By Knezevic K.H.
During this PhD thesis, the compressible fluid dynamics of high-speed impactof a round liquid droplet on a inflexible substrate is investigated. The influence phenomenonis characterized via the compression of the liquid adjoining to the targetsurface, while the remainder of the liquid droplet continues to be blind to the impression. Initially,the region of compressed liquid is believed to be bounded via a surprise envelope,which propagates either laterally and upwards into the majority of the motionlessliquid. using a high-resolution axisymmetric solver for the Euler equations, itis proven that the compressibility of the liquid medium performs a dominant position inthe evolution of the phenomenon. Compression of the liquid in a region outlined bya surprise wave envelope, lateral jetting of very excessive speed and growth wavesin the majority of the medium are an important mechanisms pointed out, simulatedand discussed.During the 1st part of effect, all wave propagation velocities aresmaller than the touch line pace, therefore the surprise wave continues to be connected to thelatter. At a definite aspect, the radial pace of the touch line decreases less than theshock pace and the surprise wave overtakes the touch line, beginning to travelalong the droplet loose floor. The ensuing excessive strain distinction throughout thefree floor on the touch line area triggers an eruption of extreme lateral jetting.The surprise wave propagates alongside the loose floor of the droplet and it's reflectedinto the majority of the liquid as a variety wave. the improvement of strain anddensity within the compressed quarter are numerically calculated utilizing a entrance trackingmethod. the precise place of the surprise envelope is computed and either onset andmagnitude of jetting are made up our minds, displaying the emergence of liquid jets of veryhigh speed (up to 6000 m/s). Computationally received jetting instances are validatedagainst analytical predictions. Comparisons of computationally obtainedjetting inception occasions with analytic effects convey that contract improves considerably if the radial movement of the liquid within the compressed sector is taken intoaccount.An analytical version of the influence method is additionally constructed and comparedto the axisymmetric numerical answer of the inviscid stream equations.Unlike the normal linear version - which considers all wave propagation velocitiesto be consistent and equivalent to the rate of sound, the built version predictsthe designated circulate kingdom within the compressed sector via accommodating the true equationof country. it truly is proven that the customarily hired assumption that the compressed areais separated from the liquid bulk via a unmarried surprise wave connected to the contactline, breaks down and leads to an anomaly. This anomaly emerges substantiallyprior to the time whilst the surprise wave departs from the touch line, starting up lateralliquid jetting. end result of the loss of extra refined mathematical versions, thistended to be missed in so much works on excessive velocity droplet impression, even thoughit is vital for the right kind knowing of the pertinent physics. it's confirmed thatthe presence of a multiple-wave constitution (instead of a unmarried surprise wave) at thecontact line sector resolves the aforementioned anomaly. The prevalence of thismore complicated a number of wave constitution can also be supported via the numerical results.Based at the constructed analytical version, a parametric illustration ofthe surprise envelope floor is demonstrated, exhibiting a considerable improvementwith admire to earlier linear version, while proven opposed to numerical findings.In the ultimate a part of the thesis, the belief of a a number of wave structurewhich gets rid of the above pointed out anomaly is underpinned with an analyticalproof exhibiting that this type of constitution is certainly a bodily applicable resolution.
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Extra resources for High-Velocity Impact of a Liquid Droplet on a Rigid Surface: The Effect of Liquid Compressibility
For the modelling of surrounding air in the numerical part of this study, the ideal gas equation of state was used. e. with the fit parameter P ∞ = 0 . e. γ = c p ⁄ c v = Γ + 1 . The quantities c p and c v represent the specific heats at constant pressure and volume, respectively. For some materials, P ∞ can be quite large; examples are water and metals, for which P ∞ is of the order of megabars. 4) Here, we substituted the specific internal energy e from Eq. 2) into Eq. 3). 13 ⋅ 10 Pa . Principal Hugoniot for the Stiffened Gas EOS The locus of possible final states due to the shock compression for a fluid initially at normal density, pressure and zero mass velocity will be referred to as principal Hugoniot.
A water droplet of radius of 100µm collides with an impact velocity of 500 m/s with a flat substrate. Due to the very small time scales ( 10 – 14 – 10 – 11 s , obtained according to CFL condition) and high velocities at which the emerging waves propagate, the first issue that should be addressed is weather the present resolution (up to 4 million grid points) can realistically capture the phenomena. Thus, as a first step, we investigate the grid independence and convergence of the solution. 1 Solution Convergence & Grid Independence The grid independence of the results has been established by both one- and two-dimensional capturing of the accurate shock position and shape.
Mathematical Model & Computational Methodology Fig. 2. Droplet and air density distribution prior to the impact: Emergence and reflection of the bow shock in the air and weak perturbations in the liquid bulk (due to the liquid-air interactions on a droplet surface). Parameters: Impact velocity 500 m/s, motionless air. [numerical result with non-linear colour map (HDF)]. 3 Numerical Modelling The code FronTier, used for the current simulations was developed by a group of researchers at the New York University and the University of Stony Brook -.