孔板消减气流脉动的数值模拟及实验研究

添加孔板是一种消减压缩机管道系统内气流脉动有效而简便的方法,尽管在工业生产中已被广泛应用,但是其设计和制作所需的各个参数尚处于靠经验取值的阶段.针对这种情况,首先阐述了孔板消减管道内气流脉动的机理;然后使用流体仿真计算软件Fluent建立了管道内气体的二维非稳定流动模型,计算了孔板对管道内气流的压力脉动的影响;并在数值模拟的基础上,搭建了往复式压缩机管道系统实验平台,在进气管线研究了孔板对气流脉动的消减作用.通过数值模拟和实验研究分析了孔板孔径比对气流脉动的影响,并指出选用恰当孔径比的孔板不仅能有效降低主管线和缓冲器至孔板段管线的压力脉动幅度而且对压缩机进口段管线内压力脉动同样具有良好的消减效果.     

车辆内部气流噪声计算方法

本文在风洞实验的基础上，提出了气流噪声向汽车内部传播的理论模型．采用边界元法，研究了车外脉动压力透过板壁和气流噪声通过孔隙向车内传播以及相互之间的耦合关系．给出由外部脉动压力和气流噪声计算车内声场的计算公式．     

爆轰驱动高焓激波膨胀管性能研究

介绍了中国科学院高温气体动力学实验室JF-16爆轰驱动高焓激波膨胀管的研制进展及其性能测试结果. 性能研究主要测量了入射激波速度和压力曲线. 根据入射激波速度,应用Mirels的黏性激波管理论计算了超高速试验气流的运动速度,然后应用Gaseq软件计算了试验气流的热力学参数. 研究结果表明:在16.35\,m长的JF-16激波膨胀管中获得了流速7\,000\,m/s以上的稳定试验气流,试验时间为50$\sim$100$\mu$s, 试验气流总焓30\,MJ/kg左右.      

涡旋式压缩机排气系统气流脉动现象研究

研究了涡旋式空气压缩机排气系统的气流脉动现象，首次提出了排气孔口侵入现象及计算方法。由一维非定常流动理论建立了排气系统气流脉动的计算模型，利用匀熵修正理论进行了边界条件处理，并运用Ｌ－Ｗ两步计算法进行了数值计算。试验样机的实测结果与数值计算结果吻合较好。研究内容对于新型压缩机——涡旋式空气压缩机的设计具有指导意义。     

SWT-120风洞稳定段的性能测量

在普通超音速风洞中,由于受到噪声干扰,很难进行有效的边界层转捩特性试验研究,针对超声速流动特点发展较低噪声风洞十分必要,而稳定段设计的好坏直接影响到下游试验段噪声水平。本文介绍一座低噪声风洞稳定段的结构和性能测量结果。先对稳定段的结构设计做了简单介绍,然后对实验结果进行分析,实验结果表明在大角度扩散段内装置孔锥,稳定段安装消音夹层和阻尼网组等部件后,气流的速度脉动和压力脉动明显降低,其中压力脉动降低一个量级,速度脉动为1%。进一步优化设计和改进工艺,速度脉动还可进一步降低。测量结果表明SWT-120稳定段的设计是成功的,对我们以后发展更高性能的静风洞有借鉴和参考价值。     

利用特征线方法计算压缩机排气管的脉动气流及预测噪声

本文根据压缩机排气管的边界条件和初始条件,用特征线方法计算排气管的脉动气流。理论计算与试验结果较为符合。并根据声学理论分析排气噪声,提出理论上的予计及试验实测压缩机排气噪声的一种方法。     

海事直升机垂直下降涡环状态实验研究

直升机涡环状态严重影响飞行安全,其气流特性非常复杂,难以准确计算。本文在旋臂机设备上开展了涡环状态的专题实验,首先介绍了旋臂机的组成以及模型子系统、控制子系统和测试及数据采集子系统的工作特点。然后说明实验过程及实验数据处理方法。进行了不同总距、不同下滑角以及不同垂直速度的直升机下降实验,并测量其气流特性。最后以实验数据为基础,分析了在悬停状态、低速下降状态、涡环状态前期、中期及后期扭矩平均值和脉动幅度、拉力平均值和脉动幅度随下降速度的变化关系,确定了涡环状态的一般规律,探讨了涡环状态的改出方法。本文结果可为保证飞行安全提供参考。     

孔板空调风口送风射流的数值模拟

介绍Ｎ点风口模型用于数值模拟室内空气流动时描述孔板类送风口的入流边界条件．然后采用该风口模型对不同的孔板风口出流条件算例进行数值计算，并就轴心速度衰减、射流扩展角以及断面流速分布等射流特性与实验数据进行了对比．比较结果表明，Ｎ点风口模型用于描述数值模拟室内空气流动的孔板类风口入流边界条件，可以获得工程上足够满意的结果．     

有限周期微穿孔波纹板吸声体吸声性能研究

为了推动微穿孔吸声体(MPA)在工程中的实际应用,本文采用数值仿真方法,研究了有限尺寸的微穿孔波纹板吸声体的吸声性能.首先,基于微穿孔板阻抗理论,并将平面波谱法和有限元分析方法耦合起来,构造了微穿孔波纹板吸声体(CMPA)的三维仿真模型,给出了在声波垂直入射和斜入射工况下,吸声体声学性能的计算列式;然后,应用有限元软件COMSOL,模拟了有限周期CMPA的吸声性能,分析了波纹深度和波纹间距与吸声性能之间的关系,以及声波入射方向对吸声性能的影响;最后,为改善吸声体对声波方向的敏感性,设计了双向波纹状微穿孔板吸声体.结果表明,在声波垂直入射和斜入射的工况下,相对于传统的平直微穿孔板吸声体,波纹板吸声体具有更好的吸声性能,包括更高的吸声系数和更宽的有效吸声频带;双向波纹板吸声体能显著改善单向波纹板对声波入射方向的敏感性,实现在更大声波入射角范围内的有效吸声,如当入射声波方位角任意且入射角在0°～45°范围内时,双向波纹板吸声体,在500～2500 Hz范围内的吸声系数都大于0.7,表现出了优良的吸声性能.     

无穷大周期加筋微穿孔板结构振动响应及吸声特性

研究在平面声波斜入射情况下,无穷大双周期加筋的微穿孔薄板结构的振动响应及吸声性能.首先在马大猷和Takahashi微穿孔板声学理论基础上,建立了微穿孔加筋薄板结构振动的半解析模型;然后应用傅里叶变换及空间波数分析方法,将周期加筋微穿孔薄板的振动位移及辐射声压表示为频域内波数的分量迭加形式;最后通过对波数分量进行求解,并利用傅里叶逆变换得到双周期加筋的微穿孔薄板的振动响应及吸声系数表达式.计算结果表明,薄板的弯曲振动在水中对吸声的影响较大,空气中仅对轻质穿孔板的低频吸声效果有一定影响;同时微穿孔率对周期加筋薄板吸声系数的影响明显,通过改变穿孔率和加筋周期等可有效地提高水中微穿孔薄板结构的吸声性能.     

基于声涡转化对穿孔板切向流效应的研究

建立了一种有关切向流对小孔声阻抗影响的小扰动势流模型,其要点是使用法向质点速度连续而非广为采用的质点位移连续边界条件来匹配小孔剪切层两侧的声场,并在小孔前缘施加 Kutta条件以反映切向流效应的机理——锐缘处的声涡转化;模型中还考虑了实际应用中经常遇到的小孔形状和穿孔板厚度两个重要因素.理论预测的声阻和声抗与实验结果吻合良好.     

Experimental investigation on the distribution uniformity and pressure drop of perforated plate distributors for the innovative spray-type packed bed thermal storage

As an innovative thermal energy technology, the spray-type packed bed has advantages of high efficiency and low cost. A liquid distributor is the key component for the spray-type packed bed for scattering heat-transfer liquid drops evenly. In this study, the distribution performance and pressure drop of the perforated plate distributors of different orifice diameters were studied experimentally. The experimental results indicate that orifice diameter has a greater effect on the distribution performance compared to flow rate. With an increase in flow rate, the flow pattern through the distributor changes from the uncovered drop to the covered drop and then to the jet flow. The covered drop pattern shows the best performance with a good distribution and a small pressure drop simultaneously, which is the design and optimization principle of the distributor for a spray-type packed bed.     

Effect of obstacle size and spacing on the initial stage of flame acceleration in a rough tube

Experiments were conducted to study flame acceleration in an orifice plate laden detonation tube. Orifice plate area blockage and spacing were varied to determine their affect on flame acceleration. The tube used in the study was 3.05 m long with an inner diameter of 14.0 cm. Experiments were primarily carried out with stoichiometric propane-air, however the affect of mixture reactivity was also investigated by varying the mixture equivalence ratio. The distance required for the flame to achieve a velocity equal to the speed of sound in the unburned gas mixture was measured. This run-up distance is used to characterize the early stage of the flame acceleration process. It was found that in all cases, the flame run-up distance decreased with increased blockage ratio and with increased mixture reactivity. It was found that for higher blockage ratios plates flame acceleration was greatest for a plate spacing of one tube diameter, but for lower blockage ratio plates the results obtained for one-half, one, and one and one-half tube diameter plate spacing were very similar. The most rapid flame acceleration was observed when the ratio of the orifice plate spacing and the orifice plate height (half of the difference between the tube and orifice plate diameter) is on the order of 5. It is proposed that this optimum acceleration corresponds to the condition where the plate spacing is roughly equal to the length of the unburned gas re-circulation zone downstream from the orifice plate. PACS 47.40.-x; 47.70.Fw This paper was based on work that was presented at the 19th Interna-tional Colloquium on the Dynamics of Explosions and Reactive Sys-tems, Hakone, Japan, July 27 - August 1, 2003     

Numerical and experimental study of an innovative pipeline design in a granular pneumatic-conveying system

During gas–solid mixture conveying in a dense phase, material is conveyed in dunes on the bottom of the pipeline, or as a pulsating moving bed. This phenomenon increases the pressure drop and power consumption. We introduce a new technique to reduce the pressure drop, which is termed the perforated double tube. To validate this new model, the gas–solid flow pattern and pressure drop were studied numerically and experimentally. The power consumption was also studied experimentally. Numerical studies were performed by the Eulerian–Lagrangian approach to predict gas and particle movement in the pipeline. Comparisons between the numerical predictions and the experimental results for the gas–solid flow patterns and pressure drop show good agreement.     

爆轰产物压力势能缓释方法研究

为扩大脉冲爆轰技术的应用领域 ,抑制其振动、噪声等不利因素 ,提高能源转换效率的可能性 ,本文通过实验和数值计算 ,研究了单次爆轰产物通过孔盘将压力势能缓慢释放到相邻腔体的现象。实验在长 2m、内径 40mm的爆轰管中进行 ,数值模拟采用自适应的有限体积方法和有限速率化学反应模型。实验和数值模拟分析的结果均表明 ,在爆轰管与相邻腔体之间放置孔径适当的隔离孔盘 ,可以使爆轰产物的压力势能逐渐地传递到腔体内 ,造成随时间逐渐上升的压力分布。     

On some conditions for detonation initiation downstream of a perforated plate

An experimental study is presented of the influence of detonation wave parameters and detonation product composition upstream of a perforated plate on the onset of detonation downstream. Experiments were performed in detonation tube 106 mm in diameter, separated into two sections by a perforated plate combined with a diaphragm. The tube was equipped with pressure sensors and a semi-cylindrical smoked foil. Hydrogen–air mixtures with different hydrogen concentrations were used upstream and downstream of the perforated plate. It is shown for mixtures containing 25 and 34 % of hydrogen in air that the onset of detonation downstream depends on detonation parameters upstream of the perforated plate. An increase in the initial pressure upstream of the plate leads to detonation initiation immediately downstream. The variation of mixture composition upstream of a perforated plate does not affect on detonation initiation downstream under the present experimental conditions.     

On cooling behavior of a vertical plate in a phase change material/water composite enclosure under pulsating heat load

This paper presents a numerical and experimental study concerning cooling characteristics of a pulsating heated vertical plate sandwiched between a substrate of phase change material (PCM) and an enclosure of water, forming a composite vertical rectangular enclosure. The vertical plate is assumed to have a uniform pulsating (on/off) volumetric heat source. The PCM considered in the present study is n-Octadecane. In the finite-difference simulation, the two-dimensional buoyancy-driven fluid flows developed in both the water-filled subenclosure and the molten PCM region of the PCM-filled subenclosure were modeled as laminar Newtonian fluid flow adhering to the Boussinesq approximation. Meanwhile, two-dimensional conduction is accounted for the plate heater as well as the solid PCM zone. Numerical results are presented to unveil the cooling behavior of the pulsating heat-generating plate through the PCM substrate and water-filled enclosure. Results of the parametric simulations reveal that the water layer has the better capability of heat dissipation than the PCM substrate. Heat dissipation from the plate through the PCM substrate is mainly via the latent heat absorption as associated with melting phenomenon. Moreover, numerical results obtained are compared with the corresponding experiments.     

Oscillations of flow past perforated and slotted plates: attenuation via a leading-edge ramp

The present investigation aims to attenuate purely hydrodynamic, long-wavelength, self-excited oscillations of flow past a perforated or slotted plate by deflection of the inflow with a small ramp located at the leading-edge of the plate. Digital particle image velocimetry is complemented by unsteady pressure measurements to determine the underlying physics associated with attenuation of the oscillations. Irrespective of whether a perforated or slotted plate is employed, complete attenuation of the pressure fluctuations associated with the oscillation can be achieved for dimensionless deflection ratios of h/L ≥ 0.035, in which h is the height of the ramp and L is the effective plate length. The attenuation of the self-excited oscillation involves: a steady jet at the trailing-edge of the plate directed into the cavity; a lower magnitude upstream-oriented counterflow along the backside of the plate; and jet-like flows through the plate openings to satisfy the entrainment demands of the separating shear layer.     

爆轰波透射孔栅形成的高速爆燃波的结构和行为

以实验为主,研究光滑直管中乙炔氧气爆轰波透射孔栅形成的高速爆燃波结构和行为。实验以基于纹影平台的高速转鼓摄影记录孔栅下游近场内初始爆燃波的结构和发展,并以压力传感器跟踪其后继走向。研究发现,高速爆燃波是前驱激波和火焰的组合结构,随着初始压力的提升,它分别表现为紧随于前驱激波的层流和湍流燃烧火焰。入射爆轰胞格尺度小于或与孔栅扰动尺度相当时,湍流燃烧在下游近场迅速形成;层流结构的爆燃波通常无法抵制背景稀疏波而走向衰弱,而湍流燃烧结构可发生加速和向爆轰的转捩;他们之间存在一个不稳定的临界状态,高速爆燃波得以以0.5~0.6倍CJ爆轰速度传播较长距离,这一状态对应于双间断Rankine-Hugoniot关系的等容燃烧解。     

Attenuation of shock waves propagating over arrayed baffle plates

The paper reports results of shock tube experiments of the attenuation of shock waves propagating over arrayed baffle plates, which is motivated to simulate shock wave attenuation created accidentally at the acoustic delay line in synchrotron radiation factory upon the rupture of a metal membrane separating the acceleration ring at high vacuum and atmospheric test chambers. Experiments were carried out, by using double exposure holographic interferometry with double path arrangement, in a 100 mm×180 mm shock tube equipped with a test section of 180 mm×1100 mm view field. Two baffle plate arrangements were tested: Oblique and staggered baffle plates; and vertical symmetric ones. Pressures were measured along the shock tube sidewall at individual compartments for shock Mach numbers ranging from 1.2 to 3.0 in air. The results were compared with a numerical simulation. The rate of shock attenuation over these baffle plates was compared for vertical and oblique baffle plates. Shock wave attenuation is more pronounced in the oblique baffle plate arrangements than in the vertical ones. PACS 47.40.Nm; 42.40.Kw Communicated by C. Needham