Laminar Flow Research Articles

Influence of Permeability and Shear-Thinning Behavior on the Hydrodynamics Flow Features Around Porous Square Cylinders

Abstract This article investigates the laminar flow of power-law fluids through two porous square cylinders in a side-by-side configuration. The effects of power-law index (n), Darcy number (Da), and gap ratio (g/W) are examined within ranges of g/W = 0.5–5, n = 0.4–0.8, and Da = 10−6–10−2, respectively. Two flow conditions are considered: first, for a creeping flow (unseparated flow) at Re = 1 where Darcy's law is applicable; second, for a viscous dominant flow at Re = 100, where Darcy–Forchheimer-extended model is exercised. Flow patterns behind the porous cylinders are analyzed using streamlines, velocity profiles, pressure distribution curves, and vorticity structural parameters (Г). In low permeability levels, the flow exhibits an irregular nonperiodic vortex shedding characterized by a single large vortex street far off the downstream for g/W = 0.5. However, synchronized wake patterns were observed in either antiphase or in-phase modes for higher gap ratios. Leading-edge separation with two-side recirculation induces quasi-periodicity in the flow for all g/W. It was found that increasing the permeability can prevent the leading edge separation. Additionally, a transition from antiphase to in-phase mode occurs when the permeability is altered while maintaining constant flow-time. The presence of a jet-like flow between cylinders significantly impacts unsteady wake patterns. The impact of g/W, power-law index, and permeability on drag is also examined. A jump in some flow parameters was observed at higher Re for the midrange Darcy number, but no such increase was noted for the high shear-thinning behavior. These findings provide a potential approach for improving the design of fluidic systems involving porous cylinders.

On the autonomous validation and comparison of particle models for a Newtonian laminar flow mixing model using PEPT

A methodology for the validation of a Computational Fluid Dynamics (CFD) mixing model using Positron Emission Particle Tracking (PEPT) was applied to a horizontal laminar stirred tank containing Newtonian glycerol. Particle trajectories recorded using PEPT were compared to three one-way particle-coupled CFD models (CFD-DEM, and CFD-Lagrangian, and CFD-Massless) through time-averaging and binning into a grid of 3-D voxels. A cell-by-cell comparison of particle velocities between the computational models and PEPT highlighted the accuracy of the CFD-DEM and CFD-Massless models over the Lagrangian model. Furthermore, using PEPT as a validation dataset the Pearson r-squared was used as a cost function to guide an autonomous calibration of a 5-dimensional DEM parameter space. A novel statistic, the simulation quality coefficient Qsim, was applied to assess accuracy between trajectory datasets and revealed the extent to which a model can be considered calibrated. Considering the balance between computational cost and precision, the CFD-massless model was the most effective particle model for this validation workflow. Further investigations will apply this methodology to calibrate non-Newtonian laminar CFD models.

Cryopreservation of sessile oak (Quercus petraea (Matt.) Liebl.) plumules using aluminium cryo-plates: influence of cryoprotection and drying

Background Quercusseeds that are recalcitrant to desiccation and freezing temperatures cannot be stored in gene banks under conventional conditions. However, the germplasm of some recalcitrant seeded species can be stored in liquid nitrogen (–196 °C). Unfortunately, for many species, among them for almost the whole genus Quercus, an effective cryostorage method is still unknown. In this study, we propose a successful cryostorage protocol for Quercus petraea (Matt.) Liebl. germplasm using plumules (a shoot apical meristem of an embryo) frozen on aluminium cryo-plates.ResultsThe plumules isolated from the acorns of ten provenances were prestored in 0.5 M sucrose solution (for 18 h). To form alginate beads (one plumule per bead), the plumules were placed in the wells of a cryo-plate and embedded in calcium alginate gel. For cryoprotection, the encapsulated plumules were immersed in cryoprotectant solution containing 2.0 M glycerol and different concentrations of sucrose (0.8–1.2 M) for 40 min at 25 °C and desiccated under a laminar flow cabinet for 1.0–4.0 h. Cryo-plates with plumules were directly immersed in liquid nitrogen and then cryostored for 30 min. For rewarming, cryo-plates with plumules were immersed in 1.0 M sucrose solution and rehydrated for 15 min at 25 °C. Survival rates varied from 25.8 to 83.4 were achieved after cryoprotection in 1.0 M sucrose solution and the drying of plumules for 2 h. The in vitro regrowth rate of cryopreserved plumules varied among provenances and was 26–77%.ConclusionsThis study presents, for the first time, a successful, simple and effective protocol for the cryopreservation of Q. petraea germplasm that could be used in gene banks. The experiment was successfully repeated on seeds from various provenances, each yielding similar, good results. However, seed quality and storage time after harvesting are important factors in plumule regrowth after cryopreservation.

Endothelial Cell Flow-Mediated Quiescence Is Temporally Regulated and Utilizes the Cell Cycle Inhibitor p27.

Endothelial cells regulate their cell cycle as blood vessels remodel and transition to quiescence downstream of blood flow-induced mechanotransduction. Laminar blood flow leads to quiescence, but how flow-mediated quiescence is established and maintained is poorly understood. Primary human endothelial cells were exposed to laminar flow regimens and gene expression manipulations, and quiescence depth was analyzed via time-to-cell cycle reentry after flow cessation. Mouse and zebrafish endothelial expression patterns were examined via scRNA-seq analysis, and mutant or morphant fish lacking p27 were analyzed for endothelial cell cycle regulation and in vivo cellular behaviors. Arterial flow-exposed endothelial cells had a distinct transcriptome, and they first entered a deep quiescence, then transitioned to shallow quiescence under homeostatic maintenance conditions. In contrast, venous flow-exposed endothelial cells entered deep quiescence early that did not change with homeostasis. The cell cycle inhibitor p27 (CDKN1B) was required to establish endothelial flow-mediated quiescence, and expression levels positively correlated with quiescence depth. p27 loss in vivo led to endothelial cell cycle upregulation and ectopic sprouting, consistent with loss of quiescence. HES1 and ID3, transcriptional repressors of p27 upregulated by arterial flow, were required for quiescence depth changes and the reduced p27 levels associated with shallow quiescence. Endothelial cell flow-mediated quiescence has unique properties and temporal regulation of quiescence depth that depends on the flow stimulus. These findings are consistent with a model whereby flow-mediated endothelial cell quiescence depth is temporally regulated downstream of p27 transcriptional regulation by HES1 and ID3. The findings are important in understanding endothelial cell quiescence misregulation that leads to vascular dysfunction and disease.

Numerical investigation on mixed convection for laminar molten salt in horizontal square tubes

Molten salts are the key working media in nuclear and new energy fields. However, the mixed convection of molten salt is rarely investigated. The mixed convection of laminar flow in horizontal square tubes with constant heat flux is analyzed using Fluent software for the first time. The effects of heat flux, inlet temperature and Reynolds number on the flow and heat transfer performances are evaluated. It is found that as the buoyancy force increases, the friction factor, flow entropy generation rate, Nusselt number, and exergy efficiency increase, while the heat transfer entropy generation rate and exergy loss decrease. Compared to the forced convection, the maximum local friction factor, flow entropy generation rate, mean Nusselt number and mean exergy efficiency for mixed convection increase by 25.8%, 50.5%, 109.0% and 7.6%, respectively. Moreover, the maximum mean heat transfer entropy generation rate and exergy loss decrease by 56.1% and 57.3%, respectively. In addition, approximately 42% of the friction factor predicted by Fluent and 30% of the heat transfer predicted by Fluent exceed 20.0% uncertainties of conventional correlations. Therefore, an accurate friction factor correlation with 12.9% uncertainty and an accurate heat transfer correlation with 9.1% uncertainty are proposed.

Deep learning-assisted concentration gradient generation for the study of 3D cell cultures in hydrogel beads of varying stiffness.

The study of dose-response relationships underpins analytical biosciences. Droplet microfluidics platforms can automate the generation of microreactors encapsulating varying concentrations of an assay component, providing datasets across a large chemical space in a single experiment. A classical method consists in varying the flow rate of multiple solutions co-flowing into a single microchannel (producing different volume fractions) before encapsulating the contents into water-in-oil droplets. This process can be automated through controlling the pumping elements but lacks the ability to adapt to unpredictable experimental scenarios, often requiring constant human supervision. In this paper, we introduce an image-based, closed-loop control system for assessing and adjusting volume fractions, thereby generating unsupervised, uniform concentration gradients. We trained a shallow convolutional neural network to assess the position of the laminar flow interface between two co-flowing fluids and used this model to adjust flow rates in real-time. We apply the method to generate alginate microbeads in which HEK293FT cells could grow in three dimensions. The stiffnesses ranged from 50Pa to close to 1kPa in Young modulus and were encoded with a fluorescent marker. We trained deep learning models based on the YOLOv4 object detector to efficiently detect both microbeads and multicellular spheroids from high-content screening images. This allowed us to map relationships between hydrogel stiffness and multicellular spheroid growth.

Turbulent flow boiling simulation based on pseudopotential lattice boltzmann method with developed wall boundary treatments and unit conversion

The lattice Boltzmann method (LBM) is widely studied for complex flow simulations, including liquid–vapor phase change phenomena. Although previous studies extended the LBM simulation capability from single-phase to two-phase boiling simulations, most of them are restricted to no-flow (pool boiling) or low-flow-rate (laminar flow) boiling conditions owing to the stability problem in collision at low viscosity, representing high Reynolds numbers. However, a high Reynolds number flow is essential for investigating the effects of turbulence on bubble dynamics. Recently, the central moment-based collision method is used to enable high Reynolds numbers for bulk flow; however, extending the method for multiphase-flow simulation with high Reynolds numbers is limited owing to the boundary treatment near the wall. In this study, we augment the previous boundary treatment in LBM simulation with a forcing term, which increases the stability of the simulation even under two-phase conditions. With the improved boundary treatment, the flow boiling phenomena at high Reynolds numbers (up to Re = 107,000) are successfully reproduced. Moreover, in this study, unit conversion is reconsidered with the relationship between conversion factors because the poor outcomes of bubble dynamics are attributed to misinterpreted unit conversion. The new unit conversion method satisfies the necessary conditions for mapping the physical bubble behavior to lattice frame, reproducing bubble dynamics effectively following the Reynolds number, with reasonable spatial and temporal resolution. Consequently, the flow boiling simulation can accurately predict the bubble departure diameter from the real experimental results and the heat transfer trend as a function of the Reynolds number.

Further insights into steady three-dimensional MHD Sakiadis flows of radiating-reacting viscoelastic nanofluids via Wakif’s-Buongiorno and Maxwell’s models

AbstractKeeping in mind the stress relaxation tendency of many viscoelastic multi-phase flows (e.g., polymer solution flows and transport phenomena of red cell suspensions within blood media), the present research investigation intends principally to develop a realistic model for revealing properly the aspects of reacting-radiating Maxwell nanofluids during their laminar boundary layer flows in the steady regime over a horizontal impermeable surface under a transversal magnetic influence. For this purpose, the principal leading differential formulation is derived theoretically by linking Wakif’s-Buongiorno approach with Maxwell’s model. By invoking fundamentally the general boundary layer assumptions and the passive control strategy for the nanoparticles, the governing PDEs’ formulation is simplified accordingly and then stated properly for the case of the convective heating condition at the impermeable bi-stretching surface. By executing a feasible non-dimensionalization technique, the monitoring ODEs’ system is achieved successfully, whose solutions are presented precisely in different illustrative scenarios using Richardson’s extrapolation method. After carrying out successfully several validating tests, it is demonstrated that the weakly viscoelastic feature has generally a slight delaying effect on the nanofluid motion. This dynamical weakening can be reinforced more with the generation of thermal energy by intensifying the external magnetic field source. Additionally, these physical factors show an intensifying influence on the surface drag forces. However, a dropping impression is seen for the local heat transfer at the contact surface. Contrary to the broadening impact of the radiative heat transfer as well as the convective heating and thermophoresis mechanisms on the thermal and mass boundary layer regions, it is witnessed that the first-order chemical reaction mechanism and Brownian’s motion exhibit a shrinking impact on the mass boundary layer region.

On the Fidelity of RANS-Based Turbulence Models in Modeling the Laminar Separation Bubble and Ice-Induced Separation Bubble at Low Reynolds Numbers on Unmanned Aerial Vehicle Airfoil

The operational regime of Unmanned Aerial Vehicles (UAVs) is distinguished by the dominance of laminar flow and the flow field is characterized by the appearance of Laminar Separation Bubbles (LSBs). Ice accretion on the leading side of the airfoil leads to the formation of an Ice-induced Separation Bubble (ISB). These separation bubbles have a considerable influence on the pressure, heat flux, and shear stress distribution on the surface of airfoils and can affect the prediction of aerodynamic coefficients. Therefore, it is necessary to capture these separation bubbles in the numerical simulations. Previous studies have shown that these bubbles can be modeled successfully using the Large Eddy Simulation (LES) and Direct Numerical Simulation (DNS) but are computationally costly. Also, for numerical modeling of ice accretion, the flow field needs to be recomputed at specific intervals, thus making LES and DNS unsuitable for ice accretion simulations. Thus, it is necessary to come up with a Reynolds-Averaged Navier–Stokes (RANS) equation-based model that can predict the LSBs and ISBs as accurately as possible. Numerical studies were performed to assess the fidelity of various RANS turbulence models in predicting LSBs and ISBs. The findings are compared with the experimental and LES data available in the literature. The structure of these bubbles is only studied from a pressure coefficient perspective, so an attempt is made in these studies to explain it using the skin friction coefficient distribution. The results indicate the importance of the use of transition-based models when dealing with low-Reynolds-number applications that involve LSB. ISB can be predicted by conventional RANS models but are subjected to high levels of uncertainty. Possible recommendations were made with respect to turbulence models when dealing with flows involving LSBs and ISBs, especially for ice accretion simulations.

Investigation of the resistance characteristics of the transverse groove for laminar flows

Transverse grooves are known to significantly affect drag reduction. However, additional investigation is required to understand the impact of groove geometry and flow velocity on resistance and flow characteristics. This study examines the impact of transverse grooves on laminar flow over a plate at various velocities. By conducting numerical simulations in three-dimensional domains, we analyze the evolution of resistance and flow characteristics over surfaces containing rectangular grooves perpendicular to the flow. The focus lies on understanding the interaction mechanisms between the evolution of the transverse groove resistance law and the flow characteristics of the external flow field of the groove. A detailed parametric study is conducted, considering a total of 32 groove size combinations, comprising 4 groove depths and 8 widths. The results demonstrate that transverse grooves in laminar flows can reduce total drag by up to 15.5% compared to a flat plate, while also causing a thousandfold increase in drag under specific operating conditions. These findings have practical implications for industries such as aerospace, automotive, and hydraulic systems to improve overall performance by reducing drag and enhancing fluid flow efficiency using transverse grooves in laminar flows.

Investigation of the Influence of Machining Parameters and Surface Roughness on the Wettability of the Al6082 Surfaces Produced with WEDM.

Electrical Discharge Machining (EDM) is a non-conventional machining technique, capable of processing any kind of conductive material. Recently, it has been successfully utilized for producing hydrophobic characteristics in inherently hydrophilic metallic materials. In this work, Wire Electrical Discharge Machining (WEDM) was utilized for producing hydrophobic characteristics on the surface of the aluminum alloy 6082, and various parameters that can affect wettability were investigated. Adopting an orthogonal Taguchi approach, the effects of the process parameter values of peak current, pulse-on time, and gap voltage on the contact angles of the machined surfaces were investigated. After machining, all samples were observed to have obtained hydrophobic properties, reaching contact angles up to 132°. The peak current was identified as the most influential parameter regarding the contact angle, while the gap voltage was the less influential parameter. A contact angle variation of 30° was observed throughout different combinations of machining parameters. Each combination of the machining parameters resulted in a distinct surface morphology. The samples with moderate roughness values (3.4 μm > Sa > 5.7 μm) were found to be more hydrophobic than the samples with high or low values, where the contact angle was measured under 115°. In addition, the finite element modeling of the experimental setup, with parametric surfaces of uniform random and Perlin noise types of roughness, was implemented. Time dependent simulations coupling phase field and laminar flow for the modelingof the wetting of surfaces with different surface roughness characteristics showed that an increase in the Sa roughness and total wetted area can lead to an increase in the contact angle. The combination of experimental and computational results suggests that the complexity of the wettability outcomes of aluminum alloy surfaces processed with WEDM lies in the interplay between variations of the surface chemical composition, roughness, micro/nano morphology, and the surface capability of forming a composite air/water interface.

Temperature uniformity analysis and multi-objective optimization of the microchannel heat sink with cavities under longitudinal vortex flow

With the development of electronic devices toward a more centralized direction, there is an urgent need to introduce new technologies in the microchannel heat sink to address thermal deformation or failure caused by uneven temperature distribution. Therefore, microchannels with longitudinal vortex generators (LVGs) and different shapes of cavity structures combination are designed innovatively to address this issue. The laminar flow solver solves for single-phase, steady, and fully developed liquid flows through microchannels in the inlet Reynolds number range of 168–793. Study finds that the longitudinal vortex flow not only mixes the fluid in the mainstream region but also effectively weakens the retention effect in the cavities. Among all microchannels, the microchannel with LVGs and triangular cavities combination (MC-LTC) shows the best performance. Subsequently, multi-objective optimization of the MC-LTC is carried out using Non-dominated Sorting Genetic II Algorithm with the pumping power (Pp) and the temperature uniformity factor (E) as objective functions, and the relative heights (α, β, γ) of the three pairs of LVGs as the three design variables. The optimal solutions set for Pp and E range from 0.706 mW to 1.018 mW and 0.547 to 0.716, respectively. Among the five selected Pareto optimal solution parameters, MC-LTC (α = 0.6001, β = 1.3528, γ = 1.3707) and MC-LTC (α = 0.6001, β = 1.0725, γ = 1.3017) show the best temperature uniformity performance.

A Sharp Version of the Benjamin and Lighthill Conjecture for Steady Waves with Vorticity

We give a complete proof of the classical Benjamin and Lighthill conjecture for arbitrary two-dimensional steady water waves with vorticity. We show that the flow force constant of an arbitrary smooth solution is bounded by the flow force constants for the corresponding conjugate laminar flows. We prove these inequalities without any assumptions on the geometry of the surface profile and put no restrictions on the wave amplitude. Furthermore, we give a complete description of all cases when the equalities can occur. In particular, that excludes the existence of one-sided bores and multi-hump solitary waves. Our conclusions are new already for Stokes waves with a constant vorticity, while the case of equalities is new even in the classical setting of irrotational waves.

Process intensification in flow chemistry using micro and millidevices: Numerical simulations of the syntheses of three different intermediate API compounds for diabetes mellitus drug production

Microreactor Technology (MRT) appears as an interesting alternative for process intensification, including the development of continuous synthesis of fine chemicals and Active Pharmaceutical Ingredients (API). The inherent proposal of MRT is to reduce the scale-up time by simply increasing the number of microreactors in parallel, the numbering-up concept using optimal designed micro or millidevices. Among the API, rosiglitazone and lobeglitazone are derivatives of thiazolidine-2,4-dione (TZD), which is used as a building block, for molecules with biological activity, sensitive to insulin and, thus, with its administration the body makes better use of the insulin it produces, being an important structural element in medicinal chemistry, especially for type 2 diabetes mellitus, one of the biggest concerns in the health area worldwide, affecting nowadays more than 180 million people. The numerical assessment of MRT for various API synthesis related to type 2 diabetes mellitus drugs indicates its comparable or superior performance compared to traditional batch process. Specifically, proposed micromixer designs facilitate successful scale-up to milliscale while maintaining microscale performance, with significantly lower pressure drops than commercial Asia microreactors. The proposed flow distributors offer good performance in ensuring uniform distribution across outlets due to their conical shape design and laminar flow regime, with low pressure drops. The flow distributor with eights outlet is preferred for higher flow rates due to its superior performance, minimizing the pressure drops. Efficient flow rate and molar concentration control at each reactor unit can be ensured by using one distributor for each reactant's feed stream. This approach guarantees accurate concentration, flow rate control and ideal residence time, ultimately facilitating higher total throughput for scale-up. The potential use of micromixer actuators lies in its ability to maintain or enhance performance while transitioning from micro to milli-scale, offering promising alternatives for process intensification and scale-up in pharmaceutical synthesis, particularly for medications targeting type 2 diabetes mellitus.

Rock Breaking Mechanism and Process Optimisation of Jet Cutting Basic Roof Rock under Submerged Jet Condition

The destruction of rock under the condition of a close submerged jet has become a hot topic of scientific research and engineering application in the past decade. With the unremitting efforts of a large number of experts and scholars around the world, gratifying progress has been made in the research of computational fluid dynamics (CFD) on the internal and external flow fields of the jet nozzle, the theoretical derivation of rock mechanics on the fracture initiation and propagation criteria of hydraulic fracturing, and the numerical simulation of jet erosion mechanism under the coupling of fluid and solid fields, however, for the rock mechanics hydraulic fracturing cutting engineering scale of non-oil drilling fracturing technology, the research on the fluid-solid coupling boundary conditions of fracturing fluid and hard dense rock under the flow state conditions of the submerged field inside and outside the borehole is not sufficient. In the calculation of the fluid-solid coupling boundary flow field under the non-submerged jet state, the control equation with Reynolds number between 2300-4000 shall be selected, while it belongs to the laminar flow state in the stage of hole sealing and pressurised fracturing. Therefore, Von-Mises equivalent plastic stress is selected in the mechanical model to calibrate the failure state of the rock-solid boundary, and the control equations of laminar flow and turbulent flow are selected to calibrate the fluid boundary. The mechanism of different stages of rock breaking by hydraulic fracturing jet can be further analysed in detail, and Comsol 6.0 multi-physical field simulation software is selected for verification. The research results will help deepen the understanding of rock breaking mechanism by jet and optimise the selection of parameters for field construction.

A pressure-loss model for flow-through round-hole perforated plates of moderate porosity and thickness in laminar and turbulent flow regimes

In this paper, we proposed a novel fluid flow model for pressure loss through plates with circular perforations in both laminar and turbulent flows. The design of this model is based on the recent measurements conducted at ONERA in the framework of the ongoing European Union H2020 INVENTOR project, as well as an existing model for laminar flows. The new model is then validated against existing numerical simulations in the laminar regime and experiments in the turbulent regime. Overall, the predictions given by the new model agree well with the numerical simulations and experiments, and are superior to other models in the literature. This is significant, considering that the present model is much simpler than these previous models. To demonstrate the applicability of the new model in numerical simulations, two-dimensional channel flows are simulated using Reynolds-averaged Navier–Stokes (RANS) equations with the new model as a pressure-drop source term added to the momentum equations. Results show that the RANS predictions agree very well with the present model predictions.

Dynamic Performance of Liquid Smooth Annular Seal Operating in the Transition Regime

Abstract This paper presents the experimental leakage and rotordynamic performance for a liquid smooth annular seal operating in the transition regime. The test conditions include pressure differentials up to 64 bars with 1∼2 bar increments for 6 rotor speeds (2.5, 3.8, 5, 7.5, 8.8, and 10 krpm), as well as nonrotating rotor case under zero preswirl condition. The rotordynamic coefficients for all the test conditions are obtained by pseudo-random excitation of the seal at multiple subsynchronous frequencies. By considering the transition Reynolds number (1000 < Re < 3000) and the Taylor Number (Ta) versus Axial Reynolds Number (Rez), the variations in the direct stiffness coefficients (K) can used as an indicator of the flow regime transition boundaries. The direct stiffness K resulting from the Lomakin and hydrodynamic effects significantly drops until Rez reaches ∼1500. For higher Rez, K increases mainly due to hydrodynamic effects. When K drops, the cross-coupled stiffness k, the direct damping C and the cross-coupled virtual mass m increase while the cross-coupled damping c and virtual mass M decrease. None of predictions based on either laminar or turbulent flow show the variations in rotordynamic coefficients obtained from experimental results. The leakage is not highly influenced by rotor speeds for low speed cases crossing laminar boundary as ΔP increases, however, results for higher speeds in the superlaminar region show reduced leakage rates as rotor speed increases.

Breaking the symmetry of a wavy channel alters the route to chaotic flow.

We numerically explore the two-dimensional, incompressible, isothermal flow through a wavy channel, with a focus on how the channel geometry affects the routes to chaos at Reynolds numbers between 150 and 1000. We find that (i) the period-doubling route arises in a symmetric channel, (ii) the Ruelle-Takens-Newhouse route arises in an asymmetric channel, and (iii) the type-II intermittency route arises in both asymmetric and semiwavy channels. We also find that the flow through the semiwavy channel evolves from a quasiperiodic torus to an unstable invariant set (chaotic saddle), before eventually settling on a period-1 limit-cycle attractor. This study reveals that laminar channel flow at elevated Reynolds numbers can exhibit a variety of nonlinear dynamics. Specifically, it highlights how breaking the symmetry of a wavy channel can not only influence the critical Reynolds number at which chaos emerges, but also diversify the types of bifurcation encountered en route to chaos itself.

A data–driven sensibility tool for flow control based on resolvent analysis

This study presents a novel application of data-driven resolvent analysis algorithm for flow control. The objective is to identify key coherent structures connected to regions of the flow that are highly sensitive to structural changes. Modifying such regions, i.e., including momentum source terms, flow stabilizers, or changing the shape of the body under study, we can control the appearance of flow instabilities. The method is tested in two different applications: the laminar flow behind a two-dimensional circular cylinder and a turbulent channel flow including heat transfer to the endwall. In the first test case, the flow unsteadiness is controlled by including two stabilizers (formed by two small cylinders) in the areas suggested by resolvent analysis. This is a benchmark problem in fluid dynamics that serves to validate the idea of using this tool for flow control. In the second test case, data-driven resolvent analysis is applied as a mean to control, enhance or reduce, convective heat transfer. Modifications in the geometry, in the form of cavities and ribs included in the areas pointed by resolvent analysis, show the possibility of enhancing heat transfer while reducing drag. The findings highlight the importance of resolvent analysis in understanding flow dynamics and designing effective flow control strategies.

Oxygenation heterogeneity facilitates spatiotemporal flow pattern visualization inside human blood vessels using photoacoustic computed tomography

Hemodynamics can be explored through various biomedical imaging techniques. However, observing transient spatiotemporal variations in the saturation of oxygen (sO2) within human blood vessels proves challenging with conventional methods. In this study, we employed photoacoustic computed tomography (PACT) to reconstruct the evolving spatiotemporal patterns in a human vein. Through analysis of the multi-wavelength photoacoustic (PA) spectrum, we illustrated the dynamic distribution within blood vessels. Additionally, we computationally rendered the dynamic process of venous blood flowing into the major vein and entering a branching vessel. Notably, we successfully recovered, in real time, the parabolic wavefront profile of laminar flow inside a deep vein in vivo—a first-time achievement. While the study is preliminary, the demonstrated capability of dynamic sO2 imaging holds promise for new applications in biology and medicine.