Numerical investigations on the rubbing process in labyrinth seals for full flight mission

Labyrinth seals are a commonly used sealing technology to prevent and control leakage flows at rotor-stator interfaces in turbo machinery. Small clearances required by higher pressure ratios and the economical use of cooling air lead to potential rubbing events. These may cause detrimental heat input into the rotating structure and can lead to severe damages. Honeycomb liners on the stator part tolerate rubbing events to a certain extent and therefore allow for smaller gap widths, which lead to minimal leakage. A unique and independently developed one-dimensional numerical model is used to investigate critical rubbing conditions in a typical aircraft flight mission. It considers kinematic contact conditions, friction, heat conduction and abrasive and plastic wear. This model allows the calculation of the loads, such as the contact pressures and temperatures on the components. First experimental investigations for an idealized contact between a metal foil, representing the honeycomb part, and a rotating seal fin are used to validate the model. Then, predictions of engine performance calculations are additionally used to calculate input parameters for the one-dimensional model. These are the relative contact velocity and the casing temperature of the honeycomb. Finally, the results of the one-dimensional rubbing model such as rub forces, temperatures and wear of the seal fin or the honeycomb liner are compared for five different operating points of the flight mission: Ground idle, Takeoff, Cruise, Approach, Re-slam. Based on these results, damaging effects on the sealing system are evaluated and the most critical operating point, in this case the Re-slam, could be identified

A valid method of gas foil bearing parameter estimation: A model anchored on experimental data

Dieser Beitrag ist mit Zustimmung des Rechteinhabers aufgrund einer (DFG geförderten) Allianz- bzw. Nationallizenz frei zugänglich.This publication is with permission of the rights owner freely accessible due to an Alliance licence and a national licence (funded by the DFG, German Research Foundation) respectively.Gas foil bearings are a smart green technology and suitable for the next generation of small turbo machinery e.g. turbochargers, micro gas turbines, range extenders and compressors of fuel cells. A combination of low power loss, high speed operation and the omission of an oil system are the major advantages. To enable access to this technology, it is essential to evaluate critical speeds and onset speeds of subharmonic vibration of the rotor system in the first design stage. Hence, robust and valid models are necessary, which correctly describe the fluid structure interaction between the lubrication film and the elastic bearing structure. In the past three decades several experimental and numerical investigations of bearing parameters have been published. But the number of sophisticated models is small and there is still a lack of validation towards experimental works. To make it easy for designers dealing with this issue, the bearing parameters are often linearised about certain operating points. In this paper a method for calculating linearised bearing parameters (stiffness and damping) of gas foil bearing is presented. Experimental data are used for validation of the model. The linearised stiffness and damping values are calculated using a perturbation method. The pressure field is coupled with a two-dimensional plate model, while the non-linear bump structure is simplified by a link-spring model. It includes Coulomb friction effects inside the elastic corrugated structure and captures the interaction between the single bumps. For solving the separated perturbed Reynolds equation a static stiffness is used for the 0. order equation (stationary case) and a dynamic stiffness is applied for 1. order equation (dynamic case). Therefore, an additional dynamic structural model is applied to calculate the dynamic stiffness. The results depend on the load level and friction state of each bump. Different case studies including the impact of clearance, frictional contacts and the comparison of a linear and non-linear structure are carried out for infinitesimal perturbations. The results show, that the linear structure underestimates main and cross-coupling effects. The impact of the clearance is notable, while the impact of the overall frictional contacts is small due to relatively small loadings. The infinitely small perturbation model is adapted to the experimental setup by using a superposition of two resulting bearing parameters identifications of two total loadings including shaker forces. Due to this adaptation a good correlation with the experimental results of the bearing parameters is achieved

Modelling the Rubbing Process in Labyrinth Seals

To understand the complex rubbing process between labyrinth seal fins and honeycomb liners, experimental investigations are considered for an idealized contact between a metal sheet, representing the honeycomb part, and a rotating seal fin. Modifications of our test rig allow to measure the resulting rub forces, temperatures and wear of the seal fin and metal sheet for a wide range of circumferential velocities and incursion rates. The rotor material is Inconel 718, and the metal sheets consist of the nickel-based super-alloys Hastelloy X and Haynes 214. To define appropriate boundary conditions for the experiment, a one-dimensional numerical model is introduced. It takes into account kinematic contact conditions, friction, heat conduction, and abrasive and plastic wear. The use of analytical relations and parallel computing enables a time-efficient computation of multiple scenarios. Therefore, it is possible to identify the effect of variations and uncertainties of the input parameters on the results and derive an optimized test plan

Continued Experimental Study on the Friction Contact between a Labyrinth Seal Fin and a Honeycomb Stator: Slanted Position

Labyrinth seals are a state-of-the-art sealing technology to prevent and control leakage flows at rotor–stator interfaces in turbomachinery. Higher pressure ratios and the economical use of cooling air require small clearances, which lead to potential rubbing events. The use of honeycomb liners allows for minimal leakage by tolerating rub events to a certain extent. A previous study within an EU project investigated the complex contact conditions of honeycomb liners, with the idealized contact of a seal fin and a single parallel metal foil representing the honeycomb double foil section. In the present work, the results for the slanted foil position are shown and compared to the previous results. The variation of rub velocity, incursion speed, incursion rate, and seal geometry in a test rig allows for the identification of the influence on contact forces, temperatures, and wear. For the slanted position, significantly lower friction temperatures are observed, leading to a higher ratio of abrasive wear. Overall, the rub test results demonstrate strong interactions between the contact forces, friction temperatures, and wear

Effects of EpCAM overexpression on human breast cancer cell lines

<p>Abstract</p> <p>Background</p> <p>Recently, EpCAM has attracted major interest as a target for antibody- and vaccine-based cancer immunotherapies. In breast cancer, the EpCAM antigen is overexpressed in 30-40% of all cases and this increased expression correlates with poor prognosis. The use of EpCAM-specific monoclonal antibodies is a promising treatment approach in these patients.</p> <p>Methods</p> <p>In order to explore molecular changes following EpCAM overexpression, we investigated changes of the transcriptome upon EpCAM gene expression in commercially available human breast cancer cells lines Hs578T and MDA-MB-231. To assess cell proliferation, a tetrazolium salt based assay was performed. A TCF/LEF Reporter Kit was used to measure the transcriptional activity of the Wnt/β-catenin pathway. To evaluate the accumulation of β-catenin in the nucleus, a subcellular fractionation assay was performed.</p> <p>Results</p> <p>For the first time we could show that expression profiling data of EpCAM transfected cell lines Hs578T^EpCAMand MDA-MB-231^EpCAMindicate an association of EpCAM overexpression with the downregulation of the Wnt signaling inhibitors SFRP1 and TCF7L2. Confirmation of increased Wnt signaling was provided by a TCF/LEF reporter kit and by the finding of the nuclear accumulation of ß-catenin for MDA-MB-231^EpCAMbut not Hs578T^EpCAMcells. In Hs578T cells, an increase of proliferation and chemosensitivity to Docetaxel was associated with EpCAM overexpression.</p> <p>Conclusions</p> <p>These data show a cell type dependent modification of Wnt signaling components after EpCAM overexpression in breast cancer cell lines, which results in marginal functional changes. Further investigations on the interaction of EpCAM with SFRP1 and TCF7L2 and on additional factors, which may be causal for changes upon EpCAM overexpression, will help to characterize unique molecular properties of EpCAM-positive breast cancer cells.</p

Genomic analysis on pygmy hog reveals extensive interbreeding during wild boar expansion

Wild boar (Sus scrofa) drastically colonized mainland Eurasia and North Africa, most likely from East Asia during the Plio-Pleistocene (2–1Mya). In recent studies, based on genome-wide information, it was hypothesized that wild boar did not replace the species it encountered, but instead exchanged genetic materials with them through admixture. The highly endangered pygmy hog (Porcula salvania) is the only suid species in mainland Eurasia known to have outlived this expansion, and therefore provides a unique opportunity to test this hybridization hypothesis. Analyses of pygmy hog genomes indicate that despite large phylogenetic divergence (~2 My), wild boar and pygmy hog did indeed interbreed as the former expanded across Eurasia. In addition, we also assess the taxonomic placement of the donor of another introgression, pertaining to a now-extinct species with a deep phylogenetic placement in the Suidae tree. Altogether, our analyses indicate that the rapid spread of wild boar was facilitated by inter-specific/inter-generic admixtures.</p

Nanofacet structures on the (110) surface of a perovskite material: STM studies and atomistic simulation of the (2x3) reconstruction of Na2/3WO3(110)

The structure of the (110) surface of the tungsten bronze Na2/3WO3 has been studied by scanning tunnelling microscopy. Two different types of image with threefold periodicity along the [1̄10] direction are observed. The ×3 periodicity is shown to be inconsistent with a model proposed in earlier work that involved an ordered arrangement of Na ions at a bulk-truncated surface. On the basis of atomistic simulation of the WO3 framework, two new structures are proposed, both of which involve {100} nanofacets