環(huán)形射流泵內(nèi)部流動機(jī)理及結(jié)構(gòu)優(yōu)化研究
發(fā)布時間：2018-07-26 09:35
【摘要】：射流泵具有結(jié)構(gòu)簡單、可靠性高、運(yùn)行和維護(hù)成本低等優(yōu)點(diǎn)。與傳統(tǒng)中心射流泵相比,環(huán)形射流泵的吸入通道沒有阻礙且被吸流體不用改變流向,因此特別適合于抽吸含有大顆粒固體(活魚、礦石、膠囊、產(chǎn)業(yè)廢棄物等)的混合流體,在工程領(lǐng)域中有著廣闊應(yīng)用前景。然而,關(guān)于其內(nèi)流機(jī)理和結(jié)構(gòu)優(yōu)化方面的研究并不充分。環(huán)形射流泵內(nèi)部流動是受限空間環(huán)形壁面射流在有逆壓梯度環(huán)境下的混合與發(fā)展,流場內(nèi)存在逆壓梯度、射流剪切層、壁面邊界層以及可能的回流區(qū)等復(fù)雜現(xiàn)象,流動機(jī)理十分復(fù)雜。為此,本文基于大渦模擬,結(jié)合湍流統(tǒng)計(jì)理論和擬序運(yùn)動理論等對環(huán)形射流泵內(nèi)部流動機(jī)理進(jìn)行了系統(tǒng)研究,并采用非傳統(tǒng)結(jié)構(gòu)來實(shí)現(xiàn)其性能的優(yōu)化。主要工作和研究成果如下： (1)為驗(yàn)證本文LES方案的可靠性以及加深對環(huán)形射流泵的直觀認(rèn)識,首先對面積比m=1.72,2.26和3.33的環(huán)形射流泵進(jìn)行了試驗(yàn)研究。結(jié)果表明：環(huán)形射流泵內(nèi)流動與傳統(tǒng)中心射流泵一樣存在自模性,且高效區(qū)較寬,而其最優(yōu)結(jié)構(gòu)尺寸隨著面積比改變；隨著面積比增加,性能曲線向較大流量比方向移動。 (2)采用LES對m=1.72和3.33的環(huán)形射流泵在不同工況下進(jìn)行了計(jì)算,并對比分析了不同的網(wǎng)格數(shù)、網(wǎng)格布置與亞格子模型的影響。通過與試驗(yàn)數(shù)據(jù)對比,結(jié)果表明本文所采用的LES方案能夠較為準(zhǔn)確地預(yù)測環(huán)形射流泵的時均外特性和內(nèi)部流動。通過對流場中監(jiān)測點(diǎn)的瞬時壓力系數(shù)進(jìn)行頻譜分析,獲得各個工況下的渦脫落頻率以及特征St數(shù)。當(dāng)m=1.72時,St數(shù)在0.2～0.22之間,隨著流量比增加,St數(shù)降低,而當(dāng)m=3.33時,St約為0.23,并幾乎不隨流量比變化。 (3)對LES所獲得的環(huán)形射流泵內(nèi)時均流場進(jìn)行分析發(fā)現(xiàn)：隨著流量比的增加,工作和被吸流體勢流核心長度近似線性增加；吸入室內(nèi)射流半寬接近線性增長,且流量比越小增長越快；而吸入室內(nèi)邊界層厚度增長速率與流量比無關(guān),但在喉管內(nèi)部,流量比越小邊界層越厚,且增長速率越大；剩余能量系數(shù)可描述泵內(nèi)能量的沿程變化情況,該系數(shù)沿流向整體呈下降趨勢,流量比越大,下降速率越小；回流區(qū)在瞬時和時均情況下差別較大,瞬時回流區(qū)的形狀及分布較不規(guī)則,甚至不連續(xù)；隨著流量比增大,回流區(qū)縮小并向下游移動,相比再附點(diǎn),分離點(diǎn)向下游移動較大。 (4)通過采用壓力判據(jù)、渦量和Q準(zhǔn)則等擬序結(jié)構(gòu)辨識方法有效提取流場中的擬序結(jié)構(gòu),結(jié)果表明：相比Q準(zhǔn)則,壓力判據(jù)對于較小尺度的擬序結(jié)構(gòu),尤其對大量存在于渦辮區(qū)內(nèi)的肋狀渦的辨識度較低；擬序結(jié)構(gòu)主要由混合層、邊界層和回流區(qū)內(nèi)產(chǎn)生并交互作用；混合層內(nèi)渦結(jié)構(gòu)在增長時,對吸入室壁面邊界層進(jìn)行壓迫,誘發(fā)吸入室壁面邊界層內(nèi)渦環(huán)結(jié)構(gòu)的產(chǎn)生,由于二者轉(zhuǎn)向相反,在二者相接處的區(qū)域流向相同,相互作用較弱；擬序結(jié)構(gòu)中的流向渦和展向渦由于產(chǎn)生機(jī)理不同,導(dǎo)致其強(qiáng)度、形態(tài)和演化方式不同,盡管流向渦渦量與展向渦渦量相比較小,然而流向渦促進(jìn)了展向渦的扭曲和破碎,并對流場中卷吸和混合的貢獻(xiàn)較大。流場內(nèi)流向渦與展向渦之間、混合層內(nèi)渦結(jié)構(gòu)與邊界層內(nèi)渦結(jié)構(gòu)甚至與回流之間的相互作用,使得環(huán)形射流泵內(nèi)部流場較為復(fù)雜。然而亦正是這些復(fù)雜的演變過程和相互作用,主宰著泵內(nèi)流場的湍流特征、流體間的摻混與傳能甚至環(huán)形射流泵的外特性。 (5)鑒于LES計(jì)算成本較高,因此采用RANS湍流模型驗(yàn)證本文所提出的結(jié)構(gòu)優(yōu)化方案。首先對射流泵模擬中常用的六種RANS湍流模型進(jìn)行了驗(yàn)證,結(jié)果表明：RNG k-ε模型能夠較為準(zhǔn)確地預(yù)測環(huán)形射流泵的外特性和內(nèi)部流動的平均特征；標(biāo)準(zhǔn)k-ε模型低估了環(huán)形射流泵的外特性,而對外特性和壁面壓力系數(shù)的變化趨勢預(yù)測較為準(zhǔn)確。 (6)提出利用等速度變化和等壓力變化方法來設(shè)計(jì)環(huán)形射流泵的擴(kuò)散器,可降低錐形擴(kuò)散器內(nèi)由于速度或壓力變化不均勻?qū)е碌牧鲃訐p失,并推導(dǎo)出簡潔易用的設(shè)計(jì)公式。數(shù)值模擬表明這兩種設(shè)計(jì)方法確實(shí)能使擴(kuò)散器內(nèi)速度或者壓力變化更為均勻,其中等壓力變化擴(kuò)散器內(nèi)壓力的確能夠呈線性增長,從而改善環(huán)形射流泵的性能；特別在擴(kuò)散器較短或擴(kuò)散角度較大時表現(xiàn)更優(yōu),因此較為適用于泵的空間和質(zhì)量受限的場合。相比等速度變化擴(kuò)散器,等壓力變化擴(kuò)散器在大流量比工況下表現(xiàn)較優(yōu),但在小流量比下較差。 (7)提出了新型夾心式環(huán)形噴嘴,使得高速環(huán)形工作流體內(nèi)外側(cè)均為被吸流體,避免了高速射流貼壁流動產(chǎn)生的較大摩擦損失,并由于增大了與被吸流體的接觸面積,使得泵的最高效率從35.8%提升至45.1%。工作噴嘴與壁面的距離以及內(nèi)外被吸流體之間的速度比對采用該噴嘴的新型泵性能具有較大影響,且在取不同的工作噴嘴與壁面距離時,相應(yīng)的最優(yōu)速度比不同。在最優(yōu)速度比未知的情況下,選擇1/1可獲得較好結(jié)果。
[Abstract]:The jet pump has the advantages of simple structure, high reliability and low cost of operation and maintenance. Compared with the traditional central jet pump, the suction channel of the annular jet pump is not hindered and is absorbed by the fluid without changing the flow direction, so it is especially suitable for the suction of mixed fluid containing large particle solids (living fish, mineral stone, capsule, industrial waste and so on). However, the research on the internal flow mechanism and structural optimization is not sufficient. The internal flow of the annular jet pump is the mixing and development of the annular wall jet under the reverse pressure gradient environment, and the flow field is in the reverse pressure gradient, the jet shear layer, the wall boundary layer and the possible reflux area. In this paper, the internal flow mechanism of the annular jet pump is systematically studied in this paper based on the large eddy simulation, combined with the turbulence statistical theory and the theory of the pseudo order motion, and the performance optimization is realized by using the non traditional structure. The main work and research results are as follows:
(1) in order to verify the reliability of the LES scheme and to deepen the intuitive understanding of the annular jet pump, the experimental study on the annular jet pump with an area ratio of m=1.72,2.26 and 3.33 is first studied. The results show that the inner flow of the annular jet pump has the same self mode as the traditional central jet pump, and the high efficiency zone is wide, and the optimum structure size is along with the surface. As the area ratio increases, the performance curve moves to a larger flow ratio direction.
(2) the m=1.72 and 3.33 annular jet pumps are calculated under different working conditions with LES, and the effects of grid number, grid arrangement and subgrid model are compared and analyzed. By comparing with the experimental data, the results show that the LES scheme used in this paper can accurately predict the time average characteristics and internal flow of the annular jet pump. Through the spectrum analysis of the instantaneous pressure coefficient of the monitoring point in the flow field, the vortex shedding frequency and the characteristic St number are obtained under each condition. When m=1.72, the number of St is between 0.2 and 0.22, with the increase of the flow ratio, the number of St decreases, and when m=3.33, the St is about 0.23, and almost does not change with the flow ratio.
(3) the analysis of the time averaged flow field in the annular jet pump obtained by LES shows that with the increase of the flow ratio, the core length of the flow and the flow is approximately linearly increased, and the half width of the jet in the suction chamber is close to linear growth, and the smaller the flow ratio is, the faster the increase of the flow ratio; but the growth rate of the inner boundary layer thickness in the suction chamber is not related to the flow ratio. In the interior of the throat, the smaller the flow ratio, the thicker the boundary layer and the greater the growth rate. The residual energy coefficient can describe the change of the energy in the pump, and the coefficient decreases along the flow direction, the greater the flow ratio, the smaller the drop rate, the larger the instantaneous and the time, the shape and distribution of the instantaneous reflux area. The rule is even discontinuous. As the flow ratio increases, the recirculation zone shrinks and moves downstream.
(4) the pseudo sequence structure identification method, such as pressure criterion, vorticity and Q criterion, is used to effectively extract the pseudo sequence structure in the flow field. The results show that, compared with the Q criterion, the pressure criterion has a lower identification degree to the smaller scale quasi order structure, especially a large number of ribbed vortices in the vortex zone; the pseudo sequence structure is mainly composed of mixed layer, boundary layer and return layer. In the flow area, the vortex structure in the mixed layer increases, and the boundary layer of the suction chamber wall surface is compressed and the vortex ring structure in the boundary layer of the suction chamber wall is induced. As the two turns opposite, the flow direction is the same and the interaction is weak, and the flow vortices and the spreading vortices in the quasi order structure are produced due to the formation of the flow vortex and the spreading vortex in the quasi sequence structure. The mechanism is different, which leads to the different intensity, morphology and evolution mode. Although the flow vorticity is smaller than the spread vorticity, the flow vortex promotes the distortion and breakage of the spreading vortex, and contributes greatly to the volume absorption and mixing in the flow field. The inner vortex structure and the inner vortex structure in the mixed layer and the boundary layer vortex structure are even between the flow flow and the flow vortex. The interaction between reflux makes the internal flow field of the annular jet pump more complex. However, it is the complex evolution process and interaction that dominates the turbulent characteristics of the internal flow field of the pump, the mixing of the fluid and the external characteristics of the annular jet pump.
(5) in view of the high cost of LES calculation, the RANS turbulence model is used to verify the structural optimization scheme proposed in this paper. First, six kinds of RANS turbulence models commonly used in the jet pump simulation are verified. The results show that the RNG k- epsilon model can accurately predict the external characteristics of the annular jet pump and the average characteristics of the internal flow, and the standard k The external characteristic of the annular jet pump is underestimated by the - E model, while the variation trend of external characteristic and wall pressure coefficient is more accurate.
(6) to design the diffuser of the annular jet pump by using the equal velocity change and the equal pressure change method, it can reduce the flow loss caused by the uneven velocity or pressure variation in the conical diffuser, and deduce the simple and easy to use design formula. The numerical simulation shows that the two methods do make the diffuser speed or pressure inside the diffuser. The change is more uniform, in which the pressure in the equal pressure variable diffuser does increase linearly, thus improving the performance of the annular jet pump, especially when the diffuser is short or the diffusion angle is larger, so it is more suitable for the space and the limited quality of the pump. It performs better under large flow rate than under low flow ratio.
(7) a new type of sandwich annular nozzle is proposed, which makes the inner and outer sides of the high speed annular working fluid be suction fluid, avoiding the large friction loss caused by the high-speed jet flow, and because of the increase of the contact area with the absorbed fluid, the maximum efficiency of the pump is raised from 35.8% to the distance between the 45.1%. working nozzle and the wall and the inside and outside. The velocity ratio between the absorbed fluid has a great influence on the performance of the new type of pump using the nozzle, and the optimum velocity ratio is different when the distance between the different working nozzles and the wall is taken. In the case of the unknown optimal velocity ratio, the selection of 1/1 can obtain better results.
【學(xué)位授予單位】：武漢大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TH38
本文編號：2145586
[Abstract]:The jet pump has the advantages of simple structure, high reliability and low cost of operation and maintenance. Compared with the traditional central jet pump, the suction channel of the annular jet pump is not hindered and is absorbed by the fluid without changing the flow direction, so it is especially suitable for the suction of mixed fluid containing large particle solids (living fish, mineral stone, capsule, industrial waste and so on). However, the research on the internal flow mechanism and structural optimization is not sufficient. The internal flow of the annular jet pump is the mixing and development of the annular wall jet under the reverse pressure gradient environment, and the flow field is in the reverse pressure gradient, the jet shear layer, the wall boundary layer and the possible reflux area. In this paper, the internal flow mechanism of the annular jet pump is systematically studied in this paper based on the large eddy simulation, combined with the turbulence statistical theory and the theory of the pseudo order motion, and the performance optimization is realized by using the non traditional structure. The main work and research results are as follows:
(1) in order to verify the reliability of the LES scheme and to deepen the intuitive understanding of the annular jet pump, the experimental study on the annular jet pump with an area ratio of m=1.72,2.26 and 3.33 is first studied. The results show that the inner flow of the annular jet pump has the same self mode as the traditional central jet pump, and the high efficiency zone is wide, and the optimum structure size is along with the surface. As the area ratio increases, the performance curve moves to a larger flow ratio direction.
(2) the m=1.72 and 3.33 annular jet pumps are calculated under different working conditions with LES, and the effects of grid number, grid arrangement and subgrid model are compared and analyzed. By comparing with the experimental data, the results show that the LES scheme used in this paper can accurately predict the time average characteristics and internal flow of the annular jet pump. Through the spectrum analysis of the instantaneous pressure coefficient of the monitoring point in the flow field, the vortex shedding frequency and the characteristic St number are obtained under each condition. When m=1.72, the number of St is between 0.2 and 0.22, with the increase of the flow ratio, the number of St decreases, and when m=3.33, the St is about 0.23, and almost does not change with the flow ratio.
(3) the analysis of the time averaged flow field in the annular jet pump obtained by LES shows that with the increase of the flow ratio, the core length of the flow and the flow is approximately linearly increased, and the half width of the jet in the suction chamber is close to linear growth, and the smaller the flow ratio is, the faster the increase of the flow ratio; but the growth rate of the inner boundary layer thickness in the suction chamber is not related to the flow ratio. In the interior of the throat, the smaller the flow ratio, the thicker the boundary layer and the greater the growth rate. The residual energy coefficient can describe the change of the energy in the pump, and the coefficient decreases along the flow direction, the greater the flow ratio, the smaller the drop rate, the larger the instantaneous and the time, the shape and distribution of the instantaneous reflux area. The rule is even discontinuous. As the flow ratio increases, the recirculation zone shrinks and moves downstream.
(4) the pseudo sequence structure identification method, such as pressure criterion, vorticity and Q criterion, is used to effectively extract the pseudo sequence structure in the flow field. The results show that, compared with the Q criterion, the pressure criterion has a lower identification degree to the smaller scale quasi order structure, especially a large number of ribbed vortices in the vortex zone; the pseudo sequence structure is mainly composed of mixed layer, boundary layer and return layer. In the flow area, the vortex structure in the mixed layer increases, and the boundary layer of the suction chamber wall surface is compressed and the vortex ring structure in the boundary layer of the suction chamber wall is induced. As the two turns opposite, the flow direction is the same and the interaction is weak, and the flow vortices and the spreading vortices in the quasi order structure are produced due to the formation of the flow vortex and the spreading vortex in the quasi sequence structure. The mechanism is different, which leads to the different intensity, morphology and evolution mode. Although the flow vorticity is smaller than the spread vorticity, the flow vortex promotes the distortion and breakage of the spreading vortex, and contributes greatly to the volume absorption and mixing in the flow field. The inner vortex structure and the inner vortex structure in the mixed layer and the boundary layer vortex structure are even between the flow flow and the flow vortex. The interaction between reflux makes the internal flow field of the annular jet pump more complex. However, it is the complex evolution process and interaction that dominates the turbulent characteristics of the internal flow field of the pump, the mixing of the fluid and the external characteristics of the annular jet pump.
(5) in view of the high cost of LES calculation, the RANS turbulence model is used to verify the structural optimization scheme proposed in this paper. First, six kinds of RANS turbulence models commonly used in the jet pump simulation are verified. The results show that the RNG k- epsilon model can accurately predict the external characteristics of the annular jet pump and the average characteristics of the internal flow, and the standard k The external characteristic of the annular jet pump is underestimated by the - E model, while the variation trend of external characteristic and wall pressure coefficient is more accurate.
(6) to design the diffuser of the annular jet pump by using the equal velocity change and the equal pressure change method, it can reduce the flow loss caused by the uneven velocity or pressure variation in the conical diffuser, and deduce the simple and easy to use design formula. The numerical simulation shows that the two methods do make the diffuser speed or pressure inside the diffuser. The change is more uniform, in which the pressure in the equal pressure variable diffuser does increase linearly, thus improving the performance of the annular jet pump, especially when the diffuser is short or the diffusion angle is larger, so it is more suitable for the space and the limited quality of the pump. It performs better under large flow rate than under low flow ratio.
(7) a new type of sandwich annular nozzle is proposed, which makes the inner and outer sides of the high speed annular working fluid be suction fluid, avoiding the large friction loss caused by the high-speed jet flow, and because of the increase of the contact area with the absorbed fluid, the maximum efficiency of the pump is raised from 35.8% to the distance between the 45.1%. working nozzle and the wall and the inside and outside. The velocity ratio between the absorbed fluid has a great influence on the performance of the new type of pump using the nozzle, and the optimum velocity ratio is different when the distance between the different working nozzles and the wall is taken. In the case of the unknown optimal velocity ratio, the selection of 1/1 can obtain better results.
【學(xué)位授予單位】：武漢大學(xué)
【學(xué)位級別】：博士
【學(xué)位授予年份】：2014
【分類號】：TH38
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