Non-uniform Velocity Research Articles

Filtration efficiency and pressure drop modelling of particulate filters with rear plug damage

A model suitable for wall-flow particulate filters with partial rear plug damage is developed and experimentally validated in this work. A ceramic filter with 16% of the rear plugs mechanically removed is tested at steady-state conditions on the engine bench and transient driving cycle conditions on the chassis dynamometer. After decanning of the monolith, destructive analysis is conducted to identify deposit loading variations and scanning electron microscopy is used to study the deposit structures in the channels. It is shown that channels without rear plugs develop distinct deposit structures in the entry zone. Hence, a local pressure loss coefficient is applied to model the effect of entrance flow constrictions, taking also into account deposit restructuring phenomena at higher flow rates. In addition, a deep-bed filtration submodel is used to capture the effect of non-uniform wall velocities on deposit accumulation in the wall. The modified model is first fitted to the engine bench data and then validated in a wider range of conditions using the driving cycle tests. With the exception of prolonged steady-state loading conditions, good pressure drop and filtration efficiency predictions are obtained throughout the tests in conjunction with correct deposit property profiles. Notably, the cold-start worldwide harmonized light vehicles test cycle shows that the current European on-board diagnosis threshold limit for particulate mass is too relaxed to trigger a malfunction indication for moderate filter faults. In conclusion, the model can be applied in damaged particulate filter studies for the assessment of leaked particulate mass, the specification of more effective legislation limits and the development of rigorous on-board diagnosis systems and algorithms.

Modeling and detailed numerical simulation of the primary breakup of a gasoline surrogate jet under non-evaporative operating conditions

The injection and atomization of gasoline fuels are critical to the performance of gasoline direct injection engines. Due to the complex nature of the primary breakup of the liquid jet in the near field, high-level details are often difficult to measure in experiments. In the present study, detailed numerical simulations are performed to investigate the primary breakup of a gasoline surrogate jet under non-evaporative “Spray G” operating conditions. The Spray G injector and operating conditions, developed by the Engine Combustion Network (ECN), represent the early phase of spray-guided gasoline injection. To focus the computational resources on resolving the primary breakup, simplifications have been made on the injector geometry. The effect of the internal flow on the primary breakup is modeled by specifying a nonzero injection angle at the inlet. The nonzero injection angle results in an increase of the jet penetration speed and also a deflection of the liquid jet. A parametric study on the injection angle is performed, and the numerical results are compared to the experimental data to identify the injection angle that best represents the Spray G conditions. The nonzero injection angle introduces an azimuthally non-uniform velocity in the liquid jet, which in turn influences the instability development on the jet surfaces and also the deformation and breakup of the jet head. The asymmetric primary breakup dynamics eventually lead to an azimuthal variation of droplet size distributions. The number of droplets varies significantly with the azimuthal angle, but interestingly, the probability density functions (PDF) of droplet size for different azimuthal angles collapse to a self-similar profile. The self-similar PDF is fitted with both lognormal and gamma distribution functions. Analysis has also been conducted to estimate the percentage and statistics of the tiny droplets that are under resolved in the present simulation. The PDF of the azimuthal angle is also presented, which is also shown to exhibit a self-similar form that varies little over time. The PDF of the azimuthal angle is well represented by a hyperbolic tangent function. Finally, a model is developed to predict the droplet number as a function of droplet diameter, azimuthal angle where a droplet is located, and time.

Modelling study of flue gas flow pattern with pressure, amount and shape variation catalytic converter

Purpose: The purpose of this study is to analyse the modelling of exhaust gas flow patterns with variations in pressure, number, and shape of filters on the catalytic converter. Design/methodology/approach: The research method used is a simulation using ANSYS, which starts by creating a converter catalytic model with pressure variations: (0.5-1.5 atm), number of filters: (2-5), and the form of filter-cut/filter-not-cut. Findings: The decrease in velocity is caused by non-uniform velocity in the exhaust gas flow that occurs when passing through a bend in the filter-cut that serves as a directional flow to create turbulence. Filter-cut type tends to have fluctuating pressure, turbulence flow pattern shape so that contact between filter and exhaust gas is more effective. Based on the analysis of flow patterns, the speed and pressure of the 5 filter-not-cut design at a pressure of 0.5 are the best, while at pressure (1-1.5 atm) the type 5 filter-cut is the best. Research limitations/implications: This study is limited to filter-not-cut and filter-cut types with variations in the number of filters: 2, 3, 4, and 5, and the inlet pressure between 0.5-1 atm. Practical implications: The practical implications of this study are to find a catalytic converter design that has advantages in the effectiveness of exhaust gas absorption. Originality/value: The results show that the filter-not-cut and filter-cut types have the best effectiveness in the number of 5 filters. Filter-not-cut at the pressure of 0.5 atm and filter-cut at pressure (1-1.5 atm).

Nonlinear interaction between bulk point vortices and an unstable interface with nonuniform velocity shear such as Richtmyer–Meshkov instability

The nonlinear interaction between bulk point vortices and a vortex sheet with initially nonuniform velocity shear is investigated theoretically and numerically by use of the vortex method, taking the incompressible Richtmyer–Meshkov instability as an example. As the point vortices approach the interface, i.e., a nonuniform vortex sheet, they increase the local sheet strength of the vortex sheet, which causes different types of interface deformation depending on the sign of their circulation of point vortices. For example, when the circulation of a point vortex is the opposite sign of the local sheet strength, it induces a new type of vortex pair with an local enhanced sheet vortex. We refer to that as a pseudo-vortex pair in the current study. The pseudo-vortex pair creates a local satellite mushroom at the fully nonlinear stage. The obtained results indicate that the complexity of the interface structure is enhanced if the bulk vortices exist.

Effect of non-uniform inlet velocity profile on flow field characteristics of a bluff body

To explore the influence of the non-uniform inlet velocity profile of the bluff body on flame stabilization, PIV measurements are carried out to investigate the characteristics of the flow field at 300 K and 0.101 MPa with seven velocity profiles, including four-velocity peaks, h/H, and three non-uniformities, δv. The experimental results indicate that the recirculation is approximately symmetric with the non-interfering dual-vortex structure under the condition of uniform inlet flow, whereas it is asymmetric and the fluid flows from one vortex core into another one when the velocity peak rises. The tendency of the dual-vortex interaction becomes more pronounced with the increase of the non-uniformity and the velocity peak. Besides, the length of the recirculation zone increases with the increase of h/H, while the largest width occurs at h/H = 0 and 4/6. At the same time, the distance of one core decreases first and then increases, while the other one is opposite to that. The width of the recirculation zone along the x-axis corresponding to δv = 30% is the same as that at δv = 0, and its value is higher than that at δv = 40% and 50%.

Oscillatory slip flow of Fe3O4 and Al2O3 nanoparticles in a vertical porous channel using Darcy's law with thermal radiation

AbstractThe heat transfer phenomena and oscillatory flow of an electrically conducting viscous nanofluid (NF) in a channel with porous walls and saturated porous media exposed to the thermal radiation are studied. The nanoparticles (NPs) Fe3O4 and Al2O3 are taken with water as base fluid along with nonuniform temperature and velocity slip at the wall of channel (y′ = 0). The basic laws of momentum and energy conservation are converted into the dimensionless system of the partial differential equations (PDEs) using similarity variables. Closed‐form solutions of these coupled PDEs are constructed for all values of time by taking the oscillatory pressure gradient. The physical insight of involved parameters on the fluid velocity, temperature profile, heat transfer rate, and surface friction is studied and analyzed graphically. It is noted from this study that the fluid velocity shows a decreasing behavior with the volume fraction of NPs. Furthermore, the amplitude of the oscillatory motion in case of skin friction decreases for a large magnetic field.

Computational simulation of variable magnetic force on heat characteristics of backward-facing step flow

The application of the nanofluid is highly increased due to its high heat rate in the attendance of the magnetic field. In current investigation, CFD is employed to model the impact of the non-homogenous magnetic force on the heat performance of backward-facing step nanomaterial flow. Current attempt tries to investigate the influence of the variable magnetic source on the flow feature of the nanofluid stream in the backward-facing step model. To study this problem, a vertical electrical wire is chosen to produce non-homogenous magnetic field. In our model, 4 Vol% nanoparticles ( $${\text{Fe}}_{3} {\text{O}}_{4}$$ ) are added to pure water to attain nanofluid. To simulate the nanofluid in our work, the FVM technique is selected. Our results initially validated with experimental studies and good agreement is achieved. Inclusive parametric evaluation is made to find the impact of non-uniform magnetic field and inflow nanofluid velocity on the thermal efficiency of backward-facing step flow.. Our results show that local heat transfer could increase up to 300% with impose of such source. Moreover, the rising number of the magnetic sources could extensively enhance the thermal feature.

Influence of non-uniform inflow swirl and hot streak on turbine vane

The turbine vane bears higher and higher temperature of upstream flow with the higher requirements for the engine thrust. The heat resistance of turbine vanes is a severe problem for the lifetime of turbine vanes. Therefore, it is essential to study the flow field and heat transfer of the vane to find better ways to improve the heat resistance of the turbine and increase the thrust of the engine. To improve the efficiency of the turbine vanes, the present paper conducted researches on the heat transfer and the pressure loss of turbine vanes under different radius ratio of swirl and hot streak. The numerical applies CFD 3D RANs solver with the SST turbulent model to get the influence of non-uniform inflow velocity and temperature distribution on turbine vanes. The present numerical model utilizes turbine vane C3X. Considering the viscosity of the fluid causes shear stress on the wall, the paper set the boundary layers mesh in the numerical model. The size of the first boundary layer mesh is 10–6 m. The results show that the hot fluid on the suction side migrates towards the hub, and the hot fluid on the pressure side migrates towards the shroud while there are coupling effect of the swirl and hot streak. The larger the radius ratio of the hot streak and the swirl (RHS) is, the higher the temperature of the local high-temperature regions exist on the suction side of leading edge and the pressure side of the trailing edge is, and the higher the pressure loss is.

A point vortex transportation model for yawed wind turbine wakes

In this study, stereo particle imaging velocimetry measurements are performed at multiple streamwise locations behind a yawed wind turbine to reveal the formation mechanisms of the counter-rotating vortex pair (CVP), and a point vortex transportation (PVT) model is proposed to reproduce the top–down asymmetric kidney-shaped wake (also referred to as a curled wake). Results indicate that the CVP formed behind a yawed wind turbine originates from the complex interactions between the hub vortex and the streamwise components of the blade tip vortices, which is fundamentally different from the case of a yawed drag disk where the hub vortex is absent. Specifically, when the yaw angle exceeds a critical value, a small part of the streamwise vorticity shed from the rotor disk edge switches its sign from negative to positive and subsequently merges with the concentrated hub vortex under mutual induction, creating a patch of positive vorticity; meanwhile, the remaining streamwise vorticity distributed along the rotor edge curls and evolves into another patch of negative vorticity. These two patches of streamwise vorticity essentially constitute the CVP. Based on the physics learnt from the experiments, the non-uniform cross-stream velocity fields are first reconstructed by a cloud of point vortices distributed along the rotor edge and a hub vortex located in the rotor centre, and subsequently used to numerically solve a simplified transportation–diffusion equation of the wake velocity deficit, which altogether constitute the PVT model. This physics-based reduced-order model is the first model capable of accurately reproducing the wake deformation behind a yawed wind turbine.

Flow of a viscous fluid over an infinite rotating and porous disk with stretching (shrinking) effects

A viscous flow is maintained over a porous and rotating disk. The porous disk is stretched (shrunk) with the non-uniform velocity in the radial direction. Note that the viscous fluid is injected (blown) normally with non-uniform velocity. The study is under taken by considering the combined and individual effects of injection (suction), stretching (shrinking) and rotation. The kinematics properties associated with the disk are depending upon the radial coordinate. The governing partial differential equations (PDE’s) are simplified and transformed into a new system of DE’s. The set of boundary value ODE’s is solved with the help of a numerical method. The transformed equations (presented over here) are new and to the best of authors knowledge, the equations are not published in literature. In particular cases, the modeled equations may reduce to the classical problems of rotating disk flows. The previous models of rotating disk flows with or without porosity and stretching (shrinking) effects are summarized into a single model. For fixed value of the governing parameters and different sizes of "infinity", no increase/decrease in the thickness of boundary layer is seen but the profiles of velocity components and pressure are significantly changed with the different levels of "infinity".

A MATLAB software platform for modelling vertically-integrated non-hydrostatic flows with moment equations

This work presents a software platform to compute depth-integrated non-hydrostatic coastal and open channel flows. The software is based on the Vertically-Averaged and Moment (VAM) equations model. The VAM model uses the weighted residual method to account for the non-hydrostaticity and non-uniformity of flow. After presenting the governing equations, numerical scheme and structure of the graphical user interface, the software is applied to solve coastal and open channel flow tests with significant non-hydrostaticity and non-uniformity of flow. The results are compared with hydrostatic model computations and laboratory measurements. Where a hydrostatic-based simulation poorly reproduces experimental observations, the higher-order model equations by this software platform generate excellent predictions. These findings highlight the potential of this user-friendly software platform for modeling open channel, river and nearshore flows and processes, where non-hydrostatic pressure and non-uniform velocity shall be accounted for, which entails a meaningful advance for the hydraulic community.

Experimental Evaluation of a Novel Sensor-Based Sorting Approach Featuring Predictive Real-Time Multiobject Tracking

Sensor-based sorting is a machine vision application that has found industrial application in various fields. An accept-or-reject task is executed by separating a material stream into two fractions. Current systems use line-scanning sensors, which is convenient as the material is perceived during transportation. However, line-scanning sensors yield a single observation of each object and no information about their movement. Due to a delay between localization and separation, assumptions regarding the location and point in time for separation need to be made based on the prior localization. Hence, it is necessary to ensure that all objects are transported at uniform velocities. This is often a complex and costly solution. In this article, we propose a new method for reliably separating particles at nonuniform velocities. The problem is transferred from a mechanical to an algorithmic level. Our novel advanced image processing approach includes equipping the sorter with an area-scan camera in combination with a real-time multiobject tracking system, which enables predictions of the location of individual objects for separation. For the experimental validation of our approach, we present a modular sorting system, which allows comparing sorting results using a line-scan and area-scan camera. Results show that our approach performs reliable separation and hence increases sorting efficiency.

Modelling coastal wave trains and wave breaking

The model of coastal waves based on the depth-averaging of the large eddy simulation equations (Kazakova and Richard, 2019) is extended to the case of regular and irregular wave trains. To take into account a stronger turbulence, the third moment of the horizontal velocity is modelled with a gradient-diffusion hypothesis. The effect of this new diffusive term is to smooth and regularize the solutions. An asymptotically equivalent model including the improvement of the dispersive properties is solved with a Discontinuous Galerkin numerical scheme. The model has a low sensitivity to the space discretization parameters. Several classical test cases of wave trains are used to validate the model. In the shoaling zone, the model is similar to the Serre–Green–Naghdi equations but the inclusion of a variable called enstrophy to take into account the large-scale turbulence and the non-uniformity of the mean velocity improves the predictive ability in the inner surf zone. In particular, the turbulent energy of the model is dissipated within one wave cycle and is transported shoreward in the case of waves with a long period whereas, in the case of short periods, it is mostly transported seaward because its dissipation is far from being complete within one period. The case of an irregular wave train propagating over a submerged bar is simulated without any breaking criterion. This benchmark test case validates further the model’s ability in predicting the nonlinear effects due to shoaling, breaking, propagation in a shallow horizontal part and in a deeper region.

Convective Type Models of Industrial Processes in Column Apparatuses 1. Chemical Reactions

A new approach for modeling chemical processes in industrial column apparatuses is presented. An exact approach for solving the equations in the convective type models is used. The use of experimental data for the average concentration at the column end for a specific process and column makes it possible to find out model parameters related with radial non-uniformity of velocity. These parameters enable application of the average-concentration model for modeling of chemical processes with different reaction rates.

Theory of Stokesian Free Jet with Nonuniform Exit Pressure and Velocity

Theory of Stokesian Free Jet with Nonuniform Exit Pressure and Velocity

Experimental response surface study of the effects of low-pressure exhaust gas recirculation mixing on turbocharger compressor performance

In Low-Pressure Exhaust Gas Recirculation (LP-EGR), clean exhaust gas is extracted downstream of the after treatment, and reintroduced upstream of the turbocharger compressor. A major pathway for engine fuel economy improvement, by employing LP-EGR, is the enhancement of compressor and turbine efficiencies by increased flow rates which moves the operating points towards higher efficiencies. However, what is often overlooked in the literature is the influence of LP-EGR/air mixing flow field on the compressor performance. Here, we systematically study this effect on a turbocharger unit for a diesel engine on a hot gas stand using response surface methodology. In addition, the mixing flow field of LP-EGR and air upstream of the compressor was scanned using a 3-dimensional directional probe. A reconfigurable T-junction mixer geometry was used, enabling the study of major mixing parameters such as mixing length, and EGR introduction angle.The mixing flow field showed a strong dependence on EGR-to-air momentum ratio, significantly affecting the EGR uniformity and axial velocity uniformity. Furthermore, multiscale stream-wise vortices were generated in the mixing section, with an intensity that increased with momentum ratio, and decreased with mixing length. In addition, by eccentric LP-EGR introduction a bulk swirl was generated in the mixing section similar to the flow field obtained using an intake guide vane.A decrease in compressor efficiency with LP-EGR introduction, compared to baseline compressor map, was observed. The efficiency degradation was larger at higher EGR momentum ratios and flow rates. In the range of mixing lengths limited by engine packaging, up to length-to-diameter ratio (L/D) = 2.5, the flow perturbations were not damped, and a decline in both compressor pressure ratio and efficiency was observed. Efficiency degradation mechanism is found to be the formation of strong vortices in the mixing zone upstream of the compressor, which are advected to the compressor impeller inlet and perturb the local incidence angle. In contrast, the EGR and axial velocity non-uniformities did not show a negative impact on the compressor.This study identifies the major flow parameters that cause significant degradation of compressor performance, and proposes a figure of merit for design of efficient LP-EGR mixers to benefit from the fuel economy advantages of LP-EGR architecture in diesel and gasoline direct injection engines.

Fingerprint Macula Artifact on Optos Fundus Imaging in Nystagmus

A fingerprint appearance to the macula was observed in both eyes of a patient with foveal hypoplasia and pendular horizontal nystagmus imaged with the Optos California (Marlborough, MA) fundus camera. (A, B) Examination under anesthesia with Natus Retcam 3 (San Carlo, CA) color fundus photography (C) and Bioptigen Envisu C2300 (Buffalo Grove, IL) portable spectral-domain OCT (D) confirmed these to be artifactual. The Optos camera utilizes sweeping red and green lasers and multi-element optics with nonlinear surfaces resulting in nonuniform scan velocities slowest across the fovea.

Experimental Studies on the Distribution of Air Flows in Air Cooled Steam Condensers

The uniformity degree of the air distribution over the heat-exchange surface of an air cooled condenser (ACC) plays an important role since it determines the efficiency of this surface’s usage. In this paper, this factor at a special stand, where all the main processes of an air flow were simulated, is studied. The typical design of the A-framed ACC was chosen as the basis for the study. Two ACC models differing from one another by the presence of a diffuser after the fan were studied. Each of the models was tested in two versions: with a low-speed electric motor and a high-speed electric motor with a gearbox. In the ACC models, heat transfer surfaces were simulated by a set of flat metal grids with a uniform distribution of square cells. The aerodynamic drag of a set of grids was preliminarily selected so that the Euler criteria were equal for the full-scale object and model. During the tests, the air velocities in front of and behind the grids were measured by traversing, and the velocity fields (isotachs) of the cooling air in these sections were plotted. A condenser with a low-speed electric motor provides the most uniform distribution of cooling air over the heat-exchange surface, while condensers with a high-speed electric motor and gearbox and with a diffuser have significantly greater nonuniformity in the air supply. During the “suction” operation, the flow distribution is more uniform but worse than that for the version with a low-speed electric motor. The effect of the nonuniform velocity field of cooling air on the heat transfer of ACC is estimated. The real condenser module was calculated for various flow and velocity distributions along the tube length. Losses of heat removal due to the nonuniformity of the air flow of the considered circuits can be estimated within 1–3% at a ±50% deviation of the flow rate from the average value.

An analytical correction to Amiet’s solution of airfoil leading-edge noise in non-uniform mean flows

Gust/turbulence–leading edge interaction is a significant source of airfoil broadband noise. An approach often used to predict the sound is based on Amiet’s flat-plate solution. Analytical studies have been conducted to investigate the influences of airfoil geometries, non-uniform mean flows and turbulence statistics, which, however, were often too convoluted. In this work, the problem is revisited by proposing simple corrections to the standard flat-plate solution to account for the effect of non-uniform mean flows of real airfoils. A key step in the method is to use a new space–time transformation that is analogous to the Prandtl–Glauert transformation to simplify the sound governing equation with spatially varying coefficients to a classical wave equation, which is then solved using the Schwarzschild technique as in Amiet’s solution. The impacts of Mach number, wavenumber and airfoil geometry on the prediction accuracy are investigated for both single-frequency and broadband cases, and the results are compared against high-fidelity simulations. It predicts the sound reduction by the airfoil thickness, and reveals that the reduction is caused by the non-uniform streamwise velocity. The limitations of the model are discussed and the approximation errors are estimated. In general, the prediction error increases with the airfoil thickness, the sound frequency and the flow Mach number. Nevertheless, in all cases studied in this work, the proposed correction can effectively improve the prediction accuracy of the flat-plate solution much more efficiently compared to numerical solutions of the Euler equations using computational aeroacoustics.

Models of dynamics of contamination propagation in surface waters using simulation of hydrodynamical processes of different level of complexity

This paper uses the ideology of solving hyperbolic equations using the Euler balance-characteristic approach, which allows economically and correctly resolving the dynamics of pollution propagation processes with large concentration gradients characteristic of an accident. The purpose of the study is to develop a three-dimensional model of advectiondiffusion in a non-uniform velocity field and non-isotropic field of turbulent diffusion, taking into account some physical processes: gravity sedimentation, sediment accumulation and their dynamics. As well as the implementation of the interaction model with the hydrodynamic module, based on solving the equations of the theory of shallow water in the approximation of Saint-Venant.