Numerical research on slamming characteristics of aircraft landing on water

In order to investigate the impact characteristic of an aircraft landing on water,a computational fluid dynamics(CFD)simulation is conducted to explore the slamming characteristics of the NACA TN 2929 A model.The flow around the model is solved by using Reynolds-averaged Navier-Stokes equations with the shear stress transport(SST)k—ωturbulence model,based on finite volume method(FVM).The free surface is captured by using the volume of fluid(VOF)method,and the aircraft impact process is realized with help of overset mesh technology.Then,the effects of horizontal and vertical velocities and initial pitch angle on the slamming load,attitude change,impact pressure and flow field evolution are investigated.The results reveal that the horizontal velocity has a considerable influence on whether the aircraft’s horizontal tail hits the water,and further affects the maximum vertical load as well as the maximum pitch angle throughout the impact process.The vertical velocity determines the slamming load before the horizontal tail strikes the water,while the horizontal velocity has a significant effect on the load after the horizontal tail hits the water.A smaller initial pitch angle results in not only a heavier slamming load but also a more dramatic change of the posture after the aircraft impacts the water.The impact pressure of the aircraft is maximized at the junction of the approaching surface of the fuselage and the free surface.In some cases,the pressure is also concentrated on the undersurface of the horizontal tail.

Numerical simulation of the effect of waves on cavity dynamics for oblique water entry of a cylinder

The water entry process associated with complicated unsteady structures,with consideration of the influence of the waves,is not well studied.In the present work,the oblique water entry of a cylinder under different regular waves is numerically investigated.The volume of fluid(VOF)method and the sub-grid scale(SGS)stress model based on the large eddy simulation(LES)method are adopted for the 3-D simulation with six degrees of freedom.The present numerical model is based on a wave model,and as shown by the previous work that the predicted cavity evolution in the calm water agrees well with the experimental results.The present model is validated and it is shown that it could be used to predict the correct wave periods and fluctuations.The cavity evolution mechanism,the dynamic characteristics and the vortex structures are analyzed.The cavity of the water entry with waves closes more quickly than in the calm water case.Finally,several parametric studies of the water entry with different wave heights and water entry locations are carried out.The results provide insights into the effects of the waves on the cavity dynamics for oblique water entry problems.

A sharp-interface immersed smoothed point interpolation method with improved mass conservation for fluid-structure interaction problems

To solve the problem of inaccurate boundary identification and to eliminate the spurious pressure oscillation in the previously developed immersed smoothed point interpolation method(IS-PIM),a new sharp-interface IS-PIM combining mass conservation algorithm,called Sharp-ISPIM-Mass,is proposed in this work.Based on the so called sharp-interface method,the technique of quadratic local velocity reconstruction has been developed by combining with the mass conservation algorithm,which enables the present method improve the accuracy of the velocity field and satisfy the mass conservation condition near the boundary field.So the proposed method would not encounter the problem of spurious mass flux.In addition,a new form of FSI force evaluation considering pressure and viscous force to perform a whole function from the fluid domain to fictitious fluid domain is introduced,which makes the present method obtain more accurate results of FSI force than the original one.Through the numerical studies of a number of benchmark examples,the performance of the Sharp-ISPIM-Mass has been examined and illustrated.