The dynamic performance and wake structure of flapping plates with different shapes were studied using multi-block lattice Boltzman and immersed boundary method.Two typical regimes relevant to thrust behavior are identified.One is nonlinear relation between the thrust and the area moment of plate for lower area moment region and the other is linear relation for larger area moment region.The tendency of the power variation with the area moment is reasonably similar to the thrust behavior and the efficiency decreases gradually as the area moment increases.As the mechanism of the dynamic properties is associated with the evolution of vortical structures around the plate,the formation and evolution of vortical structures are investigated and the effects of the plate shape,plate area,Strouhal number and Reynolds number on the vortical structures are analyzed.The results obtained in this study provide physical insight into the understanding of the mechanisms relevant to flapping locomotion.
Nitrogen injection under conditions close vicinity of the liquid-gas critical point is studied numerically. The fluid thermodynamic and transport properties vary drasti- cally and exhibit anomalies in the near-critical regime. These anomalies can cause distinctive effects on heat-transfer and fluid-flow characteristics. To focus on the influence of ther- modynamics on the flow field, a relatively low injection Reynolds number of 1 750 is adopted. For comparisons, a reference case with the same configuration and Reynolds number is simulated in the ideal gas regime. The model accommodates full conservation laws, real-fluid thermody- namic and transport phenomena. Results reveal that the flow features of the near-critical fluid jet are significantly differ- ent from their counterpart. The near-critical fluid jet spreads faster and mixes more efficiently with the ambient fluid along with a more rapidly development of the vortex pairing pro- cess. Detailed analysis at different streamwise locations in- cluding both the flat shear-layer region and fully developed vortex region reveals the important effect of volume dilata- tion and baroclinic torque in the near-critical fluid case. The former disturbs the shear layer and makes it more unstable. The volume dilatation and baroclinic effects strengthen the vorticity and stimulate the vortex rolling up and pairing pro- cess
