Entrainment Phenomena Research Articles

Experimental and Numerical Investigation of the Non-Reacting Flow in a High-Fidelity Heavy-Duty Gas Turbine DLN Combustor

A dry, low-NOx (DLN) combustor for a heavy-duty gas turbine using lean premixed technology was studied. A high-fidelity test model was built for the experimental study using particle image velocimetry (PIV). The non-reacting flow in the DLN combustion chamber was investigated experimentally and numerically. The numerical results are in good agreement with the experimental data. The results show that recirculation zones were formed downstream of each swirl nozzle and that the flow pattern in each section was self-similar under different working conditions. For two adjacent swirl nozzles with opposite swirling directions, the entrainment phenomenon was present between their two flows. The two flows gradually mixed with each other and obtained a higher speed. If the two adjacent swirl nozzles had the same swirling direction, then the mixing of the two flows out of the nozzles was not present, resulting in two separate downstream recirculation zones. The interaction of swirling flows out of different nozzles can enhance the turbulent fluctuation inside the combustion chamber. Based on the analysis of the recirculation zones and turbulent kinetic energy (TKE) distribution downstream of each nozzle, it can be found that nozzle coupling results in stronger recirculation and turbulent mixing downstream counterclockwise surrounding nozzles.

Observation of Human Entrainment with Robot Assistance Towards Education

At present, the world faces the challenge of making education available to all the people of the world, especially in under-developed areas, where there is a lack of human resources. To improve educational standards and address this lack of human resources, we believe that robots can be a good teaching aid, to assist both the teacher and the student. This study investigated the entrainment phenomenon between human interactions with a robot as a third-party influence to provide learning packages that will be suited for students and will reduce the strain on teachers. We used dynamic time warping (DTW) algorithm in our time series analysis to effectively calculate the similarity of the brainwaves of the subjects. Then, we defined the entrainment phenomenon between the subjects. To ensure the complexity of this experiment, crosswords were used for this task, which subjects were required to complete in cooperation with each another. At different points of time, the robot would use different expressions, actions, and words as reminders or hints, aiding communication and better cooperation between subjects. The timing of the robotic reminders, synchronization, conversations between the subjects in the crossword tasks, and the completion rate of the crossword puzzles were recorded. The average completion rate improved by 10% with the aid of the robot, as opposed to not using the robot. The results of this study prove that robotic participation in human interaction is beneficial, and that implementing robotic assistance will improve education.

How organizations can benefit from entrainment: a systematic literature review

PurposeTo provide ways of how organizations can benefit from entrainment, the purpose of this paper is to create a better theoretically grounded understanding of entrainment in organizations by reviewing the literature, describing managerial implications and identifying future research directions.Design/methodology/approachA systematic literature review of relevant literature based on peer-reviewed research papers published in highly ranked scientific journals.FindingsIt provides a clear understanding as to what constitutes entrainment in organizations and emphasizes its complexity. Further, six benefits of entrainment are highlighted, including the positive relationship between entrainment and organizational outcomes. The review may also provide entrepreneurs and practitioners a scientific basis for developing innovative tools to help managers’ foster entrainment in organizations.Research limitations/implicationsThe review indicates that entrainment plays a much larger role in organizations than we think. Change leaders' actions may impact the emotions and actions of change recipients through entrainment. The selected keywords used in the search and the researcher's bias of including or excluding articles for this review are the major research limitations.Originality/valueIt is one of the first papers, to our knowledge, to provide a structured overview and understanding of the entrainment phenomenon in an organizational context, based on 41 peer-reviewed articles.

Simulation study on ventilation design for controlling gaseous pollutants in urban sentry boxes with opening window

In cities, sentry boxes with various service functions can be seen everywhere, such as mobile security booths, toll booths, etc., which play an important role in public social services of their compactness and convenience. To realize the office function, the sentry boxes located by the road often need to open the work window continuously or frequently. With the flow of natural wind, various pollutants easily intrude into the sentry box from the open window, resulting in the deterioration of the indoor air quality and a threat to employees' health. In this paper, two attached ventilation modes are used as the carrier, and NO2 is selected as the outdoor gaseous pollutant to discuss the ventilation scheme design to improve air quality in the sentry box with an opening. The barrier performance of the air curtain formed at the window to outdoor pollutants was studied in the vertical wall-attached ventilation (VAV) mode. The conclusion is that although there is an entrainment phenomenon, as long as the supply air velocity is sufficient to generate a covering air curtain (Us > 1 m/s) at the window, the intrusion of pollutants can be effectively blocked. The horizontal wall-attached ventilation (HAV) mode represents the scheme that the supply air jet's mainstream area is far from the opening. The analysis shows that the reasons for improving indoor air quality are the dilution of fresh supply air and the suppression of positive pressure. This paper's conclusions can guide the ventilation design of sentry boxes with openings.

Numerical and experimental investigation into powder entrainment and denudation phenomena in laser powder bed fusion process

This paper investigates the formation and dynamics of the powder entrainment and denudation phenomena in the L-PBF process. A new three-dimensional (3D) coupled Computational Fluid Dynamics (CFD) – Discrete Element Method (DEM) model is constructed to simulate not only the powder entrainment and powder denudation effects, but also the powder absorption effect of the moving melt-pool. Numerical simulations are performed to simulate the denudation width in single-track L-PBF processing. It is clearly found that significant difference between the denudation widths is obtained for different metal vapor ejection angles. To enhance the accuracy of the simulated denudation zone, a pre-defined virtual moving melt-pool is incorporated to consider the powder absorption effect of the moving melt-pool. The simulated results qualitatively have a good agreement with both self-conducted experiments and published experimental results.

Lessons from Entrainment to Enhance Spiritual Practices

Entrainment is a phenomenon what we all have experienced in our personal daily life, typically as an elevated emotion, feeling or energy. But also in organizations, studies highlighted a positive relationship between entrainment and organizational outcomes. In these challenging times, spiritual practices can bring people closer to create a better world together. Hence, the objective of this article is to draw lessons from the phenomenon of entrainment for spiritual practices, because entrainment is a natural process that can be influenced and facilitated. Seven lessons were drawn from the learnings of entrainment to enhance spiritual practices: (1) an effective spiritual practice is a practice that enhances the level of entrainment in one or more quadrants of the Integral Entrainment Matrix; (2) a spiritual practice should focus initially on improving intra-entrainment, which will influence and enhance the other types of entrainment; (3) spiritual practices are ideally done in a healthy natural environment of your liking; (4) spend spiritual practice time with those people that really care about themselves, their environment and you; (5) pace the timing of the spiritual practice to establish a rhythm; (6) pace the spiritual practice itself to fit with your own biological rhythm, your own likes and environment; (7) enhance emotional and behaviour entrainment by selecting a spiritual practice that fits your values.

Study on criteria and prediction method of liquid fall type gas entrainment in pool-type sodium-cooled fast reactors

Liquid fall type entrainment, a kind of gas entrainment phenomenon which may undesirably occur in sodium-cooled fast reactors (SFRs) due to complex immersed structures and high-velocity flowing coolants of SFRs, will involve bubbles into coolants and lead a series of safety risks. Aiming at providing a guideline for avoiding this phenomenon, the computational fluid dynamics (CFD) method was adopted to investigate the influences of fluid properties on entrainment initiation. Before the simulation case study, a small-scale experiment was conducted for verification which demonstrated the numerical model and VOF method are suitable for this study. The modeling criteria of simulating sodium entrainment by other liquids were determined by simulation results. It was also found that the relation between critical inlet velocity and σ/ρ, and the relation between critical re-submergence velocity and critical inlet velocity can be accurately estimated by the case validation. Based on which, an improved wide-applicable prediction method was proposed for entrainment situation judgment.

Drop breakup and entrainment in the updraft

AbstractThis study aims to investigate the characteristics of gas–liquid countercurrent contact processes. In spray towers or other applications, several drops containing pollutants are entrained by the updraft flue gas, which can easily cause environmental pollution. Traditionally, this drop entrainment phenomenon is alleviated by increasing the diameter of the drops. However, the breakup of a large drop would also cause drop entrainment to become serious, a process referred to as secondary atomization. Herein, we propose the boundary of three drop modes in the updraft: drop falling mode, reverse entrainment mode, and breakup entrainment mode. The critical Weber number (We) is the key dimensionless number marking the beginning of the drop breakup. The ratio of the drag force to gravity and We are proposed as criteria for the drop entrainment.

Extended detrended cross-correlation analysis of nonstationary processes

We propose an extension of the detrended cross-correlation analysis (DCCA) for signals with highly inhomogeneous structure. The proposed approach evaluates two scaling exponents, one of which characterizes the detrended covariance, and the second exponent quantifies the effects of nonstationarity caused by the distribution of local fluctuations of signal profiles from the trend. Using simulated datasets produced by a system of coupled Lorenz models, we describe entrainment phenomena associated with chaotic synchronization and the role of nonstationarity in their description. The processing of experimental data related to cerebral blood flow in neighboring vessels of different size confirm the general conclusion of this study and shows the possible advantages of the proposed extension of the DCCA-method for diagnosing changes in cooperative dynamics in physiological systems, where the combined effects of dynamics, nonstationarity and noise may occur.

Analyzing multidimensional movement interaction with generalized cross-wavelet transform.

Humans are able to synchronize with musical events whilst coordinating their movements with others. Interpersonal entrainment phenomena, such as dance, involve multiple body parts and movement directions. Along with being multidimensional, dance movement interaction is plurifrequential, since it can occur at different frequencies simultaneously. Moreover, it is prone to nonstationarity, due to, for instance, displacements around the dance floor. Various methodological approaches have been adopted for the study of human entrainment, but only spectrogram-based techniques allow for an integral analysis thereof. This article proposes an alternative approach based upon the cross-wavelet transform, a state-of-the-art technique for nonstationary and plurifrequential analysis of univariate interaction. The presented approach generalizes the cross-wavelet transform to multidimensional signals. It allows to identify, for different frequencies of movement, estimates of interaction and leader-follower dynamics across body parts and movement directions. Further, the generalized cross-wavelet transform can be used to quantify the frequency-wise contribution of individual body parts and movement directions to overall movement synchrony. Since both in- and anti-phase relationships are dominant modes of coordination, the proposed implementation ignores whether movements are identical or opposite in phase. The article provides a thorough mathematical description of the method and includes proofs of its invariance under translation, rotation, and reflection. Finally, its properties and performance are illustrated via four examples using simulated data and behavioral data collected through a mirror game task and a free dance movement task.

Computational fluid dynamics modelling of air entrainment for a plunging jet

This study focuses on computational fluid dynamics (CFD) modelling of the air entrainment phenomena in water columns which are commonly used in processing plants. The CFD model is first validated against experimental data. Then, a comprehensive set of CFD simulations are conducted to understand the effect of inlet jet velocity, nozzle diameter, tank diameter, and tank height on the bubble formation. Three main patterns are identified: dispersed bubbles, medium air pockets (MAP) and large air pockets (LAP). For the dispersed bubble case, the initially formed air pockets break into smaller bubbles and hence the water level rises linearly. For the MAP case, the size of the air pockets remains larger than for the dispersed bubble case, though, with time they burst at the surface. Finally, for the LAP case, the inkling jet interacts violently with the wall and hence large air pockets are trapped within the column, causing the overflow of the fluid. The flows are further analysed using non-dimensionless Reynolds and Froude numbers, providing an acceptable range of operating parameters that ensure the fluid does not overflow.

Competition between Entrainment Phenomenon and Chaos in a Quantum-Cascade Laser under Strong Optical Reinjection

The topic of external optical feedback in quantum-cascade lasers is relevant for stability and beam-properties considerations. Albeit less sensitive to external optical feedback than other lasers, quantum-cascade lasers can exhibit several behaviors under such feedback, and those are relevant for a large panel of applications, from communication to ranging and sensing. This work focused on a packaged Fabry–Perot quantum-cascade laser under strong external optical feedback and shows the influence of the beam-splitter characteristics on the optical power properties of this commercially available laser. The packaged quantum-cascade laser showed extended conditions of operation when subject to strong optical feedback, and the maximum power that can be extracted from the external cavity was also increased. When adding a periodic electrical perturbation, various non-linear dynamics were observed, and this complements previous efforts about the entrainment phenomenon in monomode quantum-cascade lasers, with the view of optimizing private communication based on mid-infrared quantum-cascade lasers. Overall, this work is a step forward in understanding the behavior of the complex quantum-cascade-laser structure when it is subjected to external optical feedback.

Air Entrainment in Drop Shafts: A Novel Approach Based on Machine Learning Algorithms and Hybrid Models

Air entrainment phenomena have a strong influence on the hydraulic operation of a plunging drop shaft. An insufficient air intake from the outside can lead to poor operating conditions, with the onset of negative pressures inside the drop shaft, and the choking or backwater effects of the downstream and upstream flows, respectively. Air entrainment phenomena are very complex; moreover, it is impossible to define simple functional relationships between the airflow and the hydrodynamic and geometric variables on which it depends. However, this problem can be correctly addressed using prediction models based on machine learning (ML) algorithms, which can provide reliable tools to tackle highly nonlinear problems concerning experimental hydrodynamics. Furthermore, hybrid models can be developed by combining different machine learning algorithms. Hybridization may lead to an improvement in prediction accuracy. Two different models were built to predict the overall entrained airflow using data obtained during an extensive experimental campaign. The models were based on different combinations of predictors. For each model, four different hybrid variants were developed, starting from the three individual algorithms: KStar, random forest, and support vector regression. The best predictions were obtained with the model based on the largest number of predictors. Moreover, across all variants, the one based on all three algorithms proved to be the most accurate.

Mixing at the interface of the sneezing/coughing phenomena and its effect on viral loading.

The primary objective of this work is to investigate the mixing of droplets/aerosols, which originates from the sneezing/coughing (of possibly COVID-19 patient) with the ambient atmosphere. Effectively, we are studying the growth/decay of droplets/aerosols in the presence of inhomogeneous mixing, which focuses on the phenomena of entrainment of the (relatively) dry ambient air. We have varied the initial standard deviation, mean radius of the droplets/aerosols size distribution, and humidity of the ambient atmosphere to understand their effects on the final size spectra of droplets. Furthermore, a rigorous error analysis is carried out to understand the relative importance of these effects on the final spectra of droplets/aerosols. We find that these are vital parameters to determine the final spectra of droplets, which govern the broadening of the size spectra. Typically, broadening the size spectra of droplets/aerosols increases the probability of the virus-laden droplets/aerosols and thus could affect the transmission of infection in the ambient atmosphere.

The use of non-spherical powder particles in Laser Powder Bed Fusion

Laser powder bed fusion (LPBF) generally involves the use of near-spherical powders due to their smooth morphology and enhanced flowability that allow for easier powder layering and laser processing. Non-spherical powders, on the other hand, are more cost-efficient to manufacture, however, the underlying mechanisms of their movement and interparticle interaction on the powder bed are still unclear. Thus, this study reports on the use of irregular iron-based powder material in LPBF, with a specific focus on particle motion and interaction behavior on the powder bed. The powder morphology, sphericity and particle size were analysed using X-ray computed microtomography and scanning electron microscopy. Based on the acquired data and by using a simplified analytical calculation, the influence of the particle shape/size on the particle movement in LPBF was established. High-speed imaging was employed to investigate the particle flow dynamics in the process zone, as well as the powder entrainment phenomenon. Particle entrainment and entrainment distances along the scanning direction were measured for near-spherical and non-spherical powders. The obtained results were compared between the powders, revealing a dissimilar particle transfer behavior. Non-spherical powder had a shorter entrainment distance partly attributed to the weaker drag force acting on these particles.

EXTENDING A VAN DER POL BASED REDUCED-ORDER MODEL FOR FLUID-STRUCTURE INTERACTION APPLIED TO NON-SYNCHRONOUS VIBRATIONS IN TURBOMACHINERY

Abstract This paper expands upon a multi-degree-of-freedom, Van der Pol oscillator used to model buffet and Nonsynchronous Vibrations (NSV) in turbines. Two degrees-of-freedom are used, a fluid tracking variable incorporating a Van der Pol oscillator and a classic spring, mass, damper mounted cylinder variable; thus, this model is one of fluid-structure interaction. This model has been previously shown to exhibit the two main aspects of NSV. The first is the lock-in or entrainment phenomenon of the fluid shedding frequency jumping onto the natural frequency of the oscillator, while the second is a stable limit cycle oscillation (LCO) once the transient solution disappears. Improvements are made to the previous model to better understand this aeroelastic phenomenon. First, an error minimizing technique through a system identification method is used to tune the coefficients in the Reduced Order Model (ROM) to improve the accuracy in comparison to experimental data. Secondly, a cubic stiffness term is added to the fluid equation; this term is often seen in the Duffing Oscillator equation, which allows this ROM to capture the experimental behavior more accurately, seen in previous literature. The finalized model captures the experimental cylinder data found in literature much better than the previous model. These improvements also open the door for future models, such as that of a pitching airfoil or a turbomachinery blade, to create a preliminary design tool for studying NSV in turbomachinery.

A correlation for pool entrainment phenomenon

The present work aims to study the phenomena of droplet entrainment from water pool in a confined atmosphere, which could be either a consequence of boiling or depressurization. Eventually, these droplets are entrained by the streaming gas (superficial gas velocity) or settling down due to gravity.The number of correlations developed so far quantify the entrainment based on empirical, semi-empirical and theoretical approaches, but they have been generally limited to a specific flow-regime in the water pool, thermal hydraulic conditions or even to a specific geometry. In this context, the present work aims to develop an empirical correlation to cover the flow regimes from bubbly to churn turbulent, and could be applied to a wide range of geometries. The present correlation shows an increase until a maximum entrainment of about 2.10-4, corresponding to superficial gas velocity of 0.05 m/s for bubbly flow regime, and then a slight decrease to 2·10−5, for the transition regime corresponding superficial gas velocity of 0.1 m/s, and a sharp increase in the churn turbulent flow regime as the gas velocity goes up to 5 m/s.The experimental database used to develop the present empirical correlation covers a broader range of boundary conditions, namely pressure [1 bar–15 bar], water pool thermal condition [subcooled – boiling], vessel diameter [0.19 m- 3.2 m], pool diameter [0.1 m–1.4 m], superficial gas velocity up to 5.0 m/s Therefore, the proposed empirical correlation aims to constitute an important tool to transfer the experimental results to reactor application.

Van der Pol equation with sine nonlinearity: dynamical behavior and real time control to a target trajectory

In this work, the dynamical behavior and real time control of a target trajectory of a modified Van der Pol model so the potential is proportional to the term is proposed. A generalization in the case of small oscillations on the function is studied. Due to function, the system presents periodical regions of stability and unstability, a very rich dynamical behavior. Analytical investigations based on the harmonic balance method came out some specific values of the excitation frequency for which the model is subjected to a phenomenon of frequency entrainment. Also, under effect of the sine function power, chaos appears for even small value of the nonlinearity coefficient, in contrast to the classical Van der Pol oscillator. An investigation as an artificial pacemaker is done based on the real frequency of the natural pacemaker. We found that the modified Van der Pol model, like the classic Van der Pol model, can play the role of an artificial pacemaker with some approximations. Due to the complexity of the analogical sine function, an experimental study was made by real implementation of an Arduino Card based on the Runge–Kutta 4th order algorithm. The results obtained show a good correlation with the numerical results.

Drop Bouncing Dynamics on Ultrathin Films

For drops to contact various surfaces, the removal of the interstitial fluid is the prerequisite to contact. While the conventional understanding is for drops to irreversibly spread on a film made of the same substance, we describe the dynamics of drops initiating contact yet carrying enough momentum to completely lift off of the substrate which we label as contact bouncing. We report new experimental results of the dynamics between drops impacting thin films described by the ratio of the liquid film hL to the drop with diameter D0 for the range of 0.004 < hL/D0 < 0.08. Using high-speed interferometry, we visualize the interfacial gas layer spatiotemporal signatures across the various film thicknesses and Weber numbers. We find that while increasing the deformability of the thin films enhances the gas entrainment phenomenon at early times, it also increases the rate of the gas purging rate, increasing the chance of contact just prior to the gas film retraction and drop lift off sequence. Drops which contact the liquid film during the retraction stage are able to bounce with <5% volume loss.

Optimization of DNS code and visualization of entrainment and mixing phenomena at cloud edges

Entrainment and mixing processes occur during the entire life of a cloud. These processes change the droplet size distribution, which determines rain formation and radiative properties. Since it is a microphysical process, it cannot be resolved in large scale weather forecasting models. Small scale simulations such as Direct Numerical Simulations (DNS) are required to resolve the most minute scale of these processes. The DNS of cloud dynamics are performed by integrating two mathematical models, Eulerian and Lagrangian, in a coupled way. Running DNS is a tedious task as it requires a huge amount of computational resources. In this work, we provide a projection of the required resources for running DNS in different size domains.Visualizing these large simulations presents an added challenge, as they generate petabytes of data. Visualization plays a vital role in analyzing and understanding these huge data outputs. Here, we experimented with multiple tools to conduct a visual analysis of this data. Two of these tools are well established and tested technologies: ParaView and VAPOR. The others are emergent technologies in the development phase. This data simulation and visualization, in addition to exploring DNS as mentioned above, provided an opportunity to test and improve development of several tools and methods.