Fluidic Research Articles

Fluidic Diode AICD Characteristic Curve Testing and Mathematical Modeling

In order to investigate an efficient water control method suitable for the bottom water occurring during the production process of horizontal wells in bottom water reservoirs, the characteristic curves of a Fluidic Diode AICD (Automatic Inflow Control Device) were tested, and a mathematical modeling method is proposed. First, the working principle of a Fluidic Diode AICD was analyzed; subsequently, a Fluidic Diode AICD test platform was designed and built independently, and pressure test experiments of the Fluidic Diode AICD under different flow conditions were carried out to obtain characteristic curves of the Fluidic Diode AICD. Finally, a mathematical model of the flow–pressure drop characteristic curves of the Fluidic Diode AICD was developed and applied to the simulation of water control production in horizontal wells in bottom water reservoirs. The results of the study showed that the Fluidic Diode AICD produces a more significant pressure drop under high water content conditions, and has a better oil and water stabilization function in production. In this study, the reservoir flow, annulus flow, AICD flow, and horizontal wellbore flow are considered, and an integrated coupling model for horizontal wells in bottom water reservoirs is established. This study provides a basis for using Fluidic Diode AICDs in horizontal wells in bottom water reservoirs.

Simulation of a confined and a free sweeping air jet impingement cooling from a fluidic oscillator

In this paper, the fluid flow behavior and cooling characteristics of a sweeping impingement jet were investigated. Also, the difference between free and confined impingement schemes was investigated. In addition, the conventional approach for the purpose of significantly reducing computational time by using a confined domain with a slip upper wall instead of an unconfined domain was evaluated. A 2D unsteady Reynolds averaged Navier-Stokes (URANS) simulation accompanied with the k-ω SST turbulence model is used in this study. The study has been conducted for a target wall with a constant heat flux of 3000 W/m2, jet-to-wall distance of 4, and a jet Reynolds number of 2500. The results show that the overall average cooling performance of the sweeping jet is better in the confined impingement scheme compared to that of the steady jet, while the steady jet is slightly better in the unconfined sweeping impingement scheme. Using a confined scheme with a slip upper wall does not reveal the complete thermal and flow behaviors, and the wall heat transfer distribution is very different from the unconfined domain.

Characterization of a novel fluidic friction-reduction tool used in extended-reach well considering periodic particle-laden jet

Fluidic oscillators (FOs) can be used as an efficient fluidic vibration tool to solve high friction problems in extended-reach wells. However, the complex mechanism of FOs makes the design challenging, and the dynamic erosion behavior inside FOs is still unclear. In this paper, new FOs are proposed and the working characteristics under the influence of periodic particle-laden jets are investigated. Firstly, the results reveal the working mechanism of new FOs, showing that the generation of pressure pulses is closely connected with periodic jet switching and the development of vortices. Secondly, the important performance parameters, i.e., pressure pulse and oscillation frequency, are extensively studied through numerical simulation and experimental verification. It is found that the performance can be optimized by adjusting the tool structure according to different engineering requirements. Finally, the oscillating solid-liquid two-phase flow inside FO is studied. It is demonstrated that the accumulation of particles leads to a significant reduction in performance. The results also reveal five locations that are susceptible to erosion and the erosion behavior of these locations are studied. It has been shown that the periodic jet causes fluctuations in the amount of erosion at the outlet and splitter. This research can provide valuable references for the design and optimization of vibration friction-reduction tools.

Relaxation Fluidic Oscillators: Design Parameters, New Operating Modes, and Characteristics of Their Internal and External Flows

AbstractFluidic oscillators are no-moving-part actuators that can be used to produce pulsating jets. The characteristics of these devices and of the flow fields they produce are of particular interest in the field of heat transfer, as pulsating impinging jets have been shown to improve heat transfer compared to steady jets. In this study, special focus is given to these characteristics as a preparation for a subsequent thermal study that will evaluate the performance of these pulsed jets against steady jets. The functioning of the device in response to different operating and design parameters is first considered. It was shown that a transition between different operating modes is possible, depending on both the inlet mass flowrate and the width of the feedback channel of the device. This was followed by a study of the velocity fields of the pulsed jets produced by the device. More specifically, attention is given to the developing characteristics and flow structures of the pulsating free jets of air which are then compared to equivalent steady jets. Finally, by taking advantage of the periodic aspect of the flow, the phase-averaged velocity field was reconstructed. Vortex dipoles were detected, tracked and their convection velocity computed from the same data and compared to a theoretical value from the literature. A proper orthogonal decomposition (POD) of the synchronized raw data was then performed to further highlight the presence of these vortex structures and other flow instabilities.

Optimal design of fluidic diode for valveless piezoelectric pump based on entropy production theory

Optimal design of fluidic diode for valveless piezoelectric pump based on entropy production theory

Scanning Ion Conductance Microscopy of Nafion-Modified Nanopores

Single nanopores in silicon nitride membranes are asymmetrically modified with Nafion and investigated with scanning ion conductance microscopy, where Nafion alters local ion concentrations at the nanopore. Effects of applied transmembrane potentials on local ion concentrations are examined, with the Nafion film providing a reservoir of cations in close proximity to the nanopore. Fluidic diodes based on ion concentration polarization are observed in the current-voltage response of the nanopore and in approach curves of SICM nanopipette in the vicinity of the nanopore. Experimental results are supported with finite element method simulations that detail ion depletion and enrichment of the nanopore/Nafion/nanopipette environment.

P29: Snore Vibro-acoustic Platelet Activation: A Thrombotic Risk Factor in Obstructive Sleep Apnea

Background: Obstructive sleep apnea (OSA) is a common disease state with prevalence in the U.S. of near 25%. of the population, characterized by snoring and apnea. Beyond intermittent hypoxemia, OSA imparts increased risk of myocardial infarction (MI) and stroke (CVA), both driven by thrombosis and thromboembolism. Central in thrombosis is platelet activation, traditionally felt to driven by biochemical agonists. We explored the possibility that mechanical vibration generated by OSA snore is also a driver of platelet activation. We hypothesized that OSA snore frequency components induce vibration capable of platelet activation. Here we characterized 1. the frequency content of OSA snore and 2. the effect of specific frequencies ranges on platelet activation, and 3. the optoacoustic vibration pattern generated by snore frequency components. Methods: Snore from OSA patients was recorded in a sleep lab. A snore emulator device (speaker platform) was constructed allowing exposure of human gel filtered platelets to snore via placement on a stage transmitting sound and associated vibration, at clinical sound intensity. Snore was analyzed as to sound frequency content. Gel filtered platelet were exposed to snore sound bandwidths (100 – 1000 Hz.) for 40 min (identical intensities) with activation assessed by thrombin generation (PAS assay). Snore vibration was characterized via assessment of optoacoustic fluid wave patterns generated. Results: OSA snore vibration led to definitive platelet activation. Notably, low frequency snore bandwidths induced greater degrees of activation than high frequency exposure - 53.26% activation at 300 hz vs. 13.44% at 900 hz. (Fig. 1a). Low frequency bandwidths induced noticeably greater fluid oscillation than high frequency bandwidth exposure. (Fig. 1b). Conclusion: OSA snore is capable of inducing vibrations which impart adequate mechanical energy to fluid to induce platelet activation. Within snore, specific frequency bandwidths, i.e. low frequencies, appear to be more activating than others. Correlating with platelet activation is detectable visual fluid disturbance which may be characterized via opto-acoustic patterns. Modulation of sound and vibration associated with OSA snore may offer opportunity as a means of limiting thrombotic consequences and adverse events associated with OSA.

Controlling fluidic oscillator flow dynamics by elastic structure vibration

In this study, we introduce a design of a feedback-type fluidic oscillator with elastic structures surrounding its feedback channel. By employing phase reduction theory, we extract the phase sensitivity function of the complex fluid–structure coupled system, which represents the system’s oscillatory characteristics. We show that the frequency of the oscillating flow inside the fluidic oscillator can be modulated by inducing synchronization with the weak periodic forcing from the elastic structure vibration. This design approach adds controllability to the fluidic oscillator, where conventionally, the intrinsic oscillatory characteristics of such device were highly determined by its geometry. The synchronization-induced control also changes the physical characteristics of the oscillatory fluid flow, which can be beneficial for practical applications, such as promoting better fluid mixing without changing the overall geometry of the device. Furthermore, by analyzing the phase sensitivity function, we demonstrate how the use of phase reduction theory gives good estimation of the synchronization condition with minimal number of experiments, allowing for a more efficient control design process. Finally, we show how an optimal control signal can be designed to reach the fastest time to synchronization.

Computational Analysis of Air/Mist Film Cooling Using a Sweeping Jet Fluidic Oscillator–Part I: Sweeping Air-Only Jet With Detailed Analysis of Vortex Dynamics

Abstract The sweeping jet can be a promising candidate in film cooling applications since it has a large lateral jet spreading which can be considered an advantage when compared to the regular steady jet film cooling. Fluidic oscillators can generate a sweeping jet without the need for any moving parts. In addition, they can be more conveniently manufactured by additive manufacturing techniques. This two-part paper presents a numerical study to investigate the application of using air/mist sweeping jets in film cooling for protecting turbine airfoils. Part I focuses on validating the computational mode by comparing the thermal-flow and heat transfer behavior between steady and sweeping air-only jets to ensure they are consistent with published information. Part II focuses on the mist behavior and its effect on heat transfer enhancement in the sweeping jet film cooling by adding micro-liquid droplets. An unsteady Reynolds-averaged Navier–Stokes (URANS) simulation accompanied by the k–ω shear stress transport (SST) turbulence model was used in this study. A comparison is made between steady and sweeping jets at two blowing ratios (BR = 1 and 2). The results show that the steady jet provided better film cooling performance along the centerline compared to that of the sweeping jet for both blowing ratios. However, the sweeping jet provided better and more uniform film cooling performance in the spanwise direction. Both jets experienced a significant jet-liftoff when the blowing ratio was 2. The entrainment was significant in the sweeping jet case for both blowing ratios. The sweeping jet caused an increase of 9.5% in total pressure losses compared to the steady jet. It was found that for the sweeping jet, a pair of counter-rotating vortices is inward-rushing toward the wall in the center rather than outward-rushing as in a typical steady jet film cooling flow field. A detailed analysis is presented to understand the instantaneous vortex dynamics of the sweeping jet that leads to the inward rotating counter-rotating vortex pair (CRVP) (i.e., reversed CRVP). The result shows that the pair of counter-rotating vortices is just a time-averaged image of a single vortex sweeping back and forth in the domain; it does not actually exist in real time.

Computational Analysis of Air/Mist Film Cooling Using A Sweeping Jet Fluidic Oscillator–Part II: Sweeping Mist Jets

Abstract An ongoing research effort has been conducted for years to investigate the feasibility of mixing the air with mist (micron-level water droplets) to enhance heat transfer. It becomes very interesting to investigate how these tiny droplets behave in conjunction with the periodic sweeping jets. Will they move synchronously with the fluid or asynchronously with a phase lag? How would the interaction between the droplets and the sweeping jets affect the film cooling effectiveness? To answer these questions, Part II of this paper specifically focuses on investigating the droplet dynamics and thermoflow behavior of droplet evaporation on film cooling effectiveness in a sweeping jet. An unsteady Reynolds Averaged Navier–Stokes simulation accompanied by the k–ω shear stress transport turbulence model is used in this study. The multiphase computational fluid dynamics model employs an Eulerian–Lagrangian approach. The Eulerian method is used for the continuous phase including air and water vapor and the Lagrangian method in terms of the discrete phase model is used to simulate the dispersed phase (e.g., liquid droplets) in a continuous phase (e.g., air). A mist ratio of 10% with a droplet size of 10 μm was used in this study. The results show that, for a blowing ratio of 1, using mist provides better film cooling performance with an average enhancement of 50–90% in comparison to that without mist. Using a mist ratio of 10% could save approximately 50% of the cooling air. It is observed that the liquid droplets mostly follow the main sweeping flow and its vortical structure and horseshoe vortices, but with a phase lag between the droplets and the main sweeping jet. This phase lag further enhances both temporal and spatial film cooling surface protection during the sweeping motion.

Thermographic Investigation on Fluid Oscillations and Transverse Interactions in a Fully Metallic Flat-Plate Pulsating Heat Pipe

The present investigation deals with the quantification of fluid oscillation frequencies in a metallic pulsating heat pipe tested at varying heat loads and orientations. The aim is to design a robust technique for the study of the inner fluid dynamics without adopting typical experimental solutions, such as direct fluid visualizations through transparent inserts. The studied device is made of copper, and it is partially filled with a water–ethanol mixture (20 wt.% of ethanol). Heat fluxes locally exchanged between the working fluid and the device walls are first assessed through the inverse heat conduction problem resolution approach by processing outer wall temperature distributions acquired by thermography. The estimated local heat transfer quantities are therefore processed to quantify the fluid oscillatory behavior in every device branch during the intermittent flow and full activation regimes, thus providing a deeper insight into the heat transfer modes. After dealing with a further validation of the inverse approach in terms of oscillation frequency restoration capability, the wall-to-fluid heat fluxes referred to each channel are processed by means of the wavelet method. Scalograms and power spectra of the considered signals are presented for a time-based analysis of the working fluid oscillations, as well as for the identification of dominant oscillation frequencies. Fluid motion is then quantified in terms of the continuity of fluid oscillations and activity of channels by applying a scalogram denoising technique named K-means clustering method. Moreover, a statistical reduction of the channel-wise dominant oscillation frequencies is performed to provide useful references for the interpretation of the overall oscillatory behavior. The link between oscillations and transverse interactions is finally investigated. The vertical bottom-heated mode exhibits stronger fluid oscillations with respect to the horizontal mode, with fluid oscillation frequencies ranging from 0.78 up to 1 Hz. Nonetheless, the fluid motion is more stable in terms of oscillation frequency between channels when the device operates in the horizontal orientation probably due to negligible buoyancy effects. Moreover, thermal interactions between adjacent channels are found to be stronger when the oscillatory behavior presents similar features from channel to channel in horizontal orientation. The proposed method for fluid oscillation analyses in fully metallic flat-plate pulsating heat pipes can be effectively adopted to other flat-plate layouts without any need for transparent windows, thus reducing the overall complexity of experimental set-ups and providing, at the same time, a good insight into the inner fluid dynamics.

Scalable Fluidic Matrix Circuits for Controlling Large Arrays of Individually Addressable Actuators

A fundamental challenge of pneumatically powered soft robotic devices is the scalability of fluidic control systems to address each actuated degree of freedom, as the required electromechanical valves are bulky and expensive. Previous solutions have compromised the reprogrammability and/or the bandwidth of the fluidic system. This article describes and models a fluidic subsystem, a fluidic matrix circuit (FMC), that enables the independent control of many () actuators using a limited number () of electromechanical valves. The fundamental unit, a fluidic logic module (FLM), generates a bidirectional pressure signal (vacuum or positive pressure) based on the state of the mass flow through it. Thus and array of pneumatic actuators can be addressed individually using an array of FLMs integrated into a matrix (i.e., an FMC), with electromechanical valves to switch the mass flow through each row and column of the matrix. The resulting refresh rates are an order of magnitude faster than previous approaches. This concept with a prototype FMC able to control 25 actuators using 10 electromechanical valves for applications including a fluidic shape display and a wearable haptic vest is demonstrated. This approach could enable more complex and sophisticated soft robotic devices with scalable control hardware.

On the diodicity enhancement of multistage Tesla valves

Tesla valve is a particular check valve that can be used as a fluidic diode, but has no moving parts, and shows promising applications in macro- and microfluidic systems. Fluidic diode indicates that the inflow direction of a Tesla valve affects the pressure drop, allowing fluid to pass easily in one direction while presenting higher resistance in the reverse direction. Although previous studies have shown that the diode performance of such valves can be significantly improved by placing a series of valve units in a compact cascade, the reason is still unclear. In this study, the effect of the internal flow, especially the inflow status of each valve unit, on the diode characteristics of a multistage Tesla valve is investigated numerically and experimentally. Through a proper mathematic treatment, we derived the limiting diodicity in terms of the number of units and demonstrated that the diodicity enhancement of a multistage Tesla valve with its number of units was mainly due to the distorted inflow from subsequent units. To further verify this hypothesis, we elongated the space between subsequent units and found as expected the diodicity declined. The results indicate that distorted inflow can enhance the diodicity of a Tesla valve.

Influence of Internal Structural Parameters on the Inner Flow and Outer Spray Characteristics for Feedback-Free Fluidic Oscillator

Feedback-free fluidic oscillators, relying on the interaction of jets to oscillate, have a wide range of operation frequencies and no moving parts, which is promising for future applications. In this paper, the sweep angle, oscillation frequency, and volume flow rate of the feedback-free fluidic oscillator with a cavity width of 4.6 mm were measured experimentally, and the sweeping mechanism was analyzed based on the internal flow simulation. The influence of the impact angle, cavity exit width, and shoulder radius on the internal flow and external spray characteristics was analyzed by the numerical method. The results show that the sweep angle and oscillation frequency are affected throughout the increase in impact angle from 80° to 120°. However, only when the SR is greater than 0.88 mm does the internal flow and spray state change significantly. The volume flow rate is mainly affected by the cavity exit width and increases linearly from 5.3 mL/s to 9.3 mL/s as the width increases from 0.45 mm to 0.85 mm. It can be surmised that the sweep angle is approximately linear with the distance between the hit point and the impact cavity centerline.

Designing with Iontronic Logic Gates─From a Single Polyelectrolyte Diode to an Integrated Ionic Circuit.

This article presents the implementation of on-chip iontronic circuits via small-scale integration of multiple ionic logic gates made of bipolar polyelectrolyte diodes. These ionic circuits are analogous to solid-state electronic circuits, with ions as the charge carriers instead of electrons/holes. We experimentally characterize the responses of a single fluidic diode made of a junction of oppositely charged polyelectrolytes (i.e., anion and cation exchange membranes), with a similar underlying mechanism as a solid-state p- and n-type junction. This served to carry out predesigned logical computations in various architectures by integrating multiple diode-based logic gates, where the electrical signal between the integrated gates was transmitted entirely through ions. The findings shed light on the limitations affecting the number of logic gates that can be integrated, the degradation of the electrical signal, their transient response, and the design rules that can improve the performance of iontronic circuits.

A Study on the Feasibility of Pre-compression in linear Compressors Using Fluid Diode

A Study on the Feasibility of Pre-compression in linear Compressors Using Fluid Diode

Numerical Modelling of Flow in Fluidic Oscillator

The systems with fluidic oscillators are intensively studied nowadays because the oscillatory flow can increase heat and mass transfer and decrease energy dissipation. Fluidic oscillators produce an active-type mixing enhancement but in a passive manner as they do not require any moving parts. They convert steady pressurized inlet flow to oscillatory or pulsatile flow at an outlet without the need for external power. In general, there are many types of fluidic oscillators, categorized by the underlying mechanism to create oscillatory output behaviour. The fluidic oscillator with the single feedback loop is analysed in this paper. A numerical simulation of oscillating flow is performed and two approaches for modelling flow, RANS, and LES are applied especially. The results of numerical simulation are compared with experimental measurement. The analysis is focused on pressure drop and oscillation frequency dependent on the inlet conditions. The energy spectrum of oscillating flow is analysed using discrete Fourier transform.

An Investigation of Bubble Motion in the Fluidic Oscillator

An Investigation of Bubble Motion in the Fluidic Oscillator

A comparison of oscillating sweeping jet and steady normal jet in cooling gas turbine leading edge: Numerical analysis

Impinging jets have emerged as a prominent cooling technology in the gas turbine industry. With the addition of fluidic oscillators as heat removal devices, steady-state impinging jets can be converted to sweeping impinging jets, presenting an opportunity to improve the heat transfer performance of current impinging jets by covering a larger cooling surface area on the leading edge of a gas turbine blade. Sweeping jets are self-oscillating devices that operate based on the Coanda effect, making them self-sustaining. In this study, the flow and heat transfer performance of an array of seven steady and sweeping impinging jets were investigated using the unsteady Reynolds-averaged Navier-Stokes turbulent SST k-ω model. The sweeping jet impingement improved the heat removal performance by cooling a larger surface area of the leading edge with a constant heat flux and by improving the overall time-averaged cooling effectiveness. Compared with the steady jet case, the sweeping jet case shows an improvement in heat transfer of 12.2%. Further, the use of fluidic oscillators (sweeping jets) produced a more uniform mass flow rate distribution from all jets compared with a simple jet.

Fluidic Oscillator with Active Phase Control

This paper demonstrates the closed-loop control of the frequency and phase of a fluidic oscillator using acoustic excitation. It is shown experimentally that the use of acoustic excitation modifies the passive feedback mechanism and slows down the jet switching process. Closed-loop control is employed to vary the oscillation frequency at a fixed flow rate and track a sinusoidal reference target without phase error, using measurements from a pitot probe in the device. The controller is demonstrated to be effective at rejecting disturbances, which is illustrated with both time and frequency domain data. The controller’s ability to track step changes to the reference signal phase is tested, and the closed-loop bandwidth is shown to be around 20% of the oscillation frequency, in close agreement with the theoretical prediction.