arXiv subjects

Christer Fureby

Publications and source records attributed to Christer Fureby.

4 recordsLinked to original sources

arXiv2025

A Coupled CFD Framework for Combustor Turbine Interaction in a Research Aeroengine

This work presents a fully coupled combustor turbine simulation framework applied to the MYTHOS aeroengine, developed within the Horizon Europe project MYTHOS, aimed at assessing the impact of Sustainable Aviation Fuels (SAFs) and hydrogen on next generation propulsion systems. The numerical setup features a dynamic, bidirectional coupling between a pressure-based solver with detailed finite rate chemistry, deployed in the combustor, and a density-based turbomachinery solver employing tabulated thermochemistry for efficiency, used for the turbine. The coupling is realised through a flux-averaging methodology that ensures conservative exchange of flow quantities and allows flow in arbitrary directions across the interface. Previous validation steps of presented methodology have shown the viability of the approach and are also shortly reviewd. The paper focuses on the chemistry handling strategy that guarantees thermochemical consistency between the two solvers. Coupled reacting simulations at cruise operating conditions demonstrate the capability of the framework to capture combustor generated hot streaks transport and their influence on turbine aerothermal loading. Comparison with segregated simulations of the two components shows that coupling captures the highly unsteady temperature and flow distributions at the turbine inlet and across the blade rows. Whilst mean aerodynamic loading are essentially unchanged, a realistic circumferential variability in blade thermal loading can be observed in the coupled simulations, thus establishing a consistent foundation for future studies on the effects of alternative fuels on core engine components.

physics.flu-dyn↗

arXiv2024

Large Eddy Simulations of Flow over Additively Manufactured Surfaces: Impact of Roughness and Skewness on Turbulent Heat Transfer

Additive manufacturing creates surfaces with random roughness, impacting heat transfer and pressure loss differently than traditional sand-grain roughness. We conducted high-fidelity heat transfer simulations over three-dimensional additive manufactured surfaces with varying roughness heights and skewness. Based on an additive manufactured Inconel 939 sample from Siemens Energy AB, we created six surfaces with different normalized roughness heights, $R_a/D = 0.001, 0.006, 0.012, 0.015, 0.020,$ and $0.028$, and a fixed skewness, ${s_k} = 0.424$. Each surface was also flipped to obtain negatively skewed counterparts (${s_k} = -0.424)$. Simulations were conducted at a constant Reynolds number of 8000 and with temperature treated as a passive scalar. We analyzed temperature, velocity profiles and heat fluxes to understand the impact of roughness height and skewness on heat and momentum transfer. The inner-scaled mean temperature profiles are of larger magnitude than the mean velocity profiles both inside and outside the roughness layer. This means the temperature wall roughness function differs from the momentum wall roughness function. Surfaces with positive and negative skewness yielded different estimates of equivalent sand-grain roughness for the same $R_a/D$ values, suggesting a strong influence of slope and skewness on the relationship between roughness function and equivalent sand-grain roughness. Analysis of the heat and momentum transfer mechanisms indicated an increased effective Prandtl number within the rough surface in which the momentum diffusivity is larger than the corresponding thermal diffusivity due to the combined effects of turbulence and dispersion. Results consistently indicated improved heat transfer with increasing roughness height and positively skewed surfaces performing better beyond a certain roughness threshold than negatively skewed ones.

physics.flu-dyn↗

arXiv2024

Large Eddy Simulations of Turbulent Pipe Flows At Moderate-To-High Reynolds Numbers

Wall-bounded turbulence is relevant for many engineering and natural science applications, yet there are still aspects of its underlying physics that are not fully understood, particularly at high Reynolds numbers. In this study, we investigate fully-developed turbulent pipe flows at moderate-to-high friction velocity Reynolds numbers ($361 \leq Re_τ \leq 2,000$), corresponding to bulk velocity-based Reynolds numbers of $11,700 \leq Re_{b} \leq 82,500$, using wall-modeled Large Eddy Simulations (LES) in OpenFOAM. A grid convergence study is performed for $Re_τ = 361$, followed by an investigation of the accuracy of various subgrid-scale stress models for the same Reynolds number. Results show that the Wall-Adapting Local Eddy (WALE) model performs well compared to experiments and Direct Numerical Simulations (DNS), while One-Equation Eddy-Viscosity Model (OEEVM) and Smagorinsky (SMG) are too dissipative. LES utilizing WALE are then performed for four different Reynolds numbers with gradually refined grids, revealing excellent agreement with DNS data in the outer region. However, a significant deviation from DNS data is observed in the sub-viscous layer region, indicating the need for further mesh refinement in the wall-normal direction to accurately capture the smallest-scale motions' behavior. Additional mesh sensitivity analysis uncovered that, as the $Re_τ$ value rises, it becomes crucial for a grid to adhere to the condition of $Δx^{+} \leq 20 - 25$ and $Δz^{+} \leq 10$ in order to precisely capture substantial large and small scale fluctuations. Overall, the WALE model enables accurate numerical simulations of high-Reynolds-number, wall-bounded flows at a fraction of the computational cost required for temporal and spatial resolution of the inner layer.

physics.flu-dyn↗

arXiv2023

Large Eddy Simulations of Fully-Developed Turbulent Flows Over Additively Manufactured Rough Surfaces

In the last decade, progresses in additive manufacturing (AM) have paved the way for optimized heat exchangers, whose disruptive design will depend on predictive numerical simulations. Typical AM rough surfaces show limited resemblance to the artificially constructed rough surfaces that have been the basis of most prior fundamental research on turbulent flow over rough walls. Therefore, a high-fidelity LES database is built to develop and assess novel wall models for AM. This article investigates the flow in rough pipes built from the surfaces created using AM techniques at Siemens based on Nickel Alloy IN939 material. We developed a code to generate the desired rough pipes from scanned planar surfaces and performed high-fidelity LES of turbulent rough pipe flows at Re = 11,700 to reveal the influence of roughness on turbulence, mainly the average roughness height and the Effective Slope. The equivalent sand-grain roughnesses, ks, of the present AM rough surfaces are predicted using the Colebrook correlation. In the present study, the existence of a logarithmic layer is marked even for high values of ks. The mean flow, the velocity fluctuations, and the Reynolds stresses show turbulence's strong dependence on the roughness topography. Profiles of turbulence statistics are compared by introducing an effective wall-normal distance. The effective distance collapses the shear stresses and the velocity fluctuations outside the roughness sublayer; thus, Townsend's similarity of the streamwise mean velocity is marked for the present roughnesses. Furthermore, a mixed scaling is introduced to improve the collapse of turbulence statistics in the roughness sublayer.

physics.flu-dyn↗