Simulation of transonic buffet with an automated zonal DES approach
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ORIGINAL PAPER
Simulation of transonic buffet with an automated zonal DES approach Maximilian Ehrle1 · Andreas Waldmann1 · Thorsten Lutz1 · Ewald Krämer1 Received: 14 January 2020 / Revised: 8 July 2020 / Accepted: 19 August 2020 © The Author(s) 2020
Abstract A study of transonic buffet on the NASA Common Research Model at flight Reynolds numbers is presented. The ability of two different hybrid RANS/LES models as well as the URANS approach for resolving three-dimensional buffet motion was evaluated by means of spectral analysis. Automated Zonal DES and URANS simulations show similar results in terms of buffet frequency and spanwise propagation of buffet cells, whereas the Delayed Detached Eddy Simulation results indicate a strong interaction between flow separation and shock motion. The extracted characteristic frequencies which are associated with transonic buffet are located in a range of Sr = 0.2–0.65 for URANS and AZDES and are therefore in accordance with findings from related recent research. Furthermore, the simulation time series were investigated and a structure of spanwise moving buffet cells with varying convection speed and wavelength could be observed. Keywords Transonic buffet · Aircraft aerodynamics · Hybrid RANS/LES · NASA Common Research Model
1 Introduction Safety and efficiency improvements play a major role in the development of modern transport aircraft. Since cruise flight in the transonic regime is the primary part of a typical flight connection, the investigation of the aerodynamics in this phase is of special interest. This requires a better understanding of the flow effects determining its boundaries. The accurate prediction of aerodynamic phenomena that occur under these conditions remains a challenging task due to the occurrence of locally supersonic flow above the upper surface of the wing and the associated shocks and shock–boundary layer interaction. If the Mach number or the angle of attack are increased, these phenomena can result in transonic buffet, a complex unsteady shock motion coupled
with shock-induced flow separation. Transonic buffet can lead to dynamic loads on the airplane structure, which causes a demand of improving its prediction. Furthermore, shock-induced flow separation results in an unsteady turbulent wake, which can interact with the aircraft’s tailplane and induces fluctuating loads [12]. Because of the complex turbulent motion in the wake, scale resolving simulation methods are necessary to ensure a proper reproduction of flow physics in this area [19]. In addition, the knowledge of the influence of these conditions on the location of flow separation is essential for the prediction of the turbulent wake’s propagation and development. As a consequence, it is imperative to validate the prediction of the phenomena in the vicinity of the wing surface with these methods, before moving on to studies on the flow physics and interactions in the wake.
* Maximilian Ehrle [email protected]‑stuttgart.de
1.1 Studies and physics of the buffet phenomenon
Andreas Waldm
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