اشترك بالحزمة الذهبية واحصل على وصول غير محدود شمرا أكاديميا
تسجيل مستخدم جديدNumerical investigation of non-condensable gas effect on vapor bubble collapse
105
0
0.0
(
0
)
اسأل ChatGPT حول البحث
ﻻ يوجد ملخص باللغة العربية
We numerically investigate the effect of non-condensable gas inside a vapor bubble on bubble dynamics, collapse pressure and pressure impact of spherical and aspherical bubble collapses. Free gas inside a vapor bubble has a damping effect that can weaken the pressure wave and enhance the bubble rebound. To estimate this effect numerically, we derive and validate a multi-component model for vapor bubbles containing gas. For the cavitating liquid and the non-condensable gas, we employ a homogeneous mixture model with a coupled equation of state for all components. The cavitation model for the cavitating liquid is a barotropic thermodynamic equilibrium model. Compressibility of all phases is considered in order to capture the shock wave of the bubble collapse. After validating the model with an analytical energy partitioning model, simulations of collapsing wall-attached bubbles with different stand-off distances are performed. The effect of the non-condensable gas on rebound and damping of the emitted shock wave is well captured.
قيم البحث
اقرأ أيضاً
The understanding of the shrinkage dynamics of plasmonic bubbles formed around metallic nanoparticles immersed in liquid and irradiated by a resonant light source is crucial for the usage of these bubbles in numerous applications. In this paper we ex
perimentally show and theoretically explain that a plasmonic bubble during its shrinkage undergoes two different phases: first, a rapid partial bubble shrinkage governed by vapor condensation and, second, a slow diffusion-controlled bubble dissolution. The history of the bubble formation plays an important role in the shrinkage dynamics during the first phase, as it determines the gas-vapor ratio in the bubble composition. Higher laser powers lead to more vaporous bubbles, while longer pulses and higher dissolved air concentrations lead to more gaseous bubbles. The dynamics of the second phase barely depends on the history of bubble formation, i.e. laser power and pulse duration, but strongly on the dissolved air concentration, which defines the concentration gradient at the bubble interface. Finally, for the bubble dissolution in the second phase, with decreasing dissolved air concentration, we observe a gradual transition from a $R(t) propto (t_0 - t) ^{1/3}$ scaling law to a $R(t) propto (t_0 - t) ^{1/2}$ scaling law, where $t_0$ is the lifetime of the bubble and theoretically explain this transition.
We consider the collapse behavior of cavitation bubbles near walls under high ambient pressure conditions. Generic configurations with different stand-off distances are investigated by numerical simulation using a fully compressible two-phase flow so
lver including phase change. The results show that the stand-off distance has significant effects on collapse dynamics, micro-jet formation, rebound, and maximum wall pressure. A relation between cavitation induced material damage and corresponding collapse mechanisms is obtained from pressure-impact data at the wall. We analyze the resolution dependence of collapse and rebound and the observed maximum pressure distributions. The comparison of the results on six different grid resolutions shows that main collapse features are already captured on the coarsest resolution, while the peak pressures are strongly resolution dependent.
In this numerical study, an original approach to simulate non-isothermal viscoelastic fluid flows at high Weissenberg numbers is presented. Stable computations over a wide range of Weissenberg numbers are assured by using the root conformation approa
ch in a finite volume framework on general unstructured meshes. The numerical stabilization framework is extended to consider thermo-rheological properties in Oldroyd-B type viscoelastic fluids. The temperature dependence of the viscoelastic fluid is modeled with the time-temperature superposition principle. Both Arrhenius and WLF shift factors can be chosen, depending on the flow characteristics. The internal energy balance takes into account both energy and entropy elasticity. Partitioning is achieved by a constant split factor. An analytical solution of the balance equations in planar channel flow is derived to verify the results of the main field variables and to estimate the numerical error. The more complex entry flow of a polyisobutylene-based polymer solution in an axisymmetric 4:1 contraction is studied and compared to experimental data from the literature. We demonstrate the stability of the method in the experimentally relevant range of high Weissenberg numbers. The results at different imposed wall temperatures, as well as Weissenberg numbers, are found to be in good agreement with experimental data. Furthermore, the division between energy and entropy elasticity is investigated in detail with regard to the experimental setup.
In the present study, simulations are directed to capture the dynamics of evacuating inner gas of a bubble bursting at the free surface, using Eulerian based volume of fluid (VOF) method. The rate by which surrounding air rushing inside the bubble ca
vity through the inner gas evacuation is estimated and compared by the collapsing bubble cavity during the sequential stages of the bubble bursting at the free surface. Further, the reachability of inner gas over the free surface is evaluated by establishing the comparison of the same through various horizontal planes, lying at different altitudes above the unperturbed surface. The evacuating inner gas accompanies vortex rings, which entrains the surrounding gas-phase. During the successive stages of air entrainment, spatiotemporal characteristics of the vortex ring are obtained. At low Bond numbers (< 1), after comparing the phase contours of evacuating inner gas from the bubble cavity, the consequences at the axial growth of gas jet and the radial expansion of the jet tip is discussed separately. Furthermore, under the respiration process, the axial growth of rising inner gas over the free surface and the radial expansion of vortex rings of a bubble bursting at the free surface is compared with the quiescent surrounding air. At last, the effects of various possible asymmetric perforation of the bubble cap keeping the same Bo are studied. The cause of bent gas jet, as a consequence of perforation of the bubble cap, asymmetrically, is explained by plotting the velocity vectors.
Electrohydrodynamic (EHD) flow induced by planar corona discharge in the wall boundary layer region is investigated experimentally and via a multiphysics computational model. The EHD phenomena has many potential engineering applications, its optimiza
tion requires a mechanistic understanding of the ion and flow transport. The corona EHD actuator consisting of two electrodes located in the wall boundary layer creates an EHD driven wall jet. The applied voltage between the electrodes is varied and the resulting effects in the charge density and flow field are measured. Constant current hotwire anemometry is used to measure velocity profile. The airflow near the wall acts a jet and it reaches a maximum of 1.7 m/s with an energy conversion efficiency of ~2%. The velocity decreases sharply in the normal direction. Multiphysics numerical model couples ion transport equation and the Navier Stokes equations to solve for the spatiotemporal distribution of electric field, charge density and flow field. The numerical results match experimental data shedding new insights into mass, charge and momentum transport phenomena. The EHD driven flow can be applied to flow control strategies and design of novel particle collectors.
سجل دخول لتتمكن من نشر تعليقات
التعليقات
جاري جلب التعليقات
سجل دخول لتتمكن من متابعة معايير البحث التي قمت باختيارها
