Drag Reduction Ratio Research Articles

Drag Reduction of a Circular Cylinder with a Highly Water-Repellent Wall.

Flow past a circular cylinder with a highly water-repellent wall has been investigated using a flow visualization technique at Re=50. Test cylinder is 20 mm in diameter. The basic material of the highly water-repellent coating is fluorine alkane modified acrylic resin with added hydrophobic silica, which was left overnight in air after it was coated to the cylinder wall. The flow patterns agreed with that of the analytical results obtained by applying the fluid slip boundary condition. The maximum value of the drag reduction ratio was about 25% for the highly water-repellent wall cylinder at Re=50.

Drag Reduction for a Rotating Disk in Surfactant Solutions.

Recently, Considerable interest has developed in surfactant additives for use in district heating and cooling systems to lower pumping energy requirement. In this study, drag reduction for an enclosed rotating disk in surfactant solutions was clarified experimentally. Experiments were carried out to measure the torque of acting on one side of the disk. Test surfactant solutions were Ethoquad O/12 with sodium salicylate at concentration of 50, 100 and 200 ppm. The temperature of test solutions were 18, 25 and 31°C. It was shown that the drag reduction of the surfactant solutions was not only depended on the concentration but also on the temperature. From flow visualization technique, it has been clarified that the amplitude of circular vortices around the rotating disk were reduced by the surfactant solution and the flow direction near the disk was turned to outward. The maximum drag reduction ratio was about 30% in 200 ppm Ethoquad O/12 solution at about Re=5×105.

Drag Reduction in Laminar Flow Between Two Vertical Coaxial Cylinders

Laminar drag reduction has been shown for the flow of a Newtonian fluid in the space between two vertical coaxial cylinders. Experiments were carried out to measure the torque of a bob with a highly water-repellent wall to clarify the effect of the contact surface of the bob on the flow behavior. The basic material of the highly water-repellent wall is fluorine alkane modified acrylic resin with added hydrophobic silica, and the contact angle of the wall is about 150 degree. The radius rations of the bob were 0.932 and 0.676. Test fluids were Newtonian aqueous solutions of 60, 70, and 80 wt% glycerin and polymer solutions. The maximum drag reduction ratio was about 12% for 80 wt% glycerin solution at a radius ratio of 0.932. The moment coefficient of the coaxial cylinder in Newtonian fluids was analyzed for fluid slip, and it was shown that the analytical results agreed well with the experimental data. For the case of non-Newtonian fluids, the fluid slip velocity of polymer solutions is not proportional to the shear stress and the relationship is approximated by power-law equations.

Drag of a sphere in dilute polymer solutions in high Reynolds number range

We have measured by means of four ultrasonic transducers the fall velocity of a sphere at high Reynolds number range in dilute polyacrylamide solutions which have viscoelastic effects. The polymer solutions were 5, 20 and 50ppm in the concentration. Basset-Bousinessq-Oseen equation for the falling sphere was analyzed numerically on Newtonian fluids in order to compare with the fall velocity of a sphere in the polymer solutions, and the experimental data of the fall velocity in tap water is in agreement with the range of no effect of the test tank wall. In polymer solutions, it was shown that the fall velocity is larger than that in Newtonian fluids within the critical Reynolds number range such that the drag reduction occurs and is smaller than that of Newtonian fluids over the range. The experimental data for the drag reduction ratio of polymer solutions is arranged by Weissenberg number calculating the experimental data of the first normal stress differences. It was shown that the maximum drag reduction ratio in the polymer solutions lies in the range of We=3∼10.

Drag Reduction for a Rotating Disk with Highly Water-Repellent Wall.

Using a highly water-repellent coating wall, new type of drag reduction for a rotating disk in Newtonian fluid have been clarified experimentally. Measurements were carried out to measure the moment of rotating disks with highly water-repellent-wall and with smooth aluminum wall. The clearance between the disk and the housing wall was varied at 5, 10, and 20 mm thick. Tested fluids were tap water and aqueous solution of glycerin at concentration of 30 wt% ahd 40 wt%. The experimental data of the moment of the rotating disk with highly water-repellent wall in housing decreased comparing with the data of smooth plane disk. It was shown that the maximum drag reduction ratio was about 45% in aqueous solution of glycerin at concentration of 40 wt%, and that the viscous properties had a slight effect upon the drag reduction.

Drag Reduction for a Rotating Disk with Highly Water Repellent Wall in Newtonian Fluids.

By use of a highly water-repellent coating wall, a new type of drag reduction for a rotating disk in a Newtonian fluid has been found experimentally. Measurements were carried out to investigate the torque of rotating disks with a highly water-repellent wall and with a smooth aluminum wall. The clearance between the disk and the wall was varied, at 5, 10, and 20mm. The tested fluids were tap water and aqueous solutions of glycerin at concentrations of 30 and 40wt%. The experimental data of the frictional moment of the rotating disk obtained using the highly water-repellent wall were smaller than those of the smooth aluminum rotating disk. It was shown that the maximum drag reduction ratio was about 45% in a 40wt% glycerin solution at about Re=105. and the viscosity of the fluid has a slight effect on the drag reduction.

ASSESSMENT OF ERFB-BB PROJECTILE

The development of extended range rounds has followed a clearly traceable line of evolution starting with the Rocket-Assisted Projectiles (RAP), passing by Extended Range Sub-Calibre (ERSC) projectiles and Extended Range Sub-Bore (ERSB) projectiles and ending with Extended Range Full Bore projectiles with Boat Tail (ERFB-BT) or Base Bleed (ERFB-BB). The most interesting of all the extended range projectiles developed so far is undoubtedly the very long range ERFB-BB ones, which incorporate the best ballistic features of the other extended range projectiles and achieve the maximum possible payload capacity. In this treatise, a historical review of the development of high-explosive, extended range projectilles is first furnished. The principle of base bleed is then discussed and its use in modern projectiles illustrated via a newly designed ERFB-BB projectile. Necessary calculations of range, accuracy and lethality are performed. In doing so, different base drag reduction ratios are considered. Effects of delayed ignition and slight variations in time of burning of the base bleed charge on range are also stu-died, and maximum range is found to be considerably sensitive to these variations. Possibility of local production of the proposed design is investigated. Anticipated technical difficulties are singled out and possible solutions proposed.

A HEAT TRANSFER CORRELATION FOR VISCOELASTIC TURBULENT PIPE FLOWS

Abstract A modified version of Kale's heat transfer correlation for viscoelastic turbulent pipe flows in terms of drag reduction ratio and Weissenberg number is presented. The proposed correlation is validated with experimental data of Kwack and this study for Separan AP-273 and Polyox WSR-301 with concentrations ranging from 10 to 1000 ppm in thermally fully developed flow in pipes with diameters of 1·11 and 1·88 cm I.D. under constant wall heat flux. The agreement between the experimental data and the predictions is within a maximum deviation of 30%.

Pressure loss of fly ash slurries in a spiral tube.

The friction factor of fly ash slurries in a spiral tube with three-shaped groove tube walls has been analytically and experimentally obtained. It is made clear that the experimental data for the laminar flow range almost agree with the obtained analytical results for a pseudo-plastic fluid for which the rheological characterization of the slurries is determined by using the pressure loss data for the circular tube from the differential method. The drag reduction on the hydraulic transport of a solid has been obtained by using the fly ash slurries. Maximum drag reduction occurs at the spiral tube of p/D=6.98. The value of the drag reduction ratio is about 40%.

Heat eddy diffusivity for viscoelastic turbulent pipe flows

A new semi-empirical equation for eddy diffusivity of heat in terms of friction drag reduction ratio and Weissenberg number was earlier reported. The assumptions made in the evaluation of the constants of the proposed equation are verified and its general applicability to various experimental data is further established. For this purpose experiments have been performed for Separan AP-273 and Polyox WSR-301 solutions with concentrations ranging from 10 to 1000 ppm and Separan AP-30 with concentration of 3000 ppm in thermally fully developed turbulent flow in pipes with diameters of 1.11 and 1.88 cm I.D. under constant wall heat flux. From the experiments it is concluded that the minimum asymptotes for friction and heat transfer and the critical Weissenberg number for heat transfer are universal and independent of the type of polymer used. The prediction of heat transfer coefficients with the use of the proposed equation for all of the experimental data is within a maximum deviation of 30%.

A new heat eddy diffusivity equation for calculation of heat transfer to drag reducing turbulent pipe flows

A new semi-empirical equation of heat eddy diffusivity in terms of friction drag reduction ratio and Weissenburg number is presented. The proposed equation was validated with heat transfer experimental results of Kwack [1] and our recent experimental results, both for aqueous solutions of polyacrylamide (Separan AP-273) for concentrations ranging from 10 to 1000 ppm in turbulent flow through pipes under constant wall heat flux condition. The predictions of heat transfer coefficients with the use of the proposed equation are in good agreement with both sets of independent experimental results. The results of this study indicate that the proposed equation for eddy diffusivity of heat has predictive capability provided experimental measurements of pressure drop and the fluid time scale are available. The fluid time scale for these prediction was estimated using the Powell-Eyring fluid model and apparent viscosity measurements.