Numerical Analysis of Sealing Flows in Gas Turbines Using RANS and LES Approaches

The flow field developing inside the stator-rotor disc cavities of gas turbines is characterized by highly complex and unsteady behavior driven by strong vortical structures and transient interactions. These features pose significant challenges for accurate prediction using standard Computational Fluid Dynamics models. In particular, the inherent unsteadiness of the flow field has a considerable impact on the sealing performance of the rim, especially when predicted by steady Reynolds-Averaged Navier-Stokes (RANS) methods, which tend to overestimate the sealing effectiveness by more than an order of magnitude. In this study, a series of numerical simulations were conducted using RANS, unsteady RANS (URANS), and large Eddy Simulation (LES) approaches to gain insight into the behaviour of the rim seal flow. The main objective was to compare the numerical results with experimental data obtained from the test rig at the University of Florence, in order to validate the accuracy of different numerical approaches. The RANS, URANS and LES simulations all demonstrated satisfactory agreement in terms of steady-state measurements of pressure coefficients and velocity fields, offering valuable insight into the time-averaged behavior of the flow. However, the Reynolds-averaged models failed to effectively capture the turbulent fluctuations between the main flow and the secondary flow. In contrast, LES simulations accurately captured the development of vortices and replicated more realistic flow conditions, resulting in a closer match with experimental data. Therefore, the resolution of these fluctuations, which are nowadays considered to be one of the fundamental factors driving the ingestion of mainstream flow into the cavity, appeared to be crucial to accurately understand the unsteady interaction between mainstream and secondary flows. Although the high computational cost and long transient phases required to reach periodic convergence make LES a resource-intensive approach, it demonstrates great potential for accurately predicting this interaction and providing valuable insights into the complex flow dynamics of rim seal flows.