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In this paper, a simple practical method to estimate the drag of super-cavitating underwater vehicles (SCUV) is proposed that can obtain the drag with only principal dimensions in an initial design stage. SCUV is divided into cavitator, forebody, afterbody, base, and control fin and the drag of each part is estimated. The formulas for the drag coef...
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Context 1
... is estimated from Eq. (14). However, in the case of the forebody, it is necessary to consider a cut-out part and a coverage of the forebody by the cavity. The pressure coefficient of the forebody part covered by the cavity becomes a negative cavitation number, which appears as a decrease in drag because the slant faces the upstream as shown in Fig. 7. After the cavity is closed, the flow follows the rest slant so that the rest forebody can still be regarded as a truncated cone. Therefore, the forebody drag can be obtained as the sum of the drag of the part covered by the cavity (F c BF ) and the rest forebody as a truncated cone (F cs BF ). This is given by Eq. ...
Context 2
... cavity by the forebody appears in the end of the forebody with decreasing the cavitation number as shown in Fig. 7. Since the forebody is assumed to a truncated cone, the drag coefficient of cone is applied differently depending on cavitating and noncavitating conditions from Eq. (19). When the cavity covers the entire forebody, the drag is calculated from Eq. (26). The forebody drag will be verified together with the numerical results in the next ...
Context 3
... the cavity by the forebody is already formed before the cavity by the cavitator covers the entire forebody so that the cavity by the forebody covers a part of the afterbody as shown in Fig. 7. The generation of the cavity by the forebody can be determined by applying the forebody drag to Eq. (19). In Eq. (31), the radius of cavitator uses that of the forebody and the radius and length of the cavity uses those of the forebody so that the length of afterbody part covered by the cavity can be obtained. From this, the effect on ...
Context 4
... dimensions for each model are shown in Table 1. Since the present drag estimation method is intended to be utilized in the initial design stage with only the main dimensions, it is modeled to be as simple as possible. The numerical analyses for the models are carried out in the same conditions with the numerical methods as mentioned above. Fig. 17 shows the total drag of SCUV estimated by the present method and the numerical analyses for the full scale (case 1). The total drag of the present method agrees well with the numerical results quantitatively and qualitatively. Fig. 18 shows the results in the model scale (case 2). In the model scale, the results of the present method ...
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Aiming at the problem of unsteady cavitation during a projectile’s vertical water-exit process, scaled model experiments were carried out based on the self-designed underwater launch platform and high-speed cameras, which focus on changes in cavitation shape and projectile posture. In this paper, the general process of the cavitation evolution and...
Citations
... The shape characteristics of a cavity can be divided into three parts (Choi & Kim, 2021). The first part of the front cavity shape is only related to the size of the cavitator. ...
Supercavitation has been recently presented as an effective method for the drag reduction of underwater vehicles. However, maintaining the supercavitating state requires a lot of energy, making vehicles difficult to control. Therefore, it is necessary to design an underwater vehicle with low drag in the fully wetted state while being able to move at ultra-high speed in the supercavitating state. In this study, a detachable fairing design for underwater vehicles is proposed, which has the advantage of increasing the total voyage and avoiding the problem of difficult steering in the supercavitating state. On the other hand, the study of non-body-of-revolution (non-BOR) has become a prevalent area of interest in the shape design of underwater vehicles. The cavity generated by an elliptical disk-shaped cavitator is studied numerically. It is found that the cavity profile on the cross-section near the cavitator is approximately elliptical. The cavity length of an elliptical disk-shaped cavitator is almost the same as that of a disk-shaped cavitator when they have the same inflow area. Based on these two characteristics, the parameters of the internal elliptical disk-shaped cavitator are optimized, which provides a promising strategy for the issue of cavitators increasing drag in a fully wetted state.
