Fluidic Research Articles

Logic-enabled textiles

Textiles hold great promise as a soft yet durable material for building comfortable robotic wearables and assistive devices at low cost. Nevertheless, the development of smart wearables composed entirely of textiles has been hindered by the lack of a viable sheet-based logic architecture that can be implemented using conventional fabric materials and textile manufacturing processes. Here, we develop a fully textile platform for embedding pneumatic digital logic in wearable devices. Our logic-enabled textiles support combinational and sequential logic functions, onboard memory storage, user interaction, and direct interfacing with pneumatic actuators. In addition, they are designed to be lightweight, easily integrable into regular clothing, made using scalable fabrication techniques, and durable enough to withstand everyday use. We demonstrate a textile computer capable of input-driven digital logic for controlling untethered wearable robots that assist users with functional limitations. Our logic platform will facilitate the emergence of future wearables powered by embedded fluidic logic that fully leverage the innate advantages of their textile construction.

Computational 2D parameter study of suction and oscillatory blowing actuator with experimental validation

Fluidic oscillators and ejectors were combined to create an effective flow control device, proved effective but have not been optimized yet. In the current study, mostly steady RANS simulations were used to optimize 11 geometric parameters of a generic-simplified suction and oscillatory blowing actuator (SaOB). Selected unsteady simulations and experiments validated the numerical optimization procedure findings. In the parameter optimization process, multiple input and output parameters are chosen to identify the strongest correlations between them. Non- or weakly- correlated parameters are eliminated from further study and others are combined to obtain a reduced set of correlated parameters. It was found that the Throat ratio (ejector to oscillator) parameter predicts the Entrainment ratio, while the cross-flow pressure gradient ratio can predict the ability of the SaOB actuator to produce effective oscillation. The optimized device performs significantly better than the starting point device.While the approach is appealing, open questions remain concerning the comparison of 2D simulations and the actual 3D geometry and compressibility effects.

Simulation of flow structure and heat transfer of sweeping jet and film composite cooling on a flat plate

Numerical simulation was performed to investigate the heat transfer characteristics of sweeping jet and film cooling along with the representative flow characteristics on a flat plate. The SST k-ω turbulence model was employed for a fluidic oscillator with 20 cylindrical film holes at four different nozzle Reynolds numbers and four different inclination angles. Time-resolved flow field and time-averaged heat transfer analyses considering the thermal convection and conduction by the coupling of fluid and solid domains are presented. The results show that the total pressure loss coefficient of the sweeping jet is larger than that of the normal jet, especially when the nozzle Reynolds numbers are relatively higher. In all cases, the Nusselt number and overall cooling effectiveness monotonically increased with the increase in the nozzle Reynolds numbers and decrease in inclination angle. However, the Nusselt number distribution on the impinging surface is insensitive to the inclination angle of the film holes. Compared with the normal jet and film composite cooling, sweeping jet and film composite cooling (SJF) has a more spatially uniform heat removal rate, and the area-averaged Nusselt number and overall cooling effectiveness are higher. Therefore, the SJF is preferred to improve the utilization rate of the coolant and to make the distribution of the flat wall heat transfer more uniform. However, the impinging distance of the fluidic oscillator should be further optimized to improve the impingement cooling effectiveness and the total pressure loss coefficient.

To the Problem of Small Oscillations of a System of Two Viscoelastic Fluids Filling Immovable Vessel: Model Problem

In this paper, we study the scalar conjugation problem, which models the problem of small oscillations of two viscoelastic fluids filling a fixed vessel. An initial-boundary value problem is investigated and a theorem on its unique solvability on the positive semiaxis is proven with semigroup theory methods. The spectral problem that arises in this case for normal oscillations of the system is studied by the methods of the spectral theory of operator functions (operator pencils). The resulting operator pencil generalizes both the well-known Kreyn’s operator pencil (oscillations of a viscous fluid in an open vessel) and the pencil arising in the problem of small motions of a viscoelastic fluid in a partially filled vessel. An example of a two-dimensional problem allowing separation of variables is considered, all points of the essential spectrum and branches of eigenvalues are found. Based on this two-dimensional problem, a hypothesis on the structure of the essential spectrum in the scalar conjugation problem is formulated and a theorem on the multiple basis property of the system of root elements of the main operator pencil is proved.

Research on Method for Detecting Pipeline Blockages Based on Fluid Oscillation Theory

To address the problem of pipeline blockage detection, a mathematical model of pipeline blockage detection is established based on fluid oscillation theory. This paper proposes a governing equation of the water hammer of fluid motion in a pipeline with a blockage point, and The Dirac function is introduced for dimensionlessness and linearization. The amplitude of the harmonic of each component in different periods is expressed by a Fourier series. The blocking position can be determined by the ratio of the two-component harmonics, and the blocking magnitude can be determined by the blocking attenuation parameters of each component’s harmonics. The numerical simulation and experimental results show that the application of fluid oscillation theory to detect the location and magnitude of pipeline blockages is effective, and the accuracy of the detection method is verified, which lays a theoretical foundation for the application of the proposed method in engineering practice.

Drag reduction of a generic transport vehicle model using a fluidic oscillator

Base blowing is performed using a sweeping jet actuator centrally located at the base of a square-back Ahmed body. Drag reduction along with a significant effect in terms of wake RSB mode suppression is reported for such fluid injection. All three scales of fluidic actuation exhibit similar wake bistability suppression characteristics. RSB mode suppression is also corroborated through independent force measurements. For all scales of actuators, the optimal blowing coefficient Cqopt is found to scale with bleed-to-base area ratio as (Sj/S)3/4, whereas the blowing coefficient corresponding to the minimum magnitude of wake asymmetry scales as Cqopt(Sj/S)5/12. The small-scale actuator also presents a more energy-efficient base blowing in terms of the amount of drag reduction achieved per energy consumed.

The Effects of Compressibility on the Performance and Modal Structures of a Sweeping Jet Emitted from Various Scales of a Fluidic Oscillator

Investigations of fluidic oscillators, or sweeping jet actuators, have primarily been conducted within the incompressible flow regime, which limits the accuracy of estimating fluidic oscillator performance for compressible flows. The objective of this study was to evaluate the effects of gas compressibility on the performance of a fluidic oscillator. A commonly used fluidic oscillator geometry (the Bray geometry) was scaled to five different sizes, 3D printed, and tested over a range of air flow rates. High-speed Schlieren images captured the sweeping jet exiting the fluidic oscillators, and custom MATLAB algorithms were used to calculate the oscillation frequencies and angles. A spectral proper orthogonal decomposition (SPOD) method was used to identify and compare the mode structures within the flow fields. All the results were compared using dimensionless parameters to observe performance trends. The results showed that the oscillation frequencies were directly proportional to the flow rate, while the oscillation angles were inversely proportional to the flow rate, regardless of scale size. The angular velocities were not proportional to the flow rate or scale size and exhibited maxima within the evaluated ranges. For all scale sizes, the mode structures were symmetric across the centerlines of the fluidic oscillators and extended further beyond the fluidic oscillators at higher flow rates. These results enable the prediction of fluidic oscillator performance, which can significantly improve the design process for an application where a fluidic oscillator may be used, such as aerospace applications, power generation, heat exchangers, or medical devices.

Fluid Oscillations in a Vessel with Triangular Base

Fluid Oscillations in a Vessel with Triangular Base

Characterization of thermal behavior of a micro pulsating heat pipe by local heat transfer investigation

The thermal behavior of Pulsating Heat Pipes (PHPs), which is inherently time-dependent, could also significantly change from local position to local position. Hence, the evaluation of local heat flux distributions could lead to a better understanding of the fundamental governing mechanisms of PHPs, which are, so far, only partially understood. In fact, most of the studies regarding the working principles of PHPs have focused on analysing the heat transfer rate averaged over the evaporator and condenser areas, or on evaluating the overall thermal resistance of the system. A 7-turn micro-PHP with an inner diameter of 0.32 mm was charged with HFC-134a at filling ratio of 46% and tested in bottom heated mode. The external wall temperature distribution of the condenser was measured by a high-speed and high-resolution infrared camera. The local heat fluxes exchanged between the fluid and the PHP wall were estimated in the whole condenser by solving the inverse heat conduction problem with the temperature maps as input data. In order to study the PHP working regimes, the local heat transfer behavior was furthermore investigated in terms of characteristic frequencies of the oscillatory flow by means of the wavelet method, coupled with a statistical approach. At low heat input the variations over time and along space of axial coordinate in the heat flux were significant and each tube showed multiple peaks in the power spectrum. On the other hand, the variation weakened under the high heat input conditions and the dominant fluid oscillation frequency was found more clearly around 1.2 Hz. All the qualitative and quantitative pieces of data are comprehensively presented to give further information regarding the device behavior at different heat input.

Study on the slurry erosion wear of polycrystalline diamond compacts for application in fluidic oscillators

Fluidic oscillator made of tungsten carbide, the core component of the fluidic hammer, has a significantly reduced service life under the erosion wear of drilling fluids with solid particles. Polycrystalline diamond composite (PDC) has the potential to solve this issue due to its extremely high hardness and wear resistance benefits. However, few studies on the slurry erosion wear of PDC have been reported. In this paper, a modified slurry erosion experimental device based on submerged abrasive water jets was used to study the erosion resistance of four grades of PDCs with grain sizes of 2–3, 5, 10 and 25 μm respectively. The erosion surface of the damaged PDC was observed by scanning electron microscope (SEM) and the erosive mechanism of the PDC was analyzed. The experimental results showed that PDC had excellent slurry erosion resistance. The erosion rate of PDC was 1/192–1/43 of that of tungsten carbide when the jet velocity was 100 m/s. The erosion rates of PDC increased with the rise of jet velocity, impact angle and erodent particle size. In addition, the erosion performance of debris represented by quartz to PDC is greater than that of weighting agents represented by barite and hematite. Further research also showed that PDC with fine grain has greater erosion resistance than PDC with coarse grain, except PDC2 ~ 3. At a high impact angle, the erosive mechanism was forming the craters due to the crushing of diamond grains and the pits due to the overall pullout of diamond grains, while at a low impact angle, the erosive mechanism was ploughing and forming directional craters.

A fluidic relaxation oscillator for reprogrammable sequential actuation in soft robots

A fluidic relaxation oscillator for reprogrammable sequential actuation in soft robots

A high‐throughput chaotic advection microreactor for preparation of uniform and aggregated barium sulfate nanoparticles

AbstractA high‐throughput (105.5 g/h) passive four‐stage asymmetric oscillating feedback microreactor using chaotic mixing mechanism was developed to prepare aggregated Barium sulfate (BaSO4) particles of high primary nanoparticle size uniformity. Three‐dimensional unsteady simulations showed that chaotic mixing could be induced by three unique secondary flows (i.e., vortex, recirculation, and oscillation), and the fluid oscillation mechanism was examined in detail. Simulations and Villermaux–Dushman experiments indicate that almost complete mixing down to molecular level can be achieved and the prepared BaSO4 nanoparticles were with narrow primary particle size distribution (PSD) having geometric standard deviation, σg, less than 1.43 when the total volumetric flow rate Qtotal was larger than 10 ml/min. By selecting Qtotal and reactant concentrations, average primary particle size can be controlled from 23 to 109 nm as determined by microscopy. An average size of 26 nm with narrow primary PSD (σg = 1.22) could be achieved at Qtotal of 160 ml/min.

Effect of control flow on main jet switching for single and double feedback channels fluidic oscillator

The fluidic down-the-hole (DTH) hammer controlled by the single feedback channel fluidic oscillator (SFO) has been to be effective in hard rock drilling. However, the unstable motion of the piston limits the performance of the fluidic DTH hammer in some cases. In this paper, a double feedback channels fluidic oscillator (DFO) is proposed to improve the smoothness of the piston motion, and the relationship between the control flow and main jet is observed through numerical simulation. The results show that the flow rate and symmetry of the control flow are the main factors affecting the switching of the main jet and the smoothness of the piston motion. The elevation of the flow rate of control flow shortens the switching time of the main jet. The symmetrical control flow of DFO is beneficial to the stable growth of the vortex and the wall attachment of the main jet. Compared with the SFO, the flow rate at the control nozzle of DFO is increased by 15.8%, and the switching time of the main jet is reduced by 25%. The bench test results show that the pause time is decreased by 61.4% and the impact frequency is raised by 38%.

Hybrid geometry trimming algorithm based on Integer Linear Programming for fluid flow topology optimization

In this work, a hybrid geometry trimming algorithm based on Topology Optimization of Binary Structures (TOBS) is proposed to design fluid flow devices with reduced seepage. The problem of solid reintroduction during optimization is solved by combining the geometry trimmed functional with the extended porous domain functional in a multi-objective function. The method is evaluated in the topology optimization of fixed-geometry fluidic diodes, which is a class of problems known to present difficulties related to high fluid penetration in the porous regions. Also, a new convergence criterion for TOBS is proposed to eliminate the necessity of selecting a convergence tolerance and to avoid running the optimization for cycles of the same designs. Fluidic diodes are designed for several Reynolds numbers (Re) to prove the effectiveness of the proposed formulation. The forward problem is solved by the Finite Element Method (FEM), and the sensitivities are calculated via automatic differentiation. The optimization problem is solved by Integer Linear Programming.

Numerical Simulation of the Flow and Heat Transfer Characteristics of Sweeping and Direct Jets on a Flat Plate with Film Holes

The internal heat transfer performance and flow structures of a sweeping jet and film composite cooling on a flat plate were numerically studied. Sweeping jet and film composite cooling consists of a fluidic oscillator and 20 cylindrical film holes; the direct jet is formed by removing the feedback from the fluidic oscillator, which is different from the traditional cylindrical nozzle. Four different mass flow rates of coolant were considered, and the inclination angle of the film hole was 30°. The Conjugate Heat Transfer method (CHT) and Unsteady Reynolds Averaged Navier Stokes equation (URANS) were employed. The results indicated that the flow resistance coefficients of the sweeping jet were larger than those of the direct jet, and the Nusselt number monotonously increased with the increase in the mass flow rate. Compared to the direct jet, the sweeping jet had a more spatially uniform heat removal rate, and the area-averaged Nusselt number was slightly lower. Therefore, the sweeping jet and film composite cooling caused the distribution of the flat plate heat transfer to be more uniform. It is worth noting that the novel direct jet nozzle in the present work had considerable area-averaged impingement cooling effectiveness.

Study of a piezoelectric energy harvester in the form of vortex oscillation for fixed disturbance fluid type.

The main purpose of this paper is to study a piezoelectric energy harvester in the form of vortex oscillation for fixed disturbance fluid type. The harvester consists of a fixed cylinder, an oscillating cylinder, flexible beams, and polyvinylidene fluorides (PVDFs). The flexible beam connects the fixed cylinder to the oscillating cylinder, and the PVDF is fixed to the flexible beam by means of adhesive, thus completing the assembly of the entire energy harvester. In this paper, the diameters of the fixed cylinder and oscillating cylinder and the length of the flexible beam are studied. In different parameter states, the harvester has different output performance; so the purpose of this study is to find a set of optimum parameters that will lead to the best harvester output. When the diameters of the fixed cylinder and oscillating cylinder are 50 and 20mm, respectively, and the length of the flexible beam is 60mm, the whole prototype has the best electrical output performance with 5.98 µW power at 18m/s. The whole prototype is sensitive to excitation at any wind speed and is able to convert and collect even weak streaming excitation energy from the environment. This structure offers greater reliability and durability than the disturbed fluid oscillation type piezoelectric harvester.

Anti-solvent crystallization: Particle size distribution with different devices

Particle size distribution (PSD) is one of the critical attributes of crystals. PSD not only influences downstream processes but also controls final product performance in crystallization. In this work, we have used the model system of methanol–water-paracetamol for carrying out anti-solvent crystallization to produce paracetamol crystals. With reference to a base case of anti-solvent crystallization in a stirred tank, we have used three devices connected to the stirred tank with an external loop with full recycling. A peristaltic pump was used to circulate the contents of the stirred tank in an external loop comprising a simple tube, a fluidic oscillator (FO), and a vortex diode (VD). Anti-solvent was introduced at a point lying between the pump and these three devices to understand the influence of these devices on mixing and potential particle breakage. The PSD of crystals obtained with these three devices are compared with that of the base case for one supersaturation ratio (SSR = 1.63). The results indicated the potential of manipulating the PSD of crystals with a strategy of using fluidic devices in an external loop. The overall arrangement can be potentially extended to continuous crystallization.

Connection Between Flow Structure and Separation Control for Various Fluidic Oscillator Spacings

The influence of actuator spacing on separation control using fluidic oscillators is experimentally investigated on a wall-mounted hump. Momentum inputs up to are tested at four different spacings (, 4.55, 6.82, and 9.09%), at and . For all spacings, the control authority is characterized by two distinct regimes associated with boundary-layer control and circulation control. The two narrow spacings show steep control authority gradients in the transition between boundary-layer control and circulation control. The time-averaged flowfields from spanwise stereoscopic particle image velocimetry (PIV) vary significantly between the presented spacings, but the circulation normalized by mass flow rate per jet remains constant for a given momentum input in the boundary-layer control regime. When the spacing is too small for a given oscillator design, the introduced vorticity is unorganized and actuation is less effective for a given momentum input. Once the flow is attached, the circulation reduces for larger momentum inputs (circulation control). This indicates a connection between increased control authority and decreased circulation in the circulation control regime. These findings are supported by novel circulation metrics that describe the level of organization in the flowfield.

Physiological Mechanisms and Significance of Intracranial B Waves.

ObjectiveRecently published studies have described slow spontaneous cerebral blood flow (CBF) and cerebrospinal fluid (CSF) oscillations measured by magnetic resonance imaging (MRI) as potential drivers of brain glymphatic flow, with a similar frequency as intracranial B-waves. Aiming to establish the relationship between these waveforms, we performed additional analysis of frequency and waveform parameters, of our previously published transcranial Doppler (TCD) and intracranial pressure (ICP) recordings of intracranial B waves, to compare to published MRI frequency measurements of CBF and CSF slow oscillations.Patients and MethodsWe analyzed digital recordings of B waves in 29 patients with head injury, including middle cerebral artery (MCA) flow velocity (FV), ICP, end tidal CO2, and arterial blood pressure (ABP). A subset of these recordings demonstrated high B wave activity and was further analyzed for parameters including frequency, interaction, and waveform distribution curve features. These measures were compared to published similar measurements of spontaneous CBF and CSF fluctuations evaluated using MRI.ResultsIn patients with at least 10% amplitude B wave activity, the MCA blood flow velocity oscillations comprising the B waves, had a maximum amplitude at 0.0245 Hz, and time derivative a maximum amplitude at 0.035 Hz. The frequency range of the B waves was between 0.6–2.3 cycles per min (0.011-0.038 Hz), which is in the same range as MRI measured CBF slow oscillations, reported in human volunteers. Waveform asymmetry in MCA velocity and ICP cycles during B waves, was also similar to published MRI measured CBF slow oscillations. Cross-correlation analysis showed equivalent time derivatives of FV vs. ICP in B waves, compared to MRI measured CBF slow oscillations vs. CSF flow fluctuations.ConclusionsThe TCD and ICP recordings of intracranial B waves show a similar frequency range as CBF and CSF flow oscillations measured using MRI, and share other unique morphological wave features. These findings strongly suggest a common physiological mechanism underlying the two classes of phenomena. The slow blood flow and volume oscillations causing intracranial B waves appear to be part of a cascade that may provide a significant driving force for compartmentalized CSF movement and facilitate glymphatic flow.

Flow Patterns of Self-Sustained Oscillations in Fluidic Diverters

A fluidic oscillator is a device capable of transforming a steady input flow into an oscillatory output using solely fluid dynamic principles and without requiring any moving components. Although the basic operation principles of fluidic oscillator are known to some extent, the unsteady and turbulent nature of its internal flow remains difficult to understand. The current study aims to further clarify the complicated flow physics involved in fluidic oscillators by investigating a device based on the fluid diverter principle. Spatiotemporally resolved velocity and pressure data obtained from a large-eddy simulation of the internal flow are decomposed into the proper orthogonal modes. The finite-time Lyapunov exponents are computed on the flowfield reconstructed using the proper orthogonal modes to perform a Lagrangian analysis of the switching mechanism. It is found that four dominant modes are sufficient to describe the jet switching. Strong coherent structures are found to separate the flow going through the oscillator from secondary flows through the feedback tube. The deflection of the jet inside the device is found to depend only on the pressure difference across the control ports, whereas the change of this pressure difference is mediated by the flows in the feedback tube.