Study on drag reduction mechanism of rotating disk with micro-grooves

2017 ◽  
Vol 232 (6) ◽  
pp. 660-673
Author(s):  
Suping Wen ◽  
Wenbo Wang ◽  
Jian Wang
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Flow Characteristics ◽  
Rotating Disk ◽  
Viscous Sublayer ◽  
Dual Function ◽  
Reduction Mechanism ◽  
Smooth Disk ◽  
Reduction Effect ◽  
Interaction Phenomenon

This paper presents the drag reduction mechanism of a rotating disk with micro-grooves. The flow characteristics of the micro-grooved disk at various rotating Reynolds numbers are investigated using experiments and large-eddy simulations. The results show that fluid in the gap between the disks undergoes circumferential movement, but fluid within the micro-grooves undergoes radial movement because of the dual function of wall rejection and boundary layer blockage. As a result, fluid within the micro-grooves moves very slowly and quietly. Hence, quiet and slow-moving fluid within the micro-grooves increases the thickness of the viscous sublayer and recedes mixed layer and suppresses the unstable motion. The mean relative velocity gradient of the immersed surface on the grooved disk becomes much lower than that of a smooth disk, and the contact area between the walls and the high-speed fluid is diminished. An interaction phenomenon between the micro-grooves and the gap could be discovered due to the micro-groove unenclosed structure. The interaction phenomenon makes the quiet fluid within the micro-grooves also suppresses the outside flow. Accordingly, a micro-grooved rotating disk has an obvious drag reduction effect compared with a rotating smooth disk.

A tracer dispersion study of the drag-reduction effect in a turbulent pipe flow

1971 ◽  
Vol 47 (2) ◽  
pp. 209-230 ◽  
Author(s):  
A. W. Bryson ◽  
Vr. Arunachalam ◽  
G. D. Fulford
Keyword(s):  
Molecular Weight ◽  
Drag Reduction ◽  
Pipe Flow ◽  
Viscous Sublayer ◽  
Turbulent Pipe Flow ◽  
Reduction Mechanism ◽  
Response Curves ◽  
Pipe Flows ◽  
Tracer Dispersion ◽  
Reduction Effect

Remarkable differences in dispersion of a tracer material injected into turbulent pipe flows of water and water containing as little as 2·5 parts per million by weight of a soluble high-molecular-weight drag-reducing polyoxyethylene additive have been measured. Analysis of the tracer response curves in terms of a simple one-parameter model shows that the observed results are compatible with a drag-reduction mechanism based on thickening of the viscous sublayer adjoining the wall. Other experiments, reported briefly, suggest that polymer adsorption on to the wall is responsible for this thickening.

Numerical study on the mechanism of drag reduction for interceptors on planning boats

2021 ◽  
Author(s):  
Lianzheng Cui ◽  
Zuogang Chen ◽  
Yukun Feng
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Degrees Of Freedom ◽  
Numerical Study ◽  
Dynamic Pressure ◽  
Motion Model ◽  
Gauge Pressure ◽  
Reduction Effect ◽  
Pressure Resistance ◽  
Viscous Pressure

The drag reduction effect of interceptors on planning boats has been widely proven, but the mechanism of the effect has been rarely studied in terms of drag components, especially for spray resistance. The resistance was caused by the high gauge pressure under the boats transformed from the dynamic pressure, and it is the largest drag component in the high-speed planning mode. In this study, numerical simulations of viscous flow fields around a planning boat with and without interceptors were conducted. A two degrees of freedom motion model was employed to simulate the trim and sinkage. The numerical results were validated against the experimental data. The flow details with and without the interceptor were visualized and compared to reveal the underlying physics. A thinner and longer waterline could be achieved by the interceptor, which made the boat push the water away more gradually, and hence, the wave-making resistance could be decreased. The improved waterline also reduced the component of the freestream normal to the hull surface and led to the less transformed dynamic pressure, resulting in the lowAer spray resistance. Furthermore, the suppression of the flow separation could also be benefited from the interceptor; the viscous pressure resistance was therefore decreased.

New Centrifugal Pump in Very Low Specific Speed Range

2011 ◽  
Author(s):  
Shusaku Kagawa ◽  
Junichi Kurokawa
Keyword(s):  
Centrifugal Pump ◽  
High Speed ◽  
Cfd Simulation ◽  
Flow Characteristics ◽  
Internal Flow ◽  
Rotating Disk ◽  
Capacity Curve ◽  
Speed Range ◽  
Low Specific Speed ◽  
Specific Speed

In the range of very low specific speed, such as ns < 80 [min.−1, m3/min., m], or Ns < 533 [min.−1, USGPM, ft.], stable head-capacity curve is one of the most important issues. The head-capacity curve of a conventional closed impeller tends to be unstable with a positive slope characteristic in such a very low ns range. To solve this problem, a new type of centrifugal pump “J-groove pump” is proposed and tested in this study. The J-groove pump is composed of a rotating disk mounted with many shallow radial grooves and a circular casing. The experimental results reveal that the proposed J-groove pump is quite effective in the very low specific speed range. The pump head is about 1.2 times higher than that of a conventional centrifugal pump and the head-capacity curve is almost stable, though the efficiency becomes a little lower because of a large friction power of the stationary wall. The cavitation performance is also measured and is shown to be almost same as that of a conventional centrifugal pump. This pump is applicable to high speed pump, as it has no small clearance, high strength due to simple impeller configuration, and easy to assemble. In order to determine the internal flow characteristics of the J-groove pump, CFD simulation is carried out. It is revealed that the high head of the J-groove pump is caused by a strong vortex flow existing in both clearances near the impeller tip over the whole flow range.

scholarly journals Numerical Investigations of Cavitation Nose Structure of a High-Speed Projectile Impact on Water-Entry Characteristics

2020 ◽  
Vol 8 (4) ◽  
pp. 265
Author(s):  
Qiang Li ◽  
Lin Lu
Keyword(s):  
Drag Reduction ◽  
High Speed ◽  
Flow Characteristics ◽  
Water Entry ◽  
Navier Stokes ◽  
Cavitation Model ◽  
Lower Velocity ◽  
Numerical Investigations ◽  
Velocity Attenuation ◽  
Trajectory Stability

In this study, a detailed analysis of the influences of cavitation nose structure of a high-speed projectile on the trajectory stability during the water-entry process was investigated numerically. The Zwart-Gerber-Belamri (Z-G-B) cavitation model and the Shear Stress Ttransport (SST)k-ω turbulence model based on the Reynolds Averaged Navier–Stokes (RANS) method were employed. The numerical methodology was validated by comparing the numerical simulation results with the experimental photograph of cavitation shape and the experimental underwater velocity. Based on the numerical methodology, the disk and the conical cavitation noses were selected to investigate the water-entry characteristics. The influences of cavitation nose angle and cavitation nose diameter of the projectile on the trajectory stability and flow characteristics were carried out in detail. The variation features of projectile trajectory, velocity attenuation and drag were conducted, respectively. In addition, the cavitation characteristics of water-entry is presented and analyzed. Results show that the trajectory stability can be improved by increasing the cavitation nose angle, but the drag reduction performance will be reduced simultaneously. Additionally, due to the weakening of drag reduction performance, the lower velocity of the projectile will cause the damage of the cavitation shape and the trajectory instability. Furthermore, the conical cavitation nose has preferable trajectory stability and drag reduction performance than the disk cavitation nose.

scholarly journals Drag Reduction Mechanism of Viscoelastic Slick-Water Fracturing Fluid in Tortuous and Rough Fractures

Geofluids ◽  
2021 ◽  
Vol 2021 ◽  
pp. 1-11
Author(s):  
Zhiyu Liu ◽  
Fan Fan ◽  
Donghang Zhang ◽  
Yang Li ◽  
Yuan Li ◽  
...  
Keyword(s):  
Molecular Weight ◽  
Drag Reduction ◽  
Flow Rate ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Flow Rule ◽  
Mechanism Analysis ◽  
Reduction Mechanism ◽  
Fracturing Fluid ◽  
Factors Affecting

Slick-water can effectively reduce the flow drag of fracturing fluid. Many studies have focused on the drag reduction performance of slick-water in wellbore and perforation, but there has been little research on drag reduction characteristics in fracture flow. In this paper, a new visualization experiment system is used to simulate real fracture. The fracture surface is produced through actual triaxial hydraulic fracturing and is copied by a three-dimensional printer using resin material to maintain its shape feature. In comparing the experimental results, it was found that the main factors affecting drag reduction in a fracture are the relative molecular weight and the added concentration. Unlike the flow rule of the drag reducer in a pipeline, when the concentration is greater than 0.10%, a negative DR effect begins to appear. The influence of molecular weight is related to the flow stage; the increasing of molecular weight causes a reduction in DR effect when the flow rate is 0.24 m/s. However, the flow rate exceeds 0.5 m/s; drag reducers with higher molecular weight demonstrate better drag reduction performance. The drag reduction mechanism analysis in fractures was obtained from visualization observations, and the flow characteristics of fluid were characterized by using tracking particles. Drag reduction effect occurs mainly on the surface of the fractures in contrast to near the centre of the flow channel. This research can provide a reference for the experimental study on drag reduction in fractures and is of great significance to the optimization and improvement of drag reducing agent.

scholarly journals Flow Characteristics of a Highly Rotating Turbine Cavity System With Discharge Hole

1999 ◽  
Author(s):  
D. J. Maeng ◽  
J. S. Lee ◽  
R. Jakoby ◽  
S. Kim ◽  
S. Wittig
Keyword(s):  
Flow Field ◽  
High Speed ◽  
Rotational Velocity ◽  
Three Dimensional ◽  
Flow Characteristics ◽  
Rotating Disk ◽  
Disk System ◽  
High Speed Rotation ◽  
Measured Flow ◽  
Cavity System

An experimental investigation is performed to analyze the flow characteristics of a turbine cavity system containing discharge holes installed in a rotating disk. The turbine cavity system is composed of a rotating disk and two stationary disks on both sides of the rotating disk. The air flow is induced into the upstream cavity, and then discharged into the downstream cavity through 8 discharge holes in the rotating disk. The flow field in each cavity at high-speed rotation of the rotor was measured by a three-dimensional LDV system. The measured flow field is analyzed to understand the flow structures, and further provide information for studying the heat transfer behaviors of the turbine disk system. The overall flow field in the upstream cavity shows a negligible axial velocity with a relatively small rotational velocity, less than 10% of the rotor speed. The downstream cavity flow has a high rotational velocity close to the rotational speed of the discharged jets, due to the direct circumferential momentum transfer from the discharged jets. The interaction between the discharged jet and the downstream stator disk induces an asymmetric development of the spreading wall jet, which results in a relative circumferential motion to the revolving discharged jet. The whole flow field in the downstream cavity is divided into several flow regions according to their features.

scholarly journals Aerodynamic Drag Reduction and Optimization of MIRA Model Based on Plasma Actuator

Actuators ◽  
2020 ◽  
Vol 9 (3) ◽  
pp. 64
Author(s):  
Chenguang Lai ◽  
Hang Fu ◽  
Bo Hu ◽  
Zhiwei Ling ◽  
Li Jiang
Keyword(s):  
Drag Reduction ◽  
Flow Control ◽  
High Speed ◽  
Aerodynamic Drag ◽  
Active Flow Control ◽  
Plasma Actuator ◽  
Efficient Global Optimization ◽  
Driving Voltage ◽  
Control Effect ◽  
Reduction Effect

Active flow control of surface dielectric barrier discharge (SDBD) plasma is a technology that converts electrical energy into kinetic energy to achieve flow control. Its main application areas are concentrated in the aviation field. Undoubtedly, few studies have applied it in the field of automobile flow control. Meanwhile, during high-speed driving, there is a serious airflow separation phenomenon at the rear of notch-back cars, which brings a large area of negative pressure to the back of the cars. Due to the huge pressure difference between the front and end of the cars, it will increase the driving drag and fuel cost of the car. In this context, we seek to discuss the control effect on the airflow separation at the rear of the notch-back by using the phenomenological numerical simulation method of plasma flow control. Firstly, the plasma actuator is arranged separately on the rear end of the roof, c-pillar, upper and side of the trunk to study the control effect of airflow separation. After that, the plasma actuators at each position are combined and actuated simultaneously. We try to observe the control effect of airflow separation and select the combination with the best drag reduction effect. In the third stage, an efficient global optimization (EGO) algorithm based on kriging response surface is applied to optimize the supply voltage of the best combination that has been obtained before and obtain the driving voltage parameter of each actuator optimized under this combination. The results show that when plasma actuation is applied at four locations, only the actuation applied to the side of the luggage compartment has a significant drag reduction effect, while in other cases, the drag coefficient will increase. Specifically, drag reduction is better when the actuation is applied at four positions simultaneously. The maximum drag reduction coefficient of the car is reduced by 13.17%.

scholarly journals Research on Control Technology of Jet and Rectifying Cone Combined Flow Field

2020 ◽  
Vol 2020 ◽  
pp. 1-20
Author(s):  
Hongqing Lv ◽  
Lei Xu ◽  
Zhenqing Wang ◽  
Xiaobin Zhang
Keyword(s):  
Shock Wave ◽  
Flow Field ◽  
Drag Reduction ◽  
High Speed ◽  
Bluff Body ◽  
Hot Spot ◽  
Pressure Ratio ◽  
Main Flow ◽  
Control Technology ◽  
Reduction Effect

As an active flow field control technology, reverse jet and rectifier cone can significantly affect the flow field around the high-speed aircraft and reduce the drag and heat of high-speed aircraft to a certain extent. In this paper, the CFD numerical method is used to simulate and analyze the flow around the bluff body front rectifier cone and the reverse jet interference flow field. Further considering the combination of the two, the flow field structure around the bluff body under the combination of rectifying cone and reverse jet flow was simulated. Research shows, for the flow field of a single reverse jet, the pressure ratio of the reverse jet to the main flow has a significant effect on the drag reduction performance. With the change of the pressure ratio of the jet to the main flow, two modes of long jet and short jet will appear. The structure of the short jet modal flow field is relatively stable. However, with the increase of attack angle, the shear layer of free flow will attach to the shock wave and form hot spot, which is a great threat to high-speed aircraft. When the rectifier cone and the reverse jet are combined, within a certain angle of attack, the wall will not form a reattachment shock wave. The area behind the bow shock and in front of the aircraft head is a free-state zone, which has a good cooling effect on the aircraft head. At the same time, the static pressure on the wall is reduced, which has a very good drag reduction effect.

Drag reduction by various micro-grooves in a rotating disk system

2019 ◽  
Vol 234 (1) ◽  
pp. 110-123 ◽  
Author(s):  
Suping Wen ◽  
Wenbo Wang ◽  
Shuhuai Wu
Keyword(s):  
Drag Reduction ◽  
Flow Characteristic ◽  
Rotating Disk ◽  
Low Pressure ◽  
Rotating Disks ◽  
Asymmetry Coefficient ◽  
Disk System ◽  
Reduction Efficiency ◽  
Pressure Area ◽  
Interaction Phenomenon

To study the effects of micro-groove cross section asymmetry on the flow characteristic and drag reduction efficiency under rotation, numerical simulations of various rotating disks with micro-grooves were performed. Experiments of two representative disks were conducted for comparison and validation. Both numerical results and experimental results show that micro-grooves are effective in drag reduction. The fluid flow is promoted at one micro-groove sidewall and suppressed on the other side. There is an extended low-pressure area between the micro-grooves and the disk clearance, which demonstrates the interaction phenomenon exists, could be discovered. The interaction phenomenon makes the micro-groove fluid suppress the clearance fluid. When the disks rotate, the micro-groove fluids are suppressed, and the extended low-pressure areas are intensified overall. Positive asymmetry coefficient micro-grooves have larger high-pressure areas, and negative asymmetry coefficient micro-grooves have larger low-pressure areas. A higher asymmetry coefficient micro-groove has a greater asymmetrical pressure distribution. In contrast, the extended low-pressure areas are slightly affected by micro-groove geometries. Positive asymmetry coefficient micro-grooves, including zero asymmetry coefficient micro-grooves, have higher drag reduction efficiencies, whereas negative asymmetry coefficient micro-grooves have lower drag reduction efficiencies. The optimal micro-groove asymmetry coefficient is 0.25–0.5 within the rotating Reynolds number limits of 0.703 × 106–1.406 × 106.

RECENT PROGRESS IN EXPLORING DRAG REDUCTION MECHANISM OF REAL SHARKSKIN SURFACE: A REVIEW

2015 ◽  
Vol 15 (03) ◽  
pp. 1530002 ◽  
Author(s):  
YUEHAO LUO
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Recent Progress ◽  
Daily Life ◽  
Reduction Mechanism ◽  
Reduction Effect ◽  
Morphology Influence ◽  
Long Chains

It has gradually developed into an undisputable fact that sharkskin surface has the obvious drag reduction effect compared with the absolutely smooth skins, and it has been put into application widely, which has brought great advantages and profits in daily life, industry and agriculture. Because some problems in turbulence are not resolved completely and perfectly, the drag reduction mechanism of real sharkskin has also not been understood absolutely and thoroughly so far. However, many researchers have carried out lots of the relevant experiments and analyses, very plentiful and important conclusions are obtained, which can explain some certain phenomena of sharkskin drag reduction effect. An overview of exploring drag reduction mechanism of real sharkskin surface is systemically presented in detail. These mechanisms include inhibition of turbulence using micro/nano structured morphology, influence of scale's attack angles, nano-long chains and boundary layer slipping based on superhydrophobicity. This paper will improve the comprehension of the drag reduction mechanism and expand biomimetic sharkskin technology into more applications.

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