Numerical Simulation Of Thickness Effect On Aerodynamic Performance Of Flapping Plate

Birds and insects flap wings to perform various flight actions.Many researchers devote themselves to study the mechanism behind this flight behavior to understand how the high maneuverability and flight efficiency are achieved.Furthermore,research on the physical mechanism of the flapping wing aerodynamics is important in the design for high performance flapping-wing aircrafts.In this thesis,the aerodynamic characteristics of flapping 2-D rigid flat plates are studied.The overset dynamic mesh technology is used to handle the moving boundary.Firstly,the thickness affects the aerodynamic performance on single flapping plate and the wake configurations are studied under the same Reynolds number,Strouhal number and the same flapping parameters.Then,the Strouhal number,based on flapping frequency,is changed to study the effect of the Strouhal number on single flapping wing and the interaction between the thickness and the Strouhal number.Finally,under the condition of tandem flapping plates configuration,the interactions between the upstream plate and downstream plate are studied.The thickness effect on the tandem flapping plates' thrust coefficients,the thrust efficiency and the interaction between the trailing eddy of upstream plate and the configuration of leading eddy of downstream plate are studied.It is found that the thickness has great influence on the timing of vortex shedding and the vortex strength increases with larger thickness in the case of a single flapping plate,while the amplitude of thrust coefficient decreases.The wake configuration changes from the von Karman's vortex street to reversed von Karman's vortex street gradually when the Strouhal number changes from 0.2 to 0.38,the values of critical Strouhal number for different flapping plates of various thickness are in the range of 0.24?0.27.Under the condition of tandem flapping flat plates configuration,the thrust coefficient amplitude of the downstream plate nearly doubled because of the modification of incoming flow caused by the upstream plate and the mean thrust coefficients have been greatly increased.The flow separation occurs quickly due to the increased effective angle of attack at the phase of thrust amplitude.The lift coefficient of upstream plate decreases with larger thickness,while the lift coefficient of downstream plate do not change much.The thrust coefficient and efficiency of downstream plate decrease with larger thickness.For upstream plates with different thickness,there are two sorts of vortex interactions with downstream plates,one is the shedding vortex with counter-clockwise rotating direction interacts with the inverted rotating direction vortex on the upper surface of downstream plate,the other is the shedding counter-clockwise vortex interacts with the same rotating direction vortex on the lower surface of downstream plate,resulting in a faster rolling up of the leading eddy of downstream plate.