Leakage reduction by optimisation of the straight–through labyrinth seal with a honeycomb and alternative land configurations Wlodzimierz Wróblewski a,⇑ , Daniel Fra ˛ czek a , Krzysztof Marugi b a Silesian University of Technology, Institute of Power Engineering and Turbomachinery, Konarskiego 18, Gliwice, Poland b Avio Polska Sp. z o.o., Michala Gra _ zyn ´skiego 141, Bielsko-Biala, Poland article info Article history: Received 11 January 2018 Received in revised form 13 April 2018 Accepted 14 May 2018 Keywords: Labyrinth seal optimisation Honeycomb land Straight-through labyrinth Leakage reduction abstract The labyrinth seal with a honeycomb land is one of the most typical sealing solutions used in gas tur- bines. The paper presents an analysis of a straight-through seal with two fins. Such seals are used in places with limited space and where design and tribological constraints are of great importance. At a small number of the labyrinth fins, an improvement in the labyrinth performance can bring notable oper- ating benefits. The paper presents optimisation of the seal labyrinth with different geometrical land configurations. The first part describes the labyrinth seal geometry and individual land types. The analysis covers seals with a honeycomb land, a squeezed-honeycomb land, a rhomboid land and a smooth land. The seal com- putational model and the optimisation task algorithm are presented. The objective function is minimiza- tion of the discharge coefficient, and the parameters are the labyrinth geometrical quantities: the fin height, the fin position, the fin thickness and the fin inclination angle. The optimisation task is solved for each land type. The results of individual optimisation tasks are presented and discussed, and the potential for improve- ment in the seal efficiency by means of appropriate selection of both the labyrinth parameters and the type of the land is pointed out. The obtained values of the reduction in the discharge coefficient reach 18% compared to the reference labyrinth configuration. However, taking account of both the labyrinth and the land shape, the benefit of 22.4% is achieved in comparison to the reference configuration with a honeycomb land. Ó 2018 Published by Elsevier Ltd. 1. Introduction In gas turbines, it is necessary to separate rotating elements from stationary ones in a manner that ensures the highest possible leak tightness of the main flow channel and of the auxiliary chan- nels responsible for the cooling of elements exposed to high tem- peratures. Due to the high temperature of the turbine elements and the working medium, combined with high peripheral speeds and considerable changes in loads, clearance (non-contact) seals are typically used as the solution applied in aero-engines. The most common are labyrinth seals. The possibility of using small clear- ances to achieve a reduction in leakage is limited by the risk of rub- bing. In order to make the clearance smaller on the one hand, and minimize the potential effect of rubbing on the other, special lands are used on the stationary elements above the seal fins. Considering the favourable density-to-rigidity ratio of the honey- comb land, this type is the most popular. Due to the complex phenomena occurring in the flow through a labyrinth seal, the flow is rather difficult to describe. Many analyt- ical formulae are known that characterize flows through seals (e.g. [1–4]), but their agreement with the experiment varies. In their design practice, manufacturers use sophisticated computational procedures incorporating a number of in-house-developed confi- dential corrections and coefficients (e.g. [5,6]). The intensive works on new turbine designs require a search for additional opportunities for an improvement in efficiency. The application of more advanced methods of the flow analysis, the precise state-of-the-art CFD analyses, in particular, enables a better understanding of the physics of the phenomena and, owing to that, implementation of new design solutions. Simulations of the flow through labyrinth seals are usually per- formed using a steady-state model based on the Reynolds- averaged Navier-Stokes (RANS) equations. In the beginning, com- putations were carried out for two-dimensional models of the https://doi.org/10.1016/j.ijheatmasstransfer.2018.05.070 0017-9310/Ó 2018 Published by Elsevier Ltd. ⇑ Corresponding author. E-mail address: wlodzimierz.wroblewski@polsl.pl (W. Wróblewski). International Journal of Heat and Mass Transfer 126 (2018) 725–739 Contents lists available at ScienceDirect International Journal of Heat and Mass Transfer journal homepage: www.elsevier.com/locate/ijhmt