控制閥口氣穴的發(fā)生和發(fā)展

1、控制閥口氣穴的發(fā)生和發(fā)展摘要?dú)庋ㄊ且簤合到y(tǒng)中常見(jiàn)的一種有害現(xiàn)象，經(jīng)常發(fā)生在閥口附近。不僅破壞了流體的連續(xù)性、降低了介質(zhì)的物理特性，而且引起振動(dòng)和噪聲。同時(shí)系統(tǒng)效率降低，動(dòng)態(tài)特性惡化。近年來(lái)隨著純水液壓技術(shù)的發(fā)展，氣穴及其引起的氣蝕問(wèn)題變得尤為突出，直接影響到閥的性能與壽命。因此，為了設(shè)計(jì)低噪聲、低能耗、高效率的液壓閥，研究如何控制閥口氣穴的發(fā)生和發(fā)展非常重要。本課題針對(duì)溢流閥閥口的氣穴現(xiàn)象，用計(jì)算流體動(dòng)力學(xué)的方法對(duì)錐閥和球閥閥口氣穴流場(chǎng)進(jìn)行了數(shù)值模擬，預(yù)測(cè)了氣穴發(fā)生區(qū)域，模擬得到的氣體體積比分布與可視化實(shí)驗(yàn)得到的數(shù)字圖像處理后的氣穴圖象非常吻合，驗(yàn)證了數(shù)值計(jì)算的正確性。進(jìn)一步分析了錐閥、球閥和

2、純水液壓錐閥閥口幾何參數(shù)與邊界條件對(duì)氣穴的影響。最后，對(duì)溢流閥閥芯形狀進(jìn)行了改進(jìn)，通過(guò)對(duì)不同結(jié)構(gòu)的化實(shí)驗(yàn)和噪聲測(cè)試，實(shí)驗(yàn)結(jié)果與流場(chǎng)分析結(jié)果一致，改進(jìn)后的閥氣穴強(qiáng)度和噪聲均得到降低。首先，本課題針對(duì)錐閥閥口噴流的特點(diǎn)，將質(zhì)量轉(zhuǎn)移方程和氣體體積比方程引入rngk-湍流模型，并與兩層近壁模型相結(jié)合，運(yùn)用商業(yè)化的cfd軟件fluent對(duì)錐閥閥口的氣穴流場(chǎng)進(jìn)行了數(shù)值模擬，預(yù)測(cè)了氣穴發(fā)生后的氣體體積比分布。可視化實(shí)驗(yàn)運(yùn)用工業(yè)纖維鏡與高速攝像機(jī)等組成流場(chǎng)可視化試驗(yàn)系統(tǒng)，多方位地觀察了閥口附近的氣穴現(xiàn)象，對(duì)其進(jìn)行數(shù)字圖像處理后，獲得了氣穴流場(chǎng)的分布信息，與仿真結(jié)果比較，吻合良好，表明rngk-湍流模型能有效地

3、描述錐閥等液壓元件的閥口氣穴流動(dòng)。實(shí)驗(yàn)同時(shí)采用渦流式位移傳器、激光位移器和數(shù)字應(yīng)變測(cè)量?jī)x等構(gòu)成的檢測(cè)系統(tǒng)，研究了氣穴流場(chǎng)誘發(fā)的閥體與閥芯振動(dòng)。而且對(duì)錐閥在不同進(jìn)口速度和不同出口面積的流場(chǎng)分別進(jìn)行了模擬。其次，在些基礎(chǔ)上，進(jìn)一步對(duì)純水液壓錐閥閥口的穴流場(chǎng)進(jìn)行了研究，給出了不同閥口開度、不同閥芯錐角、不同進(jìn)口流速和不同出口壓力下的氣穴流場(chǎng)分布。分析了進(jìn)口流速、出口壓力、閥口開度和閥芯錐角對(duì)純水液壓錐閥閥口氣穴強(qiáng)度的影響。然后，對(duì)實(shí)驗(yàn)觀察到的球閥閥口周期性氣穴現(xiàn)象進(jìn)行了流場(chǎng)分析?？梢暬瘜?shí)驗(yàn)運(yùn)用高速攝像機(jī)觀察到球閥閥口氣穴現(xiàn)象以2500hz的頻率周期性的發(fā)生。并對(duì)球閥有無(wú)氣穴現(xiàn)象分別進(jìn)行了噪聲測(cè)試和頻

4、譜分析。小球及小球彈性系統(tǒng)在軸向的固有頻率遠(yuǎn)小于2500hz。因此推測(cè)小球有橫向振動(dòng)，而且小球的橫向振動(dòng)使氣穴現(xiàn)象周期性發(fā)生。為了驗(yàn)證實(shí)驗(yàn)的結(jié)論，本課題對(duì)球閥閥口三維氣穴流場(chǎng)進(jìn)行了數(shù)值模擬。比較了模擬得到的對(duì)稱與非對(duì)稱氣穴區(qū)域與實(shí)驗(yàn)觀察到的氣穴云變化，比較吻合。進(jìn)一步合理地預(yù)測(cè)小球的橫向振動(dòng)使的氣穴現(xiàn)象周期性發(fā)生，提示了球閥內(nèi)的周期性氣穴的影響，為了抑制球閥內(nèi)的周期性氣穴內(nèi)發(fā)生機(jī)理振動(dòng)、噪聲的關(guān)系。最后，針對(duì)閥口形狀對(duì)氣穴的影響，為了抑制閥口氣穴，對(duì)溢流閥閥芯形狀進(jìn)行了改進(jìn)，設(shè)計(jì)了幾種不同的閥芯結(jié)構(gòu)，分別對(duì)不同的閥芯進(jìn)行了氣穴流場(chǎng)分析和比較，來(lái)尋求優(yōu)化的閥芯結(jié)構(gòu)。實(shí)驗(yàn)采用透明的閥體，分別對(duì)改進(jìn)

5、前后不同閥芯閥口氣穴現(xiàn)象進(jìn)行了可視化實(shí)驗(yàn)觀察和相應(yīng)的噪聲測(cè)試和頻譜分析。比較相同條件下氣穴發(fā)生過(guò)程，氣穴云的變化形態(tài)及噪聲頻譜分析。實(shí)驗(yàn)結(jié)果與數(shù)值分析結(jié)果比較吻合，最后得到一種優(yōu)化的閥芯結(jié)構(gòu)，在相同的工況下，它的氣穴區(qū)域和強(qiáng)度均比較小，而且噪聲得到降低。關(guān)鍵詞：溢流閥 氣穴 流場(chǎng)仿真 流動(dòng)可視化實(shí)驗(yàn) 噪聲測(cè)試 頻譜分析abstract cavitation is a common harmful phenomenon in hydraulic transmission systems, frequently occurs near the orifice of the valves. it n

6、ot only damages flow continuity and reduces medium physical performance, but also induces vibration and noise. at the same time, the efficiency of a system is reduced due to cavitation, especially dynamic performances are deteriorated. in recent years, with the development of water hydraulic technol

7、ogy, cavitation problem and erosion due to cavitation became especially predominant, which directly effect performance and lifetime of the valves. therefore, the research of how to control cavitation inception and development is absolutely important in order to design low noise, low energy loss and

8、high efficiency valve. in this article, aiming at the cavitation near the orifce of the relief valves, computational fluid dynamics (cfd) simulations of cavitating flow through poppet valve and ball valve were performed, cavitation region were predicted. the numerically obtained air volume fraction

9、distribution showed a good agreement with the experimentally visualized cavitation image through digital processing, which verifies the accuracy of simulation. furthermore, the effects of inlet velocity, outlet pressure, opening size as well as cone angle on cavitation intensity in the poppet valve,

10、 ball valve and water hydraulic poppet valve were numerically investigated. at last, the configuration of a relief valve were improved, the cavitating flow simulation. at the same time, flow visualization and noise measurement were conducted for different configurations of relief valve. the experime

11、ntal results agree well with numerical results. the cavitation intensity and noise and noise level of the developed relief valve are decreased. first, applying commercial cfd software fluent, the cavitating flow issuing from the orifice of a poppet valve was numerically investigated using rng - turb

12、ulence model combined with mass transfer equation, volume fraction equation and two layer zonal model. the air volume fraction distribution was predicted. the finished experiments are conducted to catch cavitation images around the valve seat of the poppet valve from the perpendicular directions, us

13、ing a pair of industrial fiberscopes and high-speed video cameras integrated visualization system. the results therefore indicate that rng turbulence model could achieve a reasonable prediction for the cavitating flow within the poppet valve as well as other hydraulic components. besides, the vibrat

14、ions of the valve body and poppet induced by the cavitating flow are detected using vortex displacement transducer, laser displacement meter and digital strain device. moreover, the cavitatig flow in poppet valve were simulated for different inlet velocity and different outlet area, respectively. se

15、condly, based on the above study, furthermore, the cavitating flow through a water hydraulic popper valve were performed. the flow field distribution were obtained with different inlet velocity, different outlet pressure, different opening size as well as different cone angle. the effects of inlet v

16、elocity, outlet pressure, opening size as well as cone angle on cavitation intensity in the water hydraulic poppet valve were numerically investigated. afterwards, the periodical cavitation inception near the orifice of a ball valve was numerically analysed. the visualized cavitation occurs near ori

17、fice periodically in experiment and its frequency is about 2500 hz using high speed video camera. furthermore, the noise spectrums of the ball valve in cavitation and non-cavitation cass are measured. the natural frequency of the ball in the axial direction is far from 2500hz. therefore, it is expec

18、ted that the ball vibrates in the lateral direction and the periodic cavitation occurs due to the lateral vibration of the ball. in order to verify above results, the three-dimensional cavitating flow issuing from the orifice of a ball valve was numerically investigated, the cavitation region was pr

19、edicted for axisymmetric and non-axisymmetric case when the ball moves to one side. the predicted cavitation region for axisymmetric and non-axisymmetric case was compared with experimentally visualized cavitation image. the predicted and observed cavitation region agrees well. therefore, it was exp

20、ected reasonably that the ball vibrates in the lateral direction and cavitation occur frequently. the relationship between periodical cavitation inception and vibration was disclosed. at last, according to the effect of orifice configuration on the cavitation, the several poppet configurations of a relief valve were designed in order to suppress cavitation, the cavitating flow simulation for different configura