Hydrodynamic Modes Research Articles

Local univalence versus stability and causality in hydrodynamic models

Our primary goal is to compare the analytic properties of hydrodynamic series with the stability and causality conditions applied to hydrodynamic modes. Analyticity, in this context, serves as a necessary condition for hydrodynamic series to behave as a univalent function. Stability and causality adhere to physical constraints, ensuring that hydrodynamic modes neither exhibit exponential growth nor travel faster than the speed of light. Through an examination of various hydrodynamic models, such as the Müller–Israel–Stewart (MIS) and the first-order hydro models like the BDNK (Bemfica–Disconzi–Noronha–Kovtun) model, we observe no new restrictions stemming from the univalence limits in the shear channels. However, local univalence is maintained in the sound channel of these models despite the global divergence of the hydrodynamic series. Notably, differences in the sound equations between the MIS and BDNK models lead to distinct limits. The MIS model’s sound mode remains univalent at high momenta within a specific transport range. Conversely, in the BDNK model, the univalence of the sound mode extends to intermediate momenta across all stable and causal regions. Generally, the convergence radius is independent of univalence, and the given dispersion relation predominantly influences their correlation. For second-order frequency dispersions, the relationship is precise; i.e., within the convergence radius, the hydro series demonstrates univalence. However, with higher-order dispersions, the hydro series is locally univalent within certain transport regions, which may fall within or outside the stable and causal zones.

Fluctuating hydrodynamics of active particles interacting via taxis and quorum sensing: static and dynamics

Abstract In this article we derive and test the fluctuating hydrodynamic description of active particles interacting via taxis and quorum sensing, both for mono-disperse systems and for mixtures of co-existing species of active particles. We compute the average steady-state density profile in the presence of spatial motility regulation, as well as the structure factor and intermediate scattering function for interacting systems. By comparing our predictions to microscopic numerical simulations, we show that our fluctuating hydrodynamics correctly predicts the large-scale static and dynamical properties of the system. We also discuss how the theory breaks down when structures emerge at scales smaller or comparable to the persistence length of the particles. When the density field is the unique hydrodynamic mode of the system, we show that active Brownian particles, run-and-tumble particles and active Ornstein–Uhlenbeck particles, interacting via quorum-sensing or chemotactic interactions, display undistinguishable large-scale properties. This form of universality implies an interesting robustness of the predicted physics but also that large-scale observations of patterns are insufficient to assess their microscopic origins. In particular, our results predict that chemotaxis-induced and motility-induced phase separation should share strong qualitative similarities at the macroscopic scale.

Towards a momentum potential theory for reacting flows

Mutual coupling of (thermofluiddynamic) modes of perturbations can affect the thermo-acoustic stability of combustors and contribute to combustion noise. For example, vortical or entropic perturbations can be transferred to acoustic perturbations if accelerated by the mean flow. The decomposition of perturbation fields into the respective modes and a linear description of their interactions in terms of fluctuating primitive variables is challenging. In contrast, Doak’s momentum potential theory promises an unambiguous decomposition in terms of momentum fluctuations, which is not limited to the linear regime. Whereas classical momentum potential theory takes into account hydrodynamic, acoustic and entropic modes in unconfined flows, the investigation of noise generation in combustion chambers requires the extension of the momentum potential theory to capture modes linked to the fluctuation of species mass fractions (“species mode”) arising from the change in chemical composition due to the reaction. Furthermore, a rigorous treatment of boundary conditions due to the confinement of the flow inside the combustor is required. The herein presented extension to reactive flows consists of two steps, (i) the formulation of a potential for momentum fluctuations related to species modes and (ii) identification of the total fluctuating enthalpy related to species modes. The extended theory is applied to post-process computational fluid dynamic simulation data of the propagation of entropy and species perturbations through one-dimensional ducts, nozzles and premixed flames. We find that although momentum potential theory offers a complete decomposition of momentum perturbations for reactive flows, the meaningful interpretation of this decomposition is rather challenging, even for non-reactive flows.

Relativistic hydrodynamics with phase transition

Assessing the applicability of hydrodynamic expansions close to phase transition points is crucial from either theoretical or phenomenological points of view. We explore this within the gauge/gravity duality, using the Einstein–Klein–Gordon model, a bottom-up string theory construction. This model incorporates a parameter, B4\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$B_4$$\\end{document}, that simulates different types of phase transitions in the strongly coupled field theory existing at the boundary. We thoroughly examine the thermodynamics and dynamics of time-dependent, linearized perturbations in the spin-2, spin-1, and spin-0 sectors. Our findings suggest that ‘hydrodynamic series breakdown near transition points” is valid exclusively for second-order phase transitions, not for crossovers or first-order phase transitions. Additionally, we observe that the high-temperature and low-temperature limits of the radius of convergence for the hydrodynamic series (qc2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q^2_c$$\\end{document}) are equal. We also discover that the relationship (Max|qc2|)spin-2<(Max|qc2|)spin-0<(Max|qc2|)spin-1\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$(\ ext {Max}|q^2_c|)_{\ ext {spin-2}}< (\ ext {Max}|q^2_c|)_{\ ext {spin-0}} < (\ ext {Max}|q^2_c|)_{\ ext {spin-1}}$$\\end{document} is consistent for different spin sectors, regardless of the phase transition type. At the chaos point, we observe the emergence of pole-skipping behavior for both gravity and scalar perturbations at ωn=-2πTni\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$\\omega _n = -2\\pi T n i$$\\end{document}. Lastly, comparing the chaos momentum with qc2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q^2_c$$\\end{document}, we find that qps2<qc2\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$q^2_{ps} < q^2_c$$\\end{document}, except for extremely high temperatures.

Exact hydrodynamic manifolds for the linear Boltzmann BGK equation I: spectral theory

We perform a complete spectral analysis of the linear three-dimensional Boltzmann BGK operator resulting in an explicit transcendental equation for the eigenvalues. Using the theory of finite-rank perturbations, we confirm the existence of a critical wave number kcrit\\documentclass[12pt]{minimal} \\usepackage{amsmath} \\usepackage{wasysym} \\usepackage{amsfonts} \\usepackage{amssymb} \\usepackage{amsbsy} \\usepackage{mathrsfs} \\usepackage{upgreek} \\setlength{\\oddsidemargin}{-69pt} \\begin{document}$$k_{\ extrm{crit}}$$\\end{document} which limits the number of hydrodynamic modes in the frequency space. This implies that there are only finitely many isolated eigenvalues above the essential spectrum at each wave number, thus showing the existence of a finite-dimensional, well-separated linear hydrodynamic manifold as a combination of invariant eigenspaces. The obtained results can serve as a benchmark for validating approximate theories of hydrodynamic closures and moment methods and provides the basis for the spectral closure operator.

Global Stability and Forced Response Analysis of Swirling Flows In Aviation Combustors

Abstract Swirling jets are canonical flow fields used to stabilize flames in many gas turbine combustion systems. These flows amplify background acoustic disturbances and perturb the flame, producing combustion noise and potentially combustion instabilities. Hydrodynamic flow response to acoustic excitations in reacting flows is an important modeling task for understanding combustion noise and combustion instabilities. This study utilizes a global hydrodynamic stability analysis in a Bi-Global and Tri-Global framework to model the vortical hydrodynamic modes of a reacting, swirling LES mean flow based on a commercial nozzle. After conducting an unforced, natural Bi-Global stability analysis to study the unstable eigenmodes of the flow, linearized equations of motion are used to study flow response of the flow to forcing. An empirical velocity transfer function is constructed by determining the flow response to a harmonically varying 150-1500 Hz u' velocity disturbance at the inflow boundary. These disturbances are strongly amplified, with amplification factors ranging from about 20 to 50 and peaking at about 1050 Hz, or st = 0.375. A comparison study with a cartesian, three-dimensional reacting base flow is also performed where the base-flow varies spatially in three-dimensions. The study utilizes a stable, high accuracy, but computationally effective centered finite difference scheme based on a three-dimensional structured mesh. Illustrative results present the qualitative modes and quantitative transfer functions for Bi-Global and Tri-Global stability analyses.

The randomness and determinacy of wall pressure fluctuations in incompressible flow

Wall pressure fluctuations caused by turbulent boundary layers have a significant impact on aircraft structural vibration and cabin noise. This study aims to investigate the mechanism of turbulence-induced pressure fluctuations by focusing on the randomness of wall pressure fluctuations, analyzed in both the time–frequency and spatial-wavenumber domains using measured data obtained from a phase array in a wind tunnel. Three roughness elements were designed and installed upstream of the plate to manipulate the turbulent boundary layer at a specific Mach number. The results of the investigation demonstrate that the disturbance strength induced by the roughness element influences the randomness of wall pressure fluctuations, in addition to the parameters utilized for data analysis. Generally, stronger turbulence fluctuations tend to decrease the randomness of pressure fluctuations. Moreover, wall pressure fluctuations also exhibit certain statistical principles that cannot be precisely calculated using mathematical expressions, highlighting their inherent randomness. Further investigation into randomness in the spatial-wavenumber domain revealed the hydrodynamic modes of turbulence fluctuations with varying convection velocity analyzed through wavenumber maps computed using the beamforming algorithm. These modes with variable convective speed significantly contribute to the generation of randomness in wall pressure fluctuations. Both the time–frequency domain and the spatial-wavenumber domain affect the randomness characteristics of wall pressure fluctuations. However, such effects are not easily discernible through a rudimentary analysis of the space–time correlation of turbulence fluctuations.

Example of the convergence of hydrodynamics in strong external fields

The anti-de-Sitter/conformal field theory (AdS/CFT) correspondence is used to provide an estimate of the radius of convergence of the linearized gradient expansion of the hydrodynamic description of N=4 supersymmetric Yang-Mills (SYM) theory minimally coupled to U(1) gauge theory subjected to strong magnetic fields. The results of this work demonstrate that the dispersion relations of hydrodynamic modes continue to converge for magnetic field strengths far beyond those values for which a hydrodynamic description is expected. For magnetic field strengths much larger then the temperature scale the bulk dual interpolates between AdS4+1 and the product of a Bañados-Teitelboim-Zanelli (BTZ) black hole and a two dimensional manifold (BTZ2+1×R2) and may be regarded as a renormalization group flow of the 3+1 dimensional CFT to a 1+1 dimensional CFT. In this regime, we clarify past literature on the quasi-normal mode (QNM) spectrum of bulk scalar fields by introducing a new way to classify the behavior of QNM collisions in the complex frequency and momentum plane. Published by the American Physical Society 2024

Identification method of the hydrodynamic and acoustic natures of wall pressure fluctuation based on dynamic mode decomposition

In this study, an analysis method is proposed to explain the dynamic mode decomposition (DMD) mode of wall fluctuating pressure from the perspective of hydrodynamics and acoustics. According to the phase velocity, the wavenumber–frequency spectrum is divided into hydrodynamic, acoustic, and subconvective regions. Multiple DMD modes of the pressure field are calculated to obtain the wavenumber–frequency spectrum of the reconstructed pressure, which is characterized by the fact that the energy is concentrated at different wavenumber positions of the same frequency. This behavioral feature enables the DMD mode to be identified as a hydrodynamic, acoustic, and hybrid property according to the wavenumber position where the energy spot appears. This method can realize the classification and contribution analysis of the hydrodynamic and acoustic properties of the wall pressure DMD mode, and establish the mapping relationship between the acoustic mode and the eddy current characteristics through the eigenvalues. The coherent structure of the trace acoustic energy radiation in the incompressible fluid is observed from the statistical perspective, which increases understanding of the flow noise. The zero-pressure gradient wall flow experiment of Abraham is numerically analyzed using the aforementioned method. The results indicate that most of the DMD modes are identified as hydrodynamic, and only the nineteenth-order DMD mode is identified as acoustic. The frequency of the acoustic mode is 23.9 Hz, which has obvious wave-packet characteristics, whereas the hydrodynamic mode exhibits nonradiative convection characteristics, and its eddy current structure is closer to the wall transfer.

Simulations of pulsed overpressure jets: formation of bellows and ripples in galactic environments

ABSTRACT Jets from active nuclei may supply the heating which moderates cooling and accretion from the circum-galactic medium. While steady overpressured jets can drive a circulatory flow, lateral energy transfer rarely exceeds 3 per cent of jet power, after the initial bow shock has advanced. Here, we explore if pulses in high-pressure jets are capable of sufficient lateral energy transfer into the surrounding environment. We answer this by performing a systematic survey of numerical simulations in an axisymmetric hydrodynamic mode. Velocity pulses along low Mach jets are studied at various overpressures. We consider combinations of jet velocity pulse amplitude and frequency. We find three flow types corresponding to slow, intermediate, and fast pulsations. Rapid pulsations in light jets generate a series of travelling shocks in the jet. They also create ripples which propagate into the ambient medium while a slow convection flow brings in ambient gas which is expelled along the jet direction. Long period pulses produce slowly evolving patterns which have little external effect, while screeching persists as in non-pulsed jets. In addition, rapid pulses in jets denser than the ambient medium generate a novel breathing cavity analogous to a lung. Intermediate period pulses generate a series of bows via a bellows action which transfer energy into the ambient gas, reaching power efficiencies of over 30 per cent when the jet overpressure is sufficiently large. This may adequately inhibit galaxy gas accretion. In addition, such pulses enhance the axial out-flow of jet material, potentially polluting the circum-galactic gas with metal-enriched interstellar gas.

Sustainable dynamics of neural connections: A new concept of the emergence of cognition

Introduction. The problem of describing cognition as a result of the biological evolution of neural processes in the brain is especially difficult due to the need to involve a whole range of sciences and the competencies accumulated in them. The aim of this work is to identify and substantiate such dynamics of interaction processes in the neural network of the brain which explains their high intensity and maximum stability in the band of physical limitations of the existence of protein bodies. An important aspect of this goal is the need to substantiate the stages of biological evolution leading to the emergence of cognition (mind). Materials and Methods. The work mainly used heuristic methods: analogy, hypothetical-deductive method, modeling and thought experiment. The analogy involved the exact results of the theory of turbulence obtained from the variation principle. The modeling used the ideas of the similarity and dimensionality method, as well as the hydrodynamic laminar-turbulent transition. The hypothetical-deductive method used the ideas of the evolutionary method of the origin of species. Results. The author formulated and substantiated the concept of dynamics of high-intensity and maximally sustainable processes of interaction of neurons of the brain. The main results include the following: the analogy is revealed between information processes in living and inanimate nature with a reasonable common key for their understanding; within the framework of hydrodynamic analogy, a continuum model of the environment of neural interactions is proposed for the first time and the stages of the evolution of the nervous network are substantiated; the hypothesis of the transition to cognition as a consequence of the biological evolution of the neural network is formulated. Conclusions. The principle of sustainable dynamics allows us to consider cognitive processes from elementary acts of cognition to the emergence of reflection as a whole as an act of consciousness from a single point of view.

Field theory of active chiral hard disks: a first-principles approach to steric interactions

A first-principles approach for active chiral hard disks is presented, that explicitly accounts for steric interactions on the two-body level. We derive an effective one-body equation for the joint probability distribution of positions and angles of the particles. By projecting onto the angular modes, we write a hierarchy for the lowest hydrodynamic modes, i.e. particle density, polarisation, and nematic tensor. Introducing dimensionless variables in the equations, we highlight the assumptions, which—though inherent—are often included implicit in typical closure schemes of the hierarchy. By considering different regimes of the Péclet number, the well-known models in active matter can be obtained through our consideration. Explicitly, we derive an effective diffusive description and by going to higher orders in the closure scheme, we show that this first-principles approach results in the recently introduced Active Model B +, a natural extension of the Model B for active processes. Remarkably, here we find that chirality can change the sign of the phenomenological activity parameters.

The pseudospectra of black holes in AdS

We study the stability of quasinormal modes (QNMs) in electrically charged black brane spacetimes that asymptote to AdS by means of the pseudospectrum. Methodologically, we adopt ingoing Eddington-Finkelstein coordinates to cast QNMs in terms of a generalised eigenvalue problem involving a non-selfadjoint operator; this simplifies the computation significantly in comparison with previous results in the literature. Our analysis reveals spectral instability for (neutral) scalar as well as gravitoelectric perturbations. This indicates that the equilibration process of perturbed black branes is sensitive to external perturbations. Particular attention is given on the hydrodynamic modes, which are found to be the least unstable. In contrast with computations in hyperboloidal coordinates, we find that the pseudospectral contour lines cross to the upper half plane. This indicates the existence of pseudo-resonances as well as the possibility of transient instabilities. We also investigate the asymptotic structure of pseudospectral contour levels and we find remarkable universality across all sectors, persistent in the extremal limit.

KrF laser-driven shock tube: Realization and first experiments

We report on the first implementation of a miniature laser-driven shock tube (LDST) of 5 × 5 mm cross section and 50-mm length for generating and studying strong shock waves (SW) and hypersonic gas flows with M > 10. Operation of the LDST is based on the acceleration of a thin CH-film by ablative plasma pressure produced when the film is irradiated by high-energy UV pulse of the GARPUN KrF laser (100 J & 100-ns). The film serves as a piston that pushes a SW in the gas filling the LDST. An optical system based on a multi-element prism raster provides focusing of KrF laser beam into 7 × 7 mm square spot with 100 J/cm2 energy fluence (1 GW/cm2 intensity) with inhomogeneity ∼3 % across the LDST aperture. It is expected that the LDST with KrF laser driver can be an effective tool for studying hydrodynamic phenomena, such as hydrodynamic instabilities and transition to a turbulence, hypersonic gas flow around bodies, reflection and cumulation of strong SW.

The Thermophysical Aspects of the Transformation of Porous Structures in Versatile Nanostructured Materials

The technology of obtaining porous nanostructures is based on ecological organosilicon materials and their uses in some spheres of human life, for example, for medical preparations, for thermal insulation of building structures and industrial equipment, and for cleaning. The purpose of this study was to establish correlations between various experimental parameters (shear stress, speed pulsations, temperature, viscosity, and processing time) and the rheological characteristics of suspensions obtained by the method of liquid-phase dispersion; it was a study of hydrodynamic effects and the processes of heat and mass exchange in liquid systems during the liquid-phase dispersion of hydrogel monoliths by means of discrete-pulse activation in a special rotary apparatus. The dehydration of hydrogels was carried out by two methods: convective drying in a layer and spraying in the coolant flow. Experiments have shown that the key parameters for obtaining stable homogeneous suspensions are a synergistic combination of concentration factors and processing time. To obtain adsorbents in the form of pastes with specified adsorption properties and a monolith size of up to 300 μm, the optimal parameters were a hydrogel concentration of 70% and a processing time in the double-recirculation mode. Xerogels obtained by convective drying are a polydisperse mixture of strong monoliths and fragile aggregates. In contrast, xerogel monoliths obtained by spray drying show great homogeneity in terms of dispersion and strength characteristics. The rheological parameters of the hydrogel dispersions, which depend on the concentration and hydrodynamic treatment modes, are the dominant factors affecting the moisture extraction during drying. This study marks the first investigation into the resilience of porous organosilicon structures against the influence of intense turbulence fields and mechanical stresses experienced within the rotor apparatus during suspension production.

Helical separation effect and helical heat transport for Dirac fermions

An ensemble of massless fermions can be characterized by its total helicity charge given by the sum of axial charges of particles minus the sum of axial charges of antiparticles. We show that charged massless fermions develop a dissipationless flow of helicity along the background magnetic field. We dub this transport phenomenon as the Helical Separation Effect (HSE). Contrary to its chiral cousin, the Chiral Separation Effect, the HSE produces the helical current in a neutral plasma in which all chemical potentials vanish. In addition, we uncover the Helical Magnetic Heat Effect which generates a heat flux of Dirac fermions along the magnetic field in the presence of non-vanishing helical charge density. We also discuss possible hydrodynamic modes associated with the HSE in neutral plasma.

Hydrodynamic correlation and spectral functions of perfect cubic crystals

We investigate the collective dynamics of the perfect cubic crystal by deriving from the hydrodynamic equations the time-dependent correlation and the spectral functions characterizing the fluctuations of mass and momentum densities. We show that the seven hydrodynamic modes of the perfect crystal can be identified from the resonances of these spectral functions. The comparison with those of a fluid is discussed. Using the numerical values of the thermodynamic, elastic, and transport coefficients computed in our previous paper (J Mabillard and P Gaspard 2024 J. Stat. Mech. 023208) for a system of hard spheres, the theoretical expressions for the correlation and spectral functions are compared to the same functions directly computed using molecular dynamics simulations. The excellent agreement between theory and simulation provides strong support for the microscopic hydrodynamic theory of perfect crystals based on the local-equilibrium approach. This work sheds light on the fundamental mechanisms governing the collective behavior of matter in the solid state.

Applications of the kinetic theory for a model of a confined quasi-two dimensional granular mixture: Stability analysis and thermal diffusion segregation

The Boltzmann kinetic theory for a model of a confined quasi-two dimensional granular mixture derived previously [Garzó et al., “Navier–Stokes transport coefficients for a model of a confined quasi-two dimensional granular binary mixture,” Phys. Fluids 33, 023310 (2021)] is considered further to analyze two different problems. First, a linear stability analysis of the hydrodynamic equations with respect to the homogeneous steady state (HSS) is carried out to identify the conditions for stability as functions of the wave vector, the coefficients of restitution, and the parameters of the mixture. The analysis, which is based on the results obtained by solving the Boltzmann equation by means of the Chapman–Enskog method to first order in spatial gradients, takes into account the (nonlinear) dependence of the transport coefficients and the cooling rate on the coefficients of restitution and applies in principle to arbitrary values of the concentration, and the mass and diameter ratios. In contrast to the results obtained in the conventional inelastic hard sphere (IHS) model, the results show that all the hydrodynamic modes are stable so that the HSS is linearly stable with respect to long enough wavelength excitations. On the other hand, this conclusion agrees with previous stability analysis performed in earlier studies for monocomponent granular gases. As a second application, segregation induced by both a thermal gradient and gravity is studied. A segregation criterion based on the dependence of the thermal diffusion factor Λ on the parameter space of the mixture is derived. In the absence of gravity, the results indicate that Λ is always positive, and hence, the larger particles tend to accumulate near the cold plate. However, when gravity is present, our results show the transition between Λ&amp;gt;0 (larger particles tend to move toward the cold plate) to Λ&amp;lt;0 (larger particles tend to move toward the hot plate) by varying the parameters of the system (masses, sizes, composition, and coefficients of restitution). Comparison with previous results derived from the IHS model is carried out.

Экспериментальное исследование гидравлических характеристик сферических насадок для массообменных аппаратов

A critical analysis of the trends in the development of nozzles for mass transfer devices is given, some designs are described in which the transfer of heat and mass is organized from the standpoint of today technically the most perfect. It is shown that the specific surface, the free specific volume of the nozzle and the hydraulic resistance of the layer are determined as the main characteristics of irregular type packing bodies. The scheme and description of an experimental setup for determining the hydrodynamic characteristics of nozzles in laboratory conditions are given. The results of studies of the hydrodynamic parameters of a layer consisting of a spherical hollow irregular nozzle for a dry and irrigated column are presented. The singular velocities of the gas flow corresponding to the transition points (points of deceleration, suspension, inversion or choking) to different hydrodynamic modes of operation of the filling mass transfer columns (film, intermediate, turbulent) and corresponding pressure drops have been experimentally determined. The dependences of the hydraulic resistance of the nozzle layer on the gas velocity in the column for dry and irrigated nozzles with a 1 m high layer are determined. The main reasons for the decrease in gas pressure in the layer of the irrigated nozzle are indicated. The singular gas flow velocities and their corresponding pressure drops are calculated using known empirical dependencies for dry and irrigated nozzles. The results of experimental studies and engineering calculations were compared, thereby proving the possibility of using computational equations with satisfactory accuracy (up to 15%). The study of the hydrodynamics of the layer and its hydraulic characteristics has shown that the spherical, hollow nozzle design with evenly spaced holes on the surface provides an effective redistribution of working phases in the mass transfer apparatus.

A novel annular slit-type emitter developed for multi-jet electrospray propulsion

Electrospray thrusters employ ionization in the liquid phase to produce and propel streams of molecular ions or highly charged droplets at significant velocities. In this study, we developed a novel annular slit-type emitter for electrospray and investigated its operational modes under varying applied potentials in both open atmosphere and vacuum conditions. To assess the performance of the annular slit-type emitter in comparison to the conventional capillary-type emitter, benchtop electrospray experiments were conducted using water and glycerin as working fluids for both emitter types. The study examined the formation of the Taylor cone, cone-to-jet transition, stable jet, whipping jet, and multi-jet, along with their dependence on fluid viscosity and electric potential for both emitter designs. Clear distinctions in hydrodynamic mode, drop-to-cone mode, and cone-to-jet transition mode were observed between the two emitters. As the electric potential increased, the capillary-type emitter exhibited a whipping and pulsating water jet, while glycerin displayed a steady tilted jet. In contrast, the annular slit-type emitter demonstrated a pulsating water jet followed by a distinctive dripping mode at higher electric potentials, while glycerin formed multiple steady jets around the annular slit. Notably, the annular slit-type emitter, when subjected to an 18.5 kV potential, produced seven electrospray jets for glycerin, a phenomenon attributed to the novel design of the emitter and the viscosity of glycerin enabling the generation of multiple cone-jets at a specific electrostatic potential around the slit peripheral meniscus. Vacuum chamber tests of the annular-type emitter using liquid indium as an ion source at 1 × 10−5 Torr revealed an ion-current density of 0.3 mA/mm, resulting in a thrust of 290 μN.