Session: 14-01 Compressor Cavities 1

Paper Number: 124239

124239 - Numerical Investigation of Windage Heating in High-Pressure Compressor Shrouded Stator Cavities 

The thermodynamic behaviour of the labyrinth seals beneath the shrouded stators has been partially understood, but the modelling of it has not yet been perfected. The various parameters, such as the presence of honeycomb structures, the number of sealing fins, the incline of the labyrinth, inlet preswirl affect the windage heating of the flowing air highly. As a result, it is very challenging to quantify the total temperature rise and windage heating power in labyrinth seals.

 

Some work has been done on this subject, either numerically or experimentally, in an attempt to improve the understanding of the physics. McGreeham&Ko (1989) developed an iterative method for predicting windage heating using shear stress relations, which includes the inlet pre-swirl effect, but can only be applied to adiabatic cases. Millward&Edwards (1994), on the other hand, developed an algebraic relation using cavity geometry parameters and flow properties. Ozturk et. al. (1998) numerically investigated the total temperature rise behaviour for different radial and axial positions of the cavity. Denecke et al. (2005) have tested some of the mentioned relationships by applying them in numerical and experimental test cases.

 

This study aims to build a high-fidelity 3D CFD model of a high-pressure compressor sealing which can emulate the total temperature rise in the labyrinth and hence the windage heating behaviour accurately. In the frame of this study, various numerical setups have been tested and the relevant cases have been compared with experimental results. The tested domain includes a single passage main gas path containing three stator vanes and two rotor blades. The cavity domain is located below the second stator stage of the model and is connected via interfaces to the main gas path. A structured mesh of the main gas path is created via TurboGrid and of the cavity via ICEM. The simulation is run using ANSYS CFX.

 

Various sensitivity studies have been carried out, including variation of the labyrinth tip gap, stacking of honeycomb structures on the stator wall in the cavity and increasing the wall roughness in the labyrinth. Furthermore, the thermal properties of the labyrinth walls were varied, i.e. the adiabatic, isothermal and heat flux walls were studied. Finally, a coupled FEM-CFD simulation was performed to eliminate the uncertainties due to the wall temperature boundary conditions. In order to further corroborate the results, these studies were also carried out at a much lower operating point, where the windage heating is expected to be less.

 

It was found that the heat pickup in the cavity downstream side was accurate in the adiabatic case, but this was not the case between and after the labyrinth fins. The basic model lacked a total temperature rise of 24K compared to the experiments. This value is also quantified as windage heating power using the energy balance equations. However, neither the use of static wall temperature boundary conditions nor the modelling of honeycomb structures has contributed to the windage heating sufficiently to match the experiments. The missing windage heating power was then calculated using the energy equation and applied as a heat source to the labyrinth walls. Hence, it was found that the overall temperature increase fitted well. This behaviour was finally also achieved by using a certain wall roughness on the rotor side to increase the frictional heating. However, at the lower operating point, the wall roughness method didn't perform as well due to the lower friction values. In contrast, the application of isothermal wall boundary conditions was sufficient to match the experiments. Furthermore, the results of the coupled FEM-CFD simulations were in good agreement with those of the 3D CFD simulations. Hence, the matching has been extended also to the model with variable material temperatures and a more complex solution is reached.

Presenting Author: Altay Damgacioglu Chair of Turbomachinery and Flight Propulsion, Technical University of Munich

Presenting Author Biography: Altay Damgacioglu is a scientific researcher and a PhD candidate at the Chair for Turbomachinery and Flight Propulsion at the Technical University of Munich. He earned his bachelor's and master's degrees in mechanical engineering from the Technical University of Munich. His research primarily focuses on the numerical investigation and optimization of compressor stator arrangements with inner shrouds.

Authors:

Altay Damgacioglu Chair of Turbomachinery and Flight Propulsion, Technical University of Munich
Francois Cottier MTU Aero Engines AG
Volker Gümmer Chair of Turbomachinery and Flight Propulsion, Technical University of Munich