Papers by Keyword: Drag Reduction

Abstract: Long chain polymers are reported to be effective in reducing drag in turbulent flow systems. However, most of the effective polymers are synthetic, which are costly, non-biodegradable, and toxic that raises environmental concerns. Natural polymers, as eco-friendly alternatives, are gaining interest as drag-reducing additives (DRA), but single natural polymers have lower drag reduction (DR) efficacy compared to synthetic ones and degrade under high shear stress. This study aims to investigate biopolymer complexes from hibiscus leaves (HL) and okra (OK) as eco-friendly DRAs, comparing their performance with individual components. Biopolymers were extracted from dried hibiscus leaves and okra and diluted to concentrations of 200–1000 ppm. Complexes were formulated by mixing 200–1000 ppm HL extract with 1000 ppm OK extract. The extracts were characterized using Fourier Transform Infrared Spectroscopy (FTIR), meanwhile all the drag reducing solutions were assessed for viscosity, viscoelasticity and DR performance using an oscillating rheometer under different shear rate (0 – 200 s^-1) and frequencies (0 – 100 Hz). All the polymer solutions showed non-Newtonian shear-thinning behavior. The biopolymers and their complexes also exhibited significant viscoelastic properties which is important for DRA stability in turbulent flow. OK solutions achieved up to 79% DR at 1000 ppm, while HL solutions reached an average of 99% DR at concentrations of 400 ppm and above. However, HL-OK complexes had lower DR efficacy, with a maximum DR of 72% at 800 ppm HL – 1000 ppm OK. This might be due to the high concentration altering the water's properties and increasing viscosity, which increases drag.In conclusion, HL and OK complexes have potential for drag reduction, but future research should optimize concentration ratios, test over a broader range of shear rates, and explore other natural polymers complexes to achieve the synergistic effect.

Abstract: Weight reduction in automotive and aerospace components can improve energy efficiency, reduce emissions, and increase performance. The adoption of light metals such as aluminium, magnesium and titanium alloys, is essential to these performance improvements; however, these alloys require protective surface coatings to prevent corrosion and resulting mechanical failures during service life. Traditional protective coatings for light-weight materials can be costly in terms of energy, raw materials, and environmental sustainability. New durable coating approaches are required to allow light-weight materials to be fully exploited in high performance applications. Novel Cirrus HybridTM coatings, a recent innovation in surface finishing, can protect a wide range of light metal alloy components using a sustainable, non-toxic process. Cirrus HybridTM coating technology deposits a thin-film, inorganic coating that bonds tightly to the light-metal alloy substrate. The process is energy efficient, does not rely on hazardous chemicals, and is up to 5 times thinner than traditional coatings for light metals. A Cirrus HybridTM coating provides excellent anti-corrosion, scratch, and wear properties, along with superior tribological, electrical, and optical performance. This paper updates the art of these innovative new coating technologies for reducing weight in industrial components without compromising functionality or performance.

Abstract: Transportation of fluids in pipelines is common in many industrial processes. The energy requirements for this transport is high because of the need to overcome the occurring frictional pressure drop or drag. However, the addition of high molecular weight polymers to fluid flows has been known to cause a reduction in the frictional pressure drop. It has also been reported to cause other changes in the flow including changes in the turbulence characteristics, holdup as well as asymmetry of the velocity profiles. In this work some experimental results are presented in order to gain better insight into the deviations from axisymmetry of velocity profiles of water flow in pipes when drag reducing agents are added. Drag reduction studies were carried out in a horizontal 14mmID acrylic pipe with hydrolyzed polyacrylamide and different molecular weights polyethylene oxide used as additives in fully developed flows. Asymmetry was observed at both transitional and turbulent flow regimes for all tested polymer types and it increased with molecular weights. While the molecular weight and degree of formation of entanglements and aggregates of the polymer fibers are indicated as the causes of the observed profile asymmetry, the contribution of system/setup imperfections can be ruled out.

Abstract: Reduction of drag and flow resistance in systems containing moving fluids is a prominenttool to increase energy efficiency. Besides active flow control – such as moving surfaces or boundarylayer suction – passive techniques such as surface patterning by means of dimples are promising sinceno additional energy consumer is introduced into the system. Even though the effect of drag reductiondue to dimples has often been observed, the physical principals responsible for this effect are not yetunderstood. Most of the research concerning dimples and drag reduction published so far has beencarried out experimentally, not many numerical investigations on this topic have been done. The mainreason for this is that the tiny, transient flow structures generated in direct vicinity of dimples can noteasily be resolved in simulations. Even in case of time dependent numerical investigations it is notclear, whether and with which method of sub-grid scale modeling Large Eddy Simulations are capableof modeling these structures sufficiently. In this work we investigated different surfaces with dimpledepth to diameter ratios h/D reaching from 0.01 to 0.1 in channels of height H = 0.417D at Reynoldsnumbers ReD 5 830 and ReD 11 650 using steady state simulations with a k-omega-SST turbulencemodel. Drag reductions were observed for all setups h/D < 0.08 compared to the smooth channel.The best results were obtained with dimple depths of 4-5 % of diameter showing a slight dependenceof Re which is in good agreement with literature. As the experimental investigation of the flow overdimpled surfaces is limited in spacial and temporal resolution we could demonstrate that numericalinvestigations give the possibility to overcome this drawback. However the solution of simulationsstrongly depends on numerous factors such as the discretization scheme, the numerical models andthe grid used to obtain results which might be a reason for slightly varying results of such simulationsfound in literature.

Abstract: The flow over bluff bodies is separated compared to the flow over streamlined bodies. The investigation of the fluid flow over a cylinder with a streamwise slit has received little attention in the past, however there is some experimental evidence that show for turbulent regime it reduces the drag coefficient. This work helps in understanding the fluid flow over such cylinders in the laminar regime. As the width of the slit increases the drag coefficient keeps on reducing resulting in a narrower wake as compared to what is expected for flow over a cylinder. In this work we have used two different approaches in modelling a 2D flow for Re=10 to compare the results for CFD using finite volume method (ANSYS FLUENT^TM) and Lattice Boltzmann methods. In all cases cylinders of circular cross section have been considered while slit width changing from 10% to 40% of the cylinder diameter. . It will be shown that drag coefficient decreases as the slit ratio increases. The effect of slit size on drag reduction is studied and discussed in detail in the paper. We have also made comparison of the results obtained from Lattice Boltzmann and finite volume methods.

Abstract: In order to improve the efficiency of centrifugal pump, based on the bionics principle, established non-smooth surfaces of various groove structure on the centrifugal pump impeller. The internal flow field of it was numerically simulated through RNG k-ε turbulence model. Research the drag reduction characteristics of non-smooth impeller in different groove shape and arrangement. The results showed that the biggest drag reduction rate of centrifugal pump with non-smooth blades is about 6.22%. The blades of non-smooth unit can effectively inhibit the near wall boundary layer flow state, reduce the shear stress on blades wall, reduce the internal fluid turbulent degree of centrifugal pump, so that the fluid flow in centrifugal pump impeller is more stable, improve the efficiency of centrifugal pump.

Abstract: The earthworm is a common terrestrial animal, its physical structure and morphology characteristics are very distinctive. Through of imitation of the special abilities of earthworms, people can get the material to research on bionic technology, such as the jet, non-smooth surface, etc. It can provide the new design ideas for engineering technology. The study of earthworm body structure and its movement mechanism, can help people to find the drag reduction method in the process of movement. In addition, the earthworm non-smooth body surface, dorsal pore jet, surface lubrication, electroosmosis and its unique moving way form a good drag reduction effect. Therefore, research on earthworm is instructive for the development of bionic technology.

Abstract: Polymers-Surfactant complex efficacy in reducing the drag is of an interest subject in drag reduction research. Turbulent drag reduction (DR) efficiency of Sodium Polystyrene Sulfonate (NaPSS) sodium Alkylbenzene sulfonate complex was studied in a rotating disk apparatus. The solution complex was prepared by varying the concentration of the polymer between 100 to 1200 ppm and the surfactant between 100 to 700ppm. Measurement of torque values were recorded for each sample. The NaPSS (Sodium Polystyrene Sulfante) was found to have an ability to reduce the drag in the turbulent flow. A significant improvement was recorded for the addition of tiny amount of surfactant to the polymer system compare to the pure polymer drag reduction. At high surfactant concentration, it was found that the polymer drag ability decrease. The polymer was degraded when it is subjected to a high shear stress. The degredation resistance was increased by the addation of the surfactant to the polymer solution at concentration range of 100ppm to 400ppm of surfactant.

Abstract: CFD modelling of drag reduction agents (also called Flow Improvers) polymer additives dissolved in a newtonian solvent (UTP tap Water) was carried out in a curved conduit, A 7 equation Reynolds stress set of equations was used to simulate this flow. The purpose of this simulation is validate experimental results that show unusual pressure drop behaviour. CFD experiments show that there is pressure build-up near the end of the curved conduit due to severe centrifugal forces produced by the fluid, confirming the validity of the experimental results.

Abstract: With the development of world’s economy, energy shortage gradually appears. Resistance has a great influence on energy consumption. In other words, drag reduction means saving energy. Development of the drag reduction technology plays a very important role to improve the energy efficiency. Therefore, drag reduction technology of jet has become a hot research field. Drag reduction technology of jet is applied on the surface, so as to reduce surface friction resistance. Through analyzing the necessity of energy efficiency increase and jet drag reduction theory improvement, research progress of lateral jet flow technology and drag reduction technology of jet in the field of aircraft are reviewed. Besides, a main trend on the drag reduction technology of jet research is presented.