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)展摘要氣穴是液壓系統(tǒng)中常見的一種有害現象，經常發(fā)生在閥口附近。不僅破壞了流體的連續(xù)性、降低了介質的物理特性，而且引起振動和噪聲。同時系統(tǒng)效率降低，動態(tài)特性惡化。近年來隨著純水液壓技術的發(fā)展，氣穴及其引起的氣蝕問題變得尤為突出，直接影響到閥的性能與壽命。因此，為了設計低噪聲、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。本課題針對溢流閥閥口的氣穴現象，用計算流體動力學的方法對錐閥和球閥閥口氣穴流場進行了數值模擬，預測了氣穴發(fā)生區(qū)域，模擬得到的氣體體積比分布與可視化實驗得到的數字圖像處理后的氣穴圖象非常吻合，驗證了數值計算的正確性。進一步分析了錐閥、球閥和

2、純水液壓錐閥閥口幾何參數與邊界條件對氣穴的影響。最后，對溢流閥閥芯形狀進行了改進，通過對不同結構的化實驗和噪聲測試，實驗結果與流場分析結果一致，改進后的閥氣穴強度和噪聲均得到降低。首先，本課題針對錐閥閥口噴流的特點，將質量轉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合，運用商業(yè)化的cfd軟件fluent對錐閥閥口的氣穴流場進行了數值模擬，預測了氣穴發(fā)生后的氣體體積比分布?？梢暬瘜嶒炦\用工業(yè)纖維鏡與高速攝像機等組成流場可視化試驗系統(tǒng)，多方位地觀察了閥口附近的氣穴現象，對其進行數字圖像處理后，獲得了氣穴流場的分布信息，與仿真結果比較，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。實驗同時采用渦流式位移傳器、激光位移器和數字應變測量儀等構成的檢測系統(tǒng)，研究了氣穴流場誘發(fā)的閥體與閥芯振動。而且對錐閥在不同進口速度和不同出口面積的流場分別進行了模擬。其次，在些基礎上，進一步對純水液壓錐閥閥口的穴流場進行了研究，給出了不同閥口開度、不同閥芯錐角、不同進口流速和不同出口壓力下的氣穴流場分布。分析了進口流速、出口壓力、閥口開度和閥芯錐角對純水液壓錐閥閥口氣穴強度的影響。然后，對實驗觀察到的球閥閥口周期性氣穴現象進行了流場分析。可視化實驗運用高速攝像機觀察到球閥閥口氣穴現象以2500hz的頻率周期性的發(fā)生。并對球閥有無氣穴現象分別進行了噪聲測試和頻

4、譜分析。小球及小球彈性系統(tǒng)在軸向的固有頻率遠小于2500hz。因此推測小球有橫向振動，而且小球的橫向振動使氣穴現象周期性發(fā)生。為了驗證實驗的結論，本課題對球閥閥口三維氣穴流場進行了數值模擬。比較了模擬得到的對稱與非對稱氣穴區(qū)域與實驗觀察到的氣穴云變化，比較吻合。進一步合理地預測小球的橫向振動使的氣穴現象周期性發(fā)生，提示了球閥內的周期性氣穴的影響，為了抑制球閥內的周期性氣穴內發(fā)生機理振動、噪聲的關系。最后，針對閥口形狀對氣穴的影響，為了抑制閥口氣穴，對溢流閥閥芯形狀進行了改進，設計了幾種不同的閥芯結構，分別對不同的閥芯進行了氣穴流場分析和比較，來尋求優(yōu)化的閥芯結構。實驗采用透明的閥體，分別對改進

5、前后不同閥芯閥口氣穴現象進行了可視化實驗觀察和相應的噪聲測試和頻譜分析。比較相同條件下氣穴發(fā)生過程，氣穴云的變化形態(tài)及噪聲頻譜分析。實驗結果與數值分析結果比較吻合，最后得到一種優(yōu)化的閥芯結構，在相同的工況下，它的氣穴區(qū)域和強度均比較小，而且噪聲得到降低。關鍵詞：溢流閥 氣穴 流場仿真 流動可視化實驗 噪聲測試 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