Backward Flow Research Articles

Pressure drop non-linearities in material extrusion additive manufacturing: A novel approach for pressure monitoring and numerical modeling

Fused Filament Fabrication is an additive manufacturing technique in which molten thermoplastic polymers are extruded through a nozzle. Therefore, the interplay between the viscoelastic nature of the polymer melt, temperature, printing conditions and nozzle shape may lead to inconsistent extrusion. To improve the extrusion control and optimize the print-head performance, a better understanding of the flow process of the polymer melt both in the nozzle and the liquefier is needed. However, several challenges need to be overcome due to the complexity of gathering experimental data on the melt pressure in the nozzle and the lack of numerical models able to capture the full rheology of the molten polymer. This research introduces an innovative approach for monitoring the pressure within a material extrusion 3D printer’s nozzle. This method involves utilizing a pin in direct contact with the molten material, which then transmits the applied force from the material to an externally mounted load cell. The setup provides reliable, repeatable pressure data in steady-state conditions for two nozzle geometries and at different extrusion flows and temperatures. Moreover, the Giesekus model enabled capturing the viscoelastic rheometric features of the melt, and the numerical predictions have been compared with the experimental data. Results show that the numerical model accurately describes the flow conditions in the nozzle and allows the estimation of the behavior of the melt in the liquefier zone, the area of the print-head where the filament is molten. It could be concluded that the backflow, which is the backward flow of the molten polymer in the gap between the filament and the liquefier towards the cold end, caused significant non-linearities in the total pressure drop measured in the feeders, which were related to normal forces induced by shear in that region.

Thermo-fluid dynamics and morphology evolution of nickel-based superalloy in a multilayer laser directed energy deposition process

The complex thermo-fluid dynamics of the molten pool determine the dimension accuracy and mechanical properties of laser directed energy deposition (L-DED) components. In this work, a three-dimensional (3D) multiphase computational fluid dynamics (CFD) model based on the Volume of Fluid (VOF) method was proposed to establish the relationship between the thermo-fluid dynamics and the molten pool morphology evolution of René N5 nickel-based superalloy in L-DED. The single-track and ten-layer deposition processes under unidirectional and bidirectional scanning strategies were studied. Results show that the predicted deposition morphology and dimensions are in good agreement with the experimental samples. The heat accumulation in the multilayer deposition process increases the size of the molten pool, thereby increasing the width of the deposit. Different from the single-layer deposition driven by the Marangoni force, gravity is the key factor in the multilayer deposition process without the side support. The hump structure at the starting position under unidirectional scanning is attributed to the backward flow of the melt of the molten pool, while the decline structure at the end position is enhanced by the forward flow of the melt. At the starting position of each layer under bidirectional scanning, the expansion of the molten pool resulted from the heat accumulation and mass addition increases the width of the two ends and compensates for the deposition height. This work can provide a theoretical basis for understanding the uneven morphology characteristics and the dimensional accuracy control in L-DED.

Programming Anisotropic Functionality of 3D Microdenticles by Staggered-Overlapped and Multilayered Microarchitectures.

Natural sharkskin features staggered-overlapped and multilayered architectures of riblet-textured anisotropic microdenticles, exhibiting drag reduction and providing a flexible yet strong armor. However, the artificial fabrication of three-dimensional (3D) sharkskin with these unique functionalities and mechanical integrity is a challenge using conventional techniques. In this study, it is reported on the facile microfabrication of multilayered 3D sharkskin through the magnetic actuation of polymeric composites and subsequent chemical shape fixation by casting thin polymeric films. The fabricated hydrophobic sharkskin, with geometric symmetry breaking, achieves anisotropic drag reduction in frontal and backward flow directions against the riblet-textured microdenticles. For mechanical integrity, hard-on-soft multilayered mechanical properties are realized by coating the polymeric sharkskin with thin layers of zinc oxide and platinum, which have higher hardness and recovery behaviors than the polymer. This multilayered hard-on-soft sharkskin exhibits friction anisotropy, mechanical robustness, and structural recovery. Furthermore, coating the MXene nanosheets provides the fabricated sharkskin with a low electrical resistance of ≈5.3 Ω, which leads to high Joule heating (≈229.9°C at 2.75V). The proposed magnetomechanical actuation-assisted microfabrication strategy is expected to facilitate the development of devices requiring multifunctional microtextures.

Quantitative 4D flow MRI-derived thoracic aortic normal values of 2Dflow MRI parameters in healthy volunteers.

To utilize 4 D flow MRI to acquire normal values of "conventional 2 D flow MRI parameters" in healthy volunteers in order to replace multiple single 2 D flow measurements with a single 4 D flow acquisition. A kt-GRAPPA accelerated 4 D flow sequence was used. Flow volumes were assessed by forward (FFV), backward (BFV), and net flow volumes (NFV) [ml/heartbeat] and flow velocities by axial (VAX) and absolute velocity (VABS) [m/s] in 116 volunteers (58 females, 43 ± 13 years). The aortic regurgitant fraction (RF) was calculated. The sex-neutral mean FFV, BFV, NFV, and RF in the ascending aorta were 93.5 ± 14.8, 3.6 ± 2.8, 89.9 ± 0.6 ml/heartbeat, and 3.9 ± 2.9 %, respectively. Significantly higher values were seen in males regarding FFV, BFV, NFV and RF, but there was no sex dependency regarding VAX and VABS. The mean maximum VAX was lower (1.01 ± 0.31 m/s) than VABS (1.23 ± 0.35 m/s). We were able to determine normal ranges for all intended parameters. This study provides quantitative 4 D flow-derived thoracic aortic normal values of 2 D flow parameters in healthy volunteers. FFV, BFV, NFV, and VAX did not differ significantly from single 2 D flow acquisitions and could therefore replace time-consuming multiple single 2 D flow acquisitions. VABS should not be used interchangeably. · 4 D flow MRI can be used to replace 2 D flow MRI measurements.. · The parameter absolute velocities can be assessed by 4 Dflow MRI.. · There are sex-dependent differences regarding forward, backward, net aortic blood flow and the aortic valve regurgitant fraction..

FLUID CHARACTERISTICS AND POLISHING EXPERIMENT OF INCLINED HOLE ARRAY USING ABRASIVE WATER FLOW

Inclined hole arrays on superalloys have important applications in aeroengines. However, defects occur during fabrication of inclined holes using thermal drilling methods, i.e. electrical discharge drilling (EDD), including a recast layer and microcracks on the hole wall. Therefore, abrasive water flow polishing (AWFP) of a superalloy inclined hole array machined via EDD was investigated in this study. Two types of specimens were designed: a hole array of identical size and a hole array with an identical inclination angle. The fluid simulation revealed that the fluid velocity and pressure on the lower edge of the inclined hole were significantly higher than those on the upper edge when the fluid flowed forward. The fluid characteristics exhibited opposite trends when backward flow was implemented. Time-division bidirectional flow can effectively compensate for flow field nonuniformity and improve material removal consistency during polishing. The experimental results show that for inclined holes with identical inclination angles, the size expansion decreases with an increase in the hole diameter owing to the lower fluid velocity and material removal volume in the relatively larger holes. Consequently, surface roughness Ra increases with hole size. For inclined holes with identical diameters, the size expansions of the entrance and exit approach the same level; whereas, Ra decreased with an increase in the inclination angle. The hole taper slightly reduced in all cases. Using garnet abrasives with 1300 mesh size, 1.5 wt.% abrasive concentration, and 3 MPa fluid pressure, the surface roughness Ra of target holes was reduced from pre-polishing [Formula: see text] 5.0 [Formula: see text]m to approximately post-polishing 1.0 [Formula: see text]m. The recast layer on the hole wall caused by EDD was completely removed.

Research on internal flow field analysis and power loss modeling of the expansion seal ring

Expansion seal rings are widely used in automobile transmission systems, and their sealing performance plays a vital role in the pressure stability and transmission efficiency of the transmission system. However, investigations into revealing the internal flow mechanism of the expansion seal ring and predicting the power loss of the expansion seal ring are still insufficient. In this study, a two-way fluid–structure interaction model consisting of the shaft, oil sleeve, and expansion seal ring was established. The flow and structural physical fields under a series of operating conditions were simulated, and the effects of oil temperature, rotational speed, and seal pressure differential on leakage rate, deformation, power loss, and contact pressure were analyzed. Further, a power loss prediction model was developed by multiple linear regression method. The results demonstrate that in the internal flow field, the oil flow into and out of the groove is characterized by backward step flow and jet flow, respectively. In the structural field, the maximum deformation and the maximum contact pressure of the main sealing surface appear at the notch of the expansion seal ring, and the seal pressure differential has the most significant influence on it. The relative error between the predicted value of the developed model and experimental values is within 9%, which meets the industrial requirements. This work facilitates scholars to understand the internal flow mechanism and deformation process of expanding seal rings and provides a method to predict sealing ring power loss.

Convergence to closed-form distribution for the backward [formula omitted] at some random times and the phase transition at [formula omitted

We study a one-dimensional SDE that we obtain by performing a random time change of the backward Loewner dynamics in H. The stationary measure for this SDE has a closed-form expression. We show the convergence towards its stationary measure for this SDE, in the sense of random ergodic averages. The precise formula of the density of the stationary law gives a phase transition at the value κ=8 from integrability to non-integrability, that happens at the same value of κ as the change in behavior of the SLEκ trace from non-space filling to space-filling curve. Using convergence in total variation for the law of this diffusion towards stationarity, we identify families of random times on which the law of the arguments of points under the backward SLEκ flow converge to a closed form expression measure. For κ=4, this gives precise characterization for the random times on which the law of the arguments of points under the backward SLEκ flow converge to the uniform law.

An approach for integrating droplet generation and detection in digital polymerase chain reaction applications based on a bifunctional microfluidic cross-structure

Digital polymerase chain reaction (dPCR) is an approach for absolute nucleic acid quantification with high sensitivity. Although several successful commercial dPCR devices have been developed to date, further miniaturizing device dimensions, decreasing cross-contamination, and improving automation level are still research highlights. In this study, we developed a fully contamination-free dPCR detection chip with fluorescence flow cytometry and micro droplet approach. A bifunctional cross-structure (BFCS) was designed to realize monodisperse sample droplet generation in forward flow and droplet detection in backward flow with simple pneumatic control and fixed chip position. In order to improve droplet detection efficiency and accuracy, droplets morphology and sequence pattern during microfluidic droplet generation and backward flow droplet detection at the same cross-structure were observed and analyzed under different pneumatic pressures. In addition, during backward flow droplet detection, an optimized declination angle of the chip was applied to increase droplet reflux rates. For the validation of PCR performance, temperature changing processes during PCR cycles were achieved by heating the monodispersed droplet array with a customized PCR amplification device. The fluorescence signal of each droplet right after passing the cross-structure was excitated and detected. The absolute quantification ability of our integrated dPCR microfluidic chip utilizing flow fluorescence cytometry was tested and verified with Influenza A virus gene (from 7.5 copies/μL to 30000 copies/μL). Thus, our platform provides a novel and integrated approach for ddPCR analysis.

Evidence of tactile arm stepping in newborns and its responsiveness to optic flows specifying self-translation.

Although the arms participate in many forms of human locomotion, we know very little about when arm movements emerge during locomotor development. Here we investigated whether newborns would make tactile arm stepping movements when we supported them almost horizontally so their hands touched a surface and blocked their leg movements. Building off prior work showing that newborns make more crawling and air stepping leg movements when exposed to optic flows specifying forward and backward self-translation, we also examined whether newborns would make more tactile arm steps when exposed to forward and backward optic flows compared to a random optic flow that did not specify translation. We found that newborns can perform arm stepping and produce a significantly higher number of tactile arm steps in the optic flow condition specifying backward translation than in the random optic flow condition. Both translating optic flow conditions had significantly higher numbers of alternating arm steps than the random optic flow condition. These findings show that tactile arm stepping exists at birth and that optic flows can facilitate their production, similar to leg stepping. We argue that these results further support the idea that a quadrupedal organization underlies early upright stepping.

Numerical study on weld pool behaviors and keyhole dynamics in magnetic-field-assisted laser-arc hybrid welding of aluminum alloy

External magnetic field has been employed to improve appearance and suppress defects in the single laser or arc welding, and its physical mechanism in magnetic-field-assisted single laser or arc welding has been clearly clarified. However, few studies on the physical processes in magnetic-field-assisted laser-arc hybrid welding (MFA-LAHW) are conducted and its influencing mechanism is unclear. In this research, a comprehensive three-dimension numerical model is established to investigate the keyhole dynamics and weld pool behaviors in MFA-LAHW under the effect of different magnetic flux density. The results suggest that the interaction between a lower magnetic flux density (≤30 mT) and welding current is induced due to the existence of arc. Compared to the magnetic-field-assisted laser beam welding (MFA-LBW), this interaction induces a stronger Lorentz force up to the order of magnitude of 105 N/m3. The weld pool width is reduced while its length and height are increased because the Lorentz force facilitates the backward flow of thermal fluid, increasing the heat transfer from the keyhole and droplet to the rear weld pool edge. Moreover, the steady magnetic field improves the keyhole stability. The deform on keyhole rear wall brought by the droplet and vortex is suppressed, and keyhole size is widened under steady magnetic field, which reduced keyhole collapse. Furthermore, the comparative analysis with the case in MFA-LBW is carried out and the MFA-LAHW is verified to be more valuable for medium-thickness aluminum alloy. This work provides the underlying physics understanding of MFA-LAHW, which will broaden the application value of LAHW.

The Influence of Nucleus Mechanics in Modelling Adhesion-independent Cell Migration in Structured and Confined Environments

Recent biological experiments (Lämmermann et al. in Nature 453(7191):51–55, 2008; Reversat et al. in Nature 7813:582–585, 2020; Balzer et al. in ASEB J Off Publ Fed Am Soc Exp Biol 26(10):4045–4056, 2012) have shown that certain types of cells are able to move in structured and confined environments even without the activation of focal adhesion. Focusing on this particular phenomenon and based on previous works (Jankowiak et al. in Math Models Methods Appl Sci 30(03):513–537, 2020), we derive a novel two-dimensional mechanical model, which relies on the following physical ingredients: the asymmetrical renewal of the actin cortex supporting the membrane, resulting in a backward flow of material; the mechanical description of the nuclear membrane and the inner nuclear material; the microtubule network guiding nucleus location; the contact interactions between the cell and the external environment. The resulting fourth order system of partial differential equations is then solved numerically to conduct a study of the qualitative effects of the model parameters, mainly those governing the mechanical properties of the nucleus and the geometry of the confining structure. Coherently with biological observations, we find that cells characterized by a stiff nucleus are unable to migrate in channels that can be crossed by cells with a softer nucleus. Regarding the geometry, cell velocity and ability to migrate are influenced by the width of the channel and the wavelength of the external structure. Even though still preliminary, these results may be potentially useful in determining the physical limit of cell migration in confined environments and in designing scaffolds for tissue engineering.

Asymmetry of flow in aortic root and its application in hypertrophic obstructive cardiomyopathy.

The aortic root (AR) performs sophisticated functions regulating the blood dynamics during the cardiac cycle. Such complex function depends on the nature of flow in the AR. Here, we investigate the potential of new quantitative parameters of flow asymmetry that could have clinical implications. We developed a MATLAB program to study the AR hemodynamics in each sinus of Valsalva using two-dimensional (2-D) cardiac magnetic resonance imaging during systole and particularly at peak systolic flow in 13 healthy volunteers and compared with 10 patients with hypertrophic obstructive cardiomyopathy (HOCM). We show that the effective area of the aortic jet in healthy volunteers is significantly higher at peak systolic flow and on average during systole. The flow asymmetry index, indicating how the jet is skewed away from the left coronary sinus (LCS), is small in healthy volunteers and much larger in HOCM at peak systole. The average of this index over systole is significantly more different between cohorts. Looking in more detail at the flow in the sinuses during systole, we show that the AR jet in healthy volunteers is more symmetrical, affecting the three sinuses almost equally, unlike the asymmetric AR jet in patients with HOCM that has decreased flow rate in the LCS and increased fractional area of backward flow in the LCS. The percentage of backward flow in the sinuses of Valsalva calculated over systole is a potential indicator of perturbed AR hemodynamics and the distribution of vortical flow and could be used as a measure of flow asymmetry.NEW & NOTEWORTHY The aortic root is a vital organ responsible for performing sophisticated functions to regulate the blood flow dynamics during the cardiac cycle. Such synchronized complex performance affects and is affected by the flow symmetry and type of flow reaching the aorta. Here, we report flow asymmetry in the aortic root which could have clinical implications, and we investigate the potential of various quantitative parameters as measures of flow asymmetry in hypertrophic obstructive cardiomyopathy.

Enhancing the mixing characteristics of multi-hydrogen jets in scramjet engines through the implementation of fuel injection strategies and vortex generator positioning

Fuel injection strategies and vortex generators (VGs) play vital roles in effectively managing temperature distribution within the combustion chamber of scramjet engines. By optimizing the fuel injection mechanism and strategically positioning VGs, the efficiency of fuel/air mixing can be significantly improved. In this study, k-epsilon turbulence model used to accurately capture shock waves. The operating Mach number was maintained at 2.0 through the use of a pressure far-field inlet. The investigation focused on three different fuel injection mechanisms: backward-facing, transverse, and forward-facing, while also examining the mixing capabilities of VGs located at varying distances from the inlet. Detailed analysis was conducted to understand the impact of these factors. Backward flow injection was found to promote efficient mixing and reduce the risk of flame blowout. Furthermore, optimizing the injection location proved instrumental in enhancing fuel and air mixing efficiency, leading to higher Mach numbers and improved combustion efficiency. However, it is important to avoid excessively high Mach numbers as they can induce flame instability and blowout. Among the different injection methods, multiple port injection demonstrated the highest Mach numbers, while backward-facing injection yielded the lowest. Multiple port injection also achieved high static pressure. Introducing VGs into the system significantly increased static pressure, and optimal fuel injection and VGs location resulted in stable combustion, improved combustion efficiency, and minimized unburned fuel. The injection method and the presence of VGs greatly influenced turbulence kinetic energy. Notably, VGs located at distances of 81 mm and 31 mm from the inlet produced the highest turbulence intensity for forward-facing injection and transverse fuel injection, respectively.

Chitosan Nanoparticles for Gastroesophageal Reflux Disease Treatment.

Gastroesophageal Reflux Disease (GERD) is a chronic ailment that results from the backward flow of stomach acid into the esophagus, causing heartburn and acid regurgitation. This review explores nanotechnology as a novel treatment approach for GERD. Chitosan nanoparticles (CSNPs) offer several advantages, including biocompatibility, biodegradability, and targeted drug delivery capabilities. CSNPs have been extensively studied due to their ability to encapsulate and release medications in a controlled manner. Different nanoparticle (NP) delivery systems, including gels, microspheres, and coatings, have been developed to enhance drug retention, drug targeting, and controlled release in the esophagus. These nanoparticles can target specific molecular pathways associated with acid regulation, esophageal tissue protection, and inflammation modulation. However, the optimization of nanoparticle formulations faces challenges, including ensuring stability, scalability, and regulatory compliance. The future may see CSNPs combined with other treatments like proton pump inhibitors (PPIs) or mucosal protectants for a synergistic therapeutic approach. Thus, CSNPs provide exciting opportunities for novel GERD treatment strategies.

Sulfur-induced transitions of thermal behavior and flow dynamics in laser powder bed fusion of 316L powders

A three-dimensional (3D) powder-scale model is developed to analyze the melt pool dynamics in laser powder bed fusion (L-PBF) of 316L powders considering the transition of melt pool dynamics induced by sulfur element. In sulfur-free situation, thermal behavior and fluid flow are modeled involving 3D details. In sulfur-considered situation, sulfur-effect on melt pool dynamics is simulated with the surface tension described by the function of local temperature and the sulfur content. It is concluded that heat transfer is dominated by convection flow, and surface tension is the most important driving force. When the sulfur-effect is absent, surface tension increases from center to the periphery, inducing a centrally outward Marangoni convection. In the situation of 0.03% sulfur, surface tension first increases then decreases from center to the boundary, resulting in the novel flow pattern of combined outward-inward flow. Probing the underlying physical details induced by sulfur-effect, it makes melt pool dynamics more complex with more vortexes, and the sulfur-induced backward branch flow at the transverse view is benefit for the reduction of surface roughness. Furthermore, more vortexes, more branch flow, and more mixing positions of branch flow (MPBF) are observed in the sulfur-considered situation, which induces the increasing flow complexity, the drop of temperature gradient and driving force, as well as the decreasing flow intensity. Moreover, the variation of sulfur content leads to significant transitions of thermal behavior, driving force, and dynamic characteristics. Fundamental conclusions contribute significantly to the comprehensive understanding of the physical process in L-PBF of 316L powders.

Flat jet electrochemical milling of TC4 alloy with tailoring backward parallel flow

In flat jet electrochemical milling, the electrolyte forms a backward parallel flow after impacting the workpiece, resulting in a weak current density distribution on the workpiece. Poor surface quality usually occurs on the machined titanium alloy surface because it inevitably suffers from the weak current density. In this study, a method of flat jet electrochemical milling with tailoring the backward parallel flow was proposed to eliminate the negative effects caused by the weak current density. Multiphysics simulations are carried out to comprehend the mechanism of flat jet-EC milling with tailoring backward parallel flow and better construct the novel tool electrode. Experiments on flat jet electrochemical milling of TC4 alloy with and without tailoring backward parallel flow are conducted. The results reveal that, compared with flat jet electrochemical milling without tailoring backward parallel flow, the recommended tool reduces the surface roughness by 86% to 93%, and improves the material removal rate by 93% to 163% with different feed rates. Additionally, the recommended tool is more conducive to maintaining the inherent hardness of the material. Finally, a surface with low Sa of 0.37 μm is obtained.

Orthography-phonology consistency in English: Theory- and data-driven measures and their impact on auditory vs. visual word recognition.

Research on orthographic consistency in English words has selectively identified different sub-syllabic units in isolation (grapheme, onset, vowel, coda, rime), yet there is no comprehensive assessment of how these measures affect word identification when taken together. To study which aspects of consistency are more psychologically relevant, we investigated their independent and composite effects on human reading behavior using large-scale databases. Study 1 found effects on adults' naming responses of both feedforward consistency (orthography to phonology) and feedback consistency (phonology to orthography). Study 2 found feedback but no feedforward consistency effects on visual and auditory lexical decision tasks, with the best predictor being a composite measure of consistency across grapheme, rime, OVC, and word-initial letter-phoneme. In Study 3, we explicitly modeled the reading process with forward and backward flow in a bidirectionally connected neural network. The model captured latent dimensions of quasi-regular mapping that explain additional variance in human reading and spelling behavior, compared to the established measures. Together, the results suggest interactive activation between phonological and orthographic word representations. They also validate the role of computational analyses of language to better understand how print maps to sound, and what properties of natural language affect reading complexity.

Anomalously strong effects of plume contraction and material redeposition in nanosecond pulsed laser vaporization

Long-term dynamics of vapor plumes induced by irradiation of a copper target in argon background gas by nanosecond laser pulses is studied numerically based on a one-dimensional hybrid computational model. The model includes a thermal model of the irradiated target and a kinetic model of the gaseous plume flow. The latter is implemented in the form of the direct simulation Monte Carlo method. The simulations, performed at moderate laser fluences in the range from 1.5 to 4 Jcm−2 and background gas pressures between 0.01 and 1 bar, show that the long-term plume dynamics can be divided into three major stages: initial inertial expansion, plume contraction, and subsequent diffusive expansion. The simulations unexpectedly predict extremely strong effects of plume contraction, when the plume size can exhibit a two-fold reduction, and delayed material redeposition back to the irradiated surface, when ∼90% of vaporized material returns to the irradiated surface. Both plume contraction and delayed redeposition originate from the strong backward flow induced by the internal (secondary) shock wave that propagates from the mixing layer towards the irradiated surface. The major part of vaporized material condenses at the surface with a long time delay with respect to the laser pulse after the plume stopping and before the onset of diffusive expansion. As a result, only a marginal part of vapor, which can be as small as ∼5%, is retained in the plume by the beginning of the diffusive expansion. The obtained simulation results suggest that the plume contraction and delayed material redeposition are common phenomena for nanosecond laser vaporization and may affect the efficiency and quality of laser surface modification in the ablation regime as well.

Smoothed particle hydrodynamics with κ-ε closure for simulating wall-bounded turbulent flows at medium and high Reynolds numbers

In this study, an improved SPH (smoothed particle hydrodynamics) method coupling the κ-ε turbulence model and the wall function is proposed to simulate wall-bounded turbulent flows at medium and high Reynolds numbers. The second-order partial derivative term of the composite function containing the turbulent viscosity coefficient is decomposed into the sum of two terms, which helps SPH to avoid numerical errors and difficulties in dealing with boundary conditions in the nested approximation of first-order partial derivatives. Particle shifting technique, δ-SPH method, and graphics processing unit parallel technology are used in the simulations to ensure uniform particles, smooth pressure field, and high computational efficiency, respectively. The SPH method with the κ-ε turbulence model and the wall function is tested and validated by simulating four classical wall-bounded turbulent flows at medium and high Reynolds numbers, which are the turbulent flat plate boundary layer at Re = 4.2 × 106 and Re = 107, backward step separation flow at ReH = 3025, the flow around the airfoil at Re = 3 × 106, and the flow around the pitching airfoil at Re = 1.35 × 105, respectively. The simulation results are consistent with the references, validating the suitability of the current SPH method for simulating wall-bounded turbulent flows at medium and high Reynolds numbers. Finally, the airfoil motion combining the pitching and deforming at Re = 3 × 106 is investigated by the current SPH method. The results show that the deformation of the airfoil's relative thickness affects the lift coefficients of the pitching airfoil. Furthermore, the increase in the relative thickness increment reduces the amplitude of the lift coefficient, while the increase in the deformation period has little effect on the amplitude of the lift coefficient.

3D passive microfluidic valves in silicon and glass using grayscale lithography and reactive ion etching transfer

A fabrication strategy for high-efficiency passive three-dimensional microfluidic valves with no mechanical parts fabricated in silicon and glass substrates is presented. 3D diffuser-nozzle valve structures were produced and characterized in their added value in comparison to conventional diffuser-nozzle valve designs with rectangular cross sections. A grayscale lithography approach for 3D photoresist structuring combined with a proportional transfer by reactive ion etching allowed to transfer 3D resist valve designs with high precision into the targeted substrate material. The efficiency with respect to the rectification characteristics or so-called diodicity of the studied valve designs is defined as the ratio of the pressure drops in backward and forward flow directions. The studied valve designs were characterized experimentally as well as numerically based on finite element simulations with overall matching results that demonstrate a significantly improved flow rectification of the 3D valves compared to the corresponding conventional structure. Our novel 3D valve structures show, for instance, even without systematic optimization a measured diodicity of up to 1.5 at low flow rates of only about 10 μl/s.