Flow Velocity Vector Research Articles

Studying the coupled axial and lateral oscillations of the drilling riser under conditions of irregular seaways

Construction of an improved mathematical model of the axial and lateral oscillations of the in the plane of action of the velocity vectors of the fluid flow washing the was considered. This model makes it possible to study the stress-strain state of the with simultaneous impact on it from the sea and the change in the force of tensioning its upper end. In addition, the model specifies the force effect exerted on the by the washing fluid flowing in it.Based on the developed mathematical model, a simulation model of operation of the drilling ship – rope-type tensioning system of the – riser system was created in the Modelica modeling language and a series of numerical experiments were performed at various levels of seaways. The obtained results show that the proposed model produces 22‒40% higher calculated values of the amplitude of lateral oscillations and 10‒25 % higher calculated values of the bending moments in critical sections compared with the results of the classical model of lateral oscillations. The greatest difference between the simulation results was observed with moderate seaways. With a growth of seaways, the difference between the two models decreases. Proceeding from the obtained results, it is not recommended to neglect the effect of variation in time of the forces tensioning the in applied problems of studying operation in conditions of slight sea.

A novel 4-sensor fast-response aerodynamic probe for non-isotropic turbulence measurement in turbomachinery flows

AbstractIn modern computational studies for turbomachinery applications, time, length scales and isotropy of turbulent structures are important for representative modelling. To this end, experimental data are essential to validate the numerical tools. The current article presents the development and application of a newly designed 4-sensor Fast Response Aerodynamic Probe (FRAP-4S) enabling time-resolved measurement of the three-dimensional unsteady flow velocity vector in turbomachines. The miniature multi-sensor probe demonstrates a 4 mm probe-tip. In the first part of this article the design, manufacturing and calibration results of the FRAP-4S are presented in detail. To assess the newly developed probe accuracy, comparison against traditional instrumentation developed at the Laboratory for Energy Conversion is also provided. In the second part of this work, measurements are performed at the rotor exit of a one-and-a-half stage, unshrouded and highly-loaded axial turbine configuration. The results showed increased level of unsteadiness and turbulence levels with peak-to-peak fluctuation from 5 to 35%. More importantly, in some regions stream-wise unsteadiness was found to be ten times higher, compared to the cross-wise components, an indication of the high degree of anisotropy.

Numerical Analysis on the Impact of Interstage Flow Addition in a High-Pressure Steam Turbine

This study analyzes the fluid dynamic characteristics of an ultrasupercritical (USC) high-pressure turbine with additional steam supplied through an overload valve between the second and third stages. The mixing between the main and admission flows causes complex flow phenomena such as swirl and changes of velocity vectors of the main flow. This causes a pressure drop between the second-stage outlet and third-stage inlet, which could potentially affect the performance of the turbine. First, a single-passage computational analysis, which is usually preferred in predicting the performance of multistage turbomachines, was performed using a simple model of an admission flow path and a single passage (SP) for the second and third stages of the turbine. However, the actual flow in the overload valve is supplied through the admission flow path, which has the shape of a casing that circumferentially surrounds the turbine, after flowing in two directions perpendicular to the turbine axis. This necessitates full-passage computational analyses of the two stages and the flow paths of the admission flow. To achieve this, we implemented a full three-dimensional (3D) geometric model of the admission flow path and conducted a full-passage computational analysis for all the flow paths, including those of the second and third stages of the turbine. The focus of analysis was on the pressure drop due to the admission flow. The results of the single and full-passage analyses were compared, and the effects of two different methods were analyzed.

Flushing Velocity Observations and Analysis during EDM Drilling

Insufficient flushing is the greatest limitation factor for material removal rate (MRR) in electrical discharge machining (EDM). In order to increase the flushing efficiency during erosion and thus to increase MRR, better understanding of the dielectric distributions and flow directions is required. Additionally the discharge development and its influence to the fluid flow and flushing efficiency must be taken into account. The dielectric flow trajectory can be tracked by high speed imaging with an auxiliary magnification lens. Consequently, flow velocity vectors, bubble development and movement can be analyzed. The flushing behavior is observed with particle tracking velocimetry (PTV), the corresponding data from the measurements are used to compare and validate the computational fluid dynamics (CFD) simulations. This paper describes a setup for high speed imaging in micro meter scale of a common EDM drilling process using electrode with multi-hole flushing. The analysis of the erosion process is performed within two conditions: first, the initial contact of the electrode with the material surface and second, erosion inside a predrilled hole. It is concluded that those two described conditions have a high influence to the flushing and therefore to the MRR, whereas the flushing efficiency drops by an increase of the drilling depth.

Sediment Transport of Fine Sand to Fine Gravel on Transverse Bed Slopes in Rotating Annular Flume Experiments

AbstractLarge‐scale morphology, in particular meander bend depth, bar dimensions, and bifurcation dynamics, are greatly affected by the deflection of sediment transport on transverse bed slopes due to gravity and by secondary flows. Overestimating the transverse bed slope effect in morphodynamic models leads to flattening of the morphology, while underestimating leads to unrealistically steep bars and banks and a higher braiding index downstream. However, existing transverse bed slope predictors are based on a small set of experiments with a minor range of flow conditions and sediment sizes, and in practice models are calibrated on measured morphology. The objective of this research is to experimentally quantify the transverse bed slope effect for a large range of near‐bed flow conditions with varying secondary flow intensity, sediment sizes (0.17–4 mm), sediment transport mode, and bed state to test existing predictors. We conducted over 200 experiments in a rotating annular flume with counterrotating floor, which allows control of the secondary flow intensity separate from the streamwise flow velocity. Flow velocity vectors were determined with a calibrated analytical model accounting for rough bed conditions. We isolated separate effects of all important parameters on the transverse slope. Resulting equilibrium transverse slopes show a clear trend with varying sediment mobilities and secondary flow intensities that deviate from known predictors depending on Shields number, and strongly depend on bed state and sediment transport mode. Fitted functions are provided for application in morphodynamic modeling.

Swirl Characteristics of Vortex Valve Variable-Thrust Solid Rocket Motor

In accordance with the flow characteristics of vortex valve variable-thrust solid rocket motors, a cold flow experimental system based on Particle Image Velocimetry was established. A flow velocity vector diagram of vortex chamber was generated, and the vortex structure was analyzed. The results provided an experimental foundation for numerical simulation. The flow characteristics in vortex chamber and in the throat and divergent sections of the nozzle were modeled and simulated. The flow in the vortex chamber conformed to the complex Rankine vortex, and the flow field was divided into three different zones. The vortex core was the primary influence factor for thrust modulation. The resultant velocity reached Mach number 1 before gas arrived at nozzle throat, and the axial velocity still reached Mach number 1 at nozzle throat. Hence, the axial velocity can be used to judge the occurrence of choking at the nozzle throat. The intensity of swirl flow in divergent section of the nozzle was evidently lower than that in vortex chamber and throat. As a result, a low-pressure zone emerged around the central axis, thereby causing thrust losses.

Hydrodynamic Influence Dabanhu River Bridge Holes Widening Based on Two-Dimensional Finite Element Numerical Model

In order to analyze the influence of bridge holes widening on hydrodynamic such as water level, a two-dimensional mathematical model was used to calculate the hydrodynamic factors, river network flow velocity vector distribution is given, water level and difference of bridge widening before and after is calculated and charted, water surface gradient in seven different river sections near the upper reaches of bridges is counted and revealed. The results of hydrodynamic calculation indicate that The Maximum and the minimum deducing numerical value of the water level after bridge widening is 0.028m, and 0.018m respective. the seven sections water surface gradient becomes smaller until it becomes negative, the influence of bridge widening on the upstream is basically over, the range of influence is about 450m from the bridge to the upstream. reach

The Seepage Simulation of Single Hole and Composite Gas Drainage Based on LB Method

Gas drainage is the most effective method to prevent and solve coal mine gas power disasters. It is very important to study the seepage flow law of gas in fissure coal gas. The LB method is a simplified computational model based on micro-scale, especially for the study of seepage problem. Based on fracture seepage mathematical model on the basis of single coal gas drainage, using the LB method during coal gas drainage of gas flow numerical simulation, this paper maps the single-hole drainage gas, symmetric slot and asymmetric slot, the different width of the slot combined drainage area gas flow under working condition of gas cloud of gas pressure, flow path diagram and flow velocity vector diagram, and analyses the influence on gas seepage field under various working conditions, and also discusses effective drainage method of the center hole slot on both sides, and preliminary exploration that is related to the combination of gas drainage has been carried on as well.

Effect of lower convective zone thickness and swirl flow on the performance of a salinity gradient solar pond

Solar ponds collect solar radiation and store it in the form of thermal energy over a period of time. The performance of a solar pond depends upon the performance of the heat exchange process. In this study, a laboratory model solar pond was fabricated and provided with an in-pond heat exchanger. To perform the computational study the lower convective zone (LCZ) of the solar pond alone was modelled using ANSYS Design Modeler. The analysis was carried out on the plain tube in-pond heat exchanger of the solar pond for different heights of LCZ for two different flow rates of heat transfer fluid. The performance parameters such as outlet water temperature, rate of heat transfer, effectiveness of heat exchanger, and pressure drop were analysed. The rate of heat transfer, pressure drop, Nusselt number and effectiveness of heat exchanger are evaluated by changing the velocity vectors of the fluid flow at the entrance of the in-pond heat exchanger. The rate of heat transfer is found to be higher for turbulent flow than laminar flow for different temperatures of LCZ.

Measurement of the absolute velocity of blood flow in early-stage chick embryos using spectral domain optical coherence tomography.

Doppler optical coherence tomography (OCT) is a noninvasive imaging modality that provides quantitative flow information with high spatial and temporal resolution. However, it is only sensitive to the flow velocity vector parallel to the incident beam. To calculate the absolute velocity, it is necessary to obtain the angle between the incident beam and flow field. In this paper, we describe a practical method to measure the Doppler angle based on the structural information of blood vessels extracted from spectral domain OCT images. In this method, a normal sectional scan of the vessel is performed where the probe beam is perpendicular to the vessel. Next, the axial diameter (Z direction) of the vessel (DA) was measured in the acquired image. For a certain scan in which the probe beam is oblique to the blood vessel, the axial diameter of the vessel (DA') can be measured. Thus, the Doppler angle can be calculated depending on the ratio of DA and DA', and absolute blood flow was determined. We validate this method in a capillary tube as well as in large blood vessels of early-stage chick embryos. This technique is suitable for early-stage embryo blood-flow measurement because most of the blood vessels are easily differentiated from the transparent surrounding structures during that time.

PARAMETERS EFFECTING FORCED VORTEX FORMATION IN BLADE PASSAGEWAY OF DYNAMIC AIR CLASSIFIER

<p>Air classification of particulate materials is a method of classifying particles into coarse and fine fractions based on their size, density, or shape. Performance of the rotor air classifier is affected by operating parameters which include the classifier rotor speed, air inlet velocity and material feed rate. Effects of operating and structural parameters on turbulent flow field patterns inside of a dynamic air classifier are investigated. Increasing the computing power, together with new turbulence models and<br />approaches, to simulate complex fully turbulent problems by solving Navier-Stokes equations allows studying and capturing smaller flow structures and properties more accurately. Velocity vector maps for varying operating parameters are studied by means of numerical simulations. The experimental section includes a visualization of flow patterns and velocity vector maps in the rotor region by the use of the particle image velocimetry (PIV). Results are compared and discussed.</p>

Comparison of Three Rotor Designs for Rubber Mixing Using Computational Fluid Dynamics

ABSTRACT In recent years, there has been an increasing demand for efficient mixers with high-quality mixing capabilities in the rubber product industry, with the focus of producing fuel-efficient tires. Depending on the functional characteristics of the tire and thus the compounding ingredients, different types of mixers can be used for the rubber mixing process. Hence, the choice of an appropriate mixer is critical in achieving the proper distribution and dispersion of fillers in rubber and a consistent product quality, as well as the attainment of high productivity. With the availability of high-performance computing resources and high-fidelity computational fluid dynamics tools over the last two decades, understanding the flow phenomena associated with complex rotor geometries such as the two- and four-wing rotors has become feasible. The objective of this article is to compare and investigate the flow and mixing dynamics of rubber compounds in partially filled mixing chambers stirred with three types of rotors: the two-wing, four-wing A, and four-wing B rotors. As part of this effort, all the 3D simulations are carried out with a 75% fill factor and a rotor speed of 20 rpm using a computational fluid dynamics (CFD) code. Mass flow patterns, velocity vectors, particle trajectories, and other mixing statistics, such as cluster distribution index and length of stretch, are presented here. All the results showed consistently that the four-wing A rotor was superior in terms of dispersive and distributive mixing characteristics compared with the other rotors. The results also helped to understand the mixing process and material movement, thereby generating information that could potentially improve productivity and efficiency in the tire manufacturing process.

The particular use of PIV methods for the modelling of heat and hydrophysical processes in the nuclear power plants

In this paper we describe PIV-system specially designed for the study of the hydrophysical processes in large-scale benchmark setup of promising fast reactor. The system allows the PIV-measurements for the conditions of complicated configuration of the reactor benchmark, reflections and distortions section of the laser sheet, blackout, in the closed volume. The use of filtering techniques and method of masks images enabled us to reduce the number of incorrect measurement of flow velocity vectors by an order. The method of conversion of image coordinates and velocity field in the reference model of the reactor using a virtual 3D simulation targets, without loss of accuracy in comparison with a method of using physical objects in filming area was released. The results of measurements of velocity fields in various modes, both stationary (workers), as well as in non-stationary (emergency).

Capabilities of optical SIV technique in measurements of flow velocity vector field dynamics

The main difference between Smoke Image Velocimetry (SIV) technique and the conventional PIV is that higher concentration of tracer particles typical of smoke visualization techniques is used in SIV. Not separate particles but smoke structures with continuous pixel intensity are visible in the recorded images. Owing to better smoke reflectivity, higher spatial and temporal resolution is obtained in the case when relatively simple equipment (camera and laser) is used. It is simple enough to perform SIV measurements of velocity vector field dynamics at the frequency exceeding 15000 Hz, which offers new opportunities in unsteady flow examination. The paper describes fundamentals of SIV technique and gives some new results obtained using this method for the measurements that require high spatial and temporal resolution. The latter include frequency spectra of turbulent velocity fluctuations, turbulence dissipation profiles in the boundary layer and higher-order moments of velocity fluctuations. It has been shown that SIV technique considerably extends the potential of experimental studies of turbulence and flow structure in high-speed processes.

Rapid measurement of transversal flow velocity vector with high spatial resolution using speckle decorrelation optical coherence tomography.

We propose and demonstrate a novel method that uses only three sets of B-scans to accurately determine both the direction and the speed of a transversal flow using speckle decorrelation optical coherence tomography. Our tri-scan method has the advantages of high measurement speed, high spatial resolution, and insensitivity to the flow speed. By introducing error maps, we show that the flow angle inaccuracy can be minimized by choosing the measurement result with a lesser error between results obtained from the x- and y-scans. Finally, we demonstrate that the flow angle measurement accuracy can be further improved for the high-speed flows by increasing the speed of the x- and y-scans.

Identifying three-dimensional nested groundwater flow systems in a Tóthian basin

Abstract Nested groundwater flow systems have been revealed in Toth's theory as the structural property of basin-scale groundwater circulation but were only well known with two-dimensional (2D) profile models. The method of searching special streamlines across stagnation points for partitioning flow systems, which has been successfully applied in the 2D models, has never been implemented for three-dimensional (3D) Tothian basins because of the difficulty in solving the dual stream functions. Alternatively, a new method is developed to investigate 3D nested groundwater flow systems without determination of stagnation points. Connective indices are defined to quantify the connection between individual recharge and discharge zones along streamlines. Groundwater circulation cells (GWCCs) are identified according to the distribution of the connective indices and then grouped into local, intermediate and regional flow systems. This method requires existing solution of the flow velocity vector and is implemented via particle tracking technique. It is applied in a hypothetical 3D Tothian basin with an analytical solution of the flow field and in a real-world basin with a numerical modeling approach. Different spatial patterns of flow systems compared to 2D profile models are found. The outcrops boundaries of GWCCs on water table may significantly deviate from and are not parallel to the nearby water table divides. Topological network is proposed to represent the linked recharge–discharge zones through closed and open GWCCs. Sensitivity analysis indicates that the development of GWCCs depends on the basin geometry, hydraulic parameters and water table shape.

Numerical simulation on convective thermal loss of a cavity receiver in a solar tower power plant

A numerical simulation model is employed to evaluate the convective thermal loss of a one-point focusing central cavity receiver with a trapezoidal cross-section cubic structure in a solar tower power plant. Due to being laid at the top of the solar tower with a height of several decameters, the cavity receiver is suffering from low temperature and cold wind from its special ambient environment. Consequently, the effect of the natural convection on its thermal performance could not be neglected while the one of the turbulent flow field inside the cavity receiver entering from its aperture is comparably significant. Therefore, a three-dimensional turbulent flow model is established to calculate mixed convection heat loss which is usually used to evaluate the thermal performance. Under the certain wall temperature condition inside the receiver, the receiver laid inclination, the wind incidence angle and wind speed around the receiver are particularly considered in the proposed convection heat loss model. The simulation results show that the trend of mixed convection heat loss changing with the laid inclination is similar to that of natural convection when wind speed is relatively low. The maximum mixed convection heat loss happened in the case of wind direction α=90°, and minimum at α=0°. Under some certain windy condition, mixed convection heat loss may be lower than the natural convection value. In order to explain the variation of mixed convection heat loss, the profiles of flow velocity vector field and the temperature contours around the receiver are illustrated accordingly for each case. Furthermore, the flow pattern and turbulent vortex for the flow field are also presented. Finally, a heat transfer coefficient correlation considering receiver laid inclinations, wind speed and wind incidence angle was proposed to estimate the convection heat loss.

Validation of numerical simulation methods in aortic arch using 4D Flow MRI

Computational fluid dynamics (CFD) are the gold standard in studying blood flow dynamics. However, CFD results are dependent on the boundary conditions and the computation model. The purpose of this study was to validate CFD methods using comparison with actual measurements of the blood flow vector obtained with four-dimensional (4D) flow magnetic resonance imaging (MRI). 4D Flow MRI was performed on a healthy adult and a child with double-aortic arch. The aortic lumen was segmented to visualize the blood flow. The CFD analyses were performed for the same geometries based on three turbulent models: laminar, large eddy simulation (LES), and the renormalization group k–ε model (RNG k–ε). The flow-velocity vector components, namely the wall shear stress (WSS) and flow energy loss (EL), of the MRI and CFD results were compared. The flow rate of the MRI results was underestimated in small vessels, including the neck vessels. Spiral flow in the ascending aorta caused by the left ventricular twist was observed by MRI. Secondary flow distal to the aortic arch was well realized in both CFD and MRI. The average correlation coefficients of the velocity vector components of MRI and CFD for the child were the highest for the RNG k–ε model (0.530 in ascending aorta, 0.768 in the aortic arch, 0.584 in the descending aorta). The WSS and EL values of MRI were less than half of those of CFD, but the WSS distribution patterns were quite similar. The WSS and EL estimates were higher in RNG k–ε and LES than in the laminar model because of eddy viscosity. The CFD computation realized accurate flow distal to the aortic arch, and the WSS distribution was well simulated compared to actual measurement using 4D Flow MRI. However, the helical flow was not simulated in the ascending aorta. The accuracy was enhanced by using the turbulence model, and the RNG k–ε model showed the highest correlation with 4D Flow MRI.

The application of backpropagation neural network method to estimate the sediment loads

Nearly all formulations of conventional sediment load estimation method were developed based on a review of laboratory data or data field. This approach is generally limited by local so it is only suitable for a particular river typology. From previous studies, the amount of sediment load tends to be non-linear with respect to the hydraulic parameters and parameter that accompanies sediment. The dominant parameter is turbulence, whereas turbulence flow velocity vector direction of x, y and z. They were affected by water bodies in 3D morphology of the cross section of the vertical and horizontal. This study is conducted to address the non-linear nature of the hydraulic parameter data and sediment parameter against sediment load data by applying the artificial neural network (ANN) method. The method used is the backpropagation neural network (BPNN) schema. This scheme used for projecting the sediment load from the hydraulic parameter data and sediment parameters that used in the conventional estimation of sediment load. The results showed that the BPNN model performs reasonably well on the conventional calculation, indicated by the stability of correlation coefficient (R) and the mean square error (MSE).

A topological method for vortex identification in turbulent flows

We present a novel vortex identification method based on structured vorticity (ωs) of the direction field of flow (velocity vectors set to unit magnitude). As a direct measure of streamline curvature is insensitive to vortex strength, ωs is effective in detecting vortices of various strengths. The effectiveness has been tested against both analytical flows (pure shear flow, Oseen vortex flow, strong outward spiraling motion, straining flow, Taylor–Green flow) and experimental flows (closed cavity flow, closed and open channel flow). Comparison of the new method with the swirling-strength method indicates that the new method shows promise as being a simple and effective criterion for vortex identification.