Mathematical Theory and Modeling www.iiste.org ISSN 2224-5804 (Paper) ISSN 2225-0522 (Online) Vol.3, No.11, 2013 51 Prediction of Carry- over Coefficient for Fluid Flow through Teeth on Rotor Labyrinth Seals Using Computational Fluid Dynamics Dr.Saba Yassoub Ahmed, (Assis. Prof.) Department of Mechanical Engineering/College ofEngineering/University of Babylon/Babylon-Iraq. E-mail:saba_ya@yahoo.com Dr.Basim Ajeel Abass, (Assis. Prof.) Department of Mechanical Engineering/College ofEngineering/University of Babylon/Babylon-Iraq. E-mail: drbajab62@yahoo.com Nuhad Abd-Allah Hamza, (Assis. Lect.) Department of Mechanical Engineering/College ofEngineering/University of Babylon/Babylon-Iraq. Abstract The analysis presented in this work deals with the computational fluid dynamics (CFD) based modeling for the carry-over coefficient of flow through teeth on rotor straight through labyrinth seal. A two dimensional model for the flow through the seal was built in FLUENT 6.3.26. A grid independence study was carried out showing the influence of grid refinement on the fluid mass flow rate. The effect of turbulence modeling, seal geometry and shaft rotational speed have been taken into consideration. Three CFD models to predict the carry-over coefficient considering the effect of the parameters mentioned before have been presented. The prediction models have been validated against experimental works conducted by Scharrer (1988) and Eser (2004). The results obtained in the present work for the effect of different parameters, namely, (Number of teeth, Reynolds number, rotational speed and seal geometry) for two labyrinth seals with (0.127mm) and (0.33mm) tooth clearance have been presented. A prediction equation for the carry-over coefficient of the labyrinth seal has been proposed through this work. Verification for some of the results obtained through this work with that published by other workers has been carried out. The results obtained through the present work found to be in a good agreement with the results of other workers. Key words: Labyrinth seal, Carry-over coefficient, CFD. 1-Introduction The main function of the labyrinth seals is to reduce the leakage flow between components of different pressure and prevent the rotor from contacting the stator at a very high speed, because any contact between the rotor and stator causes seal damage, deterioration of seal performance and engine failure. Labyrinth seals have proved to be quite effective and long-lived as evidenced by their widespread use, chiefly on rotating machinery such as gas compressors and turbines. The straight type labyrinth seal is the most used in turbomachinery because of its greater kinetic energy carry over in comparison with other types of seals. Most previous works show that the modeling of seals was mainly based on the bulk flow model (Child, D.W and Scharrer, J. (1986), Esser, D., Kazakia, J.Y., (1995), Yilmaz, D. and Esser, D., (2004), Gamal, A.M., (2007)).The main drawback of this model, due to the simplifying assumptions, is that sometimes it fails to predict the flow of labyrinth seal. Due to the bulk flow model limitation, its claimed by Pugachev, (2012) that the computational fluid dynamics (CFD) method for solving Navier- Stokes equations were applied to obtain more satisfactory predictions for various seal types at different boundary and operating conditions. The previous studies on the application of (CFD) methods focus on modeling the fluid flow through labyrinth seals of small clearances with teeth on the stator, Saikishan and Morrison (2009), Anand and Woo (2011) and Sunil,(2011) (2010). Vamish (2011) studied the effect of shaft rotation on flow parameters without modeling carry-over coefficient. A model for labyrinth seal with large clearance has been developed. In the present work a (CFD) model for the carry-over coefficient of teeth on rotor straight labyrinth seal has been developed in order to propose a numerical correlation for the carry over coefficient of the seal. Effects of flow parameters and seal geometry with and without rotational speed effect, for compressible and incompressible fluid flow on carry-over coefficient of labyrinth seal have been investigated. 2. Mathematical Modeling 2-1 Labyrinth Seal Geometry and Coordinates. The analysis presented here is applicable to straight labyrinth seal with teeth on the rotor. Figure (1) shows the geometry and coordinates system for a single cavity with two teeth on rotor labyrinth seal and axisymmetric flow (i.e., two dimensional flow simulation in radial and axial direction).