Plane Jet Research Articles

Numerical simulation of a flat turbulent near-wall jet in the OpenFOAMv7 package

In this research, the numerical simulation of a planar stationary near-wall turbulent jet using the OpenFOAMv7 package at Reynolds number, Re, equal to 9600 has been performed. Comparison of numerical results with corresponding experimental data on longitudinal velocity profiles shows the adequacy of the used mathematical model of the problem under consideration. This model should be used in further studies of turbulent jet flows.

Ambient-temperature liquid jet targets for high-repetition-rate HED discovery science

High-power lasers can generate energetic particle beams and astrophysically relevant pressure and temperature states in the high-energy-density (HED) regime. Recently-commissioned high-repetition-rate (HRR) laser drivers are capable of producing these conditions at rates exceeding 1 Hz. However, experimental output from these systems is often limited by the difficulty of designing targets that match these repetition rates. To overcome this challenge, we have developed tungsten microfluidic nozzles, which produce a continuously replenishing jet that operates at flow speeds of approximately 10 m/s and can sustain shot frequencies up to 1 kHz. The ambient-temperature planar liquid jets produced by these nozzles can have thicknesses ranging from hundreds of nanometers to tens of micrometers. In this work, we illustrate the operational principle of the microfluidic nozzle and describe its implementation in a vacuum environment. We provide evidence of successful laser-driven ion acceleration using this target and discuss the prospect of optimizing the ion acceleration performance through an in situ jet thickness scan. Future applications for the jet throughout HED science include shock compression and studies of strongly heated nonequilibrium plasmas. When fielded in concert with HRR-compatible laser, diagnostic, and active feedback technology, this target will facilitate advanced automated studies in HRR HED science, including machine learning-based optimization and high-dimensional statistical analysis.

Data-driven global stability of vertical planar liquid jets by dynamic mode decomposition on random perturbations

A data-driven approach to estimate the global spectrum of gravitational planar liquid jets (sheet or curtain flows) is presented in this work. The investigation is carried out by means of two-dimensional numerical simulations performed through the solver BASILISK, based on the one-fluid formulation and the volume-of-fluid approach. The dynamic mode decomposition technique is applied to extract the underlying linear operator, considering random perturbations of the base flow. The effectiveness of this procedure is first evaluated comparing results with those of a simplified one-dimensional curtain model in terms of spectrum and eigenfunctions. The methodology is then applied to a two-dimensional configuration obtaining the BiGlobal spectra for both supercritical (Weber number We > 1) and subcritical (We < 1) regimes. Results highlight that in supercritical regime, the spectrum presents three branches: the upper and lower ones exhibit a purely sinuous behavior with frequencies quite close to those predicted by the one-dimensional model; the middle branch presents a predominant varicose component, increasing with the frequency. The subcritical spectrum, instead, shows that the first two less stable eigenvalues, sorted by increasing frequency, exhibit, respectively, a sinuous and a varicose behavior, while their growth rate is almost the same. As expected, the subcritical regime does not reveal the slow branch. The effect of the density ratio, rρ, between the two phases is investigated, revealing that the flow system is unstable for rρ>0.05. Topological inspections of the leading modes in this unstable configuration show that the predominance of a varicose behavior is related to the rupture of the curtain.

Implicit large-eddy simulation of turbulent plane jet at Re = 104

In this study, implicit large-eddy simulations (ILESs) are performed for a turbulent plane jet at a Reynolds number 104 to assess the capability of ILESs in simulating turbulent transport in free shear flows. To investigate the effect of resolved turbulent scales on the self-similar behavior of the plane jet, ILESs are conducted using fifth- (ILES+P5), seventh- (ILES+P7), and ninth-order polynomial (ILES+P9) interpolation methods, as well as the third-order MUSCL method (ILES+M3). ILES+P5, ILES+P7, and ILES+P9 reproduced the results of the direct numerical simulation (DNS) for a plane jet at Re = 104. The resolution of the power spectral density of ILESs with high-order interpolation schemes, which agrees well with the DNS, increases as the order of spatial accuracy increases and resolves more than 80% of the total energy. Hence, we conclude that the spatial resolution to resolve up to the frequency region that contains approximately 80% of the turbulent energy is required to obtain good agreement with the results of DNS, which is widely accepted in LES with the subgrid-scale (SGS) model and is also valid for ILES.

Large eddy simulation of temperature-variation effect of impinging planar lobed synthetic jet on flat plate and the semi-cylindrical concave plate

Temperature-variation becomes increasingly evident when an impinging synthetic jet is restricted and confined excessively by the target plate. However, the confinement effect of the target plate on the temperature-variation effect during impinging heat transfer by a synthetic jet has not been clarified. In this study, impinging heat transfer by a synthetic jet induced by a planar lobed orifice on a flat plate and a semi-cylindrical concave plate is investigated by means of Large Eddy Simulation. The planar lobed synthetic jet is characterized by the geometry of the lobed nozzle, and the velocity along its major diameter is larger than that along its minor diameter. As the mainstream jet moves downstream, the difference between the major and minor diameters decreases gradually. At dimensionless jet-to-surface distance of H/d = 8, the flow field attached to the flat plate along the major diameter is similar to that along the minor diameter. The results show that two types of mechanisms have induced the temperature-variation. For the flat plate, its temperature-variation comes from the suction of the wall jet near the stagnation region confined by the target plate, which becomes more conspicuous particularly at small dimensionless jet-to-surface distance. By contrast, the temperature-variation is less conspicuous at large dimensionless jet-to-surface distance because the inhaling region is distant from the target plate. For the concave plate, its temperature-variation is due to the large recirculation zone along the curvilinear direction. During the suction process of the cycle, the heated wall jet attached to the plate surface is re-inhaled into the cavity through the large recirculation zone, and the temperature of the air inside the cavity increases. During the ejection process of the cycle, the wall jet is entrapped into the jet mainstream and then returns to the target plate. Correspondingly, the mean velocity of the wall jet and the wall shear stress of the target plate are less than those of the flat plate. Time and frequency analyses had revealed the characteristics of inherent aggressive pulsation inside the planar lobed synthetic jet. The velocity in the primary frequency dominates the planar lobed synthetic jet, whereas higher-order velocities are negligible.

Dynamics of a liquid sheet with a broken time reversal

With the presence of the odd viscosity, the linear instability of a planar jet (sheet) surrounded by an inviscid gas medium is explored for varicose and sinuous modes. The previous studies on sheet mechanics did not consider the role of the odd viscosity when measuring the maximum growth rate, dominant wave number, instability limit, and breakup length. Semi-dominant characteristic of the odd viscosity is that it is a stabilizing factor for the state of a liquid sheet. It is an unstable factor in a few cases as dictated by the model parameters, such as the odd viscosity number, aerodynamic force, Reynolds number, ambient gas density, and Weber number. In the production of metal alloys, metal powders, and the cooling and descaling stages of downstream metal manufacturing processes, particularly in the steel industry, sprays may be employed in a variety of ways.

Two-Phase Flow Modeling for Bed Erosion by a Plane Jet Impingement

This paper presents experimental and numerical studies on the erosion of a horizontal granular bed by a two-dimensional plane vertical impinging jet to predict the eroded craters’ size scaling (depth and width). The simulations help understand the microscopic processes that govern erosion in this complex flow. A modified jet-bed distance, accounting for the plane jet virtual origin, is successfully used to obtain a unique relationship between the crater size and a local Shields parameter. This work develops a two-phase flow numerical model to reproduce the experimental results. The numerical techniques are based on a finite volume formulation to approximate spatial derivatives, a projection technique to calculate the pressure and velocity for each phase, and a staggered grid to avoid spurious oscillations. Different options for the sediment’s solid-to-liquid transition during erosion are proposed, tested, and discussed. One model is based on unified equations of continuum mechanics, others on modified closure equations for viscosity or momentum transfer. A good agreement between the numerical solutions and the experimental measurements is obtained.

Resuspension of trace explosive particle residues by planar impinging jet: Effects of exposure duration and wall shear stress

Aerodynamic particle resuspension is important in many practical applications, such as surface cleaning, understanding particle fate in the environment, and surface sampling. In practical application, the probability of particle resuspension from the surface depends on several parameters, such as particle size, morphology, chemical composition, surface properties, environmental and flow conditions. The wall shear stress (τw) links fluid motion and forces acting on the particle and can be used to characterize particle resuspension. The literature reports that the resuspension rates decay as 1/t at long exposure times; however, the effect of very short exposures to aerodynamic forces on the resuspension of irregular microparticles has not been characterized. This work examines the effect of τw and exposure duration utilizing planar jet pulses. We evaluated resuspension silica spheres and irregular Trimethylenetrinitramine (RDX) microparticles from a smooth glass surface with a 10–100 ms pulse duration and extended exposure (60 s) for the same wall shear stresses. Reducing the jet duration shows that the removal rate is inversely proportional to exposure time; the trend is more visible at lower τw. At higher shear stresses, up to 80% of particles are removed in the first 10 ms of exposure to aerodynamic force.

Air curtains: validation of results from small-scale laboratory waterbath experiments by real-scale measurements in climate chambers and numerical simulations

An air curtain is a planar turbulent air jet, which is used to separate two zones maintained at different temperatures. One of the aims of using an air curtain in the doorway of a building is to minimise the heat losses from the warm room to the cold environment and thus, to save energy. It is important to know how well an air curtain performs in a given operating scenario in order to assess its energy saving potential. In recent literature, it was proposed to use the waterbath experimental technique as a quick and inexpensive tool for testing the performance of an air curtain in a given scenario. The first central objective of the present study is to validate whether results obtained from small-scale waterbath experiments (WB) are adequate to describe the performance of a real-scale air curtain. To this end, we selected scenarios previously investigated by means of WB experiments and conducted real-scale measurements (RS) with a commercially available air curtain device (ACD) in a climate chamber, and RANS numerical simulations (NS) reproducing the configuration of the ACD in the climate chamber. These scenarios include (I) the base case of a downwards discharging air curtain when the doorway is the only connection between the two rooms, (II) the case when there is an additional top-level ventilation pathway between the rooms as well as (III) the case of a downwards blowing heated air curtain when the rooms are again joined only by the doorway. The second main goal of the present study is to verify the previously developed theoretical models for scenarios (II) and (III) by real-scale measurements and numerical simulations. As the main results, we establish that the effectiveness curves for an ACD obtained from WB experiments on the one hand as well as RS and NS measurements on the other exhibit the same general trends but also possess some minor differences for which we offer possible explanations. Furthermore, we find that RS and NS data are very well described by the previously proposed theoretical models in scenarios (II) and (III). The main finding of the present study is that the waterbath technique can be used as a reliable investigation tool to assess the general trends of the performance of an ACD in a given scenario but should be complemented by a small amount of RS or NS measurements if the finer details are important.

Direct numerical simulation of planar turbulent jets: Effect of a pintle orifice

The effects of a pintle-shaped orifice on a planar turbulent jet flow at Reynolds number 4000, based on the inlet bulk mean velocity and the jet width, are studied using direct numerical simulations. Flapping of the jet along with a low-frequency modulation of the Kelvin–Helmholtz (KH) instability, in the presence of a pintle-shaped orifice, is observed. To compare the pintle-jet behavior, a free-jet is simulated as a reference case. The effects of the near-field region on the far-field flow characteristics have been investigated. In both the cases, the KH instability in the near-field influences the far-field jet, whereas the pintle-jet also exhibits a low-frequency flapping. In addition, oblique vortex pattern has been observed in the case of pintle-jet. The far-field flow statistics of the pintle-jet with a top-hat inlet interestingly agree with those of the free-jet with a hyperbolic tangent inlet. Temporal variation of the jet characteristics has been analyzed using spatiotemporal plots. In addition, the large- and small-scale turbulent motion have been studied using three anisotropic invariant maps (turbulence triangles, eigenvalue, and barycentric maps). Moreover, that the barycentric map gives a better visualization of the anisotropic behavior has been observed in the current study.

Low-energy activation of large convective heat transfer via flow resonance triggered by impinging jet

Cooling performance by natural convection is generally enhanced by increasing the surface area using fin arrays, but their implementation is problematic in large surfaces such as a building facade. We recently reported a phenomenon whereby flow resonance triggered by an impinging jet can enhance convective heat transfer without the need of increased surface area. Here, we propose and investigate the concept of a low-energy activation method (i.e. using moderate jets) based on flow resonance for convective heat transfer enhancement over extensive surfaces. We focus on varying the impinging location yimp near the leading edge of the heated plate (local Rayleigh number of Ray≤5×107 or yimp≤300 mm), the momentum of the impinging planar jet (Reynolds number of Re≤400), and the net buoyancy of the thermal boundary layer (global Rayleigh number of Ra≤1.12×1011, i.e. ≤4m vertical walls heated at 316 K). Instability waves were observed downstream over the heated surface via simulations (computational fluid dynamics) and experiments (large-aperture interferometry), resulting in a downstream heat transfer enhancement compared to that of pure natural convection of about 40% to 60% depending on the impinging position for plates shorter than 1 m. However, turbulent convective heat transfer was reduced from the natural convection case at high Ray. As a means of introducing flow resonance in the thermal boundary layer, we demonstrate that the frequency of the oscillating flow in the mixed convection region can be tuned by selecting appropriate Reynolds number and impinging position of the jet. A combination of flow resonance generation (downstream) and boundary layer thinning around the impinging region (upstream) yields a low-energy activation method for enhancing convective heating and cooling performance.

Zonal modeling of air distribution impact on the long-range airborne transmission risk of SARS-CoV-2

A widely used analytical model to quantitatively assess airborne infection risk is the Wells-Riley model which is limited to complete air mixing in a single zone. However, this assumption tends not to be feasible (or reality) for many situations. This study aimed to extend the Wells-Riley model so that the infection risk can be calculated in spaces where complete mixing is not present. Some more advanced ventilation concepts create either two horizontally divided air zones in spaces as displacement ventilation or the space may be divided into two vertical zones by downward plane jet as in protective-zone ventilation systems. This is done by evaluating the time-dependent distribution of infectious quanta in each zone and by solving the coupled system of differential equations based on the zonal quanta concentrations. This model introduces a novel approach by estimating the interzonal mixing factor based on previous experimental data for three types of ventilation systems: incomplete mixing ventilation, displacement ventilation, and protective zone ventilation. The modeling approach is applied to a room with one infected and one susceptible person present. The results show that using the Wells-Riley model based on the assumption of completely air mixing may considerably overestimate or underestimate the long-range airborne infection risk in rooms where air distribution is different than complete mixing, such as displacement ventilation, protected zone ventilation, warm air supplied from the ceiling, etc. Therefore, in spaces with non-uniform air distribution, a zonal modeling approach should be preferred in analytical models compared to the conventional single-zone Wells-Riley models when assessing long-range airborne transmission risk of infectious respiratory diseases.

Evaluating surface heat flux in planar water-jet cooling of moving hot solid by inversely solving steady-state heat conduction

In steel-manufacturing industries, water-jet quenching of a moving hot solid is commonly used for run-out table cooling in hot rolling mills. Hence, the evaluation of the surface heat flux in the jet-impact region is necessary for precise temperature control. In this study, we developed an evaluation method for surface heat flux in the impact region by inversely solving the steady-state heat-conduction equation, considering the temperature profile on the reverse side of jet impingement. The main advantage was that the heat-flux distribution could be evaluated with a high spatial resolution. The developed method was validated using the exact solution of the heat-conduction equation. The inverse analysis was highly sensitive to the numerical scheme and small errors in the temperature profile on the reverse side. An appropriate numerical scheme and smoothing operation of the temperature profile allowed the reasonable evaluation of surface heat flux on the cooled surface. In addition, the developed method was applied to laboratory-scale cooling experiments to confirm its applicability. The heat-transfer characteristics of planar jet impinging on a moving solid were studied in the conditions that the temperature of the solid with 0.5 mm thickness was 200–600 °C, and its velocity was 1.5, 3.0, and 4.4 m/s. The heat flux in the jet-impact region depended significantly on these parameters.

Theoretical Model and Solution of Dynamic Evolution in Initial Stage of Lacustrine Delta

Sediment is carried by flows into lake during the formation of lacustrine deltas. The subsequent movement of sediment-laden flow is maintained by the initial momentum at the early stage of delta growth. A theoretical model of the plane jet boundary layer in the initial stage of a lacustrine delta, including the consideration of gravity action on the slope and bottom friction, was established according to characteristics of this process, and a similarity solution method was used to solve the model. A coefficient ε was introduced that describes the characteristics of sediment-laden flow spreading along a straight line and its value is given. The theoretical expression of morphological characteristics of the initial stage was derived based on the general mathematical model of river bed evolution, and the erosion and deposition patterns were quantitatively analyzed. It was verified through experimental data that the theoretical model can be solved accurately and, can satisfactorily describe the trend in erosion and deposition and morphological characteristics of the initial stage of a delta.

Turbulent planar wakes of viscoelastic fluids analysed by direct numerical simulations

Direct numerical simulations employing the finitely extensible nonlinear elastic constitutive model closed with Peterlin's approximation (FENE-P) are used to investigate the far-field region of turbulent planar wakes of viscoelastic fluids and to develop the theory describing these flows. The theoretical results display excellent agreement with the simulations and provide new scaling laws for the evolution of the shear layer thickness $\delta (x) \sim x^{1/2}$ , mean velocity deficit ${\rm \Delta} U(x) \sim x^{-1/2}$ and, for very high Deborah numbers, of the maximum polymer shear stresses $\sigma ^{[p]}_c(x) \sim x^{-2}$ and averaged polymer chain extension $\textrm {tr}(\bar {C}(x) - \boldsymbol{\mathsf{I}}) \sim x^{-2}$ , where $x$ is the streamwise distance from the solid body generating the wake. The theory is able to show the existence of self-similarity for the profiles of mean velocity, mean polymer shear stress, averaged polymer chain extension and the conditions for similarity of the turbulent shear stress, and is very well supported by the numerical simulations. Similarly to the case of viscoelastic turbulent planar jets (Guimarães et al., J. Fluid Mech., vol. 899, 2020, p. A11), when the inlet Weissenberg and Deborah numbers are sufficiently large, turbulent viscoelastic wakes exhibit a considerable reduction of the spreading rate and of the normalised Reynolds stresses. However, for very large downstream locations the turbulent viscoelastic wake recovers the classical evolution laws observed for Newtonian turbulent planar wakes.

Evaluation of entropy driven jet symmetry transitions

Here we determine whether entropy drives planar turbulent jets into round turbulent jets. Determining when a jet flow transitions from one symmetry to the next is an important but incompletely resolved problem. The constructal view argues that the transition between symmetries of jet flows is governed by the minimization or maximization of entropy. Here we explore whether entropy increases with the transition of a planar turbulent jet into a round turbulent jet and whether entropy maximization (or minimization) predicts the same location of symmetry transition as velocity matching. We find that entropy considerations presented do not predict this transition.

Model for Wall Shear Stress from Obliquely Impinging Planar Underexpanded Jets

Though inclined under-expanded planar jets are used in many practical applications, the wall stress resulting from their impingement has not been adequately characterized. Reduced-order models for wall shear as a function of jet parameters have not been reported. This work uses computational fluid dynamics to determine wall shear stress as a function of the nozzle parameters and jet angle. The simulations of the impinging jet are validated against the experimental data and direct numerical simulation; then, the jet parameters are varied to formulate an empirical relationship for maximum wall shear stress as a function of a nozzle pressure ratio, standoff distance, jet Reynolds number, and impingement angle. The global expression for shear stress agrees with the numerical results within a mean deviation of 3%. The relationship can be used for applications where shear stress information is required to design or assess the performance of practical systems, such as surface cleaning, particle resuspension from the surface, and surface cooling.

Modal analysis and interface tracking of multiphase flows using Dynamic Mode Decomposition

Non-invasive visualization techniques for multiphase flows are critical to understanding primary atomization and sprays. We use back-lit imaging to identify the liquid–gas interface of two-phase flows at high temporal and spatial resolutions and employ Dynamic Mode Decomposition (DMD) to study the shape and frequency of instabilities of a liquid jet surrounded by a coaxial annular airblast atomizer. However, DMD is not suitable for interface tracking, so we develop a data-driven two-step approach using the optical sensor data. The method uses DMD on the optical flow field estimated from image snapshot pairs. We demonstrate our method to a representative toy problem of an oscillating drop and on the primary atomization of a numerical planar liquid jet. Finally, we apply our method to the experimental liquid jet from the coaxial airblast atomizer using back-lit imaging. Our method is able to accurately reconstruct and predict the flow and preserves the sharpness of the fluid interface.

Rotationally resolved gas-phase spectrum of the [formula omitted]2Σ+–[formula omitted]2Π3/2 electronic transition for the cyanogen halide radical cation ICN+

A rotationally resolved gas-phase absorption spectrum of the A∼2Σ+–X∼2Π3/2 electronic transition of the cyanogen iodide radical cation ICN+ was observed by cavity ring-down spectroscopy for the first time. This cation was produced in a supersonic planar discharge jet through a mixture of ICN in helium. By the aid of a program for rotational, vibrational and electronic spectra PGOPHER, the rotational constants were determined to be 0.10700(12) and 0.11002(12) cm−1 for the A∼2Σ+ and X∼2Π3/2 electronic states, respectively, and the band origin to be 18262.083(3) cm−1. The rotational constant ratio β {= (B′−B″)/B″} was determined to be −2.8%. The β values for FCN+, ClCN+, BrCN+, and ICN+ were also evaluated theoretically by CAM-B3LYP/CEP-121G using Gaussian 09W. The rotational profile of the absorption band and its temperature dependence for ClCN+, one of the important candidates for Diffuse Interstellar Bands, were simulated, aiding us in the identification of this cation as in interstellar space.

Linear stability analysis of sediment-laden planar turbulent jets in shallow waters

When a river debouches into a shallow receiving basin, it behaves as a sediment-laden shallow jet which plays a key role in the subsequent sediment transport and morphological evolution at the river mouth. A linear stability analysis that directly incorporates the effect of the presence of suspended sediment on the hydrodynamic instability of shallow jets was performed in this study. The sediment effect was accounted for using a two-way coupling. The onset of the instability was found to be generally insensitive to the addition of moderate quantities of suspended sediment particles. However, an eigenfunction analysis indicated that the nonlinear development of the instabilities may indeed be affected by the presence of sediment. The results of this study have important implications for estuarine and deltaic geomorphology, and can inform delta restoration projects such as artificial diversion to achieve maximum land building potential.