To characterize contactless seals in turbo machinery, their discharge behavior, the development of the circumferential velocity (swirl) and the loss induced total temperature increase (windage heating) are of special interest for the designer. For the discharge behavior of non-rotating labyrinth seals, a well established set of non-dimensional numbers already exists: the discharge coefficient of two seals with different sizes but similar geometry is identical, if pressure ratio, axial Reynolds number, fluid properties and turbulence level are also identical. In this paper, the set of non-dimensional numbers is extended to cover swirl and windage heating using the well established Buckingham-π theorem to derive possible candidates. First, as a proof of concept, the known set of numbers for the non-rotating case was redeveloped and subsequently the influence of rotation was included. To validate the candidates, a comprehensive numerical parametric study was conducted. A variety of convergent and divergent stepped labyrinth seals was scaled from laboratory to typical engine conditions such that the dimensionless numbers stayed constant. Then, simulations at different rotational speeds, radii, and inlet circumferential velocities were performed to investigate the effects of rotation while maintaining nearly constant discharge behavior. The numerical data were used to validate the new non-dimensional numbers and to derive laws for the scaling of labyrinth seals. The non-dimensional numbers can also be applied to other seal types, such as brush or finger seals, because their theoretical deduction does not imply a specific geometry.
Labyrinth seals are widely used as reliable components in many areas of turbo machines, e.g. the cooling air system in gas turbines. While the discharge behavior is generally well predictable, the uncertainty predicting the exit circumferential velocity (exit-swirl) and the total temperature increase due to internal losses (windage heating) is comparably large. In order to evaluate analytical correlations and for the validation of numerical simulations convergent and divergent stepped labyrinth seals were investigated experimentally. The change in total temperature across the labyrinth seal was measured in a test rig capable to establish different rotational speeds, pressure ratios and various inlet swirls. In an engine, honeycomb abrasive liners on the stator protect the seal fins. To simulate real engine conditions honeycombs were applied in the test setup, too and the influence of these liners on the windage heating was compared to smooth stator configurations. Detailed velocity profiles within the seal chambers were determined using a 2D Laser-Doppler-Velocimeter. Additionally, the ability of axisymmetric numerical k-ε simulations to predict the data was evaluated. The present study provides important data for the design of future turbo machines, because the exact knowledge of the labyrinth seal exit swirl and temperature is expected to further improve the design of downstream components such as the pre-swirl system. Additionally, more accurate boundary conditions for the thermal analysis will be available and the rotor dynamic stability of the seal can be estimated better.
A DEM-CFD coupling for the simulation of gas-solid flows was successfully implemented and simulations were performed for the application to industrial-scale pneumatic conveying. Therefore, all particle collisions and phase interactions were considered and porosity determination was optimized. The aim of this work is to show the applicability of the presented simulation model to the different regimes of pneumatic conveying systems. As a first test case a dense vertical pneumatic conveying system was chosen and an individual plug was investigated in detail. Variations of the conveying air velocity were also considered. As a second test case dilute conveying in a horizontal-to-vertical pipe bend was simulated. The occurrence of roping and the reduction of particle velocity is of high interest for the design of specific pneumatic systems. It is shown that both regimes can be captured reasonably well and the results are rich in details.
An experimental investigation on the influence of stator rub-grooves on labyrinth seal leakage is presented in the present paper. In current labyrinth seal designs, abradable lands allow the rotor labyrinth teeth to rub grooves into the stator. These rub-grooves have a large influence on the seal leakage characteristic and impair the overall engine efficiency. To improve the understanding of rub-groove effects, discharge coefficients were determined using a plain nonrotating labyrinth seal model of scale 4:1 considering a wide variation of rub-groove geometries at different seal clearances. Three labyrinth seal types were covered in this investigation that are generally used in gas turbines, namely 1) straight-through labyrinth seals, 2) stepped labyrinth seals with forward facing steps, and 3) stepped labyrinth seals with backward facing steps. To attain a deeper insight into the flow mechanisms, water-channel visualizations were performed. The large data set generated in this study, provides the basis to analyze and quantify the influence of rub-grooves on the seal leakage for the three aforementioned labyrinth seal types. Current results were in agreement with previous studies on worn labyrinth seals for several seal geometries.
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