shock on the airfoil shock means a reduced strength of the airfoil shock resulting in a less developed buffet. The perturbation of the general flow field is evaluated as to established buffet models and the dynamic features of the shock waves are analyzed by the sparsity-promoting dynamic mode decomposition. This analysis shows the existence of a shared dynamic mode of the nacelle and the airfoil shock which suggests a coupling mechanism between them.