Large Drag Reduction Research Articles

Blunt-Body Wave Drag Reduction Using Focused Energy Deposition

A parametric computational study of energy deposition upstream of generic two-dimensional and axisymmetric blunt bodies at Mach numbers of 6.5 and 10 is performed utilizing a full Navier-Stokes computational fluid dynamics code. The energy deposition modifies the upstream shock structure and results in large wave drag reduction and very high power effectiveness. Specifically, drag is reduced to values as low as 30% of baseline drag (no energy deposited into flow) and power effectiveness ratios (ratio of thrust power saved to power deposited into the flow) of up to 33 are obtained. The fluid dynamic and thermodynamic bases of the observed drag reduction are examined

Vorticity flux control for a turbulent channel flow

A feedback control algorithm using wall only information has been applied in simulations of low Reynolds number (Reτ=180) turbulent channel flow. The present control scheme is based on the manipulation of the vorticity flux components, which can be obtained as a function of time by measuring the instantaneous pressure at the wall and calculating its gradient. The strength of the unsteady mass transpiration actuators can be derived explicitly by inverting a system of equations whose terms depend on the relative locations of the sensors and actuators. The results of the simulations indicate a large (up to 40%) drag reduction. Moreover it appears that using the present methodology open-loop control laws can be devised.

界面活性剤水溶液の抵抗減少流れにおけるストリーク構造

The characteristics of low-speed streaks in the turbulent channel flow of a drag-reducing surfactant solution are studied by employing the hydrogen-bubble flow visualization method. The mean velocity profiles and the distributions of streamwise turbulence intensity are also obtained. It is shown that, at a large drag reduction rate DR, the profile of the streamwise turbulence intensity has a plateau region around its peak. In the drag-reducing flow, the mean spanwise streak spacing reaches minimum at some distance from the wall. In the drag-reducing flow of high-density(1000 ppm)surfactant solution, the low-speed streaks appear intermittently at the Reynolds number smaller than those for the 'hump' of the f-Re curve(f:friction factor). The mean spanwise streak spacing very near the wall increases as DR becomes large. It is speculated that the nondimensional wall-normal distance y+ of the center of streamwise vortices is larger for the flow of large DR compared with that for the Newtonian fluid flow.

Characteristics of Low-Speed Streaks in the Flow of Drag-Reducing Surfactant Solution.

The characteristics of low-speed streaks in the turbulent channel flow of a drag-reducing surfactant solution are studied by employing the hydrogen-bubble flow visualization method. The mean velocity profiles and the distributions of streamwise turbulence intensity are also obtained. It is shown that, at a large drag reduction rate DR, the profile of the streamwise turbulence intensity has a plateau region around its peak. In the drag-reducing flow, the mean spanwise streak spacing reaches minimum at some distance from the wall. In the drag-reducing flow of high-density(1000 ppm)surfactant solution, the low-speed streaks appear intermittently at the Reynolds number smaller than those for the 'hump' of the f-Re curve(f:friction factor). The mean spanwise streak spacing very near the wall increases as DR becomes large. It is speculated that the nondimensional wall-normal distance y+ of the center of streamwise vortices is larger for the flow of large DR compared with that for the Newtonian fluid flow.

AN INNOVATIVE ENERGY SAVING PROPULSION SYSTEM FOR NAVAL SHIPS

ABSTRACTThe propulsion system on most naval combatants is inherently wasteful of fuel since the propellers, shafts, and engines are sized for dash speed, but operate most of the time at low speed cruiser power. Energy consumption is particularly high on twin shaft, gas turbine driven ships which use controllable reversible pitch (CRP) propellers for reversing.On a typical destroyer such as DD 963, the drag of the propulsion appendages is very high, 10–15% of the total ship drag. This drag is present even when operating at low cruise speed where a system with much lower drag could provide the required thrust.This study evaluates several alternate propulsion systems which could be used on a DD 963 type ship to reduce annual fuel consumption. An innovative system, which uses a single DD 963 type propeller system for cruise and two marine jet boosters for added thrust during high speed dash, shows promise of reducing annual fuel consumption by 23 percent. This fuel saving is due to reduced propulsion appendage drag and lower specific fuel consumption during cruise.Annual fuel saving can be further increased to 45% by replacing the two LM‐2500 turbines which drive the propeller with a single turbine equipped with Rankine Cycle Energy Recovery System (RACER) and changing the CRP propeller to a more efficient fixed pitch (FP) propeller with reverse gear for astern operation.In addition to reduced energy consumption, the propulsion systems using marine jet boosters for dash speed show promise of significant benefits in other areas such as reduced weight and improved survivability and reliability. The marine jets, which use state‐of‐the‐art technology and have demonstrated performance, provide the same top speed as the baseline propeller system. Improved low speed maneuvering and crash stop capability is provided by reversers on the marine jets. Improved propulsion system redundancy is provided by the three shaft system. A single marine jet will provide nineteen knots speed with a non‐operating (trail shaft) cruise propeller.While marine jet propulsors are inherently less efficient than propellers, the large drag reduction for eliminating one propeller system more than compensates for the additional fuel burned by the marine jet turbines during high speed operation. The single propeller, twin marine jet propulsion system is particularly attractive when combined with RACER since it permits elimination of one gas turbine without significant effect on top speed.

A Note on Lift and Drag Effects Due to Polymer Injections from Several Locations on a Symmetric Hydrofoil

Introduction - It is well known that the injection of dilute polymer solutions into the boundary layer on two-dimensional hydrofoils produces changes in both the drag and lift of the foils, with the changes being dependent on the polymer [1], 3 its concentration [2], the injection technique [8], the location of the injection slit [1], and the rate of injection [1, 4, 5]. Previous tests [4] have also shown that the observed drag reduction does not necessarily increase linearly with the rate of injection of the polymer. Indeed, beyond a certain injection rate, further increases lead to little or no drag reduction and, in some cases, actually lead to a drag increase. Thus, one question that is of considerable practical interest is the effect of multiple injections of a given amount of polymer from several chordwise locations as compared with that due to the injection from a single location. The present study investigates the effects on lift and drag of a 20.16-cm (8 in) chord NACA 684–010 two-dimensional hydrofoil due to multiple injections of 200-ppm Polyox WSR 301 solution from several chordwise locations. The results indicate that, for a given flux of polymer injection, multiple injections from properly selected locations as compared with the injection from a single location result in a larger drag reduction without adversely affecting the foil lift.

An observation of the effect of integral scale on drag reduction

AbstractDrag reduction pipe flow experiments using random coiling polymers have been dominated by the small scales of turbulence. An experiment is reported using polyelectrolytes DNA and collagen, which have extended conformations in solution that shows a relationship between the large scales and drag reduction. Turbulent or molecular interactions can explain the observed increase in drag reduction with an increase in pipe diameter.

Aerodynamic Design of High-Perf ormance Biplane Wings

LTHOUGH biplanes were quite popular during the early days of aviation, they had virtually disappeared from service by the mid-1930's. The biplane seemed to be plagued by inherently high drag and low maximum lift coefficient. The purpose of the present study was to re-examine the reasons for the biplane's decline. It was found that for any practical biplane configuration, it is possible to design a wing system which has a much lower weight per unit area and which has essentially the same maximum useable lift coefficient as that of a comparable, well-designed, monoplane wing, in either clean or flapped configurations. Improvements in the design of fairings permit large drag reductions, relative to the earlier designs. Because of these improvements, it is possible to design a biplane whose performance is superior, for some applications, to that of a well-designed monoplane. These applications are those for which excellent low-speed maneuverability, good short-field performance, good loadcarrying ability, low cost, and rugged construction are of primary importance.! Content If a biplane wing system is to develop a high CLmax, both wings must stall nearly together. A method presented by Fuchs was used to identify those configurations for which a good stall match could be obtained. Each wing is idealized in this method as a single horseshoe vortex, with the bound part of each vortex located at the center of pressure. Satisfactory stall match was defined as a ratio of leading wing to trailing wing Coequal to unity at an assumed CLmax for the combination. Some results of this analysis are given in Fig. 1, and some nomenclature is defined in the sketch. The airfoil chord lines are parallel; results of this study showed no advantage to be gained from the use of decalage. The geometric stagger angle a for best stall match is quite insensitive to the gap/chord ratio, and it decreases as the aspect ratio increases. The best stall match always corresponds to small values of 0, the aerodynamic stagger angle. The chordwise variation in vertical velocity induced by one airfoil upon the other corresponds to a local curvature of the flow. Since within the framework of thin airfoil theory, this effect is identical to the effect of a change in the mean camber line, it will be referred to as induced camber. Data for NACA airfoils of the four- and five-digit series show increases in the maximum section lift coefficient Cfmax

The Turbulent Dynamics of an Elastic Fibre Suspension: a Mechanism for Drag Reduction

IT is well known that certain macromolecules in dilute solution give spectacular reductions in turbulent friction. This effect still lacks an adequate physical explanation. It is perhaps less well known that elastic fibres in suspension also give large drag reductions. Indeed, such suspensions behave very like the polymer solutions, with the fibre aspect ratio playing the same role as the polymer molecular weight1. The object of this letter is to report some work which offers an explanation of drag reduction in fibre suspensions and may therefore cast some light on the polymer case.

Flight and Tunnel Test Research on Boundary-Layer Control

Between 1941 and 1945 an experimental investigation was conducted a t the Lockheed Aircraft Corporation to determine whether drag reductions could be obtained a t level flight speeds by removing the boundary layer from the wing by means of suction slots. Prior to that time it was known that substantial lift increases could be achieved by this means under certain circumstances, and, as early as 1935, dataf were available showing large drag reductions at high lift coefficients with flaps deflected. Also, attention had been called to the growing importance of the possibility that the large drag increases caused by flow separation when shock waves occurred could be reduced or eliminated by suction slots. Nevertheless, the data available on the use of boundary-layer control at low lift coefficients did not indicate drag reductions, probably because the internal losses were large in the elementary slot-duct systems employed, Furthermore, it was felt that the early application of boundarylayer control hinged upon the success of this method in reducing the drag for high-speed and long-range flight. Otherwise, the performance gains were considered insufficient to justify the complication and developmental difficulties involved. Because of the recognition of the importance of the internal losses in the slot and ducts, an at tempt was made to develop satisfactory internal systems, after which a wing was tested in the Lockheed wind tunnel with suction applied. Finally, a series of tests was made at full scale and high Reynolds Numbers in flight when an opportunity arose to apply boundary-layer control to an envelope tha t had been employed in a low-drag-airfoil investigation.