Numerical Analysis of Drag Reduction Characteristics of Biomimetic Puffer Skin: Effect of Spinal Height and Tilt Angle

2021 ◽  
Vol 21 (9) ◽  
pp. 4615-4624
Author(s):  
Hong-Gen Zhou ◽  
Chang-Feng Jia ◽  
Gui-Zhong Tian ◽  
Xiao-Ming Feng ◽  
Dong-Liang Fan
Keyword(s):  
Drag Reduction ◽  
Tilt Angle ◽  
Fluid Velocity ◽  
Viscous Drag ◽  
Total Drag ◽  
Pressure Drag ◽  
Reduction Efficiency ◽  
Distribution Parameters ◽  
Reduction Effect ◽  
Reduction Characteristics

Based on the migratory phenomenon of the puffer and the cone-shaped structures on its skin, the effects of spinal height and tilt angle on the drag reduction characteristics is presented by numerical simulation in this paper. The results show that the trend of total drag reduction efficiency changes from slow growth to a remarkable decline, while the viscous drag reduction efficiency changes from an obvious increase to steady growth. The total and viscous drag reduction efficiencies are 19.5% and 31.8%, respectively. In addition, with the increase in tilt angle, the total drag reduction efficiency decreases gradually; the viscous drag reduction efficiency first increases and then decreases, finally tending to be stable; and the total and viscous drag reduction efficiency reaches 20.7% and 26.7%, respectively. The flow field results indicate that the pressure drag mainly originates at the front row of the spines and that the total pressure drag can be effectively controlled by reducing the former pressure drag. With the increase in low-speed fluid and the reduction in the near-wall fluid velocity gradient, the viscous drag can be weakened. Nevertheless, the drag reduction effect is achieved only when the decrement of viscous drag is greater than the increment of pressure drag. This work can serve as a theoretical basis for optimizing the structure and distribution parameters of spines on bionic non-smooth surfaces.

Study of Drag Forces on a Designed Surface in Bubbly Water Lubrication Using Electrolysis

2006 ◽  
Vol 128 (6) ◽  
pp. 1383-1389 ◽  
Author(s):  
Haosheng Chen ◽  
Jiang Li ◽  
Darong Chen
Keyword(s):  
Drag Reduction ◽  
Side Wall ◽  
Water Electrolysis ◽  
Disk Surface ◽  
Viscous Drag ◽  
Fluid Viscosity ◽  
Bubble Behavior ◽  
Pressure Drag ◽  
Drag Forces ◽  
Reduction Effect

To study the drag reduction effect of a bubbly fluid, a pin-disk experiment is performed on the Universal Micro Tribotester system. Bubbles are generated by water electrolysis in holes that are specially designed on the disk surface. Experiment result shows that the drag force experiences a dynamic process, both drag reduction and drag increment effects appear in the process depending on the bubble behavior. This process is numerically simulated using computational fluid dynamics (CFD), and the explanations for the drag variation are given based on the analysis of drag forces on each wall of the disk surface. The drag reduction occurs when the bubble fills the hole, as the viscous drag on the air-liquid surface is small, and the pressure drag is reduced as the side wall of the hole is covered by the bubble. The drag increment is thought to be caused by the increment of the fluid viscosity when the bubble leaves the hole and flows in the fluid.

On the Effects of Aero Boundary Layer Control on Pressure Drag Reduction in Supercavitating Bodies

2005 ◽  
Author(s):  
Yasmin Khakpour ◽  
Miad Yazdani
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Pressure Distribution ◽  
Constant Pressure ◽  
Viscous Drag ◽  
Cavity Surface ◽  
Gradient Flows ◽  
Supercavitating Vehicles ◽  
Pressure Drag ◽  
Layer Control

Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Furthermore as we’ll see, pressure distribution on cavity surface caused due to overall conditions, induct nonaxisymetric forces and they may need to be investigated. Primarily we describe how pressure distribution into the cavity can cause separation of the aero boundary layer. Then we present some approaches by which this probable separation can be controlled. Comparisons of several conditions exhibits that at very low cavitation numbers, constant pressure assumption fails particularly for gradient shaped profiles and separation is probable if the flow is sufficiently turbulent. Air injection into the NATURALLY FORMED supercavity is found as an effective way to delay probable separation and so significant pressure drag reduction is achieved. In addition, the position of injection plays a major role to control the aero boundary layer and it has to be considered. Moreover, electromagnetic forces cause to delay or even prevent separation in high pressure gradient flows and interesting results obtained in this regard shows significant drag reduction in supercavitating vehicles.

Drag Reduction of Gas-Liquid Two-Phase Flow in Steel Pipes with Different Inclination Geometry

2012 ◽  
Vol 433-440 ◽  
pp. 463-470
Author(s):  
Lei Liu ◽  
Xin Feng Guo ◽  
Qiu Yue Guo ◽  
Hui Qing Fan ◽  
Zhu Hai Zhong
Keyword(s):  
Drag Reduction ◽  
Two Phase Flow ◽  
Vertical Section ◽  
High Energy ◽  
Phase Flow ◽  
Two Phase ◽  
Steel Pipes ◽  
Horizontal Pipes ◽  
Reduction Efficiency ◽  
Reduction Characteristics

It is significant to make researches on drag reduction in two-phase transport pipeline because two-phase flow has high energy dissipation. API X 52 steel pipe with diameter of 40mm is used in this paper to simulate pipeline with different inclination geometry including horizontal, up-inclined and vertical sections. The up-inclined section has an inclination angle of eight degree. Experiments and theoretical analysis are carried out to study the drag reduction characteristics of gas-liquid two-phase flow in these three sections. The drag reducing agents used here is polyacrylamide. It is found that two-phase drag reduction varies with pipe inclination geometry. The largest drag reduction efficiency occurs in horizontal pipes and which is up to seventy percent. Drag reduction efficiency in up-inclined section is up to sixty percent. Drag reduction in vertical section is the lowest and which can be up to about thirty percent. A mechanistic drag reduction model is proposed to predict drag reduction in gas-liquid two-phase flow. The results predicted are in good agreement with the experiment data.

scholarly journals Research Progress on the Collaborative Drag Reduction Effect of Polymers and Surfactants

Materials ◽  
2020 ◽  
Vol 13 (2) ◽  
pp. 444 ◽  
Author(s):  
Yunqing Gu ◽  
Songwei Yu ◽  
Jiegang Mou ◽  
Denghao Wu ◽  
Shuihua Zheng
Keyword(s):  
Drag Reduction ◽  
Reynolds Numbers ◽  
Research Progress ◽  
Polymer Additives ◽  
Factors Affecting ◽  
Mechanism Model ◽  
Reduction Effect ◽  
Reduction Characteristics ◽  
Degradation Properties ◽  
Degradation Ability

Polymer additives and surfactants as drag reduction agents have been widely used in the field of fluid drag reduction. Polymer additives can reduce drag effectively with only a small amount, but they degrade easily. Surfactants have an anti-degradation ability. This paper categorizes the mechanism of drag reducing agents and the influencing factors of drag reduction characteristics. The factors affecting the degradation of polymer additives and the anti-degradation properties of surfactants are discussed. A mixture of polymer additive and surfactant has the characteristics of high shear resistance, a lower critical micelle concentration (CMC), and a good drag reduction effect at higher Reynolds numbers. Therefore, this paper focuses more on a drag reducing agent mixed with a polymer and a surfactant, including the mechanism model, drag reduction characteristics, and anti-degradation ability.

Characteristics of Multi-Cavity Trapped Vortex Combustors

2010 ◽  
Author(s):  
Alejandro M. Briones ◽  
Balu Sekar
Keyword(s):  
Heat Release ◽  
Temperature Profile ◽  
Viscous Drag ◽  
Reacting Flow ◽  
Total Drag ◽  
Pressure Drag ◽  
Air Jets ◽  
Exit Temperature ◽  
Trapped Vortex ◽  
Single Cavity

This research is motivated towards improving and optimizing the performance of AFRL’s Inter-Turbine Burner (ITB) in terms of greater combustion efficiency, reduced losses and exit temperature profile requirements. The ITB is a minicombustor concept, situated in between the high and low pressure turbine stages and typically contains multiple fueled and non-fueled Trapped Vortex Combustor (TVC) cavities. The size, placement, and arrangement of these cavities have tremendous effect on the combustor exit temperature profile. The detailed understanding of the effect of these cavities in a three-dimensional ITB configuration would be very difficult and computationally prohibited. Therefore, a simple but somewhat similar conceptual axi-symmetric burner is used here the design variations of Trapped Vortex Combustor (TVC) through modeling and simulation. The TVC can be one single cavity or can be represented by multi-cavity combustor. In this paper, both single cavity TVC and multi-cavity TVCs are studied. The single cavity TVC is divided into multiple cavities while the total volume of the combustor remains constant. Four combustors are studied: Baseline, Staged, Three-Staged, and Interdigitated TVC. An extensive computational investigation on the characteristics of these multi-cavity TVCs is presented. FLUENT is used for modeling the axisymmetric reacting flow past cavities using a global eddy dissipation mechanism for C3H8-air combustion with detailed thermodynamic and transport properties. Calculations are performed using Standard, RNG, and Realizable k-ε RANS turbulence models. The numerical results are validated against experimental temperature measurements on the Base TVC. Results indicate that the pressure drag is the major contributor to total drag in the Base TVC. However, viscous drag is still significant. By adding a concentric cavity in sequential manner (i.e. Staged TVC), the pressure drag decreases, whereas the viscous drag remains nearly constant. Further addition of a secondary concentric cavity (i.e. Three-Staged TVC), the total drag does not further decrease and both pressure and viscous drag contributions do not change. If instead a non-concentric cavity is added to the Base TVC (i.e. Interdigitated TVC), the pressure drag increases while the viscous drag decreases slightly. The effect of adding swirl flow is to increase the fuel-air mixing and as a result, it increases the maximum exit temperature for all the combustors modeled. The jets and heat release contribute to increase pressure drag with the former being greater. The fuel and air jets and heat release also modify the cavity flow structure. By turning off the fuel and air jets in the Staged TVC, lower drag (or pressure loss) and exit temperature are achieved. It is more effective to turn off the fuel and air jets in the upstream (front) cavity in order to reduce pressure losses. Based on these results, recommendations are provided to the engineer/designer/modeler to improve the performance of the ITB.

Separation Control of Aero Boundary Layer in Supercavitating Bodies and Its Effect on Pressure Drag Reduction

2005 ◽  
Author(s):  
Yasmin Khakpour ◽  
Miad Yazdani
Keyword(s):  
Boundary Layer ◽  
Drag Reduction ◽  
Constant Pressure ◽  
Flow Region ◽  
Air Injection ◽  
Viscous Drag ◽  
Cavity Surface ◽  
Cavitation Flow ◽  
Two Phase ◽  
Pressure Drag

Supercavitation is known as the way of viscous drag reduction for the projectiles, moving in the liquid phase. In recent works, there is distinct investigation between cavitation flow and momentum transfer far away from the cavity surface. In fact such methodologies consider cavitation flow statically, rather than taking dynamic effects of overall flow into account. However, it seems that there is strong connection between overall flow and what takes place in the sheet cavity where a constant pressure distribution is assumed. Thereby, in order to configure the system conditions which may be cause of cavity perturbation and so system oscillation, we need to use proper methodologies in which turbulence shear stress effects and role of their distribution, are suitably come into account. Numerical simulation of supercavitating flows is pursued in this paper. The effect of air injection in the cavity as a means of stabilization is examined. A k-epsilon model is employed for the liquid flow region while a single-fluid two phase model is applied in the cavity region. Comparisons of several conditions exhibits that at very low cavitation numbers, constant pressure assumption fails particularly for gradient shaped profiles and separation is probable if the flow is sufficiently turbulent. Air injection into the NATURALLY FORMED supercavity is found as an effective way to prevent the probable separation and so significant pressure drag reduction up to 70% is observed. In addition, the position of injection plays a major role to control the aero boundary layer and it has to be considered.

scholarly journals Experimental Study on Drag Reduction Characteristics of Bionic Earthworm Self-Lubrication Surface

2019 ◽  
Vol 2019 ◽  
pp. 1-8
Author(s):  
Guomin Liu ◽  
Xueqiao Wu ◽  
Meng Zou ◽  
Yuying Yan ◽  
Jianqiao Li
Keyword(s):  
Drag Reduction ◽  
Flow Rate ◽  
Experimental Testing ◽  
Reduction Rate ◽  
Normal Pressure ◽  
Secondary Effects ◽  
Quadratic Regression ◽  
Regression Test ◽  
Reduction Effect ◽  
Reduction Characteristics

In the present study, a coupling bionic method is used to study the drag reduction characteristics of corrugated surface with lubrication. In order to test the drag reduction features, bionic specimen was prepared inspired by earthworm surface and lubrication. Based on the reverse engineering method, nonsmooth curve of earthworm surface was extracted and the bionic corrugated sample was designed, and the position of lubrication hole was established by experimental testing. The lubricating drag reduction performance, the influence of normal pressure, the forward velocity, and the flow rate of lubricating fluid on the forward resistance of the bionic specimens were analyzed through a single factor test by using the self-developed test equipment. The model between the forward resistance and the three factors was established through the ternary quadratic regression test. The results show that the drag reduction effect is obvious, the drag reduction rate is 22.65% to 34.89%, and the forward resistance decreases with the increase of the forward velocity, increases with the increase of the normal pressure, and decreases first and then becomes stable with the increase of flow rate of lubricating fluid. There are secondary effects on forward resistance by the three factors, and the influencing order is as follows: normal pressure>flow rate of lubricating fluid>forward velocity.

Drag Reduction Effect of Dimples Arranged in Two-Dimensional Quasicrystal Structure

2010 ◽  
Vol 146-147 ◽  
pp. 331-335
Author(s):  
Wen Hui Xue ◽  
Xing Guo Geng ◽  
Feng Li ◽  
Jie Li ◽  
Yao Zhang ◽  
...  
Keyword(s):  
Shear Stress ◽  
Drag Reduction ◽  
Two Dimensional ◽  
Rotating Fluids ◽  
Periodic Arrays ◽  
Visualization Experiment ◽  
Reduction Efficiency ◽  
Reduction Effect ◽  
Coherent Effect ◽  
Quasicrystal Structure

Rotating fluids experiments were carried out by CAP2000+ cone viscometer, to examine the drag reduction properties of dimples arranged in quasicrystal structure. The dimples were fabricated on the surface of duralunmin (LY12) plates. Compared with the periodic arrays, the dimples arranged in quasicrystal structure, especially the 12-fold quasicrystal structure, could significantly reduce the wall shear stress. And the relative drag reduction efficiency changes periodically with the depth of dimple. Flow-visualization experiment verified that the coherent effect of dimples arranged in quasicrystal structure and the fluids could efficiently inhibit the extending intensity of radial secondary flow, which strengthens the drag reduction effect.

scholarly journals Numerical Study of Effect of Sawtooth Riblets on Low-Reynolds-Number Airfoil Flow Characteristic and Aerodynamic Performance

Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2102
Author(s):  
Xiaopei Yang ◽  
Jun Wang ◽  
Boyan Jiang ◽  
Zhi’ang Li ◽  
Qianhao Xiao
Keyword(s):  
Reynolds Number ◽  
Drag Reduction ◽  
Numerical Study ◽  
Low Reynolds Number ◽  
Aerodynamic Performance ◽  
Operating Conditions ◽  
Viscous Drag ◽  
Airfoil Flow ◽  
Low Reynolds ◽  
Reduction Effect

Riblets with an appropriate size can effectively restrain turbulent boundary layer thickness and reduce viscous drag, but the effects of riblets strongly depend on the appearance of the fabric that is to be applied and its operating conditions. In this study, in order to improve the aerodynamic performance of a low-pressure fan by using riblet technology, sawtooth riblets on NACA4412 airfoil are examined at the low Reynolds number of 1 × 105, and the airfoil is operated at angles of attack (AOAs) ranging from approximately 0° to 12°. The numerical simulation is carried out by employing the SST k–ω turbulence model through the Ansys Fluent, and the effects of the riblets’ length and height on aerodynamic performance and flow characteristics of the airfoil are investigated. The results indicate that the amount of drag reduction varies greatly with riblet length and height and the AOA of airfoil flow. By contrast, the riblets are detrimental to the airfoil in some cases. The most effective riblet length is found to be a length of 0.8 chord, which increases the lift and reduces the drag under whole AOA conditions, and the maximum improvements in both are 17.46% and 15.04%, respectively. The most effective height for the riblet with the length of 0.5 chord is 0.6 mm. This also improves the aerodynamic performance and achieves a change rate of 12.67% and 14.8% in the lift and drag coefficients, respectively. In addition, the riblets facilitate a greater improvement in airfoil at larger AOAs. The flow fields demonstrate that the riblets with a drag reduction effect form “the antifriction-bearing” structure near the airfoil surface and effectively restrain the trailing separation vortex. The ultimate cause of the riblet drag reduction effect is the velocity gradient at the bottom of the boundary layers being increased by the riblets, which results in a decrease in boundary thickness and energy loss.

Experimental Study of Air Layer Sustainability for Frictional Drag Reduction

2014 ◽  
Vol 58 (01) ◽  
pp. 30-42 ◽  
Author(s):  
Bhat Nikhil Jagdish ◽  
Tay Zhi Xian Brandon ◽  
Tiaw Joo Kwee ◽  
Arun Kr. Dev
Keyword(s):  
Drag Reduction ◽  
Experimental Studies ◽  
Hydrophobic Surface ◽  
Viscous Drag ◽  
Total Resistance ◽  
Frictional Drag ◽  
Form Drag ◽  
Friction Resistance ◽  
Slow Steaming ◽  
Pressure Drag

Frictional drag reduction by microbubbles is a promising engineering method for reducing ship fuel consumption, especially for large, slow steaming vessels. Total resistance can be broken down into frictional drag and form drag (also known as pressure drag or profile drag). Ship's hull form optimization is commonly to reduce the form drag of a ship. Another technique would be required to deal with the frictional (viscous) portion of the total resistance. One such technique that reduces the friction resistance is the air lubrication technique. This research looks at possible enhancement for the microbubbles drag reduction technique with the use of hydrophobic plates to trap and retain an air layer. The hydrophobic surface cannot sustain bubbles by itself. Laser-machined microstructure coupled with hydrophobic coatings allows the rapid formation of air layer rapidly and sustainability of the air layer is recorded. With extensive experimental studies, we have shown that an air layer can be entrained around a moving flat plate thereby reducing friction. This could pave the way for applying this technique around the wall of moving ship hulls thereby minimizing the viscous drag and reducing the shipping costs.

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