一种制作超高频全息光栅的新方法

为了满足测量的高分辨率和灵敏度，基于光栅为关键元件的光学测量方法要求光栅有很高的频率。在已有的高折射率介质制栅方法的基础上提出了一种新的制作超高频全息光栅的方法，该方法制栅准确、简单、方便，其特点是所制光栅的频率与激光波长及介质的折射率无直接关系，而是等于制栅光路所得频率与两倍母栅频率之和。实验表明，利用该方法制得１００００线／ｍｍ的光栅是完全可能的     

Extension of the Coherent Gradient Sensor (CGS) to the Combined Measurement of In-Plane and Out-of-Plane Displacement Field Gradients

The Coherent Gradient Sensor (CGS) is extended to the optical differentiation of specular, diffracted wave fronts leading to the combined measurement of in- and out-of-plane displacement field gradients. A derivation of the underlying optical interference principles is presented along with an analysis of the effective instrument sensitivity. In order to demonstrate the capabilities of the technique, experimental measurements of crack-tip deformation fields were conducted under various loading conditions corresponding to mode-I, mode-II, and mixed mode near-tip crack fields. The experimental procedures and results of these tests are presented as validation of the technique.     

超声速燃烧火焰稳定凹腔质量交换特性的数值研究

对超声速冷流条件下用于超燃冲压发动机的凹腔火焰稳定器的质量交换特性进行研 究. 采用混合RANS/LES方法对非定常流场进行数值模拟，考虑了凹腔的长深比和后缘角度两 个关键参数. 计算得到了凹腔剪切层拟序结构的演化过程. 对凹腔压力振荡历程进行幅频分 析，所得到的频率和理论分析结果及一些计算结果十分吻合. 结果表明，凹腔的长深比和后 缘倾角对凹腔质量交换过程都有较大的影响. 凹腔驻留时间随着长深比的增加而增加. 随着 后缘倾角减小，长深比较小的凹腔的驻留时间增加，长深比较大的凹腔则完全相反. 该计算 结果为凹腔设计提供了新认识.     

Shocks in local supersonic zones

The results of numerical integration of the Euler equations governing two-dimensional and axisymmetric flows of an ideal (inviscid and non-heat-conducting) gas with local supersonic zones are presented. The subject of the study is the formation of shocks closing local supersonic zones. The flow in the vicinity of the initial point of the closing shock is calculated on embedded, successively refined grids with an accuracy much greater than that previously achieved. The calculations performed, together with the analysis of certain controversial issues, leave no doubt that it is the intersection of C ^?-characteristics proceeding from the sonic line inside the supersonic zone that is responsible for the closing shock formation.     

Experimental study of the reverse flow in the forward separation region in a pulsating flow around a spiked body

The flow with a free-stream Mach number M _∞ = 6 around a cylindrical body with a sharp spike is studied. The existence of a supersonic reverse flow for one of the phases of the pulsating flow regime is experimentally validated. A range of spike lengths is determined, which ensures a region of a supersonic reverse flow near the side surface of the spike. The time of existence of the supersonic reverse flow region is shown to be 0.15 of the period of pulsations if the spike length equals the model diameter. __________ Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 48, No. 4, pp. 30–39, July–August, 2007.     

Large-Scale Streamwise Vortices in the Supersonic Part of a Permeable Nozzle

Large-scale streamwise vortices in the vicinity of a perforated wall in the supersonic part of the nozzle are studied. The governing effect of gas inflow through a perforated wall on origination and parameters of streamwise vortices is experimentally established.__________Translated from Prikladnaya Mekhanika i Tekhnicheskaya Fizika, Vol. 46, No. 5, pp. 68–75, September–October, 2005.     

云纹干涉制栅新技术

本文介绍了两种新的光栅复制技术,它们具有快速、高质量、低成本、操作简单、使用方便、不需特殊仪器等特点.该技术从我国一般力学实验室条件出发,解决了试件栅制作困难,其中漆栅方法可极大地缩短云纹干涉方法的实验周期,该技术也为光栅测试技术的广泛应用提供了方便.     

球面波照明下利用阿贝滤波制作全息光栅

在阿贝成像理论基础上,提出了一种球面波照明方式下的阿贝滤波制作全息光栅方法。该方法所用光学元件较少,光路简单易排,很容易制作出需要的低频光栅。     

Propagation characteristics of annular laser beams passing through the reflection Bragg grating with deformation

When high-power annular laser beams produced by the unstable resonator pass through the volume Bragg grating (VBG), absorption of light in the VBG will induce a temperature increment, resulting in changes in surface distortion. Considering that the surface distortion of the grating induces index and period differences, the scalar wave equations for the annular laser beams propagating in the VBG have been solved numerically and iteratively using finite-difference and sparse matrix methods. The variation in intensity distributions, the total power reflection coefficient, and the power in the bucket (PIB) for the annular laser beams passing through the reflection VBG with deformation have been analyzed quantitatively. It can be shown that the surface distortion of the VBG and the beam orders of the annular beams affect evidently the intensity distributions, the power reflection coefficient, and the PIB of the output beam. The peak intensity decreases as the deformation of the VBG increases. The total power reflection efficiency decreases significantly with the increase in deformations of the VBG. The PIB of the output beam decreases as the obscuration ratio β and the deformation of the VBG increase. For the given obscuration ratio β, the influence of deformation of reflection VBG on the PIB of the annular beams is more sensitive with increase in distortion of the VBG and decrease in beam order.