Pulsating Flow Research Articles

A simulation on field distribution and particle capture characteristics in a multi-wire PHGMS system

ABSTRACT In the development history of high gradient magnetic separation (HGMS), the introduction of pulsating flow was extremely important, it successfully solved the problem of matrix clogging and allowed continuous and stable operation in the industry. However, the current pulsating HGMS (PHGMS) theory remains inadequately understood. In this paper, a 2D simulation model was established in COMSOL Multiphysics to reveal the magnetic field characteristics, flow field distribution, and particle capture dynamics in a PHGMS system. Quantitative comparisons were carried out between single-wire and multi-wire systems in the presence and absence of pulsation flow. The simulation results indicated that due to the coupled effect of neighboring magnetic wires in matrix, the magnetic field strength around an individual magnetic wire would slightly drop while the flow field velocity would increase. The introduction of pulsating flow could increase the peak value of fluid velocity and give particles a chance to move up and down. The analysis of particles travels length and capture probability indicated that the recovery for fine particles might be improved by increasing the strength of pulsating flow. This study provided a novel strategy for the highly efficient recovery of fine, weakly magnetic materials.

Advanced design strategies and applications for enhanced higher-order multisegment denatured Pascal curve gears

The existing Pascal curve gears are limited by inflexible pitch curves and constrained transmission ratio changes, which hinders the application in a range of mechanical systems that require more adaptable gear solutions. To address this, a design procedure for higher-order multisegment denatured Pascal curve gear is proposed. A unified mathematical expression for the Pascal curve gear family is derived, enabling the construction of non-circular gears with free-form pitch curves by adjusting key parameters and offering more flexible pitch curve and a wider range of transmission ratios. Compared with elliptical gears and eccentric circular gears, its transmission ratio range can be expanded by up to 35%. Then the transmission characteristics of these gears are analyzed in detail. To validate the design, the visual analysis and design software of the gear is compiled based on Visual Basic, and is verified with the example. The novelty Pascal curve gears is applied to drive the differential velocity vane pump. The displacement, instantaneous flow rate, and pulsation rate of the differential velocity vane pump are calculated. The comparison with the differential pumps driven by eccentric non-circular gears and Fourier non-circular gears shows that when the pitch curves are not concave, the displacement driven by Pascal curve circular gears is the highest (compared to differential pumps driven by eccentric non-circular gears, and Fourier non-circular gears, their flow rates increased by 50.6%, and 175.7%, respectively), and the instantaneous flow pulsation rate of single pump is the smallest.This study shows that the higher-order multisegment denatured Pascal curve gear provides a viable solution for systems requiring flexible transmission mechanisms and improved operational performance.

Study of High-Frequency Pulsating Flow Control Valves

Pulsating flow signals are widely used in the fields of dynamic calibration of flow meters and reliability testing of fluid transmission pipelines. A high-frequency pulsating flow control valve is proposed, its structure and working principle are introduced, and its mathematical model is also established. Finally, an experimental platform is built to experimentally verify the performance of the high-frequency pulsating flow signal generation of this flow control valve prototype. When applying sinusoidal flow signals of 1–25 Hz, the amplitude of the output flow starts to decay after 2 Hz, and the frequency corresponding to the decay to −3 dB is about 23.5 Hz. The experimental results show that the valve can effectively generate unidirectional sinusoidal flow with a maximum amplitude of 25 L/min and a frequency of 23.5 Hz.

Impact of density ratio on droplet dynamics in pulsating flow

Secondary atomization is extensively studied by investigating a droplet subjected to a steady air/gas stream. However, droplets are often subjected to unsteady or pulsating flows, such as in aero-engines or rockets, because of thermo-acoustic instabilities in the combustion chambers. The investigation focuses on the droplet dynamics and breakup in a pulsating flow for a range of density ratios (ρr), 1000 to 10, under sinusoidal airflow of different amplitudes and frequencies as compared to the dynamics in a steady flow. The volume of fluid multiphase model tracks the liquid–gas interface, and the governing equations are solved using the finite volume method. The two-dimensional axisymmetric pulsating simulations demonstrate accuracy comparable to the corresponding three-dimensional simulations at a much lower computational cost and are used for parametric studies. The droplets under the pulsating flow show a wavy surface, and larger vortex structures are observed during the deceleration period. At a high-density ratio (1000), pulsating flow enhances droplet deformation for a faster breakup, with the flow amplitude having more impact than its frequency. For a medium-density ratio (100), where breakup occurs under steady flow, droplet breakup is inhibited in the pulsating flow at low amplitude and high frequency. In the case of a low-density ratio (10), there is no breakup under steady flow, but pulsating flow promotes breakup, except at low amplitude and high frequency. The droplet breakup is always achieved for the highest amplitude, while lower frequencies push the liquid mass from the center of the droplet to the rim.

Piezoelectric energy harvests by the usage of a laminar pulsating flow circulating in a rectangular channel

Abstract This work develops a theoretical study of a piezoelectric energy harvester, perturbed through a fully developed laminar flow with an oscillating pressure gradient. Considering a fully developed hydrodynamic flow, the electric energy generated in the piezoelectric element is due only to shear stresses yielded at the inner surfaces of the channel. In this manner, a fraction of the viscous forces is converted into unitary deformations at the piezoelectric, and the other fraction is transformed to induced electric piezoelectric energy.
Using dimensionless analysis, the formulation of resulting dimensionless governing equations for the fluid and the corresponding deformation and electric potential fields for the piezoelectric material constitute a conjugate problem, solved by considering harmonic solutions. Although the dimensionless power output is a multi-parametric function, due to the large number of dimensionless parameters involved, we find that
the main behavior of the electrical power depends very sensitively on two fundamental dimensionless parameters: the Womersley number, α, associated with the oscillating flow and a parameter that measures the physical importance of the electrical energy produced by the action of the velocity field. For the first case, it is seen that the power increases if the Womersley number is decreased while for the second case, the inverse behavior is predicted. Therefore, there is a clear operation of the physical system for which better conditions can be reached by selecting and varying appropriately the assumed values of different dimensionless parameters.

Nonlinear deterministic dynamic analysis of a GPL micropipe conveying pulsating laminar flow

In several industries, the handling of fluid-filled micropipes is common. New-brand structures are increasingly being manufactured using advanced materials. This article tackles one of the crucial dynamic analyses that an advanced fluid-filled micropipe encounters. The dynamics of a graphene nanoplatelets-reinforced micropipe (GPL micropipe) under pulsating laminar flow for the first time is examined. The Euler-Bernoulli beam model follows the modified couple stress theory (MCST) and von-Karman’s nonlinear strain to formulate the problem. The impression of the flow profile exerted by a real flow as a consequence of fluid viscosity, is taken into account. The plug flow model results are compared to those regarding real flow consideration. Using the method of multiple scales (MMS), we determine the instability area and the steady state response of the GPL micropipe subjected to the principal parametric resonance of one of its modes due to pulsating laminar flow by applying this method to the discretized couple nonlinear gyroscopic governing equations. The Floquet theory treats the linear equations and fourth-order Runge–Kutta (RK4) method attacks nonlinear ones to validate MMS findings. It is confirmed that the 0.3 % addition of the GPL to matrix phase significantly enhances its advanced attributes, making it a highly effective material. The GPL reinforcement phase in the FGO pattern increases the critical flow velocity that exhibits the micropipe to static instability by 37.98 % , and critical flow stimulation amplitude fraction by 152.19 % , while declines instability area bandwidth by 36.95 % , and steady state response by 67.17 % relative to a non-reinforced micropipe. A denser flow degrades the corresponding values by 18.40 % , 42.59 % , 41.67 % , and 227.28 % in comparison to a lighter fluid. The declared findings provide crucial insights into the key design elements affecting significantly the functioning of fluid-filled GPL micropipes system, and regulate future research and expand openings for industry applications.

How Irregular Geometry and Flow Waveform Affect Pulsating Arterial Mass Transfer.

Alzheimer's disease is a progressive degenerative condition that has various levels of effect on one's memory. It is thought to be caused by a buildup of protein in small fluid-filled spaces in the brain called perivascular spaces (PVS). The PVS often takes on the form of an annular region around arteries and is used as a protein-clearing system for the brain. To analyze the modes of mass transfer in the PVS, a digitized scan of a mouse brain PVS segment was meshed and used for computational fluid dynamics (CFD) studies. Tandem analyses were then carried out and compared between the mouse PVS section and a cylinder with commensurate dimensionless parameters and hydraulic resistance. The geometry pair was used to first validate the CFD model and then assess mass transfer in various advection states: no-flow, constant flow, sinusoidal flow, sinusoidal flow with zero net solvent flux, and an anatomically correct asymmetrical periodic flow. Two mass transfer situations were considered, one being a protein build-up and the other being a protein blend-down using a multitude of metrics. Bulk arterial solute transport was found to be advection-controlled. The consideration of temporal evolution and trajectories of contiguous protein bolus volumes revealed that flow pulsation was beneficial at bolus break-up and that additional local wall curvature-based geometry irregularities also were. Using certain measures, local solute peak concentration blend-down appeared to be diffusion-dominated even for high Peclet numbers; however, bolus size evolution analyses showed definite advection support.

Numerical study and mechanism analysis of heat transfer in a helical tube enhanced by sinusoidal pulsating flow combined with an annular corrugated structure

Numerical study and mechanism analysis of heat transfer in a helical tube enhanced by sinusoidal pulsating flow combined with an annular corrugated structure

Influence of deflector on the internal flow characteristics and pulsation characteristics of the roots-type hydrogen circulation pump

The internal flow instability and high pulsation characteristics in the Roots-type hydrogen circulation pump (RHCP) are the main causes of its aerodynamic noise. This study proposes two mathematical models of new deflectors combined in the static domain to improve flow stability and reduce gas pulsations. Meanwhile, this study also compares the simulation results of different cases with a combination of different deflectors and then chooses the best performance case to research with the original model. Results found that placing the V-shaped deflector at the inlet of the rotor domain effectively reduces pressure pulsations in the RHCP at low rotary speeds. The pressure pulsation index at the inlet of the rotor domain decreased by about 26% compared to the original modal, and the outlet pressure pulsation index decreased by about 10%. Additionally, at low rotary speed, the V-shaped deflector significantly reduces the impact of radial clearance leakage flow on the flow characteristics inside the suction chamber, which improves the gas flow characteristics in the suction chamber. These research findings provide new ideas and methods for designing and manufacturing RHCPs.

Thermal performance of a novel hybrid heat pipe with composite heat transfer characteristics

Considering the capillary threshold of oscillating heat pipes (OHP), a novel hybrid heat pipe (HHP) was designed with channels with hydraulic diameters that alternately exceed and fall below this threshold, parallelly arrayed within a unified copper substrate. This technology attains a comprehensive heat transfer performance within the HHP, seamlessly transitioning from pure phase change heat transfer to hybrid pulsating flow heat transfer to effectively accommodate the escalating demands of heat load. Performance and visualization are used to analyze the operational characteristics of HHP. The results indicate that the HHP mainly transfers heat through the phase change in the large channels in lower heat input, while the working fluid in the small channels remains calm. Once the heat input is sufficient, the geyser boiling in the large channels and the liquid slug pulsating in the small channels jointly carry out heat transfer. Furthermore, the liquid content in the large and small channels can be adaptively adjusted to each other. The high-speed liquid in the small channels can be squeezed into the large channels to ensure the sufficient pulsating space and achieve efficient heat transfer under high heat input. In addition, the operation of the HHP can be significantly impacted by the filling ratio (FR). In the phase change stage, the FR of 47.6 % can be considered as the turning point. After transitioning to the hybrid pulsating flow stage, the HHP with low FR can get a better performance. This new type of heat pipe with gradually changing operation characteristics may be critical to solve thermal problems in variable heat load domain.

Numerical simulation of thermal enhancement in pulsating inflow grooved channel based on hydrodynamic instability

In this paper, a numerical simulation study of flow and heat transfer in a grooved channel consisting of ten rectangular grooves with steady and pulsating flow is carried out. Numerical simulations of the steady flow with small perturbations applied at Re = 800, 1200, 1600, and 2000 show that the same intrinsic frequency fN exists at different positions, amplitudes, and durations, and it disappears gradually with the development of the flow. A sinusoidal pulsating flow with different frequencies is applied to the grooved channel with the dimensionless amplitude A fixed at 0.2. The flow and heat transfer properties of the grooved channel are investigated in the case of pulsating inflow, and it is found that there exists a vortex periodic formation–development–convergence–dissipation process inside each groove. The results show that the increase in the time-averaged Nusselt number is 44.12%, 57.75%, 53.21%, 52.93%, the time-averaged friction factor is increased by 58.23%, 133.04%, 140.80%, 151.26%, and the PECs is decreased with the increase in Reynolds number to be 1.24, 1.19, 1.14, and 1.12, respectively, when compared with the constant flow. When the forcing frequency is equal to the hydrodynamic instability frequency, the time-averaged Nusselt number of the grooved channel will reach its maximum value. Also, the dynamic mode decomposition analysis shows that the pulsation mode energy is maximum when the forcing frequency is equal to the hydrodynamic instability frequency. It shows that the applied pulsating flow has a positive effect of enhanced heat transfer, and the positive effect decreases with the increase in Reynolds number.

Analysis of the unsteady flow characteristics of underwater supersonic gaseous jets

To examine the unsteady flow characteristics of underwater supersonic gaseous jets under different jet expansion conditions, a sophisticated numerical model is created. This model accurately predicts the intricate multiphase flow by considering the compressibility of the jet gas and energy exchange, which is then rigorously validated against experimental data. The development process of underwater supersonic gaseous jets displays notably unsteady features in terms of jet morphology, flow structure, and various flow field parameters when compared to atmospheric conditions. The unsteady phenomena, such as necking, breaking, bulging, and back-attack, are observed alongside significant pressure pulsations. These unsteady phenomena occur at a considerable distance from the nozzle exit under under-expanded conditions, while pressure pulsations do not impact the internal gas flow within the nozzle. However, under full-expanded and over-expanded conditions, unsteady phenomena near the nozzle exit lead to oscillatory pressure, causing shock waves to propagate inside the nozzle. This results in a notable increase in internal pressure pulsation and mass flow rate within the nozzle, ultimately affecting engine performance significantly.

Numerical Modelling of a Pulsating Flow Generator for Simulating Blood Pressure

Abstract Hypertension is a leading risk factor that deserves to be taken seriously, therefore researches on blood pressure measurement play a critical role. In this work, a liquid-operated pulsating flow circulation system with a bionic arm is set as a blood pressure simulator and a related numerical model is built to analyse the flow under different settings. The motion patterns of the flow generator and the medium used are two of the main factors discussed in this work. By comparing the pressure curves under different conditions and actual experimental data, the numerical model is validated, and so as to find the suitable parameters of the actual system.

On the asymptotic analysis of pulsating planar Poiseuille flow instabilities

The linear stability analysis of a pulsating flow between parallel plates at finite amplitudes and different frequencies demonstrates the presence of instability with a different nature to that initially reported in earlier studies at W o < 25 . The time-dependent stability problem is formulated using a Floquet expansion of the perturbation and solved in a matrix approach. At higher pulsation frequencies (i.e. W o > 30 ), pulsation amplitudes and sufficiently large Reynolds numbers, the time-dependent baseflow displays multiple inflexion points throughout the entire duration of the pulsation. A scaling analysis of the temporal growth rate reveals that the instability is of inviscid type and scales with R e − 1 . Freezing the time-dependent baseflow for a particular set of parameters, the growth rate is simultaneously controlled by viscosity solely acting on the perturbation, and the pulsating frequency coupling the harmonics. In the asymptotic limit ( R e → + ∞ ), we demonstrate that the temporal problem simplifies to a set of steady stability analyses dependent on the phase of the pulsation. In particular, we show that in this limit, Rayleigh and Fjørtoft’s criteria for instability become valid again, that sub-harmonic periodic orbits can be used to estimate the inviscid growth rate and match with the asymptotic values predicted from the viscous stability analysis.

Flow characteristics and factors affecting flow pulsation of external meshing herringbone gear pump

To enhance the outlet flow stability of the external herringbone gear pump, an analysis was conducted on the main influencing factors, key geometric parameters were identified, and a numerical model was developed for fluid analysis. A numerical model was then established for fluid analysis. The accuracy of the numerical model was verified by comparing it with experimental results, with simulation errors of displacement and volumetric efficiency being < 5%, ensuring the simulation's accuracy. The simulation results indicated that the pump's head (49.7808 m) and outlet pressure (4.9285 bar) remained stable. At 700 rev/min, the simulated volumetric efficiency was 82.94%. Subsequently, the impact of helix angle, changes in center distance, and tip clearance on outlet flow stability were analyzed. The analysis revealed that increasing the helix angle from 27° to 30° could reduce flow pulsation. A slight reduction in center distance from 180.3 (δ = +0.3 mm) to 179.9 mm (δ = −0.1 mm) effectively decreased mass flow difference and outlet pressure pulsation, enhancing outlet output stability. Reducing tip clearance from 0.25 to 0.12 mm, while meeting design requirements, resulted in more stable pressure and lift output. These results ensured smooth pump operation, improved outlet output stability, and met low-flow pulsation requirements. This study offered valuable insights into the design and production of the external meshing herringbone gear pump.

Assessment of the long-term trend in angiodystonic syndrome of the upper extremities in stage I vibration disease using the ultrasound method

Introduction. Diseases of the upper extremities caused by exposure to local vibration at the workplace are a ubiquitous problem. These diseases occur or are aggravated by exposure to vibration at the workplace when using vibration-hazardous equipment. Purpose of the study – is to identify the features of upper limb angiodystonic syndrome in vibration disease at stage I, depending on work experience. Materials and methods. Ultrasound scanning of the arteries of the upper extremities was performed in seventy patients. Spectral and velocity indices such as resistance index (RI), diastolic blood flow rate (V ED), systolic (pulse) blood flow rate (V PS) and pulsation index (PI) were measured in the distal part of the forearm. Results. Upon contact with a vibration tool, for each year of work experience, the systolic (pulse) blood flow rate (V PS) in the radial and left ulnar arteries significantly were found to decrease by an average of 0.57–0.58 (p<0.05). In the ulnar artery, PI increases on average by 0.03–0.062, but the changes are not statistically significant (p>0.05). With an increase in the length of service by 1 year, the RI in the left radial and ulnar arteries significantly increases by 0.0003–0.0012 (p<0.05). Limitations of the study. The main disadvantages of ultrasound are the long-term and operator-dependent method. Conclusion. With an increase in work experience, the indices characterizing angiodistonic disorders: pulsation index (PI), resistance index (RI) – significantly increase with each year of experience when exposed to local vibration. This can be used for differential diagnosis of peripheral angiodistonic upper limb syndrome of occupational etiology, in particular, vibration disease associated with exposure to local vibration at stage 1. With an increase in work experience, the indices characterizing angiodistonic disorders: pulsation index (PI), resistance index (RI) – significantly elevate with each year of experience when exposed to local vibration. As part of the ultrasound screening study, scanning of the arteries of the upper extremities in patients at the clinic of occupational pathology can be performed at the preclinical stage to prevent prolonged chronic ischemia of the upper extremities. This diagnostic method can be especially valuable in differentiating peripheral angiodistonic upper limb syndrome of occupational etiology, in particular, vibration disease at the stage 1.

The Influence of Gas-Dynamic Non-Stationarity of Air Flow on the Heat Transfer Coefficient in Round and Triangular Straight Pipes with Different Turbulence Intensities

Unsteady gas-dynamic phenomena in pipelines of complex configuration are widespread in heat exchange and power equipment. Therefore, studying the heat transfer level of pulsating air flows in round and triangular pipes with different turbulence intensities is a relevant and significant task for the development of science and technology. The studies were conducted on a laboratory stand based on the thermal anemometry method and an automated system for collecting and processing experimental data. Rectilinear round and triangular pipes with identical cross-sectional areas were used in the work. Flow pulsations from 3 to 15.8 Hz were generated by means of a rotating flap. The turbulence intensity (TI) of the pulsating flows varied from 0.03 to 0.15 by installing stationary flat turbulators. The working medium was air with a temperature of 22 ± 1 °C moving at a speed from 5 to 75 m/s. It was established that the presence of gas-dynamic unsteadiness leads to an increase in the TI by 47–72% in a round pipe and by 36–86% in a triangular pipe. The presence of gas-dynamic unsteadiness causes a heat transfer intensification in a round pipe by 26–35.5% and by 24–36% in a triangular pipe. It was shown that a significant increase in the TI of pulsating flows leads to an increase in the heat transfer coefficient by 11–16% in a round pipe and a decrease in the heat transfer coefficient by 7–24% in a triangular pipe. The obtained results can be used in the design of heat exchangers and gas exchange systems in power machines, as well as in the creation of devices and apparatuses of pulse action.

Research on a new pressure pulsator

Pulsators are widely used to study the dynamic characteristics of liquid flow components. However, it is difficult to adapt the existing actuators to the excitation requirements under high pressures, low temperatures, and toxic media. This study describes the design of a novel pressure pulsation device and presents the results of simulations and experimental tests. The flow field is simulated under a series of working conditions, and the effects of the rotation speed, flow rate, inlet pressure, and gap between the rotor and stator on the peak-to-peak amplitude, spectral amplitude, and flow resistance coefficient of the actuator outlet are analyzed. A prediction model for the corresponding parameters is developed using multiple linear regression. In high-pressure (20 MPa) hydraulic pipeline tests, the excitation device can generate pulsating flow with peak-to-peak amplitudes of more than 7 MPa in the time domain and 2 MPa in the frequency domain. The upstream and downstream regions of the internal flow field are periodically joined and detached by the blade rotation, which results in periodic variations in flow velocity and pressure. The relative error between the model predictions and the three-dimensional simulation and experimental values is less than 7%, satisfying industrial requirements. This work facilitates a solution to the problem of dynamic excitation when analyzing the response characteristics of fluid equipment in high-pressure pipelines and provides a method for forecasting actuator output effects.

Dynamic Characteristics of Pressure-Balanced Metal Bellows in Fluid–Structure Interaction

As a flexible component in high-pressure vessels and pipeline systems, bellows experience significant fluid–structure interaction effects under high-speed internal fluids and external vibrations. Nevertheless, their dynamic response mechanisms coupled with fluid–structure interaction mentioned below have not yet been clarified so far. In this work, a novel pressure-balanced metal bellow (PBMB) for low-stiffness and high-pressure resistance is firstly proposed. Several fluid–structure interaction models were considered to study the dynamic response characteristics of the PBMB. An experimental platform associated with fluid–structure interaction was established to validate the effectiveness of its vibration attenuation performance. The results indicate that the PBMB has an obvious vibration attenuation effect in the range of 5–90[Formula: see text]Hz, and super-harmonic and sub-harmonic resonance phenomena occur in the range of 90–200[Formula: see text]Hz. Under constant fluid conditions, fluid density, viscosity, flow velocity, and pressure are positively correlated with the response amplitude of the PBMB. The response of the PBMB oscillates at the fluid entry point due to both pulsating flow velocity and pulsating pressure. After several cycles, the response caused by pulsating flow velocity gradually decays and stabilizes. Thus, the impact of pulsating frequency on the stability of the response of bellows is insignificant during the initial cycles.

Large eddy simulation of turbulent transport and thermal enhancement in a steam-cooled ribbed channel

Pulsating flow, as an active heat transfer enhancement technique, is expected to further improve thermal performance. To demonstrate the potential value of pulsating flow in blade cooling, a numerical investigation is conducted on the flow and heat transfer in a steam-cooled ribbed channel under steady and pulsating inflow at Re = 12000. LES, based on OpenFOAM-8, is employed and precursor simulation method is used to generate fully developed turbulent inflow. Three operating conditions, steady inflow (StF = 0), low frequency pulsation (StF = 0.02) and medium frequency pulsation (StF = 0.08), are studied. The features under steady inflow condition (StF = 0) are firstly discussed, indicating that, due to the entry effect, the ribbed channel can be divided into two regions with different vortex motion behaviors. The ejections induced by vortex evolution enhance turbulent and energy transport between the sidewall and mainstream. Two cases of pulsating inflow are then carried out, finding that stronger ejections appear and low heat transfer area is significantly improved. Corresponding to low frequency pulsation (StF = 0.02) and medium frequency pulsation (StF = 0.08), the Nusselt number has an increase of 3.511 % and 14.242 %, respectively, and friction factor has a rise of 3.934 % and 8.253 %, compared with steady inflow. The thermal performance factor is increased by 11.262 % at StF = 0.08, indicating better cooling performance than the rise of 2.188 % at StF = 0.02. It is suggested that pulsating flow with medium frequency pulsation has positive performance in a steam-cooled ribbed channel.