密度分层流体中带尾喷拖曳球动量尾迹演化特性实验

采用带L型尾喷管拖曳球方法,模拟水下航行体艇体与冷却水排放等产生的阻力与射流动量尾迹,实验研究了这种组合式动量尾迹在密度分层流体中的演化特性.研究表明,当JD/J〉CD时,这种组合式动量尾迹的演化特性主要受拖曳球阻力动量尾迹控制,形成正卡门型准二维偶极子涡街结构,其中JD为拖曳球产生的阻力动量流量,J是L型尾喷管产生的射流动量流量,CD是球体阻力系数;当JD/J〈CD时,这种组合式动量尾迹的演化特性与（Rej,Frj）的组合条件密切相关,主要受射流动量尾迹控制,在（Rej,Frj）的某些组合下可能会形成反卡门型准二维偶极子涡街结构,但也可能不产生任何形式的大尺度相干结构,其中Rej和Frj分别为射流Reynolds数与Froude数.在系列实验基础上,获得了这种组合式动量尾迹在密度分层流体中能够演化为反卡门型准二维偶极子涡街结构的（Rej,Frj）组合条件,并对不同的Rej取值,获得了准二维偶极子涡街无量纲形成时间及其无量纲涡街平均波长倒数与Frj之间的相关关系,结果表明它们都是不依赖于Rej的,而且与Frj近似为幂指数关系.

Experiments on evolution characteristics of momentum wakes generated by the towed sphere with a horizontal jet

The model of the towed sphere with a L-shape nozzle jet was used to generate both drag and jet momentum wakes due to the body and cooling discharge water of the underwater vehicle,the results of experiments were presented for the evolution characteristics of such combined momentum wakes in a stratified fluid.It is shown that for J D/JC D,the evolution characteristics for the combined momentum wakes are mainly attributed to the drag momentum wake generated by the towed sphere,and the far wake becomes quasi two-dimensional （2D） in the form of a Karman-like dipolar vortex street,where J D is the drag momentum flux due to the towed sphere,J is the jet momentum flux due to the L-shape nozzle jet and C D is the drag coefficient of the sphere.For J D/JC D,the evolution characteristics for the combined momentum wakes are strongly dependent of the （Re j,Fr j） combinations,and the far wake can become quasi 2D in the form of an anti-Karman-like dipolar vortex street being mainly attributed to the jet momentum wake under some （Re j,Fr j） combinations,but there may be no occurrence of large-scale coherent structures,where Re j and Fr j are Reynolds and Froude numbers duo to the L-shape nozzle jet respectively.The conditions under different Reynolds and Froude numbers （Re j,Fr j） combinations where the anti-Karman-like dipolar vortex streets can be formed by such combined momentum wakes were determined by use of data based on the present series experiments,and the dependence of the dimensionless formation time and inverse dimensionless average wavelength of the quasi 2D dipolar vortex streets on Fr j for different values of Re j was obtained,results indicate that these parameters are independent of Re j and approximately follow some power exponent laws on Fr j.