垂向双蝠鲼变攻角滑翔水动力性能研究

为了探究垂向间距和攻角对双蝠鲼在沿垂向分布集群滑翔时的水动力性能影响,根据蝠鲼的实际外形建立了蝠鲼计算模型,设置了4种间距排布即0.25, 0.5, 0.75, 1倍体厚排布以及9种攻角状态即-8°～8°,随后借助Fluent软件进行了双蝠鲼变攻角、变垂向间距的集群滑翔数值模拟,结合流场压力云图以及速度云图对集群系统平均升/阻力以及集群中各单体的升/阻力进行了分析.数值计算结果表明:双蝠鲼沿垂向分布在攻角范围为-8°～8°进行集群滑翔时系统平均阻力均高于单体滑翔时所受阻力.单体在集群滑翔过程中获得减阻收益,当双蝠鲼以负攻角集群滑翔时,下方蝠鲼阻力减小,且垂向间距越小,减阻效果越明显;当以正攻角集群滑翔时,上方蝠鲼获得减阻收益.当双蝠鲼以负攻角滑翔时,系统平均升力大于单体滑翔时所受升力;当双蝠鲼以负攻角滑翔时,系统平均升力小于单体滑翔时所受升力,系统平均升力几乎不受垂向间距影响.下方蝠鲼升力始终大于上方蝠鲼升力,但随着垂向间距的增大,升力差距逐渐减小.

INVESTIGATION ON THE HYDRODYNAMIC PERFORMANCE OF A VERTICAL DOUBLE MANTA RAY GLIDING WITH VARIABLE ATTACK ANGLES

In order to investigate the effects of vertical spacing and angle of attack on the hydrodynamic performance of double manta rays when gliding in clusters along the vertical distribution, a computational model of manta rays was developed based on the actual shape of manta rays. Four spacing arrangements, including 0.25, 0.5, 0.75 and 1 times the body thickness, and nine angle of attack states, namely ?8°?8°, were set up. Then, the numerical simulation of the double manta ray with variable attack angle and vertical distance was carried out by Fluent software. The mean lift/drag of the system and the lift/drag of each individual in the cluster were analyzed by combining the flow field pressure and velocity clouds. Numerical calculations showed that the average drag of the two manta rays was higher than that of a single manta ray when they glided in groups with attack angles ranging from ?8° to 8° in the vertical direction. When the two manta rays glide at negative attack angle, the drag of the lower manta ray decreases, and the smaller the vertical spacing, the more obvious the drag reduction effect is; when the two manta rays glide at positive attack angle, the upper manta ray gains drag reduction. When the two manta ray glide at negative attack angle, the system average lift is greater than that of the single glider; when the two manta rays glide at negative attack angle, the system average lift is less than that of the single glider, and the system average lift is almost independent of the vertical spacing. The lift of the lower manta ray is always greater than that of the upper manta ray, but the difference in lift decreases as the vertical spacing increases.