The present investigation targets the generation of airfoil trailing-edge broadband noise that arises from the interaction of turbulent boundary layer with the airfoil trailing edge. Large-eddy simulations, carried out using a massively parallel compressible solver CharLES X , are conducted for a Controlled-Diffusion (CD) airfoil with rounded trailing edge for seven configurations, characterized with a Reynolds number, angle of attack and Mach number. An analysis of the unsteady pressure signals in the boundary layer is proposed in regard to classical trailing edge noise modelling ingredients.

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Cavity flows are essential components of many aeronautical and spatial engines. For example, in gas turbines a network of cavities is calibrated and managed to divert part of the main cold stream which is then re-injected in the hot regions of the engine to shield walls from the hot combustion products. For pumps, cavities are naturally present at the junction of fixed and rotating parts. In both contexts, mastering the flow stability in rotor/stator cavities is essential to avoid imposing too large flow variations which could lead to miss-tuned operating conditions in the engine and a drastic loss of performance or life-span. Although stability of these flows has been widely studied in the literature, a lack of clear understanding of the triggering mechanisms from stable to unstable flow solutions remains, especially in the context of industrial applications where Reynolds numbers are very high and difficult to handle. To cope with such complex geometry, fully unsteady flows, the so-called Large Eddy Simulation (LES) approach appears as a very promising method. However and for such high Reynolds number industrial applications, wall modeling still remains a necessity to alleviate the computational cost of LES. Understanding the impact of such a strong modeling hypothesis on the mean flow features and unsteady energetic content is hence mandatory and the objective of the present discussion. To do so, the present paper studies LES flow solutions in an enclosed rotor-stator configuration with a stationary shroud. These simulations are performed using a two-steps Taylor-Galerkin finite-element scheme coupled to a WALE subgrid scale model giving a better prediction of the eddy viscosity in zones of strong shear. This allows capturing the unsteady structures known to be present in the boundary layers. Two sets of statoric boundary conditions are investigated: the dynamics of the boundary layer is either resolved using a fine mesh grid or modeled using a classic boundary layer law of the wall. It is shown that the modeling of the stationary disc layer induces an underestimation of the flow velocity at low radii and loss of accuracy in the radial description of the boundary layer structures. Despite these differences, the most energetic structures are found to have the same azimuthal organization as in the wall resolved configuration as well as the same pulsation, which in turn produces a boundary layer with the same spectral content as in the wall resolved test case.

Self-sustained oscillations of rotor/stator cavity flows are well known to industry. This unsteady phenomenon can be very dangerous and jeopardize the structural integrity of aeronautical engines by damaging turbomachinery components or turbopumps in the context of space applications. Today, the origin of such flow instability and resulting limit-cycle is not well understood and still difficult to predict numerically. In order to have more insight of this phenomenon dynamic, an academic rotor/stator cavity is investigated in the present paper. The main motivation of this study is to highlight the benefit of conjunct numerical strategies relying on Large Eddy Simulations (LES) and flow stability analyses to understand driving instability mechanisms. More specifically, results of a local and global methods are devised and compared to a Dynamic Mode Decomposition (DMD) of LES predictions. Good agreements between the stability methods studied and the present features in the LES limitcycle are found. On this basis, a sensitivity and receptivity analysis of the flow is realized to point the origin of the two most unstable modes: i.e the position within the flow where the problem issues.

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