Supercavitating Flow over High-Speed Underwater Vehicles (original) (raw)
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Egyptian Journal for Engineering Sciences and Technology
Body shape of high-speed underwater vehicles has a great effect on the Supercavitation behaviour. The transient flow around either partially cavitating or supercavitating body affects the trajectory of high-speed underwater vehicles. Commercial code (ESI-CFD ACE+, V 2010) was used to simulate the supercavitation around two different shapes of a projectile with their noses of hemispherical shape and telescopic shape. Also, conical and blunt projectile shapes were considered. Also, a comparison between two different designs of grid was performed numerically. Grid designs were structured and unstructured grids. Navier-Stokes equations were used as governing equations for simulating supercavitation. Cavity shape was determined over projectile body and around wake. Also, two-dimensional flow field around the cavitating body was determined. Projectile body has a diameter about 0.4 times its length (0.4L). In the case of the Blunt end there is a strong wake effect. The ESI-CFD code (2010) is valid for observing the supercavitation phenomena. Unstructured grid is more accurate than structured one in simulating supercavitation.
Numerical Modeling of Supercavitating Flows
2001
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.
An experimental and numerical study of supercavitating flows tric cavitators
Journal of Theoretical and Applied Mechanics, 2016
It has been shown that developing a supercavitating flow around underwater projectiles has a significant effect on their drag reduction. As such, it has been a subject of growing attention in the recent decades. In this paper, a numerical and experimental study of supercavitating flows around axisymmetric cavitators is presented. The experiments are conducted in a semi-open loop water tunnel. According to the Reynolds-Averaged Navier-Stokes equations and mass transfer model, a three-component cavitation model is proposed to simulate the cavitating flow. The corresponding governing equations are solved using the finite element method and the mixture Rayleigh-Plesset model. The main objective of this research is to study the effects of some important parameters of these flows such as the cavitation number, Reynolds number and conic angle of the cavitators on the drag coefficient as well as the dimensions of cavities developed around the submerged bodies. A comparison of the numerical and experimental results shows that the numerical method is able to predict accurately the shape parameters of the natural cavitation phenomena such as cavity length, cavity diameter and cavity shape. The results also indicate that the cavitation number declines from 0.32 to 0.25 leading to a 28 percent decrease in the drag coefficient for a 30 • cone cavitator. By increasing the Reynolds number, the cavity length is extended up to 322% for a 60 • cone cavitator.
Experimental investigation of supercavitating flows
International Journal of Naval Architecture and Ocean Engineering, 2012
When the object is traveling in the water at tremendously high speeds, the cavity forms and grows up at a fore part of the object called cavitator, and the object is eventually enveloped by vaporized water, supercavitation. As a result, the only part of the object in direct contact with the water is the cavitator, so skin-friction drag is significantly reduced. This is why recently supercavitating objects have been interested in many applicable fields. In this study we are focused out attention on supercavitating flows around various shapes of two and three dimensional cavitators. First, general features of supercavitation are examined by analyzing results obtained by the previously developed numerical method. Second, experimental observations are carried out at a cavitation tunnel at the Chungnam National University (CNU CT), and supercavity dimensions are scrutinized.
Results of selected experiments involving supercavitating flows
2001
has conducted basic research and development involving supercavitating projectiles. Under this program, the theory of high-Mach-number underwater flows has been investigated and first-principles modeling of cavity development and projectile dynamics and stability have all been addressed. To support these analytical efforts, a sophisticated experimental program has similarly matured. The NUWC Division Newport Supercavitating High-Speed Bodies (SHSB) Test Range has been designed to safely test underwater gun-launched projectiles traveling in excess of the speed of sound in water. This range was installed as an upgrade to a facility originally designed as a tow tank for testing tactical scale undersea vehicles. Currently the test range is 17 m long and approximately 4 m deep. Armor plates positioned-1.5 m apart ensure that even unstable projectile trajectories are confined to the range. This lecture describes the experimental facility and the tests performed there through the end of the author's tenure at NUWC circa December, 1998. A description of the test range, its instrumentation suite, and the extensive photographic capabilities developed to capture these high-speed projectiles are discussed. A summary of the experimental milestones through December, 1998, is also presented.
THE MODELS OF THE SUPERCAVITATION PREDICTION FOR HIGH SPEED MOTION IN WATER
The International Summer Scientific School "High Speed Hydrodynamics", June 2002, Chebocsary, Russia
The results of the approximate methods development and the number of existing possibilities for modeling and prediction of the flow and motion processes apply to high speed motion in the water with supercavitation are presented. Two characteristic ranges of speeds for not large Mach Numbers till up 0.1-0.2 M~ and super high speeds in water for 0.5-2.5 M~ are considered. Every ones of this ranges the different applications and developed parts of the theory are corresponded. The preference are given to the consideration of the problem as whole on base of simple physical models. Consideration is based on the " Matched Asymptotic Expansion Method" in the approximation of the "Slender Body Theory" with applying another approximations and simple heuristics models with application dimension analysis and integral conservation laws. The calculation problems of prolate mainly axisymmetric steady and unsteady cavities with account of numbers of factors and cavities with gas injections are considered and analyzed. The possibilities an the problem station of supercavitation prediction for super high sub-and supersonic speeds are analyzed with account of key compressibility effects. The forming of the cavitation drag and drag reduction problems are considered and analyzed. The possibilities of the suprcavitating bodies motion prediction are considered taking into account also influence of hydro elastics effects.
Control Strategies For Supercavitating Vehicles
Journal of Vibration and Control, 2002
#DUVTCEV 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. However, as discussed in this article, control and maneuvering present special challenges. Strategies for meeting those challenges are also presented. The first section describes example vehicle configurations, and discusses the nonlinear forces acting on the cavitator, the fins (if present), and any portions of the hull that penetrate the cavity boundary during excursions from the fully-enveloped condition. The need for a bank-to-turn maneuvering strategy is also discussed. The second section describes simulation of vehicle flight, including system stability and system performance during execution of a banked turn. Without control, some vehicle configurations can be unstable, whereas a feedforward-feedback strategy can control some configurations over a range of turn rates.
Simplified dynamical systems analysis of supercavitating high-speed bodies
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. However, control and maneuvering present special challenges. This article presents a simplified dynamical systems model that captures what may be considered the key features of the system: namely forces curves that are nearly slope-discontinuous as the vehicle afterbody impacts the cavity boundary, and a time delay associated with the advection of cavity disturbances downstream from the cavitator to the point of afterbody impact. The model is then employed to map the stability of the system as key design parameters are varied, and to investigate the behavior of the system under various conditions. INTRODUCTION A vari...
Dynamics of supercavitating vehicles with cone cavitators
Mechanics and Advanced Technologies
The work is devoted to theoretical and experimental investigations of dynamics of high-speed underwater supercavitating vehicles with cone cavitators. The cone cavitators are considered as operating controls of the supercavitating vehicle motion. The mathematical model of a “slender” unsteady cavity based on the G.V.Logvinovich principle of independence of the cavity section expansion is used. Experimental studies of the rotary cone cavitators were carried out at the high-speed experimental tank of the Institute of Hydromechanics of the NAS of Ukraine. Based on test results, the approximate dependences of both the drag coefficient and the lift coefficient of an inclined cone cavitator on the rotary angle in a wide range of cone angles are proposed. The range of cone angles is determined when the cone cavitators are the more effective operating controls in comparison with equivalent disk cavitator. With the help of computer simulation, a number of problems of dynamics of the supercav...
An integrated approach to the design of supercavitating underwater vehicles
2007
Optimal design configuration for fins and planing-supported level flight.. . 10 Performance of optimal vehicle in fins and planing-supported level flight.. . 11 Reduced optimal design configuration for fins-supported level turning flight. 12 Performance of reduced optimal vehicle in fins-supported level turning flight.