Sharif Digital Repository

In this thesis, cavitating flow over 2D/3D geometries of cavitators and projectile bodies in stationary and moving conditions are simulated using the "Volume of Fluid" (VOF) technique. The main application of VOF model is for simulating free surface flows. In this work, another capability is added to the VOF algorithm to solve for gas phase and by applying analytical-numerical mass transfer models, cavitation phenomenon is simulated. The developed algorithm precisely simulates the geometrical parameters of supercavities such as dimension and shape in a wide range of cavitation numbers. In addition, the flow parameters of supercavity such as drag coefficient, pressure coefficient inside the... 

Cavitation phenomenon is defined as the process of rupturing of liquid by a decrease in pressure at nearly constant temperature and it is a very complex non- linear phenomenon. Therefore the theoretical and numerical analysis of cavitation is very difficult and even impossible. A high speed cavitation tunnel is designed and manufactured for experimental understanding of cavitation. The effects of cavitation on drag force of several models such as circular cylinder, hydrofoil and wedge with after body were studied. There was a sufficient turbulence provided at upstream flow, during the tests of circular cylinder and hydrofoil within Reynolds number 105 to .Boundary layer on the cylinder is... 

In this study, the numerical simulation of cavitating flows for cryogens fluids is performed. The algorithm employs the homogenous, multiphase Euler/Navier-Stokes equations with the interface capturing method. The thermodynamic and thermal effects substantially impact the cavitation dynamics of cryogenic fluids and therefore these effects should be considered by solving the energy equation in conjunction with the mass and momentum conservation, and updating the fluid physical properties. Here, two cavitation modeling strategies, namely, the barotropic cavitation model and the transport equation-based model are used. Both laminar and turbulent cavitating flows are studied in this work. For... 

Bubble cluster has attracted the interests of many researches since the early twentieth century. Despite its easy generation and numerous occurrences, its study is extremely complex. Describing the dynamical behavior of bubble clusters is possible when quite a few simplifying assumptions are utilized. In other words, one can observe that with current approaches, the relevant theoretical researches are not very valuable. In this research, however, lattice Boltzmann method, a rather recent mesoscopic approach, was used to study the behavior of bubbles in a bubble cluster. Of course, this is only the beginning and there is a long way before getting close to experimental results. However, there... 

A complete understanding of high-intensity focused ultrasound-induced temperature changes in tissue requires insight into all potential mechanisms for heat deposition. Applications of therapeutic ultrasound often utilize acoustic pressures capable of producing cavitation activity. Recognizing the ability of bubbles to transfer acoustic energy into heat generation, a study of the role bubbles play in tissue hyperthermia becomes necessary. These bubbles are typically less than 50μm.
This dissertation examines the contribution of bubbles and their motion to an enhanced eating effect observed in a tissue-mimicking phantom. A series of experiments established a lationship between bubble... 

Mechanical behavior of aluminum-magnesium alloy, AA5083, was studied at high temperatures using hot tensile testing together with uniaxial creep experiments. In the first place, the as-received AA5083 sheet was subjected to annealing heat treatment to remove the effect previous plastic straining. Then, creep experiments were conducted at temperatures in the range of 190°C to 300 ° C under constant the stress varied between 30 MPa to 100 MPa. The hot tensile testing was also carried out from room temperatures up to 400 °C under nominal constant strain rates of 0.0005, 0.005, 0.01 and, 0.05 (1/s). In addition to the mechanical testing, optical metallography and scanning electron microcopy were... 

Simulation of the flow inside a turbopump inducer of a cryogenic engine, can help to reduce the number of experimental tests in the design phase. In cryogenic engines, high speed of the turbo pump, engine working at off-design conditions, startup and shutdown of the engine, can cause the pressure to drop below the vapor pressure at the inducer blades. In such circumstances, cavitation bubbles start to grow and collapse as they are washed by the flow to the regions with higher pressure. Cavitation is the rapid formation and collapse of vapour cavities in a liquid.The energy required for evaporation is received from the surrounding liquid which causes the temperature to drop in the... 

Recent studies show a great number of micro hydro power potentials all over Iran. They have the capability to generate electricity for shops, residential areas, agricultural communities, and recreational tourism centers. In order to cover the micro hydro power potentials of the country, Sharif University of Technology and Iran Water and Power Resources Development Corporation decided to conduct a project to design and fabricate three types of micro hydropower for the first time in Iran. The potentials with low head and high discharge are located beside rivers and are appropriate places to install axial micro hydro turbine. In this project we tried to prototype an axial micro hydro turbine... 

In this study, creep behavior and cavitation as well as high temperature deformation of Al-Zn-Mg aluminum alloy were investigated by means of uni-axial creep and tensile tests. The as-received material i.e. AA7075 plate, was first stabilized utilizing over-aging heat treatment and then stress-controlled creep tests were performed in the temperatures ranging between 120℃ to 210℃ under the applied stresses varying 130MPa to 250MPa. Accordingly, the stress exponent and creep activation energy were determined as 5.7 and 149kJ/mol.K to 189kJ/mol.K, respectively. Considering these parameters, it was found that the governing creep mechanism, in the mentioned temperature range, would be dislocation... 

In this study, the factors affecting cavitation in the crest of an ogee spillway were investigated. One of the factors affecting the occurrence of cavitation on the ogee crest is the ratio of the head to the design head. As the head ratio increases, the probability of cavitation on the crest increases. The value of the head is also an effective parameter for the occurrence of cavitation. The spillway crest curve is also one of the factors affecting the occurrence of cavitation on the ogee-crested spillways. In this study, the ogee crested spillway that consists of three circular arcs upstream has been investigated. 5 different head ratios have been used. For this study, OpenFOAM software,... 

Bubble collapse near a rigid wall with rapid and non-spherical compression of the internal gas can lead to destructive and unfavorable effects such as erosion, noise, and a fall-off in the performance of devices. Despite the fact that several investigations on this phenomena have been carried out under various conditions, studies indicate that the collapse of a single cavitation bubble next to the liquid jet injected from the wall's side and their interaction have not been studied so far. To achieve this goal, the present study deals with the three-dimensional simulation of the two-phase flow field from the Eulerian point of view. OpenFOAM has been used to solve the equations of conservation...