Session: 34-09 High-fidelity CFD – General

Submission Number: 177691

Sensitivity of Pressure Losses to Geometric Parameters in Straight-Through Labyrinth Seals Based on Large-Eddy Simulations 

Among other uses, seals in aircraft engines prevent oil leakage by sealing bearing chambers. As pointed out by Chew (1996) and Wittig et al. (1994), any unwanted leakage may lead to safety and performance issues. An incoming positive pressure gradient is imposed at the dynamic seals entry (Michaelis, 2016), which ensure the sealing of bearing sumps. One of the most commonly used seal technologies is the labyrinth seal. The latter is made up of several successive teeth and cavities inducing pressure drops as the flow crosses the seal. Li et al. (2019) and Michaelis (2016) highlight its affordability, resistance to wear and reliability. The typical small aspect ratios of labyrinth seals between clearance and inner/outer diameters (Chen et al., 2011; Sun and Liu, 2023) make it difficult to reach an acceptable compromise between computational cost and mesh-independant results. Labyrinth seals are widely studied using Reynolds Averaged Navier Stokes (RANS) (Baek and Ahn, 2021; Chun and Ahn, 2023). However, RANS models have shown limitations for the prediction of anisotropic turbulence or air entrainement and mixing. For these reasons, (Wein et al., 2022) carried out an Large-Eddy Simulation (LES) study on a 2-teeth labyrinth seal and identified adapted meshing constraints. They confronted LES to RANS and DNS and showed that RANS leads to an overpredicted pressure in the cavity.

Furthermore, several geometric parameters affect the efficiency of these seals. Baek and Ahn (2021) investigated the sensitivity of discharge coefficient Cd to five of them. They concluded that clearance has the strongest impact on labyrinth seal efficiency, followed by cavity width and tooth width. Chen et al. (2020) numerically studied the influence of tooth bending -due to wear- on Cd. No parametric study on the impact of tooth tip sharpness on pressure drop has been encountered yet. The sharper the tooth tip is, the greater the pressure drop will be. However, the specific mechanisms beneath this observation are yet to be investigated.

This work focuses on: i) providing a method to evaluate the quality of LES studies of small aspect ratio cases, and ii) studying the influence of some geometric parameters on pressure drops in a labyrinth seal -the conge radius R at the tooth tip and the ratio between the cavity width L_CAV and the clearance c-. To do so, an LES study of a labyrinth seal is carried out using the YALES2 code. A mesh convergence study at a fixed R value is performed first to ensure mesh-independent results. The characteristic curves of the studied seal are then identified. These results are confronted to experimental results of a previous work to evaluate the quality of LES simulations. The sensitivity of the boundary layer separation (BLS) angle to R is then investigated through a parametric study. This intermediate work aims to study the influence of R on the BLS angle and on the BLS position, which in fine modify the vena contracta effect in clearance . Finally, a sensitivity study of the pressure drop to the ratio L_CAV/c is carried out. The results of both studies are confronted to experimental data.

Presenting Author: Pierre Portais SAFRAN AIRCRAFT ENGINES

Presenting Author Biography: After studying in ESTP Paris and Arts et Métiers (ENSAM, Paris), I hold two engineering degrees (in Mechanical and Electrical engineering and General engineering). I am currently doing a CIFRE PhD at CORIA laboratory (76) with SAFRAN AIRCRAFT ENGINES.

Authors:

Pierre Portais SAFRAN AIRCRAFT ENGINES
Julien Carmona CORIA
Vincent Moureau CORIA
Melody Cailler SAFRAN Tech, Modelling & Simulation
Nicolas Stoliaroff-Pepin SAFRAN AIRCRAFT ENGINES