本文選題：低比轉(zhuǎn)速離心泵 + 縫隙引流葉片　； 參考：《上海大學(xué)》2014年博士論文

【摘要】：低比轉(zhuǎn)速離心泵應(yīng)用廣泛，但其效率卻偏低。在實(shí)際運(yùn)行過程中，也可能會(huì)發(fā)生空化，致使泵的性能下降，甚至影響機(jī)組運(yùn)行。提高低比轉(zhuǎn)速離心泵的水力性能和抗空化性能，對(duì)于保證機(jī)組的安全、穩(wěn)定和高效運(yùn)行意義重大。 前期研究工作證明基于流動(dòng)控制思想設(shè)計(jì)的帶有縫隙引流葉片的葉輪在一定的工況范圍內(nèi)可提高離心泵的水力性能。然而目前對(duì)其內(nèi)部流動(dòng)機(jī)理尚缺乏清晰的認(rèn)識(shí)，對(duì)該離心泵的空化特性也缺乏考量，也沒有一套有效的數(shù)值預(yù)測(cè)方法可以較為準(zhǔn)確地描述帶有縫隙引流葉片的離心泵內(nèi)部流動(dòng)結(jié)構(gòu)。 作者在發(fā)展一套含多尺度特征的數(shù)值預(yù)測(cè)方法的基礎(chǔ)上，系統(tǒng)地開展了縫隙引流葉片式低比轉(zhuǎn)速離心泵內(nèi)部流動(dòng)的數(shù)值和實(shí)驗(yàn)研究工作，旨在探索其內(nèi)部流動(dòng)機(jī)理，為低比轉(zhuǎn)速離心泵的優(yōu)化設(shè)計(jì)、性能預(yù)測(cè)和流動(dòng)控制提供理論、數(shù)值和實(shí)驗(yàn)基礎(chǔ)。全文的主要工作如下： 一、發(fā)展尺度自適性分離渦模擬方法 通過引入基于局部流場(chǎng)信息的馮·卡門尺度，對(duì)傳統(tǒng)DES方法進(jìn)行了修正，并經(jīng)過多個(gè)算例測(cè)試，驗(yàn)證了該方法的有效性。新發(fā)展的尺度自適應(yīng)性分離渦模擬SDES方法改進(jìn)了傳統(tǒng)DES方法在分區(qū)辨識(shí)方面存在直接依賴網(wǎng)格的不足，可實(shí)現(xiàn)穩(wěn)態(tài)與非穩(wěn)態(tài)區(qū)域自適應(yīng)性切換RANS/LES方法進(jìn)行求解。 二、離心泵內(nèi)部流場(chǎng)PIV實(shí)驗(yàn)研究 搭建了適用于離心泵性能實(shí)驗(yàn)、PIV流場(chǎng)實(shí)驗(yàn)和空化觀察實(shí)驗(yàn)的閉式實(shí)驗(yàn)平臺(tái)，設(shè)計(jì)并制作了便于PIV流場(chǎng)測(cè)量和空化觀察實(shí)驗(yàn)的離心泵模型。水力性能測(cè)試結(jié)果表明，隨著流量的增大，縫隙引流葉輪的效果逐漸顯現(xiàn)，設(shè)計(jì)的模型泵外特性再現(xiàn)了縫隙引流葉片離心泵的主要特征。PIV流場(chǎng)測(cè)試結(jié)果表明，離心葉輪內(nèi)部的流動(dòng)在各流量工況下主要沿葉片吸力面?zhèn)攘鲃?dòng)，在壓力面?zhèn)攘鞯纼?nèi)存在一個(gè)與葉輪轉(zhuǎn)動(dòng)方向相反的旋渦。隨著流量的增大，渦旋的強(qiáng)度會(huì)受主流的抑制而逐漸減弱，并逐步被約束在近壓力面?zhèn)鹊妮^小范圍內(nèi)。 三、縫隙引流葉片提高離心泵水力性能的數(shù)值研究 采用獲得的離心泵水力性能和PIV流場(chǎng)實(shí)驗(yàn)數(shù)據(jù)對(duì)SDES方法進(jìn)行了驗(yàn)證，在此基礎(chǔ)上，通過數(shù)值實(shí)驗(yàn)對(duì)比分析了傳統(tǒng)葉輪和縫隙葉輪離心泵內(nèi)部流動(dòng)特性之間的差異，探討了縫隙葉輪在一定的工況范圍內(nèi)提高離心泵水力性能的機(jī)理，認(rèn)為縫隙葉輪前緣小葉片會(huì)導(dǎo)引部分流體經(jīng)縫隙從葉片壓力面?zhèn)攘飨蛭γ鎮(zhèn)�，且前緣偏置和重疊設(shè)計(jì)的小葉片增大了流道進(jìn)口區(qū)面積，使得流道內(nèi)部速度場(chǎng)分布更加均勻，從而降低了強(qiáng)剪切湍流引起的葉輪內(nèi)能量損失。此外，還發(fā)現(xiàn)縫隙葉輪離心泵內(nèi)的壓力脈動(dòng)強(qiáng)度總體低于傳統(tǒng)葉輪離心泵，這說明縫隙引流葉片結(jié)構(gòu)還有望提高離心泵的運(yùn)行穩(wěn)定性。 四、離心泵空化實(shí)驗(yàn)研究 為考察縫隙引流葉輪離心泵的抗空化特性，分別針對(duì)傳統(tǒng)葉輪和縫隙引流葉輪離心泵，開展了多個(gè)流量工況下的空化性能實(shí)驗(yàn)、高速攝影和鎖相拍照的空化觀察實(shí)驗(yàn)。結(jié)果表明縫隙引流葉輪在大流量工況區(qū)比傳統(tǒng)葉輪有更好的抗空化特性，而在小流量工況下，兩種葉輪的空化特性基本相當(dāng)；在大流量工況區(qū)，縫隙引流葉輪發(fā)生空化的位置主要集中于葉片吸力面?zhèn)�，隨著空化數(shù)的降低，，空穴占據(jù)流道的體積表現(xiàn)為逐步從葉片吸力面?zhèn)认驂毫γ鎮(zhèn)仍鲩L(zhǎng)。而傳統(tǒng)葉輪則在葉片前緣壓力面較早發(fā)生空化，隨著空化數(shù)的降低，空穴會(huì)從進(jìn)口區(qū)流道兩側(cè)同時(shí)向中間增長(zhǎng)。 五、縫隙引流葉片提高離心泵空化性能的數(shù)值研究 在空化實(shí)驗(yàn)數(shù)據(jù)驗(yàn)證的基礎(chǔ)上，應(yīng)用SDES方法對(duì)傳統(tǒng)葉輪和縫隙引流葉輪離心泵在不同的流量工況下進(jìn)行了空化流場(chǎng)數(shù)值模擬，并分別針對(duì)離心泵空化流場(chǎng)的周向演化特征、大流量工況出現(xiàn)的隔舌空化現(xiàn)象、縫隙引流葉輪離心泵在小流量工況出現(xiàn)的交錯(cuò)固定空化現(xiàn)象以及縫隙引流葉輪的抗空化機(jī)理進(jìn)行了詳細(xì)分析。結(jié)果表明縫隙引流葉輪前緣小葉片的導(dǎo)流、縫隙葉片結(jié)構(gòu)的引流以及小葉片對(duì)主葉片的擾動(dòng)應(yīng)是其抑制空化的發(fā)生和發(fā)展的主要原因；在蝸殼軸向中心平面上，等半徑圓弧上的平均靜壓力總體上呈現(xiàn)隨著向蝸殼出口區(qū)域靠近而逐漸減小的趨勢(shì)，因此葉輪流道出口向蝸殼出口靠近時(shí)空化增強(qiáng)，而遠(yuǎn)離時(shí)空化減弱；在大流量工況下，發(fā)現(xiàn)在隔舌區(qū)發(fā)生了空化，并會(huì)引起離心泵揚(yáng)程下降。這是由于大流量工況改變了繞流蝸殼隔舌的入流攻角，引起了隔舌靠近蝸殼出水管的面產(chǎn)生局部分離的低壓空化區(qū)。繞流隔舌的外部環(huán)境壓力隨葉片周向位置的變化決定了隔舌空化的周向演化特征；流量變化、一定體積空穴區(qū)的形成和縫隙射流的共同作用引起了繞流葉片的入流角發(fā)生了變化，從而使得縫隙引流葉輪離心泵在小流量工況下出現(xiàn)了相間（交錯(cuò)）流道固定空化現(xiàn)象。 綜上，尺度自適性SDES方法為離心泵內(nèi)部流動(dòng)分析提供了一種有效的數(shù)值手段。實(shí)驗(yàn)和數(shù)值的研究結(jié)果均表明，基于流動(dòng)控制思想設(shè)計(jì)的縫隙引流葉片結(jié)構(gòu)具有導(dǎo)、引流作用，可在一定的工況范圍內(nèi)同時(shí)提高低比轉(zhuǎn)速離心泵的水力性能和抗空化性能。
[Abstract]:The low specific speed centrifugal pump is widely used, but its efficiency is low. In the process of actual operation, cavitation may also occur, which can cause the performance of the pump to decline and even affect the operation of the unit. It is of great significance to improve the hydraulic performance and anti cavitation performance of the low specific speed centrifugal pump for ensuring the safety, stability and efficiency of the unit.
The previous research proves that the impeller with the flow control idea designed with the gap drainage blade can improve the hydraulic performance of the centrifugal pump in a certain range of working conditions. However, there is still a lack of clear understanding of the internal flow mechanism and the lack of consideration on the cavitation characteristics of the centrifugal pump, and there is no effective set of numerical prediction parties. The method can accurately describe the internal flow structure of centrifugal pumps with slot drainage blades.
On the basis of developing a set of numerical prediction method with multi-scale characteristics, the numerical and experimental research work on the internal flow of a low specific speed centrifugal pump with gap drainage is carried out systematically. The purpose is to explore the internal flow mechanism and provide the theory, numerical value and numerical value for the optimization design, performance prediction and flow control of the low specific speed centrifugal pump. The main work of the full text is as follows:
One, development scale self-adaptive separation vortex simulation method
By introducing the von Carmen scale based on the information of local flow field, the traditional DES method is modified, and the effectiveness of the method is verified by several examples. The new developed scale adaptive separation vortex simulation SDES method improves the shortage of the traditional DES method in the partition identification square directly dependent on the grid, and can realize the steady state. The adaptive switching RANS/LES method is applied to solve the problem.
Two, PIV experimental study on internal flow field of centrifugal pump
A closed test platform is built for centrifugal pump performance test, PIV flow field experiment and cavitation observation experiment. A centrifugal pump model is designed and produced to facilitate the measurement of PIV flow field and cavitation observation. The hydraulic performance test results show that the effect of the gap drainage blade gradually appears with the increase of flow rate and the design of the model outside the pump. The main characteristics of the centrifugal pump with gap drainage blade centrifugal pump.PIV flow field test results show that the flow inside the centrifugal impeller is mainly flowing along the suction side of the blade under each flow condition, and the vortex in the side channel of the pressure surface is in the opposite direction to the rotating direction of the impeller. With the increase of the flow, the strength of the vortex will be suppressed by the mainstream. Gradually weakened, and gradually restricted to the smaller side of the near pressure side.
Three, numerical study on improving hydraulic performance of centrifugal pump with slot drain blades
By using the hydraulic performance of the centrifugal pump and the experimental data of the PIV flow field, the SDES method is verified. On this basis, the difference between the flow characteristics of the centrifugal pump and the centrifugal pump of the traditional impeller and the gap impeller is analyzed by the numerical experiments. The mechanism of the gap impeller to improve the hydraulic performance of the centrifugal pump in a certain range of working conditions is discussed. The blade of the front edge of the gap impeller leads to the flow of some fluid through the gap from the blade pressure side to the suction surface, and the area of the inlet area of the channel is increased by the bias and overlap of the front edge, which makes the velocity distribution in the channel more uniform, thus reducing the energy loss in the impeller caused by the strong shear turbulence. In addition, the gap is also found. The pressure pulsation strength of impeller centrifugal pump is lower than that of traditional impeller centrifugal pump. This shows that the structure of slot drain blade is also expected to improve the operation stability of centrifugal pump.
Four, experimental study on cavitation of centrifugal pump
In order to investigate the cavitation resistance characteristics of the centrifugal pump of the gap drainage impeller, the cavitation performance experiments of the centrifugal pumps with the traditional impeller and the gap drainage impeller were carried out respectively. The results showed that the gap drainage impeller had better cavitation resistance than the traditional impeller in the large flow condition. The cavitation characteristics of the two kinds of impellers are basically equal in the small flow condition. In the large flow condition, the cavitation position of the gap drainage impeller mainly concentrates on the suction side of the blade. With the decrease of the cavitation number, the volume of the hole occupying channel increases gradually from the side pressure side of the blade suction surface. Cavitation occurs at the leading edge of the blade, and with the decrease of cavitation number, the hole will grow from the inlet to the middle.
Five, numerical study on improving cavitation performance of centrifugal pump with slot drain blades
On the basis of the verification of the cavitation experiment data, the SDES method is used to simulate the cavitation flow field of the centrifugal pump of the traditional impeller and the gap drainage impeller under different flow conditions, and the characteristics of the circumferential evolution of the cavitation flow field of the centrifugal pump, the cavitation phenomenon in the large flow condition and the small flow of the centrifugal pump of the gap drainage impeller in the small flow are taken. The staggered fixed cavitation and the anti cavitation mechanism of the gap drainage impeller are analyzed in detail. The results show that the diversion of the blade of the front edge of the gap drainage impeller, the drainage of the structure of the gap blade and the disturbance of the leaf blade to the main blade should be the main reason for the development and development of the cavitation. On the heart plane, the average static pressure on the arc of the equal radius is gradually decreasing as the outlet area of the volute is near, so the outlet of the outlet of the impeller flow to the volute is close to the space-time enhancement, but it is far away from the time and space, and the cavitation occurs in the tongue zone in the large flow condition and will cause the drop of the centrifugal pump head to fall. This is due to the change of the angle of attack on the tongue of the spiral case, which causes the local separation of the low pressure cavitation area near the surface of the outlet pipe of the volute. The external environmental pressure of the tongue around the tongue determines the circumferential evolution characteristic of the tongue cavitation with the change of the circumferential position of the blade; the flow change, the shape of a certain volume hole area The interaction between the formation and the slit jet causes the change of the inflow angle of the flow around the blade, which makes the centrifugal pump of the gap drainage impeller appear the phenomenon of the fixed cavitation in the interphase (interlaced) flow channel under the small flow condition.
To sum up, the scale self-adaptive SDES method provides an effective numerical method for the internal flow analysis of centrifugal pumps. Both experimental and numerical results show that the structure of the gap drainage blade based on the flow control idea has the guiding and drainage effects, and the hydraulic performance of the low specific speed centrifugal pump can be improved simultaneously in a certain range of working conditions. And anti cavitation performance.
【學(xué)位授予單位】：上海大學(xué)
【學(xué)位級(jí)別】：博士
【學(xué)位授予年份】：2014
【分類號(hào)】：TH311

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