Paul G. Tucker

A state-of-the-art large eddy simulation code has been developed to solve compressible flows in turbomachinery. The code has been engineered with a high degree of scalability, enabling it to effectively leverage the many-core architecture of the new Sunway system. A consistent performance of 115.8 DP-PFLOPs has been achieved on a high-pressure turbine cascade consisting of over 1.69 billion mesh elements and 865 billion Degree of Freedoms (DOFs). By leveraging a high-order unstructured solver and its portability to large heterogeneous parallel systems, we have progressed towards solving the grand challenge problem outlined by NASA [1], which involves a time-dependent simulation of a complete engine, incorporating all the aerodynamic and heat transfer components.

Flow separations occur in the tip region when the fan is operating at the approach condition. To reduce computational cost without degrading accuracy, the hierarchical modeling approach has been developed to predict such fan flow. This allows both flow and geometry to be treated with various fidelity levels in different zones. To be specific, this is achieved by zonalizing large-eddy simulation (LES) in the fan tip region and modeling downstream stators with low-order blade body forces. This approach provides an accurate and economical prediction of separated fan flows in the stage environment. The predicted fan wake profiles show a reasonably good agreement with the hot-wire measurements considering passage-to-passage variations. Finally, the simulation data are used to assess the isotropic turbulence hypothesis that is made on fan wake in low-order acoustics models.

Leading edge instrumentation used in compressor and turbine blades for jet-engine test rigs can cause significant obstruction and lead to a marked increase in downstream pressure loss. Typical instrumentation used in such a scenario could be a Kiel-shrouded probe with either a thermocouple or pitot-static tube for temperature/pressure measurement. High fidelity analysis of a

Leading edge instrumentation used in compressor and turbine blades for jet-engine test rigs can cause significant obstruction and lead to a marked increase in downstream pressure loss. Typical instrumentation used in such a scenario could be a Kiel-shrouded probe with either a thermocouple or pitot-static tube for temperature/pressure measurement. High fidelity analysis of a coupled blade and probe requires the generation of a high-quality mesh which can take a significant amount of an engineers time. The application of an immersed boundary method (IBM) and large eddy simulation (LES) is shown in this paper to enable the use of an extremely simple mesh to observe the primary flow features generated due to the blade and probe interaction effects, as well as quantify downstream pressure loss to within a high level of accuracy. IBM is utilized to approximately model the probe, while fully resolving the blade itself through a series of LES simulations. This method has shown to be able to capture downstream loss profiles as well as integral quantities compared to both experiment and fully wall-resolved LES without the need to spend a significant amount of time generating the ideal mesh. Additionally, it is also able to capture the turbulence anisotropy surrounding the probe and blade regions.

Purpose The purpose of this paper is to outline the extensive multi-scale and multi-physics challenges when simulating future aircraft and offer strategies to help deal with some of these challenges. Design/methodology/approach To help with the multi-scale challenges, in a hierarchical, zonal fashion both the handling of turbulence and geometry is considered. Findings Such modelling of geometry is necessary to help deal with the increasingly coupled nature of many aerodynamic problems more economically and the drive towards considering ever increasing levels of geometrical complexity/scale. Originality/value The proposed unified framework could be exploited all the way, through initial fast preliminary design to final numerical test involving various bespoke combinations of hierarchical components.

The successful application of eddy resolving simulations to most areas of a modern gas turbine aeroengine is considered. A coherent modeling framework is presented to address coupling challenges. A flow classification is also given. The extensive results presented are shown to be promising but many challenges remain. In the short term, the use of eddy resolving simulations should see greater use in Reynolds-averaged Navier–Stokes (RANS) and lower-order model calibration/development—this is starting to happen already. Ideally, in the near future, RANS, large eddy simulation (LES), and test should work in harmony. It is advocated that currently, certain costly engineering design problems can be avoided or understood using scale resolving simulations.

The individual and cumulative effects of forced frequency oscillations and free stream turbulence (FST), on the separation-induced transition caused by an adverse pressure gradient on a flat plate geometry, are numerically investigated by solving the Navier–Stokes equation. The flat plate is subjected to a streamwise pressure gradient via a contoured wall, representative of a low pressure turbine blade. The results are validated against existing numerical data, and insights into flow physics of the pre-transitional and turbulent regimes are gained using instantaneous, time-averaged, and phase-averaged flow fields, turbulent kinetic energy budgets, and a disturbance enstrophy-based nonlinear analysis based on direct numerical simulations. Oscillations are imposed at two values of reduced frequency (k_osc). Higher reduced frequency oscillations are more effective in triggering early transition and reducing the separated region. This suppression of the separated region is more pronounced with FST. A reduction in the size of the separation bubble is noted along with enhanced near-wall mixing resulting in a shift in the inflection point of the velocity profile toward the wall, with FST and oscillations. The budget of the turbulent kinetic energy shows the dominance of the production term for the case with FST and forced oscillations. The disturbance enstrophy-based analysis provides insight into budget terms of the enstrophy equation, specifically on the role of vortex stretching. Finally, spatiotemporal linear receptivity of the case with oscillations near the separation bubble is reported. This provides a quantitative description of the instability triggered by the pressure gradient and oscillations.

Three-dimensional corner separation significantly affects compressor performance, but turbulence models struggle to predict it accurately. This paper assesses the capability of the original shear stress transport (SST) turbulence model to predict the corner separation in a linear highly loaded prescribed velocity distribution (PVD) compressor cascade. Modifications for streamline curvature, Menter’s production limiter, and the Kato-Launder production term are examined. Comparisons with experimental data show that the original SST model and the SST model with different modifications can predict the corner flow well at an incidence angle of −7 deg, where the corner separation is small. However, all the models overpredict the extent of the flow separation when the corner separation is larger, at an incidence angle of 0 deg. The SST model is then modified using the helicity to take account of the energy backscatter, which previous studies have shown to be important in the corner separation regions of compressors. A Reynolds stress model (RSM) is also used for comparison. By comparing the numerical results with experiments and RSM results, it can be concluded that sensitizing the SST model to helicity can greatly improve the predictive accuracy for simulating the corner separation flow. The accuracy is quite competitive with the RSM, whereas in terms of computational cost and robustness it is superior to the RSM.