王 勇，陳 杰，劉厚林，邵 昌，張 翔

（1. 江蘇大學(xué)國(guó)家水泵及系統(tǒng)工程技術(shù)研究中心，鎮(zhèn)江 212013；2. 西華大學(xué)流體及動(dòng)力機(jī)械教育部重點(diǎn)實(shí)驗(yàn)室，成都 610039）

超低比轉(zhuǎn)速離心泵關(guān)閥啟動(dòng)瞬態(tài)特性分析

王 勇1，陳 杰1，劉厚林1，邵 昌1，張 翔2※

（1. 江蘇大學(xué)國(guó)家水泵及系統(tǒng)工程技術(shù)研究中心，鎮(zhèn)江 212013；2. 西華大學(xué)流體及動(dòng)力機(jī)械教育部重點(diǎn)實(shí)驗(yàn)室，成都 610039）

為探究超低比轉(zhuǎn)速離心泵關(guān)閥啟動(dòng)瞬態(tài)特性，該文以一臺(tái)比轉(zhuǎn)速為25的超低比轉(zhuǎn)速離心泵為研究對(duì)象，在關(guān)死點(diǎn)工況下對(duì)穩(wěn)態(tài)和關(guān)閥啟動(dòng)瞬態(tài)過(guò)程進(jìn)行數(shù)值模擬，并與試驗(yàn)結(jié)果進(jìn)行對(duì)比，研究表明：在關(guān)死點(diǎn)穩(wěn)態(tài)工況下性能曲線與試驗(yàn)測(cè)得結(jié)果變化趨勢(shì)相同，最大偏差小于5%，驗(yàn)證了數(shù)值模擬的準(zhǔn)確性；關(guān)閥啟動(dòng)過(guò)程，不同啟動(dòng)加速度下啟動(dòng)過(guò)程的末期均出現(xiàn)一個(gè)沖擊揚(yáng)程；在相同轉(zhuǎn)速時(shí)，穩(wěn)態(tài)過(guò)程中間截面的靜壓分布、相對(duì)速度流線分布和進(jìn)口管路內(nèi)相對(duì)速度與關(guān)閥啟動(dòng)瞬態(tài)過(guò)程分布趨勢(shì)存在差異。關(guān)閥啟動(dòng)瞬態(tài)過(guò)程內(nèi)部流場(chǎng)的發(fā)展總體上滯后于關(guān)死點(diǎn)穩(wěn)態(tài)過(guò)程內(nèi)部流場(chǎng)。研究結(jié)果可為進(jìn)一步研究超低比轉(zhuǎn)速離心泵啟動(dòng)的瞬態(tài)過(guò)程特性提供參考。

離心泵；計(jì)算機(jī)仿真；試驗(yàn)；關(guān)死點(diǎn)工況；穩(wěn)態(tài)特性；瞬態(tài)特性

0 引 言

超低比轉(zhuǎn)速離心泵（簡(jiǎn)稱超低比速泵）一般是指比轉(zhuǎn)速小于等于30的離心泵，具有小流量、高揚(yáng)程的特點(diǎn)，在航空航天、石油化工和農(nóng)業(yè)灌溉等國(guó)民經(jīng)濟(jì)領(lǐng)域有著廣泛的應(yīng)用[1-6]。通常超低比速泵運(yùn)行工況基本穩(wěn)定，其流量、轉(zhuǎn)速和壓力等參數(shù)保持不變或者在一定范圍內(nèi)緩慢變化，但超低比速泵除了在穩(wěn)態(tài)工況下運(yùn)行之外，還需短期在各種各樣的瞬態(tài)工況下運(yùn)行，如啟動(dòng)過(guò)程，往往伴隨著轉(zhuǎn)速、流量和壓力等參數(shù)的劇烈變化，嚴(yán)重時(shí)將造成機(jī)組設(shè)備沖擊破壞。因此，研究泵開(kāi)啟過(guò)程的瞬態(tài)特性，對(duì)系統(tǒng)的安全和穩(wěn)定運(yùn)行具有重要意義。

目前已有學(xué)者對(duì)非設(shè)計(jì)工況下離心泵內(nèi)部瞬態(tài)流動(dòng)特性進(jìn)行了研究[7-9]。Dazin等[10]發(fā)現(xiàn)采用角動(dòng)量方程和能量方程可以很好的預(yù)測(cè)離心泵瞬態(tài)運(yùn)行過(guò)程中的葉輪扭矩、揚(yáng)程和功率。Farhadi等[11]建立了適用于預(yù)測(cè)離心泵啟動(dòng)過(guò)程瞬態(tài)特性的數(shù)學(xué)模型，該模型將整個(gè)系統(tǒng)內(nèi)部的湍動(dòng)能考慮在內(nèi)，預(yù)測(cè)精度較高。Rochuon等[12]提出POD方法（proper orthogonal decomposition method）在提取瞬態(tài)流場(chǎng)的主導(dǎo)模式方面是有效的。李貴東等[13]基于Eulerian-Eulerian非均相流模型對(duì)離心泵內(nèi)部流場(chǎng)進(jìn)行三維瞬態(tài)數(shù)值模擬，結(jié)果表明當(dāng)初始?xì)庀囿w積分?jǐn)?shù)逐漸增大時(shí)，葉輪流道內(nèi)流動(dòng)紊亂，氣液兩相流動(dòng)不均勻。張玉良等[14]研究低比轉(zhuǎn)速離心泵流量突然減小瞬態(tài)過(guò)程的外特性和內(nèi)流場(chǎng)，發(fā)現(xiàn)變工況過(guò)程結(jié)束后的穩(wěn)定流量越小，瞬態(tài)效應(yīng)愈發(fā)明顯。王玉川等[15]基于RNG k-ε湍流模型和滑移網(wǎng)格，對(duì)不同工況下離心泵內(nèi)部瞬態(tài)流場(chǎng)進(jìn)行數(shù)值模擬，模擬得到的揚(yáng)程和效率曲線與試驗(yàn)結(jié)果吻合較好。韓偉等[16]以導(dǎo)葉式離心泵為研究對(duì)象，研究過(guò)渡過(guò)程動(dòng)靜葉柵內(nèi)固液兩相流的瞬態(tài)流動(dòng)特性，研究表明：動(dòng)葉柵流道內(nèi)的渦持續(xù)產(chǎn)生、合并、破碎和耗散，使得動(dòng)葉進(jìn)口處的流動(dòng)滯止，導(dǎo)致動(dòng)葉進(jìn)口逐漸產(chǎn)生旋渦。

Thanapandi等[17-18]以較低的啟動(dòng)加速度對(duì)不同閥門(mén)開(kāi)度的離心泵進(jìn)行試驗(yàn)研究，研究發(fā)現(xiàn)在啟動(dòng)加速度很低的情況下，啟動(dòng)過(guò)程與準(zhǔn)穩(wěn)態(tài)理論基本相符。Wu等[19-24]研究發(fā)現(xiàn)快速啟動(dòng)使離心泵出現(xiàn)較高的揚(yáng)程峰值，閥門(mén)開(kāi)啟過(guò)程中的流體流動(dòng)加速效應(yīng)使得其外特性曲線整體上位于穩(wěn)態(tài)計(jì)算結(jié)果之下，流量瞬態(tài)增加過(guò)程的性能曲線低于穩(wěn)態(tài)過(guò)程的性能曲線。劉竹青等[25]采用數(shù)值模擬手段研究雙吸離心泵關(guān)閥啟動(dòng)過(guò)程的瞬態(tài)特性，研究發(fā)現(xiàn)全回路三維模型用來(lái)模擬泵啟動(dòng)過(guò)程得到的瞬態(tài)揚(yáng)程相比于局部邊界的數(shù)值模擬結(jié)果更為接近試驗(yàn)值。袁建平等[26]針對(duì)離心泵啟動(dòng)過(guò)程瞬態(tài)內(nèi)部流場(chǎng)和結(jié)構(gòu)場(chǎng)進(jìn)行了雙向流固耦合聯(lián)合求解，獲得了離心泵啟動(dòng)過(guò)程中瞬時(shí)效應(yīng)對(duì)葉片應(yīng)力和應(yīng)變的影響規(guī)律。

綜上所述，盡管國(guó)內(nèi)外學(xué)者對(duì)離心泵瞬態(tài)過(guò)程做了大量研究工作，但是對(duì)超低比速泵的瞬態(tài)特性研究還較少，因此開(kāi)展對(duì)超低比速泵啟動(dòng)過(guò)程瞬態(tài)特性的研究顯得尤為重要。本文以一臺(tái)比轉(zhuǎn)速ns=25的超低比轉(zhuǎn)速離心泵為研究對(duì)象，在關(guān)死點(diǎn)工況下對(duì)其分別進(jìn)行穩(wěn)態(tài)和瞬態(tài)關(guān)閥啟動(dòng)過(guò)程的數(shù)值計(jì)算，并與試驗(yàn)結(jié)果進(jìn)行對(duì)比，分析不同啟動(dòng)加速度對(duì)瞬態(tài)啟動(dòng)過(guò)程中超低比轉(zhuǎn)速泵非定常特性的影響。最后對(duì)啟動(dòng)時(shí)間為2 s的關(guān)閥啟動(dòng)過(guò)程內(nèi)部流場(chǎng)進(jìn)行分析并與穩(wěn)態(tài)過(guò)程關(guān)死點(diǎn)工況的內(nèi)流場(chǎng)進(jìn)行對(duì)比，為深入研究超低比轉(zhuǎn)速離心泵啟動(dòng)的瞬態(tài)過(guò)程特性提供參考。

1 超低比轉(zhuǎn)速泵瞬態(tài)特性測(cè)試系統(tǒng)

1.1 試驗(yàn)測(cè)試系統(tǒng)

試驗(yàn)用超低比速泵主要參數(shù)如下：設(shè)計(jì)流量Qd=12.5 m3/h，揚(yáng)程Hd=74 m，額定轉(zhuǎn)速nd=2 950 r/min，比轉(zhuǎn)速ns=25，葉輪入口直徑Dj=68 mm，葉輪出口直徑D2=228 mm，葉片出口寬度b2=7 mm，葉片數(shù)z=6，葉片出口安放角β2=40°，蝸殼基圓直徑D3=245 mm。本試驗(yàn)在國(guó)家水泵及系統(tǒng)工程技術(shù)研究中心實(shí)驗(yàn)室閉式試驗(yàn)臺(tái)上進(jìn)行，圖1為超低比速泵瞬態(tài)特性測(cè)試試驗(yàn)臺(tái)結(jié)構(gòu)示意圖。該試驗(yàn)臺(tái)包括真空泵1、真空罐3、電磁流量計(jì)5、模型泵7、穩(wěn)壓罐9和管路閥門(mén)等。

圖1 瞬態(tài)特性測(cè)試試驗(yàn)臺(tái)結(jié)構(gòu)示意圖Fig.1 Schematic diagram of transient characteristic experimental set-up

1.2 瞬態(tài)試驗(yàn)測(cè)量裝置

1.2.1 壓力脈動(dòng)的測(cè)量

用于進(jìn)口壓力脈動(dòng)測(cè)量的傳感器型號(hào)為HM90-H10（武漢環(huán)宇高科測(cè)控有限公司），工作頻率為0～2 kHz，量程為0～300 kPa，用于出口壓力脈動(dòng)測(cè)量的傳感器型號(hào)為HY6305（武漢環(huán)宇高科測(cè)控有限公司），工作頻率為0～2 kHz，量程為0～1 MPa，輸出信號(hào)為大小4～20 mA的電流信號(hào)，精度為±0.25%。分別在離心泵進(jìn)出口管道上一倍管徑處進(jìn)行打孔，孔徑為10 mm，安裝壓力脈動(dòng)傳感器，用于測(cè)量模型泵進(jìn)出口處的壓力脈動(dòng)。

1.2.2 電機(jī)瞬態(tài)轉(zhuǎn)速測(cè)量裝置

采用霍爾轉(zhuǎn)速傳感器對(duì)超低比轉(zhuǎn)速離心泵啟動(dòng)過(guò)程中的轉(zhuǎn)速變化過(guò)程進(jìn)行監(jiān)測(cè)。圖2所示為CZ400型霍爾轉(zhuǎn)速傳感器安裝示意圖（上海傳振電子科技有限公司，量程為0～20 Hz，精度為±1%，方波電壓脈沖輸出）。將霍爾傳感器安裝在可調(diào)節(jié)支架上，并將支架固定在離心泵底座上，同時(shí)在離心泵聯(lián)軸器處裸露軸上安裝一個(gè)感應(yīng)磁鐵，通過(guò)調(diào)節(jié)傳感器上的安裝螺母，使得傳感器正對(duì)感應(yīng)磁鐵，并保持兩者距離為0.5～3 mm，每當(dāng)感應(yīng)磁鐵掃過(guò)霍爾轉(zhuǎn)速傳感器時(shí)，傳感器便輸出一個(gè)方波信號(hào)，2個(gè)脈沖方波間隔為一個(gè)葉輪旋轉(zhuǎn)周期，從而得出此時(shí)刻葉輪的轉(zhuǎn)速，當(dāng)感應(yīng)磁鐵連續(xù)掃過(guò)傳感器時(shí)，便可以得到一個(gè)時(shí)間段內(nèi)電機(jī)軸轉(zhuǎn)速的變化過(guò)程，從而擬合出超低比速泵啟動(dòng)過(guò)程葉輪轉(zhuǎn)速的變化曲線，為后期關(guān)閥啟動(dòng)過(guò)程的數(shù)值模擬提供參考。

圖2 傳感器安裝示意圖Fig.2 Schematic diagram of sensor installation

2 數(shù)值計(jì)算模型及參數(shù)設(shè)置

2.1 計(jì)算域建模及網(wǎng)格劃分

采用三維造型軟件Pro/E 5.0對(duì)超低比轉(zhuǎn)速模型泵整個(gè)流場(chǎng)計(jì)算域進(jìn)行三維建模，計(jì)算域包括：進(jìn)口延伸段、吸入室、葉輪水體、蝸殼水體和出口延伸段。其中進(jìn)口延伸長(zhǎng)度為離心泵進(jìn)口直徑的5倍，出口延伸長(zhǎng)度為蝸殼出口直徑的5倍，以保證流動(dòng)的充分發(fā)展。采用商用軟件ANSYS-ICEM 14.5對(duì)計(jì)算域進(jìn)行網(wǎng)格劃分，為了保證較高的網(wǎng)格質(zhì)量和邊界層網(wǎng)格尺寸，對(duì)所有計(jì)算域采用六面體結(jié)構(gòu)化網(wǎng)格，經(jīng)過(guò)網(wǎng)格無(wú)關(guān)性驗(yàn)證，最終網(wǎng)格數(shù)量為176.7萬(wàn)，模型泵計(jì)算域三維造型如圖3所示。

圖3 計(jì)算域三維造型Fig.3 Three-dimension model of computational domain

2.2 湍流模型

SSTk-ω模型整合了k-ε模型和k-ω模型，在自由流區(qū)和邊界層外層使用k-ε模型，在近避面區(qū)采用k-ω模型，在混合區(qū)通過(guò)一個(gè)加權(quán)函數(shù)F1來(lái)表示2種模型，并通過(guò)函數(shù)F2來(lái)修正函數(shù)F1在剪切流計(jì)算時(shí)的誤差[27-28]。

Menter等[29]對(duì)SST k-ω湍流模型適用性的研究表明：該湍流模型能夠較好的處理近壁面與自由流區(qū)的流動(dòng)，對(duì)流場(chǎng)細(xì)節(jié)的處理能力較好。因此本文在超低比速泵穩(wěn)態(tài)過(guò)程的數(shù)值計(jì)算中采用SST k-ω湍流模型完成雷諾方程組的封閉。

2.3 邊界條件

采用商用軟件ANSYS CFX 14.5全隱式耦合技術(shù)對(duì)方程組進(jìn)行求解，計(jì)算模型邊界條件設(shè)置為總壓進(jìn)口和質(zhì)量流量出口，系統(tǒng)參考?jí)毫υO(shè)置為0，固壁面邊界設(shè)置成無(wú)滑移壁面，壁面粗糙度設(shè)置為20 μm。

求解過(guò)程中，關(guān)死點(diǎn)穩(wěn)態(tài)過(guò)程求解時(shí)，選取時(shí)間步長(zhǎng)為?t=1.122 33×10-4s，即葉輪每旋轉(zhuǎn)2°為1個(gè)時(shí)間步長(zhǎng)，總計(jì)算步數(shù)為1 080步，即葉輪旋轉(zhuǎn)6圈；關(guān)閥啟動(dòng)過(guò)程求解時(shí)，對(duì)不同啟動(dòng)加速度下的求解取相同的分析頻率f=2 000 Hz，對(duì)應(yīng)的時(shí)間步長(zhǎng)分別為?t=0.001 s、?t=0.001 5 s、?t=0.002 s，計(jì)算總時(shí)間分別為2、3和4 s。

2.4 關(guān)死點(diǎn)流量

離心泵在關(guān)死點(diǎn)處運(yùn)行時(shí)，一般認(rèn)為此時(shí)的流量為0。吳賢芳[30]在對(duì)離心泵關(guān)死點(diǎn)工況進(jìn)行數(shù)值模擬時(shí)，認(rèn)為離心泵在關(guān)死點(diǎn)工況下運(yùn)行時(shí)，離心泵的內(nèi)部流動(dòng)在很小的流量下循環(huán)，此流量大致與口環(huán)泄漏量相近，并通過(guò)式（1）求解口環(huán)泄漏量。

式中q為扣環(huán)泄流量，kg/s；Qd為設(shè)計(jì)流量，m3/h；ns為比轉(zhuǎn)速。Dyson等[31]認(rèn)為，口環(huán)泄漏量的大小約為泵設(shè)計(jì)流量的1%～5%。本文在計(jì)算時(shí)，取這個(gè)很小的流量為0.01Qd=0.035 kg/s，在對(duì)關(guān)閥啟動(dòng)過(guò)程進(jìn)行求解時(shí)，認(rèn)為關(guān)死點(diǎn)流量足夠小時(shí)，這個(gè)很小的流量在整個(gè)啟動(dòng)過(guò)程中可以看作一個(gè)不變常數(shù)。

3 結(jié)果對(duì)比與分析

3.1 關(guān)死點(diǎn)工況穩(wěn)態(tài)揚(yáng)程

圖4所示為模型泵不同轉(zhuǎn)速下關(guān)死點(diǎn)處揚(yáng)程的模擬值與試驗(yàn)值對(duì)比圖。

由圖4可知，數(shù)值模擬得到的揚(yáng)程-轉(zhuǎn)速曲線與試驗(yàn)結(jié)果的變化趨勢(shì)相同，數(shù)值模擬結(jié)果均略高于試驗(yàn)結(jié)果，隨著轉(zhuǎn)速的增加，模型泵關(guān)死點(diǎn)揚(yáng)程逐漸增大；額定轉(zhuǎn)速處關(guān)死點(diǎn)揚(yáng)程的模擬值為76.91 m，試驗(yàn)測(cè)得關(guān)死點(diǎn)揚(yáng)程為74.02 m，模擬值與試驗(yàn)值的絕對(duì)偏差為3.9%，其余工況最大偏差均小于5%。因此，本文對(duì)超低比轉(zhuǎn)速離心泵關(guān)死點(diǎn)工況的數(shù)值計(jì)算方法具有一定的準(zhǔn)確性。

3.2 關(guān)閥啟動(dòng)過(guò)程瞬態(tài)揚(yáng)程

為了研究啟動(dòng)加速度對(duì)超低比轉(zhuǎn)速模型泵關(guān)閥啟動(dòng)過(guò)程瞬態(tài)特性的影響，分別在啟動(dòng)加速度為154.38、102.92和77.19 rad/s2，即加速時(shí)間分別為2、3和4 s共3種不同啟動(dòng)加速度時(shí)，對(duì)超低比轉(zhuǎn)速離心泵關(guān)閥啟動(dòng)過(guò)程進(jìn)行數(shù)值計(jì)算。圖5為關(guān)閥啟動(dòng)過(guò)程揚(yáng)程曲線的計(jì)算結(jié)果和試驗(yàn)結(jié)果。

圖4 關(guān)死點(diǎn)揚(yáng)程-轉(zhuǎn)速曲線模擬值與試驗(yàn)值Fig.4 Head-speed curve of simulation and experiment in shut-off condition

圖5 瞬態(tài)模擬和試驗(yàn)結(jié)果Fig.5 Transient computational and experimental results

由圖5可知，隨著啟動(dòng)過(guò)程發(fā)展，即轉(zhuǎn)速的線性增加，揚(yáng)程逐漸增大，揚(yáng)程在啟動(dòng)初期增加緩慢，隨后隨時(shí)間增加揚(yáng)程增加速率逐漸增大，揚(yáng)程脈動(dòng)幅度逐步加劇，3種不同啟動(dòng)加速度下啟動(dòng)過(guò)程的末期，揚(yáng)程均達(dá)到最大值。當(dāng)加速時(shí)間為2、3和4 s時(shí)，數(shù)值計(jì)算得到揚(yáng)程的峰值分別為83.31、81.62和80.13 m；3種加速時(shí)間下試驗(yàn)測(cè)得的揚(yáng)程峰值分別為80.05、79.28和78.53 m，相對(duì)偏差分別為4.07%、2.95%和2.04%，均在5%以內(nèi)，表明對(duì)超低比轉(zhuǎn)速離心泵關(guān)閥啟動(dòng)過(guò)程的數(shù)值模擬方法具有一定的準(zhǔn)確性。模型泵關(guān)死點(diǎn)處的揚(yáng)程計(jì)算值為76.91 m，3種不同啟動(dòng)加速度下，啟動(dòng)完成時(shí)的瞬態(tài)揚(yáng)程分別比穩(wěn)態(tài)揚(yáng)程高出8.32%、6.13%和4.19%，這表明關(guān)閥啟動(dòng)過(guò)程中揚(yáng)程的變化具有明顯的瞬態(tài)效應(yīng)，啟動(dòng)過(guò)程結(jié)束時(shí)會(huì)產(chǎn)生一個(gè)明顯的沖擊揚(yáng)程，且隨著啟動(dòng)加速度的增大，這個(gè)沖擊揚(yáng)程也逐漸增大，表明啟動(dòng)加速度對(duì)超低比速泵關(guān)閥啟動(dòng)過(guò)程的瞬態(tài)特性有明顯的影響。

3.3 內(nèi)部流場(chǎng)結(jié)果對(duì)比與分析

通過(guò)上述的研究結(jié)果發(fā)現(xiàn)，隨著啟動(dòng)加速度的減小，啟動(dòng)過(guò)程中的瞬態(tài)效應(yīng)逐漸削弱。因此，為了深入分析超低比速泵關(guān)閥啟動(dòng)過(guò)程中的瞬態(tài)特性，本文選取啟動(dòng)加速度最大的一組啟動(dòng)方案，分析加速時(shí)間t=2 s時(shí)關(guān)閥啟動(dòng)瞬態(tài)和關(guān)死點(diǎn)穩(wěn)態(tài)過(guò)程中內(nèi)流場(chǎng)的演化過(guò)程。

3.3.1 靜壓分布

圖6分別為關(guān)死點(diǎn)穩(wěn)態(tài)過(guò)程與啟動(dòng)總時(shí)間為t=2 s下關(guān)閥啟動(dòng)瞬態(tài)過(guò)程不同時(shí)刻泵中間截面的靜壓分布云圖。

圖6 穩(wěn)態(tài)與瞬態(tài)中間截面靜壓分布Fig.6 Static pressure of steady state and transient state in middle section

由圖6可知，不同轉(zhuǎn)速工況下，靜壓最低處均位于葉輪進(jìn)口區(qū)域，葉輪流道出口靠近蝸殼附近斷面中間區(qū)域出現(xiàn)高壓區(qū)。隨著葉輪旋轉(zhuǎn)對(duì)流體做功，葉輪流道內(nèi)靜壓隨著半徑的增大逐漸增大，除靠近隔舌的葉輪流道外，其余流道內(nèi)壓力分布均勻，隔舌處壓力梯度較大，表明在關(guān)死點(diǎn)工況，蝸殼隔舌結(jié)構(gòu)對(duì)泵內(nèi)靜壓分布有重要影響。隨著轉(zhuǎn)速的增加，泵內(nèi)靜壓逐漸增加，泵進(jìn)出口壓差逐漸增大，不同轉(zhuǎn)速下葉輪流道內(nèi)靜壓分布趨勢(shì)相似。不同時(shí)刻靜壓最低處均位于葉輪進(jìn)口區(qū)域，隨著葉輪旋轉(zhuǎn)對(duì)流體做功，葉輪流道內(nèi)靜壓隨著半徑的增大逐漸增大，葉輪流道內(nèi)壓力分布均勻，隔舌處壓力梯度較大，不同時(shí)刻靜壓分布趨勢(shì)相似。當(dāng)t=0.4 s時(shí)，葉輪出口靠近葉片工作面處出現(xiàn)高壓集中區(qū)，隨著轉(zhuǎn)速的增加，這個(gè)高壓區(qū)逐漸消失，泵內(nèi)靜壓逐漸增加，泵進(jìn)出口壓差逐漸增大，泵內(nèi)靜壓分別逐漸分布均勻。

由圖6可知，在相同轉(zhuǎn)速時(shí)，穩(wěn)態(tài)過(guò)程泵內(nèi)靜壓分布與關(guān)閥啟動(dòng)過(guò)程泵內(nèi)靜壓明顯不同，在啟動(dòng)過(guò)程初期，靜壓分布差別最大，隨著轉(zhuǎn)速的增加，泵內(nèi)靜壓分布的差別逐漸減小。

3.3.2 相對(duì)速度分布

圖7為關(guān)死點(diǎn)穩(wěn)態(tài)過(guò)程與啟動(dòng)總時(shí)間為t=2 s下關(guān)閥啟動(dòng)瞬態(tài)過(guò)程不同時(shí)刻泵中間截面的相對(duì)速度分布與流線。

圖7 穩(wěn)態(tài)與瞬態(tài)中間截面相對(duì)速度分布Fig.7 Relative velocity of steady state and transient state in middle section

由圖7a可知，不同轉(zhuǎn)速下，葉輪流道內(nèi)均存在大面積的低速區(qū)，葉輪出口處相對(duì)速度最大，葉輪流道內(nèi)存在數(shù)量不等，大小不一的漩渦，葉輪內(nèi)流動(dòng)損失很大，隨著轉(zhuǎn)速的增加，葉輪內(nèi)相對(duì)速度逐漸增大，低速區(qū)面積逐漸減小，漩渦區(qū)的范圍和數(shù)量逐漸減小，葉輪內(nèi)相對(duì)速度分布逐漸變的均勻。不同時(shí)刻葉輪出口處相對(duì)速度最大，葉輪流道內(nèi)同樣存在數(shù)量不等，大小不一的漩渦，當(dāng)啟動(dòng)初期t=0.4 s時(shí)，漩渦區(qū)幾乎充滿整個(gè)葉輪流道，葉輪內(nèi)流動(dòng)損失很大，隨著轉(zhuǎn)速的增加，葉輪內(nèi)相對(duì)速度逐漸增大，低速區(qū)面積逐漸減小，漩渦區(qū)的范圍和數(shù)量逐漸減小。

由圖7可知，在相同轉(zhuǎn)速時(shí)，穩(wěn)態(tài)過(guò)程時(shí)泵內(nèi)相對(duì)速度大于關(guān)閥啟動(dòng)過(guò)程泵內(nèi)相對(duì)速度，在啟動(dòng)過(guò)程初期，相對(duì)速度流線分布的差別最大，隨著轉(zhuǎn)速的增加，泵內(nèi)部流場(chǎng)的差別逐漸減小。

3.4 進(jìn)口管路內(nèi)速度分布

圖8為關(guān)死點(diǎn)穩(wěn)態(tài)過(guò)程與啟動(dòng)總時(shí)間為t=2 s下關(guān)閥啟動(dòng)瞬態(tài)過(guò)程不同時(shí)刻進(jìn)口管路軸截面的速度分布與流線圖。

圖8 穩(wěn)態(tài)與瞬態(tài)過(guò)程進(jìn)口管路內(nèi)速度分布Fig.8 Velocity of steady state and transient state in inlet pipe

由圖8a可知，不同轉(zhuǎn)速下，進(jìn)口管路內(nèi)速度沿流動(dòng)方向逐漸增大，進(jìn)口管路靠近來(lái)流處速度流線分布均勻，在靠近吸水室進(jìn)口處出現(xiàn)大量類似卡門(mén)渦街的對(duì)稱分布漩渦區(qū)，隨著轉(zhuǎn)速的增加，進(jìn)口管路內(nèi)速度逐漸增加，在吸水室進(jìn)口處速度最大，漩渦區(qū)范圍逐漸擴(kuò)大，漩渦數(shù)量逐漸增加，當(dāng)漩渦區(qū)充滿進(jìn)口管路約一半時(shí)，漩渦區(qū)范圍不再擴(kuò)大。由圖8b可知，在啟動(dòng)初期t=0.4 s時(shí)，進(jìn)口管路內(nèi)速度流線分布均勻，當(dāng)t=1.2 s時(shí)，靠近吸水室進(jìn)口出出現(xiàn)漩渦區(qū)，隨著轉(zhuǎn)速的增加，漩渦區(qū)范圍向來(lái)流方向擴(kuò)大，漩渦數(shù)量增加，漩渦區(qū)分布與穩(wěn)態(tài)過(guò)程相似，呈對(duì)稱分布。

對(duì)比圖8a與8b可以看出，在相同轉(zhuǎn)速時(shí)，穩(wěn)態(tài)過(guò)程進(jìn)口管路內(nèi)速度大于關(guān)閥啟動(dòng)過(guò)程進(jìn)口管內(nèi)的速度，漩渦區(qū)的范圍及漩渦數(shù)量均大于同一時(shí)刻瞬態(tài)過(guò)程。

基于對(duì)關(guān)死點(diǎn)穩(wěn)態(tài)過(guò)程和啟動(dòng)過(guò)程內(nèi)流場(chǎng)的分析發(fā)現(xiàn)：在相同轉(zhuǎn)速時(shí)，關(guān)閥啟動(dòng)過(guò)程內(nèi)部瞬態(tài)流場(chǎng)的發(fā)展總體上滯后于關(guān)死點(diǎn)處穩(wěn)態(tài)過(guò)程內(nèi)部流場(chǎng)。

4 結(jié) 論

本文對(duì)一臺(tái)超低比速泵在關(guān)死點(diǎn)工況進(jìn)行穩(wěn)態(tài)和關(guān)閥啟動(dòng)瞬態(tài)過(guò)程進(jìn)行了數(shù)值模擬，并與試驗(yàn)結(jié)果進(jìn)行對(duì)比，分析了不同啟動(dòng)加速度對(duì)瞬態(tài)沖擊揚(yáng)程的影響，同時(shí)對(duì)比了關(guān)死點(diǎn)工況穩(wěn)態(tài)過(guò)程與瞬態(tài)過(guò)程揚(yáng)程和內(nèi)流場(chǎng)的區(qū)別，得到以下結(jié)論：

1）關(guān)死點(diǎn)工況下?lián)P程的數(shù)值模擬結(jié)果與試驗(yàn)結(jié)果偏差均在5%以內(nèi)，表明本文采用的數(shù)值計(jì)算方法是可行的。

2）關(guān)閥啟動(dòng)過(guò)程中，3種啟動(dòng)加速度下啟動(dòng)完成時(shí)的瞬態(tài)揚(yáng)程分別比穩(wěn)態(tài)揚(yáng)程高出8.32%、6.13%和4.19%，這表明關(guān)閥啟動(dòng)過(guò)程中揚(yáng)程的變化具有明顯的瞬態(tài)效應(yīng)，啟動(dòng)過(guò)程結(jié)束時(shí)會(huì)產(chǎn)生一個(gè)明顯的沖擊揚(yáng)程，且沖擊揚(yáng)程隨啟動(dòng)加速度的增大而增大。

3）相同轉(zhuǎn)速時(shí)，啟動(dòng)過(guò)程初期的靜壓分布差別最大；啟動(dòng)過(guò)程蝸殼流道內(nèi)的漩渦區(qū)明顯多于穩(wěn)態(tài)過(guò)程；穩(wěn)態(tài)過(guò)程進(jìn)口管路內(nèi)相對(duì)速度、漩渦區(qū)的范圍及漩渦數(shù)量均大于瞬態(tài)過(guò)程。隨著啟動(dòng)過(guò)程中轉(zhuǎn)速增加，這些差異逐漸縮小。

4）相同轉(zhuǎn)速時(shí)，關(guān)閥啟動(dòng)過(guò)程內(nèi)部瞬態(tài)流場(chǎng)的發(fā)展總體上滯后于關(guān)死點(diǎn)處穩(wěn)態(tài)過(guò)程內(nèi)部流場(chǎng)。

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Transient characteristic analysis of ultra-low specific-speed centrifugal pumps during startup period under shut-off condition

Wang Yong1, Chen Jie1, Liu Houlin1, Shao Chang1, Zhang Xiang2※
(1. National Research Center of Pumps, Jiangsu University, Zhenjiang 212013, China; 2. Key Laboratory of Fluid and Power Machinery, Ministry of Education, Xihua University, Chengdu 610039, China)

In order to explore the characteristics of the ultra-low specific-speed centrifugal pump during startup period under shut-off condition, an ultra-low specific-speed centrifugal pump with the specific-speed of 25 was chosen as the research object. Unsteady numerical calculation under shut-off condition and transient condition was conducted for the ultra-low specific-speed centrifugal pump. The accuracy of numerical simulation was verified by experimental contrast. Based on the numerical results, the influence of different starting acceleration on the transient impact head, the difference between steady state and transient impact head, and the internal flow field were analyzed. The results showed that: The variation tendency of performance curve on shut-off condition under steady state condition was similar with the experiment, and along with the increase of rotational speed, the head under shut-off condition increased gradually. When the start was completed, the transient head was 8.32%, 6.13% and 4.19% higher than the steady state head, respectively, at 3 different starting accelerations, which indicated that the valve head change during the startup process had a significant transient effect. There was a significantly higher impact head at the end of startup processes with 3 different start accelerations, and with the increase of start acceleration, the impact head was also increased. With the rotation of the impeller acting fluid, the static pressure increased gradually with the increase of the radius. In addition to the impeller flow close to the tongue, the pressure distribution in the other channels was uniform, and the pressure gradient of the tongue was larger, which indicated that the volute tongue structure had an important influence on the distribution of the static pressure in the pump. With the increase of rotation speed, the static pressure increased gradually, and the pressure difference between the inlet and outlet of the pump increased gradually. When the time was 0.4 s, a high pressure concentration area occurred at impeller outlet near the blade pressure surface, and along with the increase of rotation speed, the high pressure concentration area gradually disappeared. The pump pressure distribution gradually grew uniform with pump pressure increasing. At the same speed, static pressure distribution, absolute speed streamline, and relative speed streamline shaft section of inlet pipe during stable process were different from the distribution during transient startup process. The differences were narrow with the increase of rotational speed. At the same speed, the development of inside transient flow field during transient startup process generally lagged after stable condition. At the same speed, static pressure of steady state and startup period under shut-off condition was obviously different. At the beginning of startup period, the static pressure distribution difference was the maximum, and with the increase of speed, the static pressure distribution difference gradually decreased. The relative velocity of steady state and startup period under shut-off condition was obviously different. At the beginning of the startup process, the difference of the streamline distribution of relative velocity was the biggest; with the increase of rotating speed, the difference of pump flow field decreased gradually. The relative velocity of inlet pipe in the process of steady state was larger than that in the process of startup, and the ranges of vortex region and vortex number were greater than the transient process at the same time. Based on the above results, it was found that with the decrease of starting acceleration, the transient effect was weakened. The research results provide the reference for the further study of the characteristics of transient process of the ultra-low specific-speed centrifugal pump.

centrifugal pump; computer simulation; experiment; shut-off condition; steady characteristic; transient characteristic

10.11975/j.issn.1002-6819.2017.11.009

TH311

A

1002-6819(2017)-11-0068-07

王 勇，陳 杰，劉厚林，邵 昌，張 翔. 超低比轉(zhuǎn)速離心泵關(guān)閥啟動(dòng)瞬態(tài)特性分析[J]. 農(nóng)業(yè)工程學(xué)報(bào)，2017，33(11)：68－74.

10.11975/j.issn.1002-6819.2017.11.009 http://www.tcsae.org

Wang Yong, Chen Jie, Liu Houlin, Shao Chang, Zhang Xiang. Transient characteristic analysis of ultra-low specific-speed centrifugal pumps during startup period under shut-off condition[J]. Transactions of the Chinese Society of Agricultural Engineering (Transactions of the CSAE), 2017, 33(11): 68－74. (in Chinese with English abstract) doi：10.11975/j.issn.1002-6819.2017.11.009 http://www.tcsae.org

2016-12-20

2017-04-23

江蘇省產(chǎn)學(xué)研聯(lián)合創(chuàng)新資金—前瞻性聯(lián)合研究項(xiàng)目（BY2015064-10）；江蘇省“六大人才高峰”高層次人才項(xiàng)目（GBZB-017）；江蘇高校優(yōu)勢(shì)學(xué)科建設(shè)工程資助項(xiàng)目；流體及動(dòng)力機(jī)械教育部重點(diǎn)實(shí)驗(yàn)室（西華大學(xué)）開(kāi)放課題（szjj2016-068）

王 勇，男，吉林白山人，博士，副研究員，主要研究方向?yàn)楸迷O(shè)計(jì)理論與方法。鎮(zhèn)江 江蘇大學(xué)國(guó)家水泵及系統(tǒng)工程技術(shù)研究中心，212013。Email：wylq@ujs.edu.cn

※通信作者：張 翔，博士，講師，主要研究方向?yàn)樗C(jī)械數(shù)值計(jì)算。成都 西華大學(xué)流體及動(dòng)力機(jī)械教育部重點(diǎn)實(shí)驗(yàn)室610039。

Email：zhangxiang@mail.xhu.edu.cn