Pulsating Flow Research Articles

Assessment of units vibration state and water supply path of Amuzang-2 pumping station

This article presents separate results of studies devoted to the study and analysis of vibrational phenomena occurring on pumping units and along the line of the pressure pipeline of the surveyed pumping stations, associated with flow pulsation in the water supply path and cavitation manifested on pumping units. As is known, the operation of pumps is accompanied by hydrodynamic oscillatory phenomena, which are expressed in the non-stationarity of the field of velocities and pressures of water at the outlet of the pump. This is especially typical for powerful centrifugal pumps with high volumetric flow rates and pressure drops on the impeller, which took place at Amuzang-2 pumping station. Thus, the analysis of the results of vibration tests of pipelines allows us to draw the following conclusions: 1. The vibration state of all pipelines is unsatisfactory. 2. The cause of increased vibration is an unfavorable combination of design, installation, and operational factors.

A model of random pulsations of radiant heat flow from a flammable liquid fire

The object of the study is the process of liquid combustion in a tank or in a spill. Unlike the standard approach that assumes the shape of the flame is constant, random pulsations of the flame due to the turbulent mode of liquid combustion are considered. The pulsations lead to the random nature of the mutual radiation coefficient and the temperature of the radiating surface of the flame. This leads to a random value of the radiant heat flux density from the fire. Using the central limit theorem allows justifying the assumption about the normal law of the distribution of the radiant heat flux density, the mutual radiation coefficient and the temperature of the radiating surface of the flame. The assumption of a normal distribution law allows calculating the mathematical expectation of the heat flux density. It is shown that the average value of the heat flux density increases with an increase in the dispersion of the temperature of the radiating surface and the coefficient of mutual radiation, as well as with an increase in the correlation coefficient between them. It means that neglecting random flame pulsations can lead to underestimates of the average heat flux density from a fire. The dispersion of the radiant heat flux density was found and it was shown that it increases with the growth of the dispersion of the flame temperature and the mutual radiation coefficient. The standard deviation of the heat flux density can be more than 40 % of its average value if the standard deviations of the flame temperature and the mutual radiation coefficient are up to 10 % of their average values. The obtained results can be used to clarify the thermal effect of a liquid fire on neighboring objects.

The influence of microstructured surfaces and liquid pulsations on increasing heat transfer in a minichannel

The paper compares two methods for improving the intensification of heat transfer during boiling in a rectangular minichannel. Studies were carried out of the influence of additive structures on the crisis of heat transfer in a minichannel with a two-phase flow, as well as studies of the influence of high-frequency pulsations of liquid flow on the intensification of heat transfer processes during flow boiling.

Математичне моделювання та результати експериментальних досліджень процесу вібропневмоімпульсного поділу насіння за густиною

The results of the mathematical simulation of the movement of grain material on the surface of the perforated deck of the vibro-pneumatic-impulse separator have been presented. Both force and kinematic models were employed, considering the geometric characteristics of the perforated deck surface in dynamic interaction with the kinematic indicators of processing. The calculations based on the proposed model allow for determining the trajectories of movement, velocities, and accelerations of the grain seeds within the grain medium under the combined action of vibrations and the pneumatic-impulse flow. As a result of the scientific research and analysis of the forces created according to the developed mathematical model, it has been established that the most significant influence on the process of grain material movement, both in the horizontal and vertical directions, is exerted by the impulse force (pulsations) of the air flow, the pressure force of the underlying layers of the grain medium (for seeds in the middle part and on the surface of the perforated deck), frictional forces, the weight of the seeds, and the Archimedean force. Therefore, in order to intensify the process of fractionation of the grain medium and increase the specific productivity of the vibro-pneumatic-impulse separator, it is necessary to increase the force of the pulsating air flow, the force of inertia of the oscillatory motion, friction, and lateral pressure on the seeds within the grain medium.

ОЦЕНКА ГОМОГЕННОСТИ ТОПЛИВОВОЗДУШНОЙ СМЕСИ В МАЛОЭМИССИОННОЙ КАМЕРЕ СГОРАНИЯ ГАЗОТУРБИННОГО ДВИГАТЕЛЯ С ПОМОЩЬЮ КОРРЕЛЯЦИИ ПУЛЬСАЦИЙ ДАВЛЕНИЯ И РАСХОДА ПИЛОТНОГО ТОПЛИВА

Connection between pilot fuel flow and pressure pulsations in dry low emission combustor is established on base of experimental data. Determining quantitative criteria of homogeneous or diffusion flame is formulated. The criteria give chance to evaluate quality of mixing fuel and air and combustion without emission measuring. The root-mean-square deviation of the dependence of the distribution of the air-fuel mixture concentration field over the combustion chamber cross section on the correlation coefficient between the pilot fuel ratio and the double amplitude of pressure pulsations in the flame tubes for a homogeneous (technically mixed air-fuel mixture) circuit was approximated based on the data obtained. The results obtained make it possible to significantly improve the quality of emission prediction by refining the semi-empirical mathematical model of the nitrogen oxides' generation, built on the basis of the Zeldovich thermal mechanism for low-emission operating modes of dry low emission combustor of the gas turbine engines. The account of heterogeneity of the process in the flame tubes makes it possible to move from the assumption of the geometric and gas-dynamic identity of the flame tubes to their actual heterogeneity. This conclusion allows refining the model. The developed mathematical model can be used as a virtual emission sensor in advanced tracking control systems of gas turbine engines.

АНАЛИЗ ВЛИЯНИЯ ПРОЦЕДУР ПРОТИВООБЛЕДЕНИТЕЛЬНОЙ ОБРАБОТКИ НА УРОВЕНЬ БЕЗОПАСНОСТИ ПОЛЁТОВ ПРИ ЭКСПЛУАТАЦИИ ПАССАЖИРСКОГО МАГИСТРАЛЬНОГО САМОЛЁТА

The purpose of this article is to investigate the barrier ice accretion after aircraft de-icing, as well as to analyze the impact of it on flight safety. The influence degree of the flight speed factor, the factor of the ice ridges location relative to the aircraft Pitot tubes on the airflow disturbance creation and the total pressure indicators pulsations is studied. It was analyzed the aviation accidents related to the aircraft icing process. A detailed study of the incident caused by the barrier ice in the fuselage nose section was performed; weather conditions and de-icing procedure by the ground personnel were analyzed. It has been presented a picture of the turbulent flow pulsations behind the ice ridges, making it possible to determine the flight conditions when the crew may receive unreliable information about the airspeed being an important parameter necessary for the autopilot normal operation.

Modeling the process of grain separation by density in a combined vibro-pneumatic and air-gravity unit

It was established that the method of intensifying the course of the work process is the organization of supplying the layer with a pulsating flow of air. Using a pulsating air flow, it is possible to change the magnitude of the aerodynamic effect on the grain mass by changing the magnitude of the force pulse under conditions of constant speed. At the same time, the effect of the pulsating flow on the ability to move grains of different mass (density) will be different, which can intensify the separation of seeds by density. The study of the combined effect of vibrations and pulsating air flow on the stratification of the grain flow and separation by density is an important scientific and technical task. The conducted analysis of publications revealed a promising possibility of using serial vibrating screen machines with a pneumatic system for the preparation of combined machines with a pneumatic system for the preparation of high-quality seeds, instead of vibro-pneumatic tables. To study the efficiency of the combined use of vibropneumoliquefied and pneumogravitational movement of the material. It is substantiated that the intensifying effect of the pulsating flow consists in the different force of influence on light and heavy grains. The mathematical description of the process of separation of loose material by density is based on the equations of motion of a particle in an oscillating medium, which is valid for any continuous medium that has the property of inertness. Formulated mathematical models of the processes of movement of components of grain material in the vibro-liquefied layer and in the air channel of the vibro-pneumocleaning machine will allow to determine the trajectories of the movement of grains in the working zones and, based on their analysis, to justify the parameters of the working bodies. The approbation of the mathematical description of the processes of separation of the components of grain material confirmed the increase in the efficiency of the use of pulsating flows for the separation of grain by density.

Thermal performance analysis of artificially roughened solar air heater under turbulent pulsating flow with various wave shapes

This paper presents a numerical investigation of the operation of a solar air heater (SAH) with cylindrical shape ribs under turbulent pulsating flow based on thermal and frictional considerations. Turbulence and thermal natures of flow physics are modeled by taking the relevant governing equations into the account using RNG k−ε turbulence model and transient state Reynolds-Averaged Navier-Stokes (RANS) equations. The pulsating flow is modeled with four different wave shapes including rectangular, sinusoidal, triangular, and sawtooth functions. The influence of various factors such as wave shape, Reynolds number (Re), frequency, and amplitude of pulsating flow on the thermal and hydraulic performance of SAH has been evaluated. Results indicated that the SAH with ribbed absorber section under pulsed flow has a larger Nu number compared to the air heater with smooth duct under steady flow. Moreover, the pulsating flow with a sawtooth velocity profile leads to the greatest value of the thermo-hydraulic performance parameter (THPP). The growth of pulsation frequency up to 200 enhances the heat transfer coefficient of the air heater while for frequencies larger than 200, the thermal performance declines. In addition, the increase in pulsation amplitude has a negative effect on the THPP. It was proved that the increment of the Re number enhances the THPP. Up to 53.3% improvement of THPP can be achieved by applying pulsed flow with sawtooth wave shape and ribbed absorber section compared to air heat with smooth duct under steady flow.

Pulsating flow and heat transfer of power-law fluid in a circular pipe

In this study, the pulsating flow of a non-Newtonian fluid and heat transfer in a pipe with uniform heat flux at its wall is examined analytically. The flow is assumed to be both hydrodynamically and thermally fully developed. The perturbation method based on the series expansion is used in the analysis. The periodic change and period-averaged values of the friction factor and Nusselt number as well as velocity and temperature profiles are obtained at varying values of dimensionless frequency and amplitude for shear-thinning, Newtonian and shear-thickening fluids. It is shown that the frequency is effective on the friction factor for a specific range of the dimensionless frequency. For some specific cases, excellent agreements are obtained with the literature. It is disclosed that the dimensionless frequency, the amplitude and the power-law index are interactively effective on the friction and heat transfer.

Pulsation Reduction Using Dual Sidewall-Driven Micropumps.

Single-cell manipulation in microfluidic channels at the micrometer scale has recently become common. However, the current mainstream method using a syringe pump and a piezoelectric actuator is not suitable for long-term experiments. Some methods incorporate a pump mechanism into a microfluidic channel, but they are not suitable for mass production owing to their complex structures. Here, we propose a sidewall-driven micropump integrated into a microfluidic device as well as a method for reducing the pulsation of flow. This sidewall-driven micropump consists of small chambers lined up on both sides along the main flow path, with a wall separating the flow path and each chamber being deformed by air pressure. The chambers are pressurized to make the peristaltic motion of the wall possible, which generates flow in the main flow path. This pump can be created in a single layer, which allows a simplified structure to be achieved, although pulsation can occur when the pump is used alone. We created two types of chips with two micropumps placed in the flow path and attempted to reduce pulsation by driving them in different phases. The proposed dually driven micropump reduced pulsation when compared with the single pump. This device enables precise particle control and is expected to contribute to less costly and easier cell manipulation experiments.

Solution of Unsteady Flow Equations for Nanoscale Heat and Mass Transfer in Diverse Applications

Abstract A new innovative stable time-dependent compressible flow solution over the order of nanoseconds is provided here for wide-ranging critically important challenging applications. Specifically, a solution of the highly complex unsteady high speed oscillating compressible flow field inside a cylindrical tube, closed at one end with a piston oscillating at very high resonant frequency at the other end, has been obtained numerically, assuming one-dimensional, viscous, and heat-conducting flow, by solving the appropriate fluid dynamic and energy equations. An iterative implicit finite difference scheme is employed to obtain the solution. The scheme permits arbitrary boundary conditions at the piston and the end wall and allows assumptions for transport properties. In successfully predicting the time-dependent results/data, an innovative simple but stable solution of unsteady fluid dynamic and energy equations is provided here for wide ranging research, design, development, analysis, and industrial applications in solving a variety of complex fluid flow heat transfer problems. The method is directly applicable to pulsed or pulsating flow and wave motion thermal energy transport, fluid-structure interaction heat transfer enhancement, nanoscale heat and mass transfer, diverse range of advanced fluidics, biofluidics/bio-engineering, and fluidic pyrotechnic initiation devices. It can further be easily extended to cover muzzle blasts and high energy nuclear explosion blast wave propagations in one-dimensional and/or radial spherical coordinates with or without including energy generation/addition terms. No other solution exists for such applications.

Theoretical analysis and simulation calculation of hydrodynamic pressure pulsation effect and flow induced vibration response of radial gate structure

This work aims to explore the characteristics of stochastic fluctuant water pressure acted on the surface of large radial gate, and to investigate the flow-induced vibration response of the whole radial gate structure. The finite element calculation model structure of the radial gate is established by taking a large-scale radial gate as prototype to discuss the hydrodynamic pressure acting on the gate leaf with different opening, analyze the dynamic pressure time curves, and achieve the flow-induced vibration response by deeming hydrodynamic pressure as dynamic load. When taking 10% opening of the radial gate, the results indicate that the hydrodynamic pressure distributed on the arc surface of the radial gate changes with the flow conditions, with the maximum pressure occurred at the center of the lower edge of the gate leaf. One point in the time history curve of fluctuating water pressure can be taken as the dynamic load for the flow-induced vibration analysis. The flow-induced vibration responses at the monitoring point of the radial gate structure show periodic changes in the X, Y, and Z directions. The finite element simulation results agree well with the theoretical calculation results, so reference can be provided for the hydrodynamic pressure testing and the flow-induced vibration response calculations.

Design of Structure Parameters of Sliding Vane Pump Based on Lifting Characteristics

Abstract Limited by the harsh downhole working environment and its structural feature, the sliding vane pump (SVP), which is an all-metal artificial lift method considered to be widely used in thermal recovery well and high gas/oil ratio well, has not been widely applied as expected. To further improve the efficiency of SVP, this study explores how to optimize the structure parameters and the usage of the pump based on its lifting characteristics, in view of the stagnation in the development of SVP. The main results show that (a) optimization of the inlet (outlet) position parameters will bring effective pre-expansion (precompression) of each chamber once it enters the closed state, to avoid ineffective suction and high-pressure backflow. (b) The mathematical model of the pressure difference between the two sides of the vane at any position is derived by means of piecewise function. (c) Increasing the number of vanes can not only increase the mean value of instantaneous displacement but also shorten the discharge period and reduce the flow pulsation. Compared with the adjacent even number of vanes, the odd number of vanes has a more uniform instantaneous displacement. (d) A larger cross-sectional area of the rotor groove can result in a lower volume efficiency at the same gas–liquid ratio, and the effect of rotor groove on volume efficiency is more significant under high gas–liquid ratio conditions.

Numerical Analysis of the Pulsating Heat Transfer of Ferrofluid in Helically Fluted Tubes

The flow and heat transfer characteristics in the corrugated tube mainly depend on flow parameters and geometric configurations of the tube, such as corrugated cross-section, corrugated angle, corrugated arrangement, corrugated pitch and depth, pulsating flow frequency, coolant types, and Reynolds number. This paper presents the pulsating thermal characteristics of ferrofluid flowing in the fluted tube using the de-ionized water and 0.015% by volume as working fluid flowing in the test section. Eulerian two-phase turbulence model validation has been performed in both steady and pulsating flow. The finite volume approach discretizes the Eulerian two-phase model. Numerical results indicate that the longitudinal and transverse secondary flows are induced differently via the pulsating flow. The heat transfer characteristics of pulsating fluid flow are significantly larger than that of continuous fluid flow. A higher pulsating frequency induces a heat transfer enhancement. However, pulsating flow increases pressure due to more flow complexity and rough augmentation. Due to the disturbed fluid flow and higher swirling motion, the heat transfer augmentation increases and corresponds with the published results.

Analysis of wave propagation and pulsation in an elastic tube using a diaphragm pump

In this research, the flow wave propagation, speed, and pulsation suppression in an elastic tube were studied using a diaphragm pump. The flow fluctuations with shocking pressure fluctuations occur in the elastic tube because the check ball was blocked, thereby preventing reverse flow. Consequently, the check ball is one of the causes of pulsating flows in diaphragm pumps. However, only a few studies have analyzed the relationship among the check ball movement, pressure, and flow fluctuations. In this study, we constructed several elastic tube experiments: (i) single-tube model; (ii) two-tube model. To predict the flow wave propagation and pulsation in an elastic tube, we developed an axisymmetric theoretical model and compared into the experimental results. Based on our study, the main results were as follows: the relationship among the check ball movement, pressure, and flow fluctuations showed that the pressure and flow rate pulsation were caused by the asymmetry of the check ball movement. Additionally, we observed that the theoretical flow wave propagation trend had a good agreement with the experimental results, although the flow wave speed in the urethane-tube experiment differed considerably from the theoretical prediction. Furthermore, the amplitude of the pulsation increased considerably owing to the reflected wave at the tube exit, although it did not increase when the resistance was added at the exit. Finally, we observed that the pulsation reduced more in the silicon tubes compared to the urethane tubes because the deformation of the silicon tubes was larger than that of the urethane tubes.

Modeling radial turbine performance under pulsating flow by machine learning method

This work presents the development and application of a machine learning model to predict the unsteady performance of a turbocharger radial turbine subject to on-engine pulsating flow conditions. The model proposed, based on a fully connected neural network, predicts the instantaneous turbine torque and circumferentially-averaged relative inflow angle when given, as only inputs, the total pressure and temperature pulses and the time derivative of the total pressure pulse upstream of the turbine. The training data set for the model is obtained from an experimentally-validated Reynolds-averaged Navier-Stokes model and consists of various operating conditions characterized by different pulse amplitudes and frequencies. Heat transfer effects are neglected by the use of adiabatic boundary conditions while the rotational speed of the rotor is otherwise maintained fixed. Based on the results obtained, the model is shown capable of accurately predicting the turbine torque and local properties of the flow, such as the relative inflow angle, with a high degree of accuracy (coefficient of determination larger than 0.98 ). At first, the model is tested for both interpolation and extrapolation conditions. Given a training data set constituted by only three pulses characterized by different amplitudes, the model accurately predicts the turbine performance both for conditions inside and outside the range of amplitudes of the training data set. Lastly, the model is trained with a larger data set, including both variations of the pulse amplitude and frequency, in order to predict the performance of the turbine subject to a more general pulse shape. The error indicators show an improvement with respect to the extrapolation case due to the larger size of the training data set, showing also a great capability of the model to predict the unsteady performance of the turbine for a more general pulse shape. The model represents a fast and efficient approach for predicting the unsteady turbine performance as compared to more complex experimental set-ups and time-consuming 3D numerical simulations and a valid alternative to the more common 0D-1D models.

Effects of diffusive Reynolds number on electro-osmotic pulsating nanofluid flow

We examine pulsating electro-osmotic nanofluid flow phenomena in a microchannel with porous walls. The combined effect of the injected nanofluid velocity and ion diffusion coefficients on the electrical potential formation is considered. A novel boundary condition is introduced so as to examine the effects of electro-osmosis and frictional forces on thermal profiles and nanoparticle volume fractions of nanofluids. Being motivated by the experimental works of Kong et al. [Phys. Chem. Chem. Phys. 19, 7678 (2017).], this paper aims to extend the study of ion diffusivity in terms of diffusive Reynolds number on nanofluid temperature in the pulsating pressure gradient setting. The semi-analytic differential transform method is used to solve the physical equations, represented as coupled ordinary differential equations, with a special emphasis on the convergence of solutions, which is presented in terms of tables and graphs. The study shows that the nanofluid velocity, temperature, and mass concentration are strongly influenced by the ion diffusion coefficient and the frequency of pulsating pressure gradient. The diffusive Reynolds number significantly influences the electric potential distribution. The velocity and temperature show an increasing trend in terms of diminishing sensitivity parameter. However, nanoparticle concentration increases with an enhancement of the sensitivity parameter. Finally, velocity and temperature increase with a diminution of the Womersley number.

Study on the flow characteristics of the pulsating intermittent liquid–solid fluidized bed with step liquid velocity by CFD approach

AbstractA new type of liquid–solid fluidized bed (LSFB), the pulsating intermittent LSFB (PI‐LSFB), which uses pulsating liquid flow, was analyzed through numerical and experimental study. A good agreement between numerical simulation results and laboratory experimental measurement data was achieved. The mass transfer efficiency between the liquid and solids phases was enhanced since the relative velocity was significantly improved. The flow characteristics of the PI‐LSFB were analyzed through the Eulerian–Eulerian approach, incorporating the kinetic theory of granular flow. The solids holdup in the middle part of the PI‐LSFB increases first and then decreases as the step liquid velocity increases. The relative velocity increases first and then decreases as the pulsation period or the liquid velocity increases. The PI‐LSFB performs similar flow regimes under step and sinusoidal liquid velocities. The proposed PI‐LSFB may provide a reference in biological wastewater treatment applications.

Study on the heat transfer enhancement of self-excited oscillating pulsating flow by the boundary vortex group

In this work, the self-excited oscillating pulsating circular pipe is the object of study. Based on the flow evolution characteristics of the boundary layer and vortex, the mechanism of enhanced heat transfer by self-excited oscillating pulsating flow is investigated. Moreover, a vital flow structure, the boundary vortex ring (BVR for short), is proposed. The study results show that the vortex evolution within the shear layer inside the self-excited oscillating pulsating chamber has an important influence on the formation of the downstream boundary vortex ring. Both have the same period but different phases. The boundary vortex group formed by the BVR is distributed at intervals in the pipe, and its role in promoting fluid flow increases first and then decreases. At the same time, the strength of the central mainstream area is gradually strengthened. The boundary vortex group's flow state determines the downstream pipe's heat transfer characteristics. The low-velocity zone on both sides determines the position of the heat transfer coefficient enhancement, and the central vorticity determines the amplitude of the enhancement. The boundary vortex group with a complete structure can effectively promote heat transfer, while the boundary vortex group with an incomplete structure can suppress heat transfer. The time-averaged boundary layer thickness increase ratio δ′ and the time-averaged equal diameter circular tube performance evaluation index ηT provide the fundamental indexes for designing and optimizing variable cross section heat transfer circular tubes. Furthermore, the heat transfer coefficient of the tube wall varies synchronously with the thickness of the boundary layer.

TRANSFER PHENOMENA IN ECOLOGICAL SYSTEMS

The phenomenon of transfer finds great application in the problems of hydromechanics of heat and mass transfer associated with structural features and rheological properties of liquid media. A wide distribution of problem solving on the use of ideas about the phenomena of transfer was found in the physicochemical processes of biological media, the processes of transfer of mechanical media, phenomena associated with systems. The article considers cases of solving hydrodynamic problems using the analysis of transport processes for different types of channel flows described by non-stabilized pulsating flow equations, as well as open channel flows that find their place in practice.