【作者】 付燕霞；

【导师】 袁寿其；

【作者基本信息】 江苏大学 ， 流体机械及工程， 2014， 博士

【摘要】 本文是在国家自然科学基金重点项目“水力机械空化特性及对策”（51239005）、国家自然科学基金项目“离心泵进口流场畸变诱导低频频率特性的研究”（51349004）和江苏省博士创新计划“离心泵内部低频汽蚀机理及规律研究”（CXLX11₀577）的资助下开展工作的。涡轮泵是液体火箭动力装置系统的重要组件之一,必须满足在高温高压的苛刻环境下安全工作的需要。随着航天技术的进一步发展,涡轮泵的高效、高抗空化性及其稳定运行是火箭动力装置的关键指标。目前,在火箭发动机涡轮泵前加装诱导轮已成为保证涡轮泵获取优越空化性能的关键技术。通过在涡轮泵前加装诱导轮,主要目的是对推进剂进行加压,从而产生一定的扬程来提高涡轮泵叶轮入口压力,进而可避免涡轮泵内部发生空化破坏和产生不稳定流动现象,以提高涡轮泵的抗空化性能。因此,本文基于数值模拟和实验相结合的方法对涡轮泵及诱导轮的水力性能、空化特性及其不稳定流动特性进行了系统的研究。本文的主要工作和创新性成果有：1.总结了火箭发动机涡轮泵及诱导轮的国内外研究现状：包括诱导轮的类型、内部流动理论及其内部流动不稳定现象,例如,旋转失速、旋转颤振、喘振现象、旋转空化、不对称叶片空化、回流漩涡空化及高阶旋转不稳定现象的发生条件,以及它们相应的特性。2.总结了意大利比萨航空推进公司Alta空化泵转子动力测试系统CPRTF的主要测试设备、测试功能及相关试验内容的实验步骤：如水力性能测试、空化性能试验以及压力脉动试验等。同时,也介绍了涡轮泵及诱导轮内部非定常流动与空化流动的数值模拟理论与方法。3.系统地研究了预测火箭涡轮泵及诱导轮内部流动及其水力性能的方法：考虑了不同网格、边界条件、湍流模型、进出管道长度、进出口静压读取位置以及工作介质温度对DAPROT3诱导轮与VAMPIRE涡轮泵水力性能的影响,并通过与其相应的试验数据对比。研究结果表明,DAPROT3诱导轮性能受湍流模型、进出口管道长度、进出口静压采集位置、叶顶间隙,以及温度的影响较大,尤其在小流量下这一影响更明显；基于较短的进出口管道与叶顶间隙较小（0.8mm）的DAPROT3诱导轮扬程-流量曲线明显较高于进出口管道较长且叶顶间隙较大的DAPROT3诱导轮扬程-流量曲线。但这些因素对VAMPIRE涡轮泵水力性能的计算结果影响较小。结果表明DAPROT3诱导轮与VAMPIRE涡轮泵水力性能的计算结果与其试验结果吻合较好。4.针对不同温度对各工况下VAMPIRE涡轮泵与2种不同叶顶间隙的DAPROT3诱导轮的空化流动同时进行了数值模拟与实验研究。结果表明,在小流量工况下,叶顶间隙为0.8mm的DAPROT3诱导轮在温度升高时其整个空化性能影响不大；随着叶顶间隙的增加,DAPROT3诱导轮内部发生了不稳定空化现象,使得诱导轮扬程出现振荡变化的趋势。另外,针对DAPROT3诱导轮的内部空化流动数值模拟结果与空化可视化试验研究结果进行对比,发现DAPROT3诱导轮叶片上的空泡分布与其空化可视化实验中各叶片前缘及叶片背面出现的空泡体积分布规律吻合较好。而在小流量下与大流量下VAMPIRE涡轮泵的空化特性出现明显不同,且受温度的影响较显著。5.首次通过数值模拟与实验相结合的方法,研究低温与高温下加装与不加装DAPROT3诱导轮对VAMPIRE涡轮泵的水力性能与空化性能的影响,发现加装DAPROT3诱导轮对各小流量工况下VAMPIRE涡轮泵的扬程影响较大,VAMPIRE涡轮泵的空化性能得到明显改善。6.首次获得基于Rayleigh-Plesset均相流空化模型预测常温下VAMPIRE涡轮泵扬程下降3%以前的空化性能相对准确,且预测高温下VAMPIRE涡轮泵扬程下降5%相对准确的结论；但当涡轮泵内部发生较严重的空化,扬程下降量为5%-10%时,该均相流空化模型预测涡轮泵的性能与其试验结果存在一定的偏差。可见,基于Rayleigh-Plesset均相流空化模型在高温与空化发生较严重时,其预测结果有局限性。7.通过DAPROT3诱导轮叶片内部非定常数值模拟与压力脉动实验研究,首次针对不同工况下DAPROT3诱导轮内部不稳定流动现象进行了分类研究。结果表明,在小流量工况下,DAPROT3诱导轮中轴频及其以下的频率占主导地位,说明小流量工况下其内部存在较复杂的不稳定流动现象。8.针对IS65-50-160型低比转速离心泵内部流动不稳定现象与空化流动进行数值模拟与试验研究,得到小流量下模型泵空化性能曲线上在扬程突降前存在的-段匍匐下降区域与σ/2a的关系。通过压力脉动试验发现,各小流量工况下,模型离心泵进口管道内的压力脉动主频均在48.2Hz-51.2Hz范围内,说明此时泵内产生了旋转空化现象。9.综合小流量工况下IS65-50-160型低比转速离心泵与VAMPIRE涡轮泵内部空化流动的数值模拟与试验研究结果,可发现它们内部均出现了不稳定空化现象,例如旋转空化或不对称叶片空化现象等。更多还原

【Abstract】 This work is supported by the State Key Program of National Natural Science Funds of China "Cavitation Characteristics and its Countermeasures of Hydraulic Machinery"（Grant No.51239005）, National Natural Science Funds of China "Low Frequency Characteristics Induced by Inlet Deformation Within Centrifugal Pumps"（Grant No.51349004）, and Jiangsu Provincial Project for Innovative Postgraduates "The Mechanism and Characteristics of Low-Frequency Cavitation in the Centrifugal Pump"（Grant No. CXLX11₀577）.As one of the critical components of the liquid propellant rocket engines, the turbopump should be capable of meeting the requirement of operating under high pressure and temperature condition. As the development of aerospace technology, the turbopump with high efficiency and cavitation performance becomes one of the key impacts of the space rocket transportation system. Current rocket turbopump often employs an inducer upstream to improve the suction performances. The main role of an inducer is to pressurize the flow sufficiently to increase the head as well as the inlet pressure of the impeller of the turbopump to avoid unacceptable cavitation and flow instabilities. Therefore, the hydraulic performances, cavitation characteristics associated with the flow instabilities in the inducer and the turbopump were studied based on CFD and experimental methods in this dissertation. The main work and creative achievements are:1. The present research work both at home and abroad on the rocket engine inducer and turbopump has been systematically reviewed, including the type of inducer, the internal flow theory as well as the onset and the characteristics of flow instabilities, for example, rotating stall, rotating chock, surge, rotating cavitation, asymmetric blade cavitation, backflow vortex cavitation and high-order rotating instabilities.2. The main test facilities, test items in the CPRTF （Cavitating Pump Rotordynamic Test Facility） at Alta, Pisa, Italy, as well as the corresponding experimental procedures such as hydraulic performances, cavitation performances and pressure fluctuation were systematically overviewed. Meanwhile, the basic theory and approaches for numerically simulating the unsteady flow and cavitating flow in the turbopump and inducer has been also briefly introduced. 3. The numerical approach of predicting the internal flow and the hydraulic performances of the VAMPIRE turbopump and DAPROT3inducer under different working fluid temperatures were systematically investigated by considering the following factors:the mesh elements, the boundary conditions, turbulence models, the lengths of inlet and outlet pipes, and the locations of the inlet and outlet pressure taps. The results showed that:these factors such as turbulence models, the lengths of the inlet and outlet pipes, the positions of the inlet and outlet pressure taps for measuring the pressure as well as the working fluid temperatures, had a significant influence on the hydraulic performances of the DAPROT3inducer, especially at low flow rates; the H-Q curves of the DAPR0T3inducer based on the short inlet and outlet pipes as well as the small tip clearance （0.8mm） is positioned above those based on the long inlet and outlet pipes. However, these above factors had less effect on predicting the hydraulic performances of the VAMPIRE Turbopump. Finally, the hydraulic performances of the VAMPIRE Turbopump and the DAPROT3inducer predicted by CFD are in good agreement with their corresponding experimental data.4. The cavitating flow in both the VAMPIRE turbopump and the DAPROT3inducer with two different tip clearances under different water temperatures were investigated for a wide range of flow rates based on numerical and experimental methods. It can be found that at low flow rates, the temperature increase has less effect on the suction performances of the DAPROT3inducer with the tip clearance of0.8mm; as the tip clearance increased, the cavitation induced flow instabilities occurs, causing an oscillating portion to the head-drop curve of the DAPROT3inducer. In addition, in comparison with the cavitating flow patterns on each blade leading edge based on the flow visualization test on DAPROT3inducer, it can be found that the vapor volume distribution obtained from the numerical simulations were in good agreement. The cavitation characteristics of the VAMPIRE turbopump at low flow rates are different from those at high flow rates, which could be easily affected by the working fluid temperature.5. The pumping and the suction performances of the VAMPIRE turbopump with or without the DAPROT3inducer under low and high water temperatures have been investigated based on CFD and experimental methods, and it could be found that the hydraulic performances of the VAMPIRE turbopump with the DAPROT3inducer has obviously changed, especially at low flow rates. The cavitation performances of the VAMPIRE turbopump have been significantly improved.6. The homogeneous cavitation model based on Rayleigh-Plesset equations could provide a more accurate prediction of the cavitating flow in the VAMPIRE turbopump as the head-drop was less than3%at low temperature, while for a high temperature that amount of the head-drop was less than5%. However, this cavitation model has the limitation in predicting the serious cavitation occurring in the turbopump when its head-drop amount was in the range between5%and10%.7. The numerical simulations for the unsteady flow in the DAPROT3inducer were carried out for different flow rates. The characteristics of flow instabilities in the DAPROT3inducer were first clarified in present study. Meanwhile, a series of pressure fluctuation tests were further carried out to investigate the cavitation induced flow instabilities. It can be found that the main frequencies in the DAPROT3inducer were or even lower than the rotational frequency in low flow rates, indicating the complex flow phenomena like flow instability occurring.8. The characteristics of flow instabilities as well as the cavitation phenomenon in a centrifugal pump typed IS65-50-160operating at low flow rates were studied by experimental and numerical methods, respectively. Cavitation proved to occur over a wide range of low flow rates, producing a characteristic creeping shape of the head-drop curve and depend on the parameter σ/2α, which is the relationship between the flow incidence angle and cavitation number. The experimental results of the pressure fluctuation showed that the unsteady behavior of the internal flow in the centrifugal pump operating at low flow rates had the characteristics of a peculiar low-frequency oscillation with the frequencies ranged from48.2Hz to51.2Hz. The pressure fluctuations were closely correlated to the flow instabilities induced by the occurrence of cavitation phenomena at low flow rates such as rotating cavitation.9. Based on numerical and experimental results of the cavitating IS65-50-160centrifugal pump and the cavitating VAMPIRE turopump, it could be found that the cavitation instabilities such as rotating cavitation or the asymmetric blade cavitation had occurred in both of them.更多还原