LIF喷流混合流浓度场定量测量

本文介绍激光诱导荧光(LIF)的瞬时浓度场定量测量技术,采用了CCD图象采集处理系统和低浓度简化校正技术等,讨论了喷流混合流浓度场测量的初步结果。     

热毛细对流速度场测试研究

为了探索微重力状态下表面张力驱动流速度场的测试技术，本文在地面进行了模拟实验，对位于热壁下流体中气泡周围的表面张力驱动流进行了研究，并用ＰＩＶ技术测量了流场的速度分布．     

用数字圆栅技术研究橡胶类材料I型断裂问题

采用数字云纹技术对橡胶类材料的大变形断裂力学问题进行了实验分析。提出了数字圆环栅和射线栅技术，给出了该技术的测量原理和方法。应用此技术对橡胶薄板材料的I型断裂的裂尖变形场进行了测量，给出了极坐标系下的实验径向位移场ur，和环向位移场uθ。的分布图，对实验结果进行了详细的分析，并结合大变形断裂的分区理论模型进行了比较与讨论。     

分子标记示踪用于氧气／空气流场速度测量

利用受激喇曼激发加激光诱导电子荧光法（ＲＥＬＩＥＦ）实现对氧气和空气中氧分子的标记示踪,用于氧气和空气流场的速度的测量． 实验装置测量氧气喷流的瞬时速度为４５±５ｍ ／ｓ,改进后精度可以优于１％ ,并适合几个马赫的高速流场测量．     

气固射流加砂方式中颗粒速度场及浓度场的实验研究

将激光数字式粒子成像测速技术(DPIV)方法应用于砂尘环境实验中颗粒速度场及浓度场的实验研究,成功地对环境风洞中颗粒速度场及浓度分布进行了无干扰瞬态测量,实验结果较真实地反映了气固射流加砂方式中粒子速度场及浓度场的分布规律。文中所获得的规律性认识为我国自行研制大型砂尘实验设备,确定加砂/尘方法及实验段参数等提供了依据。     

双反射技术对自由射流三维速度场的测量及显示

应用摄影测量和图像处理技术对自由射流的三维速度场进行了ＰＩＶ测量。构造了一种全新的双反射测量技术，使得二维测量中的多点同步和空间定位得到解决和提高。在精确计算了水与空气的折射关系之后，两幅像片间的同名点寻找更加可靠。重建和再现了ＰＩＶ中射流的连续三维瞬态粒子分布场和速度矢量场。     

基于Haar小波变换的位移场测量方法

本文提出了一种应用小波变换对固体表面位移场进行测量的新方法，在图像分析时，用各点属于不同尺度的小波变换系数来表征该点周围的子区。将试件表面位移前后的两幅数字图像进行小波变换，通过变形前后两幅图像小波变换系数之间的相互匹配，使位移前后两幅图中的子区对应起来，从而确定图像的位移场。本文应用Haar小波变换进行了计算机模拟实验和实物位移实验。引入亚像素技术，获得了0．02的位移测量精度。     

悬丝技术在加速器物理实验中的应用

悬丝技术一直是加速器建造和调整中的一项重要技术，广泛应用于束流模拟，磁轴校准，ｗｉｇｇｌｅｒ测量和校正，束截面精确测量及加速器部件阻抗测量等领域。简要总结了近年来我们在上述领域所作的工作，显示这种技术的一些新发展。     

用PVDF实时测量激光诱导的冲击波压力

本文用自己研制的ＰＶＤＦ（ｐｏｌｙｖｅｎｙｌｉｄｅｎｆｌｕｏｒｉｄｅ）压电传感器测量了０．２ｍｍ厚铝和２．０８ｍｍ厚Ｔ３００／环氧复合材料中激光诱导的冲击波压力，首次获得了这些材料中激光冲击波压力的时间演化波形。实验在中国科大强激光实验室的ＹＡＧ脉冲激光器上进行，激光波长１．０６μｍ，脉宽３３ｎｓ，靶面平均功率密度为１０９Ｗ／ｃｍ２量级。从所得数据估计了表面入射压力，其值与已有结果符合良好。实验结果证实，ＰＶＤＦ压电传感器频响高，量程宽，多次使用重复性好，可有效应用于激光冲击波压力的实时测量     

用数字圆栅技术研究橡胶类材料I型断裂问题

采用数字云纹技术对橡胶类材料的大变形断裂力学问题进行了实验分析.提出了数字圆环栅和射线栅技术,给出了该技术的测量原理和方法.应用此技术对橡胶薄板材料的I型断裂的裂尖变形场进行了测量,给出了极坐标系下的实验径向位移场ur和环向位移场uθ的分布图,对实验结果进行了详细的分析,并结合大变形断裂的分区理论模型进行了比较与讨论.     

Numerical investigation on effects of induced jet on boundary layer and turbulent models around airfoils

In this study the effects of induced jet at trailing edge of a two dimensional airfoil on its boundary layer shape, separation over surface and turbulent parameters behind trailing edge are numerically investigated and compared against a previous experimental data. After proving independency of results from mesh size and obtaining the required mesh size, different turbulent models are examined and RNG k-epsilon model is chosen because of good agreement with experimental data in velocity and turbulent intensity variations. A comparison between ordinary and jet induced cases, regarding numerical data, is made. The results showed that because of low number of measurement points in experimental study, turbulent intensity extremes are not captured. While in numerical study, these values and their positions are well calculated and exact variation of turbulent intensity is acquired. Also a study in effect of jet at high angles of attack is done and the results showed the ability of jet in controlling separation and reducing wake region.     

Flow and mixing characteristics of swirling double-concentric jets subject to acoustic excitation

Characteristic flow modes, flow evolution processes, jet spread width, turbulence properties, and dispersion characteristics of swirling double-concentric jets were studied experimentally. Jet pulsations were induced by means of acoustic excitation. Streak pictures of smoke flow patterns, illuminated by a laser-light sheet, were recorded by a high-speed digital camera. A hot-wire anemometer was used to digitize instantaneous velocity instabilities in the flow. Jet spread width was obtained through a binary edge identification technique. Tracer-gas concentrations were measured for information on jet dispersions. Two characteristic flow patterns were observed: (1) synchronized vortex rings appeared in the low excitation intensity regime (the excitation intensity less than one) and (2) synchronized puffing turbulent jets appeared in the high excitation intensity regime (the excitation intensity greater than one). In the high excitation intensity regime, the “suction back” phenomenon occurred and therefore induced in-tube mixing. The jet spread width and turbulent fluctuation intensity exhibited particularly large values in the high excitation intensity regime at the excitation Strouhal numbers smaller than 0.85. At the excitation Strouhal numbers >0.85, the high-frequency effect caused significant decay of jet breakup and dispersion—the jet spread width and fluctuation intensity decreased sharply and may, at very high Strouhal numbers, asymptotically approach values almost the same as the values associated with unexcited jets. Exciting the jets at the high excitation intensity regime, the effects of puffing motion and in-tube mixing caused breakup of the jet in the near field and therefore resulted in a small Lagrangian integral time and small length scales of fluctuating eddies. This effect, in turn, caused drastic dispersion of the central jet fluids. It is possible that the excited jets can attain 90 % more improvements than the unexcited jets. We provide a domain regarding excitation intensity and Strouhal number to facilitate identification of characteristic flow modes.     

Effect of sound on a supersonic jet

It is known that under the influence of sound from an external source or the sound emitted by the supersonic jet itself at discrete frequencies in nonoptimal flow regimes the supersonic jet expands more rapidly and its range is reduced [1, 2], However, the mechanism of action of the sound on the supersonic jet has not been adequately investigated and, in particular, no one has determined the intensity of the external source capable of producing a marked change in the gas dynamic parameters of the jet, its characteristics or how the interaction process develops. These questions are examined below. By means of shadow photography with a pulsed light source it is shown that a significant change in the gas dynamic characteristics of the supersonic jet can be achieved by directing at its base along the normal to the jet boundary sound with an intensity corresponding to 0.1–0.2% of the total pressure in the jet. The appearance of large-scale disturbances on the irradiated side of jet and the directional emission of sound by the jet at the frequency of the external source are noted.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 6, pp. 170–174, November–December, 1989.The author is grateful to A. A. Kochetkov for assisting with the work.     

PIV measurements of a turbulent jet issuing from round sharp-edged plate

An experimental investigation is presented of a turbulent jet issuing from a round sharp-edged orifice plate (OP) into effectively unbounded surroundings. Planar measurements of velocity were conducted using Particle Image Velocimetry (PIV) in the near and transition regions. The Reynolds number, based on the jet initial diameter and velocity, is approximately 72,000. The instantaneous and mean velocities, Reynolds normal and shear stresses were obtained. The centerline velocity decay and the half-velocity radius were derived from the mean velocity. It is revealed that primary coherent structures occur in the near field of the OP jet and that they are typically distributed asymmetrically with respect to the nozzle axis. Comparison of the present PIV and previous hot-wire measurements for the OP jet suggests that high initial turbulence intensity leads to reduced rates of decay and spread of the mean flow field and moreover a lower rate of variation of the turbulence intensity. Results also show that self-similarity of the mean flow is well established from the transition region while the turbulent statistics are far from self-similar within the measured range to 16 diameters.     

Mathematical simulation of unsteady flow past a wing with jets

The various approximate approaches to the investigation of the unsteady aerodynamic characteristics of an airfoil with jet flap [1–3] are applicable only for an airfoil, low jet intensity, and low oscillation frequencies. In the present paper, the method of discrete vortices [4] is generalized to the case of unsteady flow past a wing with jets and arbitrary shape in plan. The problem is solved in the linear formulation; the conditions used are standard: no flow through the wing and jet, finite velocities at the trailing edges where there is no jet, and also a dynamical condition on the jet. The wing and jet are assumed to be thin and the medium inviscid and incompressible.Translated from Izvestiya Akademii Nauk SSSR, Mekhanika Zhidkosti i Gaza, No. 3, pp. 139–144, May–June, 1982.     

Symmetric shapes of contact of a jet with the surface of a heavy liquid

The plane linearized problem of oblique impingement of a weightless jet of an ideal incompressible fluid on the surface of a heavy fluid is considered. Flows are sought with symmetric forms of the contact region. Mathematically we arrive at the problem of the eigenvalues and eigenfunctions of an integral equation; solving this problem we obtain various contact forms. The fundamental result for the infinitesimally thin jet of finite intensity is derived by passing to the limit, yielding a result analagous with the forms of free vibrations of a string. Some results are presented for the problem under consideration in the nonlinear formulation.The two-dimensional problem on (vertical) impingement of a jet on a liquid was solved by Olmstead and Raynor [1]. Some results for oblique impingement of a sufficiently thin, slightly curved jet are presented by Frolov [2], Information on other studies, primarily experimental, is presented in [3].This problem is related to the model of a jet curtain of an air-cushion vehicle; in this regard we note the study of Stepanov [4] in which, in particular, a result is obtained for an infinitesimally thin jet curtain.     

Absolute, convective, and global instability of a magnetic liquid jet

An infinite or semi-infinite jet of non-conductive magnetic liquid in a uniform longitudinal magnetic field can be absolutely or convectively unstable for different values of the flow parameters. Though the higher field inhibits the absolute instability, this inhibition is maximum at some field intensity. A critical value of the surface tension exists, above which the instability is absolute for any intensity of the field. If the jet has a large but finite length and proper boundary conditions are held at its beginning and end, it is always globally unstable. The unstable global mode is based on a pair of waves that propagate in opposite directions and reflect from one into the other at the flow boundaries.     

Experimental study of ventilated cavity flow over a 3-D wall-mounted fence

Ventilated cavity flow over a fixed height 3-D wall-mounted fence is experimentally investigated in a cavitation tunnel for a range of free-stream conditions. The impact of 3-D effects on cavity topology is examined, along with the dependence of the cavitation number and drag on the volumetric flow rate coefficient, fence height based Froude number and vapour pressure based cavitation number. Three different flow regimes are identified throughout the range of cavitation numbers for a particular free-stream condition. Generally, the cavity has a typical re-entrant jet closure the intensity of which is found to increase linearly with increasing Froude number. This increase in re-entrant jet intensity causes an increase in drag with Froude number for constant volumetric flow rate coefficient. At low Froude numbers the closure mechanism transitions from a single to a split re-entrant jet. The parameters used to characterize the cavity topology show a linear dependence on Froude number irrespective of the closure mode. The cavity topology and drag are found to be independent of vapour pressure based cavitation number.     

Numerical simulation on micromixer based on synthetic jet

This paper studied a concept of micromixer with a synthetic jet placed at the bottom of a rectangular channel. Due to periodic ejections from and suctions into the channel, the fluids are mixed effectively. To study the effects of the inlet velocity, the jet intensity and frequency, and the jet location on the mixing efficiency, 3-D numerical simulations of the micromixer have been carried out. It has been found that when the jet intensity and the frequency are fixed, the mixing efficiency increases when Re 〈 50, and decreases when Re 〉 50 with the best mixing efficiency achieved at Re = 50. When the ratio of the jet velocity magnitude to the inlet velocity is taken as 10 and the jet frequency is 100 Hz, the mixing index reaches the highest value. It has also been found that to get better mixing efficiency, the orifice of the synthetic jet should be asymmetrically located away from the channel＇s centerline.     

Modeling transonic weakly underexpanded turbulent jets

The results of the calculations of model and actual turbulent jet flows with shock waves at low supersonic Mach numbers are presented. The gasdynamic flow features characterizing shock reflection from a mixing layer are analyzed. A possible version of the modified model for the turbulent viscosity is proposed; the model makes it possible to improve the prediction of the shock (rarefaction wave) intensity distribution along jet flows.