環(huán)形射流泵內部流動機理及結構優(yōu)化研究
發(fā)布時間：2018-07-26 09:35
【摘要】：射流泵具有結構簡單、可靠性高、運行和維護成本低等優(yōu)點。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、產業(yè)廢棄物等)的混合流體,在工程領域中有著廣闊應用前景。然而,關于其內流機理和結構優(yōu)化方面的研究并不充分。環(huán)形射流泵內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)等復雜現象,流動機理十分復雜。為此,本文基于大渦模擬,結合湍流統(tǒng)計理論和擬序運動理論等對環(huán)形射流泵內部流動機理進行了系統(tǒng)研究,并采用非傳統(tǒng)結構來實現其性能的優(yōu)化。主要工作和研究成果如下： (1)為驗證本文LES方案的可靠性以及加深對環(huán)形射流泵的直觀認識,首先對面積比m=1.72,2.26和3.33的環(huán)形射流泵進行了試驗研究。結果表明：環(huán)形射流泵內流動與傳統(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)結構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行了計算,并對比分析了不同的網格數、網格布置與亞格子模型的影響。通過與試驗數據對比,結果表明本文所采用的LES方案能夠較為準確地預測環(huán)形射流泵的時均外特性和內部流動。通過對流場中監(jiān)測點的瞬時壓力系數進行頻譜分析,獲得各個工況下的渦脫落頻率以及特征St數。當m=1.72時,St數在0.2～0.22之間,隨著流量比增加,St數降低,而當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)形射流泵內時均流場進行分析發(fā)現：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；而吸入室內邊界層厚度增長速率與流量比無關,但在喉管內部,流量比越小邊界層越厚,且增長速率越大；剩余能量系數可描述泵內能量的沿程變化情況,該系數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,分離點向下游移動較大。 (4)通過采用壓力判據、渦量和Q準則等擬序結構辨識方法有效提取流場中的擬序結構,結果表明：相比Q準則,壓力判據對于較小尺度的擬序結構,尤其對大量存在于渦辮區(qū)內的肋狀渦的辨識度較低；擬序結構主要由混合層、邊界層和回流區(qū)內產生并交互作用；混合層內渦結構在增長時,對吸入室壁面邊界層進行壓迫,誘發(fā)吸入室壁面邊界層內渦環(huán)結構的產生,由于二者轉向相反,在二者相接處的區(qū)域流向相同,相互作用較弱；擬序結構中的流向渦和展向渦由于產生機理不同,導致其強度、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,然而流向渦促進了展向渦的扭曲和破碎,并對流場中卷吸和混合的貢獻較大。流場內流向渦與展向渦之間、混合層內渦結構與邊界層內渦結構甚至與回流之間的相互作用,使得環(huán)形射流泵內部流場較為復雜。然而亦正是這些復雜的演變過程和相互作用,主宰著泵內流場的湍流特征、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計算成本較高,因此采用RANS湍流模型驗證本文所提出的結構優(yōu)化方案。首先對射流泵模擬中常用的六種RANS湍流模型進行了驗證,結果表明：RNG k-ε模型能夠較為準確地預測環(huán)形射流泵的外特性和內部流動的平均特征；標準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的變化趨勢預測較為準確。 (6)提出利用等速度變化和等壓力變化方法來設計環(huán)形射流泵的擴散器,可降低錐形擴散器內由于速度或壓力變化不均勻導致的流動損失,并推導出簡潔易用的設計公式。數值模擬表明這兩種設計方法確實能使擴散器內速度或者壓力變化更為均勻,其中等壓力變化擴散器內壓力的確能夠呈線性增長,從而改善環(huán)形射流泵的性能；特別在擴散器較短或擴散角度較大時表現更優(yōu),因此較為適用于泵的空間和質量受限的場合。相比等速度變化擴散器,等壓力變化擴散器在大流量比工況下表現較優(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)形工作流體內外側均為被吸流體,避免了高速射流貼壁流動產生的較大摩擦損失,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.
【學位授予單位】：武漢大學
【學位級別】：博士
【學位授予年份】：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.
【學位授予單位】：武漢大學
【學位級別】：博士
【學位授予年份】：2014
【分類號】：TH38
【參考文獻】
相關期刊論文 前10條
1 李同卓,鄭邦民,陸宏圻,鄧珊,向清江;蒙特卡羅法對射流泵模型內部流場的數值模擬[J];華北水利水電學院學報;2005年01期
2 龍新平;程茜;韓寧;張改蘭;;射流泵最佳喉嘴距的數值模擬[J];核動力工程;2008年01期
3 龍新平;王豐景;俞志君;;噴射泵內部流動模擬與其擴散角優(yōu)化[J];核動力工程;2011年01期
4 王常斌,林建忠,石興;射流泵最佳參數的確定方法[J];流體機械;2004年09期
5 黃小華;郭根喜;陶啟友;;射流式吸魚泵關鍵技術研究及設計[J];南方水產;2007年03期
6 袁丹青;白濱;王冠軍;叢小青;陳向陽;;多噴嘴射流泵流場的數值模擬與PIV測量[J];排灌機械;2009年01期
7 龍新平;鄢恒飛;張松艷;姚鑫;;喉管長度對環(huán)形射流泵性能影響的數值模擬[J];排灌機械工程學報;2010年03期
8 龍新平;姚鑫;楊雪龍;;多孔噴嘴射流泵流動模擬與渦結構分析[J];排灌機械工程學報;2012年02期
9 龍新平，劉景植，陸宏圻，，朱勁木;射流泵外特性與其內部流場關系的研究[J];水動力學研究與進展(A輯);1996年05期
10 何培杰,龍新平,梁愛國,劉景植,陸宏圻;射流泵流場的PIV測量[J];水科學進展;2004年03期
本文編號：2145586
本文鏈接：http://www.wukwdryxk.cn/kejilunwen/jixiegongcheng/2145586.html
