Shedding Process Research Articles

Endoglin Expression and Surface Renewal in Mesenchymal Stem Cells and Endothelial Cells

Endoglin (CD105) is one of the major marker antigens of mesenchymal stem cells (MSC) and endothelial cells. While the functions of endoglin in endothelial cells have been widely declared, little is known about its role in MSC biology. Here, we present a comparative study of CD105 expression, interna-lization and shedding by human endothelial cell line EA.hy926 and human adipose tissue-derived MSC from various sources. While the fraction of CD105-positive cells in all MSC cultures and EA.hy926 endothelial cells was consistently high, over 97% of the population, the density of CD105 molecules on the surface of MSC isolated from visceral and subcutaneous adipose tissue was substantially different. The total expression level of endoglin mRNA in MSC and endothelial cells was similar, whereas the contribution of the transcripts that yield a short CD105 isoform was higher in endothelial cells. Using a set of monoclonal antibodies (mAbs) directed against different endoglin epitopes, we revealed significant differences in the dynamics of CD105 metabolism on the membranes of endothelial cells and MSC. On EA.hy926 endothelial cells, CD105 molecules bound with antibodies were internalized and remained in the perinuclear space. In MSC cultures, on the contrary, the CD105-mAbs complexes were not subjected to endocytosis and remained on the cell membrane for a long time. We demonstrated that MSC, similarly to the endothelial cells, do shed the extracellular endoglin fragment into the environment as a soluble CD105 isoform. The shedding process in MSC was, however, substantially less intensive compared with the endothelial cells. Thus, we revealed, for the first time, that in MSC, unlike the endothelial cells, endoglin persists on cell surface for a long time and is not interna-lized after binding with antibodies. Endoglin shedding from MSC surface and the concomitant generation of the soluble endoglin form were also demonstrated for the first time.

Vortex-induced vibration mechanism of the NACA 0012 airfoil based on a method of separating disturbances

Vortex-induced vibration (VIV) is the result of the interaction between the airfoil vibration and vortex shedding, and it frequently achieves the peak vibration amplitude in the lock-in region. Therefore, distinguishing the effect of the two disturbances in the lock-in region is important for understanding VIV. In this study, the NACA 0012 airfoil was investigated at high angles of attack; thus, the vortex could form and shed regularly downstream. The VIV was analyzed numerically and verified using the test data in references. The process of the vortex shedding was observed to be similar under different incoming flows, vibration amplitudes, and frequency ratios. In the V-shape lock-in region, the phase between the airfoil vibration and vortex shedding changes with the frequency ratio. When the frequency ratio is 1, the phase and strength of the vortex shedding remain almost constant with the vibration amplitude. Based on the features of the vortex shedding, a method of separating the disturbances caused by the airfoil vibration and the vortex shedding is proposed to investigate the mechanism of VIV from the perspective of energy balance. As the phase between the airfoil vibration and vortex shedding changes in the lock-in region, the vortex shedding provides negative aerodynamic damping (AD) in some phases and positive AD in other phases. The stability of the airfoil depends on the two disturbances mentioned above. VIV occurs only when the disturbance of the vortex shedding performs positive work (negative AD) and the disturbance of the airfoil vibration performs negative work (positive AD). When the vibration amplitude is small, VIV is dominated by the disturbance of the vortex shedding. When the vibration amplitude is high, the VIV is dominated by the disturbance of the airfoil vibration. As the vibration amplitude increases, the two form a balance, and the airfoil exhibits limit cycle oscillations. Based on the assumption of linear superposition, the theoretical limit vibration amplitudes of the airfoil under the two conditions in this study were 3° and 13.4°, respectively.

Formation and Stability of Thin Condensing Films on Structured Amphiphilic Surfaces.

We present a microamphiphilic surface to promote the formation of a thin, stable liquid film during condensation. The surface consists of a hydrophilic micropillar array with hydrophobic pillar tips and was made using photolithography, deep reactive ion etching, and liftoff. The hydrophobic tips prevent the liquid film from growing thick, thereby keeping the thermal resistance low without the cyclical growth and shedding process of dropwise condensation. The wetting behavior was modeled analytically, and the parameters required for film formation were determined and verified with ESEM experiments. When a surface filled with condensate and lacked a low-pressure zone for the water to leave, a rupture event occurred, and a large Wenzel droplet emerged to flood the surface irreversibly. A number of strategies were found to combat rupture events. Tilting the surface vertically and dipping in a liquid pool gave the condensate a low-pressure region and prevented rupture. Irreversible flooding can also be avoided by ensuring that the emerged droplet was a nonwetting, highly mobile Cassie droplet. Parameters for Cassie-stable amphiphilic surfaces were determined analytically, but the high aspect ratios required prevented the manufacture of these surfaces for this study. Instead a hierarchical design was presented that demonstrated emerged Cassie droplets without challenging the manufacturing limits of the microfabrication procedure. This design avoided Wenzel droplet flooding without the need for a designated low-pressure zone. Additionally, sites for Cassie emergence could be engineered by removing a single pillar from the array at a designated location.

Numerical investigation of cavitation-vortex interaction with special emphasis on the multistage shedding process

The objective of this paper is to investigate the physical interaction of the cavitation-vortex dynamics around a 3D Delft hydrofoil by large eddy simulations combined with the Zwart–Gerber–Belamri cavitation model. Transient sheet/cloud cavitating flows around the twisted hydrofoil involves the primary and secondary cavity shedding characterized by a U-shape structure, which is consistent with previous experimental data. Different vortex identification methods, namely, the ω criterion, Q criterion, Ω method and Liutex method, are applied to identify and analyze the vortex structure. The Liutex method is further utilized to visualize the detail of vortex structure in the primary and secondary cavity shedding process, especially for formation and development of the U- shape structure. For the primary cavity shedding process, the U- shape structure is the main feature of the shedding process. The primary U- shape vortex structure experiences distortion, and breaks into two parts at the vortex neck. Then, the front part develops into a O-shape structure, whereas the rear part still maintains a U- shape structure. Finally, both parts are dissipative completely in the form of U-shape structures. The shear plays a major role in the primary cavity shedding. For the secondary cavity shedding, U-shape, Ω-shape, O-shape, and hairpin vortexes are observed. The secondary U-shape vortex structure twists and deforms to form a hairpin vortex when the secondary cavity sheds completely, and finally dissipates with a smaller magnitude hairpin vortex. Rotation plays a major role in the secondary cavity shedding.

A further study on a disturbance of intestinal epithelial cell population and kinetics in APC1638T mice.

Adenomatous polyposis coli (APC), a well-known anti-oncogene, is considered to have multiple functions through its several binding domains. We have continuingly studied APC1638T/1638T mice (APC1638T mice) to elucidate the functions of APC other than tumor suppression. A distinctive feature of the APC1638T mice is they are tumor free and live as long as APC+/+ mice (WT mice). Previously, we found the length of crypt-villus axis in the jejunum was significantly elongated in APC1638T mice compared with that of WT mice. The populations of goblet cells, Paneth cells, and enteroendocrine cells were also disordered in APC1638T mice. Here, we further analyzed the intestinal dyshomeostasis in APC1638T mice, focusing on the proliferation and differentiation of intestinal stem cell (ISC) lineages, and apoptotic cell shedding at the villus tips. We found that the proliferation of ISC lineages was normally controlled; however, the shedding process of apoptosis cells was significantly delayed in the APC1638T mouse jejunum. Furthermore, the number of microfold cells (M cells) was significantly increased in the APC1638T mouse jejunum. Our data suggested both differentiation process of ISCs and turnover process of intestinal epithelia were disturbed in APC1638T mice, and that contributed to the villus elongation in the APC1638T mouse jejunum.

Lagrangian Analysis of Unsteady Partial Cavitating Flow Around a Three-Dimensional Hydrofoil

Abstract This study employs an incompressible homogeneous flow framework with a transport-equation-based cavitation model and shear stress transport turbulence model to successfully reproduce the unsteady cavitating flow around a three-dimensional hydrofoil. Cavity growth, development, and break-off during the periodic shedding process are adequately reproduced and match experimental observations. The predicted shedding frequency is very close to the experimental value of 23 ms. By monitoring the motions of the seeding trackers, growth-up of attached cavity and dynamic evolution of U-type cavity are clearly displayed, which indicating the trackers could serve as an effective tool to visualize the cavitating field. Repelling Lagrangian coherent structure (RLCS) is so complex that abundant flow patterns are highlighted, reflecting the intricacy of cavity development. The formation of cloud cavities is clearly characterized by the attracting Lagrangian coherent structure (ALCS), where bumbling wave wrapping the whole shedding cavities indicates the rotating transform of cavities, and stretching of the wave eyes shows the distortion of vortices. Generation of the re-entrant jet is considered to be not only associated with the adverse pressure gradient due to the positive attack angle but also the contribution of cloud cavitating flow, based on the observation of a buffer zone between the attached and cloud cavities.

LES study on the working mechanism of large-scale precessing vortices and energy separation process of Ranque-Hilsch vortex tube

In this paper, a large eddy simulation model (LES) was adopted to analyse the large-scale precessing vortices and energy separation in a Ranque–Hilsch vortex tube. By comparing the time-averaged axial velocity field between the Laser Doppler velocimetry data and the numerical results, the feasibility of the LES model was confirmed. The 2D instant flow field presents two vortex structures of secondary circulation flow at the cold end, and precessing vortices inside the tube. It also reveals two opposite flows in the axial and radial directions, and the precessing vortices formed by the reverse flow turn towards the main flow. Then, the 3D coherent structure inside the vortex tube was obtained by the vortex identification method for the first time. The basic vortex structure inside the vortex tube consists of the vortex body, detached vortex, and fragmentised detached vortex. Through the evolution of the 3D vortex structure, it was found that the detached vortices experienced a life cycle of growth, shedding, fragmenting, and vanishing. Benefitting from the vortex shedding processes, the precessing vortices overcame the adverse radial pressure gradient and drove part of the reverse flow towards the main flow from the low-pressure zone to the high-pressure zone. Through these processes, the vortex core precession that drives the reciprocating motion of the gas parcels near the reverse flow boundary was established, and energy could be transferred from the inner layer to the outer layer through a heat pump cycle.

Investigation of Optimum Conditions for Flow Control Around Two Inline Square Cylinders

Numerical investigations are carried out for the flow around two inline square cylinders with a flat plate, placed in the wake, using the lattice Boltzmann method. Main emphasis of this work is to find the optimum values of the gap ratio (L/d) between cylinders and plate for maximum vortex shedding control and suppression of flow induced forces. The gap ratio between both cylinders as well as between second cylinder and plate is varied in the range 0.5 to 10 by fixing Reynolds number at 150. Three different flow structures are observed by systematically increasing the gap ratio: solo body (L/d = 0.5), reattachment flow (1 ≤ L/d 2.5. An interesting fact revealed through this study is that the control plate, with dimensions chosen in present study, does not always suppress the fluid forces and controls vortex shedding process. In some cases, its presence in the wake may be critical in terms of fluid forces and vortex shedding.

Steady flow around a square cylinder near a plane boundary

Steady flow around a square cylinder placed near a plane wall boundary is investigated experimentally in the present work covering the range of Reynolds number of Re = 7.34 × 104–4.12 × 105, gap ratios of G/D = 0–3 with two different freestream turbulent intensity Iu = 1% and 9%. The influence of Reynolds number, gap ratios and turbulent intensity on the hydrodynamic characteristics have been studied systematically. Two-dimensional Large-eddy simulation (LES) were employed for flow visualizations. It is found that the hydrodynamic forces on a square cylinder are independent of Re even for the very small gap ratio cases. For the influence of the low turbulent intensity (Iu = 1%), the hydrodynamic features and vortex shedding are insensitive to the gap effect as G/D > 1. With the decrease of G/D, the increase of the base pressure Cpb results in the decrease of the drag coefficient CD. The amplitude of the periodic fluctuations of the vortex shedding process decreases with the vortex shedding process continuing. As G/D ≤ 0.3, the vortex shedding is observed to be completely suppressed. The blockage effect leads to an entrainment of the flow passing through the gap and a low-speed recirculation is formed at the plane boundary in the region of x/D < 7.75. High turbulence tends to increase the base pressure and reduce the drag coefficient of the square cylinder for large gap ratio. For G/D ≤ 0.8, the high turbulence triggers the growth of separated shear layer and inherent instabilities for the near-wall cylinder, which results in the higher fluctuating drag and lift coefficient. The critical gap ratio for the vortex shedding suppression is reduced to G/D = 0.2.

Ultrastructural observations on the oncomiracidium epidermis and adult tegument of Discocotyle sagittata, a monogenean gill parasite of salmonids

During their different life stages, parasites undergo remarkable morphological, physiological, and behavioral “metamorphoses” to meet the needs of their changing habitats. This is even true for ectoparasites, such as the monogeneans, which typically have a free-swimming larval stage (oncomiracidium) that seeks out and attaches to the external surfaces of fish where they mature. Before any obvious changes occur, there are ultrastructural differences in the oncomiracidium’s outer surface that prepare it for a parasitic existence. The present findings suggest a distinct variation in timing of the switch from oncomiracidia epidermis to the syncytial structure of the adult tegument and so, to date, there are three such categories within the Monogenea: (1) Nuclei of both ciliated cells and interciliary cytoplasm are shed from the surface layer and the epidermis becomes a syncytial layer during the later stages of embryogenesis; (2) nuclei of both ciliated cells and interciliary syncytium remain distinct and the switch occurs later after the oncomiracidia hatch (as in the present study); and (3) the nuclei remain distinct in the ciliated epidermis but those of the interciliary epidermis are lost during embryonic development. Here we describe how the epidermis of the oncomiracidium of Discocotyle sagittata is differentiated into two regions, a ciliated cell layer and an interciliary, syncytial cytoplasm, both of which are nucleated. The interciliary syncytium extends in-between and underneath the ciliated cells and sometimes covers part of their apical surfaces, possibly the start of their shedding process. The presence of membranous whorls and pyknotic nuclei over the surface are indicative of membrane turnover suggesting that the switch in epidermis morphology is already initiated at this stage. The body tegument and associated putative sensory receptors of subadult and adult D. sagittata are similar to those in other monogeneans.

Experimental and numerical investigation of turbulent wake flow around wall-mounted square cylinder of aspect ratio 2

The turbulent wake velocity fields around a short wall-mounted square cylinder of aspect ratio 2 fully immersing into a thick turbulent boundary layer are obtained experimentally with PIV and numerically with LES. Comparison between the two sets of data is made on the time-averaged mean velocities, turbulent fluctuating velocities, and the detailed characteristics of energetic large-scale coherent structures. It is noted that a good comparison of the low-order statistics of velocity fields does not guarantee a satisfactory reproduction of the coherent structures. These flow structures show great similarities in the spatial patterns and dynamic performance between PIV and LES, but apparent differences in turbulent kinetic energy contribution. On the horizontal plane parallel to the wall, the dominant antisymmetric spatial mode pair illustrates the evolution process of Karman vortex shedding with a clear spectral peak around the characteristic frequency while three extra frequency peaks are found in the symmetric spatial modes. Further investigation on the velocity field on the central vertical plane reveals the connection between the unsteadiness of shear layer flow at the free end and the spanwise symmetric vortex shedding activities. It is confirmed that the flapping motion and vortex convection mechanisms observed for the present cylinder could modulate the symmetric wake dynamics. The three-dimensional extreme wake patterns, available from LES results, are related to the most energetic Karman vortex shedding demonstrate upward flow in the vortex weakening side. Meanwhile, the downwash flow at the extreme time instants is found to become stronger always for this kind of short cylinder with a dipole wake pattern.

A Finite Element Model of Unsteady Cavitating Fluid Flow around a Hydrofoil

The present study deals with the unsteady dynamics of cavitation around the NACA 0015 hydrofoil in a channel. A finite element model is proposed to solve the governing equations of momentum and mass conservation. Turbulent flows around the hydrofoil are described by the Prandtl-Kolmogorov model. The cavitation phenomenon is modeled through a mixture model involving liquid and vapor flows and the Zwart-Gerber-Belamri (ZGB) model is considered to evaluate the transport of the water vapor fraction. The variational finite element model formulation includes the mixing of the characteristic method and the finite element. Also, at the open sides of the channel flow, an open boundary condition is imposed. Numerical experiments are performed for cavitation numbers 0.8 and 0.4. The presented model predicts the essential features of unsteady cavitating flows, the generation of vapor cavities, the time-dependent oscillations of the variables and the presence of vortical flow structures associated to vapor volume concentrations during the shedding process.

Dermal denticle shedding rates vary between two captive shark species

Shark dermal scale (denticle) accumulation in the fossil record can provide information about the abundance and composition of past shark communities. Denticles are shed continuously, such that a single shark leaves a scattered composite of many isolated denticles in sediments. However, the rate of denticle shedding as well as how these rates vary among shark species with different life modes and their consistency over time are unknown, limiting the interpretation of denticle assemblages. To better understand the process of denticle shedding and calibrate the relationship between absolute shark abundance in the environment and denticle deposition in sediments, we captured denticles shed by 2 shark species in a large aquarium over 9 mo. We then simulated how these aquarium-derived shedding rates shape the relationship between shark abundance and denticle accumulation. Bonnethead sharks Sphyrna tiburo, a more active, benthopelagic species with small, thin denticles, shed 3.6 times faster on average than zebra sharks Stegostoma fasciatum, a more sedentary, demersal species with large, robust denticles. This pattern persisted when shedding rates were corrected by estimated denticle quantities, shark space use, and methodological factors (2.2- to 3.8-fold difference). Over the study, bonnethead shark shedding rates declined while zebra shark shedding rates increased slightly. Finally, denticle assemblage composition corresponded with the relative abundance of denticles on the body of each species, consistent with natural shedding rather than selective loss. Overall, we show that shark taxa contribute unevenly to the denticle record, indicating that shedding rate measurements can help inform and constrain ecological interpretations of denticle assemblages.

The Shed Skin of the Snake: Image of Growth and Renewal

In this article the therapeutic process of inner maturation and growth and the consequent need to shed what no longer serves the self is likened to the process of a snake shedding its skin. Reflecting on the sandplay processes of three women, the author offers perspectives on the shed skin of the snake as a symbol and also on the process of psychological shedding that takes place in the course of therapy. These clients' presenting problems included depression, anxiety, low self-esteem, traumatic loss and lack of "good enough" parenting.

Influence of Stratification and Yucatan Current Transport on the Loop Current Eddy Shedding Process

AbstractThe effects of stratification and Yucatan Current (YC) transport on the dynamics of the Loop Current (LC) and Loop Current Eddies (LCEs) are studied using a primitive equation, 2½ nonhomogeneous layered model, which reproduces the main dynamical features of the upper ocean circulation in the Gulf of Mexico (GoM). The analysis considers the observed variations in stratification and YC transport, and their expected changes due to climate change. The study is based on a set of long‐term simulations considering the combination of seven stratification configurations with seven transport configurations resulting in 49 cases. The LCE shedding period and diameter (LCE metrics) and kinetic energy, eddy kinetic energy, available potential energy, eddy available potential energy, and the energy Burger number (energy metrics) are analyzed. The stratification and transport contribute to the current and future LC and LCE variability, with their dynamics being more sensitive to transport variations than to stratification variations. The LCE detachment is associated with the increase in the mass of the LC and its available potential energy budget, which is a primary determinant for the LC and LCE dynamics and a condition for eddy shedding. For the expected changes due to climate change, the LCE response is contrary: larger stratification causes increments in the LCE metrics and energy metrics, except the energy Burger number that decreases; conversely, smaller transport causes the opposite response. A combined occurrence of increased stratification and reduced transport, as expected with climate change, causes decrements in the LCE metrics and energy in the GoM.

COAST GEOMORPHOSYSTEMS OF THE RIGHT BANK OF THE VOTKINSK RESERVOIR

Methods and results of field studies of the complex of coastal processes on the right Bank of the Votkinsk reservoir are presented. They include observations of the rate of destruction and retreat of the walls of landslide-scree slopes, cut by abrasion, and processes that develop on the emerging shallows. For the first time, the processes of slow mass displacement of material entering the shallows due to the destruction of the banks were established and quantified within the shallow coastal waters. The main morphological types of coastal geomorphosystems are identified and the rates of re-formation are determined for their surface and underwater parts. It is noted that the most productive processes in relation to the flow of loose material into the reservoir bowl are the processes of shedding. Accordingly, weathering, as a source of loose material formation, acquires the importance of the most important shore-forming factor in the surface part of coastal geomorphosystems in the reservoir conditions. Among the most important lithodynamic flows of underwater sections of the coastal zone, the underwater "creep" is singled out. It was found that the layer of loose sediment lining the bench with a layer of 20-25 cm by the beginning of ice formation completely slides in the drying zone at a distance of 15-20 meters by the beginning of spring water discharge. Mass displacement of fine-grained earth occurs in the summer, but the slid material is actively replenished with abrasive products in the summer. Banks are destroyed by parallel retreat of the underwater and surface parts of the coast. At present, the rate of coastal destruction often increases rather than decreases, which makes it necessary to review some theoretical provisions concerning the laws of coastal development and forecast estimates. The results obtained can be used to estimate the rate of siltation of the reservoir basin.

Numerical analysis of unsteady cloud cavitating flow around a 3D Clark-Y hydrofoil considering end-wall effects

This study employs an incompressible homogeneous flow framework with a transport equation based cavitation model and density corrected Shear Stress Transport (SST) k-ω turbulence model to successfully reproduce the unsteady cavitating flow around a 3D Clark-Y hydrofoil with an end wall. Cavity growth, development, and break-off during the periodic shedding process are adequately reproduced and match experimental observations. The predicted shedding frequency is very close to the experimental value of 43.48 Hz. The existence of an end wall brings about the generation and convection of wall-side cavity. Moreover, large horse-type cavity structure is captured, which agrees with experimental results. Cavities at the closure region easily detach from the main pocket part resulting in a secondary vortical structure. Differences between numerical and experimental lift are observed, however, similar to our previous findings, the experimental lift coefficient appears to correlate with the inverse of the second derivative of the total cavity volume. Based on the analysis of vorticity transportation, compressibility source occupies the highest contribution of vorticity transportation and is significantly higher than other two terms, which serves the promotion effect at the trailing region of growing attached cavity while inhibits the development of vorticity within the leading area.

Combined Two-phase Co-flow and Counter-flow in a Gas Channel/Porous Transport Layer Assembly

Polymer electrolyte fuel cells and electrolyzers are low temperature devices whereby both gases and liquids intermingle within the porous transport layers and open channels. The flow of the liquid and gas is of paramount importance to the functioning of the unit. This motion is poorly understood. Cell-level models typically employ volume-averaging techniques to describe the motion of the flowing reactants and products. Until recently, detailed analysis of the two-phase liquid gas mixture, employing front-tracking methods has proved too computationally prohibitive. Previous work [1,2] has considered the motion of liquid drops in gas channels, it being assumed the drops are formed at specific nucleation sites on the sides of the channels. The present work considers a detailed numerical analysis of combined liquid-gas co-flow in a gas channel with liquid-gas counter-flow in a porous transport layer (PTL). The geometry considered is a ‘T-shape’ with the porous transport layer in the form of a thin rectangular prism of dimensions 0.5×0.5×0.1 mm3 located at the base of the ‘T’, and the gas flowing across the top channel, as shown in Fig. 1. The PTL is reproduced by digital reconstruction of nano-computer tomography images of a Freudenberg H2315 PTL as a stereolithography file*, see Figure 2(a). From this, the domain is tessellated with an unstructured castellated, or octree, type mesh, Fig. 2(b). Liquid water is introduced at an electrode at the base of the PTL and gaseous oxygen is simultaneously removed by electrochemical reduction; the resulting liquid-gas counter-flow in the porous transport layer effects liquid droplets being entrained in co-flow in the gas channel and being convected downstream, thereafter.The equations of mass and momentum are solved by means of the open source software library OpenFOAM. A volume-of-fluid approach based on the multidimensional universal limiter for explicit solution was employed. At t = 0, the channel is presumed to be filled with gas, and the PTL partially saturated with liquid water. Gas is introduced at the inlet at a given velocity. Water is added and gas removed at the electrode (counter-flow), whereas both water and gas are removed at the outlet (co-flow). At the channel walls and on the PTL fibres, the static contact angle is fixed.Some results are shown in Fig. 3(a-d). It can be seen that the location and size of the drops shed varies somewhat in space and time, i.e., there is a stochastic component to the motion of the fluid, due to the spatial distribution of the fibres in the PTL, the transient shedding process, and the merging of liquid streams flowing into the gas channel. Nonetheless a definite periodicity is observed, with drops being injected into the channel at a fairly regular rate. Some relatively minor switching with time is observed within the PTL due to the random packing of fibres, but these transients are relatively quiescent. In addition to providing important new information about flow and pressure losses in electrochemical cells as a function of current density and stoichiometry, the present model may be also used to enumerate properties such as relative permeability which can subsequently be employed in cell-scale models.* The authors wish to thank Mr. Eugen Hoppe for constructing a stereolithography file of the porous material used in this study.[1] Andersson, M., Beale, S.B., Reimer, U., Lehnert, W., Stolten, D., Int. J. Hydrog. Energy, 2018, 43(5): 2961-2976.[2] Andersson, M., Mularczyk, A., Lamibrac, A., Beale, S.B., Eller, J., Lehnert, W., Büchi, F.N., J. Power Sources, 2018. 404: 159-171. Figure 1

Numerical Investigation of the Cavitation Effects on the Vortex Shedding from a Hydrofoil with Blunt Trailing Edge

Vortex cavitation can appear in the wake flow of hydrofoils, inducing unwanted consequences such as vibrations or unstable behaviors in hydraulic machinery and systems. To investigate the cavitation effects on hydrofoil vortex shedding, a numerical investigation of the flow around a 2D NACA0009 with a blunt trailing edge at free caviation conditions and at two degrees of cavitation developments has been carried out by means of the Zwart cavitation model and the LES WALE turbulence model which permits predicting the laminar to turbulent transition of the boundary layers. To analyze the dynamic behavior of the vortex shedding process and the coherent structures, two identification methods based on the Eulerian and Lagrangian reference frames have been applied to the simulated unsteady flow field. It is found that the cavitation occurrence in the wake significantly changes the main vortex shedding characteristics including the morphology of the vortices, the vortex formation length, the effective height of the near wake flow and the shedding frequency. The numerical results predict that the circular shape of the vortices changes to an elliptical one and that the vortex shedding frequency is significantly increased under cavitation conditions. The main reason for the frequency increase seems to be the reduction in the transverse separation between the upper and lower rows of vortices induced by the increase in the vortex formation length.

Aerodynamic pressures on a 5:1 rectangular cylinder in sinusoidal streamwise oscillatory flows with non-zero mean velocities

In this paper, the aerodynamic pressures on a 5:1 rectangular cylinder in sinusoidal streamwise oscillatory flows (SSOFs) with non-zero mean velocities are studied through wind tunnel experiments. First, the mean and fluctuating pressure coefficients are determined based on the measurements in SSOFs with different reduced frequencies and gust amplitudes. The results are compared with those of smooth flow and grid-generated turbulent flow. Next, the power spectral densities of surface pressures are presented to study their energy distributions in the frequency domain. Then, the spanwise correlations of surface pressures in SSOFs are compared with those of smooth flow to explore their three-dimensional characteristics. The testing results show that the reduced frequency, varying from 0.012 to 0.032 has little effect on the streamwise pressure distributions of the 5:1 rectangular cylinder, and the influences of the gust amplitude of SSOFs are significant. The maximum RMS pressure coefficient increases and the separation bubble length reduces to a large degree as the gust amplitude increases. The spectral analysis demonstrates that the energy of fluctuating pressures in SSOFs is primarily from oscillatory streamwise gusts, while it is mainly provided by vortex shedding in smooth flow. The SSOF can accelerate the vortex shedding process and the Strouhal number increases as the increased gust amplitude. The spanwise correlations of pressures are strong in the majority region of the side surface of the 5:1 rectangular cylinder in SSOFs.