滑翔增程弹的气动特性仿真研究

研究了滑翔增程弹气动布局对弹道增程效果的影响,建立了不同气动布局下的弹体模型,并对其进行气动仿真,得出了不同空气动力数据.通过建立适合增程弹的弹体模型,得到了舵片在不同布局时的增程能力数据.仿真结果表明,舵片位置越远离弹体头部,相应增大舵偏角,增程能力将会增强,因此,在满足全弹气动布局、飞行稳定的基础上,尽量使舵片远离弹体头部,并相应增大舵偏角,可提高増程的能力.     

尾翼式弹道修正弹Hopf分岔特性分析

为分析尾翼式二维弹道修正弹锥形运动失稳原因,提高其修正精度,建立了该弹丸有控飞行阶段四维非线性角运动方程。利用Matcont软件确定系统分岔点后,运用中心流形定理对系统进行降维,并对降维后系统的Hopf分岔点类型进行判别,最后数值仿真验证了理论分析方法的正确性。在此分析方法基础上针对修正机构参数对角运动稳定性影响进行分析。结果表明,为保证弹箭飞行稳定性并使其具有良好气动布局,应将修正机构靠近质心位置安装。     

基于最小值原理的一维修正弹弹道优化

在研究弹道优化的过程中,采用Pontryagin最小值原理与一维修正弹数学模型相结合的方法,对一维修正弹进行弹道优化.在标准气象条件下,弹丸所受切向过载的大小直接决定着弹丸速度的变化,继而影响着弹丸的修正能力,故选取合适的切向过载可以有力打击目标.通过Matlab仿真软件,得到了弹丸切向过载、射程、射高、飞行速度以及弹道倾角的变化规律,同时验证了弹丸的修正效果.仿真结果表明,最小值原理与一维修正弹数学模型相结合的方法是解决弹道优化的一种有效途径.     

弹道修正机构永磁电机的仿真设计及应用测试

依据弹道修正基本原理,对弹道修正装置的气动布局进行分析.完成了弹道修正机构中永磁电机的设计,并对永磁电机齿槽力矩的影响因素进行分析.通过仿真,减小硅钢片槽口宽度可以减小永磁电机的齿槽力矩.利用应变式测力装置,对永磁电机的力矩实际测量可知,修正弹飞行在可修段时永磁电机的力矩大于风阻力矩的20%.结果表明,设计的永磁电机能够满足对舵机的精确控制要求.     

舵轴位置对全动舵面气动弹性稳定性的影响

研究舵轴位置对全动舵面气动弹性特性的影响,用有限元方法分析舵面模态,当地流活塞理论计算非定常气动力,应用Lagrange方程,建立基于模态坐标运动方程。结果表明：当舵轴在根弦相对位置从前向后移动过程中,失稳形态由颤振转变为发散,并引起临界动压突变现象。失稳形态转变位置会随着攻角增大而逐渐后移。在转变位置之前,颤振临界动压随着舵轴后移,呈现先减小后小幅度增大趋势;在转变位置之后,发散临界动压随着舵轴后移单调减小。     

超空泡射弹并联入水多相流场与弹道特性研究

弹丸并联入水工况在实际作战环境中时有发生,然而针对超空泡射弹并联入水的研究较少。基于重叠网格技术,采用RANS方程、Schnerr-Sauer空化模型、Realizable k-ε湍流模型对超空泡射弹入水过程进行数值模拟,计算值与试验数据吻合情况良好,验证了数值方法的有效性。对不同弹丸间距及不同初速下的超空泡射弹开展多工况数值模拟,详细分析并联超空泡射弹的入水流场特性及弹道特性。研究结果表明：弹丸间距过小将对弹道稳定性产生不利影响;初速一定时,弹丸间距越小,弹丸产生的空泡对称性越差,弹丸所受横向力越大,弹道稳定性越差;弹丸间距越小,弹丸内侧沾湿现象越明显,速度衰减越快;随着弹丸间距的增大,弹丸之间的干扰将逐渐减弱,当弹丸间距增加到3D时,两弹丸之间几乎无干扰。     

滚珠丝杠式燃气舵结构仿真与运动控制EI北大核心CSCD

针对燃气舵在启动瞬间会产生很大的冲击力,采用ADAMS和ANSYS软件对传动机构进行了动力学分析和有限元分析的联合仿真,得到了变负载下相邻零件的冲击力,并分析了危险零件的瞬态动力响应。分析结果表明,在一定范围内,冲击力随响应时间的增加响应速度变慢,最大值和最小值分别基本保持一致。建立了燃气舵系统的数学模型,在MATLAB Simulink软件中进行了系统的比例-积分-微分(proportional-integral-derivative, PID)控制仿真分析,并基于仿真结果进行了单片舵系统的运动控制试验。试验结果表明,该控制平台能达到良好的控制效果。     

弹道逼近及其在炮兵校射系统中的应用

弹道逼近利用非标准条件下弹道微分方程组解箅各时间点弹丸的空间位置,与雷达所测量的弹道高相比较,求取最大的弹道高偏差量,并根据最大的弹道高偏差量修正射角.应用弹道逼近算法的炮兵校射系统,满足对目标试射时的精度指标要求,其试射成果可用于同炮种和不同炮种.所确定的效力射开始诸元,完全满足精测精修以及效力射诸元精度要求,可明显提高炮兵射击精度,提高火力打击效果;应用弹道逼近算法的炮兵校射系统,生存能力强,且不需精确气象保障,可缩短射击指挥周期,提高火力反应速度.     

基于MEMS IMU的舵面运动测量仪

针对飞行器升降舵、副翼角运动的测试需求,提出了单轴捷联姿态系统的原理及算法,介绍了基于MEMS陀螺仪和加速度计的舵面运动测量仪的构成,并对测量仪的工作过程进行了仿真.仿真表明,测量仪的性能满足舵面运动测量的需要.     

基于气泡型非光滑表面的弹丸减阻性能研究

为了研究非光滑表面弹丸减阻的效果,利用Pro/Engineer建立几何模型,导入Gambit划分网格,基于Fluent软件,并采用S-A单方程湍流模型对弹丸飞行的气动特性进行三维数值模拟.分别对不同马赫数和攻角下非光滑表面的弹丸气动特性进行数值模拟,分析了微气泡数量和大小对非光滑表面弹体的升力、阻力影响,获得了不同工况下阻力系数和升力系数的变化规律.结果表明,气泡型非光滑表面弹丸可以在一定程度上减小飞行阻力.     

水线-雷诺数效应-斜拉索振动关系的试验研究

通过对不同位置粘贴有水线的斜拉索模型进行测力和测振风洞试验,分析了不同雷诺数下的阻力系数、升力系数和振幅等参数,研究了水线影响雷诺数效应及通过影响雷诺数效应导致振动的机理,研究结果表明:水线能影响力系数随雷诺数的变化规律,力系数的大小和变化规律与振动有着十分密切的关系;在较低的水线位置,随着雷诺数的上升,伴随着阻力系数的减小,升力系数大幅增大,发生类似临界雷诺数的效应,力系数随水线位置的变化规律导致驰振系数为负,在这种情况下发生大幅振动,用临界雷诺数效应和驰振均可解释;在较高的雷诺数下,伴随着阻力系数的减小,升力系数大幅变化,每个水线位置都发生了不同程度的振动,该振动的机理可能与临界雷诺数效应导致的振动机理类似。     

Numerical Simulation of Particle Saltation Process

A numerical model for simulation of particle single-step saltation was developed. The model includes drag force, shear lift force, rotational lift force, buoyancy force, added mass force, and torque. The governing equations were solved using the fourth-order Runge-Kutta scheme. The model was calibrated and verified using the experimental data. The computational results include particle trajectory, longitudinal velocity of particle and flow, relative velocity of particle and flow, dimensionless drag, and lift forces along the trajectory. Sensivity analysis was performed to determine the influence of various parameters. Saltation characteristics were also calculated for various Reynolds numbers in the range of 2.5 to 7.7. It was found that very close to the bed, drag force decreases as Reynolds number increases. An increase of about three times the Reynolds number has a decreasing effect of three times and two times on the drag and lift force, respectively. The influence of Reynolds number increase on the falling phase was less than that on the rising phase.     

轴对称航行体通气超空泡的特性实验研究

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(V=7m/s～15m/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,给出了不同空泡长度下的模型阻力系数。研究结果表明,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;重力场造成了空泡形态的严重不对称,通过比较模型上下表面的空泡长度,定量的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。     

平流层飞艇气动阻力的参数分析

为了研究环境参数及外形布局对平流层飞艇气动阻力的影响,在验证CFD数值模拟方法的基础上,从气动阻力包括压差阻力与摩擦阻力的角度探讨了风速、动力粘度系数、空气密度、Re数、长细比及尾翼对飞艇气动阻力的影响规律及机理。结果表明:气动阻力系数随风速与空气密度的增加而减小,随动力粘度系数的增加而增加;气动阻力系数随Re数减小的趋势,取决于摩擦阻力系数随Re数的减小趋势;随长细比的增加,摩擦阻力系数呈现增加趋势,但气动阻力系数呈现先减小后增加的趋势;尾翼对气动阻力系数的影响主要体现在压差阻力系数的改变。     

Effect of the blockage ratio on the flow in a channel with a built-in square cylinder

The structures wakes behind a square cylinder in a laminar channel flow is conducted numerically. The Strouhal number, drag and lift coefficients were studied in a periodic flow for different blockage ratios =1/4, 1/6 and 1/8 at Reynolds number ranging from 62 to 300. The governing equations are solved by using control volume finite element method (CVFEM) adapted to the staggered grid. The SIMPLER algorithm is used for the velocity-pressure coupling. The critical Reynolds numbers corresponding to the onset of vortex shedding and its change from simple periodic to complex periodic motion are established. A discussion about the effect of the blockage ratio on the Strouhal number, the time-averaged drag coefficient and the amplitude of the lift coefficient is also presented.     

Experimental investigation of lift and drag on a ball rotated by an inclined water jet

Abstract

The lift and drag of rotating balls with Reynolds numbers from 4500 to 6500 were obtained using a ping‐pong ball impinged by a water jet with inclination angles ranging from θ = 3.43° to 11.3°. Results show that water strikes the ball surface and leaves from the wake region behind the ball, which spins more slowly when a large amount of water stays on the ball surface, causing low lift and low drag forces to be exerted on the ball. In contrast, the ball spins quickly when a small amount of water stays on the ball surface. This causes high lift force to be exerted on the ball, which verifies the Magnus effect of a rotating ball. The drag force increases nonlinearly with the angular speed of the ball because there is a branch flow out from the stretched wake behind the ball. Results also indicate that the lift force of the ball increases with jet exit speed, but the drag force does not change significantly with the jet exit speed. This reveals that the momentum change in the direction parallel to gravity is more significant than that in the direction normal to gravity.     

Drag coefficients for a sphere rolling down an inclined channel

Abstract

Forces acting on a sphere rolling down an inclined smooth or rough channel include submerged weight of the sphere, fluid drag, fluid lift, and rolling resistance from the channel bed. When the acting forces are in equilibrium, the sphere rolls down the inclined channel with a terminal velocity. The steady movements of such a sphere rolling down smooth and rough channel beds with the terminal velocity are studied through laboratory experiments and a simplified theoretical analysis. A method is proposed to evaluate the rolling resistance that consists of collision and friction parts of resistance. The coefficients of rolling resistance and the drag coefficients are determined by regression analysis with experimental data. The relationships of the drag coefficients and the Reynolds numbers for a sphere rolling over smooth and rough channel beds are also obtained. It is found that at the same Reynolds number, the drag coefficient for a sphere rolling down a rough bed is larger than that for a sphere down a smooth one, and that both are much larger than that of a sphere in the free fall.     

后置分流平板对并列双圆柱流场特性的影响

数值模拟了Re=200情况下分流板对并列双圆柱流场的影响,并列双圆柱的间距比为1.5 D(D为圆柱的直径),分流板放置在并列双圆柱下游中心线G/D=0.5～1.5的位置;采用有限元法进行数值求解.计算表明,在合适的位置分流板可以抑制并列圆柱后的偏流,减小升阻力.分流板并不能很好地控制旋涡脱落但有一定的削弱作用.     

上游小圆柱对并列双圆柱尾流的影响

采用有限元方法数值模拟了控制小圆柱对并列双圆柱偏流的控制作用.计算区域为60 D×20 D,并列双圆柱距上游10 D,下游50 D,控制小圆柱的大小d/D=0.15和0.25,分别放置于并列双圆柱上游中心线上L/D=2.0,2.5,3.0,3.5的位置处.数值模拟着重研究了流场形态、升阻力系数变化曲线及升力系数频谱图.结果发现,控制小圆柱不能完全抑制并列双圆柱后宽的和窄的尾流,但对并列双圆柱旋涡脱落有一定的削弱作用.