空泡群溃灭时作用于固壁上的压强

采用文献[3]中提出的方法,计算绕流场中空泡群溃灭时诱生的辐射压强,用它作为驱动压强对弱可压液体中固体边界附近的空泡非球对称溃灭过程及其作用于固壁的压强进行了分析。计算结果表明,近壁空泡溃灭时,因吸收其它空泡溃灭释放的能量,故增大自身空泡的溃灭压强。     

可压缩液体中游移空泡群的溃灭压力

本文建立了一个数学模型,用来计算可压缩液体中群空泡的溃灭压力。概括地说,本文认为空泡群的溃灭是分层进行的,先是与液体交界处的空泡由于液体压力作用而溃灭,先溃灭空泡的辐射压强与液体本身压强迭加,成为下一层空泡溃灭的驱动压强。应用概率理论对空泡群溃灭的统计特性进行了分析计算,结果表明空泡间的相互作用使最后溃灭的空泡产生的辐射压强提高了一个量级以上。     

有限元/边界元法求解多连通域声辐射问题

本文用混合有限元／边界元法求解浸没在无限流域中任意形状结构物的声辐射问题。求解多连通域声辐射问题时，采用有限元构建内流域和结构域，边界元构建外流域，应用流体结构域交界面法向速度连续性条件耦合声流域和结构间的相互作用。对球形结构的数值计算同其理论结果的比较表明其有效性。对环肋双层柱形结构分别对考虑和不考虑腔间进水做了计算，计算结果表明了考虑腔间进水的必要性。     

液流中边壁附近的空泡溃灭研究

本文利用高速摄影方法观测了液流中的空泡溃灭过程,分析了空泡在流动系统中溃灭时的泡壁稳定性,和由于空泡射流挟带其表面分裂出的微小泡冲击边壁,从而使微小泡在高压强作用下溃灭,造成壁面破坏的可能性。本文还研究了液体粘性变化和液体挟带颗粒对空泡微射流速度及溃灭历时的影响     

泄水建筑物防空蚀措施

空泡在流场中初生、发育、溃灭与再生过程称为空化(或称空穴)。空泡在水流边界或在边界附近溃灭时,在小面积上产生高压冲击波,固体边界受冲击波作用,导致材料剥蚀,由于水流中的空穴现象所引起固体边界的剥蚀称为空蚀。空蚀现象出现在船舶螺旋浆,水轮机、水泵及水工建筑物上。本文仅就水工建筑物上空蚀现象作简要介绍。     

固液两相流体中刚性平面边壁附近的空泡溃灭计算

本文中利用数值方法分析了固液两相流体中刚性平面边壁附近的空泡溃灭问题,讨论了固相浓度、颗粒尺寸等因素对空泡溃灭的影响以及空泡溃灭过程中的颗粒运动,并用高速摄影实测结果进行了验证。     

掺气对空泡溃灭压力的影响

本文应用空泡动力学理论计算了可压缩液体中固体边壁附近空化空泡的溃灭过程及边壁上的最大压强P_(max),比较了不同掺气量对空泡溃灭压强的影响。计算结果表明,掺气减蚀的主要原因之一是降低了流体中的音速。     

空泡溃灭的Bjerknes效应

根据Ｂｊｅｒｋｎｅｓ力的基本理论和空泡动力学方程，推导出了空泡运动时Ｂｊｅｒｋｎｅｓ力的表达式。在此基础上，对空泡溃灭时的Ｂｊｅｒｋｎｅｓ力进行了计算和分析。     

平板闸门底缘上托力的数值计算

讨论了作用在闸门上的动水压力的数值计算问题,并针对闸门底缘上托力计算引入了边界元法。计算结果表明:边界元法对于此类问题的求解是经济而有效的。     

空泡在固液两相液体中靠近刚性边壁附近溃灭的实验研究

本文利用高速摄影机观察了空泡在固液两相液体中,靠近刚性边壁附近的溃灭过程。研究了颗粒浓度及粒径对空泡溃灭的影响,以及观察和分析了空泡溃灭过程中的颗粒运动。     

掺气气泡对减压实验测量结果的影响

根据气泡的声学特性,对掺气水流中气泡可能对减压实验中声压级差和空化噪声强度测量结果造成的影响作了初步的理论探讨。研究表明,气泡对声波的吸收对空化初生的判别并无影响,对空化噪声强度的影响不可忽略。     

水吸收及距离对减压试验的影响

根据水吸收及距离引起的声波衰减计算公式,对水吸收及距离可能对减压实验中空化噪声强度测量结果造成的影响作了初步的理论探讨。研究表明,水吸收及距离产生的声衰减在一定距离范围内对空化初生的判别并无影响,超过一定距离范围则水听器监测到的空化初生判别结果不再准确。     

空化形成机理和比尺效应

高速水流容易发生空化，为进一步研究空化的形成机理和影响因素。对空化形成机理和液体粘性、表面张力、气核状况等影响因素的最新研究成果进行了综合分析。水流空化试验中存在比尺效应，指出并建立了空化比尺效应的经验公式。对空化机理的研究还有待进一步深入。     

水流初生空化噪声机理分析及试验研究

根据水流的初生空化特性,对其发生发展过程在模型和原型进行系统的试验观测。试验和理论分析表明,水流的初生空化和空蚀可以利用常压水洞来模拟。与减压箱试验结果的比较可知常压水洞更可信和合理。水流的初生空化噪声频率不仅与汽化压力和流体的特性有关,而且还与流体的环境压力分布和速度分布有关,与空化类型关系更为密切。试验和计算表明初生空化噪声频率的分布频段为10kHz—12.5kHz。     

NUMERICAL PREDICTION OF BLADE FREQUENCY NOISE OF CAVITA- TING PROPELLER

The blade frequency noise of a cavitating propeller in a uniform flow is analyzed in the time domain. The unsteady loading (of a dipole source) and the sheet cavity volume (of a monopole source) on the propeller surface are calculated by a potential-based surface panel method. Then the time-dependent pressure and the cavity volume data are used as the input for the Fowcs Williams-Hawkings formulation to predict the acoustics pressure. The integration of the noise source is performed over the true blade surface rather than the ideal blade surface without thickness. The noise characteristics of the cavitating propeller are discussed. With the sheet cavitation, the thickness (cavitation) noise is larger than the loading noise and is the dominant noise source.The noise directivity is not as clear as that of the noise under a non-cavitation condition. The cavitation noise is attenuated mores lowly than the non-cavitation noise.     

小浪底工程1号孔板泄洪洞水流空化原型试验研究

在库水位为210.18～210.28 m之间时,对小浪底水利枢纽工程1号孔板泄洪洞泄洪情况下多级孔板水流空化特性进行了原型试验。对弧形工作闸门在连续开启过程中各级孔板水流噪声的频谱分析发现,闸门孔口相对开度e/a为0.9时,第二级和第三级孔板处水流噪声声压级突然增加10 dB以上,表明开始出现空化水流,相应三级孔板的水流空化数分别为5.85、5.65和5.03,该结果与考虑缩尺影响修正后的模型试验研究结果基本一致。     

THE SIMULATION AND ANALYSIS OF TANK SLOSHING WITH POROSITY GIRDER BY MULTI-DOMAIN BOUNDARY ELEMENT METHOD

The simulations of nonlinear sloshing in both two-dimensional and three-dimensional liquid tanks with porosity girder are carried out in time domain by using the Multi-domain Boundary Element Method (MBEM). The comparison of the present results and the references is conducted and shows they agree well with each other. The three-dimensional effect and the influence of the width of liquid tank and the height and porosity of the girder on the natural period of the model are also discussed.     

Application of signal processing techniques to the detection of tip vortex cavitation noise in marine propeller

The tip vortex cavitation and its relevant noise has been the subject of extensive researches up to now. In most cases of experimental approaches, the accurate and objective decision of cavitation inception is primary, which is the main topic of this paper. Although the conventional power spectrum is normally adopted as a signal processing tool for the analysis of cavitation noise, a faithful exploration cannot be made especially for the cavitation inception. Alternatively, the periodic occurrence of bursting noise induced from tip vortex cavitation gives a diagnostic proof that the repeating frequency of the bursting contents can be exploited as an indication of the inception. This study, hence, employed the Short-Time Fourier Transform (STFT) analysis and the Detection of Envelope Modulation On Noise (DEMON) spectrum analysis, both which are appropriate for finding such a repeating frequency. Through the acoustical measurement in a water tunnel, the two signal processing techniques show a satisfactory result in detecting the inception of tip vortex cavitation.     

EXPERIMENTAL ESTIMATION OF A SCALING EXPONENT FOR TIP VORTEX CAVITATION VIA ITS INCEPTION TEST IN FULL- ANDMODEL-SHIP

Tip vortex cavitation noise of marine propeller became primary concerns to reduce hazardous environmental impacts from commercial ship or to keep the underwater surveillance of naval ships. The investigations of the tip vortex and its induced noise are normally conducted through the model test in a water cavitation tunnel. However the Reynolds number of model-test is much smaller than that of the full-scale, which subsequently results in the difference of tip vortex cavitation inception. Hence, the scaling law between model-and full-scales needs to be identified prior to the prediction and assessment of propeller noise in full scale. From previous researches, it is generally known that the incipient caivtation number of tip vortex can be represented as a power of the Reynolds number. However, the power exponent for scaling, which is the main focus of this research, has not been clearly studied yet. This paper deals with the estimation of scaling exponent based on tip vortex cavitation inception test in both full-and model-scale ships. Acoustical measurements as well as several kind of signal processing technique for an inception criterion suggest the scaling exponent as 0.30. The scaling value proposed in this study shows slight difference to the one of most recent research. Besides, extrapolation of model-ship noise measurement using the proposed one predicts the full-scale noise measurement with an acceptable discrepancy.     

三峡工程表孔体型空化试验研究

根据三峡工程溢流坝表孔设计体型,通过减压试验 ,研究了体型的空化特性。成果表明：WES曲线坝面为免空蚀体型; 挑流鼻坎虽有弱空化现象,但空蚀的可能性不大;工作门槽体现为蒸汽型空化特征,其强度 随工作水头增大而加剧。对两道门槽进行局部体型修改后,两者的空化特性均有明显的改善 。要达到完全免除空化之目的,有待进一步优化。