TY - THES ID - 134548640 TI - STUDY OF HELICAL STRUCTURES IN SWIRLING FLOWS USING COMPUTATIONAL FLUID DYNAMICS AU - Grimard, Guillaume AU - Vanierschot, Maarten AU - Yang, Zhu AU - KU Leuven. Faculteit Industriële Ingenieurswetenschappen. Opleiding Master in de industriële wetenschappen. Elektromechanica (Leuven) PY - 2022 PB - Leuven KU Leuven. Faculteit Industriële Ingenieurswetenschappen DB - UniCat UR - https://www.unicat.be/uniCat?func=search&query=sysid:134548640 AB - Introducing a swirl can lead to many positive effects such as flame stabilization or enhanced mixing. On the other hand, there are also negative effects such as the chance of resonance that can damage components. This thesis contains an investigation of various flow structures in a swirling flow. The flow contains an annular jet and the swirl is generated by a swirl generator. This setup imitates the setup of a combustion chamber of a gas turbine or an airplane engine for example. By simulating these experiments in CFD, the influence of several parameters of the vortex generator can be adjusted to investigate additional effects. Based on an experiment, this flow case is modeled and solved via numerical simulations/CFD (Computational fluid dynamics). It is characterized by turbulence with a Reynolds number of 8500, so it is necessary to choose the right turbulence model for this case. This can be verified by the experiments acquired beforehand. We opt for a transient and 3D solution, because of the transient non-axisymmetric structures. The first and second central recirculation zones (CRZ) belong to stationary structures while the precessing vortex core (PVC), induced by vortex breakdown, is a transient phenomenon. The first turbulence model tested is the Reynolds stress model (RSM). This model falls under the category of Reynolds averaged Navier-Stokes (RANS), which means that a more coarse mesh can be chosen whereby a considerable part of the solution field is modeled. In this category, RSM is the model with the smallest modeled share, but still large with respect to LES and DNS, about which more later. It introduces 6 extra equations on top of the Navier-Stokes equations to determine the Reynold stresses in each direction. RSM can be used for non-isentropic flow cases and is thus appropriate for cyclone, swirling, rotating flows and flows with a lot of separation. Besides RANS, there is also Large Eddy Simulation (LES). This is the second turbulence model we will use in order to make the comparison with RSM. Here, the mesh size is smaller than that of RANS. All structures smaller than the mesh size are modeled, while those larger than the mesh size are solved. The modeled proportion is lower here, indicating a more accurate solution but a longer simulation time. To be able to perceive the helical structures in the LES solution SPOD is used. This technique can decompose the velocity field into modes of different frequencies, energies and amplitudes. Some of these modes contained the helical structures and could be visualized with the Q-criterion. ER -