弹丸阻力曲线随高度变化的计算研究

当弹丸的飞行高度在0-3000米之间变化时,弹丸的阻力曲线不再仅仅只依赖于弹形参数和马赫数,而应当随高度变化而有所变化.本文研究了雷诺数随高度的变化,计算了阻力曲线随高度的变化,并编制了相应的计算程序.     

Transonic flow past thin wings

This paper is devoted to a discussion of steady inviscid transonic flow past thin wings, with subsonic free-stream Mach number M_∞ < 1, by the integral equation method. The integral equation formulation is developed for a thin unsymmetric wing at small incidence. A simple approximate analytical solution is presented for shock-free supercritical flow past a thin symmetric wing at zero incidence. The direct iteration scheme of Niyogi and Chakraborty is then extended to the three-dimensional zero incidence case, which may be used to obtain more accurate solutions for shockfree flows as well as for flows with shocks. The question of the existence and the uniqueness of a solution has been studied by means of the Banach contraction mapping principle in the spaceL ₂ (E₃), which establishes the condition of convergence of the direct iteration scheme. Simultaneously it provides us with an error estimate for the solution.     

Low‐frequency dynamics of a floating wind turbine in wave tank–scaled experiments with SiL hybrid method

The design of floating wind turbines needs the validation of numerical models against measurements obtained from experiments that accurately represent the system dynamics. This requires solving the conflict in the scaling of the hydrodynamic and aerodynamic forces that arises in tests with wind and waves. To sort out this conflict, we propose a hybrid testing method that uses a ducted fan to replace the rotor and introduce a force representing the aerodynamic thrust. The force is obtained from a simulation of the rotor coupled in real time with the measured platform displacements at the basin. This method is applied on a test campaign of a semisubmersible wind turbine with a scale factor of 1/45. The experimental data are compared with numerical computations using linear and non‐linear hydrodynamic models. Pitch decays in constant wind show a good agreement with computations, demonstrating that the hybrid testing method correctly introduces the aerodynamic damping. Test cases with constant wind and irregular waves show better agreement with the simulations in the power spectral density's (PSD's) low‐frequency region when non‐linear hydrodynamics are computed. In cases with turbulent wind at rated wind speed, the low‐frequency platform motions are dominated by the wind, hiding the differences from hydrodynamic non‐linearities. In these conditions, the agreement between experiments using the proposed hybrid method and computations is good in all the frequency range both for the linear and the non‐linear hydrodynamic models. Conversely, for turbulent winds producing lower rotor thrust, non‐linear hydrodynamics are relevant for the simulation of the low‐frequency system dynamics.     

竞技运动服功能性研究进展

随着竞技体育的竞争日益激烈,运动服已成为影响竞技成绩的重要因素.本文从克服运动阻力、提高运动员表现水平、避免运动损伤、改善运动技术这4个方面对竞技体育运动服的研究进展进行综述.     

Molecular dynamics-based unstructured grid generation method for aerodynamic applications

A new approach to triangular mesh generation based on the molecular dynamics method is proposed. Mesh nodes are considered as interacting particles. After the node placement by molecular dynamics simulation, well-shaped triangles or tetrahedra can be created after connecting the nodes by Delaunay triangulation or tetrahedrization. Some examples are considered in order to illustrate the method’s ability to generate a mesh for an aircraft with a complicated boundary. Mesh adaptation technology for molecular dynamics simulation is presented.     

高速列车车内低频气动噪声预测

为研究气动载荷下高速列车的车内低频噪声,建立高速列车空气动力学模型,采用大涡模拟(Large Eddy Simulation,LES)法计算中间车的表面脉动压力.将脉动压力加载到高速列车的有限元模型上,通过瞬态分析得到车体的振动位移响应;将位移响应作为边界条件,采用边界元法(Boundary Element Method,BEM)分析车内噪声.结果表明：车窗振动位移最大,车顶和车底次之;中间车车厢的两端声压比中部大;在低频范围内,车厢内声压呈强弱交替分布,声场强弱界限较明显,且随着频率的增大,沿车体纵向和横向干涉条纹增多;车内低频气动噪声随速度二次方的增大而增加.     

带有气动参数不确定性的导弹自动驾驶仪设计

针对一类不确定导弹系统,考虑系统中存在气动参数不确定性,研究其自动驾驶仪的设计问题;由导弹俯仰面的力学模型及气动参数的多项式模型,考虑舵偏角为控制输入建立二阶导弹系统模型,基于自适应控制得到导弹自动驾驶仪的设计方法,使得闭环系统稳定且攻角快速跟踪指令信号;文章充分考虑系统模型攻角通道中存在舵偏项的影响且不需假设导弹攻角为小量,使得系统模型更具有一般性;仿真中马赫数分别取为2.5、1.8、3.0并考虑50%的参数摄动,结果表明文章设计的自动驾驶仪指令跟踪精度高,鲁棒性强。     

微型扑翼飞行器诱导角与几何攻角的研究

基于准稳态模型和动量理论,探讨了微型扑翼飞行器诱导角和最佳几何攻角的计算问题.针对高斯-牛顿法求解诱导角方程时存在的不收敛问题,使用能保证计算过程收敛的列文伯格-马夸尔特算法求解,得到实验样机的诱导角为15°.实验样机的实际升力为40 g,忽略诱导角后准稳态模型理论升力为46 g,而考虑诱导角的理论升力为37 g,验证了计算诱导角可以提高准稳态模型预测升力的准确性.基于实验样机翅膀被动扭转的实际,采用最小二乘法计算出实际最佳几何攻角为55°,能有效指导微型飞行器翅膀的设计,从而提高飞行器最大升力和飞行效率.     

轿车并列行驶湍流特性的数值模拟

为了研究复数车辆并列行驶的湍流特性对交通安全的影响,采用移动地面模拟轿车相对地面的运动和旋转壁面模拟车轮转动的方法,进行了两辆轿车并列行驶外部流场湍流特性的数值模拟研究。以单倍车宽侧向间距的两辆轿车为典型算例,给出了汽车车身表面的速度和压力分布,并讨论了右侧轿车尾部流场3个典型截面的速度分布和尾部流线分布情况。重点对比了0.1、0.3、0.5、1、2倍车宽间距的两车流场的流线分布情况。右侧轿车侧向力系数的对比分析说明:随着两车侧向间距的减小,迅速增大的侧向力将两车压向彼此。为保证行驶安全性和操纵稳定性,两车并列行驶的安全距离应该在单倍车宽与0.5倍车宽之间。     

新型有害气体净化器动力学性能的研究

对新型有害气体净化器气道内的气体流动规律进行了分析 ,并建立了数学模型 ,对气道内流速及滤速进行了计算机模拟 ,为设计净化器提供了理论依据 .