Impact of Spatial and Temporal Stability of Aneurismal Flow Vortices on Vascular Endothelial Cells

Disturbed flow vortices are linked with altered vascular endothelial cell (EC) morphology and protein expression indicative of intracranial aneurysms (IA). Unfortunately, lesser known is the impact of vortex spatial and temporal stability on EC changes. In this study, the interplay between vortex stability and EC changes was investigated by a novel combination of parallel plate flow chamber (PPFC) design and computational analysis. ECs were exposed to laminar (7.5 dynes/cm wall shear stress) or low (<1 dynes/cm) stress vortical flow using PPFCs. Immunofluorescent imaging analyzed EC morphology, while ELISA tests quantified VE-cadherin (cell-cell adhesion), VCAM-1 (macrophage-EC adhesion), and cleaved caspase-3 (apoptotic signal) expression. PPFC flow was simulated, then vortex stability calculated via the temporally averaged degree of (volume) overlap (TA-DVO) of vortices within a given area. EC morphological changes were independent of vortex stability. Increased stability promoted VE-cadherin degradation (correlation coefficient r = -0.84) and 5-fold increased cleaved caspase-3 post 24-hrs in stable (TA-DVO 0.736+0.05) vs unstable (TA-DVO 0.606+0.2) vortices. ECs in stable vortices displayed a 4.5-fold increase in VCAM-1 than unstable counterparts after 12-hrs flow. Flow vortices of greater spatial and temporal stability impart greater degrees of EC changes related to inflammation, cell-cell adhesion, and apoptosis, than unstable vortices.

Engineering Application of an Identification Method to Shock-Induced Vortex Stability in the Transonic Axial Fan Rotor

In the present paper, the steady RANS (Reynolds-Averaged Navier-Stokes) simulations based on our independently developed CFD (Computational Fluid Dynamics) solver NUAA-Turbo 2.0, are carried out to investigate the shock wave/tip leakage vortex (SW/TLV) interaction in two representative transonic axial fan rotors, NASA Rotor 67 and NASA Rotor 37. The intent of this study is mainly to verify if an identification method derived from relevant theories is suitable for shock-induced vortex stability in the real engineering environment. As the additional findings, a universal tip vortex model is established and the characteristics of vortex breakdown or not are also summarized under different load levels. To ensure the prediction accuracy of all numerical methods selected in this research, detailed comparisons are made between computational and experimental results before flow analysis. The excellent agreement between the both indicates that the current code is capable of capturing the dominant secondary flow structures and aerodynamic phenomenon, especially the vortex system in tip region and SW/TLV interaction. It is found that three vortical structures such as tip leakage vortex (TLV), shock-induced vortex (SIV), tip separation vortex (TSV) in addition the tip leakage vortex-induced vortex (TLV-IV, which only occurs when the TLV strength increases to a certain extent) frequently exist near the blade tip and then abstracted as a tip vortex model. A stable TLV after passing through the passage shock is commonly characterized by tight rolling-up, slow deceleration and slight expansion. Conversely, the vortex behaves in a breakdown state. The final verification results show that the above two vortex states can be satisfactorily detected by the theoretical discriminant introduced in this work.

Numerical simulation of shock wave/tip leakage vortex interaction for a transonic axial fan rotor

This paper presents the steady numerical investigation on SW/TLV interaction with SST turbulence model at two characteristic operating conditions for a transonic fan rotor, NASA Rotor 67. The main purpose of the present work is to reveal the main flow structures and properties during the SW/TLV interaction, and a theoretical criterion for vortex stability is engineeringly utilized to determine such shock wave-induced vortex stability. The validations for all numerical schemes have been conducted by comparing the RANS solutions with detailed experimental data before the analyses of flow phenomenon and mechanism. The simulation results indicate that numerical methods used in NUAA-Turbo 2.0 solver, independently developed by our team, enable to accurately capture the complex flow structures including shock wave and vortex systems within the blade passages, especially in the tip region. Similar to wing-tip vortex created by vortex generator, the TLV has the same wake-type characteristics. The flow pattern generated by such interaction is characterized by the bulged-forward shock front followed by a subsonic flow region and a slight expansion of vortex core. No apparent vortex breakdown was examined by both intuitive visualization of three-dimensional vortex structure and a theoretical criterion.

Investigating the Coupled Effects Between Rotor-Blade Aeroelasticity and Tip Vortex Stability

The relationship between rotor-blade aeroelasticity and tip-vortex stability is investigated numerically. An aeroelastic framework based on the free-vortex wake and finite element methods is employed to model a subscaled helicopter rotor in hover and forward-tilted conditions. A linear eigenvalue stability analysis is performed on tip vortices to associate the coupled impact of aeroelastic effects and vortex evolution. Prior numerical investigations have shown that highly flexible wind turbine rotor-blades have the potential to decrease levels of the instability of tip vortices. The present work focuses on testing these findings against a subscaled rotor within the range of helicopter operational rotation frequencies. The presented work aims to develop further insight into rotor-wake interactions and blade-vortex interaction to explore the mitigation of adverse rotorcraft operational conditions, such as their effect on aerodynamic-induced airframe vibrations and the associated life-cycle fatigue performance.

Influence of Bottom Topography on Vortex Stability

The effects of topography on the linear stability of both barotropic vortices and two-layer, baroclinic vortices are examined by considering cylindrical topography and vortices with stepwise relative vorticity profiles in the quasigeostrophic approximation. Four vortex configurations are considered, classified by the number of relative vorticity steps in the horizontal and the number of layers in the vertical: barotropic one-step vortex (Rankine vortex), barotropic two-step vortex, and their two-layer, baroclinic counterparts with the vorticity steps in the upper layer. In the barotropic calculation, the vortex is destabilized by topography having an oppositely signed potential vorticity jump while stabilized by topography of same-signed jump, that is, anticyclones are destabilized by seamounts while stabilized by depressions. Further, topography of appropriate sign and magnitude can excite a mode-1 instability for a two-step vortex, especially relevant for topographic encounters of an otherwise stable vortex. The baroclinic calculation is in general consistent with the barotropic calculation except that the growth rate weakens and, for a two-step vortex, becomes less sensitive to topography (sign and magnitude) as baroclinicity increases. The smaller growth rate for a baroclinic vortex is consistent with previous findings that vortices with sufficient baroclinic structure could cross the topography relatively easily. Nonlinear contour dynamics simulations are conducted to confirm the linear stability analysis and to describe the subsequent evolution.