• <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 ?

    Effect of polymer and fiber additives on pressure drop in a rectangular channel *

    2017-11-02 09:09:15AmirEshghinejadfardKashyapaSharmaDominiqueThvenin
    水動力學研究與進展 B輯 2017年5期

    Amir Eshghinejadfard, Kashyapa Sharma, Dominique Thévenin

    Laboratory of Fluid Dynamics and Technical Flows, University of Magdeburg “Otto von Guericke”,Universit?tsplatz 2, 39106 Magdeburg, Germany, E-mail: amir.eshghinejadfard@ovgu.de

    Effect of polymer and fiber additives on pressure drop in a rectangular channel*

    Amir Eshghinejadfard, Kashyapa Sharma, Dominique Thévenin

    Laboratory of Fluid Dynamics and Technical Flows, University of Magdeburg “Otto von Guericke”,Universit?tsplatz 2, 39106 Magdeburg, Germany, E-mail: amir.eshghinejadfard@ovgu.de

    The influence of minute amounts of additives on pressure drop is an interesting fundamental phenomenon, potentially with important practical applications. Change of the pressure drop in a quasi-two-dimensional channel flow using various additives is experimentally investigated. Tests were conducted for a wide range of concentrations (100 ppm-500 ppm) and Reynolds numbers(16 000-36 000) with two polymers and four rigid fibers used as additive. Maximum drag reduction of 22% was observed for xanthan gum. However, xanthan gum loses its drag-reducing property rapidly. It was also seen that drag reduction percentage of xanthan gum remains almost constant for different Reynolds numbers. Guar flour demonstrated good drag reduction property at high Reynolds numbers. Drag reduction of 17.5% at R e = 33200 using 300 ppm solution was observed. However, at low Reynolds numbers guar flour will cause an increase in pressure drop. Fiber fillers (aspect ratio=21) have been tested as well. In contrast to polymers, they increased the drag for the range of examined concentrations and Reynolds numbers. Polyacrylonitrile fiber with three different aspect ratios (106, 200, 400) was also used, which showed an increase in pressure drop at low aspect ratios. Polyacrylonitrile fibers of larger lengths (6 mm) demonstrated minor drag-reducing effects (up to 3%).

    Pressure drop, polymer, fiber, channel flow

    Introduction

    Effect of suspended particles and additives on flow properties is always an important topic for both experimental and numerical studies. In this regard,some types of additives lead to lower pressure drop in the flow[1-3]while some others increase it[4,5]. Particle and fluid type in addition to flow regime and geometry play the main roles in this regard. Therefore, recognizing the conditions that can result in reduction or enhancement of pressure drop is of great importance.

    Reduction of pressure drop and consequently pumping cost is an interesting topic for many liquid transportation systems. This can be achieved by addition of small amounts of drag-reducing agents(DRA)[6]. The concept of drag reduction (DR) can be traced back to the work of Toms[7]. He discovered that introduction of a few parts per million (ppm) of longchain polymers can result in reduction of wall friction.DR leads to an increase of pipeline flow rate for the same pressure head. Most studies focus on polymers as drag reduction agent[8-11]. In this regard, long-chain and flexible polymers such as polyacrylamide and polyethylene oxide (PEO) are recognized as DRA.Onset of DR occurs when polymers are unraveled from the coiled to an extended conformation. Therefore, DR due to polymer solutions is expected to happen beyond a certain Reynolds number for a unique concentration. Below this Reynolds number usually no DR is observed.

    Two types of explanation have been given for the onset of DR when polymers are utilized. Some researchers[12-14]attribute DR to viscous effects. They reason that stretching of polymers in the regions of strong deformations of flow field leads to a higher effective viscosity in this turbulent region and consequently the thickness of buffer region is increased and velocity gradient is reduced. On the other hand, the elastic theory of Tabor and De Gennes[15]postulates that DR occurs when the elastic energy of polymers is large enough to terminate the Kolmogorov-type energy cascade. A major practical problem associated with flexible polymers is their fast thermal, biological, chemical, or mechanical degradation. This would limit their application to one-passsystems. Nowadays, rigid polymers[16], surfactants[17],bubbles[18], nanoparticles[19]and fibers[20,21]have been proven as possible alternatives for flexible polymers.

    In most cases from dilute to dense regimes,however, pressure drop increases after addition of rigid particles[22-27]. This effect is highly dependent on particle shape, Stokes number ()St and solid phase volume fraction ()φ. There are many practical cases,in which, fibers or polymers are transported by the piping system. It would be thus important to recognize the conditions that can lead to each of above mentioned pathways and to understand the effect of different additives on decrease or increase of pressure drop.

    The current work aims at experimentally investigating the influence of different additives on pressure drop in a straight rectangular channel. The experimental set-up includes a long channel of rectangular cross section to mimic a quasi-two-dimensional flow.Pressure drop measurements are performed and results are compared with those of pure water to calculate the pressure drop change. The first part of the results deals with behavior of semi-rigid polymers (xanthan gum, guar flour) and investigates their effect for different flow rates. Since less attention has been paid to rigid particles so far, the second part considers the effect of rigid particle shape, concentration and size on pressure drop in semi-dilute regime. In the end, we aim to arrive at a final method on the selection of rigid fibers to lower the pressure drop in particle-laden systems.

    1. Turbulent channel flow characteristics

    For theoretical calculations, a fully developed turbulent flow through a channel is assumed in this study. Pressure drop and flow characteristics are thus related through

    where is the fluid density,Df is Darcy friction factor,Ff is Fanning friction factor, L is distance,Dhis the hydraulic diameter and Ubis the mean(bulk) velocity. Due to large width to height ratio of the channel, Dhis considered to be equal to 4H with H being the half-channel height. Consequently,the friction velocity (uτ) is given by

    withwτ being the mean shear stress at the wall and Δ p a constant pressure gradient. The Reynolds number based on the friction velocity reads

    where is the fluid kinematic viscosity. The bulk Reynolds number is given based on the channel height by

    The Fanning friction factor for turbulent fluid flow in smooth pipes is usually described by the Prandtl-von Karman (PK) expression[28]

    In the case of water as carrier fluid, the Blasius approximation can be used as well

    Based on the Virk's maximum drag reduction(MDR) asymptote[29], the lowest friction factor that can be attained in a turbulent flow is defined by

    Therefore, the friction factor of a drag-reducing system must fall between the PK law and Virk's MDR asymptote for a given Reynolds number. In multiphase flows, DR percent is defined as the ratio of reduction in the pressure drop to the pressure drop without DRA

    Here, subscripts 0 and DR denote the states in the absence and presence of DRA, respectively. Both pressure drops are measured at the same Reynolds number based on water properties.

    Another important parameter in particle-laden turbulent flows (mainly for rigid particles) is the particle Stokes number. It is defined as the ratio of the particle response time (τp) to the characteristic time scale of the turbulent flow. A particle with low Stokes number responds quickly to the flow. Characteristic time scale of the fluid flow can be either theone is denoted by S tKand the latter one by S t+.Elghobashi[30,31]presented a classification map for particle-laden turbulent flows based on the volume fraction and Stokes number. This map shows whether the turbulent kinetic energy (TKE) in the presence of particles in dilute regime will increase or decrease.For dilutesuspension of rigid particleshe recognized two main zones based on the Kolmogorov Stokes number. Normally, for very low Stokes numbers(Microparticles) TKE increases.Forparticles do not respond immediately to velocity fluctuations of surrounding fluid. Thus,reduction of both TKE and dissipation relative to the single-phase flow is expected. For10≥ , due to vortex shedding behind the particle, TKE increases.However, in dense regimes with finite-size particles reduction of TKE and Reynolds shear stress was observed[4,32]. In contrast to TKE whose changes can be distinguished based on the solid phase volume fraction and Stokes number, changes in the pressure drop show strong dependency on particle shape and Reynolds number as well. It means that reduction of turbulence intensity does not necessarily lead to drag reduction and many other parameters must be considered. For example, in numerical studies of Zhao and van Wachem[25], the turbulence kinetic energy decreased by 6.0% for the flow with spherical particles and by 4.8% for the ellipsoidal particles, but the mean flow velocity is reduced as compared with single-phase flow. These effects will be discussed in the following sections.

    Fig.1(a) Sketch of the experimental set-up

    Fig.1(b) Channel cross section

    2. Experimental set-up and procedure

    Figure 1(a) depicts a sketch of the experimental set-up. A rectangular channel is used as the main test section. Channel length is 6 m and its cross section is rectangular with aspect ratio of 200 mm to 10 mm(Fig.1(b)). A stainless steel tank, pressure transmitter,temperature sensor (thermometer), flow meter and flow regulating pump were used in the set-up as well.The set-up works as a closed loop where the fluid runs from an open stainless steel tank through aΦ50mm diameter pipe section followed by the channel, and finally returns to the tank. Transition from the circular cross section of the pipe to the rectangular section of the channel has very gentle slope to prevent any sudden change in the flow. The screw pump regulates the fluid flow rate.

    The pressure drop measurements were performed between two pressure taps that are placed 1 m apart using a Hottinger-Baldwin differential pressure transmitter. To obtain a hydrodynamically fully developed flow region, the pressure sensors were located far (2.8 m) from the transition zone between circular and rectangular cross-section. The zero error of the sensors was noted before each measurement and subsequently used in the final results calculation. The thermometer installed on the discharge line of the tank records the temperature; the flow rate of the fluid is measured using a magnetic flow meter (Endress and Hauser). Tap water was used as working fluid and the influence of the following additives on the pressure drop was investigated:

    (1) Xanthan gum, which is a high molecular weight polysaccharide with a semi-rigid structure.Its primary structure consists of repeated pentasaccharide units formed by two glucose units, two mannose units, and one glucuronic[33]. Xanthan gum increases the viscosity of the liquid when it is added in very low concentrations at moderate temperatures.Owing to its distinct rheological properties, it is known as an important industrial biopolymer and has broad applications in food and cosmetic products.The xanthan gum E-415 from Carl Roth Co. (size 80 mesh) was used in the experiments.

    (2) Guar flour, from Carl Roth Co. (CAS 9000-30-0) was used. Guar flour mainly consists of high molecular weight polysaccharides with an average size of up to some hundred microns obtained from the guar plant seed and composed of watersoluble galactomannans which are formed from a linear chain of (14→)-linked β-D-mannopyranosyl units with (16→)-linked α-D-galactopyranosyl residues as side chains. Its main applications are in the food industry.

    (3) Carbon filler, SFC-B10 (from Schwarzw?lder Textil-Werke group) which is a short length carbon fiber consisting of very thin strands of the element carbon with density of 1 780 kg/m3was also tested. Its average diameter and length are 7 μm and 150 μm,respectively, which results in aspect ratio equal to 21.The elastic modulus of this fiber is 190 GPa.

    (4) Polyacrylonitrile fiber, which is a high strength and high modulus of elasticity white-yellowish fiber from Schwarzw?lder Textil-Werke group known as PAC251 with a specific gravity of 1.18 was used. It has various applications in textile, composite materials and aircraft industry. The fiber diameter is approximately 15 μm and available in various lengths.For the experiment, 1.6, 3 and 6 mm fibers at different concentrations were used. The elastic modulus of this type of additive is 10 GPa-12 GPa.

    Different preparation procedures were used for individual additives. For xanthan gum, the required quantity of the gum was added directly into the tank and mixed for 30 min using a hydrofoil blade mixer(tank stirrer). The system was left alone for at least 24 h to let the gum dissolve gradually in the water.The drag-reducing capacity of the xanthan gum was not instantly retrieved. Therefore, the experiments were carried out with batches of 8 h continuous operation each. Above this duration, the DR effect of the xanthan solution decreased noticeably. For each concentration, the entire set-up was cleaned and a fresh batch of sample and water was used.

    To obtain a homogeneous mixture for the fibers the samples were prepared outside the system. Small quantities of the sample (50 g-70 g) were dispersed in 3 to 5 liters of water and stirred using a small stirrer in a separate set-up. Small quantity of soap solution was used in order to obtain good dispersion of the sample.Batches of prepared sample solutions were later transferred into the main tank. Along with the above mentioned procedure, the tank stirrer was finally used for at least 2 h to obtain a homogeneous dispersed phase. For higher concentration, new batches of fiber solutions were added to the existing mixture. Each experiment took at least 3 h of continuous run.

    Fig.2 Friction factor vs. Re for water and xanthan gum

    Fig.3 DR percentage vs. Re for xanthan gum and carbon fillers

    3. Experimental results

    3.1Part I: Polymers

    3.1.1 Xanthan gum

    In this section the measurement results for water and 100 ppm and 200 ppm solutions of xanthan gum are presented. Friction factor versus Reynolds number is plotted in Fig.2. It is observed that, for the examined range of Reynolds number (Re=18000-36000), the pressure drop measured from water circulation is in close consistency with the Prandtl-von Karman (PK) correlation (Eq.(5)). Brown squares represent Virk's MDR theory (Eq.(7)). DR capability of xanthan gum can be clearly observed for both 100 and 200 ppm solutions. As expected, a higher DR percentage is achievable at higher concentrations of polymer.However,for current concentrations(100 ppm and 200 ppm) DR is lower than maximum DR asymptote.

    On the other hand, it is seen that xanthan gum loses its effectiveness rapidly. In this regard, degraded solution of 200 ppm has a lower efficiency than 100 ppm fresh solution. This occurs after only 15 h of running the apparatus. DR percentage for various Reynolds numbers is reported in Fig.3. DR percentage is computed from Eq.(8) at the same temperature of water and xanthan solution to exclude the effect of temperature on water density and viscosity. It is seen that DR initially shows some dependency on Reynolds number but tends to reach a constant value. This transition to constant DR percentage occurs at higher Reynolds number when the polymer concentration is higher. Maximum DR percentage in the range of examined flow rates was observed atRe=33890 standing at 22% for a solution containing 200 ppm xanthan gum.

    It must be noted that the current channel is rather narrow. In larger systems, use of higher concentrations of polymers is easier without formation of clumps. The reduced efficiency of polymers can be obviously observed from Fig.3. This reduction of efficiency is mainly attributed to de-aggregation of rigid polymers[34].

    3.1.2 Guar flour

    The next polymer that is studied in this part is guar flour. Two concentrations of 100 ppm and 300 ppm are considered. The results of changes in pressure drop are shown in Fig.4. This figure illustrates that guar flour does not demonstrate any drag reduction at Reynolds numbers less than 21 000.In the range of low Reynolds numbers, both concentrations led to pressure drop increase. A maximum increase of 9.4% was observed for 100 ppm guar gum solution. Furthermore, the amount of this increase is almost similar for both 100 ppm and 300 ppm solutions. AtRe? 2 2000 guar flour neither increases, nor decreases the pressure drop. At higher Reynolds numbers (Re>2 2000),a noticeable drag reduction is seen from the graph. Higher concentration (300 ppm) yields higher DR percentage.Its corresponding graph has a higher slope as well.This trend is approximated by a third order polynomial fit for both concentrations. One can get 17.5% drag reduction atRe= 33200 when 300 ppm guar flour is used. This percentage remained constant after 3 h of running the system. Maximum DR percentage attained by using 100 ppm solution was 10.8% atRe= 31300.

    Fig.4 DR percentage vs. Re for guar flour

    Fig.5 DR percentage vs. Re for Polyacrylonitrile fiber

    3.2Part II: Fibers

    3.2.1 Carbon fillers

    The influence of carbon fillers (SFC-B10) (with concentrations of 300 ppm and 500 ppm) on pressure drop is shown in Fig.3 as a function of Reynolds number and compared with those from xanthan gum.It is interesting to see that carbon fillers produce no DR effect. In contrast, this type of rigid fibers leads to extra pressure drop in the system. The pressure drop increase was up to 5%. This effect can be attributed to their low length to diameter ratio and relatively high specific gravity and will be discussed in more details in Section 3.3. Carbon fillers are not able to modify the near-wall turbulence structure even at higher concentration of 500 ppm. Although the increase in pressure drop is slightly higher at low Re values, the slope of the trend line is very low. It can be seen also that results of both 300 ppm and 500 ppm are very close to each other.

    3.2.2 Polyacrylonitrile fiber

    The results corresponding to this type of fiber(PAC251) are given in Fig.5. Three different particle lengths namely 1.6 mm, 3 mm and 6 mm have been examined. It is seen from the figure that, the shortest fiber increases the pressure drop in the pipeline for the whole range of flow rates examined. Maximum increase of 5% in the pressure drop was observed for 300 ppm of 1.6 mm length fiber. The results for both 300 and 500 ppm concentrations are in the same range.This effect is due to low Stokes number of particles.By using 3 mm long fibers, pressure drop remains close to that of pure water but minor drag reduction effect was observed. Interestingly, 6 mm length fibers atc=500ppm showed drag reduction up to 3%.This part of the experiment proves that, in the case of rigid fibers, the ratio of fiber length to diameter plays the main role in DR. At low aspect ratios, particles cannot change the flow field structures. They can lead to a lower pressure drop only when their aspect ratio is sufficiently high.

    It must be pointed out that, we should not expect high levels of drag reduction in dilute regimes of fiber-laden flows. This statement is supported by numerical studies of Zhao et al.[35]. They examined elongated ellipsoids with major and minor radii of 480 μm and 96 μm at volume fraction ofφ= 3.6×10-4andSt+=τp/τV=30. Drag reduction of less than 1% was observed in their simulations.

    3.3Physical effect of additives

    We are interested in the effect of additives on flow field based on the results given. In particular,finding the conditions that fibers decrease the pressure drop is important.

    In DR by polymers the change of polymer structure from a coiled to a stretched one is an important factor. The strain rate and vorticity fields in the buffer layer make it possible that this stretching leads to a larger thickness of the buffer layer[11]. Therefore,higher effective viscosity in this region leads to the reduction of momentum flux to the wall more than viscous drag enhancement and consequently dissipative eddies are damped. This effect is also influenced by Reynolds number because this transition to stretched formation is triggered easier at higher Reynolds numbers. For xanthan gum the transition occurs at relatively low Reynolds numbers.

    Now the reason behind the change in pressure drop by rigid fibers will be discussed. Turbulence intensity and pressure drop of particle-laden flows are influenced by particle shape, density, diameter (Stokes number) and volume fraction.

    The particle response time for ellipsoid particles can be evaluated by[36]

    where and a are the aspect ratio and length of minor-axis of the particle, respectively.

    For carbon fillers examined in this paper(SFC-B10, Section 3.2.1) particle size and density lead to very low Stokes number of particle based on friction velocity+0.04-0.13 St ≈ . These particles are referred to as “microparticles”[30]. Due to relatively small size of particles they can follow the streamlines which leads to higher flow turbulence.

    In general, total change of stresses in the system can be understood by the streamwise momentum budget which can be expressed by three terms[26]

    where is the total stress, τTis the turbulent Reynolds shear stress, τVis the viscous stress and τSis the stress induced by solid phase. In dilute regimes of carbon fillers, the increase of pressure drop can be justified by particle-induced stresses along with the increase of turbulence intensity of the fluid itself.The effect of particle-induced stresses on pressure drop enhancement was also reported in numerical studies of Ref.[26].

    Polyacrylonitrile fibers' behavior depends strongly on particle size and aspect ratio. By increasing the particle length from lp=1.6 mm to 6 mm particle Stokes number ( S t+) increases (from 0.58 to 0.75).Consequently, particle effect on the flow is expected to change from “ghost” particles (for lp=1.6mm) to“critical” particles (for lp=6mm). Ghost particle does not influence the TKE. However, viscous stressesVτ and particle-induced stressesSτ lead to higher pressure drop in the system. By further increasing the particle length (and aspect ratio) critical regime is reached. In the scope of critical regime,TKE of the fluid phase is reduced. These two effects of reduction of fluid flow turbulent intensity and particle-induced stress, counteract each other at some point and further increase of particle Stokes number results in drag reduction for 6 mm long fibers.

    Larger particleStokes numbers+( 1)St≥which can occur as a result of big particle selection(not present in this study) induce extra effect on turbulence intensity augmentation in dilute regime.Vortex shedding behind these particles gives rise to turbulence intensity even in the dilute regime.

    Effect of volume fraction in this study can be explained by tendency of the system to move from a dilute to dense regime. Approaching dense regime means that particle can change the structure of streamwise vortices, weaken their strength, thus reducing turbulence intensity. It must be noted also that fibers are more efficient in systems with large enough pipes and less elbows so that high volume fraction without any worry on system blockage can be reached. Furthermore, fibers are more resistant,particularly at high Reynolds numbers, where polymers are subject to high scission rates. It would also be helpful to select particles of better elasticity.

    4. Conclusions

    The influence of polymers and fibers on pressure drop in a channel flow of rectangular cross section has been experimentally investigated. Xanthan gum, guar flour, carbon filler and polyacrylonitrile fibers have been considered as additive. Based on our observations, following conclusions can be drawn:

    (1) A solution of 200 ppm xanthan gum revealed a noticeable DR of 22% at R e = 33000. However,this DRA loses its efficiency rapidly. Guar flour is another polymer examined in this experiment. At low Reynolds numbers, guar flour increased pressure drop for both 100 ppm and 300 ppm solutions. However, a drag reduction of up to 18% can be achieved with 300 ppm of guar flour.

    (2) Carbon fillers at 300 ppm and 500 ppm were tested as well. In both concentrations, an increase in pressure drop was seen, which is justified by their low ratio of length to diameter and low Stokes number.

    (3) Polyacrylonitrile fiber is another additive which is examined and introduced as a potential DRA with good rigidity. It demonstrates up to 3% drag reduction at high particle lengths with only 500 ppm concentration. Therefore, rigid particles decrease the pressure drop in the channel flow only when they have sufficiently high aspect ratios. However, due to their better resistance, mechanical degradation does not occur. This fiber is expected to yield more drag reduction if used in higher concentrations. In this study, due to small diameter of piping we tested concentrations up to 500 ppm.

    Based on the results shown, for future studies with rigid particles it would be helpful to use particles with following characteristics:

    (1) It is recommended to use particles of high aspect ratios (>100) to get more DR. For the same aspect ratio, moderate particle Stokes numbers are preferred. For Stokes numbers in the upper range of criteria mentioned, lower particle aspect ratios can be used. However, it must be noted that very large particles (with higher Stokes numbers) experience wake shedding, which increases turbulence and pressure drop consequently. Then, very large volume fractions and Reynolds numbers are probably required to get small levels of DR.

    (2) The next point is the proper selection of solid-phase volume fraction. Higher volume fractions of moderate Stokes number particles usually lead to more attenuation of turbulence.

    (3) Fibers can be preferably used as DRA in systems of relatively large size with few elbows to make high solid-phase volume fractions possible without any pipe blockage.

    (4) Better elasticity of particle is useful to reduce the pressure drop more but it is not a necessary parameter.

    For future studies, using higher volume fractions of rigid particles and high Stokes number particles are recommended.

    Acknowledgements

    The financial support of the German research foundation (DFG) within the graduate college for micro-macro-interactions in structured media and particle systems (GRK 1554) is gratefully acknowledged.

    [1] Shao X., Lin J., Wu T. et al. Experimental research on drag reduction by polymer additives in a turbulent pipe flow [J]. Canadian Journal of Chemical Engineering,2002, 80(2): 293-298.

    [2] Edomwonyi-Otu L. C., Chinaud M., Angeli P. Effect of drag reducing polymer on horizontal liquid–liquid flows[J]. Experimental Thermal and Fluid Science, 2015, 64:164-174.

    [3] Steele A., Bayer I. S., Loth E. Pipe flow drag reduction effects from carbon nanotube additives [J]. Carbon, 2014,77(2): 1183-1186.

    [4] Shao X., Wu T., Yu Z. Fully resolved numerical simulation of particle-laden turbulent flow in a horizontal channel at a low Reynolds number [J]. Journal of Fluid Mechanics, 2012, 693: 319-344.

    [5] Uhlmann M. Interface-resolved direct numerical simulation of vertical particulate channel flow in the turbulent regime [J]. Physics of Fluids, 2008, 20(5): 53305.

    [6] Gyr A., Bewersdorff H.-W. Drag reduction of turbulent flows by additives [M]. Dordrecht, The Netherlands:Kluwer Academic, 1995.

    [7] Toms B. A. Some observations on the flow of linear polymer solutions through straight tubes at large Reynolds numbers [C]. First International Congress on Rheology.Scheveningen, The Netherlands, 1948, 135-141.

    [8] Warholic M. D., Massah H., Hanratty T. J. Influence of drag-reducing polymerson turbulence:Effectsof Reynolds number, concentration and mixing [J]. Experiments in Fluids, 1999, 27(5): 461-472.

    [9] Ptasinski P. K., Nieuwstadt F. T. M., Van Den Brule B. et al. Experiments in turbulent pipe flow with polymer additives at maximum drag reduction [J]. Flow, Turbulence and Combustion, 2001, 66(2): 159-182.

    [10] Mowla D., Naderi A. Experimental study of drag reduction by a polymeric additive in slug two-phase flow of crude oil and air in horizontal pipes [J]. Chemical Engineering Science, 2006, 61(5): 1549-1554.

    [11] White C. M., Mungal M. G. Mechanics and prediction of turbulent drag reduction with polymer additives [J].Annual Review of Fluid Mechanics, 2008, 40(1): 235-256.

    [12] Lumley J. L. Drag reduction by additives [J]. Annual Review of Fluid Mechanics, 1969, 1(1): 367-384.

    [13] Ryskin G. Turbulent drag reduction by polymers: A quantitative theory [J]. Physical Review Letters, 1987,59(18): 2059.

    [14] Gillissen J. J. J. Polymer flexibility and turbulent drag reduction [J]. Physical Review E Statistical Nonlinear and Soft Matter Physics, 2008, 78(4): 046311.

    [15] Tabor M., De Gennes P. G. A cascade theory of drag reduction [J]. Europhysics Letters, 1986, 2(7): 519-522.

    [16] Japper-Jaafar A., Escudier M. P., Poole R. J. Turbulent pipe flow of a drag-reducing rigid “rod-like” [J]. Journal of Non-Newtonian Fluid Mechanics, 2009, 161(1-3):86-93.

    [17] Cai S. P., Higuchi Y. Drag-reduction behavior of an unusual nonionic surfactant in a circular pipe turbulent flow[J]. Journal of Hydrodynamics, 2014, 26(3): 400-405.

    [18] Elbing B. R., Winkel E. S., Lay K. A. et al. Bubble-induced skin-friction drag reduction and the abrupt transition to air-layer drag reduction [J].Journal of Fluid Mechanics, 2008, 612: 201-236.

    [19] Pouranfard A. R., Mowla D., Esmaeilzadeh F. An experimental study of drag reduction by nanofluids through horizontal pipe turbulent flow of a Newtonian liquid [J].Journal of Industrial and Engineering Chemistry, 2014,20(2): 633-637.

    [20] Radin I.,. Zakin J. L., Patterson G. K. Drag reduction in solid-fluid systems [J]. AIChE Journal, 1975, 21(2):358-371.

    [21] You Z. J., Lin J. Z., Shao X. M. et al. Stability and drag reduction in transient channel flow of fibre suspension [J].Chinese Journal of Chemical Engineering, 2004, 12(3):319-323.

    [22] Ko G. H., Heo K., Lee K. et al. An experimental study on the pressure drop of nanofluids containing carbon nanotubes in a horizontal tube [J]. International Journal of Heat and Mass Transfer, 2007, 50(23-24): 4749-4753.

    [23] Liu Z. H., Liao L. Forced convective flow and heat transfer characteristics of aqueous drag-reducing fluid with carbon nanotubes added [J]. International Journal of Thermal Sciences, 2010, 49(12): 2331-2338.

    [24] Lin J. Z., Xia Y., Ku X. K. Flow and heat transfer characteristics of nanofluids containing rod-like particles in a turbulent pipe flow [J]. International Journal of Heat and Mass Transfer, 2016, 93: 57-66.

    [25] Zhao F., van Wachem B. G. M. Direct numerical simulation of ellipsoidal particles in turbulent channel flow [J].Acta Mechanica, 2013, 224(10): 2331-2358.

    [26] Picano F., Breugem W.-P., Brandt L. Turbulent channel flow of dense suspensions of neutrally buoyant spheres [J].Journal of Fluid Mechanics, 2015, 764: 463-487.

    [27] Lin J. Z., Xia Y., Ku X. K. Pressure drop and heat transfer of nanofluid in turbulent pipe flow considering particle coagulation and breakage [J]. Journal of Heat Transfer,2014 , 136(11): 111701.

    [28] von Kármán T. Mechanische ?hnlichkeit und turbulenz[C]. Proceedings of the 3rd International Congress for Applied Mechanics. Stockholm, Sweden, 1930, 85-105.

    [29] Virk P. S. Drag reduction fundamentals [J]. AIChE Journal, 1975, 21(4): 625-656.

    [30] Elghobashi S. An updated classification map of particleladen turbulent flows [C]. IUTAM Symposium on Computational Approaches to Multiphase Flow. Berlin,Germany: Springer, 2006, 3-10.

    [31] Elghobashi S. On predicting particle-laden turbulent flows[J]. Applied Scientific Research, 1994, 52(4): 309-329.

    [32] Fornari W., Formenti A., Picano F. et al. The effect of particle density in turbulent channel flow laden with finite size particles in semi-dilute conditions [J]. Physics of Fluids, 2016, 28(3): 033301.

    [33] Garc?a-Ochoa F., Santos V. E., Casas J. A. et al. Xanthan gum: Production, recovery, and properties [J]. Biotechnology Advances, 2000, 18(7): 549-579.

    [34] Soares E. J., Sandoval G. A. B., Silveira L. et al. Loss of efficiency of polymeric drag reducers induced by high Reynolds number flows in tubes with imposed pressure [J].Physics of Fluids, 2015, 27(12): 125105.

    [35] Zhao F., George W. K., van Wachem B. G. M. Four-way coupled simulations of small particles in turbulent channel flow: The effects of particle shape and Stokes number [J].Physics of Fluids, 2015, 27(8): 083301.

    [36] Shapiro M., Goldenberg M. Deposition of glass fiber particles from turbulent air flow in a pipe [J]. Journal of Aerosol Science, 1993, 24(1): 65-87.

    March 16, 2017, Revised April 10, 2017)

    * Biography: Amir Eshghinejadfard (1983-), Male,Ph. D. Candidate

    好男人在线观看高清免费视频| 欧美三级亚洲精品| 久久精品国产亚洲av香蕉五月| 亚洲自偷自拍三级| 激情 狠狠 欧美| 97热精品久久久久久| 色视频www国产| 久久久久久久亚洲中文字幕| 国产av不卡久久| 国产黄a三级三级三级人| 免费人成视频x8x8入口观看| 欧美成人免费av一区二区三区| 18+在线观看网站| 久久精品国产亚洲av香蕉五月| 久久精品综合一区二区三区| 好男人在线观看高清免费视频| 亚洲图色成人| 亚洲色图av天堂| 99国产极品粉嫩在线观看| 高清日韩中文字幕在线| 观看美女的网站| 麻豆国产av国片精品| 免费黄网站久久成人精品| 少妇的逼水好多| 高清午夜精品一区二区三区 | 免费在线观看成人毛片| 午夜视频国产福利| 久久热精品热| 变态另类丝袜制服| av女优亚洲男人天堂| 十八禁国产超污无遮挡网站| 我的老师免费观看完整版| 99久久中文字幕三级久久日本| 国产精品久久久久久av不卡| 特大巨黑吊av在线直播| 免费看光身美女| 日日啪夜夜撸| 亚洲av第一区精品v没综合| 国产精品一二三区在线看| 午夜视频国产福利| 波多野结衣高清无吗| 哪里可以看免费的av片| 三级毛片av免费| 国产探花在线观看一区二区| 免费观看在线日韩| 免费不卡的大黄色大毛片视频在线观看 | 国产老妇女一区| 26uuu在线亚洲综合色| 日本爱情动作片www.在线观看| 麻豆av噜噜一区二区三区| 在线播放无遮挡| 国产极品天堂在线| 黑人高潮一二区| 18禁裸乳无遮挡免费网站照片| 国产乱人偷精品视频| 岛国毛片在线播放| 菩萨蛮人人尽说江南好唐韦庄 | 欧美成人一区二区免费高清观看| 在线播放国产精品三级| 身体一侧抽搐| 黑人高潮一二区| 久久九九热精品免费| 观看免费一级毛片| 成人毛片a级毛片在线播放| 欧美精品国产亚洲| 国产人妻一区二区三区在| 亚洲三级黄色毛片| 国产极品精品免费视频能看的| 亚洲精品色激情综合| 最近手机中文字幕大全| 成人欧美大片| 欧美+亚洲+日韩+国产| 日韩强制内射视频| 国产亚洲欧美98| 欧美激情国产日韩精品一区| 少妇被粗大猛烈的视频| 日韩高清综合在线| a级一级毛片免费在线观看| 国产精品综合久久久久久久免费| av在线天堂中文字幕| 亚洲成a人片在线一区二区| 免费av观看视频| 久久欧美精品欧美久久欧美| 69av精品久久久久久| 午夜福利成人在线免费观看| 看十八女毛片水多多多| 亚州av有码| 麻豆国产av国片精品| 亚洲丝袜综合中文字幕| 国产高潮美女av| 国产黄a三级三级三级人| 国产美女午夜福利| 亚洲性久久影院| 久久人人精品亚洲av| 久久久久久久久久成人| 久久亚洲精品不卡| 久久国内精品自在自线图片| 国产午夜精品一二区理论片| 97人妻精品一区二区三区麻豆| 国产黄片视频在线免费观看| 久久久a久久爽久久v久久| 日本-黄色视频高清免费观看| 国产精品一区二区三区四区久久| 国产黄色视频一区二区在线观看 | 日韩av不卡免费在线播放| 激情 狠狠 欧美| 成人二区视频| 99视频精品全部免费 在线| 亚州av有码| 亚洲欧美中文字幕日韩二区| 熟妇人妻久久中文字幕3abv| 看非洲黑人一级黄片| 美女内射精品一级片tv| 国产大屁股一区二区在线视频| 全区人妻精品视频| 一级毛片电影观看 | 精品99又大又爽又粗少妇毛片| 久久久久久久久久久免费av| 国产亚洲91精品色在线| 国产成人aa在线观看| 久久久久久久久中文| 日本与韩国留学比较| 校园人妻丝袜中文字幕| 直男gayav资源| 你懂的网址亚洲精品在线观看 | 亚洲欧美中文字幕日韩二区| 亚洲国产精品合色在线| 菩萨蛮人人尽说江南好唐韦庄 | 欧美色欧美亚洲另类二区| 亚洲性久久影院| 男女下面进入的视频免费午夜| 性色avwww在线观看| 中文字幕久久专区| 精华霜和精华液先用哪个| 日韩av在线大香蕉| 青春草视频在线免费观看| 亚洲av中文av极速乱| 午夜亚洲福利在线播放| 国产高清三级在线| 亚洲真实伦在线观看| 国产黄色小视频在线观看| 亚洲美女搞黄在线观看| 男女啪啪激烈高潮av片| 日韩av在线大香蕉| 久久这里有精品视频免费| 国产av在哪里看| 久久6这里有精品| 国内久久婷婷六月综合欲色啪| 国产极品精品免费视频能看的| 九九热线精品视视频播放| 欧美丝袜亚洲另类| 国产老妇女一区| 麻豆国产97在线/欧美| 麻豆乱淫一区二区| 在线a可以看的网站| 五月玫瑰六月丁香| 晚上一个人看的免费电影| av天堂中文字幕网| 97在线视频观看| 国产精品伦人一区二区| 国内精品美女久久久久久| 国产精品精品国产色婷婷| 成年免费大片在线观看| 在线天堂最新版资源| 男女边吃奶边做爰视频| 亚洲人成网站在线播| 日本黄色视频三级网站网址| 免费大片18禁| 国内精品久久久久精免费| av天堂在线播放| 狠狠狠狠99中文字幕| 亚洲国产精品国产精品| 久久99精品国语久久久| 午夜免费激情av| 久久这里有精品视频免费| 日本色播在线视频| 99久久精品国产国产毛片| 麻豆一二三区av精品| 哪个播放器可以免费观看大片| 亚洲va在线va天堂va国产| 午夜视频国产福利| av免费在线看不卡| 免费看av在线观看网站| 亚洲中文字幕一区二区三区有码在线看| 青春草亚洲视频在线观看| 亚洲人成网站在线播| 日本黄大片高清| 欧美一区二区亚洲| 国产 一区 欧美 日韩| 在线观看av片永久免费下载| 一级毛片我不卡| 波多野结衣巨乳人妻| www日本黄色视频网| 国产亚洲av嫩草精品影院| 人人妻人人看人人澡| 看非洲黑人一级黄片| 日韩亚洲欧美综合| 免费无遮挡裸体视频| 亚洲av成人av| 干丝袜人妻中文字幕| 在线天堂最新版资源| 听说在线观看完整版免费高清| 亚洲美女搞黄在线观看| 亚洲欧美精品专区久久| 亚洲欧美清纯卡通| 国产精品乱码一区二三区的特点| 九九热线精品视视频播放| 亚洲不卡免费看| 91久久精品电影网| 好男人视频免费观看在线| 小蜜桃在线观看免费完整版高清| 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 熟女电影av网| 搡老妇女老女人老熟妇| 国产精品电影一区二区三区| 日韩制服骚丝袜av| 免费看日本二区| 精品一区二区三区人妻视频| а√天堂www在线а√下载| 成人美女网站在线观看视频| 少妇丰满av| 乱系列少妇在线播放| 黄色一级大片看看| 国产视频首页在线观看| 国产大屁股一区二区在线视频| 久久99精品国语久久久| 亚洲精品国产av成人精品| 亚洲欧美成人精品一区二区| 国产黄a三级三级三级人| 精品99又大又爽又粗少妇毛片| 久久热精品热| 一级毛片我不卡| 国产午夜精品论理片| 99久久中文字幕三级久久日本| 欧美色欧美亚洲另类二区| 亚洲中文字幕日韩| 欧美在线一区亚洲| 尾随美女入室| 欧美一区二区国产精品久久精品| 国产大屁股一区二区在线视频| 久久99蜜桃精品久久| 一本一本综合久久| 欧美不卡视频在线免费观看| 国产一区二区在线av高清观看| 亚洲久久久久久中文字幕| 成人毛片60女人毛片免费| а√天堂www在线а√下载| 一级毛片aaaaaa免费看小| 26uuu在线亚洲综合色| 国产成人aa在线观看| 一级黄色大片毛片| 亚洲七黄色美女视频| 日韩一区二区视频免费看| 久久精品夜夜夜夜夜久久蜜豆| 乱系列少妇在线播放| 在线a可以看的网站| 在线观看美女被高潮喷水网站| 99热这里只有是精品50| 少妇被粗大猛烈的视频| 99热6这里只有精品| 看十八女毛片水多多多| 日本爱情动作片www.在线观看| 久久这里有精品视频免费| www.色视频.com| 99热这里只有是精品在线观看| 国产一级毛片七仙女欲春2| 欧美在线一区亚洲| 国产成人freesex在线| 床上黄色一级片| 国产久久久一区二区三区| 国产极品天堂在线| 好男人在线观看高清免费视频| 国语自产精品视频在线第100页| 成人漫画全彩无遮挡| 黄色欧美视频在线观看| 亚洲av.av天堂| 女人被狂操c到高潮| 日本免费一区二区三区高清不卡| 给我免费播放毛片高清在线观看| .国产精品久久| 舔av片在线| 精品久久久久久久久久免费视频| 国产精品av视频在线免费观看| 久久精品久久久久久久性| 人妻夜夜爽99麻豆av| 卡戴珊不雅视频在线播放| 人人妻人人看人人澡| 国产高清视频在线观看网站| 中文字幕人妻熟人妻熟丝袜美| 深夜a级毛片| 午夜爱爱视频在线播放| 成年女人看的毛片在线观看| 久久久久九九精品影院| 国产精品.久久久| 久久综合国产亚洲精品| 亚洲国产日韩欧美精品在线观看| a级毛片免费高清观看在线播放| 国产在线精品亚洲第一网站| 国产精品免费一区二区三区在线| 国内久久婷婷六月综合欲色啪| av免费观看日本| 麻豆乱淫一区二区| 亚洲精品久久久久久婷婷小说 | 女人被狂操c到高潮| 久久精品人妻少妇| 精品一区二区三区视频在线| 亚洲第一区二区三区不卡| 亚洲婷婷狠狠爱综合网| 人人妻人人澡人人爽人人夜夜 | 最好的美女福利视频网| 午夜激情福利司机影院| 国产三级中文精品| av女优亚洲男人天堂| 精品不卡国产一区二区三区| 一区二区三区免费毛片| 免费无遮挡裸体视频| 日本av手机在线免费观看| 97超碰精品成人国产| 有码 亚洲区| 精品久久久久久久久久免费视频| 深夜精品福利| 观看免费一级毛片| 亚洲av免费在线观看| 亚洲不卡免费看| www日本黄色视频网| 夜夜夜夜夜久久久久| 国产三级中文精品| 99热全是精品| 人人妻人人澡欧美一区二区| 国产中年淑女户外野战色| 久久久久久九九精品二区国产| 男人的好看免费观看在线视频| 欧美不卡视频在线免费观看| 嫩草影院新地址| 国产成人一区二区在线| av在线天堂中文字幕| 赤兔流量卡办理| 久久久久久久久大av| 能在线免费观看的黄片| 三级国产精品欧美在线观看| 日本欧美国产在线视频| 两性午夜刺激爽爽歪歪视频在线观看| 有码 亚洲区| 成人综合一区亚洲| 亚洲国产欧洲综合997久久,| 乱码一卡2卡4卡精品| 成人国产麻豆网| 婷婷色av中文字幕| 精品久久久久久久久亚洲| 女人被狂操c到高潮| 免费看a级黄色片| 久久精品国产亚洲网站| av天堂在线播放| 少妇熟女欧美另类| 欧美+亚洲+日韩+国产| 可以在线观看的亚洲视频| 12—13女人毛片做爰片一| 禁无遮挡网站| 两个人的视频大全免费| 男人的好看免费观看在线视频| 在线观看免费视频日本深夜| 国产精华一区二区三区| 人妻夜夜爽99麻豆av| 老司机影院成人| 成人亚洲欧美一区二区av| 色播亚洲综合网| 婷婷亚洲欧美| 97热精品久久久久久| 在线观看66精品国产| 一个人观看的视频www高清免费观看| 天天一区二区日本电影三级| 91在线精品国自产拍蜜月| 日本熟妇午夜| 99国产精品一区二区蜜桃av| 夫妻性生交免费视频一级片| 日韩欧美精品免费久久| 你懂的网址亚洲精品在线观看 | 国产高清三级在线| 哪里可以看免费的av片| 亚洲人成网站在线观看播放| 久久综合国产亚洲精品| www.av在线官网国产| av视频在线观看入口| 国产探花极品一区二区| 少妇猛男粗大的猛烈进出视频 | 亚洲欧美日韩高清专用| 日韩一本色道免费dvd| 狂野欧美白嫩少妇大欣赏| 国内少妇人妻偷人精品xxx网站| 国产真实乱freesex| 在线观看av片永久免费下载| 桃色一区二区三区在线观看| 中文欧美无线码| 免费看日本二区| 黄片wwwwww| 亚洲不卡免费看| 免费av毛片视频| 最近最新中文字幕大全电影3| 99热只有精品国产| 日韩一区二区视频免费看| a级毛片免费高清观看在线播放| 久久久欧美国产精品| 综合色av麻豆| 国产探花极品一区二区| 夜夜爽天天搞| 久久精品91蜜桃| 国产老妇伦熟女老妇高清| 成人毛片a级毛片在线播放| 亚洲人与动物交配视频| 91aial.com中文字幕在线观看| 国产精品久久久久久久久免| 久久99热这里只有精品18| 乱码一卡2卡4卡精品| 国产成年人精品一区二区| 99热这里只有是精品50| 色综合站精品国产| 亚洲在久久综合| 女人十人毛片免费观看3o分钟| 欧美激情久久久久久爽电影| 日韩高清综合在线| 一进一出抽搐gif免费好疼| 美女 人体艺术 gogo| 日本与韩国留学比较| 晚上一个人看的免费电影| 男女做爰动态图高潮gif福利片| 别揉我奶头 嗯啊视频| 色综合亚洲欧美另类图片| 99热网站在线观看| 国产久久久一区二区三区| 国产一区二区在线观看日韩| 啦啦啦啦在线视频资源| 波多野结衣高清无吗| 熟女人妻精品中文字幕| 欧美日韩一区二区视频在线观看视频在线 | 免费看a级黄色片| 非洲黑人性xxxx精品又粗又长| 身体一侧抽搐| 最近手机中文字幕大全| 国产精品国产高清国产av| 亚洲最大成人av| 久久久a久久爽久久v久久| 18禁黄网站禁片免费观看直播| 国产老妇伦熟女老妇高清| 永久网站在线| 韩国av在线不卡| 精华霜和精华液先用哪个| 国内久久婷婷六月综合欲色啪| 一本—道久久a久久精品蜜桃钙片 精品乱码久久久久久99久播 | 久久精品人妻少妇| 亚洲精品456在线播放app| 欧美高清成人免费视频www| 青春草亚洲视频在线观看| 天天一区二区日本电影三级| 一边摸一边抽搐一进一小说| ponron亚洲| 久久精品久久久久久久性| 男女下面进入的视频免费午夜| 国产大屁股一区二区在线视频| 国产黄a三级三级三级人| 中国美白少妇内射xxxbb| 99国产精品一区二区蜜桃av| 亚洲第一区二区三区不卡| 三级毛片av免费| 免费观看a级毛片全部| 久久精品国产亚洲av天美| 亚洲精品色激情综合| 看黄色毛片网站| 欧美日韩乱码在线| 九九在线视频观看精品| 少妇人妻精品综合一区二区 | 中文字幕精品亚洲无线码一区| 国产三级在线视频| 蜜桃久久精品国产亚洲av| 国产一区亚洲一区在线观看| 欧美日本视频| 嫩草影院入口| 悠悠久久av| 麻豆av噜噜一区二区三区| 搡女人真爽免费视频火全软件| 最近最新中文字幕大全电影3| 国产精品日韩av在线免费观看| 不卡视频在线观看欧美| 最后的刺客免费高清国语| 精品人妻偷拍中文字幕| 中出人妻视频一区二区| 久久久久久久久久黄片| 人人妻人人看人人澡| 欧美激情在线99| 成年女人看的毛片在线观看| 麻豆精品久久久久久蜜桃| 久久亚洲精品不卡| av专区在线播放| 青青草视频在线视频观看| av福利片在线观看| 国产真实乱freesex| 深夜a级毛片| 老女人水多毛片| or卡值多少钱| av福利片在线观看| 美女 人体艺术 gogo| 久久精品久久久久久噜噜老黄 | 亚洲第一区二区三区不卡| 少妇熟女欧美另类| 久久99热这里只有精品18| 亚洲丝袜综合中文字幕| 两个人视频免费观看高清| 成年女人看的毛片在线观看| 国产精品一二三区在线看| 精品一区二区免费观看| 久久久久久久久中文| 99久久无色码亚洲精品果冻| 午夜福利高清视频| 精品日产1卡2卡| 亚洲av成人av| 久久鲁丝午夜福利片| 男插女下体视频免费在线播放| 又粗又爽又猛毛片免费看| 欧美成人免费av一区二区三区| 精品午夜福利在线看| 欧美人与善性xxx| 亚洲精品国产av成人精品| 国产亚洲5aaaaa淫片| 尤物成人国产欧美一区二区三区| 欧美性猛交黑人性爽| h日本视频在线播放| 亚洲成人久久爱视频| 男人舔女人下体高潮全视频| 成人欧美大片| 男女视频在线观看网站免费| 又粗又爽又猛毛片免费看| 亚洲国产精品久久男人天堂| 丰满乱子伦码专区| 欧美最新免费一区二区三区| 精品无人区乱码1区二区| 菩萨蛮人人尽说江南好唐韦庄 | 婷婷亚洲欧美| 可以在线观看的亚洲视频| 日韩精品有码人妻一区| 成人一区二区视频在线观看| 亚洲国产精品成人综合色| 国产免费一级a男人的天堂| 晚上一个人看的免费电影| 又粗又硬又长又爽又黄的视频 | 国产高清视频在线观看网站| 青春草视频在线免费观看| 亚洲欧洲日产国产| kizo精华| 日韩av在线大香蕉| 精品熟女少妇av免费看| 午夜激情欧美在线| av免费观看日本| 99久久成人亚洲精品观看| 亚洲av男天堂| 国产色婷婷99| 一级二级三级毛片免费看| 国产精品一区二区三区四区免费观看| 午夜老司机福利剧场| 我的老师免费观看完整版| 午夜激情福利司机影院| 亚洲精品成人久久久久久| 尤物成人国产欧美一区二区三区| 中文精品一卡2卡3卡4更新| 国产激情偷乱视频一区二区| 黄色视频,在线免费观看| 人妻制服诱惑在线中文字幕| 嫩草影院入口| 精品一区二区三区人妻视频| 国产精品一二三区在线看| avwww免费| 精品久久久噜噜| 我要看日韩黄色一级片| 麻豆成人av视频| 69人妻影院| 插逼视频在线观看| 老司机影院成人| 日本五十路高清| 中出人妻视频一区二区| 日韩欧美一区二区三区在线观看| 啦啦啦观看免费观看视频高清| 中文字幕熟女人妻在线| 亚洲色图av天堂| 禁无遮挡网站| 蜜臀久久99精品久久宅男| 欧洲精品卡2卡3卡4卡5卡区| eeuss影院久久| 精品人妻一区二区三区麻豆| 日韩三级伦理在线观看| a级一级毛片免费在线观看| 美女xxoo啪啪120秒动态图| 国产精品.久久久| 给我免费播放毛片高清在线观看| 欧美精品一区二区大全| 国产精品免费一区二区三区在线| 大又大粗又爽又黄少妇毛片口| 成人特级av手机在线观看| 国产成人午夜福利电影在线观看| 国产黄色小视频在线观看| 三级男女做爰猛烈吃奶摸视频| 久久九九热精品免费| 国产av在哪里看| 蜜桃久久精品国产亚洲av| 我的女老师完整版在线观看| 中文字幕久久专区| 久久人人爽人人爽人人片va| kizo精华| 99国产精品一区二区蜜桃av| 人体艺术视频欧美日本| 午夜精品在线福利| 夜夜看夜夜爽夜夜摸| 成人性生交大片免费视频hd| 日韩人妻高清精品专区| 91精品国产九色| 亚洲自偷自拍三级| 久久精品国产亚洲av涩爱 | 网址你懂的国产日韩在线|