Background: Lymphatic vessels are responsible for tissue drainage, and their malfunction is associated with chronic diseases. Lymph uptake occurs via specialized open cell-cell junctions between capillary lymphatic endothelial cells (LECs), whereas closed junctions in collecting LECs prevent lymph leakage. LEC junctions are known to dynamically remodel in development and disease, but how lymphatic permeability is regulated remains poorly understood. Methods: We used various genetically engineered mouse models in combination with cellular, biochemical, and molecular biology approaches to elucidate the signaling pathways regulating junction morphology and function in lymphatic capillaries. Results: By studying the permeability of intestinal lacteal capillaries to lipoprotein particles known as chylomicrons, we show that ROCK (Rho-associated kinase)-dependent cytoskeletal contractility is a fundamental mechanism of LEC permeability regulation. We show that chylomicron-derived lipids trigger neonatal lacteal junction opening via ROCK-dependent contraction of junction-anchored stress fibers. LEC-specific ROCK deletion abolished junction opening and plasma lipid uptake. Chylomicrons additionally inhibited VEGF (vascular endothelial growth factor)-A signaling. We show that VEGF-A antagonizes LEC junction opening via VEGFR (VEGF receptor) 2 and VEGFR3-dependent PI3K/AKT activation of the small GTPase RAC1, thereby restricting RhoA/ROCK–mediated cytoskeleton contraction. Conclusions: Our results reveal that antagonistic inputs into ROCK-dependent cytoskeleton contractions regulate the interconversion of lymphatic junctions in the intestine and in other tissues, providing a tunable mechanism to control the lymphatic barrier.
Proportionally large relative radial clearances can be found within the rear stages of multistage axial compressors of gas turbines and aero engines, with significant impact on their efficiency. A new three-dimensional design for cantilevered stators in axial compressors is presented, with the aim of improving the overall efficiency and losses of rear stage vanes with large relative hub clearances. The new vane design comprises an unconventional dihedral, with special consideration to reduce the losses caused by the hub clearance vortex. The design was tested in a 4-stage low speed axial research compressor under rear stage conditions. The results are compared to the nominal design to validate the reduction of hub clearance losses and blockage. For both designs, the hub clearances over the third and fourth stator were varied from 1.5% up to 6.0% of span. Overall performance data and flow field traverses upstream and downstream of stator 3 and rotor 4 will be presented in this article in comparison with 3D CFD results.
The ventilation flow of a gas turbine enclosure was investigated both experimentally and numerically in a scaled test rig. Its gas turbine components were inactive and mainly functioned as flow obstructions. Measurements were used to provide realistic boundary conditions and verification data for URANS CFD investigations. In the test rig the active generator cooling flow was created by several fans, modelled by momentum sources in the CFD. Two different modelling approaches were compared to PIV data. The modelling of the ventilation flow was found to impact flow regions nearby the generator but also far downstream with one method showing better agreement with the experiment. Examining the flow predicted by the chosen CFD model, no relevant backflow from the engine to the upstream gear section could be observed. Therefore, the investigation of stagnation regions was focused on the engine section to identify worst case leakage configurations for future investigations.
A major goal in axial compressor development is to increase the efficiency and to reduce the weight of the module. In order to do so the power density has to be increased by raising the work per stage. Higher capability to do work can be achieved by increasing the circumferential velocity component of the fluid. Tandem stators might offer the ability to turn high swirling flow with lower losses compared to a single blade stator. In terms of higher aerodynamic loading the use of tandem vanes can be a key feature to allow the design of highly efficient and compact compressor modules. This paper presents the design and experimental validation of a single stage low speed axial compressor with a tandem outlet guide vane, representative for a modern jet engine high pressure compressor. Additionally to the overall compressor performance the 3D flow field of the tandem stator has been measured with a five hole probe at different operating points. The results will be discussed in comparison with numerical results. Furthermore, oil flow pictures are used to get a deeper insight into flow conditions inside the vane passage and to validate the numerically predicted secondary flow structures.
Linear cascades are commonly used as surrogate geometries when performing fundamental studies of turbomachinery blading. Several effects are not accounted for in linear cascades, among them the relative motion between blade and endwall. In this study three different relative endwall velocities are analysed. The effect of the relative motion between endwall and blade in a linear compressor cascade is studied through Direct Numerical Simulations. Results show a significant change in the secondary flow structure within the passage. Most notably, the tip leakage vortex is displaced away from the blade. Still, the blade spanwise range affected by the secondary flow field is similar to the case without relative endwall motion. At the outlet plane, a stratification of the total pressure losses and the exit flow angle is found, which overshadows any blade wake effects near the endwall.
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