ABSTRACT

The water-entry of 2D circular cylinder at high impact velocity is studied numerically. The flow model treats the fluid as a compressible mixture of air and water with homogeneous material properties. High- resolution Godunov-type method is employed to solve the governing equations numerically. The impact loads in both pure water and aerated water conditions are investigated. The aerated water is modeled using the analogy with problems of shock wave propagation in compressible foam. It turns out that the impact force is found to increase with the velocity as expected and the aerated gas have a significant reduction on the impact load.

INTRODUCTION

Predicting the Hydrodynamic loads of high-speed entry is one importance aspect in the design of aeronautical and aerospace structures. The load during the impact period is characterized by huge transient pressures and loads which may potentially damage the structure (Faltinsen, 1993). Assuming inviscid and incompressible fluid, as the first order approximation, the pioneering works on water entry originate from von Karman and extended by taking the pile up of water surface into accounted using a linearized asymptotic analysis. The Second-order Wagner theory was proposed by Korobkin (2007) and Oliver (2007), for the impact of a liquid parabola onto a rigid flat plate and respectively. Applying the linearized free-surface boundary conditions on the horizontal plane at the splash-up height and imposing the body boundary condition on the actual position of the body, numerical solution of the boundary-integral equation has been obtained by Zhao & Faltinsen (1993). Following the same initial-boundary-value formulation, conformal mapping technique was successfully used to solve the water impact of general two-dimensional sections (Mei et al, 1999). The inviscid and incompressible liquid are considered in all these analytical approaches.

The nonlinear jet flow in the intersection region between the body and free surface was investigated using asymptotic matching by Howison et al (1991). For wedges and a section with flare, it was found that the local jet flow at the water intersection does not play an appreciable role in the overall dynamics of the impact (Zhao & Faltinsen, 1993).