Vortex Flow Research Articles

On anomalous transport of multi-species plasma associated with the resistive ballooning and resistive drift waves driven turbulence

Anomalous transport of multi-species plasma related to the resistive ballooning and resistive drift wave turbulence is considered in a “cold” ion approximation. It is found that similar to the resistive drift wave turbulence [see A. R. Knyazev and S. I. Krasheninnikov, Phys. Plasmas 31, 012502 (2024); and S. I. Krasheninnikov and R. D. Smirnov, Phys. Plasmas (to be published)] the addition of the ballooning drive does not change the main features of anomalous transport of the multi-species plasma: (i) The transport of all ion species is described as a transport of the passive scalars in the turbulent field of the electrostatic potential and electron density perturbation; (ii) the density of ion species with a larger ratio of the mass to charge has the tendency to the accumulation/depletion in the vortices of plasma flow; and (iii) the cross-field transport of all plasma species (including electrons and ions) is described by the same anomalous transport coefficient.

Performance evaluation of modified pintle-type fuel injector for LRE (liquid rocket engine)

This research focuses on the fluid dynamics analysis and empirical validation of a modified pintle-type fuel injector through computational modeling. The primary aim is to assess the injector's performance metrics, including spray dispersion and orientation, flow velocity, turbulence levels, and vortex formation, by adjusting the pintle's positioning, which inherently modulates the flow rate. The observed effects draw parallels with the interactions seen in conical spray and hollow cone swirl atomizers. A pintle-type fuel injector model was developed using geometric design software, and computational fluid dynamics simulations were conducted to ensure effective fuel and oxidizer blending. This study evaluates key performance indicators, such as thrust output and combustion efficiency, under specific operational pressures and velocities at the injector's orifice.

Controlling Couette flow by alternating axial mass flux

This paper presents numerical simulations of the Taylor vortex flow under the influence of an externally applied alternating axial mass flux (through-flow) in a Taylor–Couette system with axial periodic boundary conditions. Such an axially modulating flow can lead to a significant variation in the onset of primary instabilities. Depending on the system parameters, the effect can be both stabilizing and destabilizing, i.e., shifting the bifurcation threshold to larger or smaller control parameters, respectively. It is found that the system response around the primary instability is sensitive to and critically influenced by an alternating mass flux, particularly the modulation frequency. We show that such an alternating axial flow represents an easily and, more importantly, precisely controllable key parameter to change the nonlinear system response from subcritical to supercritical behavior and vice versa. Furthermore, we observe different parameter regimes with regular and irregular intermittent flow dynamics.

DBN-GABP model for estimation of aircraft wake vortex parameters using Lidar data

Aircraft wake turbulence is an inherent outcome of aircraft flight, presenting a substantial challenge to air traffic control, aviation safety and operational efficiency. Building upon data obtained from coherent Doppler Lidar detection, and combining Dynamic Bayesian Networks(DBN) with Genetic Algorithm-optimized Backpropagation Neural Networks(GA-BPNN), this paper proposes a model for the inversion of wake vortex parameters. During the wake vortex flow field simulation analysis, the wind and turbulent environment were initially superimposed onto the simulated wake velocity field. Subsequently, Lidar-detected echoes of the velocity field are simulated to obtain a data set similar to the actual situation for model training. In the case study validation, real measured data underwent preprocessing and were then input into the established model. This allowed us to construct the wake vortex characteristic parameter inversion model. The final results demonstrated that our model achieved parameter inversion with only minor errors. In a practical example, our model in this paper significantly reduced the mean square error of the inverted velocity field when compared to the traditional algorithm. This study holds significant promise for real-time monitoring of wake vortices at airports, and is proved a crucial step in developing wake vortex interval standards.

Turbulence-assisted shear controllable synthesis of silicon oxide micro/nano particles using a counter axial-swirling impinging jet flow reactor

It has been recognised that turbulence shear can be used to effectively control and affect the synthesis of micro/nano particles. The present study focuses on turbulence-assisted shear controllable synthesis of silica (SiO2) micro/nano particles and investigates such shear controllable synthesis process using a counter axial-swirling impinging jet flow vortex flow reactor. Two counter swirling flow streams impinge in the reaction chamber to significantly intensify the local turbulence shear with the aid of ultrasound irradiation. The consequence of the turbulent shear leads to either the trapping of nano-particle nucleus into the turbulent eddies to form the aggregated micro/nana particles or the confinement of the growth of agglomerated micro/nano particles so as to form highly uniform and better morphological micro/nano particles. The experimental results have affirmed the postulation that the local turbulent shear generated by the turbulent eddies with the length scales down to the Kolmogorov length scale may directly interact with the aggregated SiO2 micro/nano particles, influencing the particle spherical morphology and size distribution. In addition, it has been found that synthesis performance can be further improved by intensifying the local turbulent shear through the ultrasound irradiation in the synthesis process. Both CFD simulation and experimental results clearly indicate the existence of the correlation in the synthesized SiO2 micro/nano particle characteristics with the local turbulence shear and mass transfer occurring in counter swirl impinge jet flow.

Comparison of high-order numerical methodologies for the simulation of the supersonic Taylor–Green vortex flow

This work presents a comparison of several high-order numerical methodologies for simulating shock/turbulence interactions based on the supersonic Taylor–Green vortex flow, considering a Reynolds number of 1600 and a Mach number of 1.25. The numerical schemes considered include high-order Finite Difference, Targeted Essentially Non-Oscillatory, Discontinuous Galerkin, and Spectral Difference schemes. The shock capturing methods include high-order filtering, localized artificial diffusivity, non-oscillatory numerical fluxes, and local low-order switching. The ability of the various high-order numerical methodologies to both capture shocks and represent accurately the development of turbulent vortices is assessed.

Modeling of separated flow over tailings storage facility

Tailings storage facilities are an integral part of modern mining and beneficiation production and the most serious threat to environmental safety. Separated flow over surfaces, even in the case of constancy of their shape, is a very complex phenomenon. The occurrence of a separation with the rise of vortexes into the flow leads to a strong unsteadiness of the flow. To consider such flows, the most common in applied aerodynamics are vortex methods, which are based on replacing the surface and the wake formed behind it with some distribution of vorticity. Numerical calculation technique based on the method of discrete vortexes is used to model the separated non-stationary flow around the tailings storage facilities. This method makes possible to describe the structure of the vortex flow over the tailings storage facilities and behind it, to study the change of vortexes over time, to see the presence and absence of stagnant zones on the windward side of the tailings storage facilities. Prediction of the aerodynamic structure of the flow is a necessary component of the process of justifying decision-making regarding the use of means and methods for dust reduction.

Exploring the combined influence of primary and secondary vortex flows on heat transfer enhancement and friction factor in a dimpled configuration twisted tape with double pipe heat exchanger using SiO2 nano fluid

The double-pipe heat exchanger has a wider application in food industries, chemical industries, and a wide variety of fields where heat transmission is necessary. This investigation focuses on optimizing heat transfer rates through active, passive, and combined approaches. Within the realm of passive methods, this study specifically examines the use of twisted tape additions in pipe flow. In this study, different factors like swirl flow, primary and secondary vortex flows caused by tape twist, and the presence of a V-cut on the tape are studied. These factors include heat transfer rate, friction factor, and the standard for judging the performance of a V-cut on the tape insert. Experiments have been conducted on a double-pipe heat exchanger with nanofluid silicon dioxide as the working medium. This study encompasses a Reynolds number range of 6000–14,000. Notably, investigations reveal that the introduction of a v-cut on the tape engenders a secondary vortex flow. The enhancement in the Nusselt number at the higher Reynolds number for the primary vortex was observed ineffective as the depth of cut increases. The friction factor is increased by 6.37 times for the e/c ratio, which equals 0.17 (tooth to the depth of the v cut) in comparison to smooth pipe, while the increase in heat transfer rate for the same is 87.73% for Re = 6000.

DUGKS-GPU: An efficient parallel GPU code for 3D turbulent flow simulations using Discrete Unified Gas Kinetic Scheme

This paper presents a parallel implementation of the Discrete Unified Gas Kinetic Scheme (DUGKS) on the GPU system using the CUDA Fortran and CUDA C++ programming languages. Firstly, we conducted an extensive revision of our original CPU-based code, resulting in a threefold decrease in memory usage. This new implementation is also paired with a novel approach to compute cell face flux using trilinear interpolation. It is shown analytically that the interpolation-based approach to flux calculation is more accurate compared to the one used in the original DUGKS. The initial simulation results using this new approach suggest that trilinear interpolation can reduce numerical errors on a coarse mesh. For example, in the case of the decaying Taylor-Green vortex flow at a 1283 mesh resolution, the relative numerical error in the energy dissipation rate at t⁎=2, using the spectral simulation result as the benchmark, is approximately 30% lower than that of the original implementation. The improved GPU DUGKS method is applied to laminar and turbulent flows in periodic and wall-bounded boundary configurations. A performance comparison of the GPU implementation is also presented and compared to the previous CPU implementation. A maximum speedup of 7.64x was achieved on a desktop-level GPU compared to a 32-core CPU. The strong scaling test, conducted on an eight-GPU node, demonstrated the efficient utilization of available multiple GPU resources by the code. Program summaryProgram Title: DUGKS-GPUCPC Library link to program files:https://doi.org/10.17632/yykv5s9g2n.1Developer's repository link:https://github.com/kairzhan/DUGKS-GPUCode Ocean capsule:https://codeocean.com/capsule/3b1e4f74-cdd3-4781-8923-8514d5923dfb/Licensing provisions: GNU General Public License 3Programming language: CUDA C++, CUDA FortranSupplementary material:Nature of problem: DUGKS-GPU is an advanced numerical code designed to accelerate the simulation of turbulent fluid flows through the application of the kinetic method known as the Discrete Unified Gas Kinetic Scheme (DUGKS). This computational tool comprises a CUDA Fortran version, tailored for a single GPU, as well as a CUDA C++ version developed for multi-GPU platforms.Solution method: The code employs a second-order finite-volume discretization of the discrete velocity Boltzmann equation with the BGK collision model. It can be used to simulate small to medium-scale problems on modern multi-GPU platforms with CUDA architecture.

Preferential formation of uniform spherical vaterite by harnessing vortex flows and integrated CO2 capture and mineralization

The use of calcium bearing resources to facilitate solvent regeneration and CO2 reuse via carbon mineralization offers a low energy pathway for the production of calcium carbonate. However, a crucial challenge is the lack of specificity in the formation of various calcium carbonate polymorphs during carbon mineralization. One of the less explored but highly effective approaches to tune the morphology and crystal structure of specific carbonate phases involves tuning vortex flows. This approach is an alternative to utilizing chemical reagents that need to be regenerated for tuning the morphologies and crystalline structures to direct the formation of specific carbonate phases. In this study, the efficacy of using homogeneous vortex flows in limiting the agglomeration of carbonate particles and directing the formation of metastable vaterite phases is discussed and contrasted with the influence of inhomogeneous conventional feed flow patterns on precipitated calcium carbonate (PCC). Herein, a Taylor-Couette Carbonate Conversion (TC3) reactor is used to direct the formation of spherical vaterite particles with uniform particle size distribution preferentially over calcite and other phases. The formed vortex patterns inside TC3 reactor provide homogeneous reaction spaces conducive to PCC formation, ensuring uniform mixing throughout the process. By increasing the rotational speed and the residence time, higher purity carbonates with more uniform sizes are obtained. Furthermore, preferential vaterite formation is also observed in leachates obtained from alkaline industrial residues such as construction and demolition waste and steel slag. Thus, the proposed approach is effective in harnessing multiple waste streams such as CO2 emissions and alkaline industrial residues to produce calcium carbonate phases such as vaterite with structural and morphological specificity.

Effect of urban street canyon aspect ratio on fire-induced air pollutants dispersion under cross wind

The incidence of vehicle fires in urban street canyons has continuously increased with the process of urban modernization. The dispersion and accumulation of fire-induced air pollutants seriously affect residents’ safety. The effects of the street canyon aspect ratio and fire source location on fire-induced air pollutants dispersion under cross wind were numerically investigated in the paper. The results show that the street canyon aspect ratio can affect flow patterns and vortex structure and then lead to different accumulation states of air pollutants. Smoke development can be divided into four different regimes according to cross wind velocity. The re-entrainment phenomenon occurs when the fire source is close to the windward building or in the center of the street, but it does not occur when the fire source is close to the leeward building. Smoke tends to accumulate in street canyons when the aspect ratio is smaller and the fire source is closer to the leeward building. The variation of critical velocity with the aspect ratio can be divided into three regions, i.e., initial linear growth region (0.5 ≤ W/H < 1), constant region (1 ≤ W/H ≤ 1.5), and second linear growth region (1.5 < W/H ≤ 2). The dimensionless critical velocity and critical Froude number are used to quantify the re-entrainment phenomenon in different fire scenarios, and prediction models are finally proposed. The main findings can provide a more detailed reference for urban layout and air pollution control to reduce fire-induced air pollutants.

Observation of current whirlpools in graphene at room temperature.

Electron-electron interactions in high-mobility conductors can give rise to transport signatures resembling those described by classical hydrodynamics. Using a nanoscale scanning magnetometer, we imaged a distinctive hydrodynamic transport pattern-stationary current vortices-in a monolayer graphene device at room temperature. By measuring devices with increasing characteristic size, we observed the disappearance of the current vortex and thus verified a prediction of the hydrodynamic model. We further observed that vortex flow is present for both hole- and electron-dominated transport regimes but disappears in the ambipolar regime. We attribute this effect to a reduction of the vorticity diffusion length near charge neutrality. Our work showcases the power of local imaging techniques for unveiling exotic mesoscopic transport phenomena.

Tetralogy of Fallot regurgitation energetics and kinetics: an intracardiac flow analysis of the right ventricle using computational fluid dynamics.

Repaired Tetralogy of Fallot (rTOF) patients suffer from pulmonary regurgitation and may require pulmonary valve replacement (PVR). Cardiac magnetic resonance imaging (cMRI) guides therapy, but conventional measurements do not quantify the intracardiac flow effects from pulmonary regurgitation or PVR. This study investigates intracardiac flow parameters of the right ventricle (RV) of rTOF by computational fluid dynamics (CFD). cMRI of rTOF patients and controls were retrospectively included. Feature-tracking captured RV endocardial contours from long-axis/short-axis cine. Ventricular motion was reconstructed via diffeomorphic mapping, serving as domain boundary for CFD simulations. Vorticity (1/s), viscous energy loss (ELoss, mJ/L) and turbulent kinetic energy (TKE, mJ/L) were quantified in RV outflow tract (RVOT) and RV inflow. These parameters were normalized against total RV kinetic energy (KE) and RV inflow vorticity to derive dimensionless metrics. Vorticity contours by Q-criterion were qualitatively compared. rTOF patients (n = 15) had mean regurgitant fraction 38 ± 12% and RV size 162 ± 35mL/m2. Compared to controls (n = 12), rTOF had increased RVOT vorticity (142.6 ± 75.6/s vs. 40.4 ± 11.8/s, p < 0.0001), Eloss (55.6 ± 42.5 vs. 5.2 ± 4.4mJ/L, p = 0.0004), and TKE (5.7 ± 5.9 vs. 0.84 ± 0.46mJ/L, p = 0.0003). After PVR, there was decrease in normalized RVOT Eloss/TKE (p = 0.0009, p = 0.029) and increase in normalized tricuspid inflow vorticity/KE (p = 0.0136, p = 0.043), corresponding to reorganization of the "donut"-shaped tricuspid ring-vortex. The intracardiac flow in rTOF patients can be simulated to determine the impact of PVR and improve the clinical indications guided by cardiac imaging.

Characterizing the Unsteady Flow Field in Low-Flow Turbine Operation

Abstract Current operational considerations require steam turbines to operate in a more flexible way, with more frequent and faster start-up and an increasing part-load operation. For very low mass flowrates, the interaction of highly separated flow with the high-speed rotor blades causes windage flow. This type of flow is characterized by increased temperature and highly unsteady flow, which forms vortex structures that rotate at a fraction of the rotor speed. If their magnitude is sufficiently high and the frequency is close to the blade eigenfrequency, non-synchronous vibration (NSV) can be induced. In this paper, low-flow turbine operation is investigated using a three-stage turbine rig that features an instrumentation concept focused on capturing aerodynamic and aeroelastic phenomena. Extensive steady probe, unsteady pressure, and tip-timing measurements are utilized. The experimental scope covers a wide range of operating points in terms of rotational speed and mass flowrates. Low-flow regimes are detected by a reversal in torque and increase in temperature. Unsteady measurements during transient operation identified large-scale vortical flow structures rotating along the circumference, so-called rotating instabilities (RIs). The onset, growth, and breakdown regimes of RI are characterized for different low-flow conditions. The quantitative characteristics of RI with regard to nodal diameter and rotational speed are derived by a cross-correlation of multiple unsteady sensors. The blade vibration measurements show a moderate structural response from unsteady aerodynamic excitation, indicating no significant NSV occurring in the present experimental setup. Later in the study, an acoustic excitation system has been applied to trigger a locked-in NSV without interrupting the coherent flow structures. From that, significant blade response has been observed, revealing a high degree of mistuning and damping of the rotor blading.

Optimisation of design parameters for a novel two-piston ionic compressor applied in hydrogen storage

The ionic compressor is an advanced and prospective compression technology for hydrogen storage. However, a complex wave phenomenon was observed inside the compression chamber due to the fluid flow vortex. This complex gas-fluid interaction can be intervened by a new mechanical design of the motion piston. In this paper, the thermodynamic performance of a novel homocentric two-piston ionic compressor was carried out by mathematical modelling of one compression cycle. The optimisation of the design parameters of the compressor proposed was conducted by the Taguchi method. This study found that the piston diameter ratio was the dominating factor accounting for more than 80 % of the contribution to the mass delivered, power consumption and specific energy consumption. The optimal design parameters were obtained as 0.7 for the piston diameter ratio, 0.5 for the stroke diameter ratio of Piston A and 0.1 for the trajectory parameter. Under the optimal design parameters, the specific energy consumption was obtained as 1563.38 kJ/kg.

Shear-Induced Nonequilibrium Patterns in Lipid Bilayer Membranes Exhibiting Phase Separation.

The nonequilibrium dynamics of a fluid lipid membrane under external stimuli is an important issue that spans disciplines such as soft matter, biophysical chemistry, and interface science. This study investigated the dynamic response of lipid vesicles with order-disorder phase separation, which mimics a plasma membrane heterogeneity, to shear flow. Lipid vesicles were immobilized in a microfluidic chamber, and shear-induced nonequilibrium patterns on the membrane surface were observed by an optical microscope. We found that phase-separated membranes exhibit a dissipative structure of stripe patterns along the vortex flow on the membrane surface, and the number of stripes increased with the flow rate. At a high flow rate, the membrane exhibited a stripe-to-wave transition, where striped domains often migrated and the replacement of two different phases happened at vortex centers with time. We obtained a dynamic phase diagram of the shear-induced wave pattern by changing the flow rate, membrane components, and temperature. These findings could provide insight into the dissipative structures of lipid membranes out of equilibrium and flow-mediated mechanotransduction of biological membranes.

Numerical investigation of fluid flow and heat transfer characteristics of MWCNT-Al 2 O 3/H 2 O hybrid nanofluid flowing through a novel semi-arc ribbed square duct

This study carried CFD analysis to study the fluid flow and heat transfer characteristics of MWCNT- Al 2 O 3 / H 2 O hybrid nanofluid flowing through square duct equipped with novel semi-arc ribs. The turbulent flow simulations are performed at varying Reynolds numbers ( Re ) between 3,000 and 18,000 and nanoparticle volume concentration ( φ ) range of 1–4% for different rib parameters, namely relative stream pitch ratio ( X pr ) range from 2.67 to 3.67, Rib height ratio ( R hr ) range from 0.05 to 0.20, number of ribs ( n ) range from 1 to 4. Different performance indicators, such as Nusselt number ( Nu ), friction factor ( f r ) , and thermal hydraulic performance (THP) was examined to evaluate the system performance. The RNG k ‐ ε model was engaged to simulate turbulent nanofluid flow within the channel under constant temperature condition (T = 300 K). The findings indicated that the development of vortex flow and increased turbulence due to the effects of arcs can improve the heat transfer enhancement. The THP, Nu and f r were found to be highest for R hr = 0.15 , X pr = 3.34 , φ = 4 % , and n = 3 , yields to the best THP at 1.94.

Study on multiple influence mechanism of airflow-dust-gas coupling diffusion under large vortex flow technology

In response to the serious dust pollution and excessive gas concentration in fully mechanized excavation face, a multi-phase coupling diffusion model of airflow-dust-gas was established, and the influence of pressure pumping ratio and air volume on dust and gas diffusion was studied. The results showed that the dust of the traditional ventilation mode was diffused to the whole roadway, and the high-concentration gas accumulated obviously. However, after adopting the new ventilation mode of large vortex flow, a quantity of dust was controlled in the eddy field, and high-concentration gas was dissipated by strong airflow, so there was no gas accumulation. As the pressure pumping ratio decreases, the extraction effect increases, the eddy current intensity also increases, and the control effect on dust is enhanced. The pressure pumping ratio with the best dust control effect is 0.6, and there is no dust pollution and no gas accumulation in the driver's location. The fixed pressure pumping ratio is 0.6, and the diffusion of dust and gas is not significantly affected by an increase in air volume, but high-speed airflow can dilute and reduce the concentration of dust and gas. When Qb = 600.0 mg/m³, the high-speed airflow can dilute the dust concentration, accelerate the dispersion of high-concentration gas, keep the gas below the safe level, and have a good dust control effect. The increase of air volume will further reduce the dust and gas concentration. This study provides a theoretical basis for the promotion and utilization of new ventilation method on-site.

High fidelity core flow measurement experiment for an advanced research reactor using a real scale mockup

Owing to spatial effects and vortex flow, flow in research reactors that use plate-type fuels can be maldistributed to the parallel channels of the core, which significantly impacts the reactor safety. In this study, the core flow of an advanced research reactor was measured in a real-scale facility under various hydraulic conditions. For flow measurement, integrated pressure lines were embedded in the mockups of 22 fuel assemblies and six fission molybdenum assemblies. Each assembly mockup was individually calibrated to obtain the relationship between the pressure drop and flow rate. Real-scale facility, which implements the characteristics of the hydraulic conditions in research reactors, was then used to evaluate the assembly-to-assembly flow distribution under normal operating condition, a partially withdrawn condition for the follower fuel assemblies, no flow for the pool water management system, and 1:1.5 asymmetric inlet flow condition. As a parallel channel system, core flow distribution was analyzed with conventional header design approach. Taking into account the measuring uncertainty, the core flow was uniformly distributed within 5 % under all conditions. This was mainly because the core flow resistance was sufficiently high and the vortex flow was minimized by the perforated plate.

Experimental and model study of swirling fluid flow in a converging channel as a simulation of blood flow in the heart and aorta

The study of swirling flows in channels corresponding to the static approximation of flow channels of the heart and major vessels with a longitudinal-radial profile zR2 = const and a concave streamlined surface at the beginning of the longitudinal coordinate has been carried out. A comparative analysis of the flow structure in channel configurations zRN = const, where N = –1; 1; 2; 3, in the absence and presence of a concave surface was carried out. The numerical modelling was compared with the results of hydrodynamic experiments on the flow characteristics and the shape of the flow lines. The numerical model was used to determine the velocity structure, viscous friction losses and shear stresses. Numerical modelling of steady-state flows for channels without a concave surface showed that in the channel zR2 = const there is a stable vortex flow structure with the lowest viscous friction losses. The presence of a concave surface of sufficient size significantly reduces viscous friction losses and shear stresses in both steady state and pulsed modes.