Non-zonal Approaches for Grey Area Mitigation

With the core activity on the development of CFD tools for aerospace applications, and the growing part of activities also oriented towards the area of fluid dynamics for industrial systems, all so-called “real-world” applications exhibit complex flow phenomena such as unsteady flow, (massive) separation, transition to turbulence and turbulence itself. All theses applications, exhibiting massive flow separation, need ideally the use of advanced turbulence models so as to capture the correct separation pattern and to resolve the frequency content of at least the mean flow. This is underlined by all test cases that have been carried out and properly investigated – see Chapter IV - during the course of the DESider project, and which at the same time allow to gain a good understanding of the pro and con’s of the methods used and the way they interact with the numerical algorithms, but also with the grid properties and their effects on the computational effort required to attain satisfactory results. In general, the outcome can be taken as means for best practice guidelines and information on the accuracy of the numerical results, their cost and, thus, the area of applications for which these new methods should be considered.

International audience

Slat Noise Prediction using Hybrid RANS-LES methods on Structured and Unstructured Grids

Improved delayed detached-eddy simulation is performed to explore the control mechanism of the transverse rod spoiler near the leading-edge of an open-type cavity at Ma = 0.9. The rod induces vertical velocity and lifts up the shear layer, significantly reducing the pressure fluctuation inside the cavity. Rossiter peaks are damped and energy is redistributed to the high frequency components near the cavity leading-edge. Vortex shedding after the rod generates high frequency peaks. Then three rod spoilers of different diameters and gap distances are numerically evaluated and compared. A narrow gap between the rod and the wall tends to weaken the lifting-up of the shear layer. Large rod diameter enhances the lifting-up, but also generates excessive perturbation, which is also the case for the gap distance.

Improvements to an industrial process for the simulation of jet-flap interaction noise are evaluated for a single-stream jet and a coaxial jet installed under a wing and flap. Prediction of the strong installation effect agrees well with measurements in a blind comparison. Alongside an advanced DES model with “grey-area” improvements, the importance of software infrastructure aspects such as meshing, numerics and process automation is demonstrated.