串、并联航行体自然超空泡数值分析方法研究

基于均质平衡流理论,应用商用流体力学软件Fluent,开展了三维带圆盘空化器的水下高速航行体在并、串联航行时自然超空泡数值模拟研究,研究了航行体间距对空泡形态和减阻特性的变化规律。结果表明,并联时,以上航行体为例,上表面的空泡长度小于下表面,随着间距的增大,上、下表面的空泡长度均不断减小,同时并联航行体摩擦阻力系数小于单航行体;串联时,前航行体的空泡尺寸大于后航行体,随着航行体间距的增大,后航行体的空泡尺寸逐渐增大,同时后航行体压差阻力系数远小于单航行体。     

水下航行体通气超空泡减阻特性实验研究

为了研究超空泡的减阻效果,保证在较低流速下生成超空泡,在水洞中开展了水下航行体通气超空泡的实验研究.采用通气的方法在较低水速下生成人工通气超空泡,通过改变通气率和弗劳德数,获得了不同条件下通气空泡的长度,以及不同空泡长度下的模型阻力系数.研究表明,来流速度不变时,空泡长度随通气率的增加而增加,阻力系数随空泡长度的增加先递增后递减;空化器直径对阻力系数的影响较大,在大弗劳德数条件下,阻力系数会因空化器直径过大而出现随通气量的增加而变大的趋势.利用商用软件对超空泡形态及阻力系数作了数值仿真,并与实验结果作了对比,两者符合较好.     

高速航行体的自然超空泡流阻力特性研究

利用Fluent6.2对水下带圆盘空化器高速航行体的自然超空泡流动进行了数值模拟,计算分析了超空泡高速航行体的阻力特性,研究了空化器直径、航行体长细比对航行体超空泡减阻效果的影响,分析了高速航行体的超空泡减阻率。结果表明,超空泡形态下随着航行体速度衰减,航行体压差阻力系数缓慢减小,粘性阻力系数迅速增大,航行体的总阻力系数增加;航行体阻力系数与头部空化器直径的平方成反比;增加航行体的长细比,可以获得更小的阻力系数;高速航行体的超空泡减阻率可达95%以上。最后将仿真计算结果与水靶道试验进行了对比,二者基本相符。     

水下航行体通气超空泡的实验研究

为了研究超空泡的减阻效果,保证在较低流速下生成超空泡,在水洞中开展了水下航行体通气超空泡的实验研究.采用通气的方法在较低水速下(V=7-15 m/s)生成人工通气超空泡,通过改变通气率和弗洛德数,获得了不同条件下通气空泡的长度,给出了通气空泡长度与通气率及弗洛德数的经验公式.研究表明,来流速度不变时,空泡长度随通气率的增加而增加,空泡长度一定时,通气率随弗洛德数的增加而减少;重力场造成了空泡形态的严重不对称,通过比较相同空化数下自然空泡与通气空泡的长度,定量地给出了弗洛德数对通气空泡长度的影响.当Fr=43.74时,重力场对通气空泡长度的影响几乎可以忽略.     

航行体锥段线型对自然空泡特性影响的数值模拟

针对多种不同锥段线型的航行体,对其自然空泡形态及减阻特性进行了数值模拟研究.得到了各条件下空泡形态随空化数的变化关系、拟合曲线,以及阻力系数随空泡长度的变化关系.通过对比分析,得出了航行体锥段线型对空泡形态及减阻特性的影响规律.结果表明,锥段线型对空泡形态影响不明显;当空泡闭合于航行体锥段时,锥段线型为圆弧的模型阻力系数较小;而当空泡闭合于航行体柱段或形成超空泡时,各模型阻力系数趋于一致,几乎不受锥段线型影响.     

非流线型水下航行体阻力测量试验中的几个问题

在高速水洞内,进行了某水下航行体模型自然状态和通气产生超空泡状态下的阻力试验,并针对实验中的尾撑影响、阻力成分和尺度效应问题,用数值模拟方法进行了分析.结果表明,自然状态下非流线型航行体的阻力比流线型的增加很多,压差阻力为主要成分;通气形成超空泡后可以大大降低航行体的阻力;尾撑使得阻力测量值偏大;自然状态下航行体原型比模型的阻力系数小,通气后二者基本相同.     

重力场中超空泡形态的数值仿真研究

根据Logvinovich独立膨胀原理,发展了一种用于计算在重力场中定常和非定常自然和通气超空泡形态的计算方法,运用该方法对重力场中超空泡形态进行数值仿真.结果表明,在重力作用下超空泡不再是对称的椭球体,自然超空泡和通气超空泡在非定常扰动下的形态特性和动力特性存在较大差异,当流场压力线性变化时,自然超空泡的空泡数呈线性变化,但长度呈非线性变化,而通气超空泡的空泡数和空泡长度都呈非线性变化.     

超空泡航行体运动过程尾部振荡流场试验研究

为了揭示超空泡航行体运动过程尾部振荡机理,文章采用试验的方法对超空泡航行体自由航行过程进行了研究。试验在水池中开展,采用高速摄影观察自由航行过程超空泡形态演化规律,采用压力传感器测量航行体表面压力,采用内测装置测量了航行体运动参数,获得了超空泡航行体运动过程空泡形态、压力和运动参数变化规律。试验结果表明,在航行体运动过程中,会出现尾部上下周期撞击空泡壁振荡现象,即为尾拍效应,表现为航行体撞击空泡壁瞬间,会形成非定常气液混合区域,相反侧则出现空泡透明区域。同时,稳定空泡内压力并非一定值,泡内压力和泡内空化数均在一定范围内波动,在尾部撞击空泡壁一侧,压力不断增大,出现压力高峰,相反侧则与稳定空泡内压力基本一致。     

超空泡回转体减阻特性研究

基于Fluent 6.0的气泡两相流模型对超空泡回转体的减阻特性进行了数值研究.内容包括:外形对阻力及超空泡形状的影响;超空泡控制;阻力系数随空泡数的变化规律;长细比对减阻率的影响.超空泡减阻机理的研究表明:超空泡不仅可以减小回转体的摩擦阻力,还可以减小回转体的压差阻力.在外形、长细比和空泡数以及工程可实现性等诸多因素中,存在着一个最佳组合,使减阻率最高.     

圆盘空化器超空泡流动数值模拟方法

为分析来流速度对圆盘空化器产生超空泡的形态,基于粘流理论和有限体积方法,对带有圆盘空化器超空泡航行体流场进行了数值模拟。得到了超空泡形态与航行体速度之间的关系。随着速度的增加,空泡长度逐渐增大。并进一步给出了流场的压力分布云图和速度矢量图。     

Wave impact underneath horizontal decks

The problem of water impact on a fixed horizontal platform deck from regular incident waves was studied. Two-dimensional potential flow was assumed, and the resulting boundary-value problem was solved by three alternative numerical methods, a method based on a generalization of the impact theory by Wagner, and two different nonlinear boundary-element methods. The Wagner-based method used a von Karman approach during the water exit phase, i.e., when the wetted surface decreases. Experiments of the impact on an idealized platform deck have been performed to validate the theory. Comparisons show that the Wagner-based method yields good results for the water entry phase, when the wetted deck area increases, but poor results when the wetted area diminishes. The boundary-element methods compare well with experiments for the entire impact process. A Kutta condition is necessary at the aft body–free surface intersection during water exit and when the flow separates from the aft edge. Gravity effects matter for the water exit phase.     

基于CFD仿真计算的襟翼舵水动力研究

襟翼舵作为一种可靠的、高升力的舵在最近几年内引起了广大设计工作者的重视影响,同时也有不少成熟的研究成果。对襟翼舵的研究主要集中在展弦比,主副舵面积比,转角比等方面,这些因素对襟翼舵的整体影响规律也已得到不少专家的解释。本文主要研究襟翼舵主副舵间间隙大小以及尺度效应对其水动力性能的影响,以普通NACA0020翼型为基本剖面建立不同间隙大小的襟翼舵模型,采用RANS方法计算得到了不同缝隙大小以及不同缩尺比下的襟翼舵升力阻力以及压力分布,并对周围涡结构以及流场进行分析,发现升力系数随着缝隙增大而减小,阻力系数先减小再增大的规律。同时随着襟翼舵尺度的增大,升力系数会随之增大,阻力系数会随之减小。文中以计算模型和实验数据进行对比,两者误差在5%以内,证明了计算结果的可靠性。     

内河航道局部缩窄段交通运行状态仿真分析

为分析内河航道局部缩窄段交通运行状态,根据航道单线交替通航特征设计仿真模型,分析不同条件下缩窄航段的交通运行状态及通过能力。仿真结果表明,船流量大小和方向分布影响缩窄航道的交通运行状态,2个方向船流量差异较大时船舶集中通行有助于提高通航效率,但会增加部分船舶的延误;缩窄航段的通过能力随缩窄段的长度增加而减小,但当缩窄段长度增加到一定值后,航段的通过能力接近某一极小值。实践中可根据航运需求,合理进行交通组织、安排航道整治方案。     

厚翼剖面的空泡特性研究

本文用奇点法解厚翼剖面局部空泡绕流问题。求解时精确考虑了空泡表面是一条流线的运动学边界条件,空泡表面压力为常数的动力学边界条件,以及水翼湿表面是一条流线的运动学边界条件,用迭代法求出了空泡表面的形状、压力分布等水动力特性,并与实验结果作了比较,得较好结果。     

The effects of free surface and end cell on flow around a finite circular cylinder with low aspect ratio

Vortex-induced motion is an oscillatory phenomenon which occurs to a floating body with low aspect ratio. The basic phenomenological study about the effects of free surface and end cell on flow around a finite fixed circular cylinder was investigated in this study using particle image velocimetry and hydrodynamic force measurement. It was found from the former experiment that the wake of the cylinder is influenced by the both end cell and free surface. Blowup and back flow are generated from the end cell, and their effects are suspended by free surface. The result of hydrodynamic force measurement showed the effect of Reynolds number, Froude number, and the aspect ratio of the floating body on the hydrodynamic force. Fluctuating components of hydrodynamic coefficients decrease for increasing Reynolds number, Froude number, and the aspect ratio. On the other hand, the mean drag coefficient increases as Froude number increases and decreases as the aspect ratio increases. The interpretation to these results was discussed in comparison with flow structures observed in the experiment. In addition, it was found that the effect of Reynolds number on the mean drag coefficient changes at different aspect ratios. A possible interpretation to this phenomenon was proposed.     

Influence of Ramjets’ water inflow on supercavity shape and cavitator drag characteristic

Water ramjets using outer water as an oxidizer have been demonstrated as a potential propulsion mode for underwater High Speed Supercavitating Vehicles (HSSVs) because of their higher energy density, power density, and specific impulse, but water flux changes the shapes of supercavity. To uncover the cavitator drag characteristics and the supercavity shape of HSSVs with water inflow for ramjets, supercavitation flows around a disk cavitator with inlet hole are studied using the homogenous model. By changing the water inflow in the range of 0–10 L/s through cavitators having different water inlet areas, a series of numerical simulations of supercavitation flows was performed. The water inflow flux of ramjets significantly influences the drag features of disk cavitators and the supercavity shape, but it has little influence on the slender ratio of supercavitaty. Furthermore, as the water inlet area increases, the drag coefficient of the cavitators’ front face decreases, but this increase does not influence the diameter of the supercavity’s maximum cross section and the drag coefficient of the entire cavitator significantly. In addition, with increasing water flux of the ramjet, both the drag coefficient of cavitators and the maximum diameter of supercavities decrease stably. This research will be helpful for layout optimization and supercavitaty scheme design of HSSVs with water inflow for ramjets.     

空化器几何参数对通气超空泡生成影响的实验研究

为了探索通气超空泡的生成机理和获取形态可控有效减阻的超空泡,文章利用中速可持续通气空泡水洞进行了空化器和通气联合生成超空泡的实验研究.详细分析了通气超空泡的生成和发展过程;给出了空化器直径、空化器线形对通气系数门限值和通气超空泡形态的影响.研究表明,在相同条件下,较大直径空化器模型形成通气超空泡需要的通气系数门限值较低,相应的超空泡尺寸也较大;平头倒角形和圆盘形空化器比圆锥形的形成通气超空泡需要的通气系数门限值低,相同条件下前者形成的超空泡尺寸也较后者大;对于圆锥形空化器,锥角较小的不易形成通气超空泡.文中实验研究结果为水下航行体的空化器合理设计提供了重要的参考依据.     

空泡闭合区压力特性试验研究(英文)

The most complicated component in cavitating flow and pressure distribution is the flow in the cavity closure line. The cavitating flow and pressure distribution provide critical aspects of flow field details in the region. The integral of pressure results of the hydrodynamic forces, indicate domination in the design of a supercavitating vehicle. An experiment was performed in a water tunnel to investigate the pressure characteristics of the cavity closure region. Ventilation methods were employed to generate artificial cavity, and the ventilation rate was adjusted accordingly to obtain the desired cavity length. An array of pressure transducers was laid down the cavity closure line to capture pressure distribution in this region. The experimental results show that there is a pressure peak in the cavity closure region, and the rise rate of pressure in space tends to be higher in the upwind side when the flow is non-axisymmetric. The transient pressure variations during the cavity formation procedure were also present. The method of measurement in this paper can be referenced by engineers. The result helps to study the flow pattern of cavity closure region, and it can also be used to analyze the formation of supercavitating vehicle hydrodynamics.