【正文】 the maximum and minimum pressures were fixed on the virtual line, being indifferent of the variations of the passage area ratio. 關(guān)于二 級(jí) 液壓 節(jié)流錐閥 的低汽蝕研究 摘要 ：汽蝕 對(duì) 于 液壓控制閥的性能和壽命有重要影響 ,如 引起 效率的降低 ,產(chǎn)生 強(qiáng)烈的噪音 和振動(dòng)。相關(guān)驗(yàn)證實(shí)驗(yàn)在一個(gè)定制的測(cè)試儀器中進(jìn)行。汽蝕對(duì)水液壓控制閥的性能和壽命有重要影響 ,如降低效率、強(qiáng)烈的噪聲以及嚴(yán)重的振動(dòng)。 Johnston[9]進(jìn)行了一項(xiàng)關(guān)于在提升和圓盤(pán)液壓閥中流動(dòng)和力學(xué)特性的實(shí)驗(yàn)研究 ,并采用水作為工作介質(zhì)。 Ueno [11]用實(shí)驗(yàn)和數(shù)值模擬的方法研究了用最基本的有限差分在假設(shè)沒(méi)有汽蝕在條件下對(duì)不同構(gòu)造壓力控制閥的油液流動(dòng) ,。汽蝕可能通過(guò)對(duì)一個(gè)不變排放量的固定開(kāi)啟度閥門(mén)進(jìn)行能量譜比較來(lái)檢測(cè)。 Oshima[14]通過(guò)試驗(yàn)研究了 (a)閥座的槽長(zhǎng)度和 (b)提升閥角度 ,和 (c)油溫對(duì)流動(dòng)特性和汽蝕現(xiàn)象的影響 ,并在液壓提升閥用水代替油作為工作介質(zhì)。然而 ,兩個(gè)節(jié)流閥之間的壓力被假設(shè)為常數(shù) ,這可能不適用于具有介質(zhì)腔的二級(jí)液壓閥。 通過(guò)過(guò)節(jié)流閥的壓降越大，汽蝕指數(shù)就越小 (節(jié)流閥發(fā)生汽蝕的可能性也越小 )。 數(shù)學(xué)模型 對(duì)于具有軸對(duì)稱結(jié)構(gòu)的二級(jí)節(jié)流閥，計(jì)算區(qū)域被簡(jiǎn)化為一種二維軸對(duì)稱幾何模型(ABCDE),如圖 1(a)。假定雷諾應(yīng)力和湍流的平均速度梯度動(dòng)能 (k)，與通過(guò)傳導(dǎo)方程（ 6）和（ 7）獲得的耗散速率有一定的關(guān)系。 仿真結(jié)果對(duì)兩個(gè)節(jié)流閥的介質(zhì)腔壓力變化隨著通道面積比和進(jìn)出口壓力等發(fā)生的變化進(jìn)行了較深入有效的研究。再循環(huán)將會(huì)導(dǎo)致低壓區(qū)的形成和潛在汽蝕的出現(xiàn)。當(dāng) r 在 ~ 之間時(shí) ,總壓降將被兩個(gè)串聯(lián)的節(jié)流閥共同分擔(dān)。通道截面積比 r 越大 ,虛線上的壓力等級(jí) 也越高。 。 在圖 4中顯示了通道面積比率 (r)對(duì)在入口壓力為 10兆帕出口為 4兆帕的條件下壓力 (pl)的影響。從圖 3可以看出 ,當(dāng) r 小于 ,壓降會(huì)在二級(jí)節(jié)流閥的前方或后方單獨(dú)的產(chǎn)生。當(dāng) r 小于 ,會(huì)在二級(jí)節(jié)流閥的介質(zhì)腔內(nèi)部形成水蒸氣，并且相應(yīng)的水蒸氣最大體積分?jǐn)?shù)會(huì)增加到 %,如圖 2(a)所示 。 在這些方程中 ,考慮到平均流速梯度 Gk代表了一系列的湍流動(dòng)能 。入口和出口邊界可以指定為需 要的壓力等級(jí)。 對(duì)于二級(jí)節(jié)流閥，相比較之下其汽蝕指數(shù) Kt的定義可以表達(dá)如下 P ou tPin P ou tP ou tPin PvP ou tK ??? ??t 實(shí)際上 ,對(duì)于每一級(jí)節(jié)流閥 ,在一個(gè)單級(jí)節(jié)流閥中避免汽蝕的臨界條件都應(yīng)該滿足如下條件 u t1??????K scP o u tinP P o u tK sco u tPP inP 然后利用兩個(gè)節(jié)流閥之間的介質(zhì)腔內(nèi)的壓力分布來(lái)計(jì)算每級(jí)的汽蝕指數(shù)。它表示：如果汽蝕指數(shù) K值小于 ,將發(fā)生汽蝕。汽蝕阻塞只是當(dāng)指數(shù)小于 的時(shí)候出現(xiàn)。實(shí)驗(yàn)表明錐閥的開(kāi)口和錐度對(duì)汽蝕的強(qiáng)度有非常重要的影響。兩種液壓閥在沒(méi)有汽蝕條件下得到的數(shù)據(jù)表明 ,由于閥門(mén)開(kāi)啟度和雷諾數(shù)的影響，閥 的高噴流方向的角度會(huì)發(fā)生變化。然而 ,在預(yù)測(cè)射流分離和復(fù)位時(shí)的錯(cuò)誤導(dǎo)致了定量的不精確性。 Ishihara[8]研究了不穩(wěn)定的油液流動(dòng)對(duì)小孔通道的汽蝕現(xiàn)象影響。這種系統(tǒng)特別是在鋼和玻璃生產(chǎn)、煤炭和金礦開(kāi)采、食品和醫(yī)藥加工、核電、海洋勘查、水下機(jī)器人等領(lǐng)域正變得越來(lái)越流行。通過(guò)該二級(jí)液壓節(jié)流閥得到設(shè)計(jì)的經(jīng)驗(yàn)準(zhǔn)則。 sk and s1 are the inverse effective turbulent Prandtl numbers for k and 1, respectively. Simulation results Sensitivity analyses of the variations of pressures inside the medium chamber along with the changing passage area ratio of the two throttles and the inlet and outlet pressures were performed. As a large number of numerical simulations were conducted, it is impossible to include all of the results here. Instead, representative outes are explicated to demonstrate important findings. The simulated contours of the volume fraction of water vapour are shown in Fig. 2. The passage area ratio (r) could significantly affect the cavitation occurrence and intensity under conditions of pin . 10 MPa and pout . 1 MPa. There are several key transferring points for passage area ratio including r . , , and . When r was less than , water vapour would be formed inside the medium chamber of the twostage throttle valve, and the corresponding maximum volume fraction of water vapour would increase up to per cent as shown in Fig. 2(a). This was ascribed to the high fluid velocity and the intense recirculation inside the medium chamber. The recirculation would cause the formation of a lowpressure zone and thus potential cavitation. With an increasing r level, the volume fraction of water vapour would be reduced. When r ranged from to , the maximum volume fraction of water vapour would fall (to per cent or below) and, consequently, the possibility of cavitation would decrease. However, with further increase of the passage area ratio (. when r . ), the maximum volume fraction of water vapour would increase up to – per cent as shown in Figs 2(c) and (d)。 中文 4400 字 外文翻譯 學(xué)生姓名 學(xué)院名稱 機(jī)電工程學(xué)院 專業(yè)名稱 指導(dǎo)教師 2020 年 05 月 27 日 Research on low cavitation in water hydraulic twostage throttle poppet valve Abstract: Cavitation has important effects on the performances and lifespan of water hydraulic control valve, such as degrading efficiency, intense noise, and severe vibration. Twostage throttle valve is a practicable configuration to mitigate cavitation, which is extensively used in water hydraulic pressure relief valves and throttle valves. The pressure distribution inside a medium chamber located between two throttles of a twostage throttle valve is investigated through numerical simulations. The effects of the passage area ratio of the two throttles and the inlet and outlet pressures on the pressure inside the medium chamber are examined. The simulation results indicate that (a) the pressure inside the medium chamber is not constant, (b) the locations of maximum and minimum pressures inside the medium chamber are both fixed, which will not vary with the passage area ratio or the inlet and outlet pressures, and (c) the ratio of the pressure drop across the front throttle to the total pressure drop across the twostage throttle valve is nearly constant. The critical cavitation index of the twostage throttle valve is then established. A semiempirical design criterion is obtained for the water hydraulic twostage throttle valve. The correlation between the critical cavitation index and the passage area ratio of the two throttles is investigat