Representation of Surface Roughness in Turbulent Boundary Layers through Blowing and Suction in Xcompact3d

The control of turbulent flows is a key area of research in fluid mechanics due to their complex dynamics and significant influence on momentum, heat, and mass transfer in engineering systems. Given their critical role in various applications, from aerospace and automotive to environmental processes, modifying turbulent flow behaviour remains essential for enhancing system performance and addressing practical engineering challenges. The present thesis investigates the active control of Turbulent Channel Flow through the manipulation of dynamically significant coherent structures, using Direct Numerical Simulation. High-order numerical methods are employed to ensure accurate resolution of turbulent motions, using the open-source code Xcompact3d. The opposition control scheme proposed by Choi et al., originally designed for drag reduction, is selected as the primary numerical reactive control method due to its simplicity and efficiency. Modifications were introduced into the Xcompact3d framework to implement this control scheme and to develop a modified control approach tailored to the objectives of this research. The base flow is a fully developed Turbulent Channel Flow, as described by Kim et al.. Validation of the modified code was achieved through comparisons with reference data for turbulent flow at low Reynolds number, ensuring both numerical accuracy and physical fidelity. Simulations provided detailed turbulence statistics for both the uncontrolled and controlled cases, thereby offering insight into the flow dynamics and control effectiveness. The study further explores the potential of active flow control to replicate the effects of surface roughness without the implementation of a physically roughened boundary. This aspect of the work aims to extend the applicability of theoretical control methods to more practical engineering scenarios. The present research advances a numerical methodology for the precise manipulation of wall-bounded turbulent flows via Blowing and Suction, implemented within a customised version of the Xcompact3d solver. This enhanced code offers a robust and efficient platform for the continued exploration of turbulence control techniques, as the implementation of the opposition control strategy proposed by Choi et al. has been fully validated against reference data. Moreover, the results indicate that the applied control scheme induces complex flow mechanisms that do not entirely replicate those associated with actual surface roughness. While the modified control approach successfully reproduces the downward shift in the mean streamwise velocity profile within the logarithmic region, it fails to accurately capture the behaviour of second-order turbulence statistics. This limitation arises from the fact that the control tries to replicate the effect of physical roughness by acting on turbulence structures, particularly influencing turbulent fluctuations. This is demonstrated through the FIK-decomposition. These findings underscore the need for further investigation into the underlying flow dynamics and their role in turbulence production. From this perspective, the tool developed within this thesis represents a valuable resource, providing significant flexibility through the ability to manipulate various control parameters directly from the input file of Xcompact3d. This work is aligned with ongoing research efforts commissioned by Scuderia Ferrari, with potential implications for aerodynamic optimisation in wind tunnel testing environments.