Modelling of Super Cavitation on Wing using Partial nonlinear model of Boundary Element Methods (original) (raw)
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Mathematical Problems in Engineering, 2016
A fixed-length Boundary Element Method (BEM) is used to investigate the super- and partial cavitating flows around various axisymmetric bodies using simple and reentrant jet models at the closure zone of cavity. Also, a simple algorithm is proposed to model the quasi-3D cavitating flows over elliptical-head bodies using the axisymmetric method. Cavity and reentrant jet lengths are the inputs of the problem and the cavity shape and cavitation number are some of the outputs of this simulation. A numerical modeling based on Navier-Stokes equations using commercial CFD code (Fluent) is performed to evaluate the BEM results (in 2D and 3D cases). The cavitation properties approximated by the present research study (especially with the reentrant jet model) are very close to the results of other experimental and numerical solutions. The need for a very short time (only a few minutes) to reach the desirable convergence and relatively good accuracy are the main advantages of this method.
In this paper, supercavitation and partial cavitation over axisymmetric bodies have been solved, using the Boundary Element Method (BEM), based on potential. In this method, the cavity and the wetted surface of the body will be estimated by some panels. Then, the cavitation will be modeled, by means of Green's third identity integral. For this purpose, the rings of the sources are distributed on the cavity surface, and the ring of the dipoles is distributed on the body and the cavity surface. The high velocity and also proper accuracy in calculating the geometry of the cavity and the drag coefficient are considerable advantages of this method.
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Cavitation causes many adverse effects in engineering applications, but this phenomenon could be used in a different way to reduce the viscous drag on objects travelling under water. As water due to its high density will impose high drag force. With the help of cavitation bubble the drag could be reduced drastically as the body of the object will be covered with less dense gas or vapour. Thus, it becomes important to study the cavitation parameters to predict the shape of cavity formed and drag force experienced by the object to ensure efficient travel under water. Cavitation number is the key factor affecting the cavitation phenomenon thus it is the independent quantity during analysis. Before running the simulation, grid independence test was performed to enhance the accuracy and reduce errors due to meshing. The article gives insight about the setting up of transient multiphase simulation for supercavitating flows. The time-stepping method selected for the simulation was “Variabl...
Modeling Cavitation over Axisymmetric Bodies: VOF Technique versus Boundary Element Method
2008
A computational study of superand partial-cavitation over axisymmetric bodies is presented using two numerical methods. The first method is based on the VOF technique where the transient Navier-Stokes equations are solved along with an equation to track the cavity interface. The second method is that of the steady boundary element method (BEM) which is a model based on the potential flow theory. The supercavitation results of the two methods for disk and cone cavitators are compared with each other and with those of the available experiments and analytical relations. Two different geometries for a cone with various cone angles are considered. Also, the results of comparison between the two methods for partial cavitation over a sphere, a blunt cylinder, and a cylinder with a spherical head are presented.
An iterative scheme for two-dimensional supercavitating flow
In the present research, supercavitating potential flow is studied numerically by the boundary element method (BEM). Using the advantages of BEM, an iterative algorithm has been introduced to capture cavity boundary in two-dimensional symmetric flows. In this algorithm, the cavity length is known and used to find the related cavitation number and cavity profile. In order to obtain finite length cavities, a cusped cavity closure model has been employed. Applying this cavity closure model, it is possible to change the cavity closure profile and its specified length. By comparing the results of the present analysis with previous analytical and numerical solutions as well as the experimental data, it can be concluded that the present iterative numerical algorithm is reliable and can be applied with BEM or other numerical methods to predict the characteristics of a supercavitating flow. Moreover, the feasibility of the cavity capturing in a flow field with low cavitation number is especially attractive.
Numerical Modeling of Supercavitating Flows
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Supercavitating bodies can achieve very high speeds under water by virtue of reduced drag: with proper design, a cavitation bubble is generated at the nose and skin friction drag is drastically reduced. Depending on the type of supercavitating vehicle under consideration, the overall drag coefficient can be an order of magnitude less than that of a fully wetted vehicle. Slender-body theory and boundary element methods are two modern computational methods applied to the design of supercavitating vehicles. These course notes present recent advances in the theory behind these two computational approaches, as well as results and application of the methods to the simulation and control of supercavitating vehicles.
Numerical and Experimental Study on Unsteady Shedding of Partial Cavitation
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Periodically unsteady shedding of partial cavity and forming of cavitation cloud have a great influence on hydraulic performances and cavitation erosion for ship propellers and hydro machines. In the present study, the unsteady cavitating flow around a hydrofoil has been calculated by using the single fluid approach with a developed cavitation mass transfer expression based on the vaporization and condensation of the fluid. The numerical simulation depicted the unsteady shedding of partial cavity, such as the process of cavity developing, breaking off and collapsing in the downstream under the steady incoming flow condition. It is noted that good agreement between the numerical results and that of experiment conducted at a cavitation tunnel is achieved. The cavitating flow field indicates that the cavity shedding was mainly caused by the re-entrant jet near cavity trailing edge, which was also clearly recorded by high-speed photographing.