Body parameters with application of optimal differential variation method in super cavity model

When a slender body moves very fast through water at sufficient speed the cavity phenomena is happened. In a cavity model the body’s lengths and cavitator diameter are determined by the differential variationoptimal method so that the velocity of body is maximum.

APPLICATION OF DATA ASSIMIMILATION FOR PARAMETER CORRECTION IN SUPER CAVITY MODELLING

On the imperfect water entry, a high speed slender body moving in the forward direction rotates inside the cavity. The super cavity model describes the very fast motion of body in water. In the super cavity model the drag coefficient plays important role in body's motion. In some references this drag coefficient is simply chosen by different values in the interval 0.8-1.0. In some other references this drag coefficient is written by the formula with is the cavity number, is the angle of body axis and flow direction, is a parameter chosen from the interval 0.6-0.85. In this paper the drag coefficient is written with fixed and the parameter is corrected so that the simulation body velocities are closer to observation data. To find the convenient drag coefficient the data assimilation method by differential variation is applied. In this method the observing data is used in the cost function. The data assimilation is one of the effected methods to solve the optimal problems by solving the adjoin problems and then finding the gradient of cost function.

Effects of Dissolved Gas on Unsteady Cavitating Flow Around a Clark Y-11.7% Hydrofoil

In the present study, the effects of dissolved gas content on the unsteady cavitating flow around a Clark Y-11.7% hydrofoil are investigated in a cavitation tunnel. Lift and drag forces in various cavitating conditions are directly measured by strain gauges attached on the cantilever supporting the hydrofoil. In addition, the cavitating flow is filmed from the top and the side simultaneously using two high speed video cameras. The high (roughly 6–8ppm) and low (1–2ppm) DO conditions are examined to obtain the qualitative tendencies of the effects of dissolved gas on unsteady cavitation behavior and lift/drag characteristics. It is found that that the relationship between the cavitation behavior and the lift/drag fluctuations does not qualitatively differ in the two different DO conditions, while the amplitude is slightly larger in the low DO condition. At transitional cavity oscillation, in the both DO conditions, the lift/drag coefficients increase during the growth stage of sheet/bubble cavities on the hydrofoil and they decrease when the developed super-cavity disappears. Moreover, it seems that the amplitude of the lift/drag forces in the low DO condition is larger than in the high DO condition but the frequency of lift force fluctuation is not very different.