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As a key component of reciprocating pump, the valve has a significant influence on its performance. However, it is difficult for the existing valve to simultaneously solve the problems such as fatigue, erosion and cavitation in engineering application. In this paper, a solution to these problems of using variable stiffness spring is proposed. And three new structures of the valve are designed. Furthermore, based on Computational Fluid Dynamics (CFD) method, a three-dimensional dynamic simulation model considering fluid-structure interaction in the suction stroke of reciprocating pump is established by using dynamic grid technique and User-Defined Functions (UDF). The performance of these new valves are compared with that of conventional valve respectively. The result shows that the new valves have significant influence on the motion characteristics of the valve disc, flow field distribution and cavitation. Besides, the simulation and experimental results of the maximum lift are compared, and it is found that they are basically in agreement. The new structures provide a new research direction for improving the performance of reciprocating pump. Simultaneously, the above simulation method can also provide guidance for valve design, structural optimization and service life improvement.

A commercial micropump should provide properties that justify the simple structure and miniaturization, high reliability, simple working principle, low cost and no need for complex controller. In this study, two novel piezoelectric actuated (lead zirconate titanate-PZT) valveless micropumps that can achieve high flow rates by pumping chambers and fixed reservoirs were designed and fabricated. Extensive experiments were conducted to investigate the effects of hydrodynamic and electromechanical on flow rates of the Single Diaphragm Micropump (SDM) and the Bi-diaphragm Micropump (BDM). BDM had two actuators facing to the same chamber at 180-degree phase shift. The primary features of the proposed designs were the high flow rates at low driving voltages and frequencies with the help of innovative design geometry. 3D-printing technique providing one-step fabrication for integrated micropumps with fixed reservoir was used. The micropump materials were biocompatible and can be used repeatedly to reduce costs. Mechanical parameters such as tensile test for silicon diaphragm, surface topography scanning by microscopy techniques and drop shape analysis for hydrophobic property were investigated to reveal surface wetting and flow stability. In addition, the effect of reservoir height was investigated and the calibration flow rates were measured during the inactive periods. The maximum diaphragm displacements were obtained at 45 V and 5 Hz. The maximum flow rate of SDM and BDM at 45 V and 20 Hz were 32.85 ml/min and 35.4 ml/min respectively. At all driving voltage and frequency levels, BDM had higher flow rates than of SDM.

A computational fluid dynamics(CFD) simulation was carried out to study on flow field characteristics in dual-Rusthton turbine stirred vessels in laminar and turbulent regimes. Model validation was conducted using experimental data in the literature. The simulation results show that flow pattern and dimensionless velocity distribution vary with Reynolds number in laminar regime, while these parameters remain almost unchanged for different Reynolds numbers in turbulent regime. For vessels with a certain geometrical configuration, flow pattern, dimensionless velocity distribution and impeller power number depend mainly on Reynolds number, and are little affected by working medium and enlargement scale. By changing impeller spacing and off-bottom clearance of lower impeller, it is obtained the parallel, merging and diverging flow patterns in turbulent regime, and the changing processes of flow patterns in laminar regime for the three configurations. Total power number has the order of parallel>diverging>merging for the three configurations at the same Reynolds number. With increasing of Reynolds number, the power number of merging configuration shows the largest drop, followed by diverging configuration, and the lowest drop for parallel configuration in laminar regime, while power number rises slightly for the three configurations in turbulent regime.

Both micro electro mechanical systems (MEMS) based and lab-on-a chip (LoC) devices demand efficient micro-scale mixing mechanisms for its effective control which necessitates the quality research towards more efficient designs. A new venture is investigated in those direction with mixing micro-channel constricted with rectangular block under pressure-driven electro-osmotic flow and is numerically simulated by a modified immersed boundary method (IBM), an alternative technique in computational fluid dynamics (CFD). The electro-osmotic flow elucidated by electrical double layer theory when simultaneously considered with pressure driven flow in micro channels can be effectively figured out by the solution of Navier-Stokes equations linked with Nernst-Planck and Poisson equations for transportation of ion and electric field respectively. In this study, the effect of varying the height of rectangular block on the flow and mixing performance are analyzed. A hybrid method, which is a combination of active and passive techniques, is introduced simultaneously in the micro-channel by the electro-osmotic effects and channel constriction. The approach is on the basis of finite volume methodology on a staggered mesh. The governing equations are solved by a time-integration technique based on a fractional step method. The velocity fields are corrected by a pseudo-pressure term to ensure the continuity in each computational time step. The extent of mixing in every cross section of the micro channel is assessed by a suitable mixing efficiency parameter. This study has shed light on the most predominant factors that influence mixing efficiency in a micro-channel, such as geometry of the block, non-dimensional numbers (Reynolds number, Re and Peclet number, Pe), zeta potential, external electric field strength and electrical double layer (EDL) thickness. The maximum efficiency in this micro mixer design is found to be 51.3% for Reynolds number of 0.05 and Peclet number of 450 with the rectangular block height of 0.75. It is clear that both electro osmotic effects and flow perturbations due to channel constriction caused a remarkable improvement in mixing efficiency. The outcomes of this investigation are widely applicable in cooling of microchips, heat sinks of MEMS based devices, drug delivery applications and Deoxyribonucleic acid (DNA) hybridization. The present IBM model is validated by experimental and numerical results from the literature.

To control secondary flow effects and enhance the aerodynamic performance of the compressor, the flow control effects of the flow suction at the endwall with different circumferential positions and at the blade tip were numerically investigated in the cantilever stator of an axial single-stage transonic compressor. The main purpose was to gain a better understanding of the application of boundary layer suction and the associated control mechanisms in the cantilever stator. The studies show that the optimal position of the endwall suction slot should be located up the stator blade, in terms of the leakage flow structures and the blade tip unloading effect. In addition, the flow control effects of the suction at the blade tip on leakage flow upstream is better than that of the endwall flow suction with the same structure. Further, the studies of compressor aerodynamic performance curves illustrate that the efficiency and pressure ratio is increased by 0.34% and 1.09% at the peak efficiency point, and are increased by 0.39% and 0.14% at the near stall point, respectively.

The slipstream caused by high-speed trains may harm pedestrians and workers trackside. In general, the characteristics of the slipstream are influenced mainly by the nose shape of the train. The present study explores the slipstream caused by high-speed trains with three different horizontal nose profiles based on the results of three-dimensional, improved delayed detached eddy simulation (IDDES) with an unsteady turbulence model and a set of 1/8th scaled train models. The results obtained using this numerical methodology are in good agreement with those obtained from corresponding wind tunnel tests. The trackside pressure changes around the train models are also captured and analyzed. The analysis reveals that the width of the nose can significantly influence the magnitude and arrival time of slipstream velocity and pressure peaks. The results and proposed numerical methodology can be used as guidelines for the design of high-speed train nose shapes.

By combining near infrared spectroscopy and differential pressure meter to measure flow rate and phase volume fraction, a new structure of the near infrared system located in the position of the Venturi tube of long throat was proposed. The flow rate and volume fraction of the bubble flow were measured in a vertical experimental line. In terms of volumetric content measurement, based on typical flow characteristics, a void age model was established and experimentally verified. In terms of flow measurement, the classical measurement model is compared, and the uniform flow model is selected as the flow measurement model and corrected. The results show that the measurement error under the bubbly flow condition of the liquid volume fraction and the gas volume fraction was within ±0.52% and ±10%, respectively. The relative error of total flow measurement was within ±1.01%.

Large Eddy Simulation (LES) of a two dimensional supersonic compressor cascade is performed in the current study. It is found that the Shock Wave Boundary Layer Interaction causes a large scale of total pressure losses and presents strong fluctuation features. Thus the pulsed and steady excitation jets are applied to suppress the flow separations and to reduce the total pressure losses. Several impacting parameters, such as jet axial location, jet hole width, jet angle to the local blade surface and jet mass flowrate are chosen based on the primary analysis by the calculations by the Reynolds Averaged Navier-Stokes equations. In addition, based on the results of frequency spectrum and POD analysis, the excitation jet frequency is chosen for the pulsed excitation jet scheme. It is concluded that the pulsed excitation jet scheme achieves a 9.8% reduction of total pressure loss in comparison to the steady excitation jet scheme under the same time-averaged excitation jet mass flow rate. The excitation jets affect both the flow field near the jet hole on the suction surface and the flow field on the pressure surface via the management of the reflection shock wave. In addition, the excitation frequency dominates not only the time-averaged flow field, but also the second and third modes which stand for the unsteady structures in the flow field under the POD analysis. The first mode contains most energy in the flow field and the energy percentage decreases dramatically with the increase of the mode number. In comparison to the steady excitation jet scheme, the pulsed excitation jet scheme gathers more energy to the low orders of the modes, especially the first four modes. With the mixing effect and high dissipation rate of the high-frequency signals, the high-frequency signals shrink in the wake and the flow field builds up more uniformity.

In hydrodynamics the applications range of incompressible flows is very wide. In this study, a robust, high order modeling approach is introduced, based on the MLPG meshfree method -based radial basis functions (RBF- MLPG) method, for solving the incompressible flow field. In other words a MLPG meshfree method based on an interpolation function is presented to solve the 2‐D unsteady incompressible fully developed fluid flows. This meshfree method is based on the quartic (4^th order) spline. The method is then compared against the Finite Element Method on a test case of unidirectional fully developed incompressible fluid. The performance of this weight function proved that the quartic (4th order) spline gains the highest accuracy, convergence and efficiency. Finally, it can be concluded that the presented method is formidable for simulating fluid dynamics.

Sudden expansion of flow in supersonic flow regime has gained relevance in the recent pasts for a wide run of applications. A number of kinematic as well as geometric parameters have been significantly found to impact the base pressure created within the suddenly expanded stream. The current research intends to create a predictive model for base pressure that is established in the abruptly extended stream. The artificial neural network (ANN) approach is being utilized for this purpose. The database utilized for training the network was assembled utilizing computational fluid dynamics (CFD). This was done by the design of experiments based L27 Orthogonal array. The three input parameters were Mach number (M), nozzle pressure ratio (NPR) and area ratio (AR) and base pressure was the output parameter. The CFD numerical demonstrate was approved by an experimental test rig that developed results for base pressure, and used a nozzle and sudden extended axis-symmetric duct to do so. The ANN architecture comprised of three layers with eight neurons in the hidden layer. The algorithm for optimization was Levenberg-Marquardt. The ANN was able to successfully predict the base pressure with a regression coefficient R2 of less than 0.99 and RMSE=0.0032. The importance of input parameters influencing base pressure was estimated by using the ANN weight coefficients. Mach number obtained a relative importance of 47.16% claiming to be the most dominating factor.

Nozzle wakes have significant effects on the heat transfer on the rotor blade and endwall surfaces. Numerical studies have been carried out in a subsonic high pressure turbine stage to investigate the rotor’s secondary flow field and endwall heat transfer. Both steady and unsteady RANS analyses were accomplished for the multiple blade rows using mixing-plane and domain-scaling techniques respectively. Special attention was focused on the particular nozzle wake structure of secondary passage vortex near the hub endwall and its effects on the endwall heat transfer characteristics. Unsteady solution indicates that the passage vortex near the rotor hub is transported toward the midspan due to the blade interaction and rotation effects. In the front passage region, the time-averaged result yields higher heat transfer up to 20% than a steady one, and the transient fluctuation amplitude reaches 40% of mean values along the passage vortex moving path. In the rear passage region, the difference between steady and unsteady solutions is negligible. Current study reveals that the major difference of wake effects between an actual turbine and a linear cascade with moving bars comes from the movement of the vortical endwall passage vortex in the incoming flow.

The current study reports the phenomenon of drop impacts on a hydrophobic surface in the substrate deposition regime (non-splashing), focusing on the characterization of each stage upon impact and different non-dimensional parameters involved such as spreading factor, recoil height and the durations of several phases. The results indicate that the drop dynamics is determined by an interplay of drop inertia, viscosity and surface tension. Apart from Reynolds number (Re) and Weber number (We) which are conventionally used to characterize drop impacts, a new non-dimensional impact parameter, ξ (= 〖We〗^(1/4) 〖Re〗^(1/5)) is introduced, and it is found out that the spreading factor and the different non-dimensional phase durations involved in the drop impact dynamics on a hydrophobic surface, scale fairly well with this newly defined impact parameter. Further, systematic studies into the non-dimensional durations of each phase upon impact, spreading factor and recoil factor (i.e. non-dimensional recoil height) with respect to different non-dimensional parameters are reported.

In recent years, numerical simulations have become key tool for diesel engine combustion system development due to the requirement of the shorter development duration for the improved performance and better emission levels. In this study, an approach, which integrates numerical and experimental methods in order to characterize the flow field in diesel engine cylinder, is presented. The steady-flow port bench testing, PIV (Particle Image Velocimetry) measurements and numerical simulation methods are used to determine the flow behavior inside the cylinder. Numerical simulation method is validated by using experimental results in terms of mass flow rate and swirl ratio in cylinder. Mass flow rate values predicted within 5 percent error and swirl ratio values predicted within 10 percent error. This proves the viability of numerical method as an important alternative to port bench measurements. In addition to that, cylinder-to-cylinder variation and effects of surface roughness are investigated by swirl ratio measurements and optical diagnostic. Results showed that surface quality and manufacturing problems have significant effects on the swirl ratio in cylinder.

Ship harmonic motion is an important and practical characteristic in ship design and performance evaluation. The development and optimization of hull-form, ship’s dynamic effects, seakeeping performance, and motion control, all require the motion data that includes wave exciting forces as well as dynamic response of the ship. This paper presents a new approach for time-domain simulation of full-scale ship model with four degrees of freedom based on computational fluid dynamics using unsteady RANS method. The key objective of this paper was the full-scale simulation of ship motion in oblique waves and assessment of time domain forces, moments, and other motion parameters. The David Taylor Model Basin (DTMB) 5415 full-scale model has been used for the numerical studies in this paper. The obtained computational results showed good conformation to the results obtained using the strip theory. It is intended to extend this research to subscale test experiments for more definite validation of the results.

Under the current global energy crisis the interests in developing a third generation of biofuels produced from non-food feedstock such as microalgae and cyanobacteria have clearly increased. Hydrodynamic stress, always present in cultivation process of these microorganisms, is an essential factor to ensure mixing inside bioreactors; however the importance of its intensity is usually ignored by applying a random agitation (energy consumption) which is unnecessarily overestimated. In this work, two types of agitation, stirring in agitated photobioreactors (APBR) and bubbling air in draft tube airlift photobioreactors (DPBR), are applied to study the effects of hydrodynamic stress on the growth and pigment content evolution of the cyanobacteria Synechocystis sp. PCC 6803, a self-propelled microorganism. The range of applied shear stress was between 0 and 400 mPa. Similar results are obtained for both agitation mechanisms, indicating that the effects of shear stress are limited to the breakdown of the cell colonies; once they are broken down any further increase in shear stress has no significant effect on their growth rate. Moreover, the variation in pigments concentration appeared to be linear with the cellular concentration and independent from shear intensity.

Design optimization has been increasingly investigated for an airfoil, aiming to reduce the vorticity in the wake and increase the aerodynamic performance. In the current work, a two-dimensional (2D) S833 airfoil equipped with a flapping fringe at the trailing edge has been studied using computational fluid dynamics (CFD) simulations. The objective is to investigate the influence of the length (Lf) and flapping frequency (f) of the fringe on shedding vortices from the airfoil and the drag and lift coefficients. The validation of the current numerical approach for both static and dynamic motions of the airfoil was conducted. First, four different computational meshes were created for the static bare airfoil S833 model, and the simulated drag and lift coefficients were compared against experimental results. It is observed that the second finest mesh contributes to the best agreement with the measurement data. In addition, the numerical accuracy of the dynamic simulation was assessed by reproducing the pressure distribution around the airfoil NACA0014 with a periodic plunging motion at different time phases within one plunging cycle. Good agreements between the simulated and previous computational results are obtained. Moreover, the investigation of S833 airfoil equipped with a flapping fringe reveals that the model with Lf =0.01 m (10% of the chord length) associated with a flapping frequency below the shedding frequency of the bare airfoil can significantly alter the coherent structure of the shedding vortices, breaking the routine large-scale vortex into small-scale weak vortices. It also results in reducing the intensity of vortices and shortening the distance between each pair of vortices to accelerate the dissipation of vorticity. In addition, the equipped flapping trailing edge fringe can achieve extra benefit in aerodynamic performance in terms of the reduction of the drag coefficients and the enhancement of lift coefficients.

Transport aerodynamic optimisation has become an increasingly important field of study in response to emerging factors, such as new human needs and market demands. This paper provides a concept in-house built sports-car aerodynamic and shape optimisation. Wind tunnel tests and numerical simulations have been set-up and conducted to understand the concept vehicle aerodynamic structure and needs for performance improvement. A computer-aided design model has been developed and implemented into the computational fluid dynamics (CFD) software of StarCCM+ for detailed analysis. A 1/4th full-scale fibreglass model has been manufactured for validation. The combined experimental and CFD analyses show that the original aesthetic design exhibits high rear-end lift-force. Modifications have been assessed to improve the drag and lift forces for the front, middle and rear regions. Several geometrical changes are introduced, including new rear-wing design. Also, the front end, roof profile and various ducting modifications have been considered. The introduced design changes lead to optimised downforce of -560.18 N with negligible increase to the accumulated drag effects with CD ≤ 0.3.

A 30 kWth Circulating fluidized bed (CFB) combustor is experimentally and numerically investigated under cold flow conditions. Barracuda software based on Computational Particle Fluid Dynamics (CPFD) method is utilized for simulations. The influences of bed inventory and drag model on flow hydrodynamics were investigated considering pressure and velocity profiles and particle concentration. Two advanced drag models, namely Energy minimization multi-scale (EMMS) and Wen-Yu/Ergun were selected for this study. The simulations were performed with initial bed material masses of 3.79, 4.55 and 5.20 kg corresponding to 2.5, 3 and 3.5 diameters height of riser, respectively. With increasing bed inventory pressure drops and solid concentration increase. The axial particle velocities slightly change with bed inventory. The comparison of simulation results with experimental measurements was resulted in good agreement (<5%) with both models. The simulation with EMMS drag model predicted the pressure profiles more accurately than Wen-Yu/Ergun drag model. The profiles of particle volume fraction and axial velocity demonstrate that core-annulus flow pattern was captured by both models. But EMMS drag model was better in revealing the meso-scale structures at instantaneous particle concentration distribution. Moreover, the influence of particle size distribution on particle volume fraction and particle velocity profiles is also investigated with two drag models.

In this paper numerical simulations were performed utilizing Computational fluid dynamics code Fluent to investigate the thermo-fluid performance of a wavy rectangular winglet supported fin-and-tube heat exchanger with five inline rows of circular tubes. The influence of wave height, number of waves, wavy winglet length and winglet attack angle on the thermo-fluid performance of the fin-and-tube heat transfer surface has been examined under laminar flow conditions. Further the Plain and wavy rectangular winglets are placed together over different tube locations and their effect on heat transfer and flow resistance is also examined. An enhancement factor has also been discussed to summarize the overall thermo-fluid performance. The results show that increase in the wave height increase both heat transfer and pressure drop, and an optimum wave height could be decided based on the enhancement factor. It is also found that the increase in wavy winglet length guides the flow more effectively towards the tubes wake region. It is also observed that with increase in number of waves the heat transfer performance initially increases and then decreases as the wave pitch becomes very small. For wavy winglet supported heat exchanger the optimum attack angle is found out for maximum enhancement factor.

Autonomous aerial refueling is a typical close formation flight process, in which the tanker wake has a strong aerodynamic influence to the receiver. In order to develop the accurate aerodynamic models in refueling simulations and design the control laws for autonomous aerial refueling, the tanker wake effects on an Unmanned Aerial Vehicle (UAV) are investigated through ANSYS CFX 15.0. A simplified boom-equipped tanker and a tailless delta wing UAV (named ZD-X) are used in this study. The aerodynamic characteristics of ZD-X in single flight are calculated first and the results are used as the benchmark for comparison. Then the aerodynamic characteristics of ZD-X under the effects of tanker wake are calculated, the final results are given in incremental form to facilitate comparative analysis. Numerical results are obtained from the tanker and receiver at varying lateral, vertical and longitudinal spacings. It is observed that the tanker wake effects on the receiver mostly come from wingtip vortices of the tanker wing and horizontal tail, and the lateral and vertical spacings have significant effects on the aerodynamic characteristics of the receiver, while the longitudinal spacing has almost no effect.

A proper design of exhaust hood geometry is very much essential in order to improve the overall efficiency of the steam turbine plant. The geometry of the non-axisymmetric exhaust hood makes the fluid flow at the exit of the steam turbine to be radially and circumferentially non-uniform. This work involves computational simulation of steam turbine asymmetric exhaust hood flows by incorporating the actuator-disc concept. The ANSYS FLUENT, finite volume based CFD solver is used for the present computational study. In the present simulation, the implementation of actuator disc boundary conditions with and without tip leakage is described in detail. The Actuator disc model approach exhibits a similar steam turbine exhaust hood flow asymmetry and static pressure recovery compared with the results reported in the literature, highlighting the applicability of the present model in coupling the rotor tip leakage jet with the steam turbine hood flow structure with less computational effort.

This paper presents an experimental study of the effect of a directionally porous wing tip on the tip vortex using particle image velocimetry (PIV) on a half wing model with NACA 653218 as its airfoil section. Four different configurations of the directionally porous wing tip are tested. The vortex generated by the wing tips are examined at four different measuring planes downstream perpendicular to the flow axis. The flow field over the porous wing tip surface along the streamwise direction is obtained as well to understand the effects of the porosity on the flow which in the end affects the vortex downstream. Furthermore, the aerodynamic performance of all different configurations is compared to study their effects on the aerodynamic coefficients of the wing. The results show a high reduction in vorticity, up to 90%; tangential velocity reduction up to 67% and a significant reduction in vortex circulation in the near-far field. Effect on the lift to drag ratio is up to 20 %.

Background-Oriented Schlieren (BOS) is a non-intrusive and non-destructive technique for measuring density gradient in transparent media. Given the dependency of the refractive index and density of a medium, its static density field can be determined as a secondary measurand from BOS measurements. For an ideal gas, if the pressure variation is negligible, the static temperature field can be determined as a tertiary measurand. While the BOS technique for far-field measurements has been extensively researched, the implementation of this technique for near-field measurements still needs to be investigated. Near-field BOS is especially important for the measurement and visualization of internal flows, such as turbomachine flows, in which access to flow passage is limited and might be feasible using endoscopes (borescopes). This paper presents the features and challenges of the endoscopic BOS technique and presents methods and solutions for the application of this method in near-field measurements. The features of endoscopic BOS records as well as the comparison of endoscopic BOS and BOS measurements with camera are presented.

One of the most important advantages of twin-fluid atomizers over other atomizers is the opportunity of atomizing liquids in a wide range of liquid properties efficiently. Thus, the fundamentals of spray dynamics, such as spray pattern, liquid breakup length, and spatial droplet size evolution using different liquid properties need to be investigated in some detail. The purpose of this study is therefore to examine and describe the influence of the liquid viscosity and surface tension on the spray performance of prefilming air-blast atomizers. A high-speed background shadowgraphy technique associated with particle tracking and Phase Doppler Anemometry (PDA) as a non-intrusive high-resolution local measurement technique were utilized to study the atomization process regarding the influence of the liquid properties on the spray quality. Generally, the break up mechanism is considerably influenced by the liquid viscosity. The breakup length ( ) is dependent on liquid viscosity with for Pa = 0.25 and 0.6 bar air pressure, respectively. Droplet size distribution profiles of different liquids in axial and radial directions are studied. No significant influences of the surface tension and viscosity were observed on the mean droplet velocity downstream of the spray. A minor increase of the droplet mean diameter was observed with liquid viscosity variations from 22 to 111 mPas, however, the liquid surface tension was verified to play an important role in the atomization process at prefilming airblast atomizers as well. According to the available experimental data, it has subsequently been possible to develop an original and descriptive model based on a dimensional approach at different air pressure ranges.

Ducted fans are widely used in unmanned aerial vehicles due to their high propulsive efficiency and safety. The aerodynamics are complex within the vicinity of the ground, including take-off, landing and hovering. In the present study, the aerodynamic stability of the ducted fan was studied with a modified Moore-Greitzer model to estimate and analyse the stability in ground effect. The model was validated and compared with three-dimensional unsteady simulations. The results indicated that the rotating stall occurred for the ducted fan in ground effect. The model results can be used to guide the design and control of the vehicles, to ensure the stability and safety of both the ducted fan and vehicles.

The present research focuses on flow oscillations in a planar rectangular cavity. The compressible URANS equations in combination with transition SST k−ω model are utilized to include the turbulence effects. The simulations are carried out for low Reynolds flow with Mach number ranging from 0.2 to 0.7. Flow features are investigated and the frequency analysis is discussed. Two flow oscillation modes, namely shear-layer mode and wake mode are thoroughly identified. The flow structure and oscillation frequencies compare well with LES and DNS results presented in the literature. Furthermore, the shear mode frequency is well aligned with that predicted by Rossiter. This research is aimed to evaluate the performance of URANS as an industrially attractive tool to capture flow phenomena, previously visualized by the aforementioned sophisticated methods.

The present research focuses on flow oscillations in a planar rectangular cavity. The compressible URANS equations in combination with transition SST k−ω model are utilized to include the turbulence effects. The simulations are carried out for low Reynolds flow with Mach number ranging from 0.2 to 0.7. Flow features are investigated and the frequency analysis is discussed. Two flow oscillation modes, namely shear-layer mode and wake mode are thoroughly identified. The flow structure and oscillation frequencies compare well with LES and DNS results presented in the literature. Furthermore, the shear mode frequency is well aligned with that predicted by Rossiter. This research is aimed to evaluate the performance of URANS as an industrially attractive tool to capture flow phenomena, previously visualized by the aforementioned sophisticated methods.

Particulate-reinforced aluminum matrix composites produced by stirring casting method exhibit many advantages and are usually used in practical industries. The particulate flow and distribution during the stirring have significant effects on composite casting properties and performances. In this investigation, to study the effect of stirring parameters on particulate distribution, an experimental quenching apparatus was designed, and then A356/50μmSiCp prepared with different stirring speeds and positions were carried out. The particulate fractions at different locations of the prepared composites were quantitatively measured with micro-image analysis, and the charts of particulate distribution along axial directions were summarized and analyzed. Based on liquid-solid multiphase flow theory and multiple rotating reference frame models, a mathematical model of particulate-reinforced aluminum matrix composites stirring process established with consideration of relative flow between liquid and solid particle phases was applied to the experimental composite preparation. By comparing the simulation and experimental results, the effect of stirring condition on the composite slurry and particulate flow as well as the final particulate distribution were analyzed. The comparison shows that the simulated particle distribution exhibits well agreement with the experiment, indicating the validity and exactitude of the established model and method for actual composite stirring preparation. The study shows that low position of impeller would force more particles at the bottom region to flow with composite slurry, improving the particle distribution, and that high stirring speed can cause strong centrifugal force and radial flow of both composite slurry and particles, decreasing the particle uniformity in the composites.

The motion of air bubbles in a yield stress fluid is analyzed numerically using a 2D approach and the finite volume technique. The multiphase flow is simulated using the volume of fluid method (VoF), which solves the conservation equations of mass and momentum coupled to a transport equation for the volume fraction of the fluids. The effects of yield stress, bubble size, number and position of bubbles rising in a viscoplastic fluid confined between vertical parallel plates are analyzed and discussed. The results indicate that the yield stress has great impact on the rising velocity. In the case of multiple bubbles flowing vertically, it is observed that the displacement of one bubble influences the rising velocity of the others, causing them to approach each other. As the distance between the bubbles increases the interference is reduced and the bubbles begin to flow as single ones. When two bubbles are horizontally positioned, they can approach or move away from each other, depending on the initial distance between them. Furthermore, the bubbles shape is analyzed as a function of the governing parameters. It is observed that for lower Reynolds number the bubbles present a circular shape, but as inertia increases the bubble becomes ellipsoidal.

Three-dimensional Eulerian-Eulerian transient simulations were conducted to represent the gas-liquid flow of a heterogeneous bubble column. Different drag closures, breakup and coalescence models were evaluated in order to verify their influence on the model prediction. Numerical simulations were compared to experimental data, with industrial conditions of gas superficial velocities: 20cm/s and 40cm/s, in order to select the most suitable models to describe the bubble’ dynamics in the heterogeneous flow. The standard k − ε model for both phases was set for turbulence. 12 combinations of breakup and coalescence models were compared and analyzed. In the case of coalescence, Models of Prince and Blanch, and Luo presented similar behavior and good agreement with experimental data, while for breakup, a breakage forming three daughter bubbles appeared to be the best choice. Simulations presented relative errors around 7.7% and 14.0%, for 20cm/s and 40cm/s respectively, for the gas axial velocity, and around 14% and 21.9%, for gas holdup. For drag force, density and viscosity were accounted by an average of the phases, which resulted in an improvement about 7% on model validation

This study aims to discuss and illustrate the role of insoluble surfactants on the stability analysis of a shear-imposed free surface motion down an oblique heated substrate. The couple effects of temperature and surfactant concentration gradient on the surface tension are assessed, in which the surface tension of the fluid is assumed to vary linearly on surfactant concentration and the temperature. The exact analytical solutions for the Stokes flow and the long-wave approximation are derived, depending on the linear stability theory, and hence the neutral curves are plotted and discussed. Due to the presence of the surfactant, there are two different modes that impact the stability process of a shear-imposed inclined flow. The current study recovers some limiting cases upon the selected data. The system parameters governing the liquid layer and the substrate geometry have a strong effect on the wave forms and so the stability of the free surface. The influences of various parameters such as Marangoni, Biot, elasticity, surfactant Péclet number and Reynolds numbers, besides the angle of inclination are considered. It is found that, the Reynolds and the surfactant Péclet numbers and the angle of inclination have destabilizing effects.