Figure 1 - uploaded by Yujie Zhu
Content may be subject to copyright.
Schematic of three interface types with respect to the computational grid: the fully-resolved, under-resolved, and sub-grid dispersed interfaces.
Source publication
In this paper, a Lagrangian-Eulerian (LE) two-way coupling model is developed to numerically study the cavitation bubble cloud. In this model, the gas-liquid mixture is treated directly as a continuous and compressible fluid and the governing equations are solved by methods in Eulerian descriptions. An isobaric closure exhibiting better consistency...
Contexts in source publication
Context 1
... general, gas-liquid interfaces can be classified into fully solved (resolved), under-resolved, and sub-grid interfaces with respect to grid size. A schematic of three different interface types is given in Figure 1. Various of numerical methods, such as those in References [9,21], have been developed to model the resolved and under-resolved interfaces. ...
Context 2
... turn, the vibration of the gas bubbles induces the pressure disturbance in the bulk fluid. The evolution of the pressure p at the cloud's center is reported in Figure 10. This results correspond to two different resolutions on x-axis. ...
Context 3
... in Figure 11, the volume fraction α g at 1.5 µs, 2.0 µs, 2.5 µs, 3.0 µs, 3.5 µs, and 4.5 µs is given. Generally, a larger gas volume fraction would be achieved when negative pressure approaches the bubbles as the bubbles expand. ...
Context 4
... the pressure wave is partially reflected at the cluster's boundary, there is no major change in the volume fraction at the cloud's center. To better understand the influence of the pressure wave on α g , the time evolution of radii for Bubble A-D is recorded in Figure 12. From Figure 12, it can be observed that the bubbles' radii are constant before the arrival of the pressure wave, which means the bubbles are in equilibrium with the carrier fluid. ...
Context 5
... better understand the influence of the pressure wave on α g , the time evolution of radii for Bubble A-D is recorded in Figure 12. From Figure 12, it can be observed that the bubbles' radii are constant before the arrival of the pressure wave, which means the bubbles are in equilibrium with the carrier fluid. The negative pressure first reaches Bubble A, inducing its violent expansion. ...
Context 6
... negative pressure first reaches Bubble A, inducing its violent expansion. This corresponds well with the larger volume fraction field at t = 2.0 µs in Figure 11. The positive pressure wave follows and condenses Bubble A, which makes the bubble unstable and oscillates actively. ...
Context 7
... difference of the bubble radius history is induced by the fact that the pressure wave is damped when it propagates to Bubble C and even becomes weak at Bubble D due to the reflection and absorbing during the interaction. This phenomenon corresponds well with the volume fraction field at t = 3.0 µs, 3.5 µs, and 4.5 µs in Figure 11. As also shown in Figure 9, the pressure wave is reflected at the interface and absorbed, and only a small amount of the pressure successfully passes the bubble cloud. ...
Context 8
... schematic of the initial set-up is shown in Figure 13. First, a spherical bubble cluster with N 0 = 200 spherical bubbles is placed into still water, the radii of which are initially randomly distributed between 100 µm and 500 µm. ...
Context 10
... is the radius of the bubble cloud. Figure 14 gives six snapshots of the collapsing process of a bubble cloud. The isosurface of volume fraction α g = 0.002 is visualized with gray color to represent the vapor bubble distributions. ...
Context 11
... the collapse, extremely high pressures are generated from the center of the bubble cloud. In Figure 14, the slices of the higher pressure region, where the pressure is greater than 10 atm, are presented at each time instant. The higher pressure increases over time. ...
Context 12
... the end of the collapse process, the extreme pressure reaches its maximum value around 174 atm when the collapse rate reaches its maximum value. In Figure 15 To analyze the influence of the bubble initial number N 0 on the cloud's collapse time, we simulate N 0 = 300 and 400 under the same initial condition as above. Figures 16 and 17 provide snapshots of the collapse process at t = 0 µs, 6 µs, 9 µs, 12 µs, 13 µs, and 14 µs. ...
Context 13
... Figure 15 To analyze the influence of the bubble initial number N 0 on the cloud's collapse time, we simulate N 0 = 300 and 400 under the same initial condition as above. Figures 16 and 17 provide snapshots of the collapse process at t = 0 µs, 6 µs, 9 µs, 12 µs, 13 µs, and 14 µs. In Figure 18, the time history of N b /N 0 (N 0 = 400) and β/β 0 are given. ...
Context 14
... 16 and 17 provide snapshots of the collapse process at t = 0 µs, 6 µs, 9 µs, 12 µs, 13 µs, and 14 µs. In Figure 18, the time history of N b /N 0 (N 0 = 400) and β/β 0 are given. We can observe that, similar to N 0 = 200 in Figure 15, the collapse time of the bubble cloud with N 0 = 300 or N 0 = 400 is also around 14.5 µs. ...
Context 15
... Figure 18, the time history of N b /N 0 (N 0 = 400) and β/β 0 are given. We can observe that, similar to N 0 = 200 in Figure 15, the collapse time of the bubble cloud with N 0 = 300 or N 0 = 400 is also around 14.5 µs. However, the larger bubble number leads to greater violent pressure at the cloud's center. ...
Context 16
... the case of the bubble cloud with N 0 = 400, the distribution of bubble radii during the collapse is analyzed according to their sizes. Figure 19 shows the bubble size density distribution at t = 0 µs, 6 µs, 9 µs, 12 µs, 13 µs, and 14 µs. The first bar on the left side indicates the density of the collapsed (inactive) vapor bubbles. ...
Context 17
... first bar on the left side indicates the density of the collapsed (inactive) vapor bubbles. From Figure 19, we can observe that the vapor bubbles become compressed all together because of the higher environmental pressure. As given in Equation (22), with a bubble radius increases, its collapse time t Rayleigh also increases. ...
Citations
... Lyu et al. [13] used the Lagrangian approach to model the simulation of a cylindrical bubble cloud interacting with a pressure wave. Wang et al. [14] used a similar approach to assess the erosion risk in a cavitating axisymmetric nozzle. ...
The concept of Hydrodynamic Cavitation (HC) has emerged as a promising method for wastewater treatment, bio-diesel production and multiple other environmental processes with Venturi-type cavitation reactors showing particular advantages. However, numerical simulations of a venturi type reactor with an elucidated explanation of the underlying flow physics remain inadequate. The present study numerically investigates and analyzes the flow inside a venturi-type reactor from
both global cavity dynamics and localized turbulence statistics perspectives. Some models in the Detached Eddy Simulation (DES) family are employed to model the turbulence with the study initially comparing 2D simulations before extending the analysis to 3D simulations. The results show that while URANS models show significantly different dynamics as a result of grid refinement, the DES models show standard flow dynamics associated with cavitating flows. Nevertheless, significant discrepancies continue to exist when comparing the turbulence statistics on the local scale. As the discussion extends to 3D calculations, the DES models are able to well predict the turbulence phenomena at the local scale and reveal some new insights regarding the role of baroclinic torque into the cavitation-vortex interaction. The findings of this study thus contribute to the fundamental understandings of the venturi-type reactor.
... Peters and Moctar [5] presented results of the numerical assessment of cavitationinduced erosion that show the dynamic behavior of collapsing bubbles in water on their passage through an axisymmetric nozzle. In a recent numerical work, Lyu et al. [6] tracked dispersed gas/vapor bubbles in a Lagrangian fashion and described bubble compression and expansion by a modified Rayleigh-Plesset equation. Their meshing is rigid in an isometric domain and the modeling effort focuses on a gas-liquid mixture that is treated as a continuous and compressible fluid. ...
... As described above there are fundamental differences between hydraulic flows in water and lubricant film flows which are organized in Table 1 for direct comparison. [4,6] type is related to bearing failure assessment [21][22][23]: suction cavitation exit cavitation impact cavitation flow cavitation [4][5][6] dynamic increase in fluid film thickness caused by the displacement of adjacent walls [8] form of cavitation full cavitation partial cavitation inertia cavitation gaseous cavitation vaporous cavitation pseudo-cavitation [14] This work targets the lubricant flow in a journal bearing selecting suction cavitation as the subject of the investigation, because other bearing-related types of cavitation require the presence of a microstructure such as an oil groove or boring according to [21] that would make the experimental set-up more complex. Suction cavitation in bearings is triggered by the dynamic displacement of the shaft, resulting in a transient film thickness [8] and it is common ground among the researchers that only vaporous cavitation may result in material erosion. ...
... As described above there are fundamental differences between hydraulic flows in water and lubricant film flows which are organized in Table 1 for direct comparison. [4,6] type is related to bearing failure assessment [21][22][23]: suction cavitation exit cavitation impact cavitation flow cavitation [4][5][6] dynamic increase in fluid film thickness caused by the displacement of adjacent walls [8] form of cavitation full cavitation partial cavitation inertia cavitation gaseous cavitation vaporous cavitation pseudo-cavitation [14] This work targets the lubricant flow in a journal bearing selecting suction cavitation as the subject of the investigation, because other bearing-related types of cavitation require the presence of a microstructure such as an oil groove or boring according to [21] that would make the experimental set-up more complex. Suction cavitation in bearings is triggered by the dynamic displacement of the shaft, resulting in a transient film thickness [8] and it is common ground among the researchers that only vaporous cavitation may result in material erosion. ...
The research of cavitation in narrow gap flows, e.g., lubrication films in journal bearings or squeeze film dampers, is a challenging task due to spatial restrictions combined with a high time-resolution. Typically, the lubrication film thickness is in the range of a few microns and the characteristic time for bubble generation and collapse is less than a few milliseconds. The authors have developed a journal bearing model experiment, which is designed according to similarity laws providing fully similar flow conditions to real journal flows while offering ideal access to the flow by means of optical measurement equipment. This work presents the high-speed photography of bubble evolution and transportation in a Stokes-type flow under the influence of shear and a strong pressure gradient which are typical for lubricant films. A paramount feature of the experiment is the dynamic variation (increase/decrease) of the minimum film thickness which triggers the onset of cavitation in narrow gap flows. Results presented in the work on hand include the time-resolved data of the gas release rate and the transient expansion of gas bubbles. Both parameters are necessary to set up numerical models for the computation of two-phase flows.
