Experimental Investigation on the Drag Reduction for an Axi-symmetric Body by Micro-bubble and Polymer Solution

Yoon, Hyun-Se,Park, Young-Ha,Van, Suak-Ho,Kim, Hyung-Tae,Kim, Wu-Joan The Society of Naval Architects of Korea 2004 Journal of ship and ocean technology Vol.8 No.1

Experiments on friction drag reduction by injecting polymer (Polyethylene oxide) solution or micro-bubbles were carried out in the cavitation tunnel of KRISO. Two different drag reduction mechanisms were applied to a slender axi-symmetric body to measure the total drag reduction. And then the amount of friction drag reduction was estimated under the assumption that the reduction mechanisms were effective only to the friction drag component. As the result of the tests, polymer solution drag reduction up to 23% of the total drag was observed and it corresponds to about 35% of the estimated friction drag of the axi-symmetric body. This result matched reasonably well to that of the flat plate test "(Kim et al, 2003)". The normalization of the controlling parameters was tried at the end of this paper. Micro-bubble drag reduction was within 1% of its total drag. This unexpected result was quite different from that of the flat plate case "(Kim et at, 2003)" The possible reasons were discussed in this paper.

횡 방향 공동을 이용한 마찰 저항 감소

김철규(Chulkyu Kim),전우평(Woo-Pyung Jeon),최해천(Haecheon Choi) 한국유체기계학회 2006 유체기계 연구개발 발표회 논문집 Vol.- No.-

In this study, we experimentally investigate the possibility of skin-friction drag reduction by series of transverse cavities in a turbulent boundary layer flow. The effects of cavity depth (d), cavity length (l) and cavity spacing (s) on the skin friction drag are examined in the range of Reθ=4030 ~ 7360, d/θ? = 0.13 ~ 1.03, l/d = 1 ~ 4 and s/d = 5 ~ 20. We perform experiments for twenty different cavity geometries and directly measure total drag force using in-house force measurement system. In most cases, the skin friction drag is increased. At several cases, however, small drag reduction is obtained. The variation of the skin friction drag is more sensitive to the cavity length than to the cavity depth or cavity spacing, and drag is reduced at s/l≥10 and l/θ?≤ l irrespective of the cavity depth. At l/θ?=0.13 and s/l = 10, maximum 2 % drag reduction is achieved. When the skin friction drag is reduced, there is little interaction between the flows inside and outside cavity, and the flow changed by the cavity is rapidly recovered at the following crest. A stable vortex is formed inside a cavity in the case of drag reduction. This vortex generates negative skin friction drag at the cavity bottom wall. Although there is form drag due to the cavity itself, total drag is reduced due to the negative skin friction drag.

관수로에서 마찰감소를 위한 고분자의 실험적 연구 I

김종섭,김재근,김만식 한밭대학교 2007 한밭대학교 논문집 Vol.24 No.-

The drag reduction is the phenomenon that occurs only when the shear stress from the wall of pipe is beyond the critical point. The drag reduction increase as the molecular weight, concentration of the polymer and Reynolds unmber increase. But it is limited by Virk's maximum drag reduction asymptote. Because of the strong shear force for the pol)'l1H on the turbulent flow, the molecular weight and the drag reduction did not decrease. Such mechanical degradation of the polymer occurs in all polymer solvent systems. We found that there is no study on vertical-up flow of close system on the drag reduction. Thus, the objectives of this paper was to identify and develop high performance polymer additives for fluid transportations with the benefits of turbulent drag reduction. In addition, we will evaluated the drag reduction in vertical flow by measuring the pressure drop on vertical-up flow of close system.

PEO가 첨가된 원형관 난류유동에서의 마찰저항 감소 측정

이보안,이동원,김신,현명택,천원기 濟州大學校 産業技術硏究所 1998 산업기술연구소논문집 Vol.9 No.2

The drag reduction by polymer additive is a well-known phenomenon and has been widely studied due to its high usefulness. In this study, in order to obtain the fundamental data on the drag reduction by polymer additive. we measured the friction factors in the polymer added turbulent flow through a circular pipe for Reynolds number ranging 10000-50000. As polymer additive, PEO (polyethylene oxide: molecular weight 4 x l0^(6)) was used. We also performed the experiments varying the concentration of PEO from 3 to 24 wppm to investigate the effect of the PEO concentration on the drag reduction. We observed more than 25% drag reduction under the above experimental conditions and the most effective drag reduction was found at 6 wppm (31% drag reduction).

Reduction of drag in heavy vehicles with two different types of advanced side skirts

Hwang, B.G.,Lee, S.,Lee, E.J.,Kim, J.J.,Kim, M.,You, D.,Lee, S.J. Elsevier Scientific Pub. Co 2016 Journal of wind engineering and industrial aerodyn Vol.155 No.-

<P>Investigating the aerodynamic reduction of drag in heavy vehicles, such as trucks or tractor-trailers, has considerable significance given the strong influence on related industries. The underbody flow that passes through the underside of heavy vehicles induces considerable drag while interacting with rolling wheels and other structures. Nonetheless, the reduction of drag caused by underbody flow has received less attention than that attributed to upper and forebody flows. Side skirts are common underbody drag reduction devices that consist of straight panels curtaining the underspace between the front and rear wheels to control the underbody flow in the ground clearance. In this study, we propose two different types of side skirts with flaps or additional inclined inner panels to maximize drag reduction. Effects of these devices are quantitatively evaluated by wind tunnel tests and computational fluid dynamics analysis. In wind tunnel tests with 1/8 scaled-down vehicle models, drag coefficient is reduced by more than 5% for both side skirts. Effects of various physical dimensions or angle variations on drag reduction are determined. Large-eddy simulation (LES) estimated similar drag reduction with reduced vortical activities, loss of streamwise momentum, strength of turbulent kinetic energy and global pressure difference, compared to the case without side skirts. (C) 2016 Elsevier Ltd. All rights reserved.</P>

Combined effects of polymers and active blowing/suction on drag reduction

Min, Taegee,Choi, Haecheon Elsevier 2005 Journal of non-Newtonian fluid mechanics Vol.131 No.1

<P><B>Abstract</B></P><P>In the present study, we investigate the combined effect of polymer additives and active blowing and suction at the wall on drag reduction using direct numerical simulation. Three different turbulent channel flows having the same bulk Reynolds number but different wall shear velocities are generated to see the role of the strength of near-wall streamwise vortices in polymer drag reduction. From this study, we show that the phenomenon of polymer drag reduction is closely related to the strength of near-wall streamwise vortices as well as the elasticity of polymer solution. On the other hand, the combined drag reduction obtained by both the polymer additives and the blowing and suction is larger than the individual drag reduction either by polymers or by blowing and suction, but is smaller than sum of the two separate drag reductions, indicating that the polymer solution is less efficient in producing drag reduction in the absence of strong near-wall streamwise vortices.</P>

PEO가 첨가된 원형관 난류운동에서의 마찰저항 감소 측정

이동원,김신,현명택,천원기,이보안 濟州大學校 工科大學 産業技術硏究所 1998 尖端技術硏究所論文集 Vol.9 No.2

The drag reduction by polymer additive is a well-known phenomenon and has been widely studied due to its high usefulness. In this study. in order to obtain the fundamental data on the drag reduction by polymer additive. we measured the friction factors in the polymer added turbulent flow through a circular pipe for Reynolds number ranging 10000∼50000. As Polymer additive, PEO (polyethylene oxide : molecular weight 4×10의 6제곱)was used. We also performed the experiments varying the concentration of PEO from 3 to 24 wppm to investigate the effect of the PEO concentration on the drag reduction. We observed more than 25% drag reduction under the above experimental conditions and the most effective drag reduction was found at 6 wppm (31% drag reduction).

Substantial drag reduction of a tractor-trailer vehicle using gap fairings

Kim, Jeong Jae,Kim, Jeongju,Lee, Sang Joon Elsevier 2017 Journal of wind engineering and industrial aerodyn Vol.171 No.-

<P>Aerodynamic drag reduction of heavy vehicles is one of the main issues in fuel saving and environmental gas emission. In general, 50% of the total aerodynamic drag is induced from the region in the front surface of the vehicle and the gap between the tractor and trailer. Various forebody drag-reducing devices for tractor trailer vehicles were introduced, however, conventional gap fairings or side extenders have technical limitations in reducing the aerodynamic drag exerting on the cab-roof space and gap between the tractor and trailer effectively. In this study, wind tunnel tests were conducted to investigate the drag reduction effects of the newly proposed gap fairings. The proposed gap fairing reduced drag by 16.4% at maximum as well as changed the gap length and deflecting angle. The aero cab fairing (ACE), which is a combination of cab-roof and gap fairings, and the extended aero cab fairing (EACF) considerably reduced the drag coefficient by approximately 11.1% and 17.5%, respectively. A particle image velocimetry was used to investigate flow characteristics, such as spatial distributions of mean velocity, vorticity, and turbulent kinetic energy around the scaled-down tractor-trailer model (1:17) with and without gap fairings to analyze the drag-reduction mechanism of the proposed gap fairings. The proposed gap fairings including ACF and EACF significantly reduced the mean velocity, vorticity in the gap region between the tractor and trailer, and the turbulent kinetic energy on the trailer's front surface. Results can provide useful information for improving the design of new additive flow control devices in reducing the aerodynamic drag of heavy vehicles.</P>

Bio-inspired cab-roof fairing of heavy vehicles for enhancing drag reduction and driving stability

Kim, Jeong Jae,Hong, Jiwoo,Lee, Sang Joon Elsevier 2017 International journal of mechanical sciences Vol.131 No.-

<P><B>Abstract</B></P> <P>Cab-roof fairing (CRF) has been developed to reduce the drag exerted on the forebody, thereby promoting fuel saving and environmental pollution control. Conventional CRFs with a 2D streamlined curvature have limitations in enhancing the driving stability and in reducing the drag at the forebody. In this study, new CRFs were designed with flow-guiding structures by mimicking the external forebody shape of sea lions. To evaluate the drag reduction effects of the proposed bio-inspired CRFs, three different types of CRFs (i.e., basic, bio-inspired, and advanced bio-inspired) were installed at scaled-down vehicle models of 15-ton (1:8) and 5-ton (1:6) heavy vehicles. The advanced bio-inspired CRF considerably reduced the drag coefficient of the 15-ton and 5-ton models by ∼20% and 22.4%, respectively. The side force was also reduced by up to 8% and 9% for the 15-ton and 5-ton models with the advanced bio-inspired CRF at a yaw angle of <I>β </I>= 3°, respectively. The flow characteristics around the forebody of the 15-ton model (1:15) with and without CRFs were analyzed by particle image velocimetry to elucidate the drag-reduction mechanism of the proposed CRFs. The bio-inspired CRFs significantly reduced the regions of separated shear flow and turbulent kinetic energy level on the side surfaces of the vehicle models. The findings provide useful information for improving the design of new forebody devices to reduce the drag and enhance the driving stability of heavy vehicles.</P> <P><B>Highlights</B></P> <P> <UL> <LI> New types of bio-mimetic cab-roof fairings (CRFs, i.e., an air deflector mounted on the top of the cab) were devised for the drag reduction of heavy vehicles. </LI> <LI> The advanced bio-inspired CRF considerably reduced the drag coefficient of the 15-ton and 5-ton models by approximately 20% and 22.4%, respectively. The side force was also reduced by up to 8% and 9% for the 15-ton and 5-ton models at a yaw angle of <I>ϕ</I> = 3°, respectively. </LI> <LI> Flow characteristics (e.g., mean velocity field and turbulent kinetic energy) around the forebody of the vehicle models with and without CRFs were thoroughly analyzed by using a PIV technique to elucidate such drag-reduction mechanism. </LI> <LI> The findings provide useful information for improving the design of new forebody devices by reducing the aerodynamic drag and enhancing the driving stability of heavy vehicles. </LI> </UL> </P> <P><B>Graphical abstract</B></P> <P>[DISPLAY OMISSION]</P>

Direct numerical simulations of viscoelastic turbulent channel flows at high drag reduction

Antony N. Beris,Kostas D. Housiadas 한국유변학회 2005 Korea-Australia rheology journal Vol.17 No.3

In this work we show the results of our most recent Direct Numerical Simulations (DNS) of turbulent viscoelastic channel flow using spectral spatial approximations and a stabilizing artificial diffusion in the viscoelastic constitutive model. The Finite-Elasticity Non-Linear Elastic Dumbbell model with the Peterlin approximation (FENE-P) is used to represent the effect of polymer molecules in solution. The corresponding rheological parameters are chosen so that to get closer to the conditions corresponding to maximum drag reduction: A high extensibility parameter (60) and a moderate solvent viscosity ratio (0.8) are used with two different friction Weissenberg numbers (50 and 100). We then first find that the corresponding achieved drag reduction, in the range of friction Reynolds numbers used in this work (180-590), is insensitive to the Reynolds number (in accordance to previous work). The obtained drag reduction is at the level of 49% and 63%, for the friction Weissenberg numbers 50 and 100, respectively. The largest value is substantially higher than any of our previous simulations, performed at more moderate levels of viscoelasticity (i.e. higher viscosity ratio and smaller extensibility parameter values). Therefore, the maximum extensional viscosity exhibited by the modeled system and the friction Weissenberg number can still be considered as the dominant factors determining the levels of drag reduction. These can reach high values, even for of dilute polymer solution (the system modeled by the FENE-P model), provided the flow viscoelasticity is high, corresponding to a high polymer molecular weight (which translates to a high extensibility parameter) and a high friction Weissenberg number. Based on that and the changes observed in the turbulent structure and in the most prevalent statistics, as presented in this work, we can still rationalize for an increasing extensional resistance-based drag reduction mechanism as the most prevalent mechanism for drag reduction, the same one evidenced in our previous work: As the polymer elasticity increases, so does the resistance offered to extensional deformation. That, in turn, changes the structure of the most energy-containing turbulent eddies (they become wider, more well correlated, and weaker in intensity) so that they become less efficient in transferring momentum, thus leading to drag reduction. Such a continuum, rheology-based, mechanism has first been proposed in the early 70s independently by Metzner and Lamley and is to be contrasted against any molecularly based explanations.