Università degli studi di Modena e Reggio Emilia

Emphysema, a chronic lung disease characterized by respiratory distress and reduced lung function, poses significant challenges. Computational Fluid Dynamics (CFD) coupled with fluid structure interaction (FSI) is a highly effective simulation technique that offers valuable insights into the mechanics of lung function and the influence of diseases like emphysema. The intricate lung alveolar sacs play a vital role in gas exchange, and CFD with FSI enables the simulation of mechanical forces that shape and impact their functionality. By employing CFD with FSI, we can simulate the fluid dynamics of emphysema and acquire a comprehensive understanding of disease progression. These simulations allow us to explore the contributions of tidal breathing and surface tension forces. This study has demonstrated through FSI that a lung alveolus affected by pulmonary emphysema, and therefore collapsed, causes reduced air intake with each breath. This is due to the significantly compromised deformability of the alveolar wall. Ultimately, this technique plays a critical role in developing therapeutic interventions to improve patient outcomes.

Cavitation is one of the most detrimental fluid-dynamic anomalies that occur to turbomachines. It mainly affects machines characterized by high rotation speeds and clear distinctions between low and high pressure zones, where cavitation first appears. During the years, starting from the well known Rayleigh formulation for the formation of bubbles in a liquid medium, many models have been proposed to analyse the phenomenon. Spanning from higher simplifications to more detailed formulations, the range of applications of these models is wide and led to different quality results, where a clear methodology is not fully established when regarding specific sectors, for example the industrial pumps. Restricting the application field to few, specific kinds of pumps, i.e centrifugal, axial flow pumps, external gear and mixed flow pumps, this article analyses the main literature sources in order to give an overall view to the Computational Fluid Dynamic applications of the different cavitation models and their applications to industrial pumps.

The geometric complexity and high-pressure gradients that characterize the design of the flow field of gear pumps make it very difficult to obtain an accurate CFD simulation of the component. Usually, assumptions are made both in terms of geometrical features and physics being included in the analysis. The contact between the teeth, which is a key factor for the correct functioning of these pumps, represents a critical challenge in 3D CFD simulations, mainly due to the intrinsic limits of the dynamic meshing techniques that can hardly effectively manage a zero or close to zero gap point forming during gear rotation. The geometric complexity and high-pressure gradients that characterize the gear pump flow field make a CFD analysis quite difficult, and the contact between the gear teeth is usually avoided, thus being an extremely important feature. In this paper, a gear pump composed of inlet and outlet pipes was considered, and the contact between the gear's teeth was modeled in two different ways, one where it is effectively implemented and one where it is avoided using distancing and a proper casing modification. Herein, a new methodology is proposed for the application of the dynamic mesh method in the Simcenter STAR-CCM+ environment using an adaptive remeshing technique. The proposed methodology is compared with the alternative overset meshing method available in the software. The new meshing method is implemented using a user-routing that reproduces the real geometry of the gears while rotating during the pump operation, with teeth contact included. The routine is optimized in order to limit the additional computation and time needed for the remeshing process. The results that can be obtained using the two meshing approaches for the gear pump are compared in terms of computational effort and the accuracy of the results. The two methods showed opposite results in almost all the reported results, with the overset being more precise in the radial pressure evaluation and the dynamic being more reliable in the cavitation/aeration extension cloud.