Research On Drag Reduction Performance Of Bionic Flexible Skin Based On Immersed Boundary Method

Underwater vehicles are subject to fluid resistance during their journey,which not only reduces the speed of the vehicle,but also accelerates energy consumption.To reduce the resistance of underwater vehicles,a new kind of biomimetic flexible skin with similar structure to dolphin skin was proposed based on the wide application of biomimetic flexible surface in the field of fluid drag reduction.Based on the flow stability theory,the structural parameters were designed.Aiming at the complex structure and large deformation of the skin,a fluid-solid coupling numerical solver based on the immersion boundary method was used to simulate the skin.The drag reduction performance of the bionic flexible skin was analyzed by the evaluating drag coefficient and the relative drag reduction ratio.This paper mainly carries out the following work:Firstly,a bionic flexible skin structure was proposed.To reduce the resistance of underwater vehicles,a new kind of biomimetic flexible skin structure was proposed,which is a mechanical simulation of dolphin skin structure.The upper flexible skin corresponds to the skin layer of a dolphin,while the middle support unit can better simulate the protrusion of the skin layer and the deformation of the subcutaneous fat layer.Based on the numerical results of flow stability theory,the material selection of the upper flexible wall,the spacing between support units,the mass ratio,and the stiffness ratio were designed.Secondly,the support unit force source term and the fluid-solid coupling numerical solver based on the immersed boundary method were constructed.Based on the principle of minimum action,the force source term of the support unit was constructed and added to the right end of the N-S equation to obtain the coupling equation of fluid and bionic flexible skin immersion boundary,and the coupling equation was discretized in time and space.Repeat the above process to solve the pressure,speed,and other related parameters.Based on the coupling equation,numerical dispersion,and relevant parameters,a fluid-solid coupling numerical solver based on the immersed boundary method was constructed.Then,the modular modeling method of the support unit was constructed and fluid-solid coupling numerical calculation of bionic flexible skin was completed.The accuracy of the numerical calculation of fluid-solid coupling was verified by a cylindrical flow example and a flexible wire case.Modular modeling of the support unit was completed based on the force source item of the support unit.By setting simulation parameters of the IB2 d software package,the feasibility of simulation grid density and time step was verified.Finally,the influence of various parameters on the drag reduction performance of the bionic flexible skin is analyzed and its drag reduction performance is verified.After processing the output result file of the IB2 d software package,the drag reduction effect of biomimetic flexible skin under different spacing,stiffness ratio,and the mass ratio is compared according to the result of the post-processing and taking the drag coefficient as the evaluation index.The drag reduction effect of the bionic flexible skin at different flow rates is compared with that of the rigid plate by taking the relative drag reduction rate as the evaluation index.