A schlieren motion estimation method for water flow velocimetry
HUANG Tianli , WANG Qian
 doi: 10.11729/syltlx20200155
[Abstract](0) [FullText HTML](0) [PDF 6988KB](0)
Abstract:
In the present study, a schlieren motion estimation algorithm is proposed for two-dimensional seedless water flow measurement. A physical constraint is derived combining the schlieren intensity and continuity equations. The space smoothness constraint adopts the second-order div-curl regularizer. Based on the two constraints, the global cost function is derived and minimized to resolve the velocity field using the variation method. As an example, a buoyant plume in the water tank is tested using a z-type schlieren imaging system. The sample images are calculated using a correlation algorithm in PIVlab, an optimized optical flow algorithm, and the newly proposed schlieren motion estimation algorithm. The results show that the new algorithm can resolve more details of the flow field with higher spatial resolution, while the velocity gradient is consistent with the continuity characteristics. It also features with good robustness without obvious outlier mistakes. The schlieren setup is simple and cost effective in setup. The proposed algorithm has shown great potentials for velocity measurement in more complex configurations.
Design and property analysis on insulation structure of cryogenic wind tunnel
SONG Yuanjia , LIAO Daxiong etc.
 doi: 10.11729/syltlx20200137
[Abstract](0) [FullText HTML](0) [PDF 6834KB](0)
Abstract:
The cryogenic wind tunnel is the best way to achieve flight Reynolds number testing in engineering application, with great strategy importance in the national defense field. The insulation structure has become one of the key technologies for building large cryogenic wind tunnels. On this account, design and property analysis on insulation structure is investigated with the help of numerical simulation and experiment. Firstly, considering the wind tunnel working condition, design and material selection for the insulation structure is carried out. Then, the finite element modeling of the insulation structure is built. On this basis, the property of the insulation structure is numerically studied based on the actual worst working condition of the wind tunnel. The insulation characteristics and stress/displacement distribution of the insulation structure are analyzed. Finally, the experimental platform able to simulate the working condition of cryogenic wind tunnel is designed and constructed to carry out the temperature and stress/strain measurement experiment for the insulation structure under cryogenic alternating pressure working condition. The obtained results show that the designed insulation structure satisfies the demands of the cryogenic wind tunnel in service, which solves the problem of insulation structure designation. Additionally, the designed experimental platform solves the problem of property evaluation of the insulation structure, which paves the way for building the cryogenic wind tunnel of our country in the future.
Wind tunnel test for aerodynamics of wing-in-ground craft flying near smooth/wavy surface
GAO Lihua , HUANG Longtai etc.
 doi: 10.11729/syltlx20200077
[Abstract](0) [FullText HTML](0) [PDF 7048KB](0)
Abstract:
In order to investigate the aerodynamics of the wing-in-ground craft flying near wavy surface the dedicated wavy ground floor and moving wavy belt are devised to simulate the real water wave with the height of one meter. The wavy ground floor is capable of varying its vertical and horizontal position. The moving wavy belt which contains two waves on the belt is suitable for the wind tunnel test of the wing-in-ground craft flying over all the phases of the wave. The wind tunnel test has been carried out which simulates the wing-in-ground craft flying in the sky, near smooth surface and wavy surface by means of flat ground floor, wavy ground floor and moving wavy belt, respectively. The wind tunnel test results show that propellers and the floor have a coupling effect on the taking-off and landing aerodynamics of the wing-in-ground craft, instead of simple superposition. What is more, the aerodynamic loads of the wing-in-ground craft fluctuate dramatically over the various phases of the wave.
Experimental study on structural characteristics of separation flow induced by 3D wedge in hypersonic laminar flow by oil visualization
WANG Junqi , CHEN Zheng etc.
 doi: 10.11729/syltlx20180026
[Abstract](0) [FullText HTML](0) [PDF 38908KB](0)
Abstract:
Experimental investigation of hypersonic laminar separation flow over a 3D wedge is carried out in the hypersonic wind tunnel by utilizing oil flow visualization technique. Two test models of rectangular/ triangular flat plate are used. The 3D wedges which have different compression angles are mounted on the afterbody of models. The experimental result shows that the forebody shape has a great influence on the structures of hypersonic laminar separation induced by the 3D wedge. For the triangular plate model, the flow in the upstream of the wedge has obvious crossflow effect, and the separation structure is completely different from that of the rectangular plate model. At different attack angles, the shapes of the separation lines are also very different. The result shows very significant 3D effect of the local laminar separation which is induced by the triangular forebody and the 3D wedge.
Design and application of launch device for free-flight test in hypersonic wind tunnel
HE Chao , XIE Fei etc.
 doi: 10.11729/syltlx20200038
[Abstract](0) [FullText HTML](0) [PDF 6636KB](0)
Abstract:
The Free-flight test launch technology is one of the key technologies in the free-flight test. Hypervelocity Aerodynamics Institute, CARDC, researched and developed the model launch device for the conventional hypersonic wind tunnel, and conducted a series of free-flight tests in the hypersonic wind tunnel with Mach number being 6. The free-flight test results indicate that: the launch device worked well, and the attitude of the model is stable. According to the different wind tunnel specific circumstances, the size of the launch device can be reformed, which can be applied to different hypersonic wind tunnels. Launch pressure and launch velocity are important parameters, which should be considered at the structure design stages. The model fixed component also needs the adaptability design according to the different model shapes.
Stage separation trajectory simulation test technique in high speed wind tunnel
QIAN Fengxue , GUO Peng etc.
 doi: 10.11729/syltlx20200125
[Abstract](14) [FullText HTML](4) [PDF 7344KB](5)
Abstract:
Stage separation trajectory capturing test technique in the FL-23 wind tunnel was developed for investigating the stage separation dynamics of future multi-stage launch vehicle systems. By making use of the tunnel's upper and lower attack angle support mechanism and modification of servo-motors, transmission mechanism and control modules, a upper rig with two degrees of freedom of alpha, x, a lower rig with three degrees of freedom of alpha, x and y, and a coupling motion control system were set up. For a two stage vehicle, the two stage models and their force balances could be mounted on the upper and lower rigs respectively, and the stage separation trajectory could be simulated in the wind tunnel under control of the stage separation test computer, with coordinated motion of the angle of attack of the fore stage model, the angle of attack of the aft stage model, and the relative position in x and y directions of the two stage models. Conclusions could be obtained from verification experiments and client experiments, namely, the upper driving mechanism of the stage separation test system could pitch from –15° to 15°, and move from 0 to 200 mm in the x direction. The lower driving mechanism could pitch from –11° to 49°, and move from 0 to 680 mm in the x direction and from 0 to 507 mm in y direction. And the system could be used to conduct the tests for force measurement, model injection experiment, grid force measurement and capture trajectory simulation.
Experimental study on spreading and breaking mechanism of droplet impinging on low temperature wall at high speed
LEI Jilin , LI Jianwei etc.
 doi: 10.11729/syltlx20210066
[Abstract](25) [FullText HTML](7) [PDF 6779KB](4)
Abstract:
In order to study the dynamic behavior of a droplet impinging on a low-temperature wall, a visualization test was carried out on a single droplet impinging on a low-temperature wall (–30 ℃ - –10 ℃) with the Weber number between 533 and 1630 by the high-speed shadowing method. The experimental results show that prompt splash and corona splash occurs when the droplet impinges on the low temperature wall at the certain speed, and the splashing of secondary droplet is obvious. However, when the droplet impinges on the normal temperature wall at the same speed, there is no droplet breakage phenomenon. With the decrease of the wall temperature, the Weber number required for the droplets to smash into the wall decreases. When the wall temperature is –30 ℃, the critical Weber number of the droplet crashing into the wall decreases to about 650. When We < 650, even if the wall temperature is lower than –30 ℃, the droplets would not smash into the wall. When the droplet hits the normal temperature wall, the attached liquid film spreads out rapidly, and the larger the Weber number is, the greater the spread and retraction speed of the attached liquid film is, and the larger the spreading factor of the droplet is. This study provides a reference for the establishment of the impingement model of the droplet impinging on the low temperature wall surface.
Experimental study on high frequency unstable waves in hypersonic boundary layer with sharp cone at 6° angle of attack
LIU Shuyi , CHEN Jianqiang etc.
 doi: 10.11729/syltlx20210059
[Abstract](11) [FullText HTML](6) [PDF 7912KB](1)
Abstract:
Transition plays an important role in the aerodynamic and aerothermal design of hypersonic vehicles. Generally, crossflow instability plays the dominant role in inducing transition in the three-dimensional boundary layer. However, in the noisy environment the influence of the second mode of the instability cannot be ignored. In order to obtain a better understanding of the development of crossflow in the hypersonic boundary layer, the measurement of instability waves in the boundary layer of a 7° half-angle sharp cone model with 6° angle of attack was carried out using focused laser differential interferometer (FLDI) and high frequency pressure fluctuation sensor (PCB) in Mach 6 Ludwieg tube tunnel. The experimental results show that the high-frequency unstable waves are detected at different circumferential positions. Through power spectrum and bi-spectrum analysis, the variation of the unstable wave along the generatrix and the nonlinear interaction between the high-frequency unstable wave and the low-frequency signal (20-40 kHz) are obtained.
2021, (4): 1-2.
Abstract(42) HTML(24) PDF(17)
Abstract:
POD analysis of the dynamic structures of a low swirl number precessing jet
FU Hao , HE Chuangxin et al.
2021, 35(4): 1-9. doi: 10.11729/syltlx20210006
Abstract(109) HTML(45) PDF(29)
Abstract:
The flow field of a low swirl number precessing jet at Reynolds number Re = 4.5×104 is measured using particle image velocimetry (PIV) and the dynamics of the large-scale flow structures are examined further using the proper orthogonal decomposition(POD) analysis. The spatial modes obtained by POD and the fluctuating velocity field obtained by POD reconstruction at three swirl numbers, i.e., S = 0, 0.26 and 0.41, are compared and analyzed. The POD results show that the precession induces an alternating flow, switching between outflow from one side of the chamber along the chamber wall and inflow from another side. When the precession occurs, the vortex structures in the upstream shear layers have not broken down completely. They will develop downstream until approaching the starting point of the precession and then deflect with the mainstream. However, the large-scale structures in the downstream shear layers are completely destroyed. As the swirl number increases, the region affected by the precession moves upstream, and the orderly vortex structures in the shear layers break down.
Experimental investigation on flow mechanism driving heat transfer enhancement in a channel with circular pin fins
DUAN Jingtian , ZHANG Ke et al.
2021, 35(4): 10-18. doi: 10.11729/syltlx20200134
Abstract(90) HTML(27) PDF(21)
Abstract:
Circular pin fins are commonly used in the internal cooling channel of the turbine blade. This paper mainly investigated experimentally the flow mechanism driving heat transfer enhancement in a wide channel with staggered circular pin fins. The flow field in the mid-plane of the channel was measured using Particle Image Velocimetry (PIV). Nusselt number distributions on the endwall was obtained by means of Thermochromic Liquid Crystal (TLC) in the same geometry under the same Reynolds number (1.0×104 or 2.0×104). Results indicate that downstream of circular pins the distribution of vrms is similar to that of Nu. However, when the flow is developed, smaller scale fluctuation increases, and the distributions of turbulent kinetic energy (Kt) and Nu are more uniform. The heat transfer enhancement and cross-stream velocity fluctuation are decreased when Re increases. It is concluded that intense lateral velocity fluctuation induced by vortex shedding is the main flow mechanism driving local heat transfer enhancement. Small scale fluctuation makes local heat transfer uniform.
Wind tunnel experimental study on the wind load interference effect of solar panel arrays
MA Wenyong , MA Chengcheng et al.
2021, 35(4): 19-25. doi: 10.11729/syltlx20200127
Abstract(41) HTML(25) PDF(10)
Abstract:
Wind load is one of the main concerns in the design of the solar panel. The wind-induced interference effect is significant in the solar panel array, which needs further investigation. Pressures on the rigid solar panel models were measured in a wind tunnel to study the interference effect of solar panels on their pressure coefficients. By changing the inclination angle, wind direction and the number of solar panels, the interference effect on the wind load on the panels is studied. The results show that the most unfavorable wind load occurs when the panel is orientated to the wind. The upstream panels obviously shield the downstream ones and reduce their wind load. This shielding effect becomes more significant with the increase of the inclination angle. The wind load on the downstream panel tends to be constant when it locates downstream three or more panel rows. Based on the above interference effect, the pressure coefficients on the solar panel arrays are recommended and compared with those in standards, which provides a reference for the wind-resistant design of the solar panel supporting system.
Wind field characteristics on a bridge site under complex mountain terrain
SHEN Guohui , ZHANG Shuaiguang et al.
2021, 35(4): 26-33. doi: 10.11729/syltlx20200020
Abstract(50) HTML(16) PDF(8)
Abstract:
In order to obtain wind field characteristics on a bridge site on a complex mountain terrain, small-scale topographic wind-tunnel model tests are employed. The variation characteristics of the mean wind speed, wind attack angle, turbulent intensity and turbulence integral scale with respect to the wind azimuth and measuring point position are analyzed. The changes of the wind speed spectrum of typical measuring points on the complex mountain terrain are also studied. The results show that the mean wind speeds of all the measuring points on the bridge site are less than that of the gradient height. When wind blows along the valley, significant positive attack angles are produced due to the wind climbing effect, with the maximum value reaching +35.3°. The along-wind and crosswind turbulent intensities in this wind direction reach their minimum values as low as nearly 10%, and become larger in other wind directions. The turbulence integral scale in this direction is much larger than that in other directions, and increases with the increasing height of the measuring point. The wind speed power spectrum in the direction has significant differences compared with the incoming wind speed spectrum, of which the energy in the high frequency section increases significantly and the feature of the single peak diminishes.
Experimental study on pipe flow transition of XG solution and drag reduction characteristics with different mass fractions of NaCl
XU Shengxuan , ZHAO Wenbin et al.
2021, 35(4): 34-40. doi: 10.11729/syltlx20200041
Abstract(76) HTML(33) PDF(11)
Abstract:
The Reynolds experiment was conducted to study the transition characteristics of Xanthan Gum (XG) solution (mass fraction: (0-400)×10–6) in a horizontal smooth circular pipe flow. The influence of different mass fractions of the salt (NaCl) environment on the drag reduction characteristics of XG solution was also investigated experimentally. The relationships of the drag reduction efficiency of XG solution (mass fraction: (100-300)×10–6) with the flow Reynolds number (Re) and the shearing time in different NaCl mass fractions (0、250×10–6、500×10–6和1000×10–6) were measured. Characterized by the generalized Reynolds number, the flow transition lower critical Reynolds number is delayed in an approximately linear mode with the increase of XG mass fraction, while the value of the upper critical Reynolds number rapidly drops to about 3000. The saturated drag reduction efficiency of XG solution decreases significantly with the dissolution of NaCl under the high Reynolds number condition. Nevertheless, a better drag reduction effect appears under the low Reynolds number condition. The shearing resistance of XG solution shows mass fraction effect, while the addition of an appropriate amount of salt can slightly improve the shearing resistance.
Improvement and evaluation of thermal flow-field quality in CARDC icing wind tunnel
GUO Xiangdong , ZHANG Pingtao et al.
2021, 35(4): 41-51. doi: 10.11729/syltlx20200118
Abstract(32) HTML(18) PDF(11)
Abstract:
The compliance of the thermal flow field quality of the large icing wind tunnel is the foundation of its airworthiness application. In order to understand the effects of upgrading of the refrigeration system on the thermal flow field quality in the CARDC icing wind tunnel, a comprehensive verification test is carried out for the main test section. Then, the thermal flow field qualities, both at the exit of the heat exchanger and in the test section, are evaluated. Finally, the correction relationship of the airflow total temperature and the thermal flow field operating envelop are achieved. Results show that the thermal flow field qualities, both at the exit of the heat exchanger and in the test section, are better than the quality index given in SAE ARP5905, under the main test conditions. Compared with the test results in 2019, the spatial uniformity in the model area of the test section is greatly enhanced. Particularly, non-uniform temperature peak points exceeding the standard in the model area are eliminated under the conditions of high airspeed and low total temperature. Finally, the upgrading of the refrigeration system in 2020 greatly extends the thermal flow field operating envelop, so that the temperature simulation capability of the CARDC icing wind tunnel is enhanced significantly.
An ice wind tunnel test study on the scaling law of a rotating cone
ZHANG Lifen , GE Xin et al.
2021, 35(4): 52-59. doi: 10.11729/syltlx20200166
Abstract(75) HTML(35) PDF(8)
Abstract:
In order to verify the scaling law of a rotating cone, a study on a rotating cone icing was carried out, and the icing scaling law of the rotating cone was derived. Taking a cone with a bottom diameter of 100 mm and cone angle of 80° as the full size model, and a cone with a bottom diameter of 50 mm and cone angle of 80° as the scaled model, the ice wind tunnel tests were carried out under different conditions. The ice shape on the surface of the cone was obtained by image method and processed in a dimensionless manner. Then the ice shape of the full size model was compared with that of the scaled model. The results show that, for glaze ice the ice shape of the front half of the cone on the full size and scaled models is in good agreement, but it is not in good agreement at the back half of the cone, and for rime ice the ice shape is in fairly good agreement on the full size and scaled models. The reasons are discussed, and suggestions are put forward for improvement.
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Practices and challenges on PIV technology in high speed complex flows
Liu Hong, Chen Fang, Li Xiaojie, Zheng Zhonghua, Xiao Baoguo
2016, 30(1): 28-42.   doi: 10.11729/syltlx20150069
[Abstract](53) [PDF 6594KB](1)
摘要:
粒子图像测速技术目前已经发展成为实验流体力学领域应用最广泛的非接触激光测试方法之一,为认知复杂流动机理提供直观的流场信息.本文基于超声速流场PIV技术研究实践,针对示踪粒子布撒器设计、粒子松弛特性模型构建、激波流场测试分析、超声速平板湍流边界层结构分析等方面具体问题的研究和认识,从理论、定量化的角度深入分析了应用于超声速流场PIV技术现阶段依然存在的问题.从应用于超声速流场PIV技术的原理出发,针对高速复杂流场的PIV测试现状,总结了应用于超声速流场PIV技术发展过程中的光学部件、示踪粒子及布撒系统所遇到的一系列挑战,以及国内外利用PIV技术在高速复杂流场研究中所取得的成就,针对PIV技术能否适用于高超声速流场的测量做了系统化地探索.并根据实践经验提出了应用于超声速流场PIV技术未来的发展方向:通用的精确的PIV方法不存在,必须从具体研究的流动机理角度改造相应的PIV测试手段.
Experimental study on Reynolds number effect on aerodynamic pressure and forces of cylinder
Liu Qingkuan, Shao Qi, Zheng Yunfei, Li Conghui, Ma Wenyong, Liu Xiaobing
2016, 30(4): 7-13.   doi: 10.11729/syltlx20150112
[Abstract](36) [FullText HTML](4) [PDF 10428KB](2)
摘要:
通过刚性模型测压风洞试验,研究了圆柱的气动阻力、气动升力系数和风压系数随雷诺数的变化规律,从流场分布的角度分析了气动力变化的原因,并研究了雷诺数影响下的流场在圆柱轴向的相关性。结果表明:在亚临界雷诺数区域,在时间平均上流场沿模型两侧呈对称分布,雷诺数对平均阻力系数和流场影响较小,平均升力系数基本为零。在临界雷诺数区域,随着特定区域大负压区的出现,流场不再对称,出现不容忽视的平均升力和脉动升力。在超临界雷诺数区域,随着对称侧大负压区的出现,流场恢复对称状态,平均升力基本消失。雷诺数对流场的轴向相关性有显著的影响。在雷诺数较低时(亚临界区域),卡门涡在轴向上的尺度相对较大,而随着雷诺数的提高,该尺度逐渐减小,各断面流场的相关性降低。
Review of research on the receptivity of hypersonic boundary layer
Jiang Xianyang, Li Cunbiao
2017, 31(2): 1-11.   doi: 10.11729/syltlx20160129
[Abstract](33) [FullText HTML](27) [PDF 7434KB](1)
摘要:
高超声速边界层感受性是边界层转捩预测与控制的关键环节,其对高超声速飞行器研究至关重要。目前关于高超声速边界层感受性的实验研究仍然十分匮乏,为了更好地理解高超声速边界层感受性过程并指导该领域的实验研究,文章梳理了近20年来国际上高超声速边界层感受性问题的研究内容,包括对自由流扰动和壁面扰动的感受性,并主要介绍了Fedorov的前缘感受性理论和模态转化机制。最后总结了自由流扰动中感受性的不同发展路径。
Investigation of several fundamental combustion problems in rocket-based combined-cycle engines
He Guoqiang, Qin Fei, Wei Xianggeng, Cao Donggang, Huang Zhiwei, Liu Bing
2016, 30(1): 1-14,27.   doi: 10.11729/syltlx20150159
[Abstract](32) [PDF 6603KB](1)
摘要:
火箭冲压组合发动机包含多个工作模态,不同模态灵活组合的优势使其具有宽速域和广空域的工作特点,兼具加速和巡航的优点.火箭冲压组合发动机燃烧室中存在着亚声速、跨声速和超声速共存的流动结构,具有流动速度高、混合时间短、反应强度大、燃烧空间受限和波系结构复杂等特点.围绕火箭射流的强剪切性、燃烧模式的多样性和燃烧过程的动态性,分析了火箭冲压组合发动机的流动与燃烧特征,总结了面向发动机的高速湍流燃烧研究进展,研究了火箭冲压组合发动机中超声速反应混合层的生长特性、燃烧模式与空间释热分布和动态燃烧特性等问题.通过对碳氢燃料详细化学动力学机理的简化、校验,获得了分别适合于工程计算和细致燃烧机理研究的总包反应与框架机理.从火箭射流主导的反应混合层生长模型,宽范围、变来流工作中流动燃烧过程的不确定性和碳氢燃料动力学的简化与加速算法研究出发,提出了火箭冲压组合发动机基础研究中需要突破的问题,为认识发动机中多尺度燃烧机理、优化多模态燃烧组织提供参考.
PIV measurement and numerical simulation of Taylor-Couette flow
Feng Junjie, Mao Yuhong, Ye Qiang, Liu Renhong, Chang Qing
2016, 30(2): 67-74.   doi: 10.11729/syltlx20150091
[Abstract](42) [PDF 5952KB](1)
摘要:
采用粒子成像速度场仪(PIV)和数值模拟(CFD)对Taylor-Couette 流场进行测量,获得各转速下涡流场信息。将同等条件下PIV测量结果与数值模拟结果相联系,对比分析不同旋转雷诺数范围内涡流场中不同径线和中轴线上各向速度的变化特征。结果表明,各种特征存在一定的转速分段范围:在2~7r/min(Re为100~350)时,各向速度特征为层流涡特性,在7~40r/min(Re为350~2000)时,各向速度特征为波状涡特性,在40~60r/min (Re为2000~3000)时,各向速度特征为调制波状涡特性,当转速大于60r/min(Re大于3000)时,各向速度特征为湍流涡特性。根据不同角度获得的各向速度特征对应的内筒转速、旋转雷诺数与流场涡形态的关系,明确分析出特定几何条件下,泰勒涡发生形态转变的旋转雷诺数,以便于深入探究泰勒涡流场的特性,定量分析涡运动形态特征。
Simultaneous OH and CH2O PLIF imaging of flame structures
Zhu Jiajian, Zhao Guoyan, Long Tiehan, Sun Mingbo, Li Qing, Liang Jianhan
2016, 30(5): 55-60.   doi: 10.11729/syltlx20160026
[Abstract](44) [FullText HTML](23) [PDF 7981KB](2)
摘要:
OH和CH2O平面激光诱导荧光(PLIF)同时成像技术在研究火焰结构和燃烧反应中间产物二维分布等方面能够发挥重要作用。OH的分布被用来表征火焰反应区的结构,而CH2O的分布则被用来显示火焰预热区的分布。利用OH和CH2O PLIF同时成像技术研究了甲烷/空气部分预混火焰的结构。从实验系统、光路调节、时序同步、OH A-X(1,0)扫谱、数据采集和处理等方面讨论了PLIF同时成像技术的实验方法。实验结果表明,OH和CH2O PLIF同时成像能够分别呈现甲烷/空气部分预混火焰反应区和预热区不同形状的瞬时结构;由于反应区在相邻位置的结合,在火焰中能够局部生成新的分裂的预热区。
Study of micro flow visualization with nuclear magnetic resonance in core
Di Qingfeng, Hua Shuai, Gu Chunyuan, Ye Feng, Pang Dongshan, Jiang Fan, Yang Peiqiang
2016, 30(3): 98-103.   doi: 10.11729/syltlx20150107
[Abstract](23) [PDF 4151KB](0)
摘要:
岩心微流动可视化是研究化学驱油微观机理的一项重要流体实验新方法,重点介绍采用低场核磁共振成像技术研究天然岩心中流体分布可视化的新进展。提出和分析了国产低场核磁共振成像岩心驱替装置面临的图像不清、材料干扰等问题,通过合理选材、优化参数,从硬件和软件2方面进行了改进与优化,消除了干扰因素。开展了天然岩心的驱替实验,采集了油水的实时 NMR信号与 MRI 成像信号,以及不同驱替阶段油水的 NMR-T2谱,得到分辨率较高的油水分布图像。结果显示残余油随着驱替PV数的增加而减少,具有初期减少明显而后趋缓的特点,并发现岩心中存在端部油残滞现象,其范围距端部4mm左右。研究了通过获得的油水分布图像计算含油饱和度的方法,其结果与传统方法一致,误差在10%以内,这也说明了油水分布图像的可靠性。这不仅为计算饱和度提供了一种新方法,而且该方法的另一个优势是可以分析任意局部位置的油水饱和度。研究结果表明,在研究岩心微流动过程中流体分布的可视化方面,核磁共振成像技术是值得深入研究的新方法。
Advances influidic thrust vectoring technique research
Xiao Zhongyun, Jiang Xiong, Mou Bin, Chen Zuobin
2017, 31(4): 8-15.   doi: 10.11729/syltlx20160207
[Abstract](35) [FullText HTML](16) [PDF 5274KB](1)
摘要:
流体推力矢量技术不采用机械偏转,以流动控制方式实现推力转向,有望成为一种更加高效的推力矢量控制方法。目前实现流体推力矢量的主要方法有激波矢量法、双喉道方法、逆流控制方法和同向流方法等,对以上方法选择具有共性的计算与试验数据,对喷管的推力矢量效率、推力损失和流量系数进行了对比分析。结果表明激波矢量方法、双喉道方法和逆流方法能够在大落压比范围内(NPR=1.89~10)实现推力矢量控制,并且具有俯仰/偏航耦合甚至多轴控制的潜力。相比激波矢量法和逆流方法,双喉道和同向流方法在减少推力损失和提高矢量效率上占有优势,不足之处是双喉道方法对喉道进行控制限制了流量系数,而同向流方法的适用落压比范围受到严重限制。为寻求更加高效的矢量喷管技术,国内外相继发展了多种新概念流体推力矢量方法,对每种方法的控制原理、潜在优势和存在的问题挑战进行了探讨,新方法着眼于从喷流出口下游进行控制,对主流的干扰很小,值得深入研究,同时也为流体推力矢量的下一步研究方向提供了借鉴参考。
Experimental study on the flow past a rotating cylinder with PIV
Sun Jiao, Zhang Bin, Tang Zhanqi, Chen Wenyi
2016, 30(1): 81-90.   doi: 10.11729/syltlx20150037
[Abstract](35) [PDF 4386KB](0)
摘要:
投弃式海流剖面仪(Expendable Current Profiler,XCP)周围流场是典型的旋转圆柱绕流.探头周围流场对探头的运动状态起决定性作用,这直接关系到探头的测量性能,因此有必要对旋转圆柱周围流场进行实验研究.实验在循环水槽中进行,通过PIV对雷诺数保持不变(Re=1000)、不同圆柱旋转速度比(α=0、0.5、1.0、1.5、2.0、2.5、3.0、3.5、4.0、4.5和5.0)的圆柱下游尾流场进行研究.通过选取不同旋转速度比的任一时刻的瞬态流场,来分析旋转对圆柱尾流结构的影响.为了获得流场的频率信息,对所获得流场信息进行能谱分析来获取涡旋的脱落频率,并进一步使用正交模态分解对流场进行分析,给出了流场主要拟序结构及其能量与转速比的变化趋势.发现圆柱旋转改变圆柱尾流结构,使尾迹尺度变小.在旋转速度比0≤α≤2.0时,存在明显的周期性涡旋脱落,并且涡旋脱落的频率有逐渐升高的趋势;而且当转速比2.0<α≤5.0时尾迹流场的周期性减弱,涡旋脱落变得不明显,流场表现出低频、剪切层的区域特征.随着转速变大,涡旋尺度变小.在较高旋转速度比时,流场中能量被重新分布.
Development and application of the force-measuring balance in impulse combustion wind tunnel tests
He Wei, Gao Chang, Zhang Xiaoqing, Yu Shien
2016, 30(4): 66-70.   doi: 10.11729/syltlx20160011
[Abstract](31) [FullText HTML](14) [PDF 4815KB](0)
摘要:
介绍了一种用于脉冲燃烧风洞高超重载模型冷、热态测力试验的腹支内式六分量应变天平研制方案。燃烧脉冲风洞试验时间短、冲击载荷大,模型重量大,要求天平能够快速响应,设计方案兼顾了刚度和灵敏度,天平静校指标满足要求。试验结果表明,天平输出信号与燃烧室压力的跟随性良好,能够正确反映模型的受力状态,轴向力系数的重复性精度达到了1.6%,天平性能稳定,由模型/天平/支架构成的测力系统在轴向力、法向力和俯仰力矩3个分量上输出信号的主频均满足脉冲风洞的测力要求。该天平方案满足重载模型在脉冲燃烧风洞试验中的测力要求。
POD analysis of the dynamic structures of a low swirl number precessing jet
FU Hao, HE Chuangxin, LIU Yingzheng
2021, 35(4): 1-9.   doi: 10.11729/syltlx20210006
[Abstract](109) [FullText HTML](45) [PDF 7588KB](45)
Abstract:
The flow field of a low swirl number precessing jet at Reynolds number Re = 4.5×104 is measured using particle image velocimetry (PIV) and the dynamics of the large-scale flow structures are examined further using the proper orthogonal decomposition(POD) analysis. The spatial modes obtained by POD and the fluctuating velocity field obtained by POD reconstruction at three swirl numbers, i.e., S = 0, 0.26 and 0.41, are compared and analyzed. The POD results show that the precession induces an alternating flow, switching between outflow from one side of the chamber along the chamber wall and inflow from another side. When the precession occurs, the vortex structures in the upstream shear layers have not broken down completely. They will develop downstream until approaching the starting point of the precession and then deflect with the mainstream. However, the large-scale structures in the downstream shear layers are completely destroyed. As the swirl number increases, the region affected by the precession moves upstream, and the orderly vortex structures in the shear layers break down.
2021年3期目录
2021, 35(3): .  
[Abstract](56) [PDF 3006KB](15)
Abstract:
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