• <tr id="yyy80"></tr>
  • <sup id="yyy80"></sup>
  • <tfoot id="yyy80"><noscript id="yyy80"></noscript></tfoot>
  • 99热精品在线国产_美女午夜性视频免费_国产精品国产高清国产av_av欧美777_自拍偷自拍亚洲精品老妇_亚洲熟女精品中文字幕_www日本黄色视频网_国产精品野战在线观看 ?

    Unsteady flow structures in centrifugal pump under two types of stall conditions *

    2019-01-05 08:08:38PeijianZhou周佩劍JiachengDai戴嘉鋮YafeiLi李亞飛TingChen陳婷JiegangMou牟介剛
    水動力學研究與進展 B輯 2018年6期
    關鍵詞:陳婷佩劍

    Pei-jian Zhou (周佩劍), Jia-cheng Dai(戴嘉鋮), Ya-fei Li(李亞飛), Ting Chen(陳婷),Jie-gang Mou (牟介剛)

    1. College of Mechanical Engineering, Zhejiang University of Technology, Hangzhou 310034, China

    2. Engineering Research Center of Process Equipment and Remanufacturing, Ministry of Education, Hangzhou 310034, China

    3. School of Science, Wuhan Institute of Technology, Wuhan 430205, China

    Abstract: The stall is an unsteady flow phenomenon that always causes instabilities and low efficiency for pumps. This paper focuses on the unsteady flow structures and evolutions under two types of stall conditions in centrifugal pump impellers. Two centrifugal pump impellers, one with 6 and another with 5 blades, are considered and a developed large-eddy simulation method is adopted. The results show that the alternative stall occurs in the impeller with 6 blades, while, the rotating stall is observed in that with 5 blades. The flow structure and the pressure fluctuation characteristics are further analyzed. For the alternative stall, the stall cells are fixed relative to the impeller, but a large vortex in the stalled passage is always swaying. The outlet vortex is generated from it, and then develops and sheds periodically. For the rotating stall, the stall cells first occur in the suction side of the blade. With the growth of the stall cells, the block area gradually increases until the inlet region is almost blocked, then moves to the pressure side with a continuous decay. When the rotating stall occurs, the amplitude of the pressure fluctuation is much larger than that under the alternative stall condition. The propagation of the stall cells has a significant effect on the pressure fluctuations in the impeller.

    Key words: Centrifugal pump, flow structures, rotating stall, alternative stall, large-eddy simulation

    Introduction

    The stall is an unsteady flow phenomenon that always causes instabilities and low efficiency for pumps[1-4]. Under the stall condition, the periodic generation and shedding of the stall cells always induce significant low frequency pressure fluctuations and vibrations, with a severe influence on the safety and stability of pumps. It is necessary to study the stall phenomenon to improve the safety and the stability of the pump operation. This study focuses on the unsteady flow structures and evolutions under two types of stall conditions in the centrifugal pump impellers.

    The stall, as an unsteady flow phenomenon,occurs in pumps due to the flow separation along the flow-guiding parts[5]. The large region of the separated flow is considered as the stall cell, which plays an important role in pumps, and can induce vibrations,noises, and even severe damages to the machine[6-7].Therefore the characteristics of the stall cells are important factors in improving not only the efficiency but also the operating safety and stability of pumps.

    So far, only a few experimental studies are found in literature for the stall phenomenon in centrifugal pumps. Pedersen et al.[8]used the particle image velocimetry (PIV) to show the internal flow through a centrifugal pump impeller, and identified the alternative stall for the first time. Further investigations were followed, including the study performed by Johnson et al.[9], which showed that these stall patterns also existed in the volute pump. Feng et al.[10], Ullum et al.[11]found similar stall cells in the vaned centrifugal pumps. Krause et al.[12]adopted the time-resolved PIV to find another type of stall called the rotating stall, where the instabilities occurred at a low flow rate. However, the PIV has some limitations,such as in the time resolution and the measurement area. Thanks to the development of the computational fluid dynamics (CFD), the stalled flows in the centrifugal pumps were numerically studied. Feng et al.[13]applied different turbulence models for unsteady flow simulations of a radial diffuser pump, and the results showed that the RANS models often failed to predict the stall phenomenon. The SST -kω model could capture the stall cells, but with a large deviation when the stall occurred[14]. The large-eddy simulation(LES) shows a promising advance for complex turbulent flows. A series of validation simulations are performed for the stall phenomenon, and the results are in an excellent agreement with the available experimental data[5,15].

    In the above studies, the stall phenomena were identified in centrifugal pumps. However, the structures and the motion of the stall cells are not yet fully understood. This study focuses on the stall cell characteristics in a centrifugal pump impeller by analyzing two types of stall phenomenon. The flow field and the stall cell structures are represented based on a developed large-eddy simulation with the dynamic mixed nonlinear model (DMNM).

    1. The investigated pump and simulation details

    The investigated pump impeller is a shrouded,low specific-speed centrifugal impeller with 6 blades,as shown in Fig. 1. Under the design condition, the pump flow rate is=3. 0 6 L/ s and the head is=1.75 m. More detailed geometric and experimental data can be found in Ref. [8]. In order to study two types of stall phenomenon, another one with 5 blades is considered in the study, with the otherwise same geometry. The large-eddy simulation is performed under the initial stall condition, the developed stall conditionand the deep stall condition

    Fig. 1 Geometry of the impeller with 6 blades

    The entire flow passages of the impeller is modelled and simulated. In order to reduce the boundary influence, extensions are made at the outlet and the inlet of the flow passage, respectively. Owing to the complexity of the computational domain, the unstructured hexahedron mesh is employed because of its fine adaptability. In the near-wall region the mesh is refined according to the requirement of the LES. In view of the Ref. [16] the grid stretching factor is chosen to allow the wall-adjacent cells to be located 0.02 mm off the wall, whilst also refining the grids in the streamwise and spanwise directions. A mesh of a total 3.2×106cells is utilized as the best compromise between the solution accuracy requirements and the available computer resources. Increasing the number of grids does not make a significant difference during the grid independent process. Figure 2 represents the mesh construction of the full passages.

    Fig. 2 Computational domain and mesh

    Fig. 3 The locations of monitor points

    A rotational reference frame is set for the flow passage, with the rotating speed of the reference frame equal to the rotating speed of the impeller. The velocity inlet boundary condition is chosen in the simulation. The inlet velocity is determined by the flow rate, including some fluctuation components,with the velocity normal to the inlet boundary. The Neumann condition, ?φ/?n=0, is considered for the pressure. At the outlet of the passage the pressure is given. The no-slip wall condition is considered, as u =0, v = 0, w = 0.

    The time step is set as 0.00023 s corresponding to a Courant number estimation smaller than 10, with a total 360 time steps per impeller revolution. The residual convergence criterion for each time step is reduced to 10-5, while the maximum number of iterations allowed per time step is limited to 15.

    The arrangement of the recording points is shown in Fig. 3. In view of the prediction for the number and the speed of the stall cells, the monitor points (P1-P6)are uniformly distributed on the shroud of the impeller for recording the pressure fluctuations.

    A developed large-eddy simulation with the dynamic mixed nonlinear model (DMNM) is performed on a full annulus of the impeller. The key to the success of the LES is to accurately represent the subgrid-scale (SGS) stress. The SGS stress can be written as follows[17]

    Fig. 4 (Color online) Evolution of outlet vortices

    In the DMNM, the resolved modified Leonard term and the modelled modified cross term are retained, with the modified Reynolds stress. This model combines the advantages of the dynamic mixed model (DMM) and the dynamic nonlinear model(DNM). The previous work shows that the DMNM,with its inclusion of the turbulent anisotropic properties, is more suitable for high curvature, strong rotational turbulence calculations[18]. The derivation details of this model can be found in the Ref. [19].

    Fig. 5 (Color online) Evolution of main vortices

    2. Alternative stall

    2.1 Flow structures analysis

    The alternative stall occurs in the impeller with 6 blades. As shown in Fig. 4, the stalled and unstalled passages can be observed, as reported by Pedersen et al.[8]. Three stall cells block the entrance of the passage, which does not rotate with respect to the impeller. Besides, one observes another two types of vortex motion in the stalled passage. The passage A is taken as an example to analyze the flow structures. A larger vortex appears downstream, which is more unsteady with characteristics of the wake flow due to the adverse pressure gradient and the centrifugal force.As the flow develops, the large vortex shakes and splits into small vortexes at the passage outlet. Then,the main vortex core gradually moves downstream,induces the shedding of the outlet vortex and disappears.

    Fig. 6 Frequency spectrum analysis

    Figure 5 shows the instantaneous streamline distributions at six equally spaced time steps during one cycle of the main vortex motion obtained by the simulation. The main vortex core starts to move downstream and another small vortex simultaneously appears upstream, to form two counter-rotating vortex pairs with the main vortex. As the small vortex grows larger, the main vortex core is forced to keep moving downstream. Then the main vortex changes dramatically, to be squashed with an increased length. The small vortex is surrounded by exterior streamlines of the main vortex. The two vortexes are emerged together, and a new main vortex is generated. In summary,the main vortex shows its obvious life cycle including decay, split, mergence and growth.

    2.2 Stall characteristics

    A frequency spectrum analysis is carried out for the series of pressure fluctuations to reveal the stall characteristics. Figure 6 shows the frequency domain of the vibration signals obtained at the location P1 at three different flow rates. It can be seen that the lower frequency is obviously the dominant frequency, which is contributed by the main vortex motion. Further, the“broadband” with a high frequency can also be seen,which is caused by the outlet vortex., the low frequency is 2.6 Hz, only 26.5% of the rotational frequency. While atshown in Figs.6(b), 6(c), the low frequencies are 3.13 Hz, 3.6 Hz,respectively. However, as the flow rate increases, the“broadband” with a high frequency keeps almost the same.

    3. Rotating stall

    3.1 Flow structures

    The rotating stall occurs in the impeller with 5 blades. Figure 7 shows instantaneous streamline distributions at six equally spaced time steps during one cycle of the rotating stall obtained by the simulation.The passage A is taken as an example to analyze the rotating stall. At =0t , we can see the stall cell almost blocks the whole entrance. At 1 6/T, the stall cell becomes larger, and no fluid can flow into the passage A. The fluid is forced to flow into the adjacent passages. In the passage E, the inlet attack angle decreases, and the flow becomes smooth.However, in the passage B, the inlet attack angle increases, then the blade suction surface produces a separation vortex, gradually developing into another stall cell, which eases the block in the passage A.Therefore, the stall cell in the passage A becomes smaller gradually. At 5 6/T, the streamline in the passage A is smooth, but the flow field in the passage B is completely blocked. This mechanism of the rotating stall is consistent with what described in Emmons et al.[20].

    3.2 Stall characteristics

    In order to determine the propagation speed and direction of the stall cells, the recorded pressure fluctuations on the monitor points P1-P5 are put in the same coordinate frame by transforming the coordinate system, as shown in Fig. 8, where n represents rotor period. At 0. 25Qd, the pressure signals at the points P1-P5 are seen to be fully periodic. The pressure fluctuations on all points have similar periods and amplitudes. But, they have a phase difference, because the stall cells propagate in a circular direction in the impeller. The numbers of stall cells can be calculated as follow

    From Fig. 8(a), TCR=3TOSC. Consequently, the number of the stall cells is 3. They propagate from P1-P5 through P2, P3 and P4. In the relative coordinate system, the stall cells rotate in the opposite direction of the impeller rotation. When the flow rate is increased to 0. 5 0 Qd, 0. 60Qd, Figs. 8(b), 8(c) show similar pressure fluctuations observed in Fig. 8(a).According to Eq. (2), the number of stall cells is also 3 at 0. 5 0 Qd, 0. 60Qd. The amplitude of the pressure fluctuations at stall point changes little from 0. 25Qd-0. 60Qd, while the periods during the same time are increased.

    A frequency spectrum analysis is carried out for the series of pressure fluctuations to reveal the rotating stall characteristics. Figure 9 shows the frequency domain of the vibration signals obtained at the location P1 at 3 different flow rates. It can be seen that the rotating stall frequency ( fstall) is obviously the dominant frequency, much lower than the rotational frequency. At 0. 2 5 Qd, fstallis 2.4 Hz. While at 0. 5 0 Qd, 0. 6 0Qdshown in Figs. 8(b), 8(c), fstallis 1.73 Hz, 1.4 Hz, respectively.

    The propagation speed of the stall cells (ωS) is determined by the angle of the pressure field rotation(Δθ) and the duration of this angle of the pressure field rotation (Δt). Consequently

    According to Eq. (3), at 0. 25Qd, the propagation speed of the stall cells is 5.03 rad/s, which is 8% of the rotor speed. While at 0. 5 0 Qd, 0. 60Qdshown in Figs. 9(a), 9(c), it is 3.8% (3.62 rad/s), 1.68% (3.11 rad/s),respectively. Therefore, it can be concluded that the rotating stall frequency is different at different flow rates. With the decrease of the flow rate, the amplitude of the pressure fluctuations tends to be larger, the propagation speed and the rotating stall frequency are lower, but the number remains the same.

    Fig. 9 Pressure fluctuation frequencies

    4. Conclusions

    The results show that the alternative stall occurs in the impeller with 6 blades, while the rotating stall is observed in that with 5 blades. The conclusions can be obtained as follows:

    (1) For the alternative stall, the stall cells are fixed relative to the impeller, but a large vortex in the stalled passage is always swaying. The outlet vortex is generated from it, and then develops and sheds periodically. The pressure fluctuation caused by the outlet vortex motion, acting on the blades, appears as a “broadband” with a high frequency. Further, the large vortex shows an obvious life cycle including decay, split, mergence and growth, which results in a low frequency compared with the impeller passing frequency. With the decrease of the flow rate, the amplitude of the low frequency fluctuation tends to be larger, but the “broadband” with a high frequency keeps almost the same.

    (2) For the rotating stall, the stall cells first occur in the suction side of the blade. With the growth of the stall cells, the block area gradually increases until the inlet region is almost blocked, then moves to the pressure side with a continuous decay. When the rotating stall occurs, the amplitude of the pressure fluctuation is much larger than that under the alternative stall condition. The propagation of the stall cells has a significant effect on the pressure fluctuations in the impeller. The dominant frequency of the pressure fluctuation on the blade is the rotating stall frequency. With the decrease of the flow rate, the amplitude of the pressure fluctuations changes little,while the rotating stall frequency decreases.

    猜你喜歡
    陳婷佩劍
    我國女子佩劍技戰(zhàn)術打法特征及發(fā)展趨勢探究
    當代體育(2021年37期)2021-11-27 13:19:42
    Germs May Make Us Ill
    一個非終止7F6-級數(shù)求和公式的q-模擬
    駐村隊里的手搟面
    黃河之聲(2019年1期)2019-03-30 03:36:16
    Influence of upstream disturbance on the draft-tube flow of Francis turbine under part-load conditions *
    Investigation of rotating stall for a centrifugal pump impeller using various SGS models*
    全國首對肺移植戀人:以愛的刺青銘記你
    How to improve the oral English communication level of rural students
    我國男子佩劍運動員比賽中進攻技術統(tǒng)計分析
    擊劍體驗課
    一边摸一边做爽爽视频免费| 国产成人av激情在线播放| 色吧在线观看| 国产精品免费大片| 91久久精品国产一区二区三区| 成年女人毛片免费观看观看9 | 精品酒店卫生间| 亚洲精品日韩在线中文字幕| 国产精品秋霞免费鲁丝片| 免费播放大片免费观看视频在线观看| 国精品久久久久久国模美| 99热全是精品| 乱人伦中国视频| 日韩,欧美,国产一区二区三区| 亚洲av中文av极速乱| 日韩三级伦理在线观看| 色播在线永久视频| 伊人久久大香线蕉亚洲五| 亚洲第一青青草原| 久久久亚洲精品成人影院| 国产97色在线日韩免费| 王馨瑶露胸无遮挡在线观看| 日日啪夜夜爽| 大香蕉久久网| 少妇被粗大猛烈的视频| 黄片播放在线免费| 国产亚洲一区二区精品| 国产精品国产av在线观看| 色网站视频免费| 免费观看av网站的网址| 久久人妻熟女aⅴ| 久久精品国产亚洲av涩爱| 亚洲久久久国产精品| 妹子高潮喷水视频| www日本在线高清视频| 一本大道久久a久久精品| 大片免费播放器 马上看| 国产精品一二三区在线看| 男人添女人高潮全过程视频| 午夜福利,免费看| 久久久亚洲精品成人影院| 熟女少妇亚洲综合色aaa.| 午夜老司机福利剧场| 在现免费观看毛片| 国产av一区二区精品久久| 久久久久久久久久人人人人人人| 大陆偷拍与自拍| 香蕉丝袜av| 人妻一区二区av| 国产毛片在线视频| 性高湖久久久久久久久免费观看| 国产免费福利视频在线观看| 午夜激情久久久久久久| 一二三四在线观看免费中文在| 欧美在线黄色| 亚洲精品视频女| 一级毛片电影观看| 欧美成人午夜精品| 另类亚洲欧美激情| 婷婷色麻豆天堂久久| 国产精品三级大全| 韩国av在线不卡| h视频一区二区三区| 制服丝袜香蕉在线| 亚洲综合色网址| 亚洲精品日本国产第一区| 精品视频人人做人人爽| 国产女主播在线喷水免费视频网站| 七月丁香在线播放| www日本在线高清视频| 久久久a久久爽久久v久久| 色94色欧美一区二区| 久久精品久久久久久噜噜老黄| 免费观看无遮挡的男女| 免费黄网站久久成人精品| 老汉色av国产亚洲站长工具| 国产黄频视频在线观看| 国精品久久久久久国模美| 飞空精品影院首页| 欧美老熟妇乱子伦牲交| 久久久久久久久久久久大奶| 丰满迷人的少妇在线观看| 三级国产精品片| 国产av一区二区精品久久| 麻豆av在线久日| 多毛熟女@视频| 狂野欧美激情性bbbbbb| 中文字幕人妻丝袜一区二区 | 黑人猛操日本美女一级片| 久久精品夜色国产| 宅男免费午夜| 69精品国产乱码久久久| 日韩欧美精品免费久久| 两个人免费观看高清视频| 亚洲av国产av综合av卡| 黄片播放在线免费| 丝袜在线中文字幕| 国产成人精品在线电影| 18禁裸乳无遮挡动漫免费视频| 一本大道久久a久久精品| 新久久久久国产一级毛片| 最近中文字幕2019免费版| 色婷婷av一区二区三区视频| av网站在线播放免费| 国产精品 欧美亚洲| 9色porny在线观看| 午夜福利影视在线免费观看| 热99国产精品久久久久久7| 亚洲av免费高清在线观看| 国产精品99久久99久久久不卡 | 三上悠亚av全集在线观看| 国产欧美亚洲国产| av片东京热男人的天堂| 亚洲欧美中文字幕日韩二区| 一本一本久久a久久精品综合妖精 国产伦在线观看视频一区 | 好男人视频免费观看在线| 亚洲精品一区蜜桃| 最近最新中文字幕大全免费视频 | 久久久精品国产亚洲av高清涩受| www日本在线高清视频| 成人午夜精彩视频在线观看| av福利片在线| 日韩免费高清中文字幕av| 丁香六月天网| 成年美女黄网站色视频大全免费| 成年女人毛片免费观看观看9 | 午夜免费观看性视频| 亚洲av中文av极速乱| 日韩成人av中文字幕在线观看| 18禁动态无遮挡网站| 美女脱内裤让男人舔精品视频| 一边亲一边摸免费视频| 热re99久久精品国产66热6| www.av在线官网国产| 亚洲伊人久久精品综合| 秋霞在线观看毛片| 叶爱在线成人免费视频播放| 久久久久人妻精品一区果冻| 亚洲伊人色综图| 永久网站在线| 亚洲,一卡二卡三卡| 极品少妇高潮喷水抽搐| 最新的欧美精品一区二区| 日本爱情动作片www.在线观看| 十八禁高潮呻吟视频| 99精国产麻豆久久婷婷| av天堂久久9| 欧美日韩亚洲高清精品| 天天操日日干夜夜撸| 久久影院123| 久热久热在线精品观看| videosex国产| 久久久久视频综合| 国产精品国产三级国产专区5o| 成年人免费黄色播放视频| av片东京热男人的天堂| 天堂俺去俺来也www色官网| 日韩,欧美,国产一区二区三区| 十分钟在线观看高清视频www| 777久久人妻少妇嫩草av网站| 一本一本久久a久久精品综合妖精 国产伦在线观看视频一区 | a级毛片黄视频| 宅男免费午夜| 日韩制服骚丝袜av| √禁漫天堂资源中文www| 91久久精品国产一区二区三区| 日日爽夜夜爽网站| av片东京热男人的天堂| 精品久久久久久电影网| 爱豆传媒免费全集在线观看| 久久久久久久久免费视频了| 精品国产国语对白av| 国产黄色视频一区二区在线观看| 18禁动态无遮挡网站| 亚洲少妇的诱惑av| 久久久久国产网址| av在线观看视频网站免费| 男女边吃奶边做爰视频| 9热在线视频观看99| 免费少妇av软件| 亚洲经典国产精华液单| 哪个播放器可以免费观看大片| 久久午夜综合久久蜜桃| 一级a爱视频在线免费观看| 老女人水多毛片| 久久女婷五月综合色啪小说| 日韩不卡一区二区三区视频在线| 日日摸夜夜添夜夜爱| 久久久久精品性色| 免费看av在线观看网站| 久久精品aⅴ一区二区三区四区 | 母亲3免费完整高清在线观看 | 久久精品久久精品一区二区三区| 亚洲精品在线美女| 熟女电影av网| 青青草视频在线视频观看| 男人舔女人的私密视频| 这个男人来自地球电影免费观看 | 国产精品蜜桃在线观看| 国产成人精品久久久久久| 777米奇影视久久| 欧美日韩精品网址| 国产成人精品在线电影| 亚洲情色 制服丝袜| 新久久久久国产一级毛片| 伊人亚洲综合成人网| 黄色怎么调成土黄色| 天天躁狠狠躁夜夜躁狠狠躁| 日韩伦理黄色片| 色婷婷久久久亚洲欧美| 亚洲精品美女久久久久99蜜臀 | 26uuu在线亚洲综合色| 国产精品久久久久成人av| a级片在线免费高清观看视频| 精品一区二区免费观看| 久久精品久久久久久久性| 精品国产露脸久久av麻豆| 成人18禁高潮啪啪吃奶动态图| videos熟女内射| 男女边摸边吃奶| 丝袜美足系列| 18+在线观看网站| 精品一区二区三区四区五区乱码 | 免费av中文字幕在线| 美女视频免费永久观看网站| 交换朋友夫妻互换小说| 精品卡一卡二卡四卡免费| 丝袜喷水一区| 亚洲欧洲国产日韩| 国产一级毛片在线| 亚洲av中文av极速乱| 国产免费一区二区三区四区乱码| 精品少妇黑人巨大在线播放| 欧美国产精品一级二级三级| 自线自在国产av| 男女啪啪激烈高潮av片| 日韩欧美精品免费久久| 国产在线视频一区二区| 中文字幕最新亚洲高清| 男女无遮挡免费网站观看| 最新中文字幕久久久久| 亚洲欧美精品综合一区二区三区 | 人人澡人人妻人| 在线观看人妻少妇| 十八禁网站网址无遮挡| 国产精品.久久久| 狠狠婷婷综合久久久久久88av| av网站免费在线观看视频| 亚洲欧美成人综合另类久久久| 黑人猛操日本美女一级片| 亚洲国产最新在线播放| 在线亚洲精品国产二区图片欧美| 国产精品不卡视频一区二区| 久久久久久伊人网av| 日韩一区二区三区影片| 欧美精品人与动牲交sv欧美| 亚洲精品国产av成人精品| 91精品三级在线观看| 精品午夜福利在线看| 国产精品久久久久久久久免| 欧美亚洲 丝袜 人妻 在线| 超碰成人久久| 久久久久精品人妻al黑| 亚洲国产精品一区三区| 久热这里只有精品99| av免费在线看不卡| 18禁观看日本| 久久精品亚洲av国产电影网| 国产精品免费视频内射| 亚洲一码二码三码区别大吗| 色播在线永久视频| 国产淫语在线视频| 亚洲图色成人| xxxhd国产人妻xxx| 美国免费a级毛片| 精品国产超薄肉色丝袜足j| 久久这里有精品视频免费| 黄频高清免费视频| 777米奇影视久久| 亚洲一区中文字幕在线| 久久婷婷青草| 国产黄色免费在线视频| 一区二区三区四区激情视频| 国产一级毛片在线| 久久国产精品大桥未久av| 日韩中文字幕视频在线看片| 国产 精品1| 免费在线观看完整版高清| av免费观看日本| 99久久综合免费| 天天影视国产精品| 午夜日本视频在线| 91在线精品国自产拍蜜月| 久久狼人影院| av片东京热男人的天堂| 丝瓜视频免费看黄片| 超色免费av| 在现免费观看毛片| 狠狠婷婷综合久久久久久88av| 一区二区三区四区激情视频| 18禁国产床啪视频网站| 一级毛片电影观看| 日韩精品免费视频一区二区三区| 日韩大片免费观看网站| av在线app专区| 亚洲天堂av无毛| 日韩 亚洲 欧美在线| videosex国产| 亚洲精品国产一区二区精华液| 日日啪夜夜爽| 国产国语露脸激情在线看| 在线免费观看不下载黄p国产| 免费观看av网站的网址| 国产精品久久久久久av不卡| 在线精品无人区一区二区三| 成人影院久久| 午夜免费男女啪啪视频观看| 最新的欧美精品一区二区| 自拍欧美九色日韩亚洲蝌蚪91| 91精品伊人久久大香线蕉| 老汉色∧v一级毛片| 久久这里有精品视频免费| 肉色欧美久久久久久久蜜桃| 香蕉国产在线看| 成人漫画全彩无遮挡| 黄色视频在线播放观看不卡| 宅男免费午夜| 久久精品亚洲av国产电影网| 中国国产av一级| 中文字幕亚洲精品专区| 在线天堂最新版资源| av天堂久久9| 熟妇人妻不卡中文字幕| 丝袜美腿诱惑在线| 欧美中文综合在线视频| 18禁动态无遮挡网站| 最近最新中文字幕大全免费视频 | 亚洲第一青青草原| 极品人妻少妇av视频| 亚洲欧美精品综合一区二区三区 | 久久久久精品久久久久真实原创| 欧美国产精品va在线观看不卡| 欧美在线黄色| 国产精品 国内视频| 一级毛片电影观看| 丝袜脚勾引网站| 久久久欧美国产精品| 国产一区二区三区av在线| 一二三四中文在线观看免费高清| 亚洲三级黄色毛片| 欧美日韩亚洲国产一区二区在线观看 | 纵有疾风起免费观看全集完整版| 欧美日韩av久久| 国产成人精品久久久久久| 国产精品久久久久成人av| 中文字幕另类日韩欧美亚洲嫩草| 春色校园在线视频观看| 香蕉丝袜av| 亚洲成人手机| 精品国产乱码久久久久久男人| 亚洲国产最新在线播放| 日本-黄色视频高清免费观看| 国语对白做爰xxxⅹ性视频网站| 国产男女超爽视频在线观看| 午夜老司机福利剧场| 日韩熟女老妇一区二区性免费视频| 午夜免费鲁丝| 不卡视频在线观看欧美| 日日爽夜夜爽网站| 久久国产精品大桥未久av| 午夜日韩欧美国产| 亚洲av电影在线进入| 精品国产国语对白av| 五月开心婷婷网| 亚洲 欧美一区二区三区| 亚洲精品美女久久av网站| 亚洲色图综合在线观看| 久久鲁丝午夜福利片| 亚洲,一卡二卡三卡| 美女高潮到喷水免费观看| 看免费av毛片| 黄色配什么色好看| av国产久精品久网站免费入址| 亚洲经典国产精华液单| 一本大道久久a久久精品| 天堂中文最新版在线下载| 国产精品久久久久成人av| 亚洲欧美精品自产自拍| 美女国产高潮福利片在线看| 国产精品 国内视频| 少妇 在线观看| 国产极品天堂在线| 国产无遮挡羞羞视频在线观看| 国产 一区精品| 久热久热在线精品观看| 国产麻豆69| 久久精品国产亚洲av天美| 久久这里只有精品19| 97在线人人人人妻| 久久久久国产一级毛片高清牌| 国产免费又黄又爽又色| 国产激情久久老熟女| 午夜福利乱码中文字幕| 美女xxoo啪啪120秒动态图| 国产毛片在线视频| 卡戴珊不雅视频在线播放| 看十八女毛片水多多多| 高清欧美精品videossex| 成年美女黄网站色视频大全免费| 男人爽女人下面视频在线观看| 纵有疾风起免费观看全集完整版| 久久久久国产精品人妻一区二区| 18在线观看网站| 三级国产精品片| 欧美精品一区二区免费开放| 国产欧美日韩一区二区三区在线| 亚洲av成人精品一二三区| 亚洲精品一区蜜桃| 午夜激情久久久久久久| 国产成人午夜福利电影在线观看| 我的亚洲天堂| 热99久久久久精品小说推荐| 一级片免费观看大全| 欧美少妇被猛烈插入视频| 黄色毛片三级朝国网站| 一个人免费看片子| 国产精品av久久久久免费| 欧美日韩一级在线毛片| 一二三四中文在线观看免费高清| 涩涩av久久男人的天堂| 交换朋友夫妻互换小说| 观看美女的网站| 精品国产一区二区三区四区第35| 国产黄频视频在线观看| 久久久久久久久免费视频了| 一二三四在线观看免费中文在| 欧美变态另类bdsm刘玥| 制服诱惑二区| 我要看黄色一级片免费的| 精品一区二区三卡| 青草久久国产| 久久国产亚洲av麻豆专区| 久久精品国产a三级三级三级| 99香蕉大伊视频| 熟妇人妻不卡中文字幕| 亚洲av成人精品一二三区| 久久精品国产a三级三级三级| 色吧在线观看| 国产成人精品一,二区| 国产精品亚洲av一区麻豆 | 亚洲精品久久成人aⅴ小说| 在线观看三级黄色| 国产av一区二区精品久久| 色视频在线一区二区三区| 亚洲精品美女久久av网站| 日日摸夜夜添夜夜爱| 熟女电影av网| 人妻少妇偷人精品九色| av在线观看视频网站免费| 久久久久久久国产电影| 日韩不卡一区二区三区视频在线| 亚洲国产毛片av蜜桃av| 国产亚洲最大av| 人人妻人人爽人人添夜夜欢视频| 在线观看免费高清a一片| 99久久中文字幕三级久久日本| 精品人妻一区二区三区麻豆| 日韩av免费高清视频| 少妇的逼水好多| 久久综合国产亚洲精品| 国产高清不卡午夜福利| 女性被躁到高潮视频| 亚洲av中文av极速乱| 国产成人欧美| 精品久久久久久电影网| 男女无遮挡免费网站观看| av天堂久久9| 久久鲁丝午夜福利片| 精品少妇内射三级| 久久99一区二区三区| 一级黄片播放器| 婷婷色综合大香蕉| 涩涩av久久男人的天堂| 伦理电影免费视频| 国产一区二区激情短视频 | 久久久久久久久久人人人人人人| 免费在线观看视频国产中文字幕亚洲 | 亚洲,一卡二卡三卡| 国产精品一区二区在线观看99| 99久国产av精品国产电影| 国产精品 国内视频| 黄网站色视频无遮挡免费观看| 免费人妻精品一区二区三区视频| 中文乱码字字幕精品一区二区三区| 国产免费现黄频在线看| 日韩成人av中文字幕在线观看| h视频一区二区三区| 成人国产av品久久久| 国产黄色免费在线视频| 久久久久网色| 精品国产一区二区三区久久久樱花| 久久99热这里只频精品6学生| av视频免费观看在线观看| av片东京热男人的天堂| 女的被弄到高潮叫床怎么办| 亚洲av中文av极速乱| 免费在线观看视频国产中文字幕亚洲 | 久久国产精品男人的天堂亚洲| 人人妻人人澡人人看| 国产精品国产三级国产专区5o| 人体艺术视频欧美日本| 啦啦啦中文免费视频观看日本| 国产又色又爽无遮挡免| 亚洲精品国产一区二区精华液| 精品亚洲成国产av| 精品一区二区免费观看| 人妻少妇偷人精品九色| 中文字幕另类日韩欧美亚洲嫩草| 看免费av毛片| 欧美激情 高清一区二区三区| 国产男人的电影天堂91| 亚洲少妇的诱惑av| 久久久久精品久久久久真实原创| 免费日韩欧美在线观看| 99精国产麻豆久久婷婷| 啦啦啦视频在线资源免费观看| 一区二区日韩欧美中文字幕| 只有这里有精品99| 一级黄片播放器| 免费观看av网站的网址| 国语对白做爰xxxⅹ性视频网站| 中文天堂在线官网| 国产一级毛片在线| 一级片'在线观看视频| a级片在线免费高清观看视频| 丰满少妇做爰视频| 男女啪啪激烈高潮av片| 欧美成人午夜免费资源| 夫妻午夜视频| 女人久久www免费人成看片| 亚洲国产色片| 午夜av观看不卡| 国产成人精品一,二区| 人人澡人人妻人| 你懂的网址亚洲精品在线观看| 少妇人妻精品综合一区二区| 一区二区av电影网| 蜜桃在线观看..| 精品少妇内射三级| 汤姆久久久久久久影院中文字幕| 欧美成人午夜免费资源| 国产视频首页在线观看| 亚洲成色77777| 一边摸一边做爽爽视频免费| 亚洲伊人久久精品综合| 国产伦理片在线播放av一区| 亚洲综合精品二区| 91国产中文字幕| 久久久a久久爽久久v久久| 观看美女的网站| 亚洲欧美一区二区三区黑人 | 久久久久视频综合| 91精品三级在线观看| 免费日韩欧美在线观看| 午夜av观看不卡| 日韩电影二区| 亚洲,一卡二卡三卡| 天天躁夜夜躁狠狠久久av| 国产精品蜜桃在线观看| 国产精品欧美亚洲77777| 日本黄色日本黄色录像| av女优亚洲男人天堂| 国产精品秋霞免费鲁丝片| 国产午夜精品一二区理论片| 午夜老司机福利剧场| 午夜日本视频在线| 一个人免费看片子| 黄片播放在线免费| 边亲边吃奶的免费视频| 中文字幕亚洲精品专区| 精品一区在线观看国产| 久久久国产精品麻豆| 亚洲五月色婷婷综合| 精品一区二区免费观看| 国产精品二区激情视频| 99久国产av精品国产电影| 久久精品久久久久久噜噜老黄| 成年动漫av网址| 热re99久久国产66热| 亚洲精品久久久久久婷婷小说| 在线观看人妻少妇| 久久久久久久精品精品| 国产女主播在线喷水免费视频网站| 久久久久久人妻| 亚洲欧洲精品一区二区精品久久久 | 91精品三级在线观看| 中文乱码字字幕精品一区二区三区| 免费观看a级毛片全部| 青春草视频在线免费观看| 91精品国产国语对白视频| 亚洲激情五月婷婷啪啪| 在线观看人妻少妇| 青青草视频在线视频观看| 成人毛片60女人毛片免费| 如何舔出高潮| 国产高清国产精品国产三级| 人体艺术视频欧美日本| 久久久久久久大尺度免费视频| 久久久久视频综合| 性高湖久久久久久久久免费观看| 亚洲欧美一区二区三区国产| 一本—道久久a久久精品蜜桃钙片| 老汉色av国产亚洲站长工具| 少妇 在线观看| 亚洲精品乱久久久久久|