Effect of the Streamwise Component of the Vorticity Formed in a Turbulent Jet Source on the Acoustic Characteristics of the Jet

The results of an experimental study of the effects of different nozzle heads on turbulent jet noise are analyzed. A configuration of four cylindrical heads, tabbed heads, and chevron nozzles are considered and the decreases in the acoustic-mechanical efficiency of the jet (acoustic power reduction) for jets exposed to different modes of action are compared.It is shown that the effects of tabbed and cylindrical heads, as well as of chevrons, share a common property which is associated with the occurrence of vorticity in the jet source and can be described on the basis of a unified criterion characterizing the action on both the jet flow structure and the jet noise.     

Effect of Gas Non-Ideality on the Performance of Laval Nozzles with an Abrupt Constriction

The flows in Laval nozzles with a ero-length region of abrupt constriction and in nozzles with smooth entrance regions are studied on the basis of the Reynolds equations supplemented by a differential turbulence model. It is established that the viscosity effect does not lead to flow separation in the vicinity of the minimum section of optimal nozzles with an abrupt constriction. In all the examples calculated, the thrust of these nozzles is greater than that of nozzles with smooth a constriction and an optimally contoured supersonic part, the flow rate through the nozzle being larger when viscosity is taken into account than in the ideal (inviscid) case.     

Calculating the Thrust Characteristics of Nozzles from Their Outlet Cross-Section Parameters

Within the framework of boundary-layer theory, simple formulas are presented for finding the viscous loss from the gas parameters in the nozzle outlet cross-section. The analysis is performed for ordinary Laval nozzles and spike nozzles. It is found that for nozzles with large expansion ratios the viscous loss is almost independent of the outlet cross-section parameters and is determined only by the parameter values on the nozzle contour. The effect of the longitudinal nozzle curvature on this loss is investigated. It is shown that the viscous losses calculated from the nozzle outlet parameters and by integrating along the nozzle contour with account for the longitudinal curvature fully coincide.     

Effect of Sudden Expansion on Entrainment and Spreading Rates of a Jet Issuing from Asymmetric Nozzles

Turbulent free jets issuing from five different nozzle geometries; smooth pipe, contracted circular, rectangular, triangular, and square, are experimentally investigated by using TSI 2-D laser Doppler velocimetry (LDV) to assess the effect of nozzle geometry and quarl (i.e. a cylindrical sudden expansion) on jet entrainment and spreading. The centerline mean velocity decay and the jet half-velocity width, which are indicators of jet entrainment and spreading rates, are determined for each nozzle’s flow configuration, i.e. with and without sudden expansion. Furthermore, turbulence quantities, such as the flow mean velocities and their mean fluctuating components, as well as Reynolds shear stresses, are all measured along the centerline plane of the jet to facilitate understanding the extent of the effect of nozzle’s geometry (i.e. nozzle’s orifice shape and sudden expansion) on jet’s entrainment and spreading. The main results show that the jet flow with the presence of sudden expansion exhibits higher rates of entrainment and spreading than without. In addition, these results reveal that sudden expansion exercises a greater effect on the asymmetric jet characteristics, especially for the triangular and rectangular nozzles compared to their axisymmetric counterparts (i.e. circular contracted nozzle).     

平面叶栅跨音流场气动特性的数值研究

通过对模型方程的分析，给出了一种新的隐格式构造思想。将它运用到关通量分裂格式中，可得到无近似因子分解、无矩阵运算的高效二阶精度隐式矢通量分裂差分格式，并用来直接求解时间平均Ｎａｖｉｅｒ－Ｓｔｏｋｅｓ方程组。数值计算标明：该方法具有精度高、稳定性好、计算量少、收敛快等优点，在平面叶栅跨音流场的计算中，较好地捕获了激波，与实验比较，结果令人满意。     

Effect of Streamline Curvature on Intensity of Streamwise Vortices in the Mixing Layer of Supersonic Jets

The structure of supersonic nonisobaric jets with Mach numbers M_a = 1 and 2 is considered experimentally to find the effect of streamline curvature on the evolution of streamwise vortices in the mixing layer. The spatial development of steady streamwise vortices in the mixing layer of supersonic jets is considered. A method for generation of steady streamwise vortices by applying microroughness elements of controlled size onto the inner surface of the nozzle is developed. Radial profiles and azimuthal variations of total pressure are obtained; the mixinglayer thickness and the curvature of streamlines in supersonic jets are determined. A significant effect of microroughness elements of prescribed shape located on the nozzle surface on the behavior of total pressure in the mixing layer of supersonic jets, as compared to natural disturbances, is obtained.     

小口径轴对称收缩喷嘴射流冲击大平板噪声指向特性研究

实验研究了3毫米口径轴对称收缩喷嘴在各种压比下射流垂直冲击和倾斜冲击坚固大平板产生的噪声的指向特性。发现噪声在过平板法线和喷嘴轴线的平面内呈近似四瓣分布，当喷嘴与平板距离减小时，指向壁射流下游的瓣得到增强，反之，指向喷嘴上游的瓣得到增强。喷嘴压比增加时，指向壁射流下游的瓣得到增强，反之，指向喷嘴上游的瓣得到增强。根据自由射流噪声的基本指向特性、射流冲击噪声基本指向特性、声波在平板处发生镜面反射和声波能量叠加的设定，建立了一个冲击射流总体噪声指向特性的模型，成功解释了实验结果，并揭示了形成冲击射流总体噪声指向特性的内在机理。     

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.     

Numerical Study of the Effect of Periodic Velocity Excitation on Aerodynamic Characteristics of an Oscillating Circular Cylinder

A finite element method based on ALE formulation has been adopted in order to examine the effect of periodic velocity excitation on the aerodynamic characteristics of an oscillating circular cylinder. Periodic excitation, which was placed on the cylinder surface, stimulated the separated shear layers around the cylinder, and numerical results showed that some excitation can reduce negative damping, which is caused by unsteady lift force, and thereby stabilize the aerodynamics of the cylinder. Furthermore, the change of lift phase caused by periodic excitation seems to be important in stabilizing the aerodynamics of the cylinder. The simulation also confirmed that periodic excitation can suppress the vortex-induced vibration of the cylinder.     

An Experimental Study of the Near-Field Mixing Characteristics of a Swirling Jet

The present experimental investigation is devoted to the mixing characteristics of a passive scalar in the near-field region of a moderately swirling jet issuing from a fully developed axially rotating pipe flow. Instantaneous streamwise and azimuthal velocity components as well as the temperature were simultaneously accessed by means of a combined X-wire and cold-wire probe. The results indicate a modification of the turbulence structures to that effect that the swirling jet spreads, mixes and evolves faster compared to its non-swirling counterpart. The high correlation between streamwise velocity and temperature fluctuations as well as the streamwise passive scalar flux are even more enhanced due to the addition of swirl, which in turn shortens the distance and hence time needed to mix the jet with the ambient air.     

涡量修正方法在切向炉内流场数值模拟中的应用

涡量是流体运动的一个基本物理量，旋涡是流体运动中常见的一种基本形态，又是湍流的一种基本结构，它在理论上和工程实践中占有相当重要的位置。本文在吴镇远（Ｊ．Ｃ．Ｗｕ）方法的基础上，提出了一种新的数值计算方法——涡量修正方法。对炉内速度场及涡量场进行了计算，其速度场的计算结果与实验基本符合，在网格划分基本相同的条件下与ＳＩＭＰＬＥ算法所得结果相比，涡量修正算法更接近于实验结果，为流场的数值模拟提供了一条新的途径。     

陷落腔的流场数值计算研究

本文对有限分析解法的近似计算方法及其对计算精度的影响进行了数值计算和分析讨论；然后采用有限分析解法，对前、后壁壁缘高度不同的三种腔内流场运动发展过程及腔口剪切层运动情况作了数值计算，得到的腔口剪切层上腔口随边相互作用情况与对应腔的流场显示实验结果进行了比较，两者一致，计算结果表明，采用本文发展的近似方法计算可靠，可以较大地提高计算效率。     

Comparing the Evolution Characteristics of Waves in Nonlinearly Elastic Micro- and Nanocomposites with Carbon Fillers

A method is proposed for studying the evolution of plane waves in micro- and nanocomposite materials. This method permits comparing the evolutions of harmonic waves and produces results that are in agreement with data obtained earlier and with the metaphysical reasoning on the nanomechanics of composite materials     

叶轮机中振动叶片非定常气动力的研究

采用“单一叶片振动方法”代替传统的“全部叶片振动方法”，用线性化的方法推导出计算振动叶片非定常气动力（引起叶片弯曲振动）及力矩（引起叶片扭转振动）方程。通过输入叶型及气流参数，它可以方便有效地估计出作用在振动叶片上的非定常气动力和力矩，以及振动叶片不稳定工况发生的条件和范围。并在氟里昂超音速风洞上进行了实验测量，结果表明，理论计算结果与实验测试结果符合较好。     

Effect of the Turbulent Energy Gradient and the Presence of a Wall on the Turbulent Process of Momentum Transport

A mathematical model of turbulent transport processes is modified to make allowance for the turbulent energy gradient and the presence of walls. The modification consists in making the variance tensor in the Gaussian probability density distribution for the initial mole velocities anisotropic for nonzero turbulent energy gradient and a ratio of the turbulence scale to the distance from the wall of the order of unity. Formulas for the variance tensor components are derived and the empirical coefficients of these formulas are determined. The expression for the dimensionless turbulent friction stress is compared with experimental data for three boundary-layer-type flows, namely, in the wake of a cylinder, in the boundary layer on a flat plate, and in a channel with parallel walls.     

Study on the dynamical characteristics of a supersonic high pressure ratio underexpanded impinging ideal gas jet through numerical simulations

The impingement of an axisymmetric underexpanded ideal gas jet on a flat surface is investigated through numerical simulations. Different injection conditions, characterized by the nozzle pressure ratio (NPR), have been considered and for each, several standoff distances were studied. The study was conducted using the commercial finite volume general purpose code Fluent^®. The numerical results are presented in terms of Mach number and static pressure to characterize the structure of the flow. Furthermore, the influence of the standoff distance upon the position and diameter of Mach disk is analysed. Some results are compared with literature data and good agreement is obtained.     

剪切弯曲下短深梁位移数值计算精度的研究

分析了短深梁位移的基本解，评述了有限元解法中关于高次分布力简化为节点力的问题。使用虚功原理和位移线性插值推导了满足二次分布力作用的精确节点力分配公式。通过矩形截面悬臂梁自由终端受集中载荷的算例，阐明了提高短深梁位移计算精度的途径。     

Study of the Effect of the Depth of the Cavity of a Braking Device on the Aerodynamic Drag of a Model in Transonic and Supersonic Flow

The flowfield and the aerodynamic drag of a model consisting of a pair of bodies (leading body a cylinder and trailing body a hollow cylinder) connected by a cylindrical bar along the axis of symmetry is experimentally investigated at Mach numbers ranging from 0.6 to 1.7. In the course of the experiments, the trailing body cavity depth and the connecting bar length were varied.__________Translated from Izvestiya Rossiiskoi Academii Nauk, Mekhanika Zhidkosti i Gaza, No. 2, 2005, pp. 186–192.Original Russian Text Copyright © 2005 by Pilyugin and Khlebnikov.