bluuebunny/crossref_metadata_2025_split huggingface dataset:
Design Optimization of Laser-Induced Bubble for Highly Efficient Generation of Microjets
Authors: Ishikawa Tatsumasa , Nishida Hiroyuki , Tagawa Yoshiyuki 
Published: September 2022

Abstract
A device generating high-speed microjets from a liquid-filled microtube with laser-induced bubbles gets attention due to possibility of various engineering applications. In this study, we optimized the placement and bubble size of the laser-induced bubbles to maximize the efficiency of microjet generation. In the optimization, we use the Covariance Matrix Adaptation Evolution Strategy, which is one of the evolutionary algorithms. And a compressible multiphase flow solver based on the 5-equation model is used to evaluate the solution. Furthermore, data mining techniques using correlation analysis and dimensionality reduction algorithms are applied for extracting features related to the efficiency of microjet generation. Our result shows that it is effective to generate a laser-induced bubble near the tube wall. In addition, it is found that smaller volume and lower energy bubbles can provide efficient microjet generation. These results from the optimization and data mining are important for producing high-speed jets at low energy.
Research on Effects of Tunnel Buffer Structures on the Aerodynamic Force of the Pantograph
Authors: Cheng Jionghao , Guo Dilong , Yang Guowei , Ji Zhanling , Chen Dawei 
Published: September 2022

Abstract
The pantograph subjected to sudden changes of the airflow while a high-speed train passes through the entrance and the exit of tunnels and the aerodynamic force acted on the pantograph fluctuate significantly, which can result in bad influence to the current characteristics of the pantograph. Aimed at studying the effect of buffer structures on such issue, the aerodynamic force of pantograph while passing through a tunnel with buffer structures, including bell mouth hoods, oblique hoods, and constant cross section (with the same cross section area to main tunnel) hoods were simulated by utilizing CFD software. The object of this study is a full-scale CRH380A train model composed of three groups with the CED400 pantograph model. The IDDES turbulence model combined the technique of overset grid is adopted in the computation. The results indicate that both the aerodynamic drag and lift fluctuation of the pantograph are reduced at the entrance and the exit of a tunnel with the bell mouth or side opening buffer structures, especially at the exit of the tunnel, the amplitude of lift force fluctuation can decrease to a quarter of the value in condition of conventional tunnels, the oblique hoods buffering structure has no obvious alleviation effects on the aerodynamic force fluctuations.
Inferring Unsteady Wake Flow Fields From Partial Data by Physics-Informed Neural Networks
Authors: Yan Chang , Ju Shengjun , Guo Dilong , Yang Guowei , Yao Shuanbao 
Published: September 2022

Abstract
Massive differential numerical computations are necessary in Computational Fluid Dynamics. In addition, the experimental results are generally noisy. Consequently, traditional methods cannot get unsteady flow fields immediately and precisely. In this research, the inferences of unsteady wake flow fields at different Reynolds numbers by Physics-Informed Neural Networks (PINNs) are studied. Unlike typical neural networks whose loss function consists of Mean Square Error only, the loss function of PINNs consists of Mean Square Error and the sum of squares of residuals of the flow governing equations. The flow governing equations are introduced to the neural networks as a regularization of the loss function. The existence of regular term reduces the dependence on labeled data during training. Then the PINNs is trained with very little labeled data (5% of the full field). After being trained, the PINNs show excellent performance in inferring the unsteady wake flow fields. When the Reynolds number is 1e2, the Mean Absolute Error (MAE) of the reconstructed velocity field is on the order of 1e−4. Meanwhile, the MAE increases with the increase of Reynolds number. In addition, even if the random noise of the training set is introduced up to 20%, the result is still acceptable, which demonstrates the great anti-noise ability of physics-informed neural networks.
Time-Resolved Measurements for the Detection of Clogging Mechanisms
Authors: Beck David , Brokhausen Florian , Thamsen Paul Uwe 
Published: September 2022

Abstract
The effects of clogging in pumps are manifold and change over time. This is demonstrated with time-resolved observations of the operating data on a test rig at the chair of fluid system dynamics of the Technische Universität Berlin. On the test rig, the head, flow, power consumption and efficiency of different pumps operating with artificial wastewater are recorded.
In the data, different clogging behavior reflect in the operating parameters. There are three major clogging-induced characteristics to be differentiated in the time-resolved measurements. For some aggregates there is a rapid drop in the hydraulic parameters right from the start due to initial clogging, with following stagnating performance. This is showcased on a semi-open two-channel impeller, where efficiency drops by 40 % at the very beginning of the measurement and subsequently stagnates. In other cases, like demonstrated here on a closed two-channel impeller, the operating parameters decline continuously over the entire measurement period due to increasing clogging. In the showcased example, the efficiency drops by over 40% in the first six minutes of the measurement due to initial clogging and keeps declining till the end for another 6%. Lastly, there are cases where self-cleansing mechanisms are identified. It is further shown that this phenomenon also highly varies in its timing and hydraulic effects.
Finally, it is concluded that all operating parameters must be monitored to generate sufficient knowledge about the clogging behavior of a given aggregate. Additionally, longer observation times are necessary to sufficiently identify effects like the self-cleansing of an impeller.
Experimental and Numerical Study on Solid Particle Erosion of Standard Elbows in Dispersed-Bubble Flow
Authors: Bilal F. S. , Othayq M. M. , Sedrez T. A. , Shirazi S. A. 
Published: September 2022

Abstract
Solid particle erosion is an important subject when it comes to pipelines carrying solid particles in mining and oil and gas operations when sand production occurs. For that, to predict erosion that occurs and to maintain equipment integrity, the erosion phenomenon has been widely investigated over recent years. For pipelines carrying multiphase (gas-liquid-sand) flows, solid particle erosion is affected by superficial gas and liquid velocities, particle size and shape, and flow regime. This work aims to investigate the effect on the erosion of two multiphase cases with similar mixture velocity but different superficial gas and liquid velocities in 2-inch (50.8 mm) standard (r/D = 1.5) elbows. Flow visualization experiments were conducted to observe the flow regime. The cases considered are dispersed-bubble flow and churn flow based on the predicted flow pattern maps. However, flow visualization studies indicated that the flow regime is dispersed-bubble flows for both cases. Also, paint removal tests were conducted using an acrylic box painted with black paint to study the erosion pattern. In addition, CFD simulations were performed to compare the erosion patterns and the location of the maximum erosion with the paint removal patterns obtained with the paint removal tests. The location of the maximum erosion and erosion patterns agrees with the paint removal tests. However, the CFD simulations showed different erosion magnitudes even though the mixture velocity is equal; one case showed higher erosion by a factor of 2.5 as compared to the other.
Experimental Investigation in Turbulent Shear Mixing Layer at Supercritical Condition
Authors: Lim Chang Hyeon , Johnston Stephen R. , Ranjan Devesh 
Published: September 2022

Abstract
With limitations of traditional power cycles on their operating temperature ranges and max efficiencies, the research community has shifted the attention to usage of supercritical fluids as the main working fluid of power cycles. Among the supercritical fluids, supercritical carbon dioxide (sCO2) is considered as the most promising candidate for its relatively low critical point, low cost, and availability. The main merit of using sCO2 is its high density near the fluid’s critical point, which reduces the required compression power. This leads to decrease in the volume of turbomachinery and increase in the overall cycle efficiency. However, non-linear property variations and mixing of different supercritical regimes in close proximity to the critical point pose great risks for cycles taking the full advantage of these benefits. The non-linear property variations close to the critical point provide a challenge in developing a multiphysics model, which can serve as a backbone for simulating more advanced geometries of sCO2 power cycle processes.
To understand the physical phenomena of property variations and mixing of supercritical fluids at differing conditions, a classical shear layer experiment is performed in a high-pressure test chamber with supporting closed-loop cycle facilities. Experiments are conducted under various fluid density and velocity ratios at multiple isobars to understand if classical mixing theories and hydrodynamics follow the same trend in supercritical conditions. Specifically, turbulent flow characteristics and the growth parameters are captured through density gradients between two channels using Schlieren visualization. The qualitative results show that the mixing interfacial features follow the classical mixing growth rate theories despite nonlinear fluid property variations. Dissipative nature of the supercritical fluids contributes to resemblance of gas-gas mixing and presents decrease in mixing intensity as inlet conditions deviate away from the critical point.
Optimizing VCC Air Conditioner Systems in Arid Climates: A Dubai Residence As Case Study
Authors: Abdalla Ahmad , Islam Md. , Al Alili Ali , Alhassan Saeed , Qureshi O. A. , Rodriguez-Ubinas Edwin 
Published: September 2022

Abstract
Given the extreme hot and humid ambient conditions of UAE, it comes no surprise that the demand for air conditioning would increase rapidly. In the UAE, roughly 90% of the electricity is consumed by the building sector. In that sector, air conditioners (A/Cs) consume about 80% of the total annual house electricity. The fact that performance of A/Cs decreases as the ambient temperature increases. Additional challenge to optimize energy consumption is that in hot and humid regions A/C units are simultaneously required to control the temperature and humidity. Thus, oversized A/C units are usually used which increases the energy consumption and affect indoor thermal comfort. This study aimed to analyze the implementation of the ASHRAE standard in a residence in Dubai. Transient System Simulation (TRNSYS) program is selected to study a detailed analysis of a residential building implementing ASHRAE building standards. The goal is to reach to an indoor temperature of 22.5°C and a 50% relative humidity according to ASHRAE standards. The values obtained from running the simulation over all the zones can now be used in order to size the A/C system. The maximum required load for all zones is 59.6 kW, however after applying the optimization method it was reduced by 4,5% to reach 56.9kW.
Study of Thixotropic Behavior of Non-Newtonian Fluids in Tool-Joints of Oil Wells
Authors: Gholami Ardeshir , Mansoori Zohreh , Saffar Avval Majid , Ahmadi Goodarz 
Published: September 2022

Abstract
The prediction of frictional pressure loss in many oil wells drillings is of the utmost importance. Most studies in this area are concerned with fluid flow in pipes and annulus to predict friction losses. However, studies on the tool-joint effect in frictional pressure estimations were limited to only a few experimental and theoretical studies on water-based power-law and Herschel-Bulkley drilling muds. Tool-joint is the piece that connects two drill strings. The tool joint plays an important role in extending the drill pipe, and its effect on pressure losses cannot be ignored. In addition, the drilling muds must have certain qualities such as providing formation integrity, transporting the cuttings from bit to surface, drilling pipe lubrication and heat transfer, and low-pressure loss to perform as a qualified and effective drilling fluid. Therefore, drilling muds have become more complex and expensive. For this reason, oil-based viscoplastic drilling muds are being used in more drilling operations. These drilling muds almost always also show a thixotropic behavior which is the key point of this study.
This paper studied the behavior of fluid flows and frictional pressure losses in weld-on tool-joints of different grades using CFD simulations. The simulations were conducted for a drilling fluid with viscoplastic (similar to the Herschel-Bulkley model) and thixotropic behavior. The characteristics of fluid flows in tool joints under different thermal boundary conditions were studied. Moreover, the different thixotropic behavior models and various thixotropic boundary conditions were compared to select the most fitting model. The results showed that tool joints significantly affect the frictional pressure loss in the annulus. The study also provided an accurate pressure loss prediction for the flow of oil-based viscoplastic muds passing through the tool-joint geometry. Furthermore, using the thixotropic behavior of the Moore-Cheng model for the drilling mud, the transient processes of the beginning of the drilling operations were investigated.
Generation Mechanism of High-Frequency Sound Induced by Supersonic Jet Impinging on Flat Plate
Authors: Suzuki Hiromasa , Endo Masaki , Sakakibara Yoko 
Published: September 2022

Abstract
The underexpanded jet is well known as one of the supersonic jets, and it is formed when the pressure ratio across a convergent nozzle from which the jet is exhausted is more than the critical value. The underexpanded jet has a characteristic barrel-shaped cellular structure. When the underexpanded jet impinges on a flat plate, a detached shock wave called “plate shock” is formed in front of the flat plate. Such flow fields are utilized in industrial applications such as laser processing and tempered glass manufacturing processes. The impinging jet oscillates and induces the high frequency sound called “screech tone”. The present study focused on the screech tone generated from the underexpanded jet impinging on the flat plate and aimed to examine a relation between the high-frequency sound and the jet structure. In the experiment, the jet impinged on a flat plate or a mesh, and the flow characteristics of each case were compared. The pressure ratio was kept constant at 3.0 and the distance between the nozzle and the object being impinged by the jet was changed. Visualization of the flow field and acoustic measurement were carried out under each condition. As a result, integral multiples of the fundamental frequency in the impingement on the mesh agreed with the frequency of the screech tone generated in the impingement on the flat plate. Since the screech tone frequency is based on the feedback loop between the nozzle and the flat plate, this agreement indicates the screech tone is caused by the agreement of the harmonic frequency of the feedback loop between the nozzle and the plate shock with that between the nozzle and the flat plate.
Vortex Identification in Large Eddy Simulations Under the Lattice Boltzmann Framework With a Smagorinsky Subgrid Model
Authors: Jaber Khodr , Essel Ebenezer Ekow , Sullivan Pierre 
Published: September 2022

Abstract
The recent emergence of turbulence modeling strategies under the Lattice Boltzmann Method (LBM) framework has opened the door towards highly efficient numerical solutions for the governing fluids equations with potential application to industry. Advantages of the LBM over traditional Navier-Stokes (NS) based methods include its straightforward parallelization and its ability to recover flow dynamics without explicit treatment for pressure. In the present work, Large Eddy Simulation within a Lattice Boltzmann framework is used to study a lid-driven cavity. In particular, a Smagorinsky subgrid scale model is chosen for the unresolved scales within a single-relaxation-time LBM. Simulations are performed in three dimensions at a Reynolds number of 105. One-dimensional energy spectra are computed and the range of energy scales in the numerical solutions are inspected to ensure that turbulence has been captured. Isosurfaces of various vortex identification criteria are examined and compared to the vorticity magnitude and pressure minima.
Photosynthetic Micro-Swimmers in Oscillating Flow
Authors: Pashmi Elnaz , Peerhossaini Hassan , Jarrahi Mojtaba 
Published: September 2022

Abstract
Swimming and transport of the photosynthetic alga Chlamydomonas reinhardtii in steady and oscillatory shear flows were investigated. Sinusoidal flow of algal suspension was generated in the microchannels using a microfluidic pressure-driven controller. The oscillating flow was expressed as Q (t) = A. sin (ωt) where Q (t), t, A, and ω, represent the instantaneous flow rate, time, amplitude and angular frequency of the oscillating flow, respectively. The different amplitudes considered in the study were A = 0.075, 0.15, 0.22, 0.3 and 0.5 μl/min. Maximum mean velocities corresponding to this range of amplitudes varies between 14.7 μm/s and 392 μm/s depending on the microchannel used in the experiment. At each amplitude, four frequencies were applied: f = 0.5, 1, 2 and 3.3 Hz. The motion of algal cells was recorded and their trajectories in the flow were analyzed. It was shown that the dynamics of cells in the steady flow varies from a random motion to a zigzag motion depending on the flow shear rate. At low shear rates, the average value of the angle (α) between the cell trajectory and flow stream was 40°, and a zigzag motion of the cells was observed between the lateral walls. However, at higher flow shear rates, the mean value of this angle was about 10° with a smaller distribution range (0° &lt; α &lt; 30°) compared to the low shear regime (10° &lt; α &lt; 70°). When the flow condition was turned to a sinusoidal flow, two strong symmetric peaks appeared close to ± 90° in the probability distribution of α. The visualizations of cell trajectories showed that the cells swim perpendicular to the flow direction in wavy-form trajectories such that regardless of the oscillation conditions, their average vertical velocity (Vy) is equal to their motility (130 μm/s).
Ventilation System Performance on the Removal of Respiratory Droplets Emitted During Speaking
Authors: Masoomi Morteza Ali , Salmanzadeh Mazyar , Ahmadi Goodarz 
Published: September 2022

Abstract
The SARS-CoV-2 infection pandemic has led to significant loss of lives and worldwide economic disruption. The leading cause of transmission of infectious respiratory diseases is through aerosolized mucous and salivary droplets containing the virus emitted into the environment through respiratory activities. Depending on their initial size, the droplets evaporate or fall to the ground due to gravitational sedimentation. When a droplet evaporates, the droplet nucleus containing all the viruses in the original droplet remains airborne in the environment for a long duration of time. The ventilation system significantly affects the dispersion and removal of particles from the environment. Therefore, poorly ventilated indoor environments increase the risk of disease transmission. The present study modeled a ventilated small office space with two mannequins sitting across a table. It was assumed that one of the mannequins was speaking and emitting small droplets. Then the effect of the ventilation system on the droplets’ transport and dispersion was simulated. In particular, the performance of the displacement and mixing ventilation systems on particle dispersion and deposition in the room were evaluated and compared. These simulations were performed using the computational fluid dynamics (CFD) approach with Ansys-Fluent software. The Eulerian approach was used to simulate the airflow field in the room, and the Lagrangian trajectory analysis approach was used for the droplets. Experimental data of the thermal plume above the mannequin’s head were used to validate the airflow simulation results. The results showed that the displacement ventilation system has better performance (almost three times more) in removing particles from the environment than the mixing ventilation system.
Dynamic Transition From Mach to Regular Reflection Over a Moving Wedge
Authors: Margha Lubna , Hamada Ahmed A. , Eltaweel Ahmed 
Published: September 2022

Abstract
The design of supersonic and hypersonic air-breathing vehicles is influenced by the transition between the Mach Reflection (MR) and Regular Reflection (RR) phenomena. The purpose of this study is to investigate the dynamic transition of unsteady supersonic flow from MR to RR over a two-dimensional wedge numerically. The trailing edge of the wedge moves downstream along the x-direction with a velocity, V(t) at a free-stream Mach number of. An unsteady compressible inviscid flow solver is used to simulate the phenomenon. Further, the Arbitrary Lagrangian-Eulerian (ALE) technique is applied to deform the mesh during the wedge motion. The dynamic transition from MR to RR is defined by two criteria, the sonic and the Von-Neumann. Moreover, the lag in the dynamic transition from the steady-state condition is studied using various reduced frequencies, κ, in the range of [0.1–2]. The lag effect in the shock system is remarkable at the high values of the reduced frequency, κ = 1.5 and 2.0. Furthermore, because the shock is bent upstream during the fast motion of the wedge, the transition from MR to RR happens below the Dual Solution Domain (DSD).