Abstract-Hemodynamics play an important role in cardiovascular development, and changes in blood flow can cause congenital heart malformations. The endothelium and endocardium are subjected to mechanical forces, of which fluid shear stress is correlated to blood flow velocity. The shear stress responsive genes lung Krüppel-like factor (KLF2), endothelin-1 (ET-1), and endothelial nitric oxide synthase (NOS-3) display specific expression patterns in vivo during chicken cardiovascular development. Nonoverlapping patterns of these genes were demonstrated in the endocardium at structural lumen constrictions that are subjected to high blood flow velocities. Previously, we described in chicken embryos a dynamic flow model (the venous clip) in which the venous return to the heart is altered and cardiac blood flow patterns are disturbed, causing the formation of congenital cardiac malformations. In the present study we test the hypothesis that disturbed blood flow can induce altered gene expression. In situ hybridizations indeed show a change in gene expression after venous clip. The level of expression of ET-1 in the heart is locally decreased, whereas KLF2 and NOS-3 are both upregulated. We conclude that venous obstruction results in altered expression patterns of KLF2, ET-1, and NOS-3, suggestive for increased cardiac shear stress. Key Words: cardiovascular physiology Ⅲ embryonic circulation Ⅲ endothelium Ⅲ gene expression Ⅲ shear stress H emodynamic forces generated by blood flow modulate the structure and function of both fetal and adult endothelial cells (reviewed by Gimbrone et al 1 ). In pathogenesis shear stress is important as atherosclerosis develops in low and unsteady shear stress areas. 2 During embryogenesis blood flow plays an important role in cardiac development. 3,4 We developed the chicken venous clip model 3 in which the right lateral vitelline vein is ligated. This results in immediate changes in blood-flow patterns through the heart, and eventually to cardiovascular malformations, including ventricular septal defects, semilunar valve anomalies, and several types of pharyngeal arch artery abnormalities. 5 Additionally, Stekelenburg-de Vos et al 6 have shown that up to 5 hours after venous clip the dorsal aortic mean and peak blood flow is decreased, demonstrating a change in hemodynamics. Shear stress is directly related to blood flow, therefore it is likely that this is also altered in the venous clip model and involved in the development of abnormalities in the cardiovascular system.Important genes encoding transcription factors and signaling molecules, eg, lung Krüppel-like factor (KLF2/LKLF), endothelin-1 (ET-1), and endothelial nitric oxide synthase (NOS-3/eNOS) are shear-dependent in their expression in vitro. 7-9 Previously, we suggested that these genes are also shear-related in vivo. 10 Endothelin-1 is a growth hormone and vasoconstrictor. NOS-3 catalyzes the conversion of L-arginine to L-citrullin, generating nitric oxide (NO). NO is involved in, eg, vasodilation. KLF2 is a member of t...

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Large-eddy simulations (LES) are used to investigate the effect of stable stratification on rural-to-urban roughness transitions. Smooth-wall turbulent boundary layers are subjected to a generic urban roughness consisting of cubes in an in-line arrangement. Two line sources of pollutant are added to investigate the effect on pollutant dispersion. Firstly, the LES method is validated with data from wind-tunnel experiments on fully-developed flow over cubical roughness. Good agreement is found for the vertical profiles of the mean streamwise velocity component and mean Reynolds stress. Subsequently, roughness transition simulations are done for both neutral and stable conditions. Results are compared with fully-developed simulations with conventional double-periodic boundary conditions. In stable conditions, at the end of the domain the streamwise velocity component has not yet reached the fully-developed state even though the surface forces are nearly constant. Moreover, the internal boundary layer is shallower than in the neutral case. Furthermore, an investigation of the turbulence kinetic energy budget shows that the buoyancy destruction term is reduced in the internal boundary layer, above which it is equal to the undisturbed (smooth wall) value. In addition, in stable conditions pollutants emitted above the urban canopy enter the canopy farther downstream due to decreased vertical mixing. Pollutants emitted below the top of the urban canopy are 85 % higher in concentration in stable conditions mostly due to decreased advection. If this is taken into account concentrations remain 17 % greater in stable conditions due to less rapid internal boundary-layer growth. Finally, it

An assessment of the cavitation erosion risk by using a contemporary unsteady Reynolds-averaged Navier–Stokes (URANS) method in conjunction with a newly developed postprocessing procedure is made for an NACA0015 hydrofoil and an NACA0018-45 hydrofoil, without the necessity to compute the details of the actual collapses. This procedure is developed from detailed investigations on the flow over a hydrofoil. It is observed that the large-scale structures and typical unsteady dynamics predicted by the URANS method with the modified shear stress transport (SST) k-ω turbulence model are in fair agreement with the experimental observations. An erosion intensity function for the assessment of the risk of cavitation erosion on the surface of hydrofoils by using unsteady RANS simulations as input is proposed, based on the mean value of the time derivative of the local pressure that exceeds a certain threshold. A good correlation is found between the locations with a computed high erosion risk and the damage area observed from paint tests.