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A transonic interaction between a shock wave and a turbulent boundary layer is experimentally and theoretically investigated. The configuration is a transonic channel flow over a bump, where a shock wave causes the separation of the boundary layer in the form of a recirculating bubble downstream of the shock foot. Different experimental techniques allow for the identification of the main unsteadiness features. As recognised in similar shock-wave/boundary-layer interactions, the flow field exhibits two distinct characteristic frequencies, whose origins are still controversial: a low-frequency motion which primarily affects the shock wave; and medium-frequency perturbations localised in the shear layer. A Fourier analysis of a series of Schlieren snapshots is performed to precisely characterise the structure of the perturbations at low-and medium-frequencies. Then, the Reynolds-averaged Navier-Stokes (RANS) equations closed with a Spalart-Allmaras turbulence model are solved to obtain a mean flow, which favourably compares with the experimental results. A global stability analysis based on the linearization of the full RANS equations is then performed. The eigenvalues of the Jacobian operator are all damped, indicating that the interaction dynamic cannot be explained by the existence of unstable global modes. The input/output behaviour of the flow is then analysed by performing a singular-value decomposition of the Resolvent operator; pseudo-resonances of the flow may be identified and optimal forcings/responses determined as a function of frequency. It is found that the flow strongly amplifies both medium-frequency perturbations, generating fluctuations in the mixing layer, and low-frequency perturbations, affecting the shock wave. The structure of the optimal perturbations and the preferred frequencies agree with the experimental observations.

This paper presents a numerical study of the transonic flow over a half wing-body configuration representative of a large civil aircraft. The Mach number is close to cruise conditions, while the high angle of attack causes massive separation on the suction side of the wing. Results indicate the presence of shock-wave oscillations inducing unsteady loads which can cause serious damage to the aircraft. Transonic shock buffet is found. Based on preliminary simulations using a baseline grid, the region relevant to the phenomenon is identified and mesh adaptation is applied to significantly refine the grid locally. Then, time-accurate Reynolds-averaged Navier-Stokes and delayed detached-eddy simulations are performed on the adapted grid. Both types of simulation reproduce the unsteady flow physics and much information can be extracted from the results when investigating frequency content, the location of unsteadiness and its amplitude. Differences and similarities in the computational results are discussed in detail and also analysed with respect to recent experimental data.

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A numerical study of the flow over a wing representative of a large civil aircraft at cruise condition is discussed. Reynolds-averaged Navier-Stokes simulations are conducted on a half wing-body configuration, at different Mach numbers and angles of attack. For small angles, the shock-induced separation is limited and the simulations converge towards a steady state. For each Mach number, a critical angle of attack exists where the separated region increases in size and begins to oscillate. This phenomenon, known as transonic shock buffet, is reproduced by the unsteady simulation and much information can be extracted analysing location, amplitude and frequency content of the unsteadiness.

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In order to evaluate the strong aerodynamic interactions between the secondary fan/OGV stage with the airframe engine integration system, and the ability of numerical methods to assess these interactions, several numerical methods have been tested. They range from RANS computation where the engine is modelled using simplified Boundary Conditions to full 360° URANS computations including the rotating fan blades. Intermediate methods such as Body-Force and Actuator Disk approaches have also been assessed. Computations were carried out on a generic configuration designed in the frame of the European ASPIRE project. The nacelle, short air intake and nozzle were designed by Airbus, the fan/OGV stage by DLR based on specifications provided by Airbus. This paper aims at presenting those results, including a grid convergence study, and at detailing the advantages and drawbacks of each method for two operating conditions: in cruise and at low speed. Nomenclature ADP = Aerodynamic Design Point LS = Low-Speed URANS = unsteady Reynolds Average Navier-Stokes AD = Actuator-Disk BF = Body-Force UP = Uniform Pressure AB = Abacus-based OGV = Outlet Guide Vane FPR = Fan Pressure Ratio BPR = By-Pass Ratio RNA = Blade number reduction (Réduction du Nombre d'Aubes in French)