结构陶瓷材料断裂强度统计预测模型

根据最弱环理论,应用Weibull和Batdorf两种断裂强度统计预测模型,对结构陶瓷含体内裂纹情况下的断裂强度进行了统计分析和预测。通过应用三点弯曲试验得到的模型参数,计算了高速旋转下圆盘断裂强度的分布概率,并对两种预测模型的预测结果与试验结果进行了分析比较。     

带冠空心冷却叶片的三维应力分析

 带冠的高温空心冷却叶片,由于它的形状复杂,工作时所承受的离心力大,温度高,气动力分布极不均匀,因此到目前为止,尚未见有准确可靠的计算方法,一般只能靠实验或统计的方法来对付生产使用中出现的问题。 为试图解决此一问题,我们采用高阶的三维等参元素来离散复杂的叶片形状。用节省内存空间而精度又高的波前法来求解此特大型方程组。用高阶双三次Coons样条插值函数来拟合叶型的空间曲面。为验证本方法和程序的可靠性,计算了各种例题,做了真实叶片的高速旋转实验,它们都证明了本方法的可靠性和计算精度是满意的。 本方法的适应性也较强,用它可以计算实心和空心的、带冠和不带冠的、伸根和非伸根的、高温和常温的各种类型叶片。     

MHD Flow Control of Oblique Shock Waves Around Ramps in Low-temperature Supersonic Flows

This article is devoted to experimental study on the control of the oblique shock wave around the ramp in a low-temperature supersonic flow by means of the magnetohydrodynamic(MHD) flow control technique. The purpose of the experiments is to take advantage of MHD interaction to weaken the oblique shock wave strength by changing the boundary flow characteristics around the ramp. Plasma columns are generated by pulsed direct current(DC) discharge, the magnetic fields are generated by Nd-Fe-B rare-earth permanent magnets and the oblique shock waves in supersonic flow are generated by the ramp. The Lorentz body force effect of MHD interaction on the plasma-induced airflow velocity is verified through particle image velocimetry(PIV) measurements. The experimental results from the supersonic wind tunnel indicate that the MHD flow control can drastically change the flow characteristics of the airflow around the ramp and decrease the ratio of the Pitot pressure after shock wave to that before it by up to 19. 66%, which leads to the decline in oblique shock wave strength. The oblique shock waves in front of the ramp move upstream by the action of the Lorentz body force. The discharge characteristics are analyzed and the MHD interaction time and consumed energy are determined with the help of the pulsed DC discharge images. The interaction parameter corresponding to the boundary layer velocity can reach 1. 3 from the momentum conservation equation. The velocity of the plasma column in the magnetic field is much faster than that in the absence of magnetic field force. The plasma can strike the neutral gas molecules to transfer momentum and accelerate the flow around the ramp.     

桨毂三维有限元应力分析

某型螺旋桨毂坐标系的确定,此桨毂为整体形结构,沿径向均匀装置四个桨叶,如图1所示,以飞机飞行方向定位,桨毂旋转平面定为XOY平面,沿桨叶轴线方向为X轴坐标,在旋转平面内与X轴垂直方向为Y坐标,Z轴坐标则为通过旋转轴心而与飞行方向相反的轴线。在旋转平面的后端面,用端齿与发动机主轴连接,以传递扭矩及轴向位伸;其前端面安装螺旋桨整流罩,罩内装置液压调节活塞,整体结构内为空心,桨叶变距机构由此空间操纵四个桨叶。桨叶的离心力和气动力通过桨轴传递至桨毂。      

Experimental Investigation into Characteristics of Plasma Aerodynamic Actuation Generated by Dielectric Barrier Discharge

This article carries out synthetic measurements and analysis of the characteristics of the asymmetric surface dielectric barrier discharge plasma aerodynamic actuation.The rotational and vibrational temperatures of an N2 (C3Пu) molecule are measured in terms of the optical emission spectra from the N2 second positive system.A simplified collision-radiation model for N2(C) and N2+(B) is established on the basis of the ratio of emission intensity at 391.4 nm to that at 380.5 nm and the ratio of emission intensity at 371.1 nm to that at 380.5 nm for calculating temporal and spatial averaged electron temperatures and densities.Under one atmosphere pressure,the electron temperature and density are on the order of 1.6 eV and 1011cm-3 respectively.The body force induced by the plasma aerodynamic actuation is on the order of tens of mN while the induced flow velocity is around 1.3m/s.Starting vortex is firstly induced by the actuation;then it develops into a near-wall jet,about 70 mm downstream of the actuator.Unsteady plasma aerodynamic actuation might stimulate more vortexes in the flow field.The induced flow direction by nanosecond discharge plasma aerodynamic actuation is not parallel,but vertical to the dielectric layer surface.