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The paper presents a numerical investigation of the flow around a NACA23012 airfoil with two ice shapes, a spanwise ridge and leading edge roughness. RANS and URANS simulations are completed with various 1st and 2nd order turbulence models (Spalart-Allmaras, Menter SST, EARSM, DRSM) for a selected number of points of the airfoil polar. To assess the ability of advanced unsteady hybrid RANS/LES models, one selected flow condition of the spanwise ridge case is also computed with a ZDES hybrid method. The results are compared with experimental data (integrated loads, pressure distribution, velocity field) obtained in the ONERA F1 wind tunnel. The Spalart-Allmaras model is the only RANS model among those assessed in this study converging efficiently towards steady-state whatever the flow condition considered. Together with DRSM, it also provides a reasonable predictive effect on the performance degradation due to ice shape. DRSM is much more expensive as it contains more physics, providing natural unsteady solutions which have to be time-averaged. DRSM first and second-order statistic fields compare well with ZDES ones, both of them indicating that geometrical three-dimensionality of the ice shapes should be taken into account. Furthermore, the unsteady content of the DRSM URANS solution is compared with that of ZDES, showing that the vortex shedding phenomenon can also be captured by DRSM. [ABSTRACT FROM AUTHOR]

The numerical simulation of dynamic stall around a 3D finite-span oscillating wing of constant OA209 airfoil section is compared to experimental results obtained in the ONERA F2 wind-tunnel, assuming fully turbulent flow. A deep dynamic stall case is considered for a reduced frequency typical of helicopter problems. A detailed comparison with the experimental data available (unsteady pressure distribution and velocity field) shows that the main flow features are captured by the numerical simulation, more especially the large spanwise flow component induced by separation. [ABSTRACT FROM AUTHOR]

Abstract: In the framework of the GOAHEAD European project, CFD simulations around a complete helicopter configuration have been performed by the different partners to validate their codes and to compare with a detailed experimental database. At ONERA, the simulation of such a complex configuration is still challenging in terms of efforts required in the pre-processing phase, and in terms of CPU time. This test-case has been in particular used to set up a pre-processing chain of tools, going from the meshes described in a CGNS tree to the calculation input. This chain including the Chimera assembly of the different components of the helicopter is described in this paper. The second part presents some results of one of the test-cases performed by ONERA in the project: the cruise/tail shake flight condition. The results are compared with the experiment data and also with pre-tests CFD computations. [Copyright &y& Elsevier]

Abstract: The second vorticity confinement scheme proposed by Steinhoff is analysed in detail. First, starting from the 1D linear transport equation applied to a pulse, various formulations for the confinement are compared. The linear 2nd-order schemes (Warming-Beam and Lax–Wendroff schemes) give oscillatory solutions, while the nonlinear confinements of same accuracy behave as limiters with artificial compression. Not only these 2nd-order schemes with confinement conserve the pulse as accurately as a 3rd-order one for identical and sufficiently fine grids, but they remain stable with a global negative diffusion which allows them to conserve the pulse endlessly concentrated over 5–8 mesh cells in the computation, although the form of the equations is then lowered to 1st-order. Application of the energy method for stability analysis indicates that the signal relaxes towards a constant energy solution, for which the energy brought in by the anti-diffusive confinement is balanced by the energy removed from the solution by the diffusive terms. Application to the Euler equations for the advection of a 2D vortex proves that a similar approach can be applied to nonlinear problems. The most appropriate formulation of compressible vorticity confinement is to apply it identically to the incompressible formulation, i.e. without source term in the energy conservation equation. [Copyright &y& Elsevier]

This article presents a new time-marching fully unsteady method for simulating helicopter rotors in manoeuvring flight conditions. The unsteady wake model is based on Mudry''s theory which rigorously derives the evolution equation for the wake considered as a vortex sheet from the fluid dynamic equations. The numerical treatment of the sheet with a high-order panel representation allows an accurate simulation of the wake without using numerical regularisation techniques. An unsteady lifting line model, based on Matched Asymptotic Expansion, is used to represent the blade and to extend the concept of induced velocities to unsteady configurations. A first application to the Bo 105 rotor in manoeuvring flight shows that the method is capable to handle such kind of complex configuration. [Copyright &y& Elsevier]

This paper describes an automatic Vorticity Confinement procedure in order to conserve vorticity in the resolution of the compressible Euler or Navier–Stokes equations. It is based on the cancellation of the leading truncation error terms in the numerical solution of the vorticity convection equation. Application to the simple case of the convection of a 2D vortex by considering the Euler equations shows that the procedure is adequate, although some problems lie at the vortex center, probably related to the compressible character of the equations and to the singularity associated to the confinement term at the vortex center. Further analysis suggests to consider the specific vorticity instead, thus imposing a corresponding density confinement term. The first results obtained so far indicate that this way of research is promising. However, it is shown that for fine grids, a regularization treatment must also be applied at the center of the vortex because of the Vorticity Confinement singularity. Finally, a first demonstration of the applicability of the method to 3D flows is given for the case of a vortex ring. [Copyright &y& Elsevier]

Predicting the laminar-turbulent transition is becoming a necessity in order to reduce margin costs in the design of turbines and helicopter rotors. Most RANS models lack the capacity to create turbulence sufficiently abruptly to accurately predict separation-induced transition. This article aims at evaluating the performances of the γ − Re θ , t strategy applied to the Spalart-Allmaras and k − ω − SST models (ν ˜ − γ − Re θ , t and k − ω − γ − Re θ , t). The chosen test case features a laminar separation bubble over a flat plate. The results are compared to the flows obtained using classical algebraic criteria and validated against DNS data. The effects of the correction by Dacles-Mariani et al. are detailed as well as those of two sets of correlations. The turbulence production mechanism of the present models is too weak downstream of the first increase of intermittency, and the laminar separation bubbles are longer than in the reference flow. More specifically, the ν ˜ − γ − Re θ , t model with Medida and Baeder's correlations fails to reach the correct levels of turbulence production in the fully turbulent boundary layer. Switching the correlations corrects this last behavior. Finally, using maps of the activation zones of the Dacles-Mariani correction, a sensor is exhibited that could be used in future separation-induced transition modeling efforts. [ABSTRACT FROM AUTHOR]