Ilia V Roisman

Ilia V Roisman
Technische Universität Darmstadt | TU · Institute of Fluid Mechanics and Aerodynamics (SLA)

PD Dr.

About

215
Publications
45,312
Reads
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6,580
Citations
Citations since 2017
95 Research Items
4468 Citations
201720182019202020212022202302004006008001,0001,2001,400
201720182019202020212022202302004006008001,0001,2001,400
201720182019202020212022202302004006008001,0001,2001,400
201720182019202020212022202302004006008001,0001,2001,400
Additional affiliations
October 2006 - present
Technische Universität Darmstadt
Position
  • Coordinator of RA Multiphase flows
September 2002 - June 2003
Technion - Israel Institute of Technology
Position
  • Professor (Associate)
August 1998 - present
Technische Universität Darmstadt
Position
  • Privat Dozent

Publications

Publications (215)
Article
Full-text available
Drop impact onto a thin liquid film of another liquid is observed and characterized using a high-speed video system. A new mode of splash – a complete, simultaneous corona detachment – has been observed, which is the result of the lamella breakup near the wall film. The abrupt outward and upward displacement of the lamella leads to an extreme stret...
Article
In the present study, the effect of graphite lubricant additives on the dynamics of a single drop impact onto a heated surface has been investigated in the nucleate boiling and and thermal atomization regimes. In the nucleate boiling regime the drop impact is accompanied by the nucleation and expansion of multiple vapor bubbles. The drop residence...
Article
Full-text available
The dynamics of solid particles of complex shapes such as airborne snowflakes are governed by aerodynamic drag forces that are a function of the relative velocity of the particle in the flow and the particle drag coefficient, which depends on the particle geometry and its orientation. In this study, artificial snowflakes are produced by additive ma...
Article
Capillary flows in corners and wedges are ubiquitous in technology and nature. Under certain conditions, the capillary flows are enhanced resulting in the rise of rivulets in the corners. These rivulets can affect the overall fluid movement in the aforementioned systems. In this work, we investigate the rivulet dynamics in a square capillary under...
Article
The initial stage of solidification of a free supercooled water drop consists of the formation of a cloud of dendrites surrounded by liquid water. Although the impact of such mushy drops onto solid surfaces can significantly influence the process of ice accretion, neither the dynamics of impact of such mushy drops, nor their material properties hav...
Article
Full-text available
The impact of a drop onto a liquid film is relevant for many natural phenomena and industrial applications such as spray painting, inkjet printing, agricultural sprays, or spray cooling. In particular, the height of liquid remaining on the substrate after impact is of special interest for painting and coating but also for applications involving hea...
Article
To ensure safe flight under snowy conditions, aircraft manufacturers must demonstrate that each engine and its air inlet system can operate throughout the flight power range of the engine (including idling) in both falling and blowing snow conditions. This study is part of an effort to develop models for snow accretion. The focus here is on the mod...
Conference Paper
Liquid atomization using supersonic gas flows is a common process in many industrial applications, one example being the atomization of liquid metals. In the present experimental and analytical work, a modeling approach for the characteristic size of drops in sprays produced by means of supersonic gas atomization has been developed. Local drop size...
Chapter
Full-text available
Spray-wall interactions take place in many technical applications such as spray cooling, combustion processes, cleaning, wetting of surfaces, coating and painting, etc. The outcome of drop impact onto hot surfaces depends on a variety of parameters like for example material and thermal properties of the liquid and wall, substrate wetting properties...
Conference Paper
A dual-mode phase Doppler measurement system has been set up for the characterization of the complex spray produced through supersonic gas atomization. The atomizer design has been based on a generic close-coupled configuration operated with water and air, which leads to high local Mach numbers and complex patterns of compression and expansion wave...
Article
Full-text available
Droplets within droplets occur in numerous situations in which two immiscible liquids interact, for instance, binary drop collisions or when a drop of one liquid impacts onto a film of a different liquid, ejecting secondary droplets containing both liquids. In the present study, an imaging technique for determining the volume fraction of each liqui...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2022-3533.vid Ice crystal icing (ICI) in aircraft engines usually starts with the capture of ingested ice particles in a liquid water film wetting the engine core surfaces. In the present work, the normal and oblique impact of ice spheres onto a wetted wall is studied experimentally to investigate...
Conference Paper
Full-text available
View Video Presentation: https://doi.org/10.2514/6.2022-3608.vid Ice crystal icing in jet engines influences the aerodynamic behavior of the stators heavily and may lead to damages to or even flame out of the engine. Efforts to study ice particle impacts, and ice layer accretion, erosion and shedding have recently increased to finally understand th...
Article
View Video Presentation: https://doi.org/10.2514/6.2022-3371.vid For the accurate prediction of snow accretion and its influence on an aircraft it is necessary to better understand the dynamics and the topology change of a single snowflake at different melting stages. Melting of snowflakes affects their trajectory and determines the liquid water co...
Article
While the phase‐field methodology is widely adopted for simulating two‐phase flows, the simulation of an arbitrary number (N ≥ 2) of fluid phases at physical fidelity is non‐trivial and requires special attention concerning mathematical modelling, numerical discretization, and solution algorithm. We present our most recent work with focus on valida...
Article
Since the technology of direct injected engines has become more and more prevalent, combustion anomalies such as pre-ignition events have been occurring with increasing frequency. The interaction between the fuel-spray and the oil wetted cylinder liner is considered to be a partial cause for these phenomena. The incoming fuel jet can lead to a deta...
Article
Capturing the relaxation of a capillary interface towards its equilibrium profile is pivotal for accurate simulations of two-phase flow at high dynamics using the phase-field method. The present contribution suggests a methodological extension of the phase-field method necessary to cope which such highly dynamic two-phase flows. For validation, we...
Preprint
Full-text available
Drop impact onto a thin liquid film of another liquid is observed and characterized using a high-speed video system. A new mode of splash - a complete, simultaneous corona detachment - has been observed, which is the result of the lamella breakup near the wall film. The abrupt outward and upward displacement of the lamella leads to an extreme stret...
Conference Paper
Additive manufacturing requires high quality, monodisperse metal powder with spherical particles of definite size. For plant operation, it is important to better understand the atomization process, i.e., to determine the influence of the operating parameters on the particle size. A project with partners from India and Germany builds on a coupled ap...
Article
Full-text available
The mass of liquid remaining on a substrate following a drop impact is a crucial quantity for modelling of numerous phenomena, e.g. spray cooling, spray coating or aircraft icing. In the present study, a method to measure this residual mass after impact of liquid drops is introduced. This method is also applicable to supercooled drops, which may fr...
Article
Full-text available
Ice particle impact onto a cold dry rigid substrate leads to particle deformation and breakup. If the impact velocity is high enough, the deformation is governed mainly by inertial and plastic stresses. Particle deformation may lead to the development of multiple cracks and the formation of a fragmented particle zone in the vicinity of the target s...
Article
Impact of a single particle onto a rigid substrate leads to its deformation and subsequent fragmentation. In this theoretical study a simplified model for the plastic flow in a deforming particle is developed which accounts for the dependence of the yield strength on the effective local strain rate. The flow in the particle is approximated by an in...
Conference Paper
Full-text available
A common method for producing metal powders used for additive manufacturing is based on the atomization of a stream of molten metal by means of a high-pressure gas flow. In the present experimental study, the influence of the liquid mass flow rate on the atomization result has been investigated for a close-coupled atomizer operated with water and a...
Article
Full-text available
Drop rebound after collision with a very hot substrate is usually attributed to the Leidenfrost effect, characterized by intensive film boiling in a thin vapour gap between the liquid and substrate. Similarly, drop impact onto a cold superhydrophobic substrate leads to a complete drop rebound, despite partial wetting of the substrate. Here we study...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2021-2671.vid Ice crystal impacts on aircraft components and their post-impact characteristics like fragment sizes and velocities are important factors influencing ice accretion on heated surfaces. Understanding the fundamental aspects of this process would allow to advance models and simulations o...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2021-2682.vid Better understanding of the transport processes in granular ice or snow layers associated with melting is of extreme importance for many engineering applications influenced by icing. These transport phenomena include melting of the bulk ice, water imbibition and freezing, as well as h...
Conference Paper
View Video Presentation: https://doi.org/10.2514/6.2021-2684.vid To ensure safe flight under snowy conditions, aircraft manufacturers must demonstrate that each engine and its air inlet system can operate throughout the flight power range of the engine (including idling) in snow, both falling and blowing. This study is part of an effort to develop...
Article
Full-text available
In this work, an experimental investigation of AdBlue film formation in a generic selective catalytic reduction (SCR) exhaust gas test bench is presented. AdBlue is injected into a generic SCR test bench resulting in liquid film formation on the lower wall of the channel. The thickness of this liquid film is measured using a film thickness sensor b...
Article
Full-text available
The present study experimentally examines the secondary atomization arising from the impingement of a water-in-oil emulsion drop onto a hot sapphire glass surface. The main aim of this study is to characterize secondary droplets emerged from the rim and lamella disruption. Drop impacts of n-dodecane and emulsions with a water volume content of 1.98...
Article
Strong electric fields may deform drops and induce their oscillation or motion on the substrate. Moreover, they can initiate partial discharges (PDs) because of the enhancement of the electric field in the vicinity of the three-phase contact lines. The partial discharges affect the drop spreading which can result in unusual drop shapes. In addition...
Article
Forced or spontaneous wetting of a solid surface in an isothermal case is governed by an outer flow and by wetting properties of the substrate. These properties are determined by the substrate wettability and morphology. Wetting and subsequent or simultaneous icing of surfaces are mutually influenced also by the microscopic processes associated wit...
Article
Full-text available
Fingering instability of a viscous liquid bridge stretched by an accelerating substrate - Volume 899 - Sebastian Brulin, Ilia V. Roisman, Cameron Tropea
Article
Drop motion on a dry solid substrate is determined by the lateral adhesion force associated with the contact angle hysteresis and by any applied external forces. In this experimental and computational study the lateral adhesion force is measured directly, through dragging of a drop along a surface by a cantilever. These force measurements are compa...
Article
Full-text available
The interaction between an air-driven, wall-bound drop and a groove in the wall of a channel flow has been investigated experimentally using a high-speed video system. Three major outcomes of drop interaction with the groove are observed: (i) the drop passes over the groove, (ii) the drop is immediately fully captured in the groove or (iii) the dro...
Preprint
Full-text available
Drop rebound after collision with a very hot substrate is usually attributed to the Leidenfrost effect, [1-5] characterized by intensive film boiling in a thin vapour gap between the liquid and substrate. Similarly, drop impact onto a cold superhydrophobic substrate [6-8] leads to a complete drop rebound, despite partial wetting of the substrate. W...
Preprint
Impact of single particle onto a rigid substrate leads to its deformation and fragmentation. The flow associated with the particle spreading on a solid substrate after impact is extremely complicated. In this theoretical study a simplified model for the plastic flow with the rate-dependent yield strength is developed. The flow in the particle is ap...
Article
Full-text available
When a drop impacts a dry surface at high velocity, it atomises into secondary droplets. These small droplets are generated by one of two types of splashes: either by a prompt splash from the spreading rim at the surface or by a thin corona splash, which levitates from the surface. This study investigates the splashing mechanisms experimentally usi...
Article
The flow of wall-bound liquid films on an inclined substrate is governed by viscous effects, inertia, gravity, and surface tension. It can also be significantly influenced by aerodynamic stresses if it is exposed to an external gas flow. Such film flows on nonwettable or partially wettable surfaces break up under certain conditions, when the capill...
Article
The interaction of drops and electric fields occurs in many applications like electrowetting, electrospinning, atomization, but also causes unwanted effects like the aging of high-voltage composite insulators. Water drops are influenced by electric fields due to the polar properties of the water molecules. The behavior of the drops depends on sever...
Article
Full-text available
Icing is a major hazard for aviation safety. Over the last decades an additional risk has been identified when flying in clouds with high concentrations of ice-crystals where ice accretion may occur on warm parts of the engine core, resulting in engine incidents such as loss of engine thrust, strong vibrations, blade damage, or even the inability t...
Article
Full-text available
The capillary rise of liquid in a perfect corner wedge has been well studied in the past, yielding a t1/3 rise behavior with no upper bound on the height of the rivulet. However, in real-world situations the wedge corner is often not exactly sharp, either because of roughness or fabrication imperfections. In the following study the behavior of capi...
Preprint
Full-text available
In this study the Leidenfrost temperature during spray cooling of very hot substrates is experimentally measured. The spray parameters, i.e. the drop diameters and velocities and the mass flux, are very accurately measured. Astonishingly, the measured Leidenfrost temperature is independent of any of the spray impact parameters, but is determined ex...
Chapter
The interaction of a drop and a hot wall is an important process encountered in a large number of industrial applications, mainly associated with spray cooling. If the wall temperature is high enough the drop impact, its spreading and breakup are influenced by micro-scale thermodynamic phenomena caused by the intensive drop evaporation, bubble or v...
Article
Spray cooling of a hot target is characterized by strong heat flux and fast change of the temperature of the wall interface. The heat flux during spray cooling is determined by the instantaneous substrate temperature, which is illustrated by boiling curves. The variation of the heat flux is especially notable during different thermodynamic regimes:...
Preprint
When a liquid viscous bridge between two parallel substrates is stretched by accelerating one substrate, its interface recedes in the radial direction. In some cases the interface becomes unstable. Such instability leads to the emergence of a network of fingers. In this study the mechanisms of the fingering are studied experimentally and analysed t...
Article
Full-text available
In this study a stretching of a viscous liquid bridge formed between two flat solid parallel substrates is investigated experimentally. The stretching of the liquid bridge is caused by the constant acceleration of one moving substrate. The geometry of the liquid bridge is observed using a high-speed video system. It is shown that at large times the...
Article
Full-text available
Drop impact onto a hot substrate leads to various hydrodynamic outcomes depending on the substrate temperature and the impact parameters: deposition, drop dancing, thermal atomization, and finally rebound at temperatures above the dynamic Leidenfrost condition. In the present experimental study this parameter space has been extended to conditions o...
Article
Rapid fluid splitting in a gravure printing press is studied using high-speed video imaging. The fluid flow and dynamics of the liquid-air meniscus in the wedge between a rigid printing cylinder and a planar substrate plate is singular at the contact point, and the capillary pressure behind the meniscus appears to diverge here. In case of lamella s...
Preprint
Spray cooling a hot target is characterized by strong heat flux density and fast change of the temperature of the wall interface. The heat flux density during spray cooling is determined by the instantaneous substrate temperature, which is illustrated by boiling curves. The variation of the heat flux density is especially notable during different t...
Article
One of the central challenges in producing water-in-diesel microemulsion fuels is to attain their thermal stability (to separate phases) for possible utilization and storage in various environmental and operating conditions. Thus, it should be possible to control the stability of the microemulsion systems at different temperatures. The present stud...
Conference Paper
Full-text available
A full-scale production plant which uses the close-coupled atomization principle for metal powder production as used in laser powder bed fusion (LPBF) has been built by SMS group. The properties of the final work piece produced using LPBF depend on the uniformity of size and consistency of the powder. The particles are produced by close-coupled ato...
Article
Full-text available
Accretion and shedding of ice layers is a serious problem for various engineering applications. In particular, ice layers growing due to ice crystal impingement on warm parts of an aircraft jet engine pose a severe hazard since they seriously affect safe operation of an aircraft. The material properties, and in the first place the strength of an ic...
Article
The motion of wall-bounded drops moving on solid substrates driven by a fully turbulent channel flow is experimentally investigated for four substrates of different wetting properties. An appropriate scaling has been found to describe the dimensionless drop velocity (capillary number) in terms of a dimensionless flow attack velocity, taking into ac...
Article
Icing of various surfaces is often a result of the collision of supercooled water drops with the substrates. Ice formation from supercooled water drops is initiated by nucleation when the size of an ice embryo reaches a critical value. The lack of controlling the inception of heterogeneous nucleation and the rate of solidification, which depend on...
Conference Paper
Full-text available
A Saffman-Taylor instability of a retracting liquid meniscus can be observed in the fluid splitting process between a rotating gravure cylinder and a planar plate in the nip of a gravure printing machine if lamella splitting is given. While the finger frequency in the case of smooth surfaces behaves proportionally to the capillary number and thus t...
Presentation
Recently, SMS group has built-up a full-scale powder production demo centre which consists of a close-coupled atomizer and a laser based powder bed fusion (LPBF) printer. For the laser powder bed fusion applications a fine metal powder is solidified in layers using a focused laser beam. The properties of the final product depend strongly on the uni...
Conference Paper
Gas-assisted atomizers are often used for the atomization of very viscous liquids, for example liquid metals. One kind of such atomizer, a close-coupled atomizer, consists of two coaxial annular openings - the inner for the injection of a liquid and the surrounding for the generation of a conical high-speed gas stream. The liquid jet is disintegrat...
Article
In this study, the impact of a liquid drop onto a thin liquid film of a different fluid is investigated experimentally using a high-speed video system and analysed theoretically to obtain expressions for predicting splashing thresholds. The study focuses on impact conditions leading to one of four outcomes: deposition, corona without splash, corona...
Article
When a single drop impacts onto a very hot substrate with a high impact velocity the collision leads to a generation of a fast vertical spray of fine secondary droplets. These small drops are generated during disintegration of a thin drop lamella by a vapor, formed by the liquid vaporization. They are formed near the moving, disordered dewetting fr...
Article
Full-text available
Spray drying is a preferred method of drying and successful agglomeration of various materials and is widely used in the chemical, food, pharmaceutical and in the power industry, e.g. to produce polymers, dairy products, foodstuff, pharmaceutics or for flue gas cleaning, etc. In spray drying applications very often rotary atomizers are used for ato...
Article
We consider the fluid splitting dynamics of a small fluid drop entrapped between two parallel solid plates, which are rapidly pulled apart such that a free liquid sheet is formed between them for a few milliseconds. Velocities, time scales and shear rates correspond to the lift-off of a printing cylinder from the substrate in an industrial printing...
Article
In this work, an absorption based laser sensor for the investigation of dynamically changing liquid film thicknesses is developed and validated. For the wavelength selection of the single-ended, fibre-coupled, diode-laser sensor, near-infrared spectra of liquid water are measured at various thicknesses and temperatures. To reduce the influence of t...
Poster
Phenomena of drop impact have been studied extensively due to their importance in many industrial applications like spray cooling, ink-jet printing and spray coating. Different outcomes of drop impact have been identified: deposition, corona and prompt splash, full and partial rebound. The outcome is determined by parameters like drop diameter and...
Article
This experimental study is focused on the mechanisms of thermal atomisation of a drop impacting onto a hot substrate. This phenomenon is characterised by the wetting and dewetting of the substrate, caused not by the rim dynamics, but induced by thermal effects. These thermal effects lead to the lamella evaporation, levitation and disintegration, ge...
Article
For many industrial applications it is important to control the outcome of drop impact. One of the means of passive control for such processes is in the application of smart, deformable, rheologically complex surfaces. In this experimental work an impact of a viscous Newtonian drop onto a substrate coated by a thin visco-elastic layer is investigat...
Article
Fluid movement in microfluidic devices, porous media, and textured surfaces involves coupled flows over the faces and corners of the media. Spontaneous wetting of simple grooved surfaces provides a model system to probe these flows. This numerical study investigates the spontaneous rise of a liquid in an array of open rectangular channels under gra...
Article
Full-text available
The article category has been published incorrectly due to processing error. The correct category should read “Review Article”. We apologize for this lapse.
Conference Paper
Capillary driven flows in non-circular channels/capillaries with corners are relevant in the field of microfluidics, porous media, etc. While the bulk capillary flows in the cornered capillaries are very much similar to the cylindrical capillaries, the presence of corners enhances the capillary effects resulting in the formation of rivulets rising...