MATHEMATICAL APPROACH TO INVESTIGATE THE BEHAVIOUR OF THE PRINCIPAL PARAMETERS IN AXISYMMETRIC SUPERCAVITATING FLOWS, USING BOUNDARY ELEMENT METHOD

摘要

In this paper, a direct boundary element method (DBEM) is formulated numerically for the problems of the unbounded potential flows past supercavitating bodies of revolution (cones and also disks which are special case of cones with tip vertex angle of 180 degree) at zero degree angle of attack. In the analysis of potential flows past supercavitating cones and disks, a cavity closure model must be employed in order to make the mathematical formulation close and the solution unique. In the present study, we employ Riabouchinsky closure model. Since the location of the cavity surface is unknown at prior, an iterative scheme is used. Where, for the first stage, an arbitrary cavity surface is assumed. The flow field is then solved and by an iterative process, the location of the cavity surface is corrected. Upon convergence, the exact boundary conditions are satisfied on the body-cavity boundary. For this work, powerful software, based on CFD code, is developed in CAE center of IUST. The predictions of the software are compared with those generated by analytical solution and with the experimental data. The predictions of software for supercavitating cones and disks are seen to be excellent. Using the obtained data from software, we investigate the mathematical behavior of axisymmetric supercavitating flow parameters including drag coefficients of supercavitating cones and disks, cavitation number and maximum cavity width for a wide range of cone and disk diameters, cone tip angles and cavity lengths. The main objective of this study is to propose appropriate mathematical functions describing the behavior of these parameters. As a result, among all available functions such as linear, polynomial, logarithmic, power and exponential, only power functions can describe the behavior of mentioned parameters, very well.