Flow Velocity Vector Research Articles

Numerical investigation of the flow characteristics around two tandem propane fires in a windy environment

Investigation of wind-blown fires is highly applicable to fire safety of scenarios associated with burning industrial fuel tanks in wind and wildland fires. This paper conducts a numerical study on the flow characteristics around two propane fire sources in the tandem arrangement under cross wind. The heat release rate, cross wind velocity and fuel source spacing were changed. The results showed that in still air, as the fuel source spacing increases, the flame interaction gradually weakens. The corresponding shapes of flow velocity vector field experience three stages: a whole circular shape, two interacting circular shapes, and two separate circular shapes. As for the wind conditions, in the span wise direction, due to the impact of Rayleigh-Taylor instability, the counter-rotating vortex pair can be generated at the downstream of the fire sources. Under the influences of the counter-rotating vortex pair and blockage effect, a wake regime through flow entrainment is formed, which can reduce the longitudinal air flow velocity along the downstream centerline of fire sources. In the vertical direction, under the impact of fire-wind enhancement, the local flow velocity there can exceed free stream velocity. When the velocity is relatively small, there will be a reverse flow region around the downstream fire source. In addition, the blockage effect shows a non-monotonous trend with the increase of wind velocity.

Computation of free surface waves in coastal waters with SWASH on unstructured grids

This paper aims to present the extension of the non-hydrostatic wave-flow model SWASH with the covolume method to build discretization schemes on unstructured triangular grids. Central to this method that is free of spurious pressure modes, is the use of dual pairs of meshes that are mutually orthogonal, such as the Delaunay-Voronoi mesh systems. The approximants sought are the components of the flow velocity vector normal to the cell faces of the primal mesh. In addition to the covolume approach, a novel upwind difference scheme for the horizontal advection terms in the momentum equation is proposed. This scheme obeys the Rankine-Hugoniot jump relations and prevents the odd-even decoupling of the velocity field accordingly. Moreover, cases with flow discontinuities, such as steady bores and broken waves, are properly treated. In spite of the low-order accuracy of the proposed method, unstructured meshes easily allow for local refinement in a way that retains the desired accuracy. The unstructured-grid version of SWASH is applicable to a wide range of 2DH wave-flow problems to investigate the nonlinear dynamics of free surface waves over varying bathymetries. Its efficiency and robustness is tested on a number of these problems employing unstructured triangular meshes.

Numerical simulation of lubrication performance on chevron textured surface under hydrodynamic lubrication

The numerical simulations were performed to investigate the lubrication performance on the chevron textured surface under hydrodynamic lubrication. The geometric parameters of the texture were systematically studied. Additionally, we investigated the pressure distribution and the flow velocity vectors to explore the mechanism of the geometric parameters influencing the lubrication performance. We found that, with the same geometric parameters, the arrangement of the chevron textures influences the pressure distribution and thus the load carrying capacity and the friction coefficient. More importantly, we designed the V-shape arrangement of chevron textures and found that the V-shape arrangement greatly improve the lubrication performance. Our results provide an effective way to further improve the lubrication performance of the chevron textured surface.

Flow processes and sedimentation in a straight submarine channel on the Qiongdongnan margin, northwestern South China Sea

ABSTRACT Straight channels are ubiquitous in deep-water settings, yet flow dynamics and sedimentation in them are far from being well understood. Stratigraphy and flow dynamics of a middle to late Miocene straight channel in Qiongdongnan Basin were quantified, in terms of angle of channel-complex-growth trajectories (Tc), stratigraphic mobility number (M), Froude number (Fr), layer-averaged flow velocity (U), flow thickness (h), and water entrainment coefficient (Ew). The documented channels are composed of three channel complexes (CC1 to CC3) all of which are all characterized by symmetrical channel cross sections without levees and by organized vertical channel-stacking patterns (represented by high mean value of Tc = 37.4° and low mean value of M = 0.038). Turbidity currents in them were estimated to have U of 1.6 to 2.0 m/s (averaging 1.8 m/s), h of 63 to 89 m (averaging 78), Fr of 0.849 to 0.999 (averaging 0.912), and Ew of 0.0003 to 0.0005. They were, in most case, subcritical over most of the channel length, and had a low degree of water entrainment and low flow height scaled to the channel depth (i.e., 0.786 to 0.81 of the channel depth), most likely inhibiting the gradual loss of sediment to form levees. With reference to modeling results of secondary flow velocity vectors of numerical straight channels with the same sinuosity, two parallel gullies seen on both sides of the interpreted channel beds are interpreted to be induced by high-velocity downward backflows produced by the negative buoyancy. Such symmetrical secondary flow structures most likely promoted symmetrical intrachannel deposition (i.e., less deposition along both channel margins but more deposition near the channel center), and thus forced individual channel complexes to progressively aggrade in a synchronous manner, forming straight-channel complexes with symmetrical channel cross sections and organized vertical channel-stacking patterns.

A discontinuous Galerkin method for mathematical simulating of gas-liquid mixture flows

We present mathematical simulating results of a gas-liquid mixture flow in a cylindrical pipe. The gas-liquid mixture consists of the mineralized water and propane gas. To analyze the mineral composition of the fluid, a sensor is mounted in the pipe. The sensor affects the topology of the flow velocity vector field. The gas-liquid mixture flow is described by the unsteady Navier-Stokes equations. When the flow rate of gas-liquid mixtures exceeds 20 m/s, eddy flows occur in the pipe with obstacles. A method of discretization should take into account the problem specifics: rapidly changing gradients, the prevalence of the convective term in the Navier-Stokes equations. A computational scheme of discontinuous Galerkin method has the local conservative property and is best suited for solving such singularly perturbed problems. To perform a spatial discretization, a computational scheme of the discontinuous Galerkin method in the function spaces H(div) and L 2 is used. Application of the multiscale approach allows breaking down the solution of the simulation problem into several smaller ones that can be solved using parallel computations. Mathematical modeling results of the gas-liquid mixture flow in the pipe with different options for the sensor location are presented.

Development and Research of the MZU­20D Air­Sieve Grain Cleaning Machine

The authors analyzed the working process and design of the machines involved in grain cleaning. It was revealed that the energy intensity of universal air-sieve machines of domestic and foreign production is 0.86-1.61 kilowatt-hours per ton, the specific metal consumption is 30-700 kilogram-hours per ton. ( Research purpose ) To develop a high-performance primary-secondary grain cleaning machine with low energy intensity, a high degree of purification of seed and food grain, as well as with the possibility of its installation in continuous grain cleaning and drying lines and complexes. ( Materials and methods ) The authors created a new structural and technological scheme of the universal grain cleaning machine MZU-20D and its pneumatic system. A prototype was produced with a capacity of 20 tons per hour, with three pneumatic separating channels and three sedimentary chambers of the pneumatic system. They investigated the dust collector of the air system of the MZU-20D machine. ( Results and discussion ) Using the finite element method, the calculated values and velocity vectors of the air flow at the nodal points of the dust collector cross-section were obtained. The louvered sieve with a porosity of 0.1 was installed at an angle of 30 degrees, in the presence of a dividing partition. The authors optimized the structural and technological parameters according to the three-level Boxing-Bencina matrix plan. Based on the results of the plan’s implementation, rational design parameters of the dust collector were chosen: the depth of the outlet pipe – 0.35 meters, the angle of blinds installation – 30 degrees, the blinds number – 8. It was determined that when the dust collector parameters were brought into line with the above values, the efficiency of the deposition of impurities in it reached 60 percent with hydraulic resistance of 260 pascals. During state tests of the MZU-20D machine at the SPK Rassvet in the Kirov region for cleaning rye grains of the Falenskaya variety, the following characteristics were confirmed: throughput – up to 20 tons per hour, installed capacity – 9 kilowatt, grain purity – at least 98 percent. ( Conclusions ) It was established that the machine was efficient, performed the technological process qualitatively and could be used, for example, during reconstruction and development of new grain cleaning and drying lines and complexes.

Simulation Studies on Centrifugal MQL-CCA Method of Applying Coolant during Internal Cylindrical Grinding Process.

This paper describes simulation studies regarding the application of the centrifugal minimum quantity lubrication (MQL) method simultaneously with the delivery of a compressed cooled air (CCA) stream in the internal cylindrical grinding process. The idea of a new hybrid cooling and lubrication method connecting centrifugal (through a grinding wheel) lubrication by MQL with a CCA stream is described. The methodology of computational fluid dynamics (CFD) simulation studies, as well as the results of numerical simulations, are presented in detail. The aim of the simulations was to determine the most favourable geometrical and kinematic parameters of the system in the context of air-oil aerosol and CCA flow, as well as heat exchange. In the simulation, the variables were the grinding arbor geometrical parameters, the angle of CCA supply line outlets, and the grinding wheel and workpiece peripheral speed. As a result of the simulation studies, the most favourable geometrical parameters were designated, determining the orientation of the ends of the two CCA supply line outlets before and after the grinding zone, the number of openings in the drilled-out grinding arbor, and the influence of the grinding speed on the parameters of the coolant flow and temperature of objects in the grinding zone. In addition, the results of simulation tests made it possible to visualise the velocity vectors of the two-phase coolant flow in a complex system of air-oil aerosol delivery centrifugally through an open structure of a very fast rotating porous layer (grinding wheel), with an additional supply of CCA using an external cold air gun (CAG).

Influence of multisource fire on temperature distribution and natural smoke exhaust effect in urban tunnels with a shaft

SummaryThe combustion characteristics of multisource fire and single‐source fire are quite different, and there is little research on the influence of multisource fire on the natural smoke extraction effect of shaft in urban tunnels. Therefore, in this article, the method of numerical simulation was used to study the influence of fire power and distance between two fire sources on the natural smoke extraction effect of shaft and the temperature distribution in tunnel in the case of multisource fire. Typical characteristics of smoke are analyzed, such as mass flow rate, temperature distribution, velocity vector, and CO concentration. The simulation results show that when there is a certain distance between the fire sources, the two flames are inclined and close to each other. The smoke temperature under the ceiling is higher under multiple fire sources than that under single fire source. In addition, when one of the fire sources is located at the downstream of the shaft, the smoke emission in the shaft is relatively high. As the distance between fire sources continues to increase, the smoke exhaust rate basically remains stable, and an empirical relationship between smoke exhaust rate and fire source location is established.

Predicting behaviour of the Indus basin aquifer susceptible to degraded environment in the Punjab province, Pakistan

Rapid changes in the irrigated system due to climate change and drastic growth in urbanization and industrialization have raised serious concerns related to available groundwater resources of the Indus basin on which millions of people depend upon for their sustenance. Under the prevailing scenario, three-dimensional numerical groundwater flow model Visual MODFLOW has been used to evaluate the regional groundwater flow from the steady-state period of 1987 (used as a base to run the model for several simulation periods) up to the predictive period of 2030 for sustainable water resource management in the Indus plain of Pakistan. The steady-state calibration of the model indicated a close agreement between the simulated and the observed heads as indicative from the residual mean value of 0.10 m and an absolute residual mean of 0.47 m. The velocity vectors of the groundwater flow indicate that in most parts of the study area groundwater is discharged into the Jhelum and Chenab rivers. In the transient-state condition, groundwater levels indicated a rising trend till 1989, but as the irrigated area tends to increase continuously, the heads started to drop from year 1991 onward at an average rate of 0.45 m/year. The Bari Doab in the south appears to be more under stress than the Rechna and the Lower Chaj Doabs because of the overexploitation of groundwater, low flows in the Ravi River and less recharge from rainfall. The negative impacts of environment changes on the underlying aquifer could be minimized through long-term monitoring of the groundwater system and adoption of integrated water resource management approach in future.

Simulation of Transient On-Road Conditions in a Closed Test Section Wind Tunnel Using a Wing System with Active Flaps

<div class="section abstract"><div class="htmlview paragraph">Typical automotive research in wind tunnels is conducted under idealized, stationary, low turbulence flow conditions. This does not necessarily reflect the actual situation in traffic. Thus, there is a considerable interest to simulate the actual flow conditions. Because of this, a system for the simulation of the turbulence intensity I, the integral linear scale L and the transient angle of incidence β measured in full-scale tests in the inflow of a test vehicle was developed and installed in a closed-loop, closed test section wind tunnel. The system consists of four airfoils with movable flaps and is installed in the beginning of the test section. Time-series of the flow velocity vector are measured in the empty test section to analyze the system’s envelope in terms of the turbulence intensity and the integral length scales. It is shown that the length scales in spanwise and in driving (streamwise) direction can be varied from 0.15 m to 7.9 m and from 0.15 m to 2.5 m, respectively, depending on the frequency of the flap movement. The maximum obtained turbulence intensity in the driving direction x is 3% and in the spanwise direction y 9.8%, depending on the flap’s amplitude. It is further shown that the turbulence intensity in driving direction can be increased to 5.6% with passive turbulence generators. Additionally, a model for predicting the flap movement reproducing the transient angle of incidence β measured in the on-road tests during an overtaking maneuver was developed. Measurements of the forces acting on the vehicle revealed an influence of the non-stationary flow on the non-stationary force coefficients. Finally, changes of up to 0.002 in Δc<sub>d</sub> and 0.157 in Δc<sub>s</sub> were measured.</div></div>

Ячеистая модель фильтрования при очистке горюче-смазочных материалов от механических примесей

The paper describes a cellular model of fuel and lubricants cleaning developed by using a filtering material with a complex structure of cells with cylindrical and spherical collectors. It was offered to carry out the correction of moving dirty particles in cells of a filtering material subject to deviations of trajectories of insoluble particles under the external forces concerning trajectory of the dispersive medium in a cell. The constrained motion of polydisperse particles (subject to parietal effects) under perturbed flow of cylindrical and spherical collectors by the dispersion medium has been considered. Modeling efficient purification of motor fuels and oils from mechanical impurities has been carried out with a complex account of the main mechanisms of dispersion phase elimination during filtration. There has been given a diagram of the cellular filtration model with the radii of the filter cell (shell) and collector, the radial coordinates of the particle position, the angular coordinates of the particle position and the boundary screening path, the direction of gravity (acceleration), the velocity vectors of the incoming flow and a particle, the vectors of the radial and tangential velocity. According to the results of solving the differential equation by numerical methods, the boundary trajectory was constructed and the fractional dropout coefficient was found. The results of a computational experiment are illustrated. It has been inferred that considering the deviation when calculating the resistance against the particle motion using Stokes method reduces the filterability of the dispersed phase due to the proximity of the collector. The complexity of numerical methods for implementing a cellular stochastic filtering model based on the finite difference method is noted. It is recommended to consider various mechanisms of restraining the insoluble impurities in the interaction

Numerical Simulation of Flow Around a Cylinder based on Fluent

In this paper, the fluid flow around a cylinder is taken as an example to study the different characteristics of fluid flow. Gambit is used to build a 2D model of the watershed and its cylinders, and divide the mesh and define the boundaries. The flow model was constructed with Fluent, the steady-state flow in this flow state is simulated and calculated. And draw the velocity vector of the steady flow of the fluid, use the velocity vector to clearly show the double vortex behind the cylinder. Finally, through Carmen vortex street flow simulation and other parameters, the single vortex frequency is calculated and compared with the single vortex frequency calculated by Fluent to verify the correctness of Fluent’s calculation.

Singular value decomposition filtering in high-frame-rate cardiac vector flow imaging

Dysfunction of the left ventricle (LV) weakens the cardiac function and affects the physical activity. Echocardiagraphy has been used to visualize the blood flow dynamics and to evaluate the cardiac function. However, the signal processing to suppress the clutter signals should be employed. In this study, we employed the singular value decomposition (SVD) clutter filtering to obtain the cardiac blood speckle images. We also employed the adaptive thresholding metric to determine the proper cutoff values at each phase during the cardiac cycle. Moreover, we employed a depth-dependent SVD clutter filter for more accurate estimation of the cardiac blood echo signals. The 2D blood flow velocity vectors were estimated by applying the block matching method to obtained blood speckle images. The obtained results show that the proposed filter suppressed the clutter signals from left ventricular wall significantly, and the contrast-to-noise ratio (CNR) was improved from -0.5 dB to 13.8 dB by the proposed SVD clutter filtering.

Experimental study on two-dimensional cross-flow impeller with a minimal splitter plate instead of casings

In the present study, the authors investigate the simplest model of cross-flow impellers, in order to provide the fundamental flow features of cross-flow impellers. The model is a two-dimensional cross-flow impeller with a very-high aspect ratio, and rotates in stationary fluid. More strictly, we occasionally place a splitter plate with minimal influence instead of casings for more precise observations and measurements. Instantaneous measurements of flow-velocity vectors on the mid-span plane are conducted using a CCD camera and a double-pulse YAG laser with a particle-image-velocimetry technique, in addition to conventional flow visualisations and hot-wire-velocimetry measurements. As a result, the authors show the revolutional motion of such an eccentric vortex as a large-scale re-circulating flow structure inside the cross-flow impeller, and reveal the detail of flow features at Reynolds number Re = 300-2500. Furthermore, the authors show the relations between Re and out-flow rate from the impeller.

Biomechanical patient-oriented analysis of influence of the aneurysm on the hemodynamics of the thoracic aorta

The aim of the study was biomechanical modeling of the development and influence of thoracic aortic aneurysm on the hemodynamics of the vessel. Aortic aneurysm is an irreversible expansion of the aorta and is one of the diseases of the cardiovascular system with a high fatal outcome. Biomechanical modeling included: setting the task, building a virtual model of the object under study, setting boundary and initial conditions and properties of materials, also assessment the results of a numerical experiment based on the physiological characteristics of the object. Two three-dimensional virtual models of the thoracic aorta were constructed on the basis of computed tomographic angiography of a real patient: with an aneurysm of the ascending division and after prosthetics. To analyze the development of pathology, were created additional virtual models with different degrees of aneurismal expansion. The calculation is carried out taking into account the parameters characterizing the work of the cardiovascular system (blood pressure value, dynamic viscosity and blood density). The analysis of the results showed a change in the character of blood flow, the formation of region of blood stagnation in the aneurysm zone. It was revealed that with the increase in the geometric dimensions of the pathology there is a drop in the blood flow rate and an increase in the flow pressure values in the aneurysm. Asymmetric distribution of pressure values on the inner surface of the aorta, triggered by the displacement of the flow velocity vector relative to the axis of the blood vessel, can to incite further development of an aneurysm.

Modelling and validation of fluid flow inside a dissipative ladle shroud and a continuous casting tundish

Fluid flow plays a significant role in the continuous casting of molten steel. In this paper, two Reynolds Averaged Naiver-Stokes (RANS) models and a Large Eddy Simulation (LES) model were comparatively employed to characterize the fluid flow inside a dissipative ladle shroud and a tundish. LES model was proved to be powerful to characterize the turbulence structure inside the ladle shroud. The effect of meshing density on the computational accuracy was considered using the LES model. The fine-mesh model can capture multiscale vortices inside the ladle shroud; while, the coarse-mesh model disables the LES to obtain the detailed flow information. The experiment of particle image velocimetry (PIV) was used to verify the flow field obtained by the LES model inside the tundish. The PIV and the LES results agree well in terms of flow pattern and velocity vector.

A particle-based model for endothelial cell migration under flow conditions

Endothelial cells (ECs) play a major role in the healing process following angioplasty to inhibit excessive neointima. This makes the process of EC healing after injury, in particular EC migration in a stented vessel, important for recovery of normal vessel function. In that context, we present a novel particle-based model of EC migration and validate it against in vitro experimental data. We have developed a particle-based model of EC migration under flow conditions in an in vitro vessel with obstacles. Cell movement in the model is a combination of random walks and directed movement along the local flow velocity vector. For model calibration, a set of experimental data for cell migration in a similarly shaped channel has been used. We have calibrated the model for a baseline case of a channel with no obstacles and then applied it to the case of a channel with ridges on the bottom surface, representative of stent strut geometry. We were able to closely reproduce the cell migration speed and angular distribution of their movement relative to the flow direction reported in vitro. The model also reproduces qualitative aspects of EC migration, such as entrapment of cells downstream from the flow-disturbing ridge. The model has the potential, after more extensive in vitro validation, to study the effect of variation in strut spacing and shape, through modification of the local flow, on EC migration. The results of this study support the hypothesis that EC migration is strongly affected by the direction and magnitude of local wall shear stress.

Impact of velocity gradient in Poiseuille flow on the statistics of coherent radiation scattered by flowing Brownian particles in optical coherence tomography.

.A closed-form expression is obtained for the temporal correlation function of the scattered radiation detected in optical coherence tomography (OCT), taking into account the flow velocity gradient across the OCT detection volume in the suspension of flowing Brownian particles. The analytical approach we use includes both the laser beam and wavefront curvature radii changing over the depth. Also, we compare our results with a previously obtained theoretical model, partially an empirical approach. Our findings suggest the importance of the flow velocity gradient for accurate measurements of flow velocity vector, particle diffusivity, shear-induced diffusion, and potentially other OCT applications.

A numerical study on the effects of naturally ventilated shaft and fire locations in urban tunnels

SummaryIn more and more tunnels, natural ventilation mode with vertical shafts has been gradually employed. However, there are few studies investigating the influences of fire and shaft positions on natural ventilation performance currently. Therefore, this study investigated the effects of the transverse distance from fire source to tunnel sidewall, the longitudinal distance from fire source to shaft, and the transverse distance from shaft to sidewall on natural ventilation effectiveness in a tunnel fire by using Fire Dynamics Simulator. The typical characteristic parameters of smoke, such as mass flow rate, temperature distribution, and velocity vector were analyzed; besides, the phenomenon of plug‐holing was discussed. The results have shown that the mass flow rate of gas exhausted by the shaft decreases slightly with the increase of longitudinal distance from fire source to shaft. When the longitudinal distance from fire source to shaft is constant, changing the transverse distance from shaft to sidewall will have a more obvious effect on the effectiveness of exhausting smoke than changing the transverse distance from fire source to sidewall; in addition, the phenomenon of plug‐holing is more serious when the shaft is close to the sidewall.

A Simple Method to Improve Smoke Exhaust Effectiveness of a Shallow-buried Urban Tunnel Fire with Natural Ventilation

ABSTRACT In order to improve the natural ventilation performance of a shallow-buried urban tunnel under the influence of external wind blowing above the shaft, a new method with installing a jet fan downstream of the shaft was proposed and a set of simulations were conducted to validate its effectiveness. The detailed smoke spread characteristics, such as mass flow rate, temperature, and velocity vector, were analyzed together with varying the ambient wind speed above the shaft, the longitudinal wind speed in the tunnel, and the velocity of the jet fan. Results show that under the coupled push effect of the longitudinal wind upstream of the fire and the airflow of jet fan downstream of the shaft, the block effect of the strong ambient wind on the vertical flow of smoke through the shaft can be overcome completely. In the tunnel, almost all the fire-induced smoke is confined between the fire and the shaft, and smoke can only be exhausted from the shaft. The findings can be a reference for tunnel ventilation design.