Drag Reduction Ratio Research Articles

Polymer degradation of dilute solutions in turbulent drag reducing flows in a cylindrical double gap rheometer device

The drag reduction by high molecular weight polymer additives in a turbulent flow is an important phenomenon that has received the attention of a number of researchers. However, the efficiency of those additives is not constant. Turbulence is also responsible for breaking the polymer molecules, decreasing their ability to reduce drag. This degradation phenomenon has recently received its deserved attention in the literature and investigations that take into account the effect of concentration, molecular weight, Reynolds number, and temperature can be found, although these parameters have not yet been explored in very wide ranges. In the present work we investigate this degradation phenomenon for aqueous solutions of two different polymers: Polyacrylamide (PAM) and Polyethylene oxide (PEO), in a cylindrical double gap rheometer device. The dependence of degradation on molecular weight, concentration, temperature, and Reynolds number is analysed for a wide range of these parameters. Our main results are displayed in terms of drag reduction (DR). All tests are performed to compute DR for a long period of time including the values obtained from the very beginning of the process. It is shown that DR increases with time until achieving a maximum value before starting to decrease as a consequence of degradation. We also display the results using a relative drag reduction quantity, DR′, defined as the ratio of the current drag reduction to the maximum one obtained for a non-degraded solution. We propose an alternative decay function that relates DR′ as a function of the Reynolds number, concentration, molecular weight, and temperature.

Drag reduction in turbulent boundary layers by spanwise traveling waves with wall deformation

The drag-reducing effect of a spanwise-traveling wave with wall deformation on a zero-pressure-gradient turbulent boundary layer over a flexible sheet was investigated. The test plate placed in the wind tunnel consisted of a flexible sheet section, where the traveling wave motion was generated by a vibration device with a crank via upstream and downstream smooth rigid wall sections. Streamwise and wall-normal velocity components were measured by single and cross hot-wire anemometers. Amplitude and frequency of the spanwise-traveling-wave motion were measured using two laser displacement sensors. The drag reduction ratio was estimated from the friction coefficients through the growth rate of the momentum thickness of the turbulent boundary layer over the flexible sheet section. A maximum drag reduction ratio of up to 13% was obtained. The relations between sheet displacement and streamwise and wall-normal velocity fluctuations were compared at a large (DR=8%) and at a very small (), which was almost the same as the no drag reduction case, taking into account the experimental uncertainty. For the larger drag reduction, a slow-velocity fluctuation with large amplitude appeared further away from the flexible sheet. Quadrant analysis of streamwise and wall-normal velocity fluctuations revealed that the drag reduction was attributed to a reduction in the sweep event and an increase in the negative contribution of the inward-interaction event to the Reynolds shear stress due to the sheet displacement fluctuation.

Drag reduction phenomenon in viscous oil‐water dispersed pipe flow: Experimental investigation and phenomenological modeling

AbstractAn experimental study on drag‐reduction phenomenon in dispersed oil‐water flow has been performed in a 26‐mm‐i.d. Twelve meter long horizontal glass pipe. The flow was characterized using a novel wire‐mesh sensor based on capacitance measurements and high‐speed video recording. New two‐phase pressure gradient, volume fraction, and phase distribution data have been used in the analysis. Drag reduction and slip ratio were detected at oil volume fractions between 10 and 45% and high mixture Reynolds numbers, and with water as the dominant phase. Phase‐fraction distribution diagrams and cross‐sectional imaging of the flow suggested the presence of a higher amount of water near to the pipe wall. Based on that, a phenomenology for explaining drag reduction in dispersed flow in a flow situation where slip ratio is significant is proposed. A simple phenomenological model is developed and the agreement between model predictions and data, including data from the literature, is encouraging. © 2011 American Institute of Chemical Engineers AIChE J, 2012

Non-Newtonian multi-phase flows: On drag reduction, pressure drop and liquid wall friction factor

The present work focuses on the non-Newtonian liquid drag reduction by gas injection. Two regimes are taken in consideration: fully stratified gas shear-thinning liquid flow and gas shear-thinning liquid slug flow regimes. Predictions of drag reduction ratio and holdup are presented for the stratified flow of gas and non-Newtonian Ostwald-de Waele liquid. Fully stratified flow is considered and the approach developed in Taitel and Dukler (1976) is used. For these regimes, CMC (CarboxyMethyl Cellulose) solution is used in order to investigate the behaviour of the gas and non-Newtonian liquids in horizontal pipes. Results have been reformulated and an extension to interfacial Andreussi and Persen (1987) correlation has been carried out for stratified regimes. For slug flow regimes, the mechanistic slug unit model is adopted in order to estimate the pressure gradients along the slug unit. The slug unit model is rearranged and reinterpreted as inviscid Burgers's equation for incompressible phases. For both stratified and slug flow regimes, three dimensional CFD (computational fluid dynamics) simulations were performed in order to compare the drag reduction ratio and pressure gradients. In stratified flows, CFD is also used in an attempt to evaluate the liquid wall friction factor and to compare the obtained values with those given by empirical standard correlations.

Drag Reduction of Bacterial Cellulose Suspensions

Drag reduction due to bacterial cellulose suspensions with small environmental loading was investigated. Experiments were carried out by measuring the pressure drop in pipe flow. It was found that bacterial cellulose suspensions give rise to drag reduction in the turbulent flow range. We observed a maximum drag reduction ratio of 11% and found that it increased with the concentration of the bacterial cellulose suspension. However, the drag reduction effect decreased in the presence of mechanical shear.

Drag Reduction by Hydrophobic Microstructures

We studied the mechanism of drag reduction due to textured hydrophobic surfaces in Newtonian laminar flow through a rectangular channel. The test wall surfaces were fabricated with different fine groove patterns and groove area ratios, and were then coated with PTFE to produce hydrophobic surfaces. Drag reduction was estimated by pressure loss measurements in a 12 × 12 mm channel. Visualization of the gas-liquid interface was carried out using a 0.5 × 5 mm microchannel to investigate the mechanism of drag reduction. A series of experiments showed that the gas-liquid contact area ratio and the air layer thickness influence the drag reduction, the maximum drag reduction ratio is 3.7 %.

S055024 バクテリアセルロース懸濁液の抵抗減少効果に関する研究([S05502]流れの抵抗低減(2))

Drag reduction due to bacterial cellulose suspensions with small environmental loading was investigated. Experiments were carried out by measuring the pressure drop in pipe flow. It was found that bacterial cellulose suspensions give rise drag reduction in the turbulent flow range. We observed a maximum drag reduction ratio of 11%, and found that it increased with the concentration of the bacterial cellulose suspension. However, the drag reduction effect decreased in the presence of mechanical shear.

S055023 非イオン性界面活性剤水溶液の抵抗低減効果に及ぼすポンプ稼働時間の影響([S05502]流れの抵抗低減(2))

There are a few studies on the drag-reducing effects of nonionic surfactant solutions which are non-toxic and biodegradable, while a lot of investigations for cationic surfactant solutions have been performed so far. We investigated the drag-reducing effects of nonionic surfactant (oleyldimethylamineoxide) solutions by measuring the pressure drop in the circuit pipe flow. The maximum drag reduction ratio at the solution concentration C = 100 ppm was about 70 %, which did not depend on solution temperature T = 10 to 40 -C. At C = 100 ppm, T = 20 -C, the drag-reducing effect disappeared within 48 hours at the Reynolds number based on dynamic viscosity of water Rew 10000, while it disappeared within 24 hours at Rew> 20000.

Comparison of turbulence structures at large and small drag reduction ratios in turbulent boundary layer of surfactant solutions

In this study, turbulence structures of drag-reducing turbulent boundary layers in surfactant solutions at the momentum-thickness Reynolds number Re θ≃800 were compared at large and small drag reduction ratios and 34% at the solution temperature, T=30°C and 35°C. Turbulence statistics and structures were obtained by a two-component laser-Doppler velocimetry (LDV) and particle image velocimetry (PIV) systems for the streamwise and wall-normal (x–y) plane and the streamwise and spanwise (x–z) plane. The quadrant analysis of streamwise and wall-normal velocity fluctuations revealed that at , the positive contribution of sweep and ejection events to the Reynolds shear stress was comparable with the negative contribution of inward-interaction and outward-interaction events, so that the Reynolds shear stress was almost zero. At , the maximum positive contributions of quadrants II and IV and the maximum negative contributions of quadrants I and III were comparable with those of the corresponding water near the wall, but the region of positive contributions in quadrants II and IV became narrower and the region of negative contributions in quadrants I and III became wider, so that the Reynolds shear stress decreased. At , in high activity, the streamwise velocity fluctuations were smaller than those of water but were relatively large even near the center of the boundary layer, in addition to the near-wall region, while in low activity, the fluctuating velocity vectors were almost parallel to the wall. At , the scale of sweep and ejection events was much larger than that of water and the inclination angle of vortex packets at was much smaller than that of water. At , the spanwise turbulence fluctuation was strongly suppressed and vortical structures were not observed on the (x–z) plane, while at , several vortical structures, which seemed to correspond to the cross section of legs of hairpin vortices, were observed near the wall. Under the assumption of frozen turbulence, it was found that for both and 34%, the high- and low-speed regions were aligned laterally, although the low-speed regions at were obscured.

LIMITING MAXIMUM DRAG REDUCTION ASYMPTOTE FOR THE MOMENT COEFFICIENT OF AN ENCLOSED ROTATING DISK WITH FINE SPIRAL GROOVES

In this study, the limiting maximum drag reduction asymptote for the moment coefficient of an enclosed rotating disk with fine spiral grooves in turbulent flow region were obtained analytically. Analysis which were based on an assumption for a simple parabolic velocity distribution of turbulent pipe flow to represent relative tangential velocity, was carried out using momentum integral equations of the boundary layer. For a certain K- parameter the moment coefficient results agree well with experimental results for maximum drag reduction in an enclosed rotating disk with fine spiral grooves and drag reduction ratio approximately was 15 %. Additionally, the experimental results for drag reduction on a rotating disk can be explained well with the analytical results.

Turbulent drag reduction in nonionic surfactant solutions

There are only a few studies on the drag-reducing effect of nonionic surfactant solutions which are nontoxic and biodegradable, while many investigations of cationic surfactant solutions have been performed so far. First, the drag-reducing effects of a nonionic surfactant (AROMOX), which mainly consisted of oleyldimethylamineoxide, was investigated by measuring the pressure drop in the pipe flow at solvent Reynolds numbers Re between 1000 and 60 000. Second, we investigated the drag-reducing effect of a nonionic surfactant on the turbulent boundary layer at momentum-thickness Reynolds numbers Reθ from 443 to 814 using two-component laser-Doppler velocimetry and particle image velocimetry systems. At the temperature of nonionic surfactant solutions, T=25 °C, the maximum drag reduction ratio for AROMOX 500 ppm was about 50%, in the boundary layer flow, although the drag reduction ratio was larger than 60% in pipe flow. Turbulence statistics and structures for AROMOX 500 ppm showed the behavior of typical drag-reducing flow such as suppression of turbulence and modification of near-wall vortices, but they were different from those of drag-reducing cationic surfactant solutions, in which bilayered structures of the fluctuating velocity vectors were observed in high activity.

S0501-1-5 バクテリアセルロース懸濁液の流動特性に関する研究([S0501-1 ]複雑流体の流動現象(1))

Drag reduction due to bacterial cellulose suspensions with small environmental loading was investigated. Experiments were curried out by measuring the pressure drop of a pipe flow. It has been reported that the bacterial cellulose suspensions cause the drag reduction phenomena in the turbulent flow range. The fiber of bacterial cellulose forms complicated network in the suspension. It is obtained about 10 % in the maximum drag reduction ratio of the friction factor. Drag reduction ratio increases with increasing the concentration of bacterial cellulose suspension. The drag reduction effect of bacterial cellulose suspension becomes lower under mechanical shear.

1315 回流式円管流における非イオン性界面活性水溶液の抵抗低減(OS13-3 流れの抵抗低減,オーガナイズドセッション)

There are a few studies on the drag-reducing effects of non-ionic surfactant solutions which are non-toxic and biodegradable, while a lot of investigations for cationic surfactant solutions have been performed so far. We investigated the drag-reducing effects of non-ionic surfactant, oleyldimethylamineoxide (ODMAO), solutions by measuring the pressure drop in the circuit pipe flow. The maximum drag reduction ratio for the ODMAO solution was over 70 %, which did not depend on solution temperature and concentration. After the solution was circulated for 158 hours, the drag reducing effect disappeared.

Hydraulics conveyances of mud slurry by a spiral pipe

Indonesia particularly East Java has been suffering from eruption of gas and mud slurry, caused by oil and gas exploration. Everyone calls this disaster as Sidoarjo mud or Lapindo mud. Mud slurry is essentially a mixture of a carrying fluid and solid particles held in suspension. When the mud slurry flow speed is not sufficiently high the particles will not be maintained in suspension. In spiral pipe twisted with a constant pitch in relation to the axis a swirling flow occurs when fluids flow in the pipe. The aim of this study is to examine characteristics of the hydraulic transport of mud slurry flowing in the spiral pipe with three-shape groove pipe walls. The shear stress and the shear strain are calculated by measuring the pressure drop and the volumetric flow rate in circular pipe, respectively. The power law exponent were about 0.93–1.0 for mud slurry solution of 45%, 30% and 20% of weight concentrations. The diameter of particles was 0.95 mm and the density was 2.19 × 103 (kg/m3). The apparent viscosity of mud slurry solution is not constant to the shear strain but the relationship is approximated by model of power law. The friction factor of mud slurries in a spiral pipe with ratio pitch per diameter 6.7 is lower than circular pipe and spiral pipe with P/Di= 3.9 and 4.3. It was shown that the spiral pipe caused drag reduction in flowing of mud slurries. The drag reduction ratio of spiral pipe was about 28% for Cw=30% at Re’=32 × 103.

내부 냉각유로에서 열전달 강화와 압력손실 감소를 위한 표면 형상체의 개발

A new surface shape of an internal cooling passage which largely reduces the pressure drop and enhances the surface heat transfer is proposed in the present study. The surface shape of the cooling passage is consisted of the concave dimple and the riblet inside the dimple which is protruded along the stream-wise direction. Direct Numerical Simulation (DNS) for the fully developed turbulent flow and thermal fields in the cooling passage is conducted. The numerical simulations for five different surface shapes are conducted at the Reynolds number of 2800 based on the mean bulk velocity and channel height and Prandtl number of 0.71 . The driving pressure gradient is adjusted to keep a constant mass flow rate in the x direction. The thermoaerodynamic performance for five different cases used in the present study was assessed in terms of the drag, Nusselt number, Fanning friction factor, volume and area goodness factor in the cooling passage. The value of maximum ratio of drag reduction is -22.86 % , and the value of maximum ratio of Nusselt number augmentation is 7.05% when the riblet angle is 60°. The remarkable point is that the ratio of Nusselt number augmentation has the positive value for the surface shapes which have over 45° of the riblet angle. The maximum volume and area goodness factors are obtained when the riblet angle is 60°.

Turbulence statistics and structures of drag-reducing turbulent boundary layer in homogeneous aqueous surfactant solutions

In our earlier work [Itoh et al., Phys. Fluids 17, 075107 (2005)], the additional maximum of the streamwise turbulence intensity near the center of the drag-reducing turbulent boundary layer was found in the homogeneous dilute aqueous surfactant solution which was a mixture of cetyltrimethyl ammonium chloride with sodium salicylate as counterion. In this work, we systematically investigated the influence of the drag-reducing surfactant on the velocity fields of the turbulent boundary layer at various Reynolds numbers Reθ from 301 to 1437 and the drag reduction ratio DR from 8% to 74% under different streamwise locations and concentration and temperature of solutions using a two-component laser-Doppler velocimetry (LDV) system. It was revealed that all data on DR versus the wall-shear rate obtained here were collapsed on a single curve. We verified the existence of the additional maximum of the streamwise turbulence intensity near the center of the boundary layer which appeared at relatively large drag reduction ratios and small Reynolds numbers. It was found that the additional maximum of streamwise turbulence intensity and its wall-normal location were independent of the streamwise location, wall-shear rate, Reynolds number, and drag reduction ratio. The additional maximum could be explained by the bilayered structure model proposed, in which the flow in the near-wall region is in shear-induced structure (SIS) and viscoelastic, whereas the flow in the region away from the wall is in non-SIS and nonviscoelastic. This model was based on measurements of the shear viscosity. We also performed particle image velocimetry measurements, which revealed that the fluctuating velocity vector fields showed two situations, with low and high activity. In low activity, the velocity fluctuations were attenuated largely across the turbulent boundary layer. In high activity, fluctuating velocity vectors were almost parallel to the wall and relatively large in both regions near the wall and the center of the boundary layer, which seemed to be a bilayered structure and supported the bilayered structure model.

スパン方向進行波動を伴う柔軟シート上乱流境界層の摩擦抵抗低減(流体工学,流体機械)

The effect of a spanwise traveling-wave motion on a zero-pressure-gradient turbulent boundary layer over a flexible sheet was investigated. The test plate placed in wind tunnel consisted of a flexible sheet section, where the traveling wave motion was generated by the vibration device with a crank, and the upstream and downstream smooth rigid wall sections. Velocity profiles were measured by single and cross hot-wire anemometry. Amplitude and frequency of the traveling wave motion were measured using two laser displacement sensors. The drag reduction ratio was estimated from the friction coefficients through the growth rate of the momentum thickness of the turbulent boundary layer over the flexible sheet section. The maximum drag reduction of up to 13% was obtained. The quadrant analysis of streamwise and wall-normal velocity fluctuations revealed that the drag reduction was attributed to the reduction in the sweep event and the increase in the negative contribution of the inward-interaction event to the Reynolds shear stress due to the sheet displacement fluctuation.

界面活性剤水溶液の抵抗低減乱流境界層における乱れ構造 : 抵抗低減率の異なる流れ場の比較(流体工学,流体機械)

In this study, turbulence structures of the drag-reducing turbulent boundary layer in the surfactant solution at the momentum-thickness Reynolds number Re_θ≃800 were compared between at the large and small drag reduction ratios. Turbulence statistics and structures were obtained by the two-component LDV system and the PIV system for the streamwise and wall-normal (x-y) section and the streamwise and spanwise (x-z) section. The surfactant solution used here was a mixture of cetyltrimethyl ammonium chloride (CTAC) with sodium salicylate as counterion, which was dissolved in tap water. The concentration of CTAC was 65ppm, and the molar ratio of counterion to CTAC was two. The drag reduction ratios DR=78% and 34% were obtained at the solution temperature T=30℃ and 35℃, respectively. The quadrant analysis of streamwise and wall-normal velocity fluctuations revealed that at DR=78%, the positive contribution of the sweep and ejection events to the Reynolds shear stress was comparable with the negative contribution of the inward-interaction and outward-interaction events, so that the Reynolds shear stress was almost zero. At DR=78%, both streamwise and spanwise velocity fluctuations were attenuated largely across the turbulent boundary layer. On the other hand, at DR=34%, turbulence structures were similar to those of water as a whole, although the scale was larger compared to the water.

0309 疎水性微細構造がマイクロチャンネル流れに及ぼす影響(OS3-2 流れの抵抗低減,オーガナイズドセッション)

We studied the effect of textured hydrophobic surfaces on drag reduction in Newtonian laminar flow through a micro channel. Fine fabrication was given to the test wall surfaces so that the groove area ratio may be changed methodically, and their surfaces are coated with PTFE. Drag reduction was estimated by pressure loss measurement in a 0.5×5mm channel. Visualization experiment was carried out to reveal a mechanism of the drag reduction from the form of air-water interface standpoint. A series of experiments showed that the air-water contact area ratio and the air layer thickness influence the drag reduction, and the maximum drag reduction ratio is 15.6%.

Drag Reduction Effects of Micro-Bubbles in Straight and Helical Pipes

Experimental investigations were conducted to study the effect of micro-bubbles injected into water flowing through straight and helical pipes with different curvature ( 0.025, 0.05 and 0.1). The micro-bubbles were produced using two hydrocyclone micro-bubble generators positioned face to face with opposite direction of swirl flow. The mean diameter of the micro-bubbles generated was about 60μ m, while the maximum diameter observed was 174μ m, with air fraction, which will be defined in Eq.(4), ranging from 0.21% to 0.44%. The effect of the Reynolds number on the drag reduction is also presented. The experimental results show that, the micro-bubble has an effect of drag reduction on both straight and helical pipes, though the drag reduction in a straight pipe is much higher than that in a helical pipe, because of the secondary flow in a helical pipe. It is found that the drag reduction increases with the decrease of curvature and the increase of air fraction. The maximum value of drag reduction ratio was 51% in case of a straight pipe, while that for a helical pipe was 16%.