出流孔型对平板气膜冷却影响机理的研究

为了研究不同孔型对平板气膜冷却的影响,针对圆形,扇形,水滴形,收敛缝形四种气膜出流孔型的流动和传热特性进行了数值模拟。研究结果表明,圆形孔、扇形孔和水滴形孔气膜出口下游出现从中心向上抬升的反向旋转涡对,将主流燃气卷吸进来；收敛缝形孔在侧向的扩张型面使得气膜出流在展向的覆盖更为均匀,这有效地阻止了高温气体的侵入；在相同吹风比下,收敛缝形孔在气膜出口附近区域的平均绝热冷却效率则明显要高于其余三种孔,随着吹风比的增大,这种差距越发明显；孔型对对流换热系数增强比的影响区域仅局限在邻近气膜孔出口大约7倍气膜孔径的范围内。      

基于快速多帧PIV方法的超声速自由射流流动结构研究

针对超声速流场速度场难以测量的特点,搭建了一套具有高时空分辨率的快速多帧PIV测量系统,对压比为5的超声速欠膨胀自由射流流场进行了测量,PIV速度场结果分别与国外的实验结果和数值模拟结果进行对比,验证了本PIV系统的良好性能。结合速度场分布图像对超声速自由射流的流场结构进行了分析,并基于速度场分布获得了涡量场分布等信息。实验结果表明,涡量场中存在两条环状涡量分布区,将自由射流的下游流场分割为三块速度、温度等参数沿径向分布规律显著不同的区域。     

基于Workbench的高压圆盘气体轴承三维流场分析

为了取得高压圆盘气体轴承的完整三维流场,基于Workbench仿真软件对高压圆盘气体轴承进行三维建模仿真,得到整个流道及圆盘缝隙射流区的流场参数分布;将三维模型的气膜对称面与轴承圆盘、稳流管的轴对称面相交,截得气膜对称线;分析气膜对称线上的流场参数分布,并将其与二维简化模型流场计算结果进行对比,同时验证2种建模分析方法的有效性。结果表明：2种建模分析方法得到的气膜内马赫数和静压分布的变化规律一致,即在绝大部分气膜区域能保持高压,仅在气膜出口处很窄的范围内压力快速下降,同时在气膜出口附近形成超音速圆盘缝隙射流,使上游气膜内高压不受下游环境低压的影响;不同湍流强度对高压圆盘气体轴承内流场的静压无明显影响,但对缝隙射流区及气流远场区域的马赫数有着小幅影响。     

煤液化调节阀流场演变特性的测试与分析

利用粒子图像测速技术（particle image velocimetry,简称PIV）和涡量分析原理对调节阀不同工况下的流场信息进行测量,研究了进口压力对液压调节阀速度场、涡量场及湍动能的影响。结果表明：调节阀节流口处有对冲射流,其在阀芯头部下游汇合后形成向下游的整体喷射;节流口下游的油液轴向速度先减小后增大,在喉部末尾处附近趋于稳定;在靠近壁面区域油液径向流动速度都较低,在流道中心区域流动速度较高;阀芯头部和下游流道存在由速度梯度引起的介质回流旋涡,高涡量区域主要分布在阀芯头部和壁面处,强的正涡与负涡呈2条斜形宽带分布;阀芯头部为高涡量区且具有贴壁特征,壁面附近高涡量区向下游延展;随着调节阀进口压力的增大,阀口流量、流场高速分布区域、旋涡的强度和尺度以及湍动能均随之增大。     

超声速流下多供气空圆盘静压止推气体轴承性能分析

应用Fluent软件对多供气节流小孔盘静压止推气体轴承进行三维流场的模拟计算,分析供气小孔数、气膜间隙和供气压力对圆盘静压止推气体轴承性能的影响,并和Reynolds方程解的结果进行比较,分析气膜内发生超音速流和不发生超音速时气膜内的压力分布和马赫数情况.结果表明,应用Fluent数值模拟可以很方便地处理节流小孔进入到气膜内区域的复杂流场流动;增加供气孔数、减小气膜间隙和降低供气压力能够避免多供气孔静压止推气体轴承气膜内发生超音速.     

Sobel算子在气膜孔图像清晰度评价过程中的研究

对高压涡轮叶片中冷却气膜孔(下简称:气膜孔)视觉测量过程中遇到的气膜孔图像清晰度评价问题展开研究。利用光学成像系统分析了系统离焦对图像清晰度的影响,并提出了一种Sobel算子与阈值相结合的图像清晰度评价方法。针对气膜孔孔径小、单晶材料反光、焦平面的获取困难、气膜孔边缘难识别等问题,进行对比实验,设计了图像清晰度评价函数归一化与阈值选取相结合的测量方法,这确保了评价功能的真实性,同时滤除了高频噪声。实验结果表明,所提出的评价方法可以准确地评价气膜孔图像的清晰度。此方法具有很强的单峰性,无偏性和良好的抗噪性能。     

冷气预旋诱导涡系重构气膜冷却机理研究

为了揭示不同进气腔配置诱导涡系重构对气膜冷却效果的影响,在圆柱形气膜孔的基础上研究了三种不同冷气腔结构以产生不同的进气预旋气膜冷却流动结构,并对三种冷气腔在吹风比分别为0.5、1.0、1.5、2.0的条件下进行了对比研究。结果表明:在低吹风比时,冷却气体出射动量小,三种进气方式的气膜冷却效率相当。随着吹风比的增加,进气预旋气膜冷却的优势逐渐显著。在吹风比为2.0时,原始进气冷却流体出射动量大且分布均匀,形成了强肾形涡,气膜冷却效率最低;第一种进气射流在孔上游形成一低动量区,该区域冷气与高温主流相互作用后绕开高动量区冷气射流后贴附壁面,在下游冷却效果明显;第二种进气冷却流体以单向旋涡的结构喷出,在下游形成一侧旋涡"压"着另一侧旋涡的流动形式,使被压旋涡中冷气更好地贴附壁面,射流侧向速度大,扩大了射流展向覆盖区域。相对于原始进气,第一种进气和第二种进气的平均绝热气膜效率,在吹风比为1.0时,分别提高了约10%和25%,在吹风比为1.5时,分别提高了约50%和550%。     

动叶片尾缘不同气膜冷却方式对涡轮气动性能的影响

计算模型选用某型燃气轮机透平的第一列动叶,通过中心差分格式对叶栅流场进行数值模拟。文中通过改变冷气喷射角度计算了多种不同的尾缘气膜冷却方案,分析了这些方案下,能量损失系数、冷却效率以及温度场的分布情况和其对透平的气动性能的影响。结果表明:在尾缘区域喷射冷气进行冷却时,冷气喷射方向与法线成80°时,由于冷气喷射方向接近主流流向,能量损失系数最低,但尾缘区域冷却效果不明显,摩擦因数较高,压力变化明显。在与法线成70°和75°喷射冷气时,能量损失系数也比较低,冷却效果比较明显,总体看来,与法线成70°喷射冷气时的气动效果和冷却效果都比较好。     

几何参数对S弯进气道气动特性的影响研究

采用数值仿真方法对某无人机S弯进气道内流场结构进行了分析,对出口截面流场特征及出口参数进行了研究。利用三维数值仿真方法,对几何参数对S弯进气道气动特性的影响进行了对比,其中包括S弯偏移距离和S弯进气道长度的影响。研究结果表明:S弯进气道内部存在典型的横向涡结构。S弯长度的增加会显著降低涡结构区域及分离区域,改善流场结构,同时提升出口总压恢复系数,控制出口畸变。     

最优影响因素下超燃冲压发动机煤油流动水平管冷却

水和煤油在管道中的温度分布是不均匀的,且超燃冲压发动机煤油流动水平管冷却过程,没有针对不同区域换热过程进行进一步细分,导致煤油流动水平管冷却通道内速度场的分布规律不够精准,最优冷却因素分析结果失真,影响煤油的冷却效果。为解决这一问题,提出一种超燃冲压发动机煤油流动水平管最优冷却因素分析。通过构建航空煤油的对流换热控制模型,将整个换热过程分成不同的阶段,获取进口温度、压力、热流密度对传热的影响,计算出加热壁面内、壁面与流体三者间的传热系数,得出的流动水平管冷却的边界条件,并以此为依据获取对水平管内超临界航空煤油传热的影响因素,完成对超燃冲压发动机煤油流动水平管优化冷却。实验结果证明：所提方法的管壁温度拟合度与实际值基本一致,且冷却效果好,表明所提方法在超燃冲压发动机煤油流动水平管冷却方面具有一定的应用价值。     

The effect of the secondary annular stream on supersonic jet

The present study addresses an experimental investigation of the near field flow structures of supersonic, dual, coaxial, free, jet, which is discharged from the coaxial annular nozzle. The secondary stream is made from the annular nozzle of a design Mach number of 1.0 and the primary inner stream from a convergent-divergent nozzle. The objective of the present study is to investigate the interactions between the secondary stream and inner supersonic jets. The resulting flow fields are quantified by pitot impact and static pressure measurements and are visualized by using a shadowgraph optical method. The pressure ratios of the primary jet are varied to obtain over-expanded flows and moderately under-expanded flows at the exit of the coaxial nozzle. The pressure ratio of the secondary annular stream is varied between 1.0 and 4.0. The results show that the secondary annular stream significantly changes the Mach disc diameter and location, and the impact pressure distributions. The effects of the secondary annular stream on the primary supersonic jet flow are strongly dependent on whether the primary jet is underexpanded or over-expanded at the exit of the coaxial nozzle.     

Experimental study on hysteresis phenomena of shock wave structure in an over-expanded axisymmetric jet

In recent studies on two-dimensional supersonic jets, it is reported that the hysteresis phenomenon for the reflection type of shock waves in the jet flow field is occurred under the quasi-steady flow condition and this phenomenon is affected by the transitional pressure ratio between the regular reflection and Mach reflection. However, so far, there are few researches on the hysteresis phenomenon for the transition of shock waves between regular and Mach reflection in over-expanded supersonic jets and the phenomenon has not been investigated satisfactorily. Therefore, the purpose of this study is to clarify the hysteresis phenomena for the reflection type of shock wave in the over-expanded axi-symmetric supersonic jet experimentally, and to discuss the relationship between hysteresis phenomenon and rate of the change of pressure ratio with time. Furthermore, the effect of Mach number at the nozzle exit on hysteresis loop was investigated for two kinds of nozzle.     

Investigation of strut-ramp injector in a Scramjet combustor: Effect of strut geometry,fuel and jet diameter on mixing characteristics

The strut-based injector has been found to be one of the most promising injector designs for a supersonic combustor, offering enhanced mixing of fuel and air. The mixing and flow field characteristics of the straight (SS) and Tapered strut (TS), with fixed ramp angle and height at freestream Mach number 2 in conjunction with fuel injection at Mach 2.3 have been investigated numerically and reported. In the present investigation, hydrogen (H₂) and ethylene (C₂H₄) are injected in oncoming supersonic flow from the back of the strut, where jet to freestream momentum ratio is maintained at 0.79 and 0.69 for H₂ and C₂H₄, respectively. The predicted wall static pressure and species mole fractions at various downstream locations are compared with the experimental data for TS case with 0.6 mm jet diameter and found to be in good agreement. Further, the effect of jet diameter and strut geometry on the near field mixing in strut ramp configuration is discussed for both the fuels. The numerical results are assessed based on various parameters for the performance evaluation of different strut ramp configurations. The SS configuration for both the injectant has been found to be an optimum candidate; also it is observed that for higher jet diameter larger combustor length is required to achieve satisfactory near field mixing.     

Effect of convex wall curvature on three-dimensional behavior of film cooling jet

The flow characteristics of film coolant issuing into turbulent boundary layer developing on a convex surface have been investigated by means of flow visualization and three-dimensional velocity measurement. The Schlieren optical system with a spark light source was adopted to visualize the jet trajectory injected at 35° and 90° inclination angles. A five-hole directional pressure probe was used to measure three-dimensional mean velocity components at the injection angle of 35°. Flow visualization shows that at the 90° injection, the jet flow is greatly changed near the jet exit due to strong interaction with the crossflow. On the other hand, the balance between radial pressure gradient and centrifugal force plays an important role to govern the jet flow at the 35° injection. The velocity measurement shows that at a velocity ratio of 0.5, the curvature stabilizes downstream flow, which results in weakening of the bound vortex structure. However, the injectant flow is separated from the convex wall gradually, and the bound vortex maintains its structure far downstream at a velocity ratio of 1.98 with two pairs of counter rotating vortices.     

喷嘴流道数对涡流管能量分离特性影响的研究

以压缩空气为工作介质,对涡流管能量分离特性进行了实验研究,获得了涡流管制冷、制热效应随喷嘴流道数、冷端流率之间的关系,研究结果表明,喷嘴流道数越多,涡流管的制冷越好,且获得最大制冷效应时的冷端流率有增大的趋势;喷嘴流道数对涡流管制热效应的影响没有对制冷效应的影响明显.     

A visual study on turnabout phenomenon of vortex roll-up in forced jet diffusion flames

An experimental study on the effect of forcing amplitude in forced jet diffusion flames has been conducted. Various flow visualization techniques are employed using optical schemes, including light scattering photography, high speed imaging by motion analysis, and determination of velocity vector and vorticity fields from PIV data. Particular attenttion is focused on the turnabout mechanism around the elongated flame, which has not been reported previously, and on the inner coherent structure of the forced jet in the attached flame regime. In particular, we present a schematic diagram that aids in the understanding of the turnabout mechanism of vortex roll-up. This diagram explains why the forced flame is elongated under moderate forcing amplitudes but shortens again when the forcing amplitude is further increased.     

Supersonic gas jets for laser-plasma experiments

We present an in-depth analysis of De Laval nozzles, which are ideal for gas jet generation in a wide variety of experiments. Scaling behavior of parameters especially relevant to laser-plasma experiments as jet collimation, sharpness of the jet edges and Mach number of the resulting jet is studied and several scaling laws are given. Special attention is paid to the problem of the generation of microscopic supersonic jets with diameters as small as 150 μm. In this regime, boundary layers dominate the flow formation and have to be included in the analysis.     

An experimental study of supersonic dual coaxial free jet

A supersonic dual coaxial jet has been employed popularly for various industrial purposes, such as gasdynamic laser, supersonic ejector, noise control and enhancement of mixing. Detailed characteristics of supersonic dual coaxial jets issuing from an inner supersonic nozzle and outer sonic nozzles with various ejection angles are experimentally investigated. Three important parameters, such as pressure ratios of the inner and outer nozzles, and outer nozzle ejection angle, are chosen for a better understanding of jet structures in the present study. The results obtained from the present experimental study show that the Mach disk diameter becomes smaller, and the Mach disk moves toward the nozzle exit, and the length of the first shock cell decreases with the pressure ratio of the outer nozzle. It was also found that the highly underexpanded outer jet produces a new oblique shock wave, which makes jet structure much more complicated. On the other hand the outer jet ejection angle affects the structure of the inner jet structure less than the pressure ratio of the outer nozzle, relatively.