Science.gov

Sample records for aerodynamic drag reduction

  1. Aerodynamic Drag and Drag Reduction: Energy and Energy Savings (Invited)

    NASA Technical Reports Server (NTRS)

    Wood, Richard M.

    2003-01-01

    An assessment of the role of fluid dynamic resistance and/or aerodynamic drag and the relationship to energy use in the United States is presented. Existing data indicates that up to 25% of the total energy consumed in the United States is used to overcome aerodynamic drag, 27% of the total energy used in the United States is consumed by transportation systems, and 60% of the transportation energy or 16% of the total energy consumed in the United States is used to overcome aerodynamic drag in transportation systems. Drag reduction goals of 50% are proposed and discussed which if realized would produce a 7.85% total energy savings. This energy savings correlates to a yearly cost savings in the $30Billion dollar range.

  2. Fuel Savings and Aerodynamic Drag Reduction from Rail Car Covers

    NASA Technical Reports Server (NTRS)

    Storms, Bruce; Salari, Kambiz; Babb, Alex

    2008-01-01

    The potential for energy savings by reducing the aerodynamic drag of rail cars is significant. A previous study of aerodynamic drag of coal cars suggests that a 25% reduction in drag of empty cars would correspond to a 5% fuel savings for a round trip [1]. Rail statistics for the United States [2] report that approximately 5.7 billion liters of diesel fuel were consumed for coal transportation in 2002, so a 5% fuel savings would total 284 million liters. This corresponds to 2% of Class I railroad fuel consumption nationwide. As part of a DOE-sponsored study, the aerodynamic drag of scale rail cars was measured in a wind tunnel. The goal of the study was to measure the drag reduction of various rail-car cover designs. The cover designs tested yielded an average drag reduction of 43% relative to empty cars corresponding to an estimated round-trip fuel savings of 9%.

  3. Structural Waveguides for Aerodynamic Turbulent Drag Reduction

    DTIC Science & Technology

    2007-12-30

    NUMBER NIA 5f. WORK UNIT NUMBER n/A 7. PERFORMING ORGANIZATION NAME(S) AND ADDRESS(ES) 8. PERFORMING ORGANIZATION REPORT NUMBER One (1) Mechanical ...accomplished by developing structural waveguides within a cylinder that underactuation impart a structural surface wave disturbance in the form of a travelling...DRAG REDUCTION BY BY PAVLOS VLACHOS, MARTY JOHNSON, JAMES P CARNEAL, AND ALESSANDRO TOSSO VIRGINIA TECH MECHANICAL ENGINEERING DEPARTMENT BLACKSBURG

  4. Aerodynamics of Drag Reduction Devices for Semi-Trucks

    NASA Astrophysics Data System (ADS)

    Ortega, Jason; Salari, Kambiz

    2014-11-01

    An increasing number of semi-trucks throughout the United States are being retrofitted with aerodynamic drag reduction devices to improve the vehicle fuel economy. Such devices typically include both trailer skirts and boattails to mitigate trailer underbody drag and base drag, respectively. Since full-scale measurements of the device performance are especially prone to experimental noise due to the effects of the driver, route, payload, or atmospheric conditions, more precise data must be obtained within a wind tunnel. In this experimental study, the wind-averaged drag coefficient is measured for a detailed 1/8th scale semi-truck model. The Reynolds number based upon the vehicle width is 1.7e6. A number of trailer skirt and boattail device configurations are considered, as well as the effects of the boattail deflection angle. The results of this study demonstrate that a combination of a trailer skirt and boattail reduces the aerodynamic drag of a semi-truck by as much as 25%. If such a combination were applied to each of the semi-trucks throughout the United States, several billion dollars in fuel savings could be achieved each year. This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344. LLNL-ABS-657810.

  5. Thermal lift generation and drag reduction in rarefied aerodynamics

    NASA Astrophysics Data System (ADS)

    Pekardan, Cem; Alexeenko, Alina

    2016-11-01

    With the advent of the new technologies in low pressure environments such as Hyperloop and helicopters designed for Martian applications, understanding the aerodynamic behavior of airfoils in rarefied environments are becoming more crucial. In this paper, verification of rarefied ES-BGK solver and ideas such as prediction of the thermally induced lift and drag reduction in rarefied aerodynamics are investigated. Validation of the rarefied ES-BGK solver with Runge-Kutta discontinous Galerkin method with experiments in transonic regime with a Reynolds number of 73 showed that ES-BGK solver is the most suitable solver in near slip transonic regime. For the quantification of lift generation, A NACA 0012 airfoil is studied with a high temperature surface on the bottom for the lift creation for different Knudsen numbers. It was seen that for lower velocities, continuum solver under predicts the lift generation when the Knudsen number is 0.00129 due to local velocity gradients reaching slip regime although lift coefficient is higher with the Boltzmann ES-BGK solutions. In the second part, the feasibility of using thermal transpiration for drag reduction is studied. Initial study in drag reduction includes an application of a thermal gradient at the upper surface of a NACA 0012 airfoil near trailing edge at a 12-degree angle of attack and 5 Pa pressure. It was seen that drag is reduced by 4 percent and vortex shedding frequency is reduced due to asymmetry introduced in the flow due to temperature gradient causing reverse flow due to thermal transpiration phenomena.

  6. Aerodynamic Drag Reduction Apparatus For Wheeled Vehicles In Ground Effect

    DOEpatents

    Ortega, Jason M.; Salari, Kambiz

    2005-12-13

    An apparatus for reducing the aerodynamic drag of a wheeled vehicle in a flowstream, the vehicle having a vehicle body and a wheel assembly supporting the vehicle body. The apparatus includes a baffle assembly adapted to be positioned upstream of the wheel assembly for deflecting airflow away from the wheel assembly so as to reduce the incident pressure on the wheel assembly.

  7. Aerodynamic drag reduction tests on a box-shaped vehicle

    NASA Technical Reports Server (NTRS)

    Peterson, R. L.; Sandlin, D. R.

    1981-01-01

    The intent of the present experiment is to define a near optimum value of drag coefficient for a high volume type of vehicle through the use of a boattail, on a vehicle already having rounded front corners and an underbody seal, or fairing. The results of these tests will constitute a baseline for later follow-on studies to evaluate candidate methods of obtaining afterbody drag coefficients approaching the boattail values, but without resorting to such impractical afterbody extensions. The current modifications to the box-shaped vehicle consisted of a full and truncated boattail in conjunction with the faired and sealed underbody. Drag results from these configurations are compared with corresponding wind tunnel results of a 1/10 scale model. Test velocities ranged up to 96.6 km/h (60 mph) and the corresponding Reynolds numbers ranged up to 1.3 x 10 to the 7th power based on the vehicles length which includes the boattail. A simple coast-down technique was used to define drag.

  8. Aerodynamic performance of a drag reduction device on a full-scale tractor/trailer

    NASA Astrophysics Data System (ADS)

    Lanser, Wendy R.; Ross, James C.; Kaufman, Andrew E.

    1991-09-01

    The effectiveness of an aerodynamic boattail on a tractor/trailer road vehicle was measured in the NASA Ames Research Center 80- by 120-Foot Wind Tunnel. Results are examined for the tractor/trailer with and without the drag reduction device. Pressure measurements and flow visualization show that the aerodynamic boattail traps a vortex or eddy in the corner formed between the device and the rear corner of the trailer. This recirculating flow turns the flow inward as it separates from the edges of the base of the trailer. This modified flow behavior increases the pressure acting over the base area of the truck, thereby reducing the net aerodynamic drag of the vehicle. Drag measurements and pressure distributions in the region of the boattail device are presented for selected configurations. The optimum configuration reduces the overall drag of the tractor/trailer combination by about 10 percent at a zero yaw angle. Unsteady pressure measurements do not indicate strong vortex shedding, although the addition of the boattail plates increases high frequency content of the fluctuating pressure.

  9. Aerodynamic performance of a drag reduction device on a full-scale tractor/trailer

    NASA Technical Reports Server (NTRS)

    Lanser, Wendy R.; Ross, James C.; Kaufman, Andrew E.

    1991-01-01

    The effectiveness of an aerodynamic boattail on a tractor/trailer road vehicle was measured in the NASA Ames Research Center 80- by 120-Foot Wind Tunnel. Results are examined for the tractor/trailer with and without the drag reduction device. Pressure measurements and flow visualization show that the aerodynamic boattail traps a vortex or eddy in the corner formed between the device and the rear corner of the trailer. This recirculating flow turns the flow inward as it separates from the edges of the base of the trailer. This modified flow behavior increases the pressure acting over the base area of the truck, thereby reducing the net aerodynamic drag of the vehicle. Drag measurements and pressure distributions in the region of the boattail device are presented for selected configurations. The optimum configuration reduces the overall drag of the tractor/trailer combination by about 10 percent at a zero yaw angle. Unsteady pressure measurements do not indicate strong vortex shedding, although the addition of the boattail plates increases high frequency content of the fluctuating pressure.

  10. Investigation of Tractor Base Bleeding for Heavy Vehicle Aerodynamic Drag Reduction

    SciTech Connect

    Ortega, J; Salari, K; Storms, B

    2007-10-25

    One of the main contributors to the aerodynamic drag of a heavy vehicle is tractor-trailer gap drag, which arises when the vehicle operates within a crosswind. Under this operating condition, freestream flow is entrained into the tractor-trailer gap, imparting a momentum exchange to the vehicle and subsequently increasing the aerodynamic drag. While a number of add-on devices, including side extenders, splitter plates, vortex stabilizers, and gap sealers, have been previously tested to alleviate this source of drag, side extenders remain the primary add-on device of choice for reducing tractor-trailer gap drag. However, side extenders are not without maintenance and operational issues. When a heavy vehicle pivots sharply with respect to the trailer, as can occur during loading or unloading operations, the side extenders can become crushed against the trailer. Consequently, fleet operators are forced to incur additional costs to cover the repair or replacement of the damaged side extenders. This issue can be overcome by either shortening the side extenders or by devising an alternative drag reduction concept that can perform just as effectively as side extenders. To explore such a concept, we investigate tractor base bleeding as a means of reducing gap drag. Wind tunnel measurements are made on a 1:20 scale heavy vehicle model at a vehicle width-based Reynolds number of 420,000. The tractor bleeding flow, which is delivered through a porous material embedded within the tractor base, is introduced into the tractor-trailer gap at bleeding coefficients ranging from 0.0-0.018. To determine the performance of tractor base bleeding under more realistic operating conditions, computational fluid dynamics simulations are performed on a full-scale heavy vehicle within a crosswind for bleeding coefficients ranging from 0.0-0.13.

  11. Aerodynamic drag reduction tests on a full-scale tractor-trailer combination with several add-on devices

    NASA Technical Reports Server (NTRS)

    Montoya, L. C.; Steers, L. L.

    1974-01-01

    Aerodynamic drag tests were performed on a conventional cab-over-engine tractor with a 45-foot trailer and five commercially available or potentially available add-on devices using the coast-down method. The tests ranged in velocity from approximately 30 miles per hour to 65 miles per hour and included some flow visualization. A smooth, level runway at Edwards Air Force Base was used for the tests, and deceleration measurements were taken with both accelerometers and stopwatches. An evaluation of the drag reduction results obtained with each of the five add-on devices is presented.

  12. Prediction of Aerodynamic Drag.

    DTIC Science & Technology

    1984-07-01

    prediction method for reasonable estimates of the drag of afterbodies for military airlifters has recently been published by Kolesar and May72 to...method predicts the drag due to lift reasonably well for quite general, assumed limit shock positions, as shown in Fig. 25. The drag at zero lift is not...investigators, a reasonable estimate for the drag polar could be obtained by numerically averaging the zero and full leading- edge suction drag polars. Drag

  13. Aerodynamic drag on intermodal railcars

    NASA Astrophysics Data System (ADS)

    Kinghorn, Philip; Maynes, Daniel

    2014-11-01

    The aerodynamic drag associated with transport of commodities by rail is becoming increasingly important as the cost of diesel fuel increases. This study aims to increase the efficiency of intermodal cargo trains by reducing the aerodynamic drag on the load carrying cars. For intermodal railcars a significant amount of aerodynamic drag is a result of the large distance between loads that often occurs and the resulting pressure drag resulting from the separated flow. In the present study aerodynamic drag data have been obtained through wind tunnel testing on 1/29 scale models to understand the savings that may be realized by judicious modification to the size of the intermodal containers. The experiments were performed in the BYU low speed wind tunnel and the test track utilizes two leading locomotives followed by a set of five articulated well cars with double stacked containers. The drag on a representative mid-train car is measured using an isolated load cell balance and the wind tunnel speed is varied from 20 to 100 mph. We characterize the effect that the gap distance between the containers and the container size has on the aerodynamic drag of this representative rail car and investigate methods to reduce the gap distance.

  14. Aerodynamic drag reduction of a simplified squareback vehicle using steady blowing

    NASA Astrophysics Data System (ADS)

    Littlewood, R. P.; Passmore, M. A.

    2012-08-01

    A large contribution to the aerodynamic drag of a vehicle arises from the failure to fully recover pressure in the wake region, especially on squareback configurations. A degree of base pressure recovery can be achieved through careful shape optimisation, but the freedom of an automotive aerodynamicist to implement significant shape changes is limited by a variety of additional factors such styling, ergonomics and loading capacity. Active flow control technologies present the potential to create flow field modifications without the need for external shape changes and have received much attention in previous years within the aeronautical industry and, more recently, within the automotive industry. In this work the influence of steady blowing applied at a variety of angles on the roof trailing edge of a simplified ¼ scale squareback style vehicle has been investigated. Hot-wire anemometry, force balance measurements, surface pressure measurements and PIV have been used to investigate the effects of the steady blowing on the vehicle wake structures and the resulting body forces. The energy consumption of the steady jet is calculated and is used to deduce an aerodynamic drag power change. Results show that overall gains can be achieved; however, the large mass flow rate required restricts the applicability of the technique to road vehicles. Means by which the mass flow rate requirements of the jet may be reduced are discussed and suggestions for further work put forward.

  15. Aerodynamic drag reduction apparatus for gap-divided bluff bodies such as tractor-trailers

    SciTech Connect

    Ortega, Jason M.; Salari, Kambiz

    2006-07-11

    An apparatus for reducing the aerodynamic drag of a bluff-bodied vehicle such as a tractor-trailer in a flowstream, the bluff-bodied vehicle of a type having a leading portion, a trailing portion connected to the leading portion, and a gap between the leading and trailing portions defining a recirculation zone. The apparatus is preferably a baffle assembly, such as a vertical panel, adapted to span a width of the gap between the leading and trailing portions so as to impede cross-flow through the gap, with the span of the baffle assembly automatically adjusting for variations in the gap width when the leading and trailing portions pivot relative to each other.

  16. DOE Project on Heavy Vehicle Aerodynamic Drag

    SciTech Connect

    McCallen, R; Salari, K; Ortega, J; Castellucci, P; Pointer, D; Browand, F; Ross, J; Storms, B

    2007-01-04

    Class 8 tractor-trailers consume 11-12% of the total US petroleum use. At highway speeds, 65% of the energy expenditure for a Class 8 truck is in overcoming aerodynamic drag. The project objective is to improve fuel economy of Class 8 tractor-trailers by providing guidance on methods of reducing drag by at least 25%. A 25% reduction in drag would present a 12% improvement in fuel economy at highway speeds, equivalent to about 130 midsize tanker ships per year. Specific goals include: (1) Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles; (2) Develop innovative drag reducing concepts that are operationally and economically sound; and (3) Establish a database of experimental, computational, and conceptual design information, and demonstrate the potential of new drag-reduction devices. The studies described herein provide a demonstration of the applicability of the experience developed in the analysis of the standard configuration of the Generic Conventional Model. The modeling practices and procedures developed in prior efforts have been applied directly to the assessment of new configurations including a variety of geometric modifications and add-on devices. Application to the low-drag 'GTS' configuration of the GCM has confirmed that the error in predicted drag coefficients increases as the relative contribution of the base drag resulting from the vehicle wake to the total drag increases and it is recommended that more advanced turbulence modeling strategies be applied under those circumstances. Application to a commercially-developed boat tail device has confirmed that this restriction does not apply to geometries where the relative contribution of the base drag to the total drag is reduced by modifying the geometry in that region. Application to a modified GCM geometry with an open grille and radiator has confirmed that the underbody flow, while important for underhood cooling, has little impact on the drag coefficient of

  17. Methods of reducing vehicle aerodynamic drag

    SciTech Connect

    Sirenko V.; Rohatgi U.

    2012-07-08

    A small scale model (length 1710 mm) of General Motor SUV was built and tested in the wind tunnel for expected wind conditions and road clearance. Two passive devices, rear screen which is plate behind the car and rear fairing where the end of the car is aerodynamically extended, were incorporated in the model and tested in the wind tunnel for different wind conditions. The conclusion is that rear screen could reduce drag up to 6.5% and rear fairing can reduce the drag by 26%. There were additional tests for front edging and rear vortex generators. The results for drag reduction were mixed. It should be noted that there are aesthetic and practical considerations that may allow only partial implementation of these or any drag reduction options.

  18. Reduction of aerodynamic drag and fuel consumption for tractor-trailer vehicles

    NASA Technical Reports Server (NTRS)

    Muirhead, V. U.; Saltzman, E. J.

    1979-01-01

    Wind-tunnel tests were performed on a scale model of a cab-over-engine tractor-trailer vehicle and several modifications of the model. Results from two of the model configurations were compared with full-scale drag data obtained from similar configurations during coast-down tests. Reductions in fuel consumption derived from these tests are presented in terms of fuel quantity and dollar savings per vehicle year, based on an annual driving distance of 160,900 km (100,000 mi.). The projected savings varied from 13,001 (3435) to 25,848 (6829) liters (gallons) per year which translated to economic savings from $3435 to about $6829 per vehicle year for an operating speed of 88.5 km/h (55 mph) and wind speeds near the national average of 15.3 km/h (9.5 mph). The estimated cumulative fuel savings for the entire U.S. fleet of cab-over-engine tractor, van-type trailer combinations ranged from 4.18 million kl (26.3 million bbl) per year for a low-drag configuration to approximately twice that amount for a more advanced configuration.

  19. Drag reduction in nature

    NASA Technical Reports Server (NTRS)

    Bushnell, D. M.; Moore, K. J.

    1991-01-01

    Recent studies on the drag-reducing shapes, structures, and behaviors of swimming and flying animals are reviewed, with an emphasis on potential analogs in vehicle design. Consideration is given to form drag reduction (turbulent flow, vortex generation, mass transfer, and adaptations for body-intersection regions), skin-friction drag reduction (polymers, surfactants, and bubbles as surface 'additives'), reduction of the drag due to lift, drag-reduction studies on porpoises, and drag-reducing animal behavior (e.g., leaping out of the water by porpoises). The need for further research is stressed.

  20. Aerodynamic Drag Reduction Technologies Testing of Heavy-Duty Vocational Vehicles and a Dry Van Trailer

    SciTech Connect

    Ragatz, Adam; Thornton, Matthew

    2016-10-01

    This study focused on two accepted methods for quantifying the benefit of aerodynamic improvement technologies on vocational vehicles: the coastdown technique, and on-road constant speed fuel economy measurements. Both techniques have their advantages. Coastdown tests are conducted over a wide range in speed and allow the rolling resistance and aerodynamic components of road load force to be separated. This in turn allows for the change in road load and fuel economy to be estimated at any speed, as well as over transient cycles. The on-road fuel economy measurements only supply one lumped result, applicable at the specific test speed, but are a direct measurement of fuel usage and are therefore used in this study as a check on the observed coastdown results. Resulting coefficients were then used to populate a vehicle model and simulate expected annual fuel savings over real-world vocational drive cycles.

  1. Aerodynamics overview of the ground transportation systems (GTS) project for heavy vehicle drag reduction

    SciTech Connect

    Gutierrez, W.T.; Hassan, B.; Croll, R.H.; Rutledge, W.H.

    1995-12-31

    The focus of the research was to investigate the fundamental aerodynamics of the base flow of a tractor trailer that would prove useful in fluid flow management. Initially, industry design needs and constraints were defined. This was followed by an evaluation of state-of-the-art Navier-Stokes based computational fluid dynamics tools. Analytical methods were then used in combination with computational tools in a design process. Several geometries were tested at 1:8 scale in a low speed wind tunnel. In addition to the baseline geometry, base add-on devices of the class of ogival boattails and slants were analyzed.

  2. FY2003 Annual Report: DOE Project on Heavy Vehicle Aerodynamic Drag

    SciTech Connect

    McCallen, R C; Salari, K; Ortega, J; DeChant, L J; Roy, C J; Payne, J J; Hassan, B; Pointer, W D; Browand, F; Hammache, M; Hsu, T; Ross, J; Satran, D; Heineck, J; Walker, S; Yaste, D; Englar, R; Leonard, A; Rubel, M; Chatelain, P

    2003-10-24

    Objective: {sm_bullet} Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles. {sm_bullet} Establish a database of experimental, computational, and conceptual design information, and demonstrate potential of new drag-reduction devices.

  3. Switchable and Tunable Aerodynamic Drag on Cylinders

    NASA Astrophysics Data System (ADS)

    Guttag, Mark; Lopéz Jiménez, Francisco; Upadhyaya, Priyank; Kumar, Shanmugam; Reis, Pedro

    We report results on the performance of Smart Morphable Surfaces (Smporhs) that can be mounted onto cylindrical structures to actively reduce their aerodynamic drag. Our system comprises of an elastomeric thin shell with a series of carefully designed subsurface cavities that, once depressurized, lead to a dramatic deformation of the surface topography, on demand. Our design is inspired by the morphology of the giant cactus (Carnegiea gigantea) which possesses an array of axial grooves, thought to help reduce aerodynamic drag, thereby enhancing the structural robustness of the plant under wind loading. We perform systematic wind tunnel tests on cylinders covered with our Smorphs and characterize their aerodynamic performance. The switchable and tunable nature of our system offers substantial advantages for aerodynamic performance when compared to static topographies, due to their operation over a wider range of flow conditions.

  4. Switchable and Tunable Aerodynamic Drag on Cylinders

    NASA Astrophysics Data System (ADS)

    Guttag, Mark; Lopez Jimenez, Francisco; Reis, Pedro

    2015-11-01

    We report results on the performance of Smart Morphable Surfaces (Smporhs) that can be mounted onto cylindrical structures to actively reduce their aerodynamic drag. Our system comprises of an elastomeric thin shell with a series of carefully designed subsurface cavities that, once depressurized, lead to a dramatic deformation of the surface topography, on demand. Our design is inspired by the morphology of the giant cactus (Carnegiea gigantea) which possesses an array of axial grooves, which are thought to help reduce aerodynamic drag, thereby enhancing the structural robustness of the plant under wind loading. We perform systematic wind tunnel tests on cylinders covered with our Smorphs and characterize their aerodynamic performance. The switchable and tunable nature of our system offers substantial advantages for aerodynamic performance when compared to static topographies, due to their operation over a wider range of flow conditions.

  5. A comprehensive plan for helicopter drag reduction

    NASA Technical Reports Server (NTRS)

    Williams, R. M.; Montana, P. S.

    1975-01-01

    Current helicopters have parasite drag levels 6 to 10 times as great as fixed wing aircraft. The commensurate poor cruise efficiency results in a substantial degradation of potential mission capability. The paper traces the origins of helicopter drag and shows that the problem (primarily due to bluff body flow separation) can be solved by the adoption of a comprehensive research and development plan. This plan, known as the Fuselage Design Methodology, comprises both nonaerodynamic and aerodynamic aspects. The aerodynamics are discussed in detail and experimental and analytical programs are described which will lead to a solution of the bluff body problem. Some recent results of work conducted at the Naval Ship Research and Development Center (NSRDC) are presented to illustrate these programs. It is concluded that a 75-per cent reduction of helicopter drag is possible by the full implementation of the Fuselage Design Methodology.

  6. Aircraft Drag Prediction and Reduction

    DTIC Science & Technology

    1985-07-01

    a) - The first example deals with the conformal weapons carriage experimentaly mounted on a F-4 " Phantom " Airplane (US Navy/Air Force/’ASA/Boeing...aerodynamic surfaces. I) ( dCm /dCL) This has, however, the disadvantage that DRAG FORWARD FIXATION one must deal with a relatively thick, though turbulent

  7. Drag reduction obtained by modifying a standard truck

    NASA Technical Reports Server (NTRS)

    Sheridan, A. E.; Grier, S. J.

    1978-01-01

    A standard two-axle truck with a box-shaped cargo compartment was tested to determine whether significant reductions in aerodynamic drag could be obtained by modifying the front of the cargo compartment. The coastdown method was used to determine the total drag of the baseline vehicle, which had a square-cornered cargo box, and of several modified configurations. Test velocities ranged from 56.3 to 94.6 kilometers per hour (35 to 60 miles per hour). At 88.5 kilometers per hour (55 miles per hour), the aerodynamic drag reductions obtained with the modified configurations ranged from 8 to 30 percent.

  8. DOE Project on Heavy Vehicle Aerodynamic Drag FY 2005 Annual Report

    SciTech Connect

    McCallen, R C; Salari, K; Ortega, J; Castellucci, P; Eastwood, C; Paschkewitz, J; Pointer, W D; DeChant, L J; Hassan, B; Browand, F; Radovich, C; Merzel, T; Plocher, D; Ross, J; Storms, B; Heineck, J T; Walker, S; Roy, C J

    2005-11-14

    Class 8 tractor-trailers consume 11-12% of the total US petroleum use. At high way speeds, 65% of the energy expenditure for a Class 8 truck is in overcoming aerodynamic drag. The project objective is to improve fuel economy of Class 8 tractor-trailers by providing guidance on methods of reducing drag by at least 25%. A 25% reduction in drag would present a 12% improvement in fuel economy at highway speeds, equivalent to about 130 midsize tanker ships per year. Specific goals include: (1) Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles; and (2) Establish a database of experimental, computational, and conceptual design information, and demonstrate the potential of new drag-reduction devices.

  9. Exploring the Aerodynamic Drag of a Moving Cyclist

    ERIC Educational Resources Information Center

    Theilmann, Florian; Reinhard, Christopher

    2016-01-01

    Although the physics of cycling itself is a complex mixture of aerodynamics, physiology, mechanics, and heuristics, using cycling as a context for teaching physics has a tradition of certainly more than 30 years. Here, a possible feature is the discussion of the noticeable resistant forces such as aerodynamic drag and the associated power…

  10. Iterative optimal subcritical aerodynamic design code including profile drag

    NASA Technical Reports Server (NTRS)

    Kuhlman, J. M.

    1983-01-01

    A subcritical aerodynamic design computer code has been developed, which uses linearized aerodynamics along with sweep theory and airfoil data to obtain minimum total drag preliminary designs for multiple planform configurations. These optimum designs consist of incidence distributions yielding minimum total drag at design values of Mach number and lift and pitching moment coefficients. Linear lofting is used between airfoil stations. Solutions for isolated transport wings have shown that the solution is unique, and that including profile drag effects decreases tip loading and incidence relative to values obtained for minimum induced drag solutions. Further, including effects of variation of profile drag with Reynolds number can cause appreciable changes in the optimal design for tapered wings. Example solutions are also discussed for multiple planform configurations.

  11. Aerodynamic drag crisis and its possible effect on the flight of baseballs

    NASA Astrophysics Data System (ADS)

    Frohlich, Cliff

    1984-04-01

    At Reynolds numbers above about 105 the aerodynamic drag force on a sphere drops sharply as the flow begins to become turbulent in the boundary layer. For baseballs, this ``drag crisis'' may occur at speeds which are typical for pitched or batted balls. The effects of the drag reduction on the behavior of both pitched and batted balls is significant, and may explain several features of the game of baseball which previously have been unexplained or attributed to other causes. In particular, the drag reduction may help to explain why pitched fastballs appear to rise, why pitched curve balls appear to drop sharply, and why home run production has increased since the introduction of the alleged ``lively ball.'' Calculations suggest that aerodynamic forces are as important a factor in fastpitch softball as in baseball, and that they are a critical factor in a number of other ball games.

  12. The maximum drag reduction asymptote

    NASA Astrophysics Data System (ADS)

    Choueiri, George H.; Hof, Bjorn

    2015-11-01

    Addition of long chain polymers is one of the most efficient ways to reduce the drag of turbulent flows. Already very low concentration of polymers can lead to a substantial drag and upon further increase of the concentration the drag reduces until it reaches an empirically found limit, the so called maximum drag reduction (MDR) asymptote, which is independent of the type of polymer used. We here carry out a detailed experimental study of the approach to this asymptote for pipe flow. Particular attention is paid to the recently observed state of elasto-inertial turbulence (EIT) which has been reported to occur in polymer solutions at sufficiently high shear. Our results show that upon the approach to MDR Newtonian turbulence becomes marginalized (hibernation) and eventually completely disappears and is replaced by EIT. In particular, spectra of high Reynolds number MDR flows are compared to flows at high shear rates in small diameter tubes where EIT is found at Re < 100. The research leading to these results has received funding from the People Programme (Marie Curie Actions) of the European Union's Seventh Framework Programme (FP7/2007-2013) under REA grant agreement n° [291734].

  13. Does an active adjustment of aerodynamic drag make sense?

    NASA Astrophysics Data System (ADS)

    Maciejewski, Marek

    2016-09-01

    The article concerns evaluation of the possible impact of the gap between the tractor and semitrailer on the aerodynamic drag coefficient. The aim here is not to adjust this distance depending on the geometrical shape of the tractor and trailer, but depending solely on the speed of articulated vehicle. All the tests have form of numerical simulations. The method of simulation is briefly explained in the article. It considers various issues such as the range and objects of tests as well as the test conditions. The initial (pre-adaptive) and final (after adaptation process) computational meshes have been presented as illustrations. Some of the results have been presented in the form of run chart showing the change of value of aerodynamic drag coefficients in time, for different geometric configurations defined by a clearance gap between the tractor and semitrailer. The basis for a detailed analysis and conclusions were the averaged (in time) aerodynamic drag coefficients as a function of the clearance gap.

  14. DOE's effort to reduce truck aerodynamic drag through joint experiments and computations.

    SciTech Connect

    Salari, Kambiz; Browand, Fred; Sreenivas, Kidambi; Pointer, W. David; Taylor, Lafayette; Pankajakshan, Ramesh; Whitfield, David; Plocher, Dennis; Ortega, Jason M.; Merzel, Tai; McCallen, Rose; Walker, Stephen M; Heineck, James T; Hassan, Basil; Roy, Christopher John; Storms, B.; Ross, James; Englar, Robert; Rubel, Mike; Leonard, Anthony; Radovich, Charles; Eastwood, Craig; Paschkewitz, John; Castellucci, Paul; DeChant, Lawrence Justin.

    2005-08-01

    Class 8 tractor-trailers are responsible for 11-12% of the total US consumption of petroleum. Overcoming aero drag represents 65% of energy expenditure at highway speeds. Most of the drag results from pressure differences and reducing highway speeds is very effective. The goal is to reduce aerodynamic drag by 25% which would translate to 12% improved fuel economy or 4,200 million gal/year. Objectives are: (1) In support of DOE's mission, provide guidance to industry in the reduction of aerodynamic drag; (2) To shorten and improve design process, establish a database of experimental, computational, and conceptual design information; (3) Demonstrate new drag-reduction techniques; and (4) Get devices on the road. Some accomplishments are: (1) Concepts developed/tested that exceeded 25% drag reduction goal; (2) Insight and guidelines for drag reduction provided to industry through computations and experiments; (3) Joined with industry in getting devices on the road and providing design concepts through virtual modeling and testing; and (4) International recognition achieved through open documentation and database.

  15. FY 2004 Annual Report: DOE Project on Heavy Vehicle Aerodynamic Drag

    SciTech Connect

    McCallen, R C; Salari, K; Ortega, J; Castellucci, P; Eastwood, C; Whittaker, K; DeChant, L J; Roy, C J; Payne, J L; Hassan, B; Pointer, W D; Browand, F; Hammache, M; Hsu, T; Ross, J; Satran, D; Heineck, J T; Walker, S; Yaste, D; Englar, R; Leonard, A; Rubel, M; Chatelain, P

    2004-11-18

    The objective of this report is: (1) Provide guidance to industry in the reduction of aerodynamic drag of heavy truck vehicles; and (2) Establish a database of experimental, computational, and conceptual design information, and demonstrate potential of new drag-reduction devices. The approaches used were: (1) Develop and demonstrate the ability to simulate and analyze aerodynamic flow around heavy truck vehicles using existing and advanced computational fluid dynamics (CFD) tools; (2) Through an extensive experimental effort, generate an experimental data base for code validation; (3) Using experimental data base, validate computations; (4) Provide industry with design guidance and insight into flow phenomena from experiments and computations; and (5) Investigate aero devices (e.g., base flaps, tractor-trailer gap stabilizer, underbody skirts and wedges, blowing and acoustic devices), provide industry with conceptual designs of drag reducing devices, and demonstrate the full-scale fuel economy potential of these devices.

  16. Spacecraft Re-Entry Impact Point Targeting Using Aerodynamic Drag

    NASA Technical Reports Server (NTRS)

    Omar, Sanny R.; Bevilacqua, Riccardo

    2017-01-01

    The ability to re-enter the atmosphere at a desired location is important for spacecraft containing components that may survive re-entry. While impact point targeting has traditionally been initiated through impulsive burns with chemical thrusters on large vehicles such as the Space Shuttle, and the Soyuz and Apollo capsules, many small spacecraft do not host thrusters and require an alternative means of impact point targeting to ensure that falling debris do not cause harm to persons or property. This paper discusses the use of solely aerodynamic drag force to perform this targeting. It is shown that by deploying and retracting a drag device to vary the ballistic coefficient of the spacecraft, any desired longitude and latitude on the ground can be targeted provided that the maneuvering begins early enough and the latitude is less than the inclination of the orbit. An analytical solution based on perturbations from a numerically propagated trajectory is developed to map the initial state and ballistic coefficient profile of a spacecraft to its impact point. This allows the ballistic coefficient profile necessary to reach a given target point to be rapidly calculated, making it feasible to generate the guidance for the decay trajectory onboard the spacecraft. The ability to target an impact point using aerodynamic drag will enhance the capabilities of small spacecraft and will enable larger space vehicles containing thrusters to save fuel by more effectively leveraging the available aerodynamic drag.

  17. Hub and pylon fairing integration for helicopter drag reduction

    NASA Technical Reports Server (NTRS)

    Martin, D. M.; Mort, R. W.; Squires, P. K.; Young, L. A.

    1991-01-01

    The results of testing hub and pylon fairings mounted on a one-fifth scale helicopter with the goal of reducing parasite drag are presented. Lift, drag, and pitching moment, as well as side force and yawing moment, were measured. The primary objective of the test was to validate the drag reduction capability of integrated hub and pylon configurations in the aerodynamic environment produced by a rotating hub in forward flight. In addition to the baseline helicopter without fairings, three hub fairings and three pylon fairings were tested in various combinations. The three hub fairings tested reflect two different conceptual design approaches to implementing an integrated fairing configuration on an actual aircraft. The design philosophy is discussed in detail and comparisons are made between the wind tunnel models and potential full-scale prototypes. The data show that model drag can be reduced by as much as 20.8 percent by combining a small hub fairing with circular arc upper and flat lower surfaces and a nontapered 34-percent thick pylon fairing. Aerodynamic effects caused by the fairings, which may have a significant impact on static longitudinal and directional stability, were observed. The results support previous research which showed that the greatest reduction in model drag is achieved if the hub and pylon fairings are integrated with minimum gap between the two.

  18. Analog VLSI system for active drag reduction

    SciTech Connect

    Gupta, B.; Goodman, R.; Jiang, F.; Tai, Y.C.; Tung, S.; Ho, C.M.

    1996-10-01

    In today`s cost-conscious air transportation industry, fuel costs are a substantial economic concern. Drag reduction is an important way to reduce costs. Even a 5% reduction in drag translates into estimated savings of millions of dollars in fuel costs. Drawing inspiration from the structure of shark skin, the authors are building a system to reduce drag along a surface. Our analog VLSI system interfaces with microfabricated, constant-temperature shear stress sensors. It detects regions of high shear stress and outputs a control signal to activate a microactuator. We are in the process of verifying the actual drag reduction by controlling microactuators in wind tunnel experiments. We are encouraged that an approach similar to one that biology employs provides a very useful contribution to the problem of drag reduction. 9 refs., 21 figs.

  19. Experimental Investigation of Convoluted Contouring for Aircraft Afterbody Drag Reduction

    NASA Technical Reports Server (NTRS)

    Deere, Karen A.; Hunter, Craig A.

    1999-01-01

    An experimental investigation was performed in the NASA Langley 16-Foot Transonic Tunnel to determine the aerodynamic effects of external convolutions, placed on the boattail of a nonaxisymmetric nozzle for drag reduction. Boattail angles of 15 and 22 were tested with convolutions placed at a forward location upstream of the boattail curvature, at a mid location along the curvature and at a full location that spanned the entire boattail flap. Each of the baseline nozzle afterbodies (no convolutions) had a parabolic, converging contour with a parabolically decreasing corner radius. Data were obtained at several Mach numbers from static conditions to 1.2 for a range of nozzle pressure ratios and angles of attack. An oil paint flow visualization technique was used to qualitatively assess the effect of the convolutions. Results indicate that afterbody drag reduction by convoluted contouring is convolution location, Mach number, boattail angle, and NPR dependent. The forward convolution location was the most effective contouring geometry for drag reduction on the 22 afterbody, but was only effective for M < 0.95. At M = 0.8, drag was reduced 20 and 36 percent at NPRs of 5.4 and 7, respectively, but drag was increased 10 percent for M = 0.95 at NPR = 7. Convoluted contouring along the 15 boattail angle afterbody was not effective at reducing drag because the flow was minimally separated from the baseline afterbody, unlike the massive separation along the 22 boattail angle baseline afterbody.

  20. An investigation of drag reduction for tractor trailer vehicles

    NASA Technical Reports Server (NTRS)

    Muirhead, V. U.

    1978-01-01

    Force and moment data were obtained from a one-twenty-fifth scale wind tunnel model of a cab-over-engine tractor trailer combination. The tests define the aerodynamic characteristics of the baseline (unmodified) vehicle and several modified configurations. The primary modifications consist of: (1) greatly increased forebody corner radii, (2) a smooth fairing over the cab-to-trailer gap, (3) a smoothed underbody, and (4) rear streamlining (boattailing)of the trailer. Tests were conducted for yaw angles from 0 deg to 30 deg. The reduction in drag, relative to the baseline, obtained by combining the modifications are compared for the zero yaw condition with full scale coast down drag results for similar configurations. The drag reductions obtained from the model and full scale tests are in good agreement.

  1. Bubble Drag Reduction Requires Large Bubbles

    NASA Astrophysics Data System (ADS)

    Verschoof, Ruben A.; van der Veen, Roeland C. A.; Sun, Chao; Lohse, Detlef

    2016-09-01

    In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. However, the exact mechanism behind bubble drag reduction is unknown. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid. The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow and opens the door for an optimization of the process.

  2. Drag Reduction by Leidenfrost Vapor Layers

    NASA Astrophysics Data System (ADS)

    Vakarelski, Ivan U.; Marston, Jeremy O.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.

    2011-05-01

    We demonstrate and quantify a highly effective drag reduction technique that exploits the Leidenfrost effect to create a continuous and robust lubricating vapor layer on the surface of a heated solid sphere moving in a liquid. Using high-speed video, we show that such vapor layers can reduce the hydrodynamic drag by over 85%. These results appear to approach the ultimate limit of drag reduction possible by different methods based on gas-layer lubrication and can stimulate the development of related energy saving technologies.

  3. Drag reduction by Leidenfrost vapor layers.

    PubMed

    Vakarelski, Ivan U; Marston, Jeremy O; Chan, Derek Y C; Thoroddsen, Sigurdur T

    2011-05-27

    We demonstrate and quantify a highly effective drag reduction technique that exploits the Leidenfrost effect to create a continuous and robust lubricating vapor layer on the surface of a heated solid sphere moving in a liquid. Using high-speed video, we show that such vapor layers can reduce the hydrodynamic drag by over 85%. These results appear to approach the ultimate limit of drag reduction possible by different methods based on gas-layer lubrication and can stimulate the development of related energy saving technologies.

  4. The influence of energy deposition parameters on laser plasma drag reduction

    NASA Astrophysics Data System (ADS)

    Dou, Zhiguo; Liu, Zhun; Yao, Honglin; Li, Xiuqian

    2013-09-01

    experiment investigation. Aerodynamic drag, laser plasma, hypersonic, drag reduction, numerical simulation

  5. Drag Reduction Tests on Supersonic Transport Design

    NASA Technical Reports Server (NTRS)

    1998-01-01

    Langley researchers recently completed supersonic tests in the Unitary Plan Wind Tunnel on a nonlinear design for a supersonic transport. Although the drag reduction measured during the tests was not as great as that predicted using computational methods, significant drag reductions were achieved. Future tests will be conducted at a higher Reynolds number, which will be more representative of flight conditions. These tests will be used to identify a supersonic transport configuration that provides maximum drag reduction. Reducing drag decreases operating cost by improving fuel consumption and lowering aircraft weight. As a result, this research has the potential to help make a future high-speed civil transport (HSCT) an affordable means of travel for the flying public.

  6. Frictional drag reduction by bubble injection

    NASA Astrophysics Data System (ADS)

    Murai, Yuichi

    2014-07-01

    The injection of gas bubbles into a turbulent boundary layer of a liquid phase has multiple different impacts on the original flow structure. Frictional drag reduction is a phenomenon resulting from their combined effects. This explains why a number of different void-drag reduction relationships have been reported to date, while early works pursued a simple universal mechanism. In the last 15 years, a series of precisely designed experimentations has led to the conclusion that the frictional drag reduction by bubble injection has multiple manifestations dependent on bubble size and flow speed. The phenomena are classified into several regimes of two-phase interaction mechanisms. Each regime has inherent physics of bubbly liquid, highlighted by keywords such as bubbly mixture rheology, the spectral response of bubbles in turbulence, buoyancy-dominated bubble behavior, and gas cavity breakup. Among the regimes, bubbles in some selected situations lose the drag reduction effect owing to extra momentum transfer promoted by their active motions. This separates engineers into two communities: those studying small bubbles for high-speed flow applications and those studying large bubbles for low-speed flow applications. This article reviews the roles of bubbles in drag reduction, which have been revealed from fundamental studies of simplified flow geometries and from development of measurement techniques that resolve the inner layer structure of bubble-mixed turbulent boundary layers.

  7. Measurements of drag reduction by SLIPS

    NASA Astrophysics Data System (ADS)

    Samaha, Mohamed A.; Shang, Jessica; Fu, Matthew; Wang, Karen; Stone, Howard; Smits, Alexander; Hultmark, Marcus

    2014-11-01

    Slippery liquid infused porous surfaces (SLIPS) consist of an omniphobic lubricant impregnated into a micro/nanoscale textured substrate. These surfaces have been shown to repel a wide range of liquids. Several techniques to fabricate such surfaces are available in the literature. Here, we report on drag reduction and slip-length measurements using a parallel plate rheometer. Skin-friction measurements of different working fluids are performed on SLIPS with fluorinated boehmite substrates infused with different lubricants. The measurements are refined by considering the evaporation effect of the working fluids. The experiments are performed for different viscosity ratios, N (viscosity of working fluid to that of the lubricant). The effect of the gap height and strain rate on the drag reduction is also investigated. The results show that drag-reduction behavior is influenced by the viscosity ratio and the lubricant-film thickness. The observed drag reduction exists even for very thin film thicknesses. Furthermore, drag reduction is observed for different working fluids even with those having low surface tension such as ethanol. Supported under ONR Grants N00014-12-1-0875 and N00014-12-1-0962 (program manager Ki-Han Kim).

  8. Bioinspired surfaces for turbulent drag reduction.

    PubMed

    Golovin, Kevin B; Gose, James W; Perlin, Marc; Ceccio, Steven L; Tuteja, Anish

    2016-08-06

    In this review, we discuss how superhydrophobic surfaces (SHSs) can provide friction drag reduction in turbulent flow. Whereas biomimetic SHSs are known to reduce drag in laminar flow, turbulence adds many new challenges. We first provide an overview on designing SHSs, and how these surfaces can cause slip in the laminar regime. We then discuss recent studies evaluating drag on SHSs in turbulent flow, both computationally and experimentally. The effects of streamwise and spanwise slip for canonical, structured surfaces are well characterized by direct numerical simulations, and several experimental studies have validated these results. However, the complex and hierarchical textures of scalable SHSs that can be applied over large areas generate additional complications. Many studies on such surfaces have measured no drag reduction, or even a drag increase in turbulent flow. We discuss how surface wettability, roughness effects and some newly found scaling laws can help explain these varied results. Overall, we discuss how, to effectively reduce drag in turbulent flow, an SHS should have: preferentially streamwise-aligned features to enhance favourable slip, a capillary resistance of the order of megapascals, and a roughness no larger than 0.5, when non-dimensionalized by the viscous length scale.This article is part of the themed issue 'Bioinspired hierarchically structured surfaces for green science'.

  9. Turbulent drag reduction by permeable coatings

    NASA Astrophysics Data System (ADS)

    Garcia-Mayoral, Ricardo; Abderrahaman-Elena, Nabil

    2015-11-01

    We present an assessment of permeable coatings as a form of passive drag reduction, proposing a simplified model to quantify the effect of the coating thickness and permeability. To reduce skin friction, the porous layer must be preferentially permeable in the streamwise direction, so that a slip effect is produced. For small permeability, the controlling parameter is the difference between streamwise and spanwise permeability lengths, scaled in viscous units, √{Kx+}-√{Kz+}. In this regime, the reduction in drag is proportional to that difference. However, the proportional performance eventually breaks down for larger permeabilities. A degradation mechanism is investigated, common to other obstructed surfaces in general and permeable substrates in particular, which depends critically on the geometric mean of the streamwise and wall-normal permeabilities, √{Kx+ Ky+}. For a streamwise-to-cross-plane permeability ratio of order Kx+/Ky+ = Kx+/Kz+ 10 -100, the model predicts a maximum drag reduction of order 15-25%.

  10. Drag reduction by rotation in granular media

    NASA Astrophysics Data System (ADS)

    Jung, Wonjong; Choi, Sung Mok; Kim, Wonjung; Kim, Ho-Young

    2016-11-01

    We present quantitative measurements and mathematical analysis of the granular drag reduction by rotation inspired by some self-burrowing seeds whose morphologies respond to environmental changes in humidity. The seeds create a motion to dig into soil using their moisture-responsive awns, which are basically helical shaped in a dry environment but reversibly deform to a linear shape in a humid environment. When the tip of the awn is fixed by an external support, the hygroscopic deformation of the awn gives the seed a thrust with rotation against the soil. By measuring the granular drag of vertically penetrating intruders with rotation, we find the drag to decrease with its rotation speed. Noting that the relative motions of the grains in contact with the intruder induce the collapse of the force chains in the granular bulk, we develop a general correlation for the drag reduction by rotation in terms of the relative slip velocity of the grains, which successfully explains the drag reduction of the rotating intruders including self-burrowing rotary seeds.

  11. Large-eddy simulation of a turbulent flow over a heavy vehicle with drag reduction devices

    NASA Astrophysics Data System (ADS)

    Lee, Sangseung; Kim, Myeongkyun; You, Donghyun

    2015-11-01

    Aerodynamic drag contributes to a considerable amount of energy loss of heavy vehicles. To reduce the energy loss, drag reduction devices such as side skirts and boat tails, are often installed to the side and the rear of a heavy vehicle. In the present study, turbulent flow around a heavy vehicle with realistic geometric details is simulated using large-eddy simulation (LES), which is capable of providing unsteady flow physics responsible for aerodynamic in sufficient detail. Flow over a heavy vehicle with and without a boat tail and side skirts as drag reduction devices is simulated. The simulation results are validated against accompanying in-house experimental measurements. Effects of a boat tail and side skirts on drag reduction are discussed in detail. Supported by the Korea Agency for Infrastructure Technology Advancement (KAIA) Grant NTIS 1615007940.

  12. Drag reduction using slippery liquid infused surfaces

    NASA Astrophysics Data System (ADS)

    Hultmark, Marcus; Stone, Howard; Smits, Alexander; Jacobi, Ian; Samaha, Mohamed; Wexler, Jason; Shang, Jessica; Rosenberg, Brian; Hellström, Leo; Fan, Yuyang

    2013-11-01

    A new method for passive drag reduction is introduced. A surface treatment inspired by the Nepenthes pitcher plant, previously developed by Wong et al. (2011), is utilized and its design parameters are studied for increased drag reduction and durability. Nano- and micro-structured surfaces infused with a lubricant allow for mobility within the lubricant itself when the surface is exposed to flow. The mobility causes slip at the fluid-fluid interface, which drastically reduces the viscous friction. These new surfaces are fundamentally different from the more conventional superhydrophobic surfaces previously used in drag reduction studies, which rely on a gas-liquid interface. The main advantage of the liquid infused surfaces over the conventional surfaces is that the lubricant adheres more strongly to the surface, decreasing the risk of failure when exposed to turbulence and other high-shear flows. We have shown that these surfaces can reduce viscous drag up to 20% in both Taylor-Couette flow and in a parallel plate rheometer. Supported under ONR Grants N00014-12-1-0875 and N00014-12-1-0962 (program manager Ki-Han Kim).

  13. Bubble drag reduction requires large bubbles

    NASA Astrophysics Data System (ADS)

    Verschoof, Ruben; van der Veen, Roeland; Sun, Chao; Lohse, Detlef

    2016-11-01

    In the maritime industry, the injection of air bubbles into the turbulent boundary layer under the ship hull is seen as one of the most promising techniques to reduce the overall fuel consumption. A few volume percent (<= 4 %) of bubbles can reduce the overall drag up to 40% and beyond. However, the exact mechanism is unknown, thus hindering further progress and optimization. Here we show that bubble drag reduction in turbulent flow dramatically depends on the bubble size. By adding minute concentrations (6 ppm) of the surfactant Triton X-100 into otherwise completely unchanged strongly turbulent Taylor-Couette flow containing bubbles, we dramatically reduce the drag reduction from more than 40% to about 4%, corresponding to the trivial effect of the bubbles on the density and viscosity of the liquid . The reason for this striking behavior is that the addition of surfactants prevents bubble coalescence, leading to much smaller bubbles. Our result demonstrates that bubble deformability is crucial for bubble drag reduction in turbulent flow. We acknowledge support from STW and FOM.

  14. Bluff-body drag reduction by passive ventilation

    NASA Astrophysics Data System (ADS)

    Suryanarayana, G. K.; Pauer, Henning; Meier, G. E. A.

    1993-12-01

    The drag of a sphere at high Re can be reduced to more than half its value by passive ventilation from the stagnation region to the base. Simultaneously, the flow field around the base is stabilized and made symmetric, leading to reduction of unsteady aerodynamic forces. At high Re, the vent flow breaks through the dead water region associated with the near wake and aerodynamically streamlines the base. The streamlining is done by virtue of a base-vortex-ring beyond the point of turbulent boundary layer separation. A mean flow model for the flow around the vented sphere is proposed. Smoke flow visualized on a laser light screen placed at two diameters behind the base of the sphere shows the effectiveness of the method in suppressing the flow oscillations. The drag reduction achieved is very sensitive to the quality of the external surface and relatively insensitive to disturbances in the internal flow. Surface roughness or boundary layer tripping wire on the external flow can completely offset the benefit obtained.

  15. Kuechemann Carrots for transonic drag reduction.

    NASA Astrophysics Data System (ADS)

    Bechert, D. W.; Hage, W.; Stanewsky, E.

    1999-11-01

    Wave drag reduction bodies on the suction side of transonic wings are investigated. Following the original invention by O. Frenzl (1942), subsequently, such bodies have been suggested by Kuechemann and Whitcomb. These devices have been used sucessfully on various TUPOLEV aircraft and on the CONVAIR 990 airliner. New transonic wind tunnel data from an unswept wing with an array of Kuechemann Carrots are presented (airfoil: CAST 10/DOA-2). In a certain parameter range (M= 0.765-0.86) the measurements exhibit a significant reduction of the shock strength on a wing between the Kuechemann Carrots. This entails a dramatic reduction of drag, in a certain Mach number and angular regime up to 50-60%.

  16. Drag Reduction On Multiscale Superhydrophobic Surfaces

    NASA Astrophysics Data System (ADS)

    Jenner, Elliot; Barbier, Charlotte; D'Urso, Brian

    2013-11-01

    Fluid drag reduction is of great interest in a variety of fields, including hull engineering, microfluidics, and drug delivery. We fabricated samples with multi-scale superhydrophobic surfaces, which consist of hexagonally self-ordered microscopic spikes grown via anodization on macroscopic grooves cut in aluminum. The hydrodynamic drag properties were studied with a cone-and-plate rheometer, showing significant drag reduction near 15% in turbulent flow and near 30% in laminar flow. In addition to these experiments, numerical simulations were performed in order to estimate the slip length at high speeds. Furthermore, we will report on the progress of experiments with a new type of surface combining superhydrophobic surfaces like those discussed above with Slippery Liquid Infused Porous Surfaces (SLIPS), which utilize an oil layer to create a hydrophobic self-repairing surface. These ``Super-SLIPS'' may combine the best properties of both superhydrophobic surfaces and SLIPS, by combining a drag reducing air-layer and an oil layer which may improve durability and biofouling resistance. This research was supported by the ORNL Seed Money Program. Oak Ridge National Laboratory is managed by UT-Battelle, LLC, for the U.S. Dept. of Energy under contract DE-AC05-00OR22725.

  17. Analog VLSI for active drag reduction

    NASA Astrophysics Data System (ADS)

    Gupta, Vidyabhusan

    In today's cost-conscious air transportation industry, fuel costs are a substantial economic concern. Drag reduction is an important way to increase fuel efficiency which reduces these costs. Even a 1% reduction in drag can translate into estimated savings of tens of millions of dollars in annual fuel costs. Fluid mechanicists believe that microscopic vortex pairs impinging on the surface play an important role in turbulent transport that may cause large skin friction drag. The microscopic nature and unpredictable appearance of these structures has limited practical approaches to their control. With the advent of micromachining technology providing the ability to build mechanical structures with microscopic dimensions, the tools finally exist with which to detect and control the vortex structures. These sensors and actuators require control circuitry between them in order to build a complete system. We propose an analog VLSI system that can process information along a surface in a moving fluid with the goal of controlling actuators to minimize the surface shear stress. We obtain the information from the surface by using microsensors which measure the surface shear stress. The actuators interact with the fluid by moving up and down in an attempt to diminish the impact of the drag-inducing structures in the fluid. We have designed the fabricated an analog control system. We have tested the system in several different experiments to verify its effectiveness in providing a control signal that energizes an actuator. We also have studied the methodology for a completely integrated wafer-scale system.

  18. Longevity and drag reduction of omniphobic surfaces

    NASA Astrophysics Data System (ADS)

    Rosenberg, Brian; Samaha, Mohamed A.; Jacobi, Ian; Shang, Jessica; Hultmark, Marcus; Smits, Alexander

    2013-11-01

    Omniphobic surfaces, which consist of an omniphobic lubricant impregnated into a micro/nanoscale textured substrate, have been shown to repel a wide range of liquids [Wong et al. (Nature 2011)]. Here, experiments are performed on these surfaces to investigate the drag reduction as well as the time-dependent omniphobicity in the presence of flow. Drag measurements are performed in number of different flows including parallel plate and Taylor-Couette rheometers, pipe flow, and bluff body flows. The longevity of the surfaces are measured using three techniques: (i) an in situ noninvasive optical method to characterize the the loss of lubricant with time; (ii) thin-film interferometry measurements of the lubricant thickness versus time; and (iii) goniometer measurements of the time-dependent threshold sliding angle as well as contact-angle hysteresis. The impact of the substrate morphology on the drag reduction and longevity is observed both with and without flow in the surrounding water environment. This work could help to investigate ways of enhancing the drag-reducing properties of omniphobic surfaces by controlling their morphologies. Supported under ONR Grants N00014-12-1-0875 and N00014-12-1-0962 (program manager Ki-Han Kim).

  19. Innovative Flow Control Concepts for Drag Reduction

    NASA Technical Reports Server (NTRS)

    Lin, John C.; Whalen, Edward A.; Eppink, Jenna L.; Siochi, Emilie J.; Alexander, Michael G.; Andino, Marlyn Y.

    2016-01-01

    This paper highlights the technology development of two flow control concepts for aircraft drag reduction. The NASA Environmentally Responsible Aviation (ERA) project worked with Boeing to demonstrate these two concepts on a specially outfitted Boeing 757 ecoDemonstrator during the spring of 2015. The first flow control concept used Active Flow Control (AFC) to delay flow separation on a highly deflected rudder and increase the side force that it generates. This may enable a smaller vertical tail to provide the control authority needed in the event of an engine failure during takeoff and landing, while still operating in a conventional manner over the rest of the flight envelope. Thirty-one sweeping jet AFC actuators were installed and successfully flight-tested on the vertical tail of the 757 ecoDemonstrator. Pilot feedback, flow cone visualization, and analysis of the flight test data confirmed that the AFC is effective, as a smoother flight and enhanced rudder control authority were reported. The second flow control concept is the Insect Accretion Mitigation (IAM) innovation where surfaces were engineered to mitigate insect residue adhesion on a wing's leading edge. This is necessary because something as small as an insect residue on the leading edge of a laminar flow wing design can cause turbulent wedges that interrupt laminar flow, resulting in an increase in drag and fuel use. Several non-stick coatings were developed by NASA and applied to panels that were mounted on the leading edge of the wing of the 757 ecoDemonstrator. The performance of the coated surfaces was measured and validated by the reduction in the number of bug adhesions relative to uncoated control panels flown simultaneously. Both flow control concepts (i.e., sweeping jet actuators and non-stick coatings) for drag reduction were the culmination of several years of development, from wind tunnel tests to flight tests, and produced valuable data for the advancement of modern aircraft designs

  20. NASA research on viscous drag reduction

    NASA Technical Reports Server (NTRS)

    Petersen, R. H.; Maddalon, D. V.

    1982-01-01

    Current NASA research points toward exciting opportunities for large reductions in viscous drag. Research is underway on natural laminar flow, laminar flow control by suction, and turbulent drag reduction. Preliminary results suggest that a significant amount of natural laminar flow can be achieved on small, straight-wing airplanes. On larger, swept-wing aircraft, laminar flow control by distributed suction is expected to result in significant fuel savings. The area over which laminar flow control is applied depends on tradeoffs involving structural complexity, maintenance, and cost. Several methods of reducing turbulent skin friction by altering the turbulence structure itself have shown promise in exploratory testing. This paper reviews the status of these technologies and indicates the benefits of applying them to future aircraft.

  1. A Passive Drag Reduction Surface Design

    NASA Astrophysics Data System (ADS)

    Wang, Cong; Jeon, David; Gharib, Morteza

    2016-11-01

    Super hydrophobic surface could induce an air layer over the surface when submerged in water. This air layer is responsible for many fascinating properties of super hydrophobic surface, such as drag reduction. Unfortunately, the air layer is fragile and can be depleted by fast shear/turbulent flow. In this work, a dimpled surface with non-uniform surface wettability is proposed to increase the air layer stability by trapping air in individual dimples. A central pumping system is connected to each dimple to supply air and regulate pressure inside air bubble. Particle Image Velocimetry (PIV) is used to investigate the drag reduction effect of different geometry designs. This work is supported by Office of Naval Research under Grant No. N00014-15-1-2479.

  2. Design of Apparatus for the Determination of Aerodynamic Drag Coefficients of Automobiles.

    DTIC Science & Technology

    1984-06-01

    RD-RI51 942 DESIGN OF APPRATUS FOR THE DETERMINATION OF 1/1 AERODYNAMIC DRAG COEFFICIENTS OF AUTOMOBILES (U) NAVAL POSTGRADUATE SCHOOL MONTEREY CA B R...LECTE MAR 141985D . - - THESIS DESIGN OF APPARATUS FOR THE DETERMINATION OF AERODYNAMIC DRAG COEFFICIENTS OF AUTOMOBILES by Brian R. Gritte June 1984...Coefficients of June 1984 Automobiles s. PERFORMING ORG. REPORT NUMBER 7. AUTNOR(s) S. CONTRACT OR GRANT NUMIER(s) Brian R. Gritte 9. PERFORMING ORGANIZATION

  3. Effects of Polymer Parameters on Drag Reduction.

    NASA Astrophysics Data System (ADS)

    Safieddine, Abbas Mohammad

    The effects of polymer parameters on fluid drag reduction using polyethylene oxide (PEO), polyacrylamide (PAM), guar gum (GG) and hydroxyethyl cellulose (HEC) were investigated. Due to the unavailability of high molecular weight (MW) water-soluble polymers having narrow molecular weight distribution (MWD), an aqueous preparative size exclusion chromatography (SEC) system capable of fractionating over wide MW ranges was constructed. An online low shear viscometer, coupled to the SEC, measured the instantaneous intrinsic viscosity of the eluting polymer solution and, therefore, served as a MW detector since Mark-Houwink "K" and "a" values for all four polymers were known. With the aid of the viscometer, the SEC system was calibrated. The preparative nature of the chromatography system allowed the collection of large volumes of nearly monodisperse fractions (MWD < 1.1) of high MW polymers. Depending on the polymer investigated, the MW of the fractions varied, but ranged between 2 times 10 ^5 and 8 times 10 ^6 daltons. Also, the preparative SEC approach allowed drag reduction (DR) experiments using well-characterized, narrowly dispersed polymer solutions under controlled tube flow conditions. Correlations of drag reduction performance with primary polymer parameters (i.e., concentration, intrinsic viscosity ((eta)), volume fraction (c(eta)), number of chain links (N), and combinations thereof) were used to test the validity of several theoretical DR models. Walsh's energy model, as well as the Deborah argument, did not completely account for drag reduction behavior under all experimental conditions. Within each of the flexible or rigid polymer groups, the extensional viscosity model was successful in correlating c(eta) N with DR under all turbulent conditions. However, it failed to account for the differences in chemical structure between the two polymer groups. However, when the cellulosic repeat unit was used instead of the carbon-carbon bond as the chain link for

  4. A design and analysis approach for drag reduction on aircraft with adaptive lifting surfaces

    NASA Astrophysics Data System (ADS)

    Cusher, Aaron Anthony

    distributions are produced which match the classical result for minimum induced drag. Application of the profile drag reduction schemes produce solutions which force the wing to operate in the low-drag-ranges of the natural-laminar-flow airfoil sections, thereby lowering profile drag. The total drag reduction schemes use a curve-fit routine that generates airfoil drag polars given flap angle and Reynolds number. The approximated drag polars allow the prediction of profile drag values to be combined with induced drag values to form a total drag function, which is utilized with a constrained nonlinear optimizer that determines best flap angles for total drag and trim. The different drag reduction schemes each produce independent flap-angle solutions and lift distributions for a given aircraft configuration and operating condition, and provide valuable insight for aerodynamic design and trade studies. The drag reduction approach is intended to be applicable to arbitrary aircraft configurations, and can be adapted to use surface incidence, twist, and flap angles as optimization variables, thereby creating a powerful and flexible aerodynamic design and analysis tool.

  5. Dielectric barrier discharge actuator for vehicle drag reduction at highway speeds

    NASA Astrophysics Data System (ADS)

    Roy, Subrata; Zhao, Pengfei; DasGupta, Arnob; Soni, Jignesh

    2016-02-01

    We propose and demonstrate reduction of aerodynamic drag for a realistic geometry at highway speeds using serpentine dielectric barrier discharge actuators. A comparable linear plasma actuator fails to reduce the drag at these speeds. Experimental data collected for linear and serpentine plasma actuators under quiescent operating conditions show that the serpentine design has profound effect on near wall flow structure and resulting drag. For certain actuator arrangement, the measured drag reduced by over 14% at 26.8 m/s (60 mph) and over 10% at 31.3 m/s (70 mph) opening up realistic possibility of reasonable energy savings for full scale ground vehicles. In addition, the power consumption data and drag reduction effectiveness for different input signals are also presented.

  6. DOE's Effort to Reduce Truck Aerodynamic Drag-Joint Experiments and Computations Lead to Smart Design

    SciTech Connect

    McCallen, R; Salari, K; Ortega, J; DeChant, L; Hassan, B; Roy, C; Pointer, W; Browand, F; Hammache, M; Hsu, T; Leonard, A; Rubel, M; Chatalain, P; Englar, R; Ross, J; Satran, D; Heineck, J; Walker, S; Yaste, D; Storms, B

    2004-06-17

    At 70 miles per hour, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck vehicle. The goal of this US Department of Energy supported consortium is to establish a clear understanding of the drag producing flow phenomena. This is being accomplished through joint experiments and computations, leading to the 'smart' design of drag reducing devices. This paper will describe our objective and approach, provide an overview of our efforts and accomplishments, and discuss our future direction.

  7. DOE's effort to reduce truck aerodynamic drag : joint experiments and computations lead to smart design.

    SciTech Connect

    Yaste, David M; Salari, Kambiz; Hammache, Mustapha; Browand, Fred; Pointer, W. David; Ortega, Jason M.; McCallen, Rose; Walker, Stephen M; Heineck, James T; Hassan, Basil; Roy, Christopher John; Storms, B.; Satran, D.; Ross, James; Englar, Robert; Chatalain, Philippe; Rubel, Mike; Leonard, Anthony; Hsu, Tsu-Ya; DeChant, Lawrence Justin.

    2004-06-01

    At 70 miles per hour, overcoming aerodynamic drag represents about 65% of the total energy expenditure for a typical heavy truck vehicle. The goal of this US Department of Energy supported consortium is to establish a clear understanding of the drag producing flow phenomena. This is being accomplished through joint experiments and computations, leading to the smart design of drag reducing devices. This paper will describe our objective and approach, provide an overview of our efforts and accomplishments, and discuss our future direction.

  8. Turbulent drag reduction over liquid infused surfaces

    NASA Astrophysics Data System (ADS)

    Arenas, Isnardo; Bernardini, Matteo; Leonardi, Stefano

    2016-11-01

    Numerical Simulations of two superposed fluids in a turbulent channel with a textured surface made of either longitudinal square bars or staggered cubes have been performed. The viscosity of the fluid inside the substrate is ten times smaller than that of the main stream (m =μ1 /μ2 = 0 . 1 where the subscripts 1 and 2 indicate the fluid in the cavities and the overlying fluid respectively). The interface between the two fluids can move due to the turbulent pressure fluctuations and it is modeled with a Level Set Approach. Two cases are compared: We = 0 , implying an interface sustained by the surface tension which can slip only in the horizontal direction, and We = ∞ where the interface can be displaced vertically and deform subject to wall normal stress. The textured surface made of staggered cubes is the most sensitive to the value of the surface tension, providing a drag reduction ranging between 15 - 30 % for We = 0 and approximately 40 % drag increase when We = ∞ . On the other hand, longitudinal square bars, even with We = ∞ present a drag smaller than that over a smooth wall. Numerical simulations were performed on XSEDE TACC under Grant CTS070066. This work was supported by ONR MURI Grants N00014-12-01-0875 and N00014-12-01-0962.

  9. NASA research on viscous drag reduction

    NASA Technical Reports Server (NTRS)

    Petersen, R. H.; Maddalon, D. V.

    1982-01-01

    Research on natural laminar flow, laminar flow control by suction, and turbulent drag reduction is discussed. Preliminary results suggest that a significant amount of natural laminar flow can be achieved on small, straight wing airplanes. On larger, swept wing aircraft, laminar flow control by distributed suction is expected to result in significant fuel savings. The area over which laminar flow control is applied depends on tradeoffs involving structural complexity, maintenance, and cost. Several methods of reducing turbulent skin friction by altering the turbulence structure itself have shown promise in exploratory testing. The status of these technologies and the benefits of applying them to future aircraft are reviewed.

  10. Computational analysis of methods for reduction of induced drag

    NASA Technical Reports Server (NTRS)

    Janus, J. M.; Chatterjee, Animesh; Cave, Chris

    1993-01-01

    The purpose of this effort was to perform a computational flow analysis of a design concept centered around induced drag reduction and tip-vortex energy recovery. The flow model solves the unsteady three-dimensional Euler equations, discretized as a finite-volume method, utilizing a high-resolution approximate Riemann solver for cell interface flux definitions. The numerical scheme is an approximately-factored block LU implicit Newton iterative-refinement method. Multiblock domain decomposition is used to partition the field into an ordered arrangement of blocks. Three configurations are analyzed: a baseline fuselage-wing, a fuselage-wing-nacelle, and a fuselage-wing-nacelle-propfan. Aerodynamic force coefficients, propfan performance coefficients, and flowfield maps are used to qualitatively access design efficacy. Where appropriate, comparisons are made with available experimental data.

  11. Drag reduction in fish-like locomotion

    NASA Astrophysics Data System (ADS)

    Barrett, D. S.; Triantafyllou, M. S.; Yue, D. K. P.; Grosenbaugh, M. A.; Wolfgang, M. J.

    1999-08-01

    We present experimental force and power measurements demonstrating that the power required to propel an actively swimming, streamlined, fish-like body is significantly smaller than the power needed to tow the body straight and rigid at the same speed U. The data have been obtained through accurate force and motion measurements on a laboratory fish-like robotic mechanism, 1.2 m long, covered with a flexible skin and equipped with a tail fin, at Reynolds numbers up to 106, with turbulence stimulation. The lateral motion of the body is in the form of a travelling wave with wavelength [lambda] and varying amplitude along the length, smoothly increasing from the front to the tail end. A parametric investigation shows sensitivity of drag reduction to the non-dimensional frequency (Strouhal number), amplitude of body oscillation and wavelength [lambda], and angle of attack and phase angle of the tail fin. A necessary condition for drag reduction is that the phase speed of the body wave be greater than the forward speed U. Power estimates using an inviscid numerical scheme compare favourably with the experimental data. The method employs a boundary-integral method for arbitrary flexible body geometry and motions, while the wake shed from the fish-like form is modelled by an evolving desingularized dipole sheet.

  12. Test, Evaluation, and Demonstration of Practical Devices/Systems to Reduce Aerodynamic Drag of Tractor/Semitrailer Combination Unit Trucks

    SciTech Connect

    Scott Smith; Karla Younessi; Matt Markstaller; Dan Schlesinger; Bhaskar Bhatnagar; Donald Smith; Bruno Banceu; Ron Schoon; V.K. Sharma; Mark Kachmarsky; Srikant Ghantae; Michael Sorrels; Conal Deedy; Justin Clark; Skip Yeakel; Michael D. Laughlin; Charlotte Seigler; Sidney Diamond

    2007-04-30

    Class 8 heavy-duty trucks account for over three-quarters of the total diesel fuel used by commercial trucks (trucks with GVWRs more than 10,000 pounds) in the United States each year. At the highway speeds at which these trucks travel (i.e., 60 mph or greater), aerodynamic drag is a major part of total horsepower needed to move the truck down the highway, Reductions in aerodynamic drag can yield measurable benefits in fuel economy through the use of relatively inexpensive and simple devices. The goal of this project was to examine a number of aerodynamic drag reduction devices and systems and determine their effectiveness in reducing aerodynamic drag of Class 8 tractor/semitrailer combination-units, thus contributing to DOE's goal of reducing transportation petroleum use. The project team included major heavy truck manufacturers in the United States, along with the management and industry expertise of the Truck Manufacturers Association as the lead investigative organization. The Truck Manufacturers Association (TMA) is the national trade association representing the major North American manufacturers of Class 6-8 trucks (GVWRs over 19,500 lbs). Four major truck manufacturers participated in this project with TMA: Freightliner LLC; International Truck and Engine Corporation; Mack Trucks Inc.; and Volvo Trucks North America, Inc. Together, these manufacturers represent over three-quarters of total Class 8 truck sales in the United States. These four manufacturers pursued complementary research efforts as part of this project. The project work was separated into two phases conducted over a two-year period. In Phase I, candidate aerodynamic devices and systems were screened to focus research and development attention on devices that offered the most potential. This was accomplished using full-size vehicle tests, scale model tests, and computational fluid dynamics analyses. In Phase II, the most promising devices were installed on full-size trucks and their effect on

  13. Characterization of aerodynamic drag force on single particles: Final report

    SciTech Connect

    Kale, S.R.

    1987-10-01

    An electrodynamic balance was used to measure the drag coefficient and also to record the size and shape of spheres, and coal and oil shale particles (100 ..mu..m to 200 ..mu..m in size). The electrodynamic balance consisted of a central, and two end electrodes. The resulting electric field stably suspended a charged particle. A suspended particle, back illuminated by a light emitting diode, was viewed by a video camera. The image was analyzed for particle position control and was calibrated to give the diameter of spheres, or the area equivalent diameter of nonspherical particles. The drag coefficient was calculated from the air velocity and the dc voltage required to keep the particle at the balance center. The particle Reynolds number varied from 0.2 to 13. Three particles each of coal and oil shale were captured and photographed by a scanning electron microscope and the motion of all the particles was recorded on video tape. Drag coefficient vs Reynolds number data for spheres agreed well with correlations. Data for thirteen particles each of coal and oil shale indicated a power law relationship between drag coefficient and Reynolds number. All these particles exhibited higher drag than spheres and were also observed to rotate. The rotation, however, did not affect the drag coefficient. The choice of characteristic dimension affects the drag characteristics of oil shale more strongly than for coal, owing to the flake-like shape of oil shale. 38 figs., 5 tabs.

  14. Viscous flow drag reduction by acoustic excitation

    NASA Technical Reports Server (NTRS)

    Nagel, Robert T.

    1986-01-01

    An experimental program in which the effectiveness of a single large eddy break up (LEBU) blade is enhanced by proper acoustic excitation is described. Acoustic waves are generated in response to the incident large scale eddies and directed at the blade trailing edge through the test surface floor below the manipulator blade. The acoustic input is phase locked to the incident flow. Control of the acoustic input apparently allows enhancement of the large eddy cancellation process leading to a decrease of skin friction coefficient. Control of this process with acoustic excitation indicates that vortex unwinding is the mechanism for large eddy destruction in the boundary layer. A deeper understanding of this phenomena could lead to better drag reduction technology and further understanding of the physics of the turbulent boundary layer.

  15. Drag reduction in turbulent MHD pipe flows

    NASA Technical Reports Server (NTRS)

    Orlandi, P.

    1996-01-01

    This is a preliminary study devoted to verifying whether or not direct simulations of turbulent Magneto-Hydro-Dynamic (MHD) flows in liquid metals reproduce experimental observations of drag reduction. Two different cases have been simulated by a finite difference scheme which is second order accurate in space and time. In the first case, an external azimuthal magnetic field is imposed. In this case, the magnetic field acts on the mean axial velocity and complete laminarization of the flow at N(sub a) = 30 has been achieved. In the second case, an axial magnetic field is imposed which affects only fluctuating velocities, and thus the action is less efficient. This second case is more practical, but comparison between numerical and experimental results is only qualitative.

  16. Mechanics of drag reduction by shallow dimples in channel flow

    NASA Astrophysics Data System (ADS)

    Tay, C. M. J.; Khoo, B. C.; Chew, Y. T.

    2015-03-01

    Arrays of shallow dimples with depth to diameter ratios of 1.5% and 5% are studied in a turbulent channel flow at Reynolds numbers between 5000 and 35 000. Pressure measurements show that drag reduction of up to 3% is possible. The mechanism of skin friction drag reduction with dimples is the same as that observed for flat surfaces using active methods such as spanwise wall motions or transverse wall jets. The three dimensional dimples introduce streamwise vorticity into the flow which results in spanwise flow components near the wall. The result is that the normal energy cascade to the smaller scales is suppressed, which leads to a reduction in turbulent skin friction drag because of the stabilized flow. Increasing the dimple depth from 1.5% to 5% of its diameter increases the streamwise vorticity introduced, which leads to a greater reduction in skin friction. However, increasing the dimple depth also results in flow separation which increases form drag. The net effect to the total drag depends on the relative dominance between the drag reducing streamwise vorticity and the drag increasing flow separation region. As the Reynolds number increases, the region of flow separation can shrink and result in increasing drag reduction. By understanding the flow physics of drag reduction in dimples, there is opportunity to minimize the form drag by passive contouring of the dimples using non-spherical shapes to optimize the dimple performance.

  17. The Aerodynamic Drag of Five Models of Side Floats N.A.C.A. Models 51-E, 51-F, 51-G, 51-H, 51-J

    NASA Technical Reports Server (NTRS)

    House, R O

    1938-01-01

    The drag of five models of side floats was measured in the N.A.C.A. 7- by 10-foot wind tunnel. The most promising method of reducing the drag of floats indicated by these tests is lowering the angle at which the floats are rigged. The addition of a step to a float does not always increase the drag in the flying range, floats with steps sometimes having lower drag than similar floats without steps. Making the bow chine no higher than necessary might result in a reduction in air drag because of the lower angle of pitch of the chines. Since side floats are used formally to obtain lateral stability when the seaplane is operating on the water at slow speeds or at rest, greater consideration can be given to factors affecting aerodynamic drag than is possible for other types of floats and hulls.

  18. An Aerodynamic Assessment of Micro-Drag Generators (MDGs)

    NASA Technical Reports Server (NTRS)

    Bauer, Steven X. S.

    1998-01-01

    Commercial transports as well as fighter aircraft of the future are being designed with very low drag (friction and pressure). Concurrently, commuter airports are being built or envisioned to be built in the centers of metropolitan areas where shorter runways and/or reduced noise footprints on takeoff and landing are required. These requirements and the fact that drag is lower on new vehicles than on older aircraft have resulted in vehicles that require a large amount of braking force (from landing-gear brakes, spoilers, high-lift flaps, thrust reversers, etc.). Micro-drag generators (MDGs) were envisioned to create a uniformly distributed drag force along a vehicle by forcing the flow to separate on the aft-facing surface of a series of deployable devices, thus, generating drag. The devices are intended to work at any speed and for any type of vehicle (aircraft, ground vehicles, sea-faring vehicles). MDGs were applied to a general aviation wing and a representative fuselage shape and tested in two subsonic wind tunnels. The results showed increases in drag of 2 to 6 times that of a "clean" configuration.

  19. Drag Reduction Obtained by the Addition of a Boattail to a Box Shaped Vehicle. M.S. Thesis

    NASA Technical Reports Server (NTRS)

    Peterson, R. L.

    1981-01-01

    Coast down tests were performed on a box shaped ground vehicle used to simulate the aerodynamic drag of high volume transports such as delivery vans, motor homes and trucks. The results of these tests define the reduction in aerodynamic drag that can be obtained by the addition of either a boattail or a truncated boattail to an otherwise blunt based vehicle. Test velocities ranged up to 96.6 km/h (60 mph) with Reynolds numbers to 1.3 x 10 the 7th power. The full boattail provided an average 32 percent reduction in drag at highway speeds whereas the truncated boattail provided an average 31 percent reduction in drag as compared to the configuration having the blunt base. These results are compared with one tenth scale wind tunnel model data.

  20. Drag reduction characteristics of small amplitude rigid surface waves

    NASA Technical Reports Server (NTRS)

    Cary, A. M., Jr.; Weinstein, L. M.; Bushnell, D. M.

    1980-01-01

    The possibility of reducing drag by using rigid, wavy surfaces is investigated both analytically and experimentally. Although pressure drag for rigid sine-wave surfaces can be predicted empirically, viscous drag for even shallow waves was poorly predicted by state-of-the-art turbulent boundary layer calculation procedures. Calculations for the effects of geometric and fluid variables on total wave drag are presented under the philosophy that trends will be nearly correct even though levels are probably incorrect. Experiments by the present authors indicate that a total drag reduction with wavy walls is possible.

  1. Evaluation of Aerodynamic Drag and Torque for External Tanks in Low Earth Orbit

    PubMed Central

    Stone, William C.; Witzgall, Christoph

    2006-01-01

    A numerical procedure is described in which the aerodynamic drag and torque in low Earth orbit are calculated for a prototype Space Shuttle external tank and its components, the “LO2” and “LH2” tanks, carrying liquid oxygen and hydrogen, respectively, for any given angle of attack. Calculations assume the hypersonic limit of free molecular flow theory. Each shell of revolution is assumed to be described by a series of parametric equations for their respective contours. It is discretized into circular cross sections perpendicular to the axis of revolution, which yield a series of ellipses when projected according to the given angle of attack. The drag profile, that is, the projection of the entire shell is approximated by the convex envelope of those ellipses. The area of the drag profile, that is, the drag area, and its center of area moment, that is, the drag center, are then calculated and permit determination of the drag vector and the eccentricity vector from the center of gravity of the shell to the drag center. The aerodynamic torque is obtained as the cross product of those vectors. The tanks are assumed to be either evacuated or pressurized with a uniform internal gas distribution: dynamic shifting of the tank center of mass due to residual propellant sloshing is not considered. PMID:27274926

  2. Experimental investigation on drag and heat flux reduction in supersonic/hypersonic flows: A survey

    NASA Astrophysics Data System (ADS)

    Wang, Zhen-guo; Sun, Xi-wan; Huang, Wei; Li, Shi-bin; Yan, Li

    2016-12-01

    The drag and heat reduction problem of hypersonic vehicles has always attracted the attention worldwide, and the experimental test approach is the basis of theoretical analysis and numerical simulation. In the current study, research progress of experimental investigations on drag and heat reduction are summarized by several kinds of mechanism, namely the forward-facing cavity, the opposing jet, the aerospike, the energy deposition and their combinational configurations, and the combinational configurations include the combinational opposing jet and forward-facing cavity concept and the combinational opposing jet and aerospike concept. The geometric models and flow conditions are emphasized, especially for the basic principle for the drag and heat flux reduction of each device. The measurement results of aerodynamic and aerothermodynamic are compared and analyzed as well, which can be a reference for assessing the accuracy of numerical results.

  3. Drag reduction by wing tip slots in a gliding Harris' hawk, Parabuteo unicinctus

    PubMed

    Tucker

    1995-01-01

    The anterior-most primary feathers of many birds that soar over land bend upwards and separate vertically to form slotted wing tips during flight. The slots are thought to reduce aerodynamic drag, although drag reduction has never been demonstrated in living birds. Wing theory explains how the feathers that form the tip slots can reduce induced drag by spreading vorticity horizontally along the wing and by acting as winglets, which are used on aircraft to make wings non-planar and to spread vorticity vertically. This study uses the induced drag factor to measure the induced drag of a wing relative to that of a standard planar wing with the same span, lift and speed. An induced drag factor of less than 1 indicates that the wing is non-planar. The minimum drag of a Harris' hawk gliding freely in a wind tunnel was measured before and after removing the slots by clipping the tip feathers. The unclipped hawk had 70­90 % of the drag of the clipped hawk at speeds between 7.3 and 15.0 m s-1. At a wing span of 0.8 m, the unclipped hawk had a mean induced drag factor of 0.56, compared with the value of 1.10 assumed for the clipped hawk. A Monte Carlo simulation of error propagation and a sensitivity analysis to possible errors in measured and assumed values showed that the true mean value of the induced drag factor for the unclipped hawk was unlikely to be more than 0.93. These results for a living bird support the conclusions from a previous study of a feathered tip on a model wing in a wind tunnel: the feathers that form the slotted tips reduce induced drag by acting as winglets that make the wings non-planar and spread vorticity both horizontally and vertically.

  4. Drag reduction through self-texturing compliant bionic materials

    PubMed Central

    Liu, Eryong; Li, Longyang; Wang, Gang; Zeng, Zhixiang; Zhao, Wenjie; Xue, Qunji

    2017-01-01

    Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, semisolid and liquid state all have good adhesion with modified mesh. The states of n-octadecane changed with temperature, thus, the surface contact angle and adhesive force all varies obviously at different state. The contact angle decreases with temperature, the adhesive force shows a lower value at semisolid state. Furthermore, the drag testing results show that the compliant n-octadecane film is more effectively in drag reduction than superhydrophobic ZnO/PDMS film, indicating that the drag reduction mechanism of n-octadecane is significantly different with superhydrophobic film. Further research shows that the water flow leads to self-texturing of semisolid state n-octadecane, which is similar with compliant fish skin. Therefore, the compliant bionic materials of semisolid state n-octadecane with regular bulge plays a major role in the drag reduction. PMID:28053309

  5. Drag reduction through self-texturing compliant bionic materials

    NASA Astrophysics Data System (ADS)

    Liu, Eryong; Li, Longyang; Wang, Gang; Zeng, Zhixiang; Zhao, Wenjie; Xue, Qunji

    2017-01-01

    Compliant fish skin is effectively in reducing drag, thus the design and application of compliant bionic materials may be a good choice for drag reduction. Here we consider the drag reduction of compliant bionic materials. First, ZnO and PDMS mesh modified with n-octadecane were prepared, the drag reduction of self-texturing compliant n-octadecane were studied. The results show that the mesh modified by ZnO and PDMS possess excellent lipophilic and hydrophobic, thus n-octadecane at solid, semisolid and liquid state all have good adhesion with modified mesh. The states of n-octadecane changed with temperature, thus, the surface contact angle and adhesive force all varies obviously at different state. The contact angle decreases with temperature, the adhesive force shows a lower value at semisolid state. Furthermore, the drag testing results show that the compliant n-octadecane film is more effectively in drag reduction than superhydrophobic ZnO/PDMS film, indicating that the drag reduction mechanism of n-octadecane is significantly different with superhydrophobic film. Further research shows that the water flow leads to self-texturing of semisolid state n-octadecane, which is similar with compliant fish skin. Therefore, the compliant bionic materials of semisolid state n-octadecane with regular bulge plays a major role in the drag reduction.

  6. Aircraft drag prediction and reduction. Addendum 1: Computational drag analyses and minimization; mission impossible?

    NASA Technical Reports Server (NTRS)

    Slooff, J. W.

    1986-01-01

    The Special Course on Aircraft Drag Prediction was sponsored by the AGARD Fluid Dynamics Panel and the von Karman Institute and presented at the von Karman Institute, Rhode-Saint-Genese, Belgium, on 20 to 23 May 1985 and at the NASA Langley Research Center, Hampton, Virginia, USA, 5 to 6 August 1985. The course began with a general review of drag reduction technology. Then the possibility of reduction of skin friction through control of laminar flow and through modification of the structure of the turbulence in the boundary layer were discussed. Methods for predicting and reducing the drag of external stores, of nacelles, of fuselage protuberances, and of fuselage afterbodies were then presented followed by discussion of transonic drag rise. The prediction of viscous and wave drag by a method matching inviscid flow calculations and boundary layer integral calculations, and the reduction of transonic drag through boundary layer control are also discussed. This volume comprises Paper No. 9 Computational Drag Analyses and Minimization: Mission Impossible, which was not included in AGARD Report 723 (main volume).

  7. March 2001 Working Group Meeting on Heavy Vehicle Aerodynamic Drag: Presentations and Summary of Comments and Conclusions

    SciTech Connect

    Greenman, R; Dunn, T; Owens, J; Laskowski, G; Flowers, D; Browand, F; Knight, A; Hammache, M; Leoard, A; Rubel, M; Salari, K; Rutledge, W; Ross, J; Satran, D; Heineck, J T; Walker, S; Driver, D; Storms, B

    2001-05-14

    A Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held at Lawrence Livermore National Laboratory on March 28 and 29, 2001. The purpose of the meeting was to present and discuss technical details on the experimental and computational work in progress and future project plans. Due to the large participation from industry and other research organizations, a large portion of the meeting (all of the first day and part of the second day) was devoted to the presentation and discussion of industry's perspective and work being done by other organizations on the demonstration of commercial software and the demonstration of a drag reduction device. This report contains the technical presentations (viewgraphs) delivered at the Meeting, briefly summarizes the comments and conclusions, and outlines the future action items.

  8. May 2003 Working Group Meeting on Heavy Vehicle Aerodynamic Drag: Presentations and Summary of Comments and Conclusions

    SciTech Connect

    McCallen, R; Salari, K; Ortega, J; Browand, F; Hammache, M; Hsu, T Y; Arcas, D; Leoard, A; Chatelain, P; Rubel, M; Roy, C; DeChant, L; Hassan, B; Ross, J; Satran, D; Walker, S; Heineck, J T; Englar, R; Pointer, D; Sofu, T

    2003-05-01

    A Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held at Lawrence Livermore National Laboratory on May 29-30, 2003. The purpose of the meeting was to present and discuss suggested guidance and direction for the design of drag reduction devices determined from experimental and computational studies. Representatives from the Department of Energy (DOE)/Office of Energy Efficiency and Renewable Energy/Office of FreedomCAR & Vehicle Technologies, Lawrence Livermore National Laboratory (LLNL), Sandia National Laboratories (SNL), NASA Ames Research Center (NASA), University of Southern California (USC), California Institute of Technology (Caltech), Georgia Tech Research Institute (GTRI), Argonne National Laboratory (ANL), Clarkson University, and PACCAR participated in the meeting. This report contains the technical presentations (viewgraphs) delivered at the Meeting, briefly summarizes the comments and conclusions, provides some highlighted items, and outlines the future action items.

  9. The Influence of Impurities in a Water Solution with Drag Reducing Surfactants on the Flow Drag-Reduction and a Recovering Method of Its Decreased Drag Reduction Effect.

    NASA Astrophysics Data System (ADS)

    Nakata, Toru; Sato, Kenji; Inaba, Hideo; Horibe, Akihiko; Haruki, Naoto

    The drag reduction of a water flow with new drag reducing surfactants (amine oxide type nonionic surfactants, mixtures of amine oxide type nonionic surfactants and betaine type amphoteric surfactants) which were selected as environmentally acceptable drag reducing additives was investigated experimentally. Addition of amine oxide type nonionic surfactants to hot or cold water can reduce flow drag in a turbulent pipe flow. The present research investigated how various ionic components dissolved in water affected this drag reducing effect. It was found that ionic impurities contained in the water affected the pipe flow drag reducing effect by amine oxide type nonionic surfactants. Moreover, it was clarified that the decrease in the pipe flow drag reducing effect was recovered by adding a mixture of amine oxide type nonionic surfactants and betaine type amphoteric surfactant to the water with ionic impurities.

  10. Slot injection for skin-friction drag reduction

    NASA Technical Reports Server (NTRS)

    Cary, A. M., Jr.; Bushnell, D. M.; Hefner, J. N.

    1977-01-01

    A description and analysis of slot injection in low-speed flow, slot injection in high-speed flow, a discussion of aircraft applications, and possibilities for future improvements of slot drag reduction capability are presented.

  11. Turbulent Drag Reduction Using Micro and Nanotextured Ultrahydrophobic Surfaces

    DTIC Science & Technology

    2010-01-01

    and Mizunuma, H., "Drag-reduction in flow through square and rectangular ducts with highly water repellent walls," Proceedings of the 2nd ASME Fluids... water - repellent wall," J. Fluid Mech., 381 (1999) 225-238. [7] Jun, T., and Qunji, X., "Plate drag-reduction with low surface-energy coating...to make them hydrophobic. When water is brought in contact with an ultrahydrophobic surface, the water is completely supported by the peaks in the

  12. Moving Model Test of High-Speed Train Aerodynamic Drag Based on Stagnation Pressure Measurements.

    PubMed

    Yang, Mingzhi; Du, Juntao; Li, Zhiwei; Huang, Sha; Zhou, Dan

    2017-01-01

    A moving model test method based on stagnation pressure measurements is proposed to measure the train aerodynamic drag coefficient. Because the front tip of a high-speed train has a high pressure area and because a stagnation point occurs in the center of this region, the pressure of the stagnation point is equal to the dynamic pressure of the sensor tube based on the obtained train velocity. The first derivation of the train velocity is taken to calculate the acceleration of the train model ejected by the moving model system without additional power. According to Newton's second law, the aerodynamic drag coefficient can be resolved through many tests at different train speeds selected within a relatively narrow range. Comparisons are conducted with wind tunnel tests and numerical simulations, and good agreement is obtained, with differences of less than 6.1%. Therefore, the moving model test method proposed in this paper is feasible and reliable.

  13. July 2004 Working Group Meeting on Heavy Vehicle Aerodynamic Drag: Presentation, Summary of Comments, and Conclusions

    SciTech Connect

    McCallen, R; Salari, K; Ortega, J; Castellucci, P; Eastwood, C; DeChant, L; Hassan, B; Browand, F; Arcas, D; Ross, J; Heineck, J; Storms, B; Walker, S; Leonard, A; Roy, C; Whitfield, D; Pointer, D; Sofu, T; Englar, R; Funk, R

    2004-08-17

    A Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held in Portland, Oregon on July 1, 2004. The purpose of the meeting was to provide a summary of achievements, discuss pressing issues, present a general overview of future plans, and to provide a forum for dialogue with the Department of Energy (DOE) and industry representatives. The meeting was held in Portland, because the DOE Aero Team participated in an exclusive session on Heavy Truck Vehicle Aerodynamic Drag at the 34th AIAA Fluid Dynamics Conference and Exhibit in Portland on the morning of July 1st, just preceding our Working Group meeting. Even though the paper session was on the last day of the Conference, the Team presented to a full room of interested attendees.

  14. Moving Model Test of High-Speed Train Aerodynamic Drag Based on Stagnation Pressure Measurements

    PubMed Central

    Yang, Mingzhi; Du, Juntao; Huang, Sha; Zhou, Dan

    2017-01-01

    A moving model test method based on stagnation pressure measurements is proposed to measure the train aerodynamic drag coefficient. Because the front tip of a high-speed train has a high pressure area and because a stagnation point occurs in the center of this region, the pressure of the stagnation point is equal to the dynamic pressure of the sensor tube based on the obtained train velocity. The first derivation of the train velocity is taken to calculate the acceleration of the train model ejected by the moving model system without additional power. According to Newton’s second law, the aerodynamic drag coefficient can be resolved through many tests at different train speeds selected within a relatively narrow range. Comparisons are conducted with wind tunnel tests and numerical simulations, and good agreement is obtained, with differences of less than 6.1%. Therefore, the moving model test method proposed in this paper is feasible and reliable. PMID:28095441

  15. Drag Reduction by Polymeric and Nonpolymeric Additives

    NASA Astrophysics Data System (ADS)

    White, Christopher; Sreenivasan, K. R.

    1997-11-01

    To investigate the ``self-healing'' property of drag reducing surfactant micelles we have conducted a comparative study between high polymers and surfactants in six turbulent pipe flows (Reynolds numbers between 2000 and 90,000) with varying intensities o f secondary flow. Friction factor values are measured in a straight pipe of 185 diameters; three pipes, each turning through four 90 degree elbows, of lengths 1085 diameters, 875 diameters, and 600 diameters; and a twice-turned coiled pipe, radius of curv ature of 24 diameters and length of 290 diameters. All the flows are gravity driven to prevent degradation effects caused by pump impellers. The large stresses set up by the secondary flows degrade the fragile polymers, thus reducing their effectivness as a drag reducer. The ``self-healing'' of the micelles enables the surfactant to maintain its effectivness. We will present the ``self-healing'' characteristics of the surfactant micelles using the polymer data as the datum.

  16. Possibilities for drag reduction by boundary layer control

    NASA Technical Reports Server (NTRS)

    Naiman, I.

    1946-01-01

    The mechanics of laminar boundary layer transition are reviewed. Drag possibilities for boundary layer control are analyzed using assumed conditions of transition Reynolds number, inlet loss, number of slots, blower efficiency, and duct losses. Although the results of such analysis are highly favorable, those obtained by experimental investigations yield conflicting results, showing only small gains, and sometimes losses. Reduction of this data indicates that there is a lower limit to the quantity of air which must be removed at the slot in order to stabilize the laminar flow. The removal of insufficient air permits transition to occur while the removal of excessive amounts of air results in high power costs, with a net drag increases. With the estimated value of flow coefficient and duct losses equal to half the dynamic pressure, drag reductions of 50% may be obtained; with twice this flow coefficient, the drag saving is reduced to 25%.

  17. Drag reduction efficiency for polymer-surfactant mixtures

    SciTech Connect

    Kim, C.A.; Kim, J.T.; Choi, H.J.

    1996-12-31

    In a high Reynolds number fluid flow, significant energy loss occurs due to friction. However, by the addition of a minute amount of additives into this turbulent flow, frictional drag can be drastically reduced. This drag reduction phenomenon provides considerable motivation for diverse research to investigate its origin and application. Drag reduction has been reported for several solvent/additive systems, including dilute solution of high molecular weight polymers, surfactants, and micellar systems. Polymer systems as drag reducers have been extensively investigated. Recently, Choi and Jhon investigated the concentration dependence of drag reduction for PEO in water and PIB in kerosene systems using the rotating disk apparatus (RDA). However, due to the thermal instability and molecular degradation of drag reducing polymers, it is necessary to select alternative drag reducers. The possible formation of a polymer-surfactant complex takes on the character of a polyelectrolyte and it is shown that such polymer-surfactant complexes may have enhanced drag reduction properties based on the investigation of the turbulent pipe flow properties of high molecular weight PEO in SDS solution. In this study, we discuss details of conformation transitions of PEO molecules depending on external conditions such as pH, SDS and shear rate by adding the surfactant (Sodium dodecyl sulfate SDS, C{sub 12}H{sub 25}O{sub 4}SNa, (Fw:288.4) from Sigma Co. was used as a surfactant) and the PAA molecules. We also investigate modes of intermolecular interactions of both non-ionic and ionic polymers with surfactant and, finally, the polymer-surfactant complex under turbulent flow in an RDA.

  18. Drag Reduction Through Distributed Electric Propulsion

    NASA Technical Reports Server (NTRS)

    Stoll, Alex M.; Bevirt, JoeBen; Moore, Mark D.; Fredericks, William J.; Borer, Nicholas K.

    2014-01-01

    One promising application of recent advances in electric aircraft propulsion technologies is a blown wing realized through the placement of a number of electric motors driving individual tractor propellers spaced along each wing. This configuration increases the maximum lift coefficient by providing substantially increased dynamic pressure across the wing at low speeds. This allows for a wing sized near the ideal area for maximum range at cruise conditions, imparting the cruise drag and ride quality benefits of this smaller wing size without decreasing takeoff and landing performance. A reference four-seat general aviation aircraft was chosen as an exemplary application case. Idealized momentum theory relations were derived to investigate tradeoffs in various design variables. Navier-Stokes aeropropulsive simulations were performed with various wing and propeller configurations at takeoff and landing conditions to provide insight into the effect of different wing and propeller designs on the realizable effective maximum lift coefficient. Similar analyses were performed at the cruise condition to ensure that drag targets are attainable. Results indicate that this configuration shows great promise to drastically improve the efficiency of small aircraft.

  19. An investigation of drag reduction on box-shaped ground vehicles

    NASA Technical Reports Server (NTRS)

    Muirhead, V. U.

    1976-01-01

    A wind tunnel investigation was conducted to determine the reduction in drag which could be obtained by making various configuration changes to a box-shaped ground vehicle. Tests were conducted at yaw (relative wind) angles of 0, 5, 10, 20, and 30 degrees and Reynolds numbers of 300,000 to 850,000. The power required to overcome the aerodynamic drag was reduced by a maximum of 73% for a head wind for the best configuration relative to the smooth bottom box-shape, or 75% relative to the rough bottom box-shape. The reduction for a 20 MPH wind at 30 deg to the vehicle path was, respectively, 77% and 79%.

  20. Numerical investigation of drag and heat reduction in hypersonic spiked blunt bodies

    NASA Astrophysics Data System (ADS)

    Tahani, M.; Karimi, M. S.; Motlagh, A. Mahmoudi; Mirmahdian, S.

    2013-10-01

    In this investigation, the effects of spike as retractable drag and aerodynamic heating reduction into the reentry Earth's atmosphere for hemispherical body flying at hypersonic flow have been numerically studied. This numerical solution has been carried out for different length, shapes and nose configuration of spike. Additional modifications to the tip of the spike are investigated in order to obtain different bow shocks, including no spike, conical, flat and hemispherical aerodisk mounted. Unsteady compressible 3-D Navier-Stokes equations are solved with k - ω (SST) turbulence model for a flow over a forward facing spike attached to a heat shield for a free stream Mach number of 6. The obtained numerical results are compared with the experimental ones, and the results shows acceptable verification. This analysis shows that the aerodisk is more effective than aerospike. The designs produced 60 and 15 % reduction in drag and wall temperature responses, respectively.

  1. Drag reduction of boat-tailed bluff bodies through transverse grooves. Part I: experiments

    NASA Astrophysics Data System (ADS)

    Mariotti, Alessandro; Buresti, Guido; Salvetti, Maria Vittoria

    2016-11-01

    The reduction of the aerodynamic drag of elongated axisymmetric bluff bodies is interesting for several applications. One well-known method to reduce the drag of this type of body is a geometrical modification called boat-tailing, consisting in a gradual reduction of the body cross-section before a sharp-edged base. We combine boat-tailing with properly contoured transverse grooves to further delay boundary-layer separation and reduce drag. The considered geometry is axisymmetric with an elliptical forebody and a cylindrical main body followed by a circular-arc boat-tail. The effectiveness of the contoured grooves was assessed through experiments and simulations. In this talk the experimental investigation is presented. Pressure measurements show that the introduction of a single transverse groove leads to a significant increase of the pressure on the body base and, consequently, to a reduction of drag compared with the boat-tail without the groove. Velocity measurements and flow visualizations highlight that this is due to a delay of flow separation over the boat tail. A steady local recirculation is present inside the groove and downstream its reattachment the boundary layer is thinner and has higher momentum than in the case with no groove, allowing separation to be delayed.

  2. September 2002 Working Group Meeting on Heavy Vehicle Aerodynamic Drag: Presentations and Summary of Comments and Conclusions

    SciTech Connect

    McCallen, R

    2002-09-01

    discussed the reorganization of the Office of Energy Efficiency and Renewable Energy and that the Office of Heavy Vehicle Technology is now part of the Office of FreedomCAR & Vehicle Technologies. Sid reviewed the FY03 budget and provided information on some plans for FY04. The soon to be posted DOE request for proposals from industry for projects related to parasitic energy losses was discussed. A minimum of 50% cost share by industry will be required and the proposal must be submitted by industry. Collaborative efforts in aerodynamic drag with members of the DOE consortium are encouraged. Sid also mentioned interest in aerodynamic drag contribution due to wheel wells and underbody flow. Sid also mentioned his continued interest in the application of our computational and experimental expertise to the area of locomotive and railcar aerodynamics for the reduction of drag effects and thus, the reduction of fuel consumption by trains. In summary, the technical presentations at the meeting included a review of experimental results and plans by GTRI, USC, and NASA Ames, the computational results from LLNL and SNL for the integrated tractor-trailer benchmark geometry called the Ground Transportation System (GTS) model, and by LLNL for the tractor-trailer gap and trailer wake flow, and turbulence model development and benchmark simulations being investigated by Caltech. USC is also investigating an acoustic drag reduction device that has been named ''Mozart'', GTRI continues their investigation of a blowing device, and LLNL presented their ideas for 2 new base drag reduction devices. ANL presented their plans for a DOE supported Cooperative Research and Development Agreement (CRADA) with Paccar Truck Company utilizing commercial software tools to simulate the flow and drag for an actual tractor and showed the results of some preliminary griding attempts. The attendees also had the opportunity to tour the 12-ft pressure wind tunnel the machine shop were the Generic Conventional

  3. Boundary-layer control for drag reduction

    NASA Technical Reports Server (NTRS)

    Harvey, William D.

    1988-01-01

    Although the number of possible applications of boundary-layer control is large, a discussion is given only of those that have received the most attention recently at NASA Langley Research Center to improve airfoil drag characteristics. This research concerns stabilizing the laminar boundary layer through geometric shaping (natural laminar flow, NLF) and active control involving the removal of a portion of the laminar boundary layer (laminar flow control, LFC) either through discrete slots or a perforated surface. At low Reynolds numbers, a combination of shaping and forced transition has been used to achieve the desired run of laminar flow and control of laminar separation. In the design of both natural laminar flow and laminar flow control airfoils and wings, boundary layer stability codes play an important role. A discussion of some recent stability calculations using both incompressible and compressible codes is given.

  4. Progress in reducing aerodynamic drag for higher efficiency of heavy duty trucks (class 7-8)

    SciTech Connect

    Brady, M; Browand, F; Hammache, M; Heineck, J T; Leonard, A; McCallen, R; Ross, J; Rutledge, W; Salari, K; Storms, B

    1999-04-01

    This paper describes research and development for reducing the aerodynamic drag of heavy vehicles by demonstrating new approaches for the numerical simulation and analysis of aerodynamic flow. In addition, greater use of newly developed computational tools holds promise for reducing the number of prototype tests, for cutting manufacturing costs, and for reducing overall time to market. Experimental verification and validation of new computational fluid dynamics methods are also an important part of this approach. Experiments on a model of an integrated tractor-trailer are underway at NASA Ames Research Center and the University of Southern California. Companion computer simulations are being performed by Sandia National Laboratories, Lawrence Livermore National Laboratory, and California Institute of Technology using state-of-the-art techniques, with the intention of implementing more complex methods in the future.

  5. Progress in Reducing Aerodynamic Drag for Higher Efficiency of Heavy Duty Trucks (Class 7-8)

    SciTech Connect

    Rose McCallen; Richard Couch; Juliana Hsu; Fred Browand; Mustapha Hammache; Anthony Leonard; Mark Brady; Kambiz Salari; Walter Rutledge; James Ross; Bruce Storms; J.T. Heineck; David Driver; James Bell; Gregory Zilliac

    1999-12-31

    This paper describes research and development for reducing the aerodynamic drag of heavy vehicles by demonstrating new approaches for the numerical simulation and analysis of aerodynamic flow. In addition, greater use of newly developed computational tools holds promise for reducing the number of prototype tests, for cutting manufacturing costs, and for reducing overall time to market. Experimental verification and validation of new computational fluid dynamics methods are also an important part of this approach. Experiments on a model of an integrated tractor-trailer are underway at NASA Ames Research Center and the University of Southern California. Companion computer simulations are being performed by Sandia National Laboratories, Lawrence Livermore National Laboratory, and California Institute of Technology using state-of-the-art techniques, with the intention of implementing more complex methods in the future.

  6. Systematic approach to analyzing and reducing aerodynamic drag of heavy vehicles

    SciTech Connect

    McCallen, R.; Browand, F.; Leonard, A.; Rutledge, W.

    1997-09-16

    This paper presents an approach for reducing aerodynamic drag of heavy vehicles by systematically analyzing trailer components using existing computational tools and moving on to the analyses of integrated tractor-trailers using advanced computational tools. Experimental verification and validation are also an important part of this approach. The project is currently in the development phase while we are in the process of constructing a Multi-Year Program Plan. Projects I and 2 as described in this paper are the anticipated project direction. Also included are results from past and current related activities by the project participants which demonstrate the analysis approach.

  7. Wind-tunnel studies of advanced cargo aircraft concepts. [leading edge vortex flaps for drag reduction

    NASA Technical Reports Server (NTRS)

    Rao, D. M.; Goglia, G. L.

    1981-01-01

    Accomplishments in vortex flap research are summarized. A singular feature of the vortex flap is that, throughout the range of angle of attack range, the flow type remains qualitatively unchanged. Accordingly, no large or sudden change in the aerodynamic characteristics, as happens when forcibly maintained attached flow suddenly reverts to separation, will occur with the vortex flap. Typical wind tunnel test data are presented which show the drag reduction potential of the vortex flap concept applied to a supersonic cruise airplane configuration. The new technology offers a means of aerodynamically augmenting roll-control effectiveness on slender wings at higher angles of attack by manipulating the vortex flow generated from leading edge separation. The proposed manipulator takes the form of a flap hinged at or close to the leading edge, normally retracted flush with the wing upper surface to conform to the airfoil shape.

  8. Numerical studies of laminar and turbulent drag reduction

    NASA Technical Reports Server (NTRS)

    Balasubramanian, R.; Orszag, S. A.

    1981-01-01

    Two-dimensional incompressible flow over wavy surfaces is studied numerically by spectral methods. Turbulence effects are modeled. Results for symmetric and asymmetric wave forms are presented. Effect of propagating surface waves on drag reduction is studied. Comparisons between computer simulations and experimental results are made.

  9. Flexible conformable hydrophobized surfaces for turbulent flow drag reduction

    PubMed Central

    Brennan, Joseph C; Geraldi, Nicasio R; Morris, Robert H; Fairhurst, David J; McHale, Glen; Newton, Michael I

    2015-01-01

    In recent years extensive work has been focused onto using superhydrophobic surfaces for drag reduction applications. Superhydrophobic surfaces retain a gas layer, called a plastron, when submerged underwater in the Cassie-Baxter state with water in contact with the tops of surface roughness features. In this state the plastron allows slip to occur across the surface which results in a drag reduction. In this work we report flexible and relatively large area superhydrophobic surfaces produced using two different methods: Large roughness features were created by electrodeposition on copper meshes; Small roughness features were created by embedding carbon nanoparticles (soot) into Polydimethylsiloxane (PDMS). Both samples were made into cylinders with a diameter under 12 mm. To characterize the samples, scanning electron microscope (SEM) images and confocal microscope images were taken. The confocal microscope images were taken with each sample submerged in water to show the extent of the plastron. The hydrophobized electrodeposited copper mesh cylinders showed drag reductions of up to 32% when comparing the superhydrophobic state with a wetted out state. The soot covered cylinders achieved a 30% drag reduction when comparing the superhydrophobic state to a plain cylinder. These results were obtained for turbulent flows with Reynolds numbers 10,000 to 32,500. PMID:25975704

  10. Assessment of dual-point drag reduction for an executive-jet modified airfoil section

    NASA Technical Reports Server (NTRS)

    Allison, Dennis O.; Mineck, Raymond E.

    1996-01-01

    This paper presents aerodynamic characteristics and pressure distributions for an executive-jet modified airfoil and discusses drag reduction relative to a baseline airfoil for two cruise design points. A modified airfoil was tested in the adaptive-wall test section of the NASA Langley 0.3-Meter Transonic Cryogenic Tunnel (0.3-m TCT) for Mach numbers ranging from 0.250 to 0.780 and chord Reynolds numbers ranging from 3.0 x 10(exp 6) to 18.0 x 10(exp 6). The angle of attack was varied from minus 2 degrees to almost 10 degrees. Boundary-layer transition was fixed at 5 percent of chord on both the upper and lower surfaces of the model for most of the test. The two design Mach numbers were 0.654 and 0.735, chord Reynolds numbers were 4.5 x 10(exp 6) and 8.9 x 10(exp 6), and normal-force coefficients were 0.98 and 0.51. Test data are presented graphically as integrated force and moment coefficients and chordwise pressure distributions. The maximum normal-force coefficient decreases with increasing Mach number. At a constant normal-force coefficient in the linear region, as Mach number increases an increase occurs in the slope of normal-force coefficient versus angle of attack, negative pitching-moment coefficient, and drag coefficient. With increasing Reynolds number at a constant normal-force coefficient, the pitching-moment coefficient becomes more negative and the drag coefficient decreases. The pressure distributions reveal that when present, separation begins at the trailing edge as angle of attack is increased. The modified airfoil, which is designed with pitching moment and geometric constraints relative to the baseline airfoil, achieved drag reductions for both design points (12 and 22 counts). The drag reductions are associated with stronger suction pressures in the first 10 percent of the upper surface and weakened shock waves.

  11. Superhydrophobic drag reduction in laminar flows: a critical review

    NASA Astrophysics Data System (ADS)

    Lee, Choongyeop; Choi, Chang-Hwan; Kim, Chang-Jin

    2016-12-01

    A gas in between micro- or nanostructures on a submerged superhydrophobic (SHPo) surface allows the liquid on the structures to flow with an effective slip. If large enough, this slippage may entail a drag reduction appreciable for many flow systems. However, the large discrepancies among the slippage levels reported in the literature have led to a widespread misunderstanding on the drag-reducing ability of SHPo surfaces. Today we know that the amount of slip, generally quantified with a slip length, is mainly determined by the structural features of SHPo surfaces, such as the pitch, solid fraction, and pattern type, and further affected by secondary factors, such as the state of the liquid-gas interface. Reviewing the experimental data of laminar flows in the literature comprehensively and comparing them with the theoretical predictions, we provide a global picture of the liquid slip on structured surfaces to assist in rational design of SHPo surfaces for drag reduction. Because the trapped gas, called plastron, vanishes along with its slippage effect in most application conditions, lastly we discuss the recent efforts to prevent its loss. This review is limited to laminar flows, for which the SHPo drag reduction is reasonably well understood.

  12. NASA aerodynamics program

    NASA Technical Reports Server (NTRS)

    Holmes, Bruce J.; Schairer, Edward; Hicks, Gary; Wander, Stephen; Blankson, Isiaiah; Rose, Raymond; Olson, Lawrence; Unger, George

    1990-01-01

    Presented here is a comprehensive review of the following aerodynamics elements: computational methods and applications, computational fluid dynamics (CFD) validation, transition and turbulence physics, numerical aerodynamic simulation, drag reduction, test techniques and instrumentation, configuration aerodynamics, aeroacoustics, aerothermodynamics, hypersonics, subsonic transport/commuter aviation, fighter/attack aircraft and rotorcraft.

  13. Inlet Aerodynamics and Ram Drag of Laser-Propelled Lightcraft Vehicles

    NASA Astrophysics Data System (ADS)

    Langener, Tobias; Myrabo, Leik; Rusak, Zvi

    2010-05-01

    Numerical simulations are used to study the aerodynamic inlet properties of three axisymmetric configurations of laser-propelled Lightcraft vehicles operating at subsonic, transonic and supersonic speeds up to Mach 5. The 60 cm vehicles were sized for launching 0.1-1.0 kg nanosatellites with combined-cycle airbreathing/rocket engines, transitioning between propulsion modes at roughly Mach 5-6. Results provide the pressure, temperature, density, and velocity flowfields around and through the three representative vehicle/engine configurations, as well as giving the resulting ram drag and total drag coefficients—all as a function of flight Mach number. Simulations with rotating boundaries were also carried out, since for stability reasons, Lightcraft are normally spun up before lift-off. Given the three alternatives, it is demonstrated that the optimal geometry for minimum drag is the configuration with a parabola nose; hence, these inlet flow conditions are being applied in subsequent "direct connect" 2D laser propulsion experiments in a small transonic flow facility.

  14. A Preliminary Flight Investigation of Formation Flight for Drag Reduction on the C-17 Aircraft

    NASA Technical Reports Server (NTRS)

    Pahle, Joe; Berger, Dave; Venti, Michael W.; Faber, James J.; Duggan, Chris; Cardinal, Kyle

    2012-01-01

    Many theoretical and experimental studies have shown that aircraft flying in formation could experience significant reductions in fuel use compared to solo flight. To date, formation flight for aerodynamic benefit has not been thoroughly explored in flight for large transport-class vehicles. This paper summarizes flight data gathered during several two ship, C-17 formation flights at a single flight condition of 275 knots, at 25,000 ft MSL. Stabilized test points were flown with the trail aircraft at 1,000 and 3,000 ft aft of the lead aircraft at selected crosstrack and vertical offset locations within the estimated area of influence of the vortex generated by the lead aircraft. Flight data recorded at test points within the vortex from the lead aircraft are compared to data recorded at tare flight test points outside of the influence of the vortex. Since drag was not measured directly, reductions in fuel flow and thrust for level flight are used as a proxy for drag reduction. Estimated thrust and measured fuel flow reductions were documented at several trail test point locations within the area of influence of the leads vortex. The maximum average fuel flow reduction was approximately 7-8%, compared to the tare points flown before and after the test points. Although incomplete, the data suggests that regions with fuel flow and thrust reduction greater than 10% compared to the tare test points exist within the vortex area of influence.

  15. Prediction of Drag Reduction in Supersonic and Hypersonic Flows with Counterflow Jets

    NASA Technical Reports Server (NTRS)

    Daso, Endwell O.; Beaulieu, Warren; Hager, James O.; Turner, James E. (Technical Monitor)

    2002-01-01

    Computational fluid dynamics solutions of the flowfield of a truncated cone-cylinder with and without counterflow jets have been obtained for the short penetration mode (SPM) and long penetration mode (LPM) of the freestream-counterflow jet interaction flowfield. For the case without the counterflow jet, the comparison of the normalized surface pressures showed very good agreement with experimental data. For the case with the SPM jet, the predicted surface pressures did not compare as well with the experimental data upstream of the expansion corner, while aft of the expansion corner, the comparison of the solution and the data is seen to give much better agreement. The difference in the prediction and the data could be due to the transient character of the jet penetration modes, possible effects of the plasma physics that are not accounted for here, or even the less likely effect of flow turbulence, etc. For the LPM jet computations, one-dimensional isentropic relations were used to derived the jet exit conditions in order to obtain the LPM solutions. The solution for the jet exit Mach number of 3 shows a jet penetration several times longer than that of the SPM, and therefore much weaker bow shock, with an attendant reduction in wave drag. The LPM jet is, in essence, seen to be a "pencil" of fluid, with much higher dynamic pressure, embedded in the oncoming supersonic or hypersonic freestream. The methodology for determining the conditions for the LPM jet could enable a practical approach for the design and application of counterflow LPM jets for the reduction of wave drag and heat flux, thus significantly enhancing the aerodynamic characteristics and aerothermal performance of supersonic and hypersonic vehicles. The solutions show that the qualitative flow structure is very well captured. The obtained results, therefore, suggest that counterflowing jets are viable candidate technology concepts that can be employed to give significant reductions in wave drag, heat

  16. Reduction of aqueous fluid drag with poly(vinylamine)

    SciTech Connect

    McAndrew, T.P.; Miller, S.

    1993-12-31

    During the past several years, Air Products and Chemicals, Inc. has developed technology to prepare a family of water-soluble polymers containing primary amine functionality. Heretofore, such amine functional polymers (AFP`s) had been commercially unavailable. One of these AFP`s poly(vinylamine) (PVAm) has been examined as a drag reducing agent for aqueous solutions. Specifically, a protonated derivative of PVAm, PVAm-HCl (Mw: 0.8 million, excluding HCl) shows outstanding performance in comparison to well-established drag reducing polymers such as poly(ethylene oxide) and poly(acrylamide). The level of drag reduction is far above that expected based upon Mw and resistance to degradation is superior to any polymer examined. Both phenomena are explained in terms of PVAm-HCl having a high intrinsic viscosity and a relatively linear form in solution. Because of the excellent performance at low Mw and superior stability, commercial use of PVAm-HCl (and potentially other AFP`s) in aqueous fluid drag reduction may be possible.

  17. Working Group Meeting on Heavy Vehicle Aerodynamic Drag: Presentations and Summary of Comments and Conclusions

    SciTech Connect

    Browand, F; Gutierrez, W; Leonard, A; McBride, D; McCallen, R; Ross, J; Roth, K; Rutledge, W; Salari, K

    1998-09-28

    The first Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held at Sandia National Laboratories (SNL) in Albuquerque, New Mexico on August 28, 1998. The purpose of the meeting was to review the proposed Multi-Year Program Plan (MYPP) and provide an update on the Group"s progress. In addition, the technical details of each organization"s activities were presented and discussed. Presentations were given by representatives from the Department of Energy (DOE) Office of Transportation Technology Office of Heavy Vehicle Technology (OHVT), Lawrence Livermore National Laboratory (LLNL), SNL, University of Southern California (USC), California Institute of Technology (Caltech), and NASA Ames Research Center. These presenters are part of a DOE appointed Technical Team assigned to developing the MYPP. The goal of the MYPP is to develop and demonstrate the ability to simulate and analyze aerodynamic flow around heavy truck vehicles using existing and advanced computational tools (A Multi-Year Program Plan for the Aerodynamic Design of Heavy Vehicles, R. McCallen, D. McBride, W. Rutledge, F. Browand, A. Leonard, .I. Ross, UCRL-PROP- 127753 Dr. Rev 2, May 1998). This report contains the technical presentations (viewgraphs) delivered at the Meeting, briefly summarizes the comments and conclusions from the Meeting participants, and outlines the future action items.

  18. Aerodynamic resistance reduction of electric and hybrid vehicles

    NASA Technical Reports Server (NTRS)

    1979-01-01

    The generation of an EHV aerodynamic data base was initiated by conducting full-scale wind tunnel tests on 16 vehicles. Zero-yaw drag coefficients ranged from a high of 0.58 for a boxey delivery van and an open roadster to a low of about 0.34 for a current 4-passenger prototype automobile which was designed with aerodynamics as an integrated parameter. Characteristic effects of aspect ratio or fineness ratio which might appear if electric vehicle shape proportions were to vary significantly from current automobiles were identified. Some preliminary results indicate a 5 to 10% variation in drag over the range of interest. Effective drag coefficient wind-weighting factors over J227a driving cycles in the presence of annual mean wind fields were identified. Such coefficients, when properly weighted, were found to be from 5 to 65% greater than the zero-yaw drag coefficient in the cases presented. A vehicle aerodynamics bibliography of over 160 entries, in six general categories is included.

  19. Analytic investigation of advancing blade drag reduction by tip modifications

    NASA Technical Reports Server (NTRS)

    Tauber, M. E.

    1978-01-01

    Analytic techniques were applied to study the effect on the performance of the nonlifting advancing blade when the outboard 5% of the blade is modified to reduce drag. The tip modifications studied consisted of reducing airfoil thickness, sweepback, and planform taper. The reductions in instantaneous drag and torque were calculated for tip speed ratios from about 0.19 to 0.30, corresponding to advancing blade tip Mach numbers of 0.855 to 0.936, respectively. Approximations required in the analysis introduce uncertainties into the computed absolute values of drag and torque; however, the differences in the quantities should be a fairly reliable measure of the effect of changing tip geometry. For example, at the highest tip speed, instantaneous drag, and torque were reduced by 20% and 24%, respectively, for tip sweep of 40 deg on a blade using an NACA 0010 airfoil and by comparable amounts for 30-deg sweep on a blade having an NACA 0012 airfoil section. The present method should prove to be a useful, inexpensive technique for identifying promising configurations for additional study and testing.

  20. Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity.

    PubMed

    Bhushan, Bharat

    2011-01-01

    The emerging field of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common in nature and possess properties of interest. There are a large number of objects including bacteria, plants, land and aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such as lotus (Nelumbo nucifera) leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical surface roughness and presence of a wax layer. In addition to a self-cleaning effect, these surfaces with a high contact angle and low contact angle hysteresis also exhibit low adhesion and drag reduction for fluid flow. An aquatic animal, such as a shark, is another model from nature for the reduction of drag in fluid flow. The artificial surfaces inspired from the shark skin and lotus leaf have been created, and in this article the influence of structure on drag reduction efficiency is reviewed. Biomimetic-inspired oleophobic surfaces can be used to prevent contamination of the underwater parts of ships by biological and organic contaminants, including oil. The article also reviews the wetting behavior of oil droplets on various superoleophobic surfaces created in the lab.

  1. Drag reduction: enticing turbulence, and then an industry.

    PubMed

    Spalart, Philippe R; McLean, J Douglas

    2011-04-13

    We examine drag-reduction proposals, as presented in this volume and in general, first with concrete examples of how to bridge the distance from pure science through engineering to what makes inventions go into service; namely, the value to the public. We point out that the true drag reduction can be markedly different from an estimate based simply on the difference between turbulent and laminar skin friction over the laminarized region, or between the respective skin frictions of the baseline and the riblet-treated flow. In some situations, this difference is favourable, and is due to secondary differences in pressure drag. We reiterate that the benefit of riblets, if it is expressed as a percentage in skin-friction reduction, is unfortunately lower at full-size Reynolds numbers than in a small-scale experiment or simulation. The Reynolds number-independent measure of such benefits is a shift of the logarithmic law, or 'ΔU(+)'. Anticipating the design of a flight test and then a product, we note the relative ease in representing riblets or laminarization in computational fluid dynamics, in contrast with the huge numerical and turbulence-modelling challenge of resolving active flow control systems in a calculation of the full flow field. We discuss in general terms the practical factors that have limited applications of concepts that would appear more than ready after all these years, particularly riblets and laminar-flow control.

  2. Biomimetics inspired surfaces for drag reduction and oleophobicity/philicity

    PubMed Central

    2011-01-01

    Summary The emerging field of biomimetics allows one to mimic biology or nature to develop nanomaterials, nanodevices, and processes which provide desirable properties. Hierarchical structures with dimensions of features ranging from the macroscale to the nanoscale are extremely common in nature and possess properties of interest. There are a large number of objects including bacteria, plants, land and aquatic animals, and seashells with properties of commercial interest. Certain plant leaves, such as lotus (Nelumbo nucifera) leaves, are known to be superhydrophobic and self-cleaning due to the hierarchical surface roughness and presence of a wax layer. In addition to a self-cleaning effect, these surfaces with a high contact angle and low contact angle hysteresis also exhibit low adhesion and drag reduction for fluid flow. An aquatic animal, such as a shark, is another model from nature for the reduction of drag in fluid flow. The artificial surfaces inspired from the shark skin and lotus leaf have been created, and in this article the influence of structure on drag reduction efficiency is reviewed. Biomimetic-inspired oleophobic surfaces can be used to prevent contamination of the underwater parts of ships by biological and organic contaminants, including oil. The article also reviews the wetting behavior of oil droplets on various superoleophobic surfaces created in the lab. PMID:21977417

  3. Determination of aerodynamic stability and drag of the Titan 3 C SRM during entry

    NASA Technical Reports Server (NTRS)

    Ramsey, P. E.

    1974-01-01

    An experimental aerodynamic investigation was conducted in the NASA/MSFC 14-inch Trisonic Wind Tunnel on a 0.00736 scale model of Titan 3 C Solid Rocket Motor (SRM). Static stability and drag data were obtained for Mach numbers of 0.6 to 4.96, angles of attack of minus 10 deg to 190 deg, and roll angles of 0 to 360 deg. The resulting data will be used to predict the dynamic motions of the SRM during entry which will then be compared to flight data. This comparison will improve and lend credibility to methods for predicting the entry dynamics of the space shuttle Solid Rocket Booster (SRB), which is needed for recovery studies and design of the parachute recovery system.

  4. Hydrodynamic and Aerodynamic Tests of Models of Flying-boat Hulls Designed Flow Aerodynamic Drag - NACA Models 74, 74-A, and 75

    NASA Technical Reports Server (NTRS)

    Truscott, Starr; Parkinson, J B; Ebert, John W , Jr; Valentine, E Floyd

    1938-01-01

    The present tests illustrate how the aerodynamic drag of a flying boat hull may be reduced by following closely the form of a low drag aerodynamic body and the manner in which the extent of the aerodynamic refinement is limited by poorer hydrodynamic performance. This limit is not sharply defined but is first evidenced by an abnormal flow of water over certain parts of the form accompanied by a sharp increase in resistance. In the case of models 74-A and 75, the resistance (sticking) occurs only at certain combinations of speed, load, and trim and can be avoided by proper control of the trim at high water speeds. Model 75 has higher water resistance at very high speeds than does model 74-A. With constant speed propellers and high takeoff speeds, it appears that the form of model 75 would give slightly better takeoff performance. Model 74-A, however, has lower aerodynamic drag than does model 75 for the same volume of hull.

  5. Investigation of an Oscillating Surface Plasma for Turbulent Drag Reduction

    NASA Technical Reports Server (NTRS)

    Wilkinson, Stephen P.

    2003-01-01

    An oscillating, weakly ionized surface plasma has been investigated for use in turbulent boundary layer viscous drag reduction. The study was based on reports showing that mechanical spanwise oscillations of a wall can reduce viscous drag due to a turbulent boundary layer by up to 40%. It was hypothesized that the plasma induced body force in high electric field gradients of a surface plasma along strip electrodes could also be configured to oscillate the flow. Thin dielectric panels with millimeter-scale, flush- mounted, triad electrode arrays with one and two-phase high voltage excitation were tested. Results showed that while a small oscillation could be obtained, the effect was lost at a low frequency (less than 100Hz). Furthermore, a mean flow was generated during the oscillation that complicates the effect. Hot-wire and pitot probe diagnostics are presented along with phase-averaged images revealing plasma structure.

  6. Mechanically Robust Superhydrophobic Surfaces for Turbulent Drag Reduction

    NASA Astrophysics Data System (ADS)

    Golovin, Kevin; Boban, Mathew; Xia, Charlotte; Tuteja, Anish

    2014-11-01

    Superhydrophobic surfaces (SHS) resist wetting by keeping a thin air layer within their texture. Such surfaces have been shown to reduce skin friction during laminar and transitional flows. However, turbulent boundary layer flows exhibit high shear stresses that damage the fragile microstructure of most SHS, and it is yet unclear to what extent these surfaces can reduce drag. Moreover, the increasing pressure fluctuations and decreasing wall unit length experienced during turbulent flow makes designing mechanically robust SHS with the correct roughness scales a challenge. In this work we evaluate many different SHS in terms of their hydrophobicity, mechanical durability and roughness. Whereas even commercially available SHS lose their superhydrophobic properties after slight mechanical abrasion, our novel coatings survive up to 200x longer. Moreover, we evaluate how the roughness of such surfaces changes with mechanical abrasion, and we design SHS with the correct roughness to display optimal drag reduction in turbulent boundary layer flows. Funding from ONR.

  7. Investigation of the Aerodynamic Drag of an Eight-Channel Centrifugal Filter

    NASA Astrophysics Data System (ADS)

    Serebryanskii, D. A.; Semenyuk, N. S.; Plashikhin, S. V.

    2015-03-01

    The aerodynamic characteristics and the structure of vortices of the central region of the channel system of an eight-channel centrifugal filter have been investigated. An overview of the foreign and home literature on the filtration of solid particles in the gas flow in centrifugal apparatuses is given [1, 2]. We present the design and the principle of operation of the eight-channel centrifugal filter based on a system of curvilinear channels with equal turn angles and equal cross-sectional areas connected in series. We have performed numerical calculations of the dependence of the aerodynamic drag of the centrifugal filter on the rate of fl ow obtained by three different methods: analytical calculation, experiments on the laboratory facility, and with the help of modern means of computer modeling. Computational modeling of the flow was carried out by solving Reynolds (RANS, Reynolds-averaged Navier-Stokes) equations by the SFD method with the use of a k-ɛ model of turbulence for three modes of operation of the apparatus. The results of computer modeling permitted visualizing the vortex structure of the central region of the separation chamber in the form of 3D graphs. The obtained results have been confirmed experimentally on a laboratory model of the centrifugal filter of capacity up to 200 m3/h of purified air.

  8. May 2005 Working Group Meeting on Heavy Vehicle Aerodynamic Drag: Presentation, Summary of Comments and Conclusions

    SciTech Connect

    McCallen, R C

    2005-08-17

    A Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held at Lawrence Livermore National Laboratory, Livermore, California on May 12th and 13th of 2005. The purpose of the first day's meeting, May 12th, was to provide a summary of achievements, discuss issues, present a general overview of future plans, and to offer a forum for dialogue with the Department of Energy (DOE) and representatives from industry, universities, and research and development organizations performing work related to heavy vehicle aerodynamics. This first meeting day was open to participants from industry and research organizations from both the US and Canada. The second day, May 13th, was attended only by representatives from the 9 organizations that form the DOE Consortium effort and their government sponsors. The purpose of the second day's meeting was to further discuss fiscal year 2005's activities, any further specific pressing issues, identify individual action items, and provide an overview of plans for fiscal year 2006. Based on discussions at the Meeting, the existing project goals remain unchanged and enhancing interactions with fleet owners and operators was emphasized: (1) Perform heavy vehicle computations and experiments, (2) Validate computations using experimental data, (3) Provide design guidance and insight into flow phenomena from experiments and computations, and (4) Investigate aero devices with emphasis on collaborative efforts with fleet owners and operators.

  9. Wind-Tunnel Investigations of Blunt-Body Drag Reduction Using Forebody Surface Roughness

    NASA Technical Reports Server (NTRS)

    Whitmore, Stephen A.; Sprague, Stephanie; Naughton, Jonathan W.; Curry, Robert E. (Technical Monitor)

    2001-01-01

    This paper presents results of wind-tunnel tests that demonstrate a novel drag reduction technique for blunt-based vehicles. For these tests, the forebody roughness of a blunt-based model was modified using micomachined surface overlays. As forebody roughness increases, boundary layer at the model aft thickens and reduces the shearing effect of external flow on the separated flow behind the base region, resulting in reduced base drag. For vehicle configurations with large base drag, existing data predict that a small increment in forebody friction drag will result in a relatively large decrease in base drag. If the added increment in forebody skin drag is optimized with respect to base drag, reducing the total drag of the configuration is possible. The wind-tunnel tests results conclusively demonstrate the existence of a forebody dragbase drag optimal point. The data demonstrate that the base drag coefficient corresponding to the drag minimum lies between 0.225 and 0.275, referenced to the base area. Most importantly, the data show a drag reduction of approximately 15% when the drag optimum is reached. When this drag reduction is scaled to the X-33 base area, drag savings approaching 45,000 N (10,000 lbf) can be realized.

  10. Drag reduction of nata de coco suspensions in circular pipe flow

    NASA Astrophysics Data System (ADS)

    Warashina, J.; Ogata, S.

    2015-04-01

    Reducing pipe friction by adding a drag-reducing agent has attracted interest as a means to reduce energy consumption. In addition to reducing drag, these agents are required to have a low environmental load and conserve natural resources. However, no drag-reducing agent currently satisfies both these conditions. We focused on nata de coco and found that the nata de coco fiber reduced drag by up to 25%. With respect to the mechanism of drag reduction by nata de coco fiber, the relationship between drag-reduction phenomena and the fiber form of nata de coco was investigated by visualization. We also found that the drag-reduction effect appeared to be due to the formation of networks of tangled fibers of nata de coco. However, drag reduction did not occur in the case in which fibers of nata de coco did not form networks.

  11. Studies of compressible shear flows and turbulent drag reduction

    NASA Technical Reports Server (NTRS)

    Orszag, S. A.

    1981-01-01

    Compressible shear flows and drag reduction were examined and three methods are addressed: (1) the analytical and numerical aspects of conformal mapping were summarized and a new method for computation of these maps is presented; (2) the computer code SPECFD for solution of the three dimensional time dependent Navier-Stokes equations for compressible flow on the CYBER 203 computer is described; (3) results of two equation turbulence modeling of turbulent flow over wavy walls are presented. A modified Jones-Launder model is used in two dimensional spectral code for flow in general wavy geometries.

  12. Bioinspired air-retaining nanofur for drag reduction.

    PubMed

    Kavalenka, Maryna N; Vüllers, Felix; Lischker, Simone; Zeiger, Claudia; Hopf, Andreas; Röhrig, Michael; Rapp, Bastian E; Worgull, Matthias; Hölscher, Hendrik

    2015-05-27

    Bioinspired nanofur, covered by a dense layer of randomly distributed high aspect ratio nano- and microhairs, possesses superhydrophobic and air-retaining properties. Nanofur is fabricated using a highly scalable hot pulling method in which softened polymer is elongated with a heated sandblasted plate. Here we investigate the stability of the underwater air layer retained by the irregular nanofur topography by applying hydraulic pressure to the nanofur kept underwater, and evaluate the gradual changes in the air-covered area. Furthermore, the drag reduction resulting from the nanofur air retention is characterized by measuring the pressure drop across channels with and without nanofur.

  13. Studies of compressible shear flows and turbulent drag reduction

    NASA Astrophysics Data System (ADS)

    Orszag, S. A.

    1981-04-01

    Compressible shear flows and drag reduction were examined and three methods are addressed: (1) the analytical and numerical aspects of conformal mapping were summarized and a new method for computation of these maps is presented; (2) the computer code SPECFD for solution of the three dimensional time dependent Navier-Stokes equations for compressible flow on the CYBER 203 computer is described; (3) results of two equation turbulence modeling of turbulent flow over wavy walls are presented. A modified Jones-Launder model is used in two dimensional spectral code for flow in general wavy geometries.

  14. Turbulent drag reduction with liquid-infused surfaces

    NASA Astrophysics Data System (ADS)

    Smits, Alexander; van Buren, Tyler

    2016-11-01

    We present turbulent skin friction reduction over liquid-impregnated surfaces in Taylor-Couette flow. The surface of the inner cylinder of the facility contains square grooves, with widths from 100 μm to 800 μm and a fixed liquid area of half the total area. Alkane liquids are infused in the surface with viscosities from 1/3 to 2 times that of water. For Reynolds numbers up to Red =10,500 corresponding to a flow shear of τ=50 Pa, we achieve drag reduction exceeding 30%, three times higher than ever reported for liquid-infused surfaces. Supported by the ONR through MURI Grant Nos. N00014-12-1-0875 and N00014-12-1-0962.

  15. Drag reduction for the combination of spike and counterflow jet on blunt body at high Mach number flow

    NASA Astrophysics Data System (ADS)

    Eghlima, Z.; Mansour, K.

    2017-04-01

    Drag reduction at high speed flows around blunt bodies is one of the major challenges in the field of aerodynamics. Using of spikes and counterflow jets each of them separately for reducing of drag force is well known. The present work is description of flow field around a hemispherical nose cylinder with a new combination of spike and counterflow jet at free stream of Mach number of 6.The air gas was injected through the nozzle at the nose of the hemispherical model at sonic speed. In this numerical analysis, axisymmetric Reynolds-averaged Navier-Stokes equations was solved by k-ω (SST) turbulence model. The results were validated with experimental results for spiked body without jet condition. Then the results presented for different lengths of spike and different pressures of counterflow jets. The results show a significant reduction in the drag coefficient about 86-90% compared to the spherical cylinder model without jet and spike for practical models (L/D=1.5 and 2). Furthermore also our results indicate that the drag reduction is increased even more with increasing of the length of the spike.

  16. The effect of plasma actuator on the depreciation of the aerodynamic drag on box model

    NASA Astrophysics Data System (ADS)

    Harinaldi, Budiarso, Julian, James; Rabbani M., N.

    2016-06-01

    Recent active control research advances have provided many benefits some of which in the field of transportation by land, sea as well as by air. Flow engineering by using active control has proven advantages in energy saving significantly. One of the active control equipment that is being developed, especially in the 21st century, is a plasma actuator, with the ability to modify the flow of fluid by the approach of ion particles makes these actuators a very powerful and promising tool. This actuator can be said to be better to the previously active control such as suction, blowing and synthetic jets because it is easier to control, more flexible because it has no moving parts, easy to be manufactured and installed, and consumes a small amount of energy with maximum capability. Plasma actuator itself is the composition of a material composed of copper and a dielectric sheet, where the copper sheets act as an electricity conductor and the dielectric sheet as electricity insulator. Products from the plasma actuators are ion wind which is the result of the suction of free air around the actuator to the plasma zone. This study investigates the ability of plasma actuators in lowering aerodynamic drag which is commonly formed in the models of vehicles by varying the shape of geometry models and the flow speed.

  17. Drag reduction - Jet breakup correlation with kerosene-based additives

    NASA Technical Reports Server (NTRS)

    Hoyt, J. W.; Altman, R. L.; Taylor, J. J.

    1980-01-01

    The drag-reduction effectiveness of a number of high-polymer additives dissolved in aircraft fuel has been measured in a turbulent-flow rheometer. These solutions were further subjected to high elongational stress and breakup forces in a jet discharging in air. The jet was photographed using a high-resolution camera with special lighting. The object of the work was to study the possible spray-suppression ability of high-polymer additives to aircraft fuel and to correlate this with the drag-reducing properties of the additives. It was found, in fact, that the rheometer results indicate the most effective spray-suppressing additives. Using as a measure the minimum polymer concentration to give a maximum friction-reducing effect, the order of effectiveness of eight different polymer additives as spray-suppressing agents was predicted. These results may find application in the development of antimisting additives for aircraft fuel which may increase fire safety in case of crash or accident.

  18. Preliminary Assessment of Optimal Longitudinal-Mode Control for Drag Reduction through Distributed Aeroelastic Shaping

    NASA Technical Reports Server (NTRS)

    Ippolito, Corey; Nguyen, Nhan; Lohn, Jason; Dolan, John

    2014-01-01

    The emergence of advanced lightweight materials is resulting in a new generation of lighter, flexible, more-efficient airframes that are enabling concepts for active aeroelastic wing-shape control to achieve greater flight efficiency and increased safety margins. These elastically shaped aircraft concepts require non-traditional methods for large-scale multi-objective flight control that simultaneously seek to gain aerodynamic efficiency in terms of drag reduction while performing traditional command-tracking tasks as part of a complete guidance and navigation solution. This paper presents results from a preliminary study of a notional multi-objective control law for an aeroelastic flexible-wing aircraft controlled through distributed continuous leading and trailing edge control surface actuators. This preliminary study develops and analyzes a multi-objective control law derived from optimal linear quadratic methods on a longitudinal vehicle dynamics model with coupled aeroelastic dynamics. The controller tracks commanded attack-angle while minimizing drag and controlling wing twist and bend. This paper presents an overview of the elastic aircraft concept, outlines the coupled vehicle model, presents the preliminary control law formulation and implementation, presents results from simulation, provides analysis, and concludes by identifying possible future areas for research

  19. Spatially distributed control for optimal drag reduction of the flow past a circular cylinder

    NASA Astrophysics Data System (ADS)

    Poncet, Philippe; Hildebrand, Roland; Cottet, Georges-Henri; Koumoutsakos, Petros

    We report high drag reduction in direct numerical simulations of controlled flows past circular cylinders at Reynolds numbers of 300 and 1000. The flow is controlled by the azimuthal component of the tangential velocity of the cylinder surface. Starting from a spanwise-uniform velocity profile that leads to high drag reduction, the optimization procedure identifies, for the same energy input, spanwise-varying velocity profiles that lead to higher drag reduction. The three-dimensional variations of the velocity field, corresponding to modes A and B of three-dimensional wake instabilities, are largely responsible for this drag reduction. The spanwise wall velocity variations introduce streamwise vortex braids in the wake that are responsible for reducing the drag induced by the primary spanwise vortices shed by the cylinder. The results demonstrate that extending two-dimensional controllers to three-dimensional flows is not optimal as three-dimensional control strategies can lead efficiently to higher drag reduction.

  20. Fluid Mechanics, Drag Reduction and Advanced Configuration Aeronautics

    NASA Technical Reports Server (NTRS)

    Bushnell, Dennis M.

    2000-01-01

    This paper discusses Advanced Aircraft configurational approaches across the speed range, which are either enabled, or greatly enhanced, by clever Flow Control. Configurations considered include Channel Wings with circulation control for VTOL (but non-hovering) operation with high cruise speed, strut-braced CTOL transports with wingtip engines and extensive ('natural') laminar flow control, a midwing double fuselage CTOL approach utilizing several synergistic methods for drag-due-to-lift reduction, a supersonic strut-braced configuration with order of twice the L/D of current approaches and a very advanced, highly engine flow-path-integrated hypersonic cruise machine. This paper indicates both the promise of synergistic flow control approaches as enablers for 'Revolutions' in aircraft performance and fluid mechanic 'areas of ignorance' which impede their realization and provide 'target-rich' opportunities for Fluids Research.

  1. Development of a plasma injector for supersonic drag reduction

    NASA Astrophysics Data System (ADS)

    Macnab, Angus; Hashim, Akel; Graham, Robert; Ziemba, Timothy; Miller, Kenneth

    2013-10-01

    Eagle Harbor Technologies, Inc. is developing and optimizing a magnetohydrodynamic (MHD) plasma injector, designed to reduce viscous skin friction of supersonic aircraft. The broad goals are to 1. Computationally investigate and verify the dominant physical mechanisms for MHD plasma drag reduction; 2. Develop a proof of concept plasma injector demo, which performs within the power limitations of an onboard flight-relevant system; and 3. Use insights gained through computational investigations to optimize the performance of our MHD plasma injector for maximum efficiency. This investigation focuses on flight-relevant Reynolds and magnetic Reynolds numbers at low supersonic (1

  2. Active viscoelastic matter: from bacterial drag reduction to turbulent solids.

    PubMed

    Hemingway, E J; Maitra, A; Banerjee, S; Marchetti, M C; Ramaswamy, S; Fielding, S M; Cates, M E

    2015-03-06

    A paradigm for internally driven matter is the active nematic liquid crystal, whereby the equations of a conventional nematic are supplemented by a minimal active stress that violates time-reversal symmetry. In practice, active fluids may have not only liquid-crystalline but also viscoelastic polymer degrees of freedom. Here we explore the resulting interplay by coupling an active nematic to a minimal model of polymer rheology. We find that adding a polymer can greatly increase the complexity of spontaneous flow, but can also have calming effects, thereby increasing the net throughput of spontaneous flow along a pipe (a "drag-reduction" effect). Remarkably, active turbulence can also arise after switching on activity in a sufficiently soft elastomeric solid.

  3. Mechanisms of Active Aerodynamic Load Reduction on a Rotorcraft Fuselage With Rotor Effects

    NASA Technical Reports Server (NTRS)

    Schaeffler, Norman W.; Allan, Brian G.; Jenkins, Luther N.; Yao, Chung-Sheng; Bartram, Scott M.; Mace, W. Derry; Wong, Oliver D.; Tanner, Philip E.

    2016-01-01

    The reduction of the aerodynamic load that acts on a generic rotorcraft fuselage by the application of active flow control was investigated in a wind tunnel test conducted on an approximately 1/3-scale powered rotorcraft model simulating forward flight. The aerodynamic mechanisms that make these reductions, in both the drag and the download, possible were examined in detail through the use of the measured surface pressure distribution on the fuselage, velocity field measurements made in the wake directly behind the ramp of the fuselage and computational simulations. The fuselage tested was the ROBIN-mod7, which was equipped with a series of eight slots located on the ramp section through which flow control excitation was introduced. These slots were arranged in a U-shaped pattern located slightly downstream of the baseline separation line and parallel to it. The flow control excitation took the form of either synthetic jets, also known as zero-net-mass-flux blowing, and steady blowing. The same set of slots were used for both types of excitation. The differences between the two excitation types and between flow control excitation from different combinations of slots were examined. The flow control is shown to alter the size of the wake and its trajectory relative to the ramp and the tailboom and it is these changes to the wake that result in a reduction in the aerodynamic load.

  4. Viscous flow drag reduction; Symposium, Dallas, Tex., November 7, 8, 1979, Technical Papers

    NASA Technical Reports Server (NTRS)

    Hough, G. R.

    1980-01-01

    The symposium focused on laminar boundary layers, boundary layer stability analysis of a natural laminar flow glove on the F-111 TACT aircraft, drag reduction of an oscillating flat plate with an interface film, electromagnetic precipitation and ducting of particles in turbulent boundary layers, large eddy breakup scheme for turbulent viscous drag reduction, blowing and suction, polymer additives, and compliant surfaces. Topics included influence of environment in laminar boundary layer control, generation rate of turbulent patches in the laminar boundary layer of a submersible, drag reduction of small amplitude rigid surface waves, and hydrodynamic drag and surface deformations generated by liquid flows over flexible surfaces.

  5. The myth and reality of Gray's paradox: implication of dolphin drag reduction for technology.

    PubMed

    Fish, Frank E

    2006-06-01

    The inconsistency for the calculated high drag on an actively swimming dolphin and underestimated muscle power available resulted in what has been termed Gray's paradox. Although Gray's paradox was flawed, it has been the inspiration for a variety of drag reduction mechanisms. This review examines the present state of knowledge of drag reduction specific to dolphins. Streamlining and special behaviors provide the greatest drag reduction for dolphins. Mechanisms to control flow by maintaining a completely laminar boundary layer over the body have not been demonstrated for dolphins.

  6. Active Aerodynamic Load Reduction on a Rotorcraft Fuselage With Rotor Effects: A CFD Validation Effort

    NASA Technical Reports Server (NTRS)

    Allan, Brian G.; Schaeffler, Norman W.; Jenkins, Luther N.; Yao, Chung-Sheng; Wong, Oliver D.; Tanner, Philip E.

    2015-01-01

    A rotorcraft fuselage is typically designed with an emphasis on operational functionality with aerodynamic efficiency being of secondary importance. This results in a significant amount of drag during high-speed forward flight that can be a limiting factor for future high-speed rotorcraft designs. To enable higher speed flight, while maintaining a functional fuselage design (i.e., a large rear cargo ramp door), the NASA Rotary Wing Project has conducted both experimental and computational investigations to assess active flow control as an enabling technology for fuselage drag reduction. This paper will evaluate numerical simulations of a flow control system on a generic rotorcraft fuselage with a rotor in forward flight using OVERFLOW, a structured mesh Reynolds-averaged Navier-Stokes flow solver developed at NASA. The results are compared to fuselage forces, surface pressures, and PN flow field data obtained in a wind tunnel experiment conducted at the NASA Langley 14-by 22-Foot Subsonic Tunnel where significant drag and download reductions were demonstrated using flow control. This comparison showed that the Reynolds-averaged Navier-Stokes flow solver was unable to predict the fuselage forces and pressure measurements on the ramp for the baseline and flow control cases. While the CFD was able to capture the flow features, it was unable to accurately predict the performance of the flow control.

  7. Aerodynamic Drag Analysis of 3-DOF Flex-Gimbal GyroWheel System in the Sense of Ground Test

    PubMed Central

    Huo, Xin; Feng, Sizhao; Liu, Kangzhi; Wang, Libin; Chen, Weishan

    2016-01-01

    GyroWheel is an innovative device that combines the actuating capabilities of a control moment gyro with the rate sensing capabilities of a tuned rotor gyro by using a spinning flex-gimbal system. However, in the process of the ground test, the existence of aerodynamic disturbance is inevitable, which hinders the improvement of the specification performance and control accuracy. A vacuum tank test is a possible candidate but is sometimes unrealistic due to the substantial increase in costs and complexity involved. In this paper, the aerodynamic drag problem with respect to the 3-DOF flex-gimbal GyroWheel system is investigated by simulation analysis and experimental verification. Concretely, the angular momentum envelope property of the spinning rotor system is studied and its integral dynamical model is deduced based on the physical configuration of the GyroWheel system with an appropriately defined coordinate system. In the sequel, the fluid numerical model is established and the model geometries are checked with FLUENT software. According to the diversity and time-varying properties of the rotor motions in three-dimensions, the airflow field around the GyroWheel rotor is analyzed by simulation with respect to its varying angular velocity and tilt angle. The IPC-based experimental platform is introduced, and the properties of aerodynamic drag in the ground test condition are obtained through comparing the simulation with experimental results. PMID:27941602

  8. Aerodynamic Drag Analysis of 3-DOF Flex-Gimbal GyroWheel System in the Sense of Ground Test.

    PubMed

    Huo, Xin; Feng, Sizhao; Liu, Kangzhi; Wang, Libin; Chen, Weishan

    2016-12-07

    GyroWheel is an innovative device that combines the actuating capabilities of a control moment gyro with the rate sensing capabilities of a tuned rotor gyro by using a spinning flex-gimbal system. However, in the process of the ground test, the existence of aerodynamic disturbance is inevitable, which hinders the improvement of the specification performance and control accuracy. A vacuum tank test is a possible candidate but is sometimes unrealistic due to the substantial increase in costs and complexity involved. In this paper, the aerodynamic drag problem with respect to the 3-DOF flex-gimbal GyroWheel system is investigated by simulation analysis and experimental verification. Concretely, the angular momentum envelope property of the spinning rotor system is studied and its integral dynamical model is deduced based on the physical configuration of the GyroWheel system with an appropriately defined coordinate system. In the sequel, the fluid numerical model is established and the model geometries are checked with FLUENT software. According to the diversity and time-varying properties of the rotor motions in three-dimensions, the airflow field around the GyroWheel rotor is analyzed by simulation with respect to its varying angular velocity and tilt angle. The IPC-based experimental platform is introduced, and the properties of aerodynamic drag in the ground test condition are obtained through comparing the simulation with experimental results.

  9. Effect of structure height on the drag reduction performance using rotating disk apparatus

    NASA Astrophysics Data System (ADS)

    Rashed, Musaab K.; Abdulbari, Hayder A.; Amran Mohd Salleh, Mohamad; Halim Shah Ismail, M.

    2017-02-01

    The drag reduction characteristics in a rotating disk apparatus were investigated by using structured disks with different riblet types and dimensions. Two disk types were fabricated with right angle triangular (RAT) grooves and space v-shape (SV) grooves, with six dimensions for each type. A high-accuracy rotating disk apparatus was fabricated and then used to investigate the turbulent drag reduction characterization of the disk in diesel fuel. In this work, the effects of several parameters are investigated; riblet types, riblet dimensions, and rotational disk speed (rpm) on the drag reduction performance. It was found that the surface structure of the disk reduced the drag, this was clearly seen from the comparison of torque values of smooth and structured disks. Drag reduction for structured disks was higher than that for smooth disks, and SV-grooves showed better drag reduction performance than RAT-grooves. In addition, it was observed that the drag reduction performance increased with decreasing groove height for both groove types. The maximum drag reduction achieved in this study was 37.368% for SV-groove at 1000 rpm, compared with 30% for RAT-groove, at the same rotational speed.

  10. Characterization of the LISA Pathfinder Drag Reduction System

    NASA Astrophysics Data System (ADS)

    Slutsky, Jacob; LISA Pathfinder Team

    2016-03-01

    The LISA Pathfinder (LPF) mission launched in December 2015 with operations beginning March 2016. LPF is a technology demonstration mission built to prove and fully characterize the performance of the use of drag free test masses as Gravitational Reference Sensors (GRS) for future space based gravitational-wave observatories. As a joint ESA-NASA mission, LPF is comprised of both European and NASA payloads, the LISA Technology Package (LTP) and Disturbance Reduction System (DRS), respectively. DRS includes Colloid Micro-Newton Thruster (CMNT) systems, to precisely maneuver the spacecraft without disturbing the GRS, and a control system that directs spacecraft and test mass actuation. In order to fully characterize DRS/CMNT performance, we have developed a series of experiments, to take place during DRS operations beginning later this year. We have built analysis pipelines, validated on simulated data, to rapidly process experimental data and to identify any performance issues as they occur. European partners have developed the LTP Data Analysis (LTPDA) Matlab extension, and we have adapted and expanded this to DRS missions as the basis of our analysis pipelines. I will discuss the anticipated DRS performance and measurement accuracy, illustrated on simulated data.

  11. Effect of Interface Curvature on Super-Hydrophobic Drag Reduction

    NASA Astrophysics Data System (ADS)

    Rastegari, Amirreza; Akhavan, Rayhaneh

    2015-11-01

    The effect of interface curvature on Super-Hydrophobic (SH) Drag Reduction (DR) has been investigated using DNS with lattice Boltzmann methods in laminar (Rebulk = 50) and turbulent (Rebulk = 3600 , Reτ0 ~ 223) channel flows. SH surfaces with longitudinal arrays of micro-grooves (MG) of size 0 . 1 <= g / h <= 0 . 47 & g / w = 1 , 7 were investigated, where g and w denote the width of the MG and the separation in between them, respectively, and h denotes the channel half-height. The liquid/gas interfaces on the SH MG were modeled as `idealized', stationary, curved, shear-free boundaries, with the interface curvatures determined from the Young-Laplace equation. The presence of interface curvature leads to enhancements of DR by up to 10% in laminar flow, and more modest enhancements or even decreases in DR in turbulent flow, compared to flat, shear-free interfaces. These enhancements or decreases in DR, relative to flat, shear-free interfaces, in both laminar and turbulent flow, are shown to arise primarily from the modified shape of the cross section of the channel in the presence of the curved interface.

  12. On the impact of size and position of semi-trailer on the aerodynamic drag of an articulated vehicle

    NASA Astrophysics Data System (ADS)

    Maciejewski, M.

    2016-09-01

    The paper relates to the numerical aerodynamic simulation of an articulated vehicle. All simulations were comparative, where variables were only three geometric parameters: the height and length of the semi-trailer, and the gap between the tractor and semi-trailer. Simulation results have been investigated and compared in terms of observed values of aerodynamic drag coefficients. These coefficients have been presented in time (for example only), but above all, as constant, averaged magnitudes which are more suitable for comparisons. Total number of simulations and thereby geometrical configurations was 125, i.e. for 5 sizes of the height and length of trailer, and 5 clearance gaps between the tractor and trailer. Results have been presented graphically and discussed.

  13. The Berlin oil channel for drag reduction research

    NASA Astrophysics Data System (ADS)

    Bechert, D. W.; Hoppe, G.; van der Hoeven, J. G. Th.; Makris, R.

    1992-03-01

    For drag reduction research an oil channel has been designed and built. It is also well suited for investigations on turbulent flow and in particular on the dynamics of the viscous sublayer near the wall. The thickness of the viscous sublayer ( y += 5) can be varied between 1 and 4 mm. Surfaces with longitudinal ribs (“riblets”), which are known to reduce drag, can have fairly large dimensions. The lateral spacing of the ribs can lie between 3 and 10 mm, as compared to about 0.5 mm spacing for conventional wind tunnels. It has been proved by appropriate tests that the oil channel data are completely equivalent to data from other facilities and with other mean flow geometries. However, the shear stress data from the new oil channel are much more accurate than previous data due to a novel differential shear force balance with an accuracy of ±0.2%. In addition to shear stress measurements, velocity fluctuation measurements can be carried out with hot wire or hot film probes. In order to calibrate these probes, a moving sled permits to emulate the flow velocities with the fluid in the channel at rest. A number of additional innovations contribute to the improvement of the measurements, such as, e.g., (i) novel adjustable turbulators to maintain equilibrium turbulence in the channel, (ii) a “bubble trap” to avoid bubbles in the channel at high flow velocities, (iii) a simple method for the precision calibration of manometers, and (iv) the elimination of (Coulomb) friction in ball bearings. This latter fairly general invention is used for the wheels of the calibration unit of the balance. The channel has a cross section of 25 × 85 cm and is 11 m long. It is filled with about 4.5 metric tons of baby oil (white paraffine oil), which is transparent and odorless like water. The kinematic viscosity of the oil is v = 1.2×10-5 m2/s, and the highest (average) velocity is 1.29 m/s. Thus, the Reynolds number range (calculated with the channel width, 0.25 m) lies between

  14. The Aerodynamic Drag of Flying-boat Hull Model as Measured in the NACA 20-foot Wind Tunnel I.

    NASA Technical Reports Server (NTRS)

    Hartman, Edwin P

    1935-01-01

    Measurements of aerodynamic drag were made in the 20-foot wind tunnel on a representative group of 11 flying-boat hull models. Four of the models were modified to investigate the effect of variations in over-all height, contours of deck, depth of step, angle of afterbody keel, and the addition of spray strips and windshields. The results of these tests, which cover a pitch-angle range from -5 to 10 degrees, are presented in a form suitable for use in performance calculations and for design purposes.

  15. A unified approach to aerodynamic damping and drag/lift instabilities, and its application to dry inclined cable galloping

    NASA Astrophysics Data System (ADS)

    MacDonald, J. H. G.; Larose, G. L.

    2006-02-01

    Inclined cables of cable-stayed bridges often experience large amplitude vibrations. One of the potential excitation mechanisms is dry inclined cable galloping, which has been observed in wind tunnel tests but which has not previously been fully explained theoretically. In this paper, a general expression is derived for the quasi-steady aerodynamic damping (positive or negative) of a cylinder of arbitrary cross-section yawed/inclined to the flow, for small amplitude vibrations in any plane. The expression covers the special cases of conventional quasi-steady aerodynamic damping, Den Hartog galloping and the drag crisis, as well as dry inclined cable galloping. A nondimensional aerodynamic damping parameter governing this behaviour is proposed, which is a function of only the Reynolds number, the angle between the wind velocity and the cable axis, and the orientation of the vibration plane. Measured static force coefficients from wind tunnel tests have been used with the theoretical expression to predict values of this parameter. Two main areas of instability (i.e. negative aerodynamic damping) have been identified, both in the critical Reynolds number region, one of which was previously observed in separate wind tunnel tests on a dynamic cable model. The minimum values of structural damping required to prevent dry inclined cable galloping are defined, and other factors in the behaviour in practice are discussed.

  16. Langley Symposium on Aerodynamics, volume 1

    NASA Technical Reports Server (NTRS)

    Stack, Sharon H. (Compiler)

    1986-01-01

    The purpose of this work was to present current work and results of the Langley Aeronautics Directorate covering the areas of computational fluid dynamics, viscous flows, airfoil aerodynamics, propulsion integration, test techniques, and low-speed, high-speed, and transonic aerodynamics. The following sessions are included in this volume: theoretical aerodynamics, test techniques, fluid physics, and viscous drag reduction.

  17. An investigation of drag reduction for tractor trailer vehicles with air deflector and boattail. [wind tunnel tests

    NASA Technical Reports Server (NTRS)

    Muirhead, V. U.

    1981-01-01

    A wind tunnel investigation was conducted to determine the influence of several physical variables on the aerodynamic drag of a trailer model. The physical variables included: a cab mounted wind deflector, boattail on trailer, flow vanes on trailer front, forced transition on trailer, and decreased gap between tractor and trailer. Tests were conducted at yaw angles (relative wind angles) of 0, 5, 10, 20, and 30 degrees and Reynolds numbers of 3.58 x 10 to the 5th power 6.12 x 10 to the 5th power based upon the equivalent diameter of the vehicles. The wind deflector on top of the cab produced a calculated reduction in fuel consumption of about 5 percent of the aerodynamic portion of the fuel budget for a wind speed of 15.3 km/hr (9.5 mph) over a wind angle range of 0 deg to 180 deg and for a vehicle speed of 88.5 km/hr (55 mph). The boattail produced a calculated 7 percent to 8 percent reduction in fuel consumption under the same conditions. The decrease in gap reduced the calculated fuel consumption by about 5 percent of the aerodynamic portion of the fuel budget.

  18. Aerodynamic Measurements of a Gulfstream Aircraft Model With and Without Noise Reduction Concepts

    NASA Technical Reports Server (NTRS)

    Neuhart, Dan H.; Hannon, Judith A.; Khorrami, Mehdi R.

    2014-01-01

    Steady and unsteady aerodynamic measurements of a high-fidelity, semi-span 18% scale Gulfstream aircraft model are presented. The aerodynamic data were collected concurrently with acoustic measurements as part of a larger aeroacoustic study targeting airframe noise associated with main landing gear/flap components, gear-flap interaction noise, and the viability of related noise mitigation technologies. The aeroacoustic tests were conducted in the NASA Langley Research Center 14- by 22-Foot Subsonic Wind Tunnel with the facility in the acoustically treated open-wall (jet) mode. Most of the measurements were obtained with the model in landing configuration with the flap deflected at 39º and the main landing gear on and off. Data were acquired at Mach numbers of 0.16, 0.20, and 0.24. Global forces (lift and drag) and extensive steady and unsteady surface pressure measurements were obtained. Comparison of the present results with those acquired during a previous test shows a significant reduction in the lift experienced by the model. The underlying cause was traced to the likely presence of a much thicker boundary layer on the tunnel floor, which was acoustically treated for the present test. The steady and unsteady pressure fields on the flap, particularly in the regions of predominant noise sources such as the inboard and outboard tips, remained unaffected. It is shown that the changes in lift and drag coefficients for model configurations fitted with gear/flap noise abatement technologies fall within the repeatability of the baseline configuration. Therefore, the noise abatement technologies evaluated in this experiment have no detrimental impact on the aerodynamic performance of the aircraft model.

  19. A theoretical prediction of friction drag reduction in turbulent flow by superhydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Fukagata, Koji; Kasagi, Nobuhide; Koumoutsakos, Petros

    2006-05-01

    We present a theoretical prediction for the drag reduction rate achieved by superhydrophobic surfaces in a turbulent channel flow. The predicted drag reduction rate is in good agreement with results obtained from direct numerical simulations at Reτ≃180 and 400. The present theory suggests that large drag reduction is possible also at Reynolds numbers of practical interest (Reτ˜105-106) by employing a hydrophobic surface, which induces a slip length on the order of ten wall units or more.

  20. Numerical Simulation of High Drag Reduction in a Turbulent Channel Flow with Polymer Additives

    NASA Technical Reports Server (NTRS)

    Dubief, Yves

    2003-01-01

    The addition of small amounts of long chain polymer molecules to wall-bounded flows can lead to dramatic drag reduction. Although this phenomenon has been known for about fifty years, the action of the polymers and its effect on turbulent structures are still unclear. Detailed experiments have characterized two distinct regimes (Warholic et al. 1999), which are referred to as low drag reduction (LDR) and high drag reduction (HDR). The first regime exhibits similar statistical trends as Newtonian flow: the log-law region of the mean velocity profile remains parallel to that of the Newtonian ow but its lower bound moves away from the wall and the upward shift of the log-region is a function of drag reduction, DR. Although streamwise fluctuations are increased and transverse ones are reduced, the shape of the rms velocity profiles is not qualitatively modified. At higher drag reductions, of the order of 40-50%, the ow enters the HDR regime for which the slope of the log-law is dramatically augmented and the Reynolds shear stress is small (Warholic et al. 1999; Ptasinski et al. 2001). The drag reduction is eventually bounded by a maximum drag reduction (MDR) (Virk & Mickley 1970) which is a function of the Reynolds number. While several experiments report mean velocity profiles very close to the empirical profile of Virk & Mickley (1970) for MDR conditions, the observations regarding the structure of turbulence can differ significantly. For instance, Warholic et al. (1999) measured a near-zero Reynolds shear stress, whereas a recent experiment (Ptasinski et al. 2001) shows evidence of non-negligible Reynolds stress in their MDR flow. To the knowledge of the authors, only the LDR regime has been documented in numerical simulations (Sureshkumar et al. 1997; Dimitropoulos et al. 1998; Min et al. 2001; Dubief & Lele 2001; Sibilla & Baron 2002). This paper discusses the simulation of polymer drag reduced channel ow at HDR using the FENE-P (Finite Elastic non

  1. Drag reduction mechanisms employed by burrowing razor clams (Ensis directus)

    NASA Astrophysics Data System (ADS)

    Winter, Amos; Hosoi, Anette

    2008-11-01

    In this work we describe how razor clams use localized fluidization to reduce drag and efficiently burrow through a granular substrate. Razor clams require nearly two orders of magnitude less force to move through sand than a blunt body of the same size and shape. By visualizing substrate deformation during burrowing, we investigate the clamshell kinematics which fluidize a small pocket of substrate around the body of the organism. Through experimentation and scaling arguments, we show that moving through a fluidized substrate rather than a packed granular medium dramatically reduces the drag force on the clam's body to a point within the animal's strength capabilities.

  2. Drag reduction through wave-current interactions with a marine hydrofoil

    NASA Astrophysics Data System (ADS)

    Tully, Susan; Viola, Ignazio Maria; Ingram, David

    2015-11-01

    A hydrofoil exposed to oscillating flow experiences a reduction in drag due to the Knoller-Betz effect. This is experimentally identifiable by an increasingly inverted von Kármán wake and a corresponding thrust force on the foil. The rate of drag reduction, dependent on plunge amplitude and frequency, reduces with unsteady flow phenomena at higher reduced frequencies. For experimental ease, investigations of this effect have relied on actively plunging/pitching a foil within a steady current. However, one potential application is to drag reduction in high-speed ships adopting submerged foils. In this case the foil is travelling through wave-current induced oscillatory flow, resulting in an additional dynamic variation of hydrostatic pressure across the chord; a phenomena not fully addressed in previous experiments. Here we investigate the effects of this pressure gradient on drag reduction for a stationary foil in combined waves and current, through a combination of force measurements and particle image velocimetry.

  3. Numerical studies of laminar and turbulent drag reduction, part 2

    NASA Technical Reports Server (NTRS)

    Balasubramanian, R.; Orszag, S. A.

    1983-01-01

    The flow over wave shaped surfaces is studied using a Navier Stokes solver. Detailed comparisons with theoretical results are presented, including the stability of a laminar flow over wavy surfaces. Drag characteristics of nonplanar surfaces are predicted using the Navier-Stokes solver. The secondary instabilities of wall bounded and free shear flows are also discussed.

  4. Feedback Control of a Square-Back Ahmed Body Flow for Form-Drag Reduction

    NASA Astrophysics Data System (ADS)

    Evstafyeva, Olga; Morgans, Aimee

    2015-11-01

    Road transport accounts for roughly 22% of CO2 emissions worldwide, and at highway speeds two thirds of usable energy is consumed overcoming aerodynamic drag. For square-back vehicles, aerodynamic drag is dominated by form- drag, originating from pressure difference between the front and the back face (base) of the vehicle. This study explores using feedback control to increase mean base pressure and thus reduce the form-drag of 3D Ahmed body flows at low (laminar) and medium (transitioning to turbulence) Reynolds numbers. Using Large Eddy Simulations as a test-bed, a linear control strategy to attenuate base-pressure force fluctuations is investigated. Body-mounted sensing and actuation is used: sensing of the base pressure force fluctuations, and actuation of a zero-mean slot jet just ahead of the base. The dynamic linearity of the response to actuation is tested and a feedback controller then designed using frequency domain harmonic forcing system identification data. Recent advances in understanding of the Ahmed body wake dynamics such as top-to-bottom and left-to-right bi-stable behaviour, are considered in the feedback control implementation.

  5. Investigation of drag reduction through a flapping mechanism on circular cylinder

    NASA Astrophysics Data System (ADS)

    Asif, Md. Asafuddoula; Gupta, Avijit Das; Rana, M. D. Juwel; Ahmed, Dewan Hasan

    2016-07-01

    During flapping wing, a bird develops sufficient lift force as well as counteracts drag and increases its speed through different orientations of feathers on the flapping wings. Differently oriented feathers play a significant role in drag reduction during flying of a bird. With an objective to investigate the effect of installation of such flapping mechanism as a mean of drag reduction in case of flow over circular cylinder, this concept has been implemented through installation of continuous and mini flaps, made of MS sheet metal, where flaps are oriented at different angles as like feathers of flapping wings. The experiments are carried out in a subsonic wind tunnel. After validation and comparison with conventional result of drag analysis of a single cylinder, effects of flapping with Reynolds number variation, implementation of different orientations of mini flaps and variation of different interspacing distance between mini flaps are studied to find the most effective angle of attack of drag reduction on the body of circular cylinder. This research show that, installation of continuous flap reduces value of drag co-efficient, CD up to 66%, where as mini flaps are found more effective by reducing it up to 73%. Mini flaps of L/s=6.25, all angled at 30O, at the 30O angular position on the body of circular cylinder has been found the most effective angle of attack for drag reduction in case of flow over circular cylinder.

  6. Skin-friction drag reduction in the turbulent regime using random-textured hydrophobic surfaces

    NASA Astrophysics Data System (ADS)

    Bidkar, Rahul A.; Leblanc, Luc; Kulkarni, Ambarish J.; Bahadur, Vaibhav; Ceccio, Steven L.; Perlin, Marc

    2014-08-01

    Technologies for reducing hydrodynamic skin-friction drag have a huge potential for energy-savings in applications ranging from propulsion of marine vessels to transporting liquids through pipes. The majority of previous experimental studies using hydrophobic surfaces have successfully shown skin-friction drag reduction in the laminar and transitional flow regimes (typically Reynolds numbers less than ≃106 for external flows). However, this hydrophobicity induced drag reduction is known to diminish with increasing Reynolds numbers in experiments involving wall bounded turbulent flows. Using random-textured hydrophobic surfaces (fabricated using large-length scalable thermal spray processes) on a flat plate geometry, we present water-tunnel test data with Reynolds numbers ranging from 106 to 9 × 106 that show sustained skin-friction drag reduction of 20%-30% in such turbulent flow regimes. Furthermore, we provide evidence that apart from the formation of a Cassie state and hydrophobicity, we also need a low surface roughness and an enhanced ability of the textured surface to retain trapped air, for sustained drag reduction in turbulent flow regimes. Specifically, for the hydrophobic test surfaces of the present and previous studies, we show that drag reduction seen at lower Reynolds numbers diminishes with increasing Reynolds number when the surface roughness of the underlying texture becomes comparable to the viscous sublayer thickness. Conversely, test data show that textures with surface roughness significantly smaller than the viscous sublayer thickness and textures with high porosity show sustained drag reduction in the turbulent flow regime. The present experiments represent a significant technological advancement and one of the very few demonstrations of skin-friction reduction in the turbulent regime using random-textured hydrophobic surfaces in an external flow configuration. The scalability of the fabrication method, the passive nature of this surface

  7. Longitudinal afterbody grooves and shoulder radiusing for low-speed bluff body drag reduction

    NASA Technical Reports Server (NTRS)

    Howard, F. G.; Quass, B. F.; Weinstein, L. M.; Bushnell, D. M.

    1981-01-01

    A new low-speed drag reduction approach is proposed which employs longitudinal surface V-shaped grooves cutting through the afterbody shoulder region. The test Reynolds number range was from 20,000 to 200,000 based on undisturbed free-stream flow and a body diameter of 6.08 cm. The V-grooves are shown to be most effective in reducing drag when the afterbody shoulder radius is zero. Reductions in drag of up to 33% have been measured for this condition. For large shoulder radius, the grooves are only effective at the lower Reynolds numbers of the test.

  8. Experimental study of delta wing leading-edge devices for drag reduction at high lift

    NASA Technical Reports Server (NTRS)

    Johnson, T. D., Jr.; Rao, D. M.

    1982-01-01

    The drag reduction devices selected for evaluation were the fence, slot, pylon-type vortex generator, and sharp leading-edge extension. These devices were tested on a 60 degree flatplate delta (with blunt leading edges) in the Langley Research Center 7- by 10-foot high-speed tunnel at low speed and to angles of attack of 28 degrees. Balance and static pressure measurements were taken. The results indicate that all the devices had significant drag reduction capability and improved longitudinal stability while a slight loss of lift and increased cruise drag occurred.

  9. Drag reduction of boat-tailed bluff bodies through transverse grooves. Part II: large-eddy simulations

    NASA Astrophysics Data System (ADS)

    Salvetti, Maria Vittoria; Mariotti, Alessandro; Buresti, Guido

    2016-11-01

    The present work focuses on strategies for aerodynamic drag reduction of elongated axisymmetric bluff bodies, which can be viewed as simplified models of a road vehicles. We combine boat-tailing, i.e. a gradual reduction of the body cross-section before a sharp-edged base, with properly contoured transverse grooves. The effectiveness of this strategy was assessed through experiments and simulations. Experiments showed that the introduction of a single groove leads to a further delay of boundary-layer separation and to a reduction of drag compared with the boat-tail configuration without grooves. In this talk, we present Large-Eddy Simulations (LES). LES results agree with the experimental findings. The success of the proposed flow control strategy is due to the relaxation of the no-slip condition in the small recirculation region inside the groove, which reduces the momentum losses near the wall and thus delays boundary layer separation. The effects of the introduction of the groove on the mean topology and on the dynamics of the near wake are also highlighted. Finally, a sensitivity analysis of the proposed control strategy efficiency to the groove location and to the boat-tail geometry is shown.

  10. Wetting behavior and drag reduction of superhydrophobic layered double hydroxides films on aluminum

    NASA Astrophysics Data System (ADS)

    Zhang, Haifeng; Yin, Liang; Liu, Xiaowei; Weng, Rui; Wang, Yang; Wu, Zhiwen

    2016-09-01

    We present a novel method to fabricate Zn-Al LDH (layered double hydroxides) film with 3D flower-like micro-and nanostructure on the aluminum foil. The wettability of the Zn-Al LDH film can be easily changed from superhydrophilic to superhydrophobic with a simple chemical modification. The as-prepared superhydrophobic surfaces have water CAs (contact angles) of 165 ± 2°. In order to estimate the drag reduction property of the surface with different adhesion properties, the experimental setup of the liquid/solid friction drag is proposed. The drag reduction ratio for the as-prepared superhydrophobic sample is 20-30% at low velocity. Bearing this in mind, we construct superhydrophobic surfaces that have numerous technical applications in drag reduction field.

  11. Re-Entry Point Targeting for LEO Spacecraft using Aerodynamic Drag

    NASA Technical Reports Server (NTRS)

    Omar, Sanny; Bevilacqua, Riccardo; Fineberg, Laurence; Treptow, Justin; Johnson, Yusef; Clark, Scott

    2016-01-01

    Most Low Earth Orbit (LEO) spacecraft do not have thrusters and re-enter atmosphere in random locations at uncertain times. Objects pose a risk to persons, property, or other satellites. Has become a larger concern with the recent increase in small satellites. Working on a NASA funded project to design a retractable drag device to expedite de-orbit and target a re-entry location through modulation of the drag area. Will be discussing the re-entry point targeting algorithm here.

  12. Aerodynamic Assessment of Flight-Determined Subsonic Lift and Drag Characteristics of Seven Lifting-Body and Wing-Body Reentry Vehicle Configurations

    NASA Technical Reports Server (NTRS)

    Saltzman, Edwin J.; Wang, K. Charles; Iliff, Kenneth W.

    2002-01-01

    This report examines subsonic flight-measured lift and drag characteristics of seven lifting-body and wing-body reentry vehicle configurations with truncated bases. The seven vehicles are the full-scale M2-F1, M2-F2, HL-10, X-24A, X-24B, and X-15 vehicles and the Space Shuttle Enterprise. Subsonic flight lift and drag data of the various vehicles are assembled under aerodynamic performance parameters and presented in several analytical and graphical formats. These formats are intended to unify the data and allow a greater understanding than individually studying the vehicles allows. Lift-curve slope data are studied with respect to aspect ratio and related to generic wind-tunnel model data and to theory for low-aspect-ratio platforms. The definition of reference area is critical for understanding and comparing the lift data. The drag components studied include minimum drag coefficient, lift-related drag, maximum lift-to drag ratio, and, where available, base pressure coefficients. The influence of forebody drag on afterbody and base drag at low lift is shown to be related to Hoerner's compilation for body, airfoil, nacelle, and canopy drag. This feature may result in a reduced need of surface smoothness for vehicles with a large ratio of base area to wetted area. These analyses are intended to provide a useful analytical framework with which to compare and evaluate new vehicle configurations of the same generic family.

  13. Drag reduction by reconfiguration of a full tree in a wind tunnel

    NASA Astrophysics Data System (ADS)

    de Langre, Emmanuel; Tadrist, Loic; Leclercq, Tristan; Hemon, Pascal; Amandolese, Xavier; Saudreau, Marc; Marquier, Andre; Knapp, Graham; Flamand, Olivier

    2015-11-01

    The results of drag measurements performed on a full 3 m-tall cherry tree in an atmospheric wind tunnel are presented. The drag on the trunk alone is shown to increase quadratically with the velocity of the flow, as expected, but the drag on the whole tree with branches and leaves follows a smaller power law with velocity, after the reconfiguration of most leaves. The transition from the quadratic law to a linear increase of the drag of the leaves with the magnitude of the flow is observed. Data is also obtained on moment loading on the base of the tree showing also an effect of the reconfiguration. Finally, these results are compared with current models of drag reduction by reconfiguration.

  14. The effect of solar forcing induced atmospheric perturbations on LEO satellites' nominal aerodynamic drag

    NASA Astrophysics Data System (ADS)

    Nwankwo, Victor U. J.; Chakrabarti, Sandip Kumar; Weigel, Robert

    2016-07-01

    Atmospheric drag is the strongest force perturbing the motion of satellites in low Earth orbits LEO, and could cause re-entry of satellites, difficulty in identifying and tracking of the satellites and other space objects, manuvering and prediction of lifetime and re-entry. Solar activities influence the temperature, density and composition of the upper atmosphere. These effects thus strongly depend on the phase of a solar cycle. The frequency of intense flares and storms increase during solar maximum. Heating up of the atmosphere causes its expansion eventually leading to accelerated drag of orbiting satellites, especially those in LEO. In this paper, we present the model of the atmospheric drag effect on the trajectory of hypothetical LEO satellites of different ballistic coefficients. We investigate long-term trend of atmospheric drag on LEO satellites due to solar forcing induced atmospheric perturbations and heating at different phases of the solar cycle, and during interval of strong geomagnetic disturbances or storms. We show the dependence of orbital decay on severity of both the solar cycle and phase, and the extent of geomagnetic perturbations. The result of the model compares well with the observed decay profile of existing LEO satellites and provides a better understanding of the issue of the orbital decay. Our result may also be useful for selection of launch window of satellites for an extended lifetime in the orbit.

  15. April 2002 Working Group Meeting on Heavy Vehicle Aerodynamic Drag: Presentations and Summary of Comments and Conclusions

    SciTech Connect

    Salari, K; Dunn, T; Ortega, J; Yen-Nakafuji, D; Browand, F; Arcas, D; Jammache, M; Leoard, A; Chatelain, P; Rubel, M; Rutledge, W; McWherter-Payne, M; Roy, Ca; Ross, J; Satran, D; Heineck, J T; Storms, B; Pointer, D; Sofu, T; Weber, D; Chu, E; Hancock, P; Bundy, B; Englar, B

    2002-08-22

    A Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held at Lawrence Livermore National Laboratory on April 3 and 4, 2002. The purpose of the meeting was to present and discuss technical details on the experimental and computational work in progress and future project plans. Representatives from the Department of Energy (DOE) Office of Transportation Technology Office of Heavy Vehicle Technology (OHVT), Lawrence Livermore National Laboratory (LLNL), Sandia National Laboratories (SNL), NASA Ames Research Center, University of Southern California (USC), and California Institute of Technology (Caltech), Georgia Tech Research Institute (GTRI), and Argonne National Laboratory (ANL), Volvo Trucks, and Freightliner Trucks presented and participated in discussions. This report contains the technical presentations (viewgraphs) delivered at the Meeting, briefly summarizes the comments and conclusions, and outlines the future action items.

  16. October 1998 working group meeting on heavy vehicle aerodynamic drag: presentations and summary of comments and conclusions

    SciTech Connect

    Browand, F; Heineck, J T; Leonard, A; McBride, D; McCallen, R; Ross, J; Rutledge, W; Salari, K; Storms, B

    1998-10-01

    A Working Group 1Meeting on Heavy Vehicle Aerodynamic Drag was held at NASA Ames Research Center, Moffett Field, California on October 22, 1998. The purpose of the meeting was to present an overview of the computational and experimental approach for modeling the integrated tractor-trailer benchmark geometry called the Sandia IModel and to review NASA' s test plan for their experiments in the 7 ft x 10 ft wind tunnel. The present and projected funding situation was also discussed. Presentations were given by representatives from the Department of Energy (DOE) Office of Transportation Technology Office of Heavy Vehicle Technology (OHVT). Lawrence Livermore National Laboratory (LLNL), Sandia National Laboratories (SNL), and NASA Ames Research Center. This report contains the technical presentations (viewgraphs) delivered at the Meeting, briefly summarizes the comments and conclusions. and outlines the future action items.

  17. Reduction of profile drag by blowing out through peg holes in areas of streamline separation bubbles

    NASA Technical Reports Server (NTRS)

    Horstmann, K. H.; Quast, A.

    1981-01-01

    Streamline separation bubbles on aircraft profiles and fuselages were investigated. The additional drag was examined in relation to increased angle of incidence and unusually high wall sheer stress. A reduction of the separation bubble and a decrease in drag is obtained with pneumatic turbulators that blow ram air out of 0.6mm pilot tubes at a distance of 16 mm. The pneumatic models are implemented at various positions and are found to be effective after the position of separation.

  18. Copolymers for Drag Reduction in Marine Propulsion: New Molecular Structures with Enhanced Effectiveness

    DTIC Science & Technology

    1993-05-31

    and C. McCormick, National ACS Meeting, Denver, CO, March 1993. "Derivatization of Chitin and Cellulose Utilizing LiC1/N,N-Dimethylacetamide Solvent...pH- and salt-responsive drag reducing systems based on zwitterionic and ionic polymer structures which have the best drag reducing properties reported...reduction efficiency as measured by a rotating disk apparatus. The polymer can be prepared by inverse emulsion or microemulsion techniques for rapid

  19. Trim drag reduction concepts for horizontal takeoff single-stage-to-Orbit vehicles

    NASA Technical Reports Server (NTRS)

    Shaughnessy, John D.; Gregory, Irene M.

    1991-01-01

    The results of a study to investigate concepts for minimizing trim drag of horizontal takeoff single-stage-to-orbit (SSTO) vehicles are presented. A generic hypersonic airbreathing conical configuration was used as the subject aircraft. The investigation indicates that extreme forward migration of the aerodynamic center as the vehicle accelerates to orbital velocities causes severe aerodynamic instability and trim moments that must be counteracted. Adequate stability can be provided by active control of elevons and rudder, but use of elevons to produce trim moments results in excessive trim drag and fuel consumption. To alleviate this problem, two solution concepts are examined. Active control of the center of gravity (COG) location to track the aerodynamic center decreases trim moment requirements, reduces elevon deflections, and leads to significant fuel savings. Active control of the direction of the thrust vector produces required trim moments, reduces elevon deflections, and also results in significant fuel savings. It is concluded that the combination of active flight control to provide stabilization, (COG) position control to minimize trim moment requirements, and thrust vectoring to generate required trim moments has the potential to significantly reduce fuel consumption during ascent to orbit of horizontal takeoff SSTO vehicles.

  20. Drag reductions and the air-water interface stability of superhydrophobic surfaces in rectangular channel flow

    NASA Astrophysics Data System (ADS)

    Zhang, Jingxian; Yao, Zhaohui; Hao, Pengfei

    2016-11-01

    Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.

  1. Drag reductions and the air-water interface stability of superhydrophobic surfaces in rectangular channel flow.

    PubMed

    Zhang, Jingxian; Yao, Zhaohui; Hao, Pengfei

    2016-11-01

    Flow in a rectangular channel with superhydrophobic (SH) top and bottom walls was investigated experimentally. Different SH surfaces, including hierarchical structured surfaces and surfaces with different micropost sizes (width and spacing) but the same solid fraction, were fabricated and measured. Pressure loss and flow rate in the channel with SH top and bottom walls were measured, with Reynolds number changing from 700 to 4700, and the corresponding friction factor for the SH surface was calculated. The statuses of the air plastron on different SH surfaces were observed during the experiment. In our experiment, compared with the experiment for the smooth surface, drag reductions were observed for all SH surfaces, with the largest drag reduction of 42.2%. It was found that the hierarchy of the microstructure can increase the drag reduction by decreasing the solid fraction and enhancing the stability of the air-water interface. With a fixed solid fraction, the drag reduction decreases as the post size (width and spacing) increases, due to the increasing curvature and instability effects of the air-water interface. A correlation parameter between the contact angle hysteresis, the air-water interface stability, and the drag reduction of the SH surfaces was found.

  2. Lubricant-impregnated surfaces for drag reduction in viscous laminar flow

    NASA Astrophysics Data System (ADS)

    Solomon, Brian; Khalil, Karim; Varanasi, Kripa; MIT Team

    2013-11-01

    For the first time, we explore the potential of lubricant impregnated surfaces (LIS) in reducing drag. LIS, inspired by the surface of the Nepenthes pitcher plant, have been introduced as a novel way of functionalizing a surface. LIS are characterized by extremely low contact angle hysteresis and have been show to effectively repel various liquids including water, oils, ketchup and blood. Motivated by the slippery nature of such surfaces, we explore the potential of LIS to reduce drag in internal flows. We observe a reduction in drag for LIS surfaces in a viscous laminar drag flow and model the impact of relevant system parameters (lubricant viscosity, working fluid viscosity, solid fraction, depth of texture, etc.).

  3. Re-examination of compliant wall experiments in air with water substrates. [for drag reduction

    NASA Technical Reports Server (NTRS)

    Hefner, J. N.; Weinstein, L. M.

    1976-01-01

    A possible alternative explanation is proposed for compliant wall drag reductions measured in previous investigations. Standing waves were observed to form on the surfaces of compliant wall models in air with water substrates as the freestream velocity was increased from 15 to 30 m/s. These waves resembled sine waves with half of the wave protruding over the upstream portion of the model and the other half being recessed over the downstream end of the model. These data coupled with results of recent drag reduction experiments suggest that standing waves could have caused a shift in the model center of gravity creating a bending moment that was interpreted as a reduction in the skin friction drag.

  4. The BMW analytic aerodynamic drag method for the Vinti satellite theory

    NASA Technical Reports Server (NTRS)

    Watson, J. S.; Mistretta, G. D.; Bonavito, N. L.

    1972-01-01

    In order to retain separability in the Vinti theory of earth satellite motion when a non conservative force such as air drag is considered, a set of variational equations for the orbital elements are introduced, and expressed as functions of the transverse, radial, and normal components of the nonconservative forces acting on the system. In particular, the atmospheric density profile is written as a fitted exponential function of the eccentric anomaly, which reproduces tabular values of static model atmospheric densities at all altitudes to within ninety-eight percent and simultaneously reduces the variational equations to indefinite integrals with closed form evaluations, whose limits are in terms of the eccentric anomaly. The values of the limits for any arbitrary time interval are obtained from the Vinti program. Results of the BMW (Bonavito, Mistretta, Watson) theory for the case of the intense air drag satellites San Marco-2 and Air Force Cannonball are given. These results indicate that the satellite ephemerides produced by the BMW theory in conjunction with the Vinti program are of very high accuracy. In addition, since the program is entirely analytic, several months of ephemerides can be obtained within a few seconds of computer time.

  5. The influence of polyvinylacetate additive in water on turbulent velocity field and drag reduction

    NASA Astrophysics Data System (ADS)

    Lodes, A.; Macho, V.

    1989-06-01

    The effect of polymer concentration on drag reduction was studied experimentally with diluted water solutions of polyvinylacetate in a 2.4 cm I. D. pipe. The instantaneous local velocities of the velocity fields were measured by a one-channel differential laser-Doppler anemometer DISA Mark II, with forward scattering. Concentrations of water-polyvinylacetate over the range from 10 to 2,000 ppm were used. The drag reduction coefficient is proportional to the concentration and hydrolysis degree of the saponificated polyvinylacetate (PVAC) employed. A mechanical degradation in the turbulent shear flow was not observed.

  6. Longitudinal Aerodynamic Characteristics and Effect of Rocket Jet on Drag of Models of the Hermes A-3A and A-3B Missiles in Free Flight at Mach Numbers From 0.6 to 2.0

    NASA Technical Reports Server (NTRS)

    Jackson, H. Herbert

    1955-01-01

    A free-flight investigation over a Mach number range from 0.6 to 2.0 has been conducted to determine the longitudinal aerodynamic characteristics and effect of rocket jet on zero-lift drag of 1/5-scale models of two ballistic-type missiles, the Hermes A-3A and A-3B. Models of both types of missiles exhibited very nearly linear normal forces and pitching moments over the angle-of-attack range of 8 deg to -4 deg and Mach number range tested. The centers of pressure for both missiles were not appreciably affected by Mach number over the subsonic range; however, between a Mach number of 1.02 and 1.50 the center of pressure for the A-3A model moved forward 0.34 caliber with increasing Mach number. At a trim angle-of-attack of approximately 30 deg, the A-3A model indicated a total drag coefficient 30% higher than the power-off zero-lift drag over the subsonic Mach number range and 10% higher over the supersonic range. Under the conditions of the present test, and excluding the effect of the jet on base drag, there was no indicated effect of the propulsive jet on the total drag of the A-3A model. The propulsive jet operating at a jet pressure ratio p(sub j)/p(sub o) of 0.8 caused approximately 100% increase in base drag over the Mach number range M = 0.6 to 1.0. This increase in base drag amounts to 15% of the total drag. An underexpanded jet operating at jet pressure ratios corresponding approximately to those of the full-scale missile caused a 22% reduction in base drag at M = 1.55 (p(sub j)/p(sub o) = 1.76) but indicated no change at M = 1.30 (p(sub j)/p(sub o) = 1.43). At M = 1.1 and p(sub j)/p(sub o) = 1.55, the jet caused a 50% increase in base drag.

  7. A mechanism of wave drag reduction in the thermal energy deposition experiments

    SciTech Connect

    Markhotok, A.

    2015-06-15

    Many experimental studies report reduced wave drag when thermal energy is deposited in the supersonic flow upstream of a body. Though a large amount of research on this topic has been accumulated, the exact mechanism of the drag reduction is still unknown. This paper is to fill the gap in the understanding connecting multiple stages of the observed phenomena with a single mechanism. The proposed model provides an insight on the origin of the chain of subsequent transformations in the flow leading to the reduction in wave drag, such as typical deformations of the front, changes in the gas pressure and density in front of the body, the odd shapes of the deflection signals, and the shock wave extinction in the plasma area. The results of numerical simulation based on the model are presented for three types of plasma parameter distribution. The spherical and cylindrical geometry has been used to match the data with the experimental observations. The results demonstrate full ability of the model to exactly explain all the features observed in the drag reduction experiments. Analytical expressions used in the model allow separating out a number of adjustment parameters that can be used to optimize thermal energy input and thus achieve fundamentally lower drag values than that of conventional approaches.

  8. Investigations on drag reduction in turbulent pipe flows by addition of ionic and nonionic high polymers

    NASA Astrophysics Data System (ADS)

    Graeger, Helmut

    Drag reduction in turbulent pipe flow is obtained by addition of polymeric flow accelerator. Turbulent flow pattern is described on the basis of existing theories and reduction of loss of pressure heads is discussed. A turbulence rheometer is developed permitting the measurement of friction reduction for Reynolds numbers 1100 to 90,000. Effectiveness of water soluble polymer systems like polyacrylamide and coacrylate is studied in dependence of concentration, chemical composition, product aging and polymer chain deformation.

  9. March 2000 Working Group Meeting on Heavy Vehicle Aerodynamic DragL Presentations and Summary of Comments and Conclusions

    SciTech Connect

    McCallen, R.; Flowers, D.; Dunn, T.; Owens, J.; Browand, F.; Hammache, M.; Loenard, A.; Brady, M.; Salari, K.; Rutledge, W.; Scheckler, R.; Ross, J.; Storms, B.; Heineck, J.T.; Arledge, T

    2000-05-15

    A Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held at Lawrence Livermore National Laboratory on March 16, 2000. The purpose of the meeting was to present technical details on the experimental and computational plans and approaches and provide an update on progress in the analysis of experimental results, model developments, simulations, and an investigation of an aerodynamic device. The focus of the meeting was a review of University of Southern California's (USC) experimental plans and results, NASA Ames experimental plans, the computational results from Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories (SNL) for the integrated tractor-trailer benchmark geometry called the Ground Transportation System (GTS) Model, and turbulence model development and benchmark simulation for a rounded cube from California Institute of Technology (Caltech). Much of the meeting discussion involved deficiencies in commercial software, needed modeling improvements, and the importance of detailed data for code validation. The present and projected budget and funding situation was also discussed. Presentations were given by representatives from the Department of Energy (DOE) Office of Transportation Technology Office of Heavy Vehicle Technology (OHVT), LLNL, SNL, NASA Ames, USC, and Caltech. Representatives from Argonne National Laboratory also participated via telephone. This report contains the technical presentations (viewgraphs) delivered at the Meeting, briefly summarizes the comments and conclusions, and outlines the future action items. There were 3 major issues raised at the meeting. (1) Our funding is inadequate to satisfy industries request for high Reynolds number experimentation and computation. Plans are to respond to the DOD and DOE requests for proposals, which require a 50-50 cost share with industry, to acquire funding for high Reynolds number experiments at NASA Ames. (2) The deficiencies in commercial software, the need for

  10. Investigation of passive shock wave-boundary layer control for transonic airfoil drag reduction

    NASA Technical Reports Server (NTRS)

    Nagamatsu, H. T.; Brower, W. B., Jr.; Bahi, L.; Ross, J.

    1982-01-01

    The passive drag control concept, consisting of a porous surface with a cavity beneath it, was investigated with a 12-percent-thick circular arc and a 14-percent-thick supercritical airfoil mounted on the test section bottom wall. The porous surface was positioned in the shock wave/boundary layer interaction region. The flow circulating through the porous surface, from the downstream to the upstream of the terminating shock wave location, produced a lambda shock wave system and a pressure decrease in the downstream region minimizing the flow separation. The wake impact pressure data show an appreciably drag reduction with the porous surface at transonic speeds. To determine the optimum size of porosity and cavity, tunnel tests were conducted with different airfoil porosities, cavities and flow Mach numbers. A higher drag reduction was obtained by the 2.5 percent porosity and the 1/4-inch deep cavity.

  11. A Base Drag Reduction Experiment on the X-33 Linear Aerospike SR-71 Experiment (LASRE) Flight Program

    NASA Technical Reports Server (NTRS)

    Whitmore, Stephen A.; Moes, Timothy R.

    1999-01-01

    Drag reduction tests were conducted on the LASRE/X-33 flight experiment. The LASRE experiment is a flight test of a roughly 20% scale model of an X-33 forebody with a single aerospike engine at the rear. The experiment apparatus is mounted on top of an SR-71 aircraft. This paper suggests a method for reducing base drag by adding surface roughness along the forebody. Calculations show a potential for base drag reductions of 8-14%. Flight results corroborate the base drag reduction, with actual reductions of 15% in the high-subsonic flight regime. An unexpected result of this experiment is that drag benefits were shown to persist well into the supersonic flight regime. Flight results show no overall net drag reduction. Applied surface roughness causes forebody pressures to rise and offset base drag reductions. Apparently the grit displaced streamlines outward, causing forebody compression. Results of the LASRE drag experiments are inconclusive and more work is needed. Clearly, however, the forebody grit application works as a viable drag reduction tool.

  12. Copolymers for Drag Reduction in Marine Propulsion: New Molecular Structures with Enhanced Effectiveness

    DTIC Science & Technology

    1989-08-01

    34 C. L. McCormick, National ACS Meeting, Miami, FL (1989). "Synthesis of Pyrene-Labeled High Molecular Weight Acrylamide Copolymers ," C. L. McCormick...and Characterization of Water-Soluble Acrylamide Copolymers for the Study of Drag Reduction," C. L. McCormick and P. S. Mumick, Abstracts MAS, 34, 55

  13. Drag reduction using metallic engineered surfaces with highly ordered hierarchical topographies: nanostructures on micro-riblets

    NASA Astrophysics Data System (ADS)

    Kim, Taekyung; Shin, Ryung; Jung, Myungki; Lee, Jinhyung; Park, Changsu; Kang, Shinill

    2016-03-01

    Durable drag-reduction surfaces have recently received much attention, due to energy-saving and power-consumption issues associated with harsh environment applications, such as those experienced by piping infrastructure, ships, aviation, underwater vehicles, and high-speed ground vehicles. In this study, a durable, metallic surface with highly ordered hierarchical structures was used to enhance drag-reduction properties, by combining two passive drag-reduction strategies: an air-layer effect induced by nanostructures and secondary vortex generation by micro-riblet structures. The nanostructures and micro-riblet structures were designed to increase slip length. The top-down fabrication method used to form the metallic hierarchical structures combined laser interference lithography, photolithography, thermal reflow, nanoimprinting, and pulse-reverse-current electrochemical deposition. The surfaces were formed from nickel, which has high hardness and corrosion resistance, making it suitable for use in harsh environments. The drag-reduction properties of various metal surfaces were investigated based on the surface structure: a bare surface, a nanostructured surface, a micro-riblet surface, and a hierarchically structured surface of nanostructures on micro-riblets.

  14. Boattail Plates With Non-Rectangular Geometries For Reducing Aerodynamic Base Drag Of A Bluff Body In Ground Effect

    DOEpatents

    Ortega, Jason M.; Sabari, Kambiz

    2006-03-07

    An apparatus for reducing the aerodynamic base drag of a bluff body having a leading end, a trailing end, a top surface, opposing left and right side surfaces, and a base surface at the trailing end substantially normal to a longitudinal centerline of the bluff body, with the base surface joined (1) to the left side surface at a left trailing edge, (2) to the right side surface at a right trailing edge, and (3) to the top surface at a top trailing edge. The apparatus includes left and right vertical boattail plates which are orthogonally attached to the base surface of the bluff body and inwardly offset from the left and right trailing edges, respectively. This produces left and right vertical channels which generate, in a flowstream substantially parallel to the longitudinal centerline, respective left and right vertically-aligned vortical structures, with the left and right vertical boattail plates each having a plate width defined by a rear edge of the plate spaced from the base surface. Each plate also has a peak plate width at a location between top and bottom ends of the plate corresponding to a peak vortex of the respective vertically-aligned vortical structures.

  15. July 1999 working group meeting on heavy vehicle aerodynamic drag: presentations and summary of comments and conclusions

    SciTech Connect

    Brady, M; Browand, F; Flowers, D; Hammache, M; Landreth, G; Leonard, A; McCallen, R; Ross, J; Rutledge, W; Salari, K

    1999-08-16

    A Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held at University of Southern California, Los Angeles, California on July 30, 1999. The purpose of the meeting was to present technical details on the experimental and computational plans and approaches and provide an update on progress in obtaining experimental results, model developments, and simulations. The focus of the meeting was a review of University of Southern California's (USC) experimental plans and results and the computational results from Lawrence Livermore National Laboratory (LLNL) and Sandia National Laboratories (SNL) for the integrated tractor-trailer benchmark geometry called the Sandia Model. Much of the meeting discussion involved the NASA Ames 7 ft x 10 ft wind tunnel tests and the need for documentation of the results. The present and projected budget and funding situation was also discussed. Presentations were given by representatives from the Department of Energy (DOE) Office of Transportation Technology Office of Heavy Vehicle Technology (OHVT), LLNL, SNL, USC, and California Institute of Technology (Caltech). This report contains the technical presentations (viewgraphs) delivered at the Meeting, briefly summarizes the comments and conclusions, and outlines the future action items.

  16. March 1999 working group meeting on heavy vehicle aerodynamic drag: presentations and summary of comments and conclusions

    SciTech Connect

    Brady, M; Browand, F; McCallen, R; Ross, J; Salari, K

    1999-03-01

    A Working Group Meeting on Heavy Vehicle Aerodynamic Drag was held at Lawrence Livermore National Laboratory, Livermore, California on March 11, 1999. The purpose of the meeting was to present technical details on the experimental and computational plans and approaches and provide an update on progress in obtaining experimental results, model developments, and simulations. The focus of the meeting was a review of the experimental results for the integrated tractor-trailer benchmark geometry called the Sandia Model in the NASA Ames 7 ft x 10 ft wind tunnel. The present and projected budget and funding situation was also discussed. Presentations were given by representatives from the Department of Energy (DOE) Office of Transportation Technology Office of Heavy Vehicle Technology (OHVT), Lawrence Livermore National Laboratory (LLNL), Sandia National Laboratories (SNL), University of Southern California (USC), California Institute of Technology (Caltech), and NASA Ames Research Center.This report contains the technical presentations (viewgraphs) delivered at the Meeting, briefly summarizes the comments and conclusions, and outlines the future action items.

  17. The economic impact of drag in general aviation

    NASA Technical Reports Server (NTRS)

    Neal, R. D.

    1975-01-01

    General aviation aircraft fuel consumption and operating costs are closely linked to drag reduction methods. Improvements in airplane drag are envisioned for new models; their effects will be in the 5 to 10% range. Major improvements in fuel consumption over existing turbofan airplanes will be the combined results of improved aerodynamics plus additional effects from advanced turbofan engine designs.

  18. Simulation of drag reduction in superhydrophobic microchannels based on parabolic gas-liquid interfaces

    NASA Astrophysics Data System (ADS)

    Li, Chunxi; Zhang, Shuo; Xue, Quanxi; Ye, Xuemin

    2016-10-01

    Based on the given parabolic gas-liquid interfaces, a two-dimensional fluid flow in superhydrophobic microchannels is numerically simulated with the steady volume of fluid model in the laminar regime. The influence of several crucial parameters on drag reduction effect is discussed. The results indicate that the superhydrophobic microchannel containing rectangular cavities displays significant drag reduction effect. With increasing inlet velocity, the pressure drop reduction decreases slightly. Augments in the pressure drop reduction tend to be large with the increase of the cavity fraction or the decrease of the channel height. The results also reveal that the variation of the normalized slip length with the cavity fraction tends to be more dramatic when the channel height is smaller. As the parabolic height of the gas-liquid interface is enlarged, both the pressure drop reduction and the normalized slip length decrease linearly, while fRe increases linearly. The impact of the cavity depth on the normalized slip length, fRe, and the pressure drop reduction is minimal supposing the depth of the cavity is greater than 40% of its width. The drag reduction effect corresponding to the dovetail cavity model is the best, and the consequence of the rectangular, trapezoidal, and triangular cavity models sequentially worsens.

  19. Traces of surfactants limit the drag reduction potential of superhydrophobic surfaces in realistic applications

    NASA Astrophysics Data System (ADS)

    Peaudecerf, Francois J.; Landel, Julien R.; Luzzatto-Fegiz, Paolo

    2015-11-01

    Large drag reductions have been measured for laminar flows over superhydrophobic surfaces (SHS), making them attractive for applications in pipelines, ships and submarines. However, experiments involving turbulent flows, typical of these applications, have often yielded limited drag reductions. A complete explanation for this issue has so far proved elusive. We propose that trace amounts of surfactants, unavoidable in the environment and in large-scale experiments, can yield poor performances of SHS, by producing Marangoni stresses when the edges of the SHS pattern are not aligned with the local flow velocity. To explore our hypothesis, we develop numerical simulations (inclusive of surfactants) for a flow over a textured SHS in a micro-channel, whose background shear is similar to a viscous sublayer. The texture consists of micro ridges perpendicular to the flow. We find that even small amounts of surfactants can prevent any drag reduction. As an experimental test, we flow de-ionised water with known surfactant concentrations through SHS micro-channels with texture similar to the simulations, while performing micro-PIV. At negligible surfactant concentrations, we find higher velocities between the ridges, as expected by classical models. However, as the concentration increases, we discover that the slip velocity drops to very small values even in the presence of a plastron. Our results show that the drag-reducing potential of superhydrophobic surfaces can be limited in realistic flow conditions

  20. An Examination of Drag Reduction Mechanisms in Marine Animals, with Potential Applications to Uninhabited Aerial Vehicles

    NASA Technical Reports Server (NTRS)

    Musick, John A.; Patterson, Mark R.; Dowd, Wesley W.

    2002-01-01

    Previous engineering research and development has documented the plausibility of applying biomimetic approaches to aerospace engineering. Past cooperation between the Virginia Institute of Marine Science (VIMS) and NASA focused on the drag reduction qualities of the microscale dermal denticles of shark skin. This technology has subsequently been applied to submarines and aircraft. The present study aims to identify and document the three-dimensional geometry of additional macroscale morphologies that potentially confer drag reducing hydrodynamic qualities upon marine animals and which could be applied to enhance the range and endurance of Uninhabited Aerial Vehicles (UAVs). Such morphologies have evolved over eons to maximize organismal energetic efficiency by reducing the energetic input required to maintain cruising speeds in the viscous marine environment. These drag reduction qualities are manifested in several groups of active marine animals commonly encountered by ongoing VIMS research programs: namely sharks, bony fishes such as tunas, and sea turtles. Through spatial data acquired by molding and digital imagery analysis of marine specimens provided by VIMS, NASA aims to construct scale models of these features and to test these potential drag reduction morphologies for application to aircraft design. This report addresses the efforts of VIMS and NASA personnel on this project between January and November 2001.

  1. Reynolds number effects on flow over twisted cylinder with drag reduction and vortex suppression

    NASA Astrophysics Data System (ADS)

    Jung, Jae Hwan; Yoon, Hyun Sik

    2015-11-01

    We investigated the Reynolds number effects on the flow over a twisted cylinder in the range of 3×103 <= Re <=1×104. To analyze the effect of the twisted cylinder, a large eddy simulation (LES) with a dynamic subgrid model was employed. A simulation of the smooth cylinder was also carried out to compare the results with those of the twisted cylinder. As Re increased, the mean drag and lift coefficient of the twisted cylinder increased with the same tendency as those of the smooth cylinder. However, the increases in the mean drag and lift coefficient of the twisted cylinder were much smaller than those of the smooth. Furthermore, elongated shear layer and suppressed vortex shedding from the twisted cylinder occurred compared to those of the smooth cylinder, resulting in a drag reduction and suppression of the vortex-induced vibration (VIV). In particular, the twisted cylinder achieved a significant reduction of over 96% in VIV compared with that of the smooth cylinder, regardless of increasing Re. As a result, we concluded that the twisted cylinder effectively controlled the flow structures with reductions in the drag and VIV compared with the smooth cylinder, irrespective of increasing Re. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) through GCRC-SOP (No. 2011-0030013) and (NRF-2015R1D1A3A01020867).

  2. Friction drag reduction achievable by near-wall turbulence manipulation in spatially developing boundary-layer

    NASA Astrophysics Data System (ADS)

    Bannier, Amaury; Garnier, Eric; Sagaut, Pierre

    2016-03-01

    Various control strategies, such as active feedback control or riblets, end up restraining near-wall turbulence. An analytical study is conducted to estimate the drag-reduction achievable by such control in zero-pressure-gradient turbulent boundary-layers. Based on an idealized control which damps all fluctuations within a near-wall layer, a composite flow profile is established. It leads to explicit models for both the drag-reduction and the boundary-layer development rate. A skin-friction decomposition is applied and gives physical insights on the underlying phenomena. The control is found to alter the spatial development of the boundary-layer, resulting in detrimental impact on the skin-friction. However, the drag-reducing mechanism, attributed to the turbulence weakening, is found predominant and massive drag reductions remain achievable at high Reynolds number, although a minute part of the boundary-layer is manipulated. The model is finally assessed against Large Eddy Simulations of riblet-controlled flow.

  3. Preparation, anti-biofouling and drag-reduction properties of a biomimetic shark skin surface

    PubMed Central

    Pu, Xia; Li, Guangji; Huang, Hanlu

    2016-01-01

    ABSTRACT Shark skin surfaces show non-smoothness characteristics due to the presence of a riblet structure. In this study, biomimetic shark skin was prepared by using the polydimethylsiloxane (PDMS)-embedded elastomeric stamping (PEES) method. Scanning electron microscopy (SEM) was used to examine the surface microstructure and fine structure of shark skin and biomimetic shark skin. To analyse the hydrophobic mechanism of the shark skin surface microstructure, the effect of biomimetic shark skin surface microstructure on surface wettability was evaluated by recording water contact angle. Additionally, protein adhesion experiments and anti-algae adhesion performance testing experiments were used to investigate and evaluate the anti-biofouling properties of the surface microstructure of biomimetic shark skin. The recorded values of the water contact angle of differently microstructured surfaces revealed that specific microstructures have certain effects on surface wettability. The anti-biofouling properties of the biomimetic shark skin surface with microstructures were superior to a smooth surface using the same polymers as substrates. Moreover, the air layer fixed on the surface of the biomimetic shark skin was found to play a key role in their antibiont adhesion property. An experiment into drag reduction was also conducted. Based on the experimental results, the microstructured surface of the prepared biomimetic shark skin played a significant role in reducing drag. The maximum of drag reduction rate is 12.5%, which is higher than the corresponding maximum drag reduction rate of membrane material with a smooth surface. PMID:26941105

  4. Effect of tail size reductions on longitudinal aerodynamic characteristics of a three surface F-15 model with nonaxisymmetric nozzles

    NASA Technical Reports Server (NTRS)

    Frassinelli, Mark C.; Carson, George T., Jr.

    1990-01-01

    An investigation was conducted in the Langley 16-Foot Transonic Tunnel to determine the effects of horizontal and vertical tail size reductions on the longitudinal aerodynamic characteristics of a modified F-15 model with canards and 2-D convergent-divergent nozzles. Quantifying the drag decrease at low angles of attack produced by tail size reductions was the primary focus. The model was tested at Mach numbers of 0.40, 0.90, and 1.20 over an angle of attack of -2 degree to 10 degree. The nozzle exhaust flow was simulated using high pressure air at nozzle pressure ratios varying from 1.0 (jet off) to 7.5. Data were obtained on the baseline configuration with and without tails as well as with reduced horizontal and/or vertical tail sizes that were 75, 50, and 25 percent of the baseline tail areas.

  5. Development of FDR-AF (Frictional Drag Reduction Anti-Fouling) Marine Coating

    NASA Astrophysics Data System (ADS)

    Lee, Inwon; Park, Hyun; Chun, Ho Hwan; GCRC-SOP Team

    2013-11-01

    In this study, a novel skin-friction reducing marine paint has been developed by mixing fine powder of PEO(PolyEthyleneOxide) with SPC (Self-Polishing Copolymer) AF (Anti-Fouling) paint. The PEO is well known as one of drag reducing agent to exhibit Toms effect, the attenuation of turbulent flows by long chain polymer molecules in the near wall region. The frictional drag reduction has been implemented by injecting such polymer solutions to liquid flows. However, the injection holes have been a significant obstacle to marine application. The present PEO-containing marine paint is proposed as an alternative to realize Toms effect without any hole on the ship surface. The erosion mechanism of SPC paint resin and the subsequent dissolution of PEO enable the controlled release of PEO solution from the coating. Various tests such as towing tank drag measurement of flat plate and turbulence measurement in circulating water tunnel demonstrated over 10% frictional drag reduction compared with conventional AF paint. This work was supported by the National Research Foundation of Korea (NRF) grant funded by the Korea government (MSIP) through GCRC-SOP(No. 2011-0030013).

  6. Liquid-Infused Surfaces with Trapped Air (LISTA) for Drag Force Reduction.

    PubMed

    Hemeda, A A; Tafreshi, H Vahedi

    2016-03-29

    Superhydrophobic (SHP) surfaces are known for their drag-reducing attributes thanks to their ability to trap air in their surface pores and thereby reduce the contact between water and the frictional solid area. SHP surfaces are prone to failure under elevated pressures or because of air-layer dissolution into the surrounding water. Slippery liquid-infused porous surfaces (SLIPS) or liquid-infused surfaces (LIS) in which the trapped air is replaced with a lubricant have been proposed in the literature as a way of eliminating the air dissolution problem as well as improving the surface stability under pressure. While an LIS surface has been shown to reduce drag for flow of water-glycerol mixture (ref 18), no significant drag reduction has yet been reported for the flow of water (a lower viscosity fluid) over LIS. In this concern, we have designed a new surface in which a layer of air is trapped underneath the infused lubricant to reduce the frictional forces preventing the LIS to provide drag reduction for water or any fluid with a viscosity less than that of the lubricant. Drag reduction performance of such surfaces, referred to here as liquid-infused surfaces with trapped air (LISTA), is predicted by solving the biharmonic equation for the water-oil-air three-phase system in transverse grooves with enhanced meniscus stability thanks to double-reentry designs. For the arbitrary dimensions considered in our proof-of-concept study, LISTA designs showed 20-37% advantage over their LIS counterparts.

  7. A bio-inspired device for drag reduction on a three-dimensional model vehicle.

    PubMed

    Kim, Dongri; Lee, Hoon; Yi, Wook; Choi, Haecheon

    2016-03-10

    In this paper, we introduce a bio-mimetic device for the reduction of the drag force on a three-dimensional model vehicle, the Ahmed body (Ahmed et al 1984 SAE Technical Paper 840300). The device, called automatic moving deflector (AMD), is designed inspired by the movement of secondary feathers on bird's wing suction surface: i.e., secondary feathers pop up when massive separation occurs on bird's wing suction surface at high angles of attack, which increases the lift force at landing. The AMD is applied to the rear slanted surface of the Ahmed body to control the flow separation there. The angle of the slanted surface considered is 25° at which the drag coefficient on the Ahmed body is highest. The wind tunnel experiment is conducted at Re H  = 1.0 × 10(5)-3.8 × 10(5), based on the height of the Ahmed body (H) and the free-stream velocity (U ∞). Several AMDs of different sizes and materials are tested by measuring the drag force on the Ahmed body, and showed drag reductions up to 19%. The velocity and surface-pressure measurements show that AMD starts to pop up when the pressure in the thin gap between the slanted surface and AMD is much larger than that on the upper surface of AMD. We also derive an empirical formula that predicts the critical free-stream velocity at which AMD starts to operate. Finally, it is shown that the drag reduction by AMD is mainly attributed to a pressure recovery on the slanted surface by delaying the flow separation and suppressing the strength of the longitudinal vortices emanating from the lateral edges of the slanted surface.

  8. Numerical Investigation of Rotorcraft Fuselage Drag Reduction Using Active Flow Control

    NASA Technical Reports Server (NTRS)

    Allan, Brian G.; Schaeffler, Norman W.

    2011-01-01

    The effectiveness of unsteady zero-net-mass-flux jets for fuselage drag reduction was evaluated numerically on a generic rotorcraft fuselage in forward flight with a rotor. Previous efforts have shown significant fuselage drag reduction using flow control for an isolated fuselage by experiment and numerical simulation. This work will evaluate a flow control strategy, that was originally developed on an isolated fuselage, in a more relevant environment that includes the effects of a rotor. Evaluation of different slot heights and jet velocity ratios were performed. Direct comparisons between an isolated fuselage and rotor/fuselage simulations were made showing similar flow control performance at a -3deg fuselage angle-of-attack condition. However, this was not the case for a -5deg angle-of-attack condition where the performance between the isolated fuselage and rotor/fuselage were different. The fuselage flow control resulted in a 17% drag reduction for a peak C(sub mu) of 0.0069 in a forward flight simulation where mu = 0:35 and CT/sigma = 0:08. The CFD flow control results also predicted a favorable 22% reduction of the fuselage download at this same condition, which can have beneficial compounding effects on the overall performance of the vehicle. This numerical investigation was performed in order to provide guidance for a future 1/3 scale wind tunnel experiment to be performed at the NASA 14-by 22-Foot Subsonic Tunnel.

  9. Drag reduction and the dynamics of turbulence in simple and complex fluids

    NASA Astrophysics Data System (ADS)

    Graham, Michael

    2013-11-01

    Addition of a small amount of very large polymer molecules or micelle-forming surfactants to a liquid can dramatically reduce the energy dissipation it exhibits in the turbulent flow regime. This rheological drag reduction phenomenon is widely used, for example in the Alaska pipeline, but it is not well-understood, and no comparable technology exists to reduce turbulent energy consumption in flows of gases, in which polymers or surfactants cannot be dissolved. The most striking feature of this phenomenon is the existence of a so-called maximum drag reduction (MDR) asymptote: for a given geometry and driving force, there is a maximum level of drag reduction that can be achieved through addition of polymers. Changing the concentration, molecular weight or even the chemical structure of the additives has no effect on this asymptotic value. This universality is the major puzzle of drag reduction. We describe direct numerical simulations of turbulent channel flow of Newtonian fluids and viscoelastic polymer solutions. Even in the absence of polymers, we show that there are intervals of ``hibernating'' turbulence that display very low drag as well as many other features of the MDR asymptote observed in polymer solutions. As viscoelasticity increases, the frequency of these intervals also increases, leading to flows that increasingly resemble MDR. A simple theory captures key features of the intermittent dynamics observed in the simulations. Additionally, simulations of ``edge states,'' dynamical trajectories that lie on the boundary between turbulent and laminar flow, display characteristics that are similar to those of hibernating turbulence and thus to the MDR asymptote, again even in the absence of polymer additives. Based on these observations, we propose a tentative unified description of rheological drag reduction. The existence of ``MDR-like'' intervals even in the absence of additives sheds light on the observed universality of MDR and may ultimately lead to new

  10. Drag reduction and the dynamics of turbulence in simple and complex fluidsa)

    NASA Astrophysics Data System (ADS)

    Graham, Michael D.

    2014-10-01

    Addition of a small amount of very large polymer molecules or micelle-forming surfactants to a liquid can dramatically reduce the energy dissipation it exhibits in the turbulent flow regime. This rheological drag reduction phenomenon is widely used, for example, in the Alaska pipeline, but it is not well-understood, and no comparable technology exists to reduce turbulent energy consumption in flows of gases, in which polymers or surfactants cannot be dissolved. The most striking feature of this phenomenon is the existence of a so-called maximum drag reduction (MDR) asymptote: for a given geometry and driving force, there is a maximum level of drag reduction that can be achieved through addition of polymers. Changing the concentration, molecular weight or even the chemical structure of the additives has little to no effect on this asymptotic value. This universality is the major puzzle of drag reduction. We describe direct numerical simulations of turbulent minimal channel flow of Newtonian fluids and viscoelastic polymer solutions. Even in the absence of polymers, we show that there are intervals of "hibernating" turbulence that display very low drag as well as many other features of the MDR asymptote observed in polymer solutions. As Weissenberg number increases to moderate values the frequency of these intervals also increases, and a simple theory captures key features of the intermittent dynamics observed in the simulations. At higher Weissenberg number, these intervals are altered - for example, their duration becomes substantially longer and the instantaneous Reynolds shear stress during them becomes very small. Additionally, simulations of "edge states," dynamical trajectories that lie on the boundary between turbulent and laminar flow, display characteristics that are similar to those of hibernating turbulence and thus to the MDR asymptote, again even in the absence of polymer additives. Based on these observations, we propose a tentative unified description

  11. Assessments of Bubble Dynamics Model and Influential Parameters in Microbubble Drag Reduction

    DTIC Science & Technology

    2006-03-01

    July 1, 2004 to December 31, 2005 Report Date: March 2006 Prepared Under Award No: N00014-04-1-0717 Submitted to Patrick Purtell Office...data of Merkle and Deutsch (1992) and the numerical model of Kunz et al. (2003). 8 Figure 6. Schematic diagram of the computational domain used for...Kim and Cleaver 1995; Meng and Uhlman 1998; Xu et al. 2002; Kunz et al. 2003) to reveal the mechanism of the microbubble drag reduction phenomenon

  12. Drag reduction effects facilitated by microridges inside the mouthparts of honeybee workers and drones.

    PubMed

    Li, Chu-Chu; Wu, Jia-Ning; Yang, Yun-Qiang; Zhu, Ren-Gao; Yan, Shao-Ze

    2016-01-21

    The mouthpart of a honeybee is a natural well-designed micropump that uses a reciprocating glossa through a temporary tube comprising a pair of galeae and labial palpi for loading nectar. The shapes and sizes of mouthparts differ among castes of honeybees, but the diversities of the functional microstructures inside the mouthparts of honeybee workers and drones remain poorly understood. Through scanning electron microscopy, we found the dimensional difference of uniformly distributed microridges on the inner galeae walls of Apis mellifera ligustica workers and drones. Subsequently, we recorded the feeding process of live honeybees by using a specially designed high-speed camera system. Considering the microridges and kinematics of the glossa, we constructed a hydrodynamic model to calculate the friction coefficient of the mouthpart. In addition, we test the drag reduction through the dimensional variations of the microridges on the inner walls of mouthparts. Theoretical estimations of the friction coefficient with respect to dipping frequency show that inner microridges can reduce friction during the feeding process of honeybees. The effects of drag reduction regulated by specific microridges were then compared. The friction coefficients of the workers and drones were found to be 0.011±0.007 (mean±s.d.) and 0.045±0.010, respectively. These results indicate that the mouthparts of workers are more capable of drag reduction compared with those of drones. The difference was analyzed by comparing the foraging behavior of the workers and drones. Workers are equipped with well-developed hypopharyngeal, and their dipping frequency is higher than that of drones. Our research establishes a critical link between microridge dimensions and drag reduction capability during the nectar feeding of honeybees. Our results reveal that microridges inside the mouthparts of honeybee workers and drones reflect the caste-related life cycles of honeybees.

  13. Sustained drag reduction in a turbulent flow using a low-temperature Leidenfrost surface

    PubMed Central

    Saranadhi, Dhananjai; Chen, Dayong; Kleingartner, Justin A.; Srinivasan, Siddarth; Cohen, Robert E.; McKinley, Gareth H.

    2016-01-01

    Skin friction drag contributes a major portion of the total drag for small and large water vehicles at high Reynolds number (Re). One emerging approach to reducing drag is to use superhydrophobic surfaces to promote slip boundary conditions. However, the air layer or “plastron” trapped on submerged superhydrophobic surfaces often diminishes quickly under hydrostatic pressure and/or turbulent pressure fluctuations. We use active heating on a superhydrophobic surface to establish a stable vapor layer or “Leidenfrost” state at a relatively low superheat temperature. The continuous film of water vapor lubricates the interface, and the resulting slip boundary condition leads to skin friction drag reduction on the inner rotor of a custom Taylor-Couette apparatus. We find that skin friction can be reduced by 80 to 90% relative to an unheated superhydrophobic surface for Re in the range 26,100 ≤ Re ≤ 52,000. We derive a boundary layer and slip theory to describe the hydrodynamics in the system and show that the plastron thickness is h = 44 ± 11 μm, in agreement with expectations for a Leidenfrost surface. PMID:27757417

  14. Drag reduction in turbulent channel laden with finite-size oblate spheroids

    NASA Astrophysics Data System (ADS)

    Niazi Ardekani, Mehdi; Pedro Costa Collaboration; Wim-Paul Breugem Collaboration; Francesco Picano Collaboration; Luca Brandt Collaboration

    2016-11-01

    Suspensions of oblate rigid particles in a turbulent plane channel flow are investigated for different values of the particle volume fraction. We perform direct numerical simulations (DNS), using a direct-forcing immersed boundary method to account for the particle-fluid interactions, combined with a soft-sphere collision model and lubrication corrections for short-range particle-particle and particle-wall interactions. We show a clear drag reduction and turbulence attenuation in flows laden with oblate spheroids, both with respect to the single phase turbulent flow and to suspensions of rigid spheres. We explain the drag reduction by the lack of the particle layer at the wall, observed before for spherical particles. In addition, the special shape of the oblate particles creates a tendency to stay parallel to the wall in its vicinity, forming a shield of particles that prevents strong fluctuations in the outer layer to reach the wall and vice versa. Detailed statistics of the fluid and particle phase will be presented at the conference to explain the observed drag reduction. Supported by the European Research Council Grant No. ERC-2013-CoG-616186, TRITOS. The authors acknowledge computer time provided by SNIC (Swedish National Infrastructure for Computing) and the support from the COST Action MP1305: Flowing matter.

  15. Drag Reduction and Performance Improvement of Hydraulic Torque Converters with Multiple Biological Characteristics.

    PubMed

    Chunbao, Liu; Li, Li; Yulong, Lei; Changsuo, Liu; Yubo, Zhang

    2016-01-01

    Fish-like, dolphin-like, and bionic nonsmooth surfaces were employed in a hydraulic torque converter to achieve drag reduction and performance improvement, which were aimed at reducing profile loss, impacting loss and friction loss, respectively. YJSW335, a twin turbine torque converter, was bionically designed delicately. The biological characteristics consisted of fish-like blades in all four wheels, dolphin-like structure in the first turbine and the stator, and nonsmooth surfaces in the pump. The prediction performance of bionic YJSW335, obtained by computational fluid dynamics simulation, was improved compared with that of the original model, and then it could be proved that drag reduction had been achieved. The mechanism accounting for drag reduction of three factors was also investigated. After bionic design, the torque ratio and the highest efficiencies of YJSW335 were both advanced, which were very difficult to achieve through traditional design method. Moreover, the highest efficiency of the low speed area and high speed area is 85.65% and 86.32%, respectively. By economic matching analysis of the original and bionic powertrains, the latter can significantly reduce the fuel consumption and improve the operating economy of the loader.

  16. Drag reduction in reservoir rock surface: Hydrophobic modification by SiO2 nanofluids

    NASA Astrophysics Data System (ADS)

    Yan, Yong-Li; Cui, Ming-Yue; Jiang, Wei-Dong; He, An-Le; Liang, Chong

    2017-02-01

    Based on the adsorption behavior of modified silica nanoparticles in the sandstone core surface, the hydrophobic surface was constructed, which consists of micro-nanoscale hierarchical structure. This modified core surface presents a property of drag reduction and meets the challenge of high injection pressure and low injection rate in low or ultra-low permeability reservoir. The modification effects on the surface of silica nanoparticles and reservoir cores, mainly concerning hydrophobicity and fine structure, were determined by measurements of contact angle and scanning electron microscopy. Experimental results indicate that after successful modification, the contact angle of silica nanoparticles varies from 19.5° to 141.7°, exhibiting remarkable hydrophobic properties. These modified hydrophobic silica nanoparticles display a good adsorption behavior at the core surface to form micro-nanobinary structure. As for the wettability of these modified core surfaces, a reversal has happened from hydrophilic into hydrophobic and its contact angle increases from 59.1° to 105.9°. The core displacement experiments show that the relative permeability for water has significantly increased by an average of 40.3% via core surface modification, with the effects of reducing injection pressure and improving injection performance of water flooding. Meanwhile, the mechanisms of drag reduction and improving water injection operation induced from the modified core surface were uncovered. The present study will establish a fundamental understanding on the drag reduction at the core surface modified by nanofluids and its applications in more industries.

  17. Drag Reduction and Performance Improvement of Hydraulic Torque Converters with Multiple Biological Characteristics

    PubMed Central

    Chunbao, Liu; Changsuo, Liu; Yubo, Zhang

    2016-01-01

    Fish-like, dolphin-like, and bionic nonsmooth surfaces were employed in a hydraulic torque converter to achieve drag reduction and performance improvement, which were aimed at reducing profile loss, impacting loss and friction loss, respectively. YJSW335, a twin turbine torque converter, was bionically designed delicately. The biological characteristics consisted of fish-like blades in all four wheels, dolphin-like structure in the first turbine and the stator, and nonsmooth surfaces in the pump. The prediction performance of bionic YJSW335, obtained by computational fluid dynamics simulation, was improved compared with that of the original model, and then it could be proved that drag reduction had been achieved. The mechanism accounting for drag reduction of three factors was also investigated. After bionic design, the torque ratio and the highest efficiencies of YJSW335 were both advanced, which were very difficult to achieve through traditional design method. Moreover, the highest efficiency of the low speed area and high speed area is 85.65% and 86.32%, respectively. By economic matching analysis of the original and bionic powertrains, the latter can significantly reduce the fuel consumption and improve the operating economy of the loader. PMID:27752220

  18. Application of reduced-order controller to turbulent flows for drag reduction

    NASA Astrophysics Data System (ADS)

    Lee, Keun H.; Cortelezzi, Luca; Kim, John; Speyer, Jason

    2001-05-01

    A reduced-order linear feedback controller is designed and applied to turbulent channel flow for drag reduction. From the linearized two-dimensional Navier-Stokes equations a distributed feedback controller, which produces blowing/suction at the wall based on the measured turbulent streamwise wall-shear stress, is derived using model reduction techniques and linearquadratic-Gaussian/loop-transfer-recovery control synthesis. The quadratic cost criterion used for synthesis is composed of the streamwise wall-shear stress, which includes the control effort of blowing/suction. This distributed two-dimensional controller developed from a linear system theory is shown to reduce the skin friction by 10% in direct numerical simulations of a low-Reynolds number turbulent nonlinear channel flow. Spanwise shear-stress variation, not captured by the distributed two-dimensional controller, is suppressed by augmentation of a simple spanwise ad hoc control scheme. This augmented three-dimensional controller, which requires only the turbulent streamwise velocity gradient, results in a further reduction in the skin-friction drag. It is shown that the input power requirement is significantly less than the power saved by reduced drag. Other turbulence characteristics affected by these controllers are also discussed.

  19. Drag Reduction CFD Simulations and Flow Visualization of Light Vehicle-Trailer Systems

    NASA Astrophysics Data System (ADS)

    Sigurdson, Lorenz; Boyer, Henry; Lange, Carlos F.

    2016-11-01

    Experiments and CFD were performed to study the effect a deflector had on the flow and drag force associated with a 2010 F-150 truck and cargo trailer Light Vehicle-Trailer System (LVTS). Image Correlation Velocimetry (ICV) on smokewire streaklines measured the velocity field on the model mid-plane. CFD estimated the drag reduction as 13% at a Re of 14,900 with a moving ground-plane, and 17% without. Experiments suggested that the low Re does not diminish the full-scale relevance of the drag reduction results. One low Re effect was the presence of a separation bubble on the hood of the tow vehicle whose size reduced with an increase in Re. Three other characteristic flow patterns were identified: separation off the lead vehicle cab, stagnation of the free-stream on the trailer face for the no-deflector case, and subsequent separation at the trailer front corner. Comparisons of the ICV and CFD results with no deflector indicated good agreement in the direction of the velocity vectors, and the smoke streaklines and CFD streamlines also agreed well. However, for the deflector case, the CFD found an entirely different topological solution absent in the experiment. A pair of vertically-oriented mid-plane vortices were wrapped around the front of the trailer. Support from the Canadian Natural Sciences and Engineering Research Council Grant 41747 is gratefully acknowledged.

  20. Experiments on the effects of aging on compliant coating drag reduction

    NASA Astrophysics Data System (ADS)

    Bandyopadhyay, P. R.; Henoch, C.; Hrubes, J. D.; Semenov, B. N.; Amirov, A. I.; Kulik, V. M.; Malyuga, A. G.; Choi, K.-S.; Escudier, M. P.

    2005-08-01

    We report the experimental results from a collaborative effort between USA, Russia, and UK on the development of compliant coatings for undersea application of reduction of drag. The focus is on "shelf-life" of coatings. The coatings are based on a linear interference theory of interaction between turbulence pressure fluctuation and the viscoelastic coating. The phase shift between boundary displacement and pressure fluctuation embodies the interference effect. The natural frequency of the coating is matched to the turbulent boundary layer region of maximum Reynolds stress production. Low-molecular weight rubber-like silicone coatings have been manufactured whose properties include slow and fast damping, slow and fast aging, and varying magnitudes of elasticity, density, and thickness as well as transparency. The dynamic modulus and loss tangent vary weakly over a range of frequencies and temperature allowing compatibility with broad spectrum of turbulence. Drag measurements have been carried out over a year by the three teams in their water tunnels independently of identical coated models. We show that, with some exceptions, drag reduction generally deteriorates with the age of the coatings.

  1. Elasto-Inertial Turbulence: From Subcritical Turbulence to Maximum Drag Reduction

    NASA Astrophysics Data System (ADS)

    Dubief, Yves; Sid, Samir; Egan, Raphael; Terrapon, Vincent

    2015-11-01

    Elasto Inertial Turbulence (EIT) is a turbulence state found so far in polymer solutions. Upon the appropriate initial perturbation, an autonomous regeneration cycle emerges between polymer dynamics, pressure and velocity fluctuations. This cycle is best explained by the Poisson equation derived from viscoelastic flow models such as FENE-P (used in this study). This presentation provides an overview of the structure of EIT in 2D channel flows for Reynolds numbers ranging from Reτ = 10 to 100 and for 3D simulations up to Ret au = 300 . For flows below the Newtonian critical Reynolds number, EIT increases the drag. For higher Reynolds numbers, EIT is surmised to be the energetic bound of Maximum Drag Reduction (MDR), the asymptotic state of drag reduction in polymer solutions. The very existence of EIT at low Reynolds numbers (Reτ < 60) highlights a backward energy transfer from the small scale polymer dynamics to larger flow scales. Similar dynamics is identified at higher Reynolds numbers, which could explain why polymer flows never become fully laminar. The authors acknowledge computational resources from CÉCI (F.R.S.-FNRS grant No.2.5020.11), the PRACE infrastructure, and the Vermont Advanced Computing Core.

  2. Changes in the turbulent boundary layer structure associated with net drag reduction by outer layer manipulators

    NASA Technical Reports Server (NTRS)

    Rashidnia, N.; Falco, R. E.

    1987-01-01

    A specially designed wind tunnel was used to examine the effects of tandemly arranged parallel plate manipulators (TAPPMs) on a turbulent boundary-layer structure and the associated drag. Momentum balances, as well as measurements of the local shear stress from the velocity gradient near the wall, were used to obtain the net drag and local skin friction changes. Two TAPPMs, identical except for the thickness of their plates, were used in the study. Results with .003 inch plates were a maximum net drag reduction of 10 percent at 58 beta sub o (using a momentum balance). At 20 beta sub o, simultaneous laser sheet flow visualization and hot-wire anemometry data showed that the Reynolds stress in the large eddies was significantly reduced, as were the streamwise and normal velocity components. Using space-time correlations the reductions were again identified. Furthermore, quantitative flow visualization showed that the outward normal velocity of the inner region was also significantly decreased in the region around 20 beta sub o. However, throughout the first 130 beta sub o, the measured sublayer thickness with the TAPPMs in place was 15 to 20 percent greater. The data showed that the skin friction, as well as the structure of the turbulence, was strongly modified in the first 35 beta sub o, but that they both significantly relaxed toward unmanipulated boundary layer values by 50 beta sub o.

  3. Skin-Friction Drag Reduction over Super-Hydrophobic Materials in Fully-Developed Turbulent Flow

    NASA Astrophysics Data System (ADS)

    Gose, James W.; Golovin, Kevin; Ceccio, Steven L.; Perlin, Marc; Tuteja, Anish

    2015-11-01

    As part an on-going research initiative to develop super-hydrophobic (SH) materials for high-speed naval applications, a team at the University of Michigan investigated SH materials for drag reduction in fully-developed turbulent flow. The SH materials were evaluated in a high-aspect ratio (width/height) channel flow facility capable of producing average flow speeds of 20 m/s, yielding a height (7 mm) based Reynolds number of 140,000. The SH materials examined were developed for large-scale application using various technologies including spraying, chemical etching, and mechanical abrasion. The materials were applied over a 100 mm (spanwise/width) by 1100 mm (streamwise/length) area. The drag measurement methods were pressure drop along the test surface over length 150H (1050 mm) and by means of the velocity profile via particle image velocimetry. The SH materials were investigated further to determine the effects of various flow conditions including low (vacuum) and high pressures. The drag reduction measurements were coupled with extensive topological evaluation of the materials to illustrate the importance of each aspect of the individual SH features, as well as the collective structure of the surface, leading to insight regarding the relevant characteristics of an SH material's ability to reduce skin-friction in fully-developed turbulent flow. The authors recognize the support of ONR.

  4. Supersonic Aerodynamic Characteristics of a Low-Drag Aircraft Configuration having an Arrow Wing of Aspect Ratio 1.86 and a Body of Fineness Ratio 20

    NASA Technical Reports Server (NTRS)

    Gillespie, Warren, Jr.

    1960-01-01

    A free-flight rocket-propelled-model investigation was conducted at Mach numbers of 1.2 to 1.9 to determine the longitudinal and lateral aero-dynamic characteristics of a low-drag aircraft configuration. The model consisted of an aspect-ratio -1.86 arrow wing with 67.5 deg. leading-edge sweep and NACA 65A004 airfoil section and a triangular vertical tail with 60 deg. sweep and NACA 65A003 section in combination with a body of fineness ratio 20. Aerodynamic data in pitch, yaw, and roll were obtained from transient motions induced by small pulse rockets firing at intervals in the pitch and yaw directions. From the results of this brief aerodynamic investigation, it is observed that very slender body shapes can provide increased volumetric capacity with little or no increase in zero-lift drag and that body fineness ratios of the order of 20 should be considered in the design of long-range supersonic aircraft. The zero-lift drag and the drag-due-to-lift parameter of the test configuration varied linearly with Mach number. The maximum lift-drag ratio was 7.0 at a Mach number of 1.25 and decreased slightly to a value of 6.6 at a Mach number of 1.81. The optimum lift coefficient, normal-force-curve slope, lateral-force-curve slope, static stability in pitch and yaw, time to damp to one-half amplitude in pitch and yaw, the sum of the rotary damping derivatives in pitch and also in yaw, and the static rolling derivatives all decreased with an increase in Mach number. Values of certain rolling derivatives were obtained by application of the least-squares method to the differential equation of rolling motion. A comparison of the experimental and calculated total rolling-moment-coefficient variation during transient oscillations of the model indicated good agreement when the damping-in-roll contribution was included with the static rolling-moment terms.

  5. Research on the drag reduction performance induced by the counterflowing jet for waverider with variable blunt radii

    NASA Astrophysics Data System (ADS)

    Li, Shi-bin; Wang, Zhen-guo; Barakos, George N.; Huang, Wei; Steijl, Rene

    2016-10-01

    Waverider will endure the huge aero-heating in the hypersonic flow, thus, it need be blunt for the leading edge. However, the aerodynamic performance will decrease for the blunt waverider because of the drag hoik. How to improve the aerodynamic performance and reduce the drag and aero-heating is very important. The variable blunt radii method will improve the aerodynamic performance, however, the huge aero-heating and bow shock wave at the head is still serious. In the current study, opposing jet is used in the waverider with variable blunt radii to improve its performance. The three-dimensional coupled implicit Reynolds-averaged Navier-Stokes(RANS) equation and the two equation SST k-ω turbulence model have been utilized to obtain the flow field properties. The numerical method has been validated against the available experimental data in the open literature. The obtained results show that the L/D will drop 7-8% when R changes from 2 to 8. The lift coefficient will increase, and the drag coefficient almost keeps the same when the variable blunt radii method is adopted, and the L/D will increase. The variable blunt radii method is very useful to improve the whole characteristics of blunt waverider and the L/D can improve 3%. The combination of the variable blunt radii method and opposing jet is a novel way to improve the whole performance of blunt waverider, and L/D can improve 4-5%. The aperture as a novel way of opposing jet is suitable for blunt waverider and also useful to improve the aerodynamic and aerothermodynamic characteristics of waverider in the hypersonic flow. There is the optimal P0in/P0 that can make the detached shock wave reattach the lower surface again so that the blunt waverider can get the better aerodynamic performance.

  6. "Fluid bearing" effect of enclosed liquids in grooves on drag reduction in microchannels

    NASA Astrophysics Data System (ADS)

    Chen, Haosheng; Gao, Yang; Stone, Howard A.; Li, Jiang

    2016-12-01

    We report details of the fluid motion formed within and above grooves when a laminar continuous phase fluid flows over a second immiscible fluid enclosed in a grooved microchannel. Vortical structures within the transverse grooves were caused by a slip velocity at the fluid-fluid interface and act as "fluid bearings" on the boundary to lubricate the flow of the continuous phase. We investigated the drag reduction in the laminar flow in the microchannel by measuring slip at the boundaries and calculating an effective slip length, taking into account the influence of the effect of the viscosity ratio of the two fluids on the effective slip length. The "fluid bearing" effect can be used to transport high viscosity fluids using low viscosity fluids trapped in cavities to reduce drag.

  7. Studies of Aerodynamic Drag.

    DTIC Science & Technology

    1982-12-01

    viscosity, but because of its involvement in the determination of other important physical constants. A good example is Millikan’s classic oil drop ...apparatus was made by Bearden (1939) with a specific interest in the oil drop experiment. This configuration is probably the simplest from the point...34-f F5 drop to zero at the surface, i.e. ui= 0. This new boundary condition is known as the "no slip" condition, and holds provided that the mean

  8. The Aerodynamic Performance of the 24 Inch Houck Configuration

    DTIC Science & Technology

    2007-03-01

    8 2.5 Winglets ... Winglets “ Winglets are aerodynamic components, placed at the tip of a wing to improve its efficiency during cruise” (6). The purpose of the winglet ...reduction in downwash, and therefore the induced drag (20; 11:1). Properly designed winglets can reduce overall drag, increase lift, provide added stability

  9. Investigation to optimize the passive shock wave/boundary layer control for supercritical airfoil drag reduction

    NASA Technical Reports Server (NTRS)

    Nagamatsu, H. T.; Dyer, R.

    1984-01-01

    The passive shock wave/boundary layer control for reducing the drag of 14%-thick supercritical airfoil was investigated in the 3 in. x 15.4 in. RPI Transonic Wind Tunnel with and without the top wall insert at transonic Mach numbers. Top wall insert was installed to increase the flow Mach number to 0.90 with the model mounted on the test section bottom wall. Various porous surfaces with a cavity underneath were positioned on the area of the airfoil where the shock wave occurs. The higher pressure behind the shock wave circulates flow through the cavity to the lower pressure ahead of the shock wave. The effects from this circulation prevent boundary layer separation and enthropy increase hrough the shock wave. The static pressure distributions over the airfoil, the wake impact pressure survey for determining the profile drag and the Schlieren photographs for porous surfaces are presented and compared with the results for solid surface airfoil. With a 2.8% uniform porosity the normal shock wave for the solid surface was changed to a lambda shock wave, and the wake impact pressure data indicate a drag coefficient reduction as much as 45% lower than for the solid surface airfoil at high transonic Mach numbers.

  10. Boundary layer drag reduction research hypotheses derived from bio-inspired surface and recent advanced applications.

    PubMed

    Luo, Yuehao; Yuan, Lu; Li, Jianhua; Wang, Jianshe

    2015-12-01

    Nature has supplied the inexhaustible resources for mankind, and at the same time, it has also progressively developed into the school for scientists and engineers. Through more than four billions years of rigorous and stringent evolution, different creatures in nature gradually exhibit their own special and fascinating biological functional surfaces. For example, sharkskin has the potential drag-reducing effect in turbulence, lotus leaf possesses the self-cleaning and anti-foiling function, gecko feet have the controllable super-adhesion surfaces, the flexible skin of dolphin can accelerate its swimming velocity. Great profits of applying biological functional surfaces in daily life, industry, transportation and agriculture have been achieved so far, and much attention from all over the world has been attracted and focused on this field. In this overview, the bio-inspired drag-reducing mechanism derived from sharkskin is explained and explored comprehensively from different aspects, and then the main applications in different fluid engineering are demonstrated in brief. This overview will inevitably improve the comprehension of the drag reduction mechanism of sharkskin surface and better understand the recent applications in fluid engineering.

  11. The mechanism of the polymer-induced drag reduction in blood.

    PubMed

    Pribush, Alexander; Hatzkelzon, Lev; Meyerstein, Dan; Meyerstein, Naomi

    2013-03-01

    Literature reports provide evidence that nanomolar concentrations of spaghetti-like, high molecular weight polymers decrease the hydrodynamic resistance of blood thereby improving impaired blood circulation. It has been suggested that the polymer-induced drag reduction is caused by the corralling of red blood cells (RBCs) among extended macromolecules aligned in the flow direction. This mechanism predicts that drag-reducing polymers must affect the conductivity of completely dispersed blood, time-dependent and steady state structural organization of aggregated RBCs at rest. However, experimental results obtained at the concentration of poly(ethylene oxide) (PEO, MW=4 × 10(6)) of 35 ppm show that neither the conductivity of completely dispersed blood, nor the kinetics of RBC aggregation occurring after the stoppage of flow, nor the structural organization of aggregated RBCs in the quiescent blood are affected by PEO. As these results are at odds with the "corralling" hypothesis, it is assumed that the effect of these polymers on the drag is associated with their interactions with local irregularities of disturbed laminar blood flow.

  12. On the Application of Contour Bumps for Transonic Drag Reduction(Invited)

    NASA Technical Reports Server (NTRS)

    Milholen, William E., II; Owens, Lewis R.

    2005-01-01

    The effect of discrete contour bumps on reducing the transonic drag at off-design conditions on an airfoil have been examined. The research focused on fully-turbulent flow conditions, at a realistic flight chord Reynolds number of 30 million. State-of-the-art computational fluid dynamics methods were used to design a new baseline airfoil, and a family of fixed contour bumps. The new configurations were experimentally evaluated in the 0.3-m Transonic Cryogenic Tunnel at the NASA Langley Research center, which utilizes an adaptive wall test section to minimize wall interference. The computational study showed that transonic drag reduction, on the order of 12% - 15%, was possible using a surface contour bump to spread a normal shock wave. The computational study also indicated that the divergence drag Mach number was increased for the contour bump applications. Preliminary analysis of the experimental data showed a similar contour bump effect, but this data needed to be further analyzed for residual wall interference corrections.

  13. Drag Reduction Devices for Aircraft (Latest Citations from the Aerospace Database)

    NASA Technical Reports Server (NTRS)

    1996-01-01

    The bibliography contains citations concerning the modeling, application, testing, and development of drag reduction devices for aircraft. Slots, flaps, fences, large-eddy breakup (LEBU) devices, vortex generators and turbines, Helmholtz resonators, and winglets are among the devices discussed. Contour shaping to ensure laminar flow, control boundary layer transition, or minimize turbulence is also covered. Applications include the wings, nacelles, fuselage, empennage, and externals of aircraft designed for high-lift, subsonic, or supersonic operation. The design, testing, and development of directional grooves, commonly called riblets, are covered in a separate bibliography.(Contains 50-250 citations and includes a subject term index and title list.)

  14. Drag reduction of motor vehicles by active flow control using the Coanda effect

    NASA Astrophysics Data System (ADS)

    Geropp, D.; Odenthal, H.-J.

    A test facility has been constructed to realistically simulate the flow around a two dimensional car shaped body in a wind tunnel. A moving belt simulator has been employed to generate the relative motion between model and ground. In a first step, the aerodynamic coefficients cL and cD of the model are determined using static pressure and force measurements. LDA-measurements behind the model show the large vortex and turbulence structures of the near and far wake. In a second step, the ambient flow around the model is modified by way of an active flow control which uses the Coanda effect, whereby the base-pressure increases by nearly 50% and the total drag can be reduced by 10%. The recirculating region is completely eliminated. The current work reveals the fundamental physical phenomena of the new method by observing the pressure forces on the model surface as well as the time averaged velocities and turbulence distributions for the near and far wake. A theory resting on this empirical information is developed and provides information about the effectiveness of the blowing method. For this, momentum and energy equations were applied to the flow around the vehicle to enable a validation of the theoretical results using experimental values.

  15. An investigation of drag reduction for a standard truck with various modifications

    NASA Technical Reports Server (NTRS)

    Muirhead, V. U.

    1981-01-01

    A wind tunnel investigation was conducted to determine the influence of several physical variables on the aerodynamic drag of a standard truck model. The physical variables included: a cab mounted air deflector; a boattail on the rear of the cargo compartment; flow-vanes on the front of the cargo compartment; and a forebody fairing over the cab. Tests were conducted at yaw angles (relative wind angle) of 0, 5, 10, 20, and 30 degrees and Reynolds numbers of 3.4 x 100,000 to 6.1 x 100,000 based upon the equivalent diameter of the vehicles. The forebody fairing and the flow-vane with the closed bottom were very effective in improving the flow over the forward part of the cargo compartment. The forebody fairing provided a calculated fuel saving of 5.6 liters per hour (1.5 gallons per hour) over the baseline configuration for a ground speed of 88.6 km/hr (55 mph) in national average winds.

  16. Direct Numerical Simulation of Air Layer Drag Reduction over a Backward-facing Step

    NASA Astrophysics Data System (ADS)

    Kim, Dokyun; Moin, Parviz

    2010-11-01

    Direct Numerical Simulation (DNS) of two-phase flow is performed to investigate the air layer drag reduction (ALDR) phenomenon in turbulent flow over a backward-facing step. In their experimental study, Elbing et al. (JFM, 2008) have observed a stable air layer on an entire flat plate if air is injected beyond the critical air-flow rate. In the present study, air is injected at the step on the wall into turbulent water flow for ALDR. The Reynolds and Weber numbers based on the water properties and step height are 22,800 and 560, respectively. An inlet section length before the step is 3h and the post expansion length is 30h, where h is the step height. The total number of grid points is about 271 million for DNS. The level set method is used to track the phase interface and the structured-mesh finite volume solver is used with an efficient algorithm for two-phase DNS. Two cases with different air-flow rates are performed to investigate the mechanism and stability of air layer. For high air-flow rate, the stable air layer is formed on the plate and more than 90% drag reduction is obtained. In the case of low air-flow rate, the air layer breaks up and ALDR is not achieved. The parameters governing the stability of air layer from the numerical simulations is also consistent with the results of stability analysis.

  17. A numerical study of air layer drag reduction phenomenon on a flat plate

    NASA Astrophysics Data System (ADS)

    Kim, Dokyun; Moin, Parviz

    2009-11-01

    The objective of the present study is to predict and understand the air layer drag reduction (ALDR) phenomenon. Recent experiments (Elbing et al. JFM 2008) have shown large net drag reductions if air is injected beyond a critical rate at the wall. The stability analysis and numerical simulations are performed to investigate mechanisms of ALDR on a flat plate using the same geometry as in the experiment. The linear stability of air-liquid interface is investigated by solving the Orr-Sommerfeld equations, and numerical simulations of two-phase flow have been performed to describe the evolution of air-water interface. The stability analysis shows that the air flow rates, Reynolds number, Weber number, and Froude number are important parameters determining the stability of the air layer. In laminar boundary layer, it is observed from the numerical simulations that the Froude number is the key to the stability of the air layer. The presentation will include a new and very efficient numerical method for two-phase flow calculations used in this study.

  18. Anomalous Drag Reduction and Hydrodynamic Interactions of Nanoparticles in Polymer Nanocomposite Thin Films

    NASA Astrophysics Data System (ADS)

    Basu, Jaydeep; Begam, Nafisa; Chandran, Sivasurender; Sprung, Michael

    2015-03-01

    One of the central dogma of fluid physics is the no-slip boundary condition whose validity has come under intense scrutiny, especially in the fields of micro and nanofluidics. Although various studies show the violation of the no-slip condition its effect on flow of colloidal particles in viscous media has been rarely explored. Here we report unusually large reduction of effective drag experienced by polymer grafted nanoparticles moving through a highly viscous film of polymer, well above its glass transition temperature. The extent of drag reduction increases with decreasing temperature and polymer film thickness. We also observe apparent divergence of the wave vector dependent hydrodynamic interaction function of these nanoparticles with an anomalous power law exponent of ~ 2 at the lowest temperatures and film thickness. Such strong hydrodynamic interactions are not expected in polymer melts where these interactions are known to be screened to molecular dimensions. We provide evidence for the presence of large hydrodynamic slip at the nanoparticle-polymer interface and demonstrate its tunability with temperature and confinement. Our study suggests novel physics emerging in dynamics nanoparticles due to confinement and interface wettability in thin films of polymer nanocomposites.

  19. Newest Results from the Investigation of Polymer-Induced Drag Reduction through Direct Numerical Simulation

    NASA Astrophysics Data System (ADS)

    Dimitropoulos, Costas D.; Beris, Antony N.; Sureshkumar, R.; Handler, Robert A.

    1998-11-01

    This work continues our attempts to elucidate theoretically the mechanism of polymer-induced drag reduction through direct numerical simulations of turbulent channel flow, using an independently evaluated rheological model for the polymer stress. Using appropriate scaling to accommodate effects due to viscoelasticity reveals that there exists a great consistency in the results for different combinations of the polymer concentration and chain extension. This helps demonstrate that our obervations are applicable to very dilute systems, currently not possible to simulate. It also reinforces the hypothesis that one of the prerequisites for the phenomenon of drag reduction is sufficiently enhanced extensional viscosity, corresponding to the level of intensity and duration of extensional rates typically encountered during the turbulent flow. Moreover, these results motivate a study of the turbulence structure at larger Reynolds numbers and for different periodic computational cell sizes. In addition, the Reynolds stress budgets demonstrate that flow elasticity adversely affects the activities represented by the pressure-strain correlations, leading to a redistribution of turbulent kinetic energy amongst all directions. Finally, we discuss the influence of viscoelasticity in reducing the production of streamwise vorticity.

  20. Active control for drag reduction in turbulent channel flow: the opposition control schemes revisited

    NASA Astrophysics Data System (ADS)

    Wang, Yin-Shan; Huang, Wei-Xi; Xu, Chun-Xiao

    2016-10-01

    The opposition control schemes first proposed by Choi et al (1994 J. Fluid Mech. 262 75) employing wall-normal (v) and spanwise (w) velocity are revisited in the present study by performing direct numerical simulation to turbulent channel flow at R{e}τ = 180. Special attention is paid to the combined control, in which the wall-normal and spanwise velocities are imposed at the wall just instantaneously opposite to those at a small distance to the wall. In comparison to the v- and w-controls, combined-control could achieve the best drag reduction rate and control efficiency, with the greatest suppression of turbulence intensities. The influence of control on the statistical properties of vortices is scrutinized. By control, the numbers of vortices with every circulation and radius apparently decrease at the same normal location near the wall, while the vortex radius scaled by the actual wall-friction velocity almost remains the same. The streamwise vortices and the induced Reynolds shear stress undergo the greatest suppression by combined control. It is shown that combined control achieves a better efficacy, attributed to the co-work of the mechanisms of the v- and w-controls. At a higher Reynolds number R{e}τ = 1000, combined control is also more effective than v- and w-controls. The better suppression effect on the outer large scales is the primary reason for the larger drag reduction rate in combined control.

  1. Stream-wise distribution of skin-friction drag reduction on a flat plate with bubble injection

    NASA Astrophysics Data System (ADS)

    Qin, Shijie; Chu, Ning; Yao, Yan; Liu, Jingting; Huang, Bin; Wu, Dazhuan

    2017-03-01

    To investigate the stream-wise distribution of skin-friction drag reduction on a flat plate with bubble injection, both experiments and simulations of bubble drag reduction (BDR) have been conducted in this paper. Drag reductions at various flow speeds and air injection rates have been tested in cavitation tunnel experiments. Visualization of bubble flow pattern is implemented synchronously. The computational fluid dynamics (CFD) method, in the framework of Eulerian-Eulerian two fluid modeling, coupled with population balance model (PBM) is used to simulate the bubbly flow along the flat plate. A wide range of bubble sizes considering bubble breakup and coalescence is modeled based on experimental bubble distribution images. Drag and lift forces are fully modeled based on applicable closure models. Both predicted drag reductions and bubble distributions are in reasonable concordance with experimental results. Stream-wise distribution of BDR is revealed based on CFD-PBM numerical results. In particular, four distinct regions with different BDR characteristics are first identified and discussed in this study. Thresholds between regions are extracted and discussed. And it is highly necessary to fully understand the stream-wise distribution of BDR in order to establish a universal scaling law. Moreover, mechanism of stream-wise distribution of BDR is analysed based on the near-wall flow parameters. The local drag reduction is a direct result of near-wall max void fraction. And the near-wall velocity gradient modified by the presence of bubbles is considered as another important factor for bubble drag reduction.

  2. Drag Reduction by Laser-Plasma Energy Addition in Hypersonic Flow

    SciTech Connect

    Oliveira, A. C.; Minucci, M. A. S.; Toro, P. G. P.; Chanes, J. B. Jr; Myrabo, L. N.

    2008-04-28

    An experimental study was conducted to investigate the drag reduction by laser-plasma energy addition in a low density Mach 7 hypersonic flow. The experiments were conducted in a shock tunnel and the optical beam of a high power pulsed CO{sub 2} TEA laser operating with 7 J of energy and 30 MW peak power was focused to generate the plasma upstream of a hemispherical model installed in the tunnel test section. The non-intrusive schlieren optical technique was used to visualize the effects of the energy addition to hypersonic flow, from the plasma generation until the mitigation of the shock wave profile over the model surface. Aside the optical technique, a piezoelectric pressure transducer was used to measure the impact pressure at stagnation point of the hemispherical model and the pressure reduction could be observed.

  3. Winglet and long duct nacelle aerodynamic development for DC-10 derivatives

    NASA Technical Reports Server (NTRS)

    Taylor, A. B.

    1978-01-01

    Advanced technology for application to the Douglas DC-10 transport is discussed. Results of wind tunnel tests indicate that the winglet offers substantial cruise drag reduction with less wing root bending moment penalty than a wing-tip extension of the same effectiveness and that the long duct nacelle offers substantial drag reduction potential as a result of aerodynamic and propulsion improvements. The aerodynamic design and test of the nacelle and pylon installation are described.

  4. Advanced Aerodynamic Control Effectors

    NASA Technical Reports Server (NTRS)

    Wood, Richard M.; Bauer, Steven X. S.

    1999-01-01

    A 1990 research program that focused on the development of advanced aerodynamic control effectors (AACE) for military aircraft has been reviewed and summarized. Data are presented for advanced planform, flow control, and surface contouring technologies. The data show significant increases in lift, reductions in drag, and increased control power, compared to typical aerodynamic designs. The results presented also highlighted the importance of planform selection in the design of a control effector suite. Planform data showed that dramatic increases in lift (greater than 25%) can be achieved with multiple wings and a sawtooth forebody. Passive porosity and micro drag generator control effector data showed control power levels exceeding that available from typical effectors (moving surfaces). Application of an advanced planform to a tailless concept showed benefits of similar magnitude as those observed in the generic studies.

  5. Robust Airfoil Optimization to Achieve Consistent Drag Reduction Over a Mach Range

    NASA Technical Reports Server (NTRS)

    Li, Wu; Huyse, Luc; Padula, Sharon; Bushnell, Dennis M. (Technical Monitor)

    2001-01-01

    We prove mathematically that in order to avoid point-optimization at the sampled design points for multipoint airfoil optimization, the number of design points must be greater than the number of free-design variables. To overcome point-optimization at the sampled design points, a robust airfoil optimization method (called the profile optimization method) is developed and analyzed. This optimization method aims at a consistent drag reduction over a given Mach range and has three advantages: (a) it prevents severe degradation in the off-design performance by using a smart descent direction in each optimization iteration, (b) there is no random airfoil shape distortion for any iterate it generates, and (c) it allows a designer to make a trade-off between a truly optimized airfoil and the amount of computing time consumed. For illustration purposes, we use the profile optimization method to solve a lift-constrained drag minimization problem for 2-D airfoil in Euler flow with 20 free-design variables. A comparison with other airfoil optimization methods is also included.

  6. Bio-inspired Gecko Micro-surface for Drag Reduction in Turbulent Flows

    NASA Astrophysics Data System (ADS)

    Arenas, Isnardo; Carrasquillo, Kenneth; Araya, Guillermo; Castillo, Luciano; Leonardi, Stefano

    2014-11-01

    Direct Numerical Simulations of a turbulent channel flow with a porous wall inspired from the Gecko lizard were performed at Reynolds number of Reτ = 450 . Two superposed fluids were considered. As initial condition, one fluid fills the microfibrillar surface, the interface with the overlying fluid being flat and corresponding to the crests plane. The code is based on a finite difference scheme with a Runge Kutta and fractional step. The porous wall is modeled with the immersed boundary method, while the dynamic of the interface between the two fluids is solved with a level set method. A parametric study has been performed varying the viscosity ratio between the two fluids. Two cases have been considered, with and without surface tension. Without surface tension the microfibrillar wall acts as a rough wall increasing the drag. However, when the surface tension is large enough to maintain the interface stable, the external fluid cannot enter into the porous wall and an effective slip is produced. When the fluid in the porous wall has a viscosity 100 times smaller than that of the overlying fluid, a drag reduction of about 60 % can be observed. In this case, the near wall coherent structures become significantly weaker. The numerical simulations were performed on XSEDE TACC under Grant No. CTS070066. S.L., I.A. and K.C. were supported by ONR MURI grant.

  7. Helicopter hub fairing and pylon interference drag

    NASA Technical Reports Server (NTRS)

    Graham, D. R.; Sung, D. Y.; Young, L. A.; Louie, A. W.; Stroub, R. H.

    1989-01-01

    A wind tunnel test was conducted to study the aerodynamics of helicopter hub and pylon fairings. The test was conducted in the 7-by 10 Foot Subsonic Wind Tunnel (Number 2) at Ames Research Center using a 1/5-scale XH-59A fuselage model. The primary focus of the test was on the rotor hub fairing and pylon mutual interference drag. Parametric studies of pylon and hub fairing geometry were also conducted. This report presents the major findings of the test as well as tabulated force and moment data, flow visualization photographs, and graphical presentations of the drag data. The test results indicate that substantial drag reduction can be attained through the use of a cambered hub fairing with circular arc upper surface and flat lower surface. Furthermore, a considerable portion of the overall drag reduction is attributed to the reduction in the hub-on-pylon interference drag. It is also observed that the lower surface curvature of the fairing has a strong influence on the hub fairing and on pylon interference drag. However, the drag reduction benefit that was obtained by using the cambered hub fairing with a flat lower surface was adversely affected by the clearance between the hub fairing and the pylon.

  8. Aerodynamic characteristics of some modified conical bodies with low lift-drag ratios at Mach numbers of 2.30 and 4.63

    NASA Technical Reports Server (NTRS)

    Davenport, E. E.

    1972-01-01

    A wind-tunnel investigation was conducted at Mach numbers of 2.30 and 4.63 to determine the static aerodynamic characteristics of three 60 deg half-angle cone models. Configuration 1 was obtained by raking off a symmetrical cone at a base angle of 6.15 deg, and configuration 2 and 3 were obtained by adding flaps to a symmetrical cone. The models were tested at angles of attack from about -5 deg to about 20 deg at roll angles of 0 deg to -180 deg and at a freestream Reynolds number of 1.09 x one million, based on body diameter. The results showed that all three configurations produced finite values of lift-drag ratio useful for lifting planetary entry. All three configurations exhibited increases in yawing moment and side force with roll angle; thus, the capability for lateral trajectory control is provided.

  9. Coupled Vortex-Lattice Flight Dynamic Model with Aeroelastic Finite-Element Model of Flexible Wing Transport Aircraft with Variable Camber Continuous Trailing Edge Flap for Drag Reduction

    NASA Technical Reports Server (NTRS)

    Nguyen, Nhan; Ting, Eric; Nguyen, Daniel; Dao, Tung; Trinh, Khanh

    2013-01-01

    This paper presents a coupled vortex-lattice flight dynamic model with an aeroelastic finite-element model to predict dynamic characteristics of a flexible wing transport aircraft. The aircraft model is based on NASA Generic Transport Model (GTM) with representative mass and stiffness properties to achieve a wing tip deflection about twice that of a conventional transport aircraft (10% versus 5%). This flexible wing transport aircraft is referred to as an Elastically Shaped Aircraft Concept (ESAC) which is equipped with a Variable Camber Continuous Trailing Edge Flap (VCCTEF) system for active wing shaping control for drag reduction. A vortex-lattice aerodynamic model of the ESAC is developed and is coupled with an aeroelastic finite-element model via an automated geometry modeler. This coupled model is used to compute static and dynamic aeroelastic solutions. The deflection information from the finite-element model and the vortex-lattice model is used to compute unsteady contributions to the aerodynamic force and moment coefficients. A coupled aeroelastic-longitudinal flight dynamic model is developed by coupling the finite-element model with the rigid-body flight dynamic model of the GTM.

  10. Drag reduction in a channel with microstructure grooves using the lattice Boltzmann method

    NASA Astrophysics Data System (ADS)

    Daeian, M. A.; Moosavi, A.; Nouri-Borujerdi, A.; Taghvaei, E.

    2017-03-01

    Using the Shan–Chen lattice Boltzmann multi-phase model, we investigate the effect of adding microstructured grooves to the walls of a 2D parallel-plate channel on the pressure drop in the channel. The effects of the size of the grooves on the pressure drop in the channel were considered. It was observed that the pitch of the grooves has a considerable effect on the pressure drop in the channel, and even for some values of the pitch we observe an increase in the pressure drop. As the pitch decreases, a lower pressure drop is achieved. The results also show that as the ratio of the solid–liquid contact surface to the whole surface is decreased, the pressure drop decreases. It is also observed that the grooves should be deep enough to yield drag reduction, otherwise it would have a negative effect.

  11. Sustained Drag Reduction in Turbulent Taylor-Couette Flows Enabled by Low-Temperature Leidenfrost Effect

    NASA Astrophysics Data System (ADS)

    Saranadhi, Dhananjai; Chen, Dayong; Kleingartner, Justin; Srinivasan, Siddarth; Cohen, Robert; McKinley, Gareth

    2015-11-01

    A submerged body can be heated past its Leidenfrost temperature to form a thick, continuous film of steam between itself and the water. Here we employ a superhydrophobic surface to drastically reduce the energy input required to create and sustain such a boiling film, and use the resulting slip boundary condition to achieve skin friction drag reduction on the inner rotor of a bespoke Taylor-Couette apparatus. We find that skin friction can be reduced by over 90% relative to an unheated superhydrophobic surface at Re = 19,200, and derive a boundary layer and slip theory to fit the data to a model that calculates a slip length of 3.12 +/- 0.4 mm. This indicates that the boiling film has a thickness of 112 μm, which is consistent with literature.

  12. Intelligent Control for Drag Reduction on the X-48B Vehicle

    NASA Technical Reports Server (NTRS)

    Griffin, Brian Joseph; Brown, Nelson Andrew; Yoo, Seung Yeun

    2011-01-01

    This paper focuses on the development of an intelligent control technology for in-flight drag reduction. The system is integrated with and demonstrated on the full X-48B nonlinear simulation. The intelligent control system utilizes a peak-seeking control method implemented with a time-varying Kalman filter. Performance functional coordinate and magnitude measurements, or independent and dependent parameters respectively, are used by the Kalman filter to provide the system with gradient estimates of the designed performance function which is used to drive the system toward a local minimum in a steepestdescent approach. To ensure ease of integration and algorithm performance, a single-input single-output approach was chosen. The framework, specific implementation considerations, simulation results, and flight feasibility issues related to this platform are discussed.

  13. Sustainable Drag Reduction in Turbulent Taylor-Couette Flows by Depositing Sprayable Superhydrophobic Surfaces

    NASA Astrophysics Data System (ADS)

    Srinivasan, Siddarth; Kleingartner, Justin A.; Gilbert, Jonathan B.; Cohen, Robert E.; Milne, Andrew J. B.; McKinley, Gareth H.

    2015-01-01

    We demonstrate a reduction in the measured inner wall shear stress in moderately turbulent Taylor-Couette flows by depositing sprayable superhydrophobic microstructures on the inner rotor surface. The magnitude of reduction becomes progressively larger as the Reynolds number increases up to a value of 22% at Re =8.0 ×1 04 . We show that the mean skin friction coefficient Cf in the presence of the superhydrophobic coating can be fitted to a modified Prandtl-von Kármán-type relationship of the form (Cf/2 )-1 /2=M ln (Re (Cf/2 )1 /2) +N +(b /Δ r )Re (Cf/2 )1 /2 from which we extract an effective slip length of b ≈19 μ m . The dimensionless effective slip length b+=b /δν, where δν is the viscous length scale, is the key parameter that governs the drag reduction and is shown to scale as b+˜Re1 /2 in the limit of high Re.

  14. Design, manufacture, and testing of compliant coatings for reduction of turbulent drag

    NASA Astrophysics Data System (ADS)

    Dickinson, S. C.; Power, J. L.; Eynck, J. J.

    1984-08-01

    The drag of three compliant coatings was measured in the DTNSRDC 36-inch water tunnel. Two coatings were of the Kramer type, while the other one was a closed-cell neoprene foam. The drag of the 2.032-m (80-in.) long and 0.737-m (29-in.) wide compliant coatings was compared to the drag of a smooth, solid reference plate.

  15. Bio-inspired dewetted surfaces based on SiC/Si interlocked structures for enhanced-underwater stability and regenerative-drag reduction capability

    PubMed Central

    Lee, By Junghan; Zhang, Zhuo; Baek, Seunghyun; Kim, Sangkuk; Kim, Donghyung; Yong, Kijung

    2016-01-01

    Drag reduction has become a serious issue in recent years in terms of energy conservation and environmental protection. Among diverse approaches for drag reduction, superhydrophobic surfaces have been mainly researched due to their high drag reducing efficiency. However, due to limited lifetime of plastron (i.e., air pockets) on superhydrophobic surfaces in underwater, the instability of dewetted surfaces has been a sticking point for practical applications. This work presents a breakthrough in improving the underwater stability of superhydrophobic surfaces by optimizing nanoscale surface structures using SiC/Si interlocked structures. These structures have an unequaled stability of underwater superhydrophobicity and enhance drag reduction capabilities,with a lifetime of plastron over 18 days and maximum velocity reduction ratio of 56%. Furthermore, through photoelectrochemical water splitting on a hierarchical SiC/Si nanostructure surface, the limited lifetime problem of air pockets was overcome by refilling the escaping gas layer, which also provides continuous drag reduction effects. PMID:27095674

  16. Bio-inspired dewetted surfaces based on SiC/Si interlocked structures for enhanced-underwater stability and regenerative-drag reduction capability

    NASA Astrophysics Data System (ADS)

    Lee, By Junghan; Zhang, Zhuo; Baek, Seunghyun; Kim, Sangkuk; Kim, Donghyung; Yong, Kijung

    2016-04-01

    Drag reduction has become a serious issue in recent years in terms of energy conservation and environmental protection. Among diverse approaches for drag reduction, superhydrophobic surfaces have been mainly researched due to their high drag reducing efficiency. However, due to limited lifetime of plastron (i.e., air pockets) on superhydrophobic surfaces in underwater, the instability of dewetted surfaces has been a sticking point for practical applications. This work presents a breakthrough in improving the underwater stability of superhydrophobic surfaces by optimizing nanoscale surface structures using SiC/Si interlocked structures. These structures have an unequaled stability of underwater superhydrophobicity and enhance drag reduction capabilities,with a lifetime of plastron over 18 days and maximum velocity reduction ratio of 56%. Furthermore, through photoelectrochemical water splitting on a hierarchical SiC/Si nanostructure surface, the limited lifetime problem of air pockets was overcome by refilling the escaping gas layer, which also provides continuous drag reduction effects.

  17. Improvement of water-repellent and hydrodynamic drag reduction properties on bio-inspired surface and exploring sharkskin effect mechanism

    NASA Astrophysics Data System (ADS)

    Luo, Yuehao; Liu, Yufei; Anderson, James; Li, Xiang; Li, Yuanyue

    2015-07-01

    Bio-inspired/biomimetic surface technologies focusing on sharkskin, lotus leaf, gecko feet, and others have attracted so lots of attentions from all over the world; meanwhile, they have also brought great advantages and profits for mankind. Sharkskin drag-reducing/low-resistance surface is the imperative consequence of nature selection and self-evolution in the long history, which can enable itself accommodate the living environments perfectly. Generally speaking, sharkskin effect can become transparent only in some certain velocity scope. How to expand its application range and enhance the drag reduction function further has developed into the urgent issue. In this article, the water-repellent and hydrodynamic drag-reducing effects are improved by adjusting sharkskin texture. The experimental results show that contact angle of more than 150° is achieved, and drag-reducing property is improved to some extent. In addition, the drag-reducing mechanism is explored and generalized from different aspects adopting the numerical simulation, which has important significance to comprehend sharkskin effect.

  18. Relevance of aerodynamic modelling for load reduction control strategies of two-bladed wind turbines

    NASA Astrophysics Data System (ADS)

    Luhmann, B.; Cheng, P. W.

    2014-06-01

    A new load reduction concept is being developed for the two-bladed prototype of the Skywind 3.5MW wind turbine. Due to transport and installation advantages both offshore and in complex terrain two-bladed turbine designs are potentially more cost-effective than comparable three-bladed configurations. A disadvantage of two-bladed wind turbines is the increased fatigue loading, which is a result of asymmetrically distributed rotor forces. The innovative load reduction concept of the Skywind prototype consists of a combination of cyclic pitch control and tumbling rotor kinematics to mitigate periodic structural loading. Aerodynamic design tools must be able to model correctly the advanced dynamics of the rotor. In this paper the impact of the aerodynamic modelling approach is investigated for critical operational modes of a two-bladed wind turbine. Using a lifting line free wake vortex code (FVM) the physical limitations of the classical blade element momentum theory (BEM) can be evaluated. During regular operation vertical shear and yawed inflow are the main contributors to periodic blade load asymmetry. It is shown that the near wake interaction of the blades under such conditions is not fully captured by the correction models of BEM approach. The differing prediction of local induction causes a high fatigue load uncertainty especially for two-bladed turbines. The implementation of both cyclic pitch control and a tumbling rotor can mitigate the fatigue loading by increasing the aerodynamic and structural damping. The influence of the time and space variant vorticity distribution in the near wake is evaluated in detail for different cyclic pitch control functions and tumble dynamics respectively. It is demonstrated that dynamic inflow as well as wake blade interaction have a significant impact on the calculated blade forces and need to be accounted for by the aerodynamic modelling approach. Aeroelastic simulations are carried out using the high fidelity multi body

  19. Stability of two-layer Couette flow with application to drag reduction

    NASA Astrophysics Data System (ADS)

    Mohammadi, Alireza; Smits, Alexander J.

    2016-11-01

    We consider the linear stability of flows composed of two superposed fluids in Couette flow in order to improve our understanding of the longevity and performance of superhydrophobic surfaces (SHS) or liquid-infused surfaces (LIS) which are important for drag reduction. Here, we assume that the fluids are immiscible, incompressible, and Newtonian with constant properties. Single-fluid Couette flow is known to be linearly stable for any Reynolds number. However, inclusion of the second layer of fluid enriches the problem and introduces five new parameters: viscosity ratio, density ratio, thickness ratio, Froude number and Weber number. Two kinds of instability can appear: an unstable interfacial mode, and a Tollmein-Schlichting mode. In this work we parametrically study the flow stability with specific emphasis on the effects of viscosity ratio, interfacial tension, and thickness ratio. Supported by the Natural Sciences and Engineering Research Council of Canada (NSERC) and the Office of Naval Research (ONR) through MURI Grants N00014-12-1-0875 and N00014-12-1-0962 (Program Manager Dr. Ki-Han Kim).

  20. Phoretic drag reduction of chemically active homogeneous spheres under force fields and shear flows

    NASA Astrophysics Data System (ADS)

    Yariv, Ehud; Kaynan, Uri

    2017-01-01

    Surrounded by a spherically symmetric solute cloud, chemically active homogeneous spheres do not undergo conventional autophoresis when suspended in an unbounded liquid domain. When exposed to external flows, solute advection deforms that cloud, resulting in a generally asymmetric distribution of diffusio-osmotic slip which, in turn, modifies particle motion. Inspired by classical forced-convection analyses [Acrivos and Taylor, Phys. Fluids 5, 387 (1962), 10.1063/1.1706630; Frankel and Acrivos, Phys. Fluids 11, 1913 (1968), 10.1063/1.1692218] we illustrate this phoretic phenomenon using two prototypic configurations, one where the particle sediments under a uniform force field and one where it is subject to a simple shear flow. In addition to the Péclet number Pe associated with the imposed flow, the governing nonlinear problem also depends upon α , the intrinsic Péclet number associated with the chemical activity of the particle. As in the forced-convection problems, the small-Péclet-number limit is nonuniform, breaking down at large distances away from the particle. Calculation of the leading-order autophoretic effects thus requires use of matched asymptotic expansions, the outer region being at distances that scale inversely with Pe and Pe1 /2 in the respective sedimentation and shear problems. In the sedimentation problem we find an effective drag reduction of fractional amount α /8 ; in the shear problem we find that the magnitude of the stresslet is decreased by a fractional amount α /4 . For a dilute particle suspension the latter result is manifested by a reduction of the effective viscosity.

  1. The streamwise drag-reduction response of a boundary layer subjected to a sudden imposition of transverse oscillatory wall motion

    NASA Astrophysics Data System (ADS)

    Lardeau, Sylvain; Leschziner, Michael A.

    2013-07-01

    A direct numerical simulation study is presented, which examines the response of a spatially developing boundary layer to oscillatory spanwise wall motion imposed over a limited streamwise stretch. At the heart of the study is the dependence of the streamwise variations in skin friction and turbulence properties on the period of the oscillatory motion, with particular emphasis placed on the behaviour downstream of the start of the actuation. The friction Reynolds number just upstream of the actuation is Reτ = 520, and the wall-scaled actuation period, T+ = Tuτ2/ν, covers the range 80-200. In contrast to channel flow, the present configuration allows the processes during the transition stretch from the unactuated state to the low-drag state and the recovery from the low-drag state to be studied. Attention focuses primarily on the former. Results are included for the time-averaged turbulent stresses, their budgets and probability-density functions, as well as a range of phase-averaged properties. The study brings out, for low-drag conditions, a number of features and processes that are common with those in actuated channel flow, but suggests that the maximum drag-reduction margins are lower than those in equivalent channel flow, and that the optimum actuation period is significantly shorter. The transition to the low-drag state occurs over about 5 boundary-layer thicknesses, and is characterised by substantial oscillations in all phase-averaged properties. These oscillations, provoked at the start of the spanwise motion, propagate convectively as waves and decay as the low-drag state is approached. The interactions contributing to the oscillations are discussed as part of the analysis of phase-averaged quantities.

  2. On the theory of compliant wall drag reduction in turbulent boundary layers

    NASA Technical Reports Server (NTRS)

    Ash, R. L.

    1974-01-01

    A theoretical model has been developed which can explain how the motion of a compliant wall reduces turbulent skin friction drag. Available experimental evidence at low speeds has been used to infer that a compliant surface selectively removes energy from the upper frequency range of the energy containing eddies and through resulting surface motions can produce locally negative Reynolds stresses at the wall. The theory establishes a preliminary amplitude and frequency criterion as the basis for designing effective drag reducing compliant surfaces.

  3. Razor clam to RoboClam: burrowing drag reduction mechanisms and their robotic adaptation.

    PubMed

    Winter, A G; V; Deits, R L H; Dorsch, D S; Slocum, A H; Hosoi, A E

    2014-09-01

    Estimates based on the strength, size, and shape of the Atlantic razor clam (Ensis directus) indicate that the animal's burrow depth should be physically limited to a few centimeters; yet razor clams can dig as deep as 70 cm. By measuring soil deformations around burrowing E. directus, we have found the animal reduces drag by contracting its valves to initially fail, and then fluidize, the surrounding substrate. The characteristic contraction time to achieve fluidization can be calculated directly from soil properties. The geometry of the fluidized zone is dictated by two commonly-measured geotechnical parameters: coefficient of lateral earth pressure and friction angle. Calculations using full ranges for both parameters indicate that the fluidized zone is a local effect, occurring between 1-5 body radii away from the animal. The energy associated with motion through fluidized substrate-characterized by a depth-independent density and viscosity-scales linearly with depth. In contrast, moving through static soil requires energy that scales with depth squared. For E. directus, this translates to a 10X reduction in the energy required to reach observed burrow depths. For engineers, localized fluidization offers a mechanically simple and purely kinematic method to dramatically reduce energy costs associated with digging. This concept is demonstrated with RoboClam, an E. directus-inspired robot. Using a genetic algorithm to find optimal digging kinematics, RoboClam has achieved localized fluidization burrowing performance comparable to that of the animal, with a linear energy-depth relationship, in both idealized granular glass beads and E. directus' native cohesive mudflat habitat.

  4. Turbulence and turbulent drag reduction in swirling flow: Inertial versus viscous forcing.

    PubMed

    Burnishev, Yuri; Steinberg, Victor

    2015-08-01

    We report unexpected results of a drastic difference in the transition to fully developed turbulent and turbulent drag reduction (TDR) regimes and in their properties in a von Karman swirling flow with counter-rotating disks of water-based polymer solutions for viscous (by smooth disks) as well as inertial (by bladed disks) forcing and by tracking just torque Γ(t) and pressure p(t) . For the viscous forcing, just a single TDR regime is found with the transition values of the Reynolds number (Re) Re turb c =Re TDR c ≃(4.8±0.2)×10(5) independent of ϕ , whereas for the inertial forcing two turbulent regimes are revealed. The first transition is to fully developed turbulence, and the second one is to the TDR regime with both Re turb c and Re TDR c depending on polymer concentration ϕ . Both regimes differ by the values of C f and C p , by the scaling exponents of the fundamental turbulent characteristics, by the nonmonotonic dependencies of skewness and flatness of the pressure PDFs on Re, and by the different frequency power spectra of p with the different dependencies of the main vortex peak frequency in the p power spectra on ϕ and Re. Thus our experimental results show the transition to the TDR regime in a von Karman swirling flow for the viscous and inertial forcings in a sharp contrast to the recent experiments [Phys. Fluids 10, 426 (1998); Phys. Rev. E 47, R28(R) (1993); and J. Phys.: Condens. Matter 17, S1195 (2005)] where the transition to TDR is observed in the same swirling flow with counter-rotating disks only for the viscous forcing. The latter result has led its authors to the wrong conclusion that TDR is a solely boundary effect contrary to the inertial forcing associated with the bulk effect, and this conception is currently rather widely accepted in literature.

  5. Surface drag reduction and flow separation control in pelagic vertebrates, with implications for interpreting scale morphologies in fossil taxa

    PubMed Central

    Palmer, Colin; Young, Mark T.

    2015-01-01

    Living in water imposes severe constraints on the evolution of the vertebrate body. As a result of these constraints, numerous extant and extinct aquatic vertebrate groups evolved convergent osteological and soft-tissue adaptations. However, one important suite of adaptations is still poorly understood: dermal cover morphologies and how they influence surface fluid dynamics. This is especially true for fossil aquatic vertebrates where the soft tissue of the dermis is rarely preserved. Recent studies have suggested that the keeled scales of mosasaurids (pelagic lizards that lived during the Late Cretaceous) aided in surface frictional drag reduction in a manner analogous to the riblets on shark placoid scales. However, here we demonstrate that mosasaurid scales were over an order of magnitude too large to have this effect. More likely they increased the frictional drag of the body and may have played a role in controlling flow separation by acting as surface roughness that turbulated the boundary layer. Such a role could have reduced pressure drag and enhanced manoeuvrability. We caution those studying fossil aquatic vertebrates from positing the presence of surface drag reducing morphologies, because as we show herein, to be effective such features need to have a spacing of approximately 0.1 mm or less. PMID:26064576

  6. Shape Optimization for Drag Reduction in Linked Bodies using Evolution Strategies and the Hybrid Wavelet Collocation - Brinkman Penalization Method

    NASA Astrophysics Data System (ADS)

    Vasilyev, Oleg V.; Gazzola, Mattia; Koumoutsakos, Petros

    2010-11-01

    In this talk we discuss preliminary results for the use of hybrid wavelet collocation - Brinkman penalization approach for shape optimization for drag reduction in flows past linked bodies. This optimization relies on Adaptive Wavelet Collocation Method along with the Brinkman penalization technique and the Covariance Matrix Adaptation Evolution Strategy (CMA-ES). Adaptive wavelet collocation method tackles the problem of efficiently resolving a fluid flow on a dynamically adaptive computational grid, while a level set approach is used to describe the body shape and the Brinkman volume penalization allows for an easy variation of flow geometry without requiring body-fitted meshes. We perform 2D simulations of linked bodies in order to investigate whether flat geometries are optimal for drag reduction. In order to accelerate the costly cost function evaluations we exploit the inherent parallelism of ES and we extend the CMA-ES implementation to a multi-host framework. This framework allows for an easy distribution of the cost function evaluations across several parallel architectures and it is not limited to only one computing facility. The resulting optimal shapes are geometrically consistent with the shapes that have been obtained in the pioneering wind tunnel experiments for drag reduction using Evolution Strategies by Ingo Rechenberg.

  7. Synthesis and characterization of high molecular weight water-soluble polymers to study the role of extensional viscosity in polymeric drag reduction

    NASA Astrophysics Data System (ADS)

    Cowan, Martin E.

    Several high molecular weight water-soluble acrylamide copolymers identified as efficient drag reducers have been synthesized, characterized, and examined for drag reduction effectiveness. Commercially supplied poly(ethylene oxide) polymers of varying molecular weight were also characterized and studied for comparison. The resistance to polymer extension was measured using a screen extensional rheometer allowing for the local extensional viscosity of each polymer to be quantified. Copolymer composition was determined using 13C NMR. Dilute solution properties and molecular weights were determined from zero shear intrinsic viscosity measurements and multi-angle laser light scattering experiments respectively. Molecular weights ranged from 0.55 to 4.3 million grams per mole. Drag reduction measurements were performed using a rotating disk instrument. Drag reduction data were analyzed by several theoretical models. The best correlation was found using the energy model of Walsh. Empirically, drag reduction was found to be directly related to the local extensional viscosity of each polymer sample. A model is presented explaining drag reduction in terms of increased local viscosity leading to decreased turbulence characterized with a decreased local Reynolds number. Molecular weight was found to be the most important molecular parameter of the polymers studied with polymers of greater molecular weight showing superior drag reduction properties.

  8. Evaluation of Drag Reduction via Superhydrophobic Surfaces and Active Gas Replenishment in a Fully-developed Turbulent Flow

    NASA Astrophysics Data System (ADS)

    Gose, James W.; Golovin, Kevin; Ceccio, Steven L.; Perlin, Marc; Tuteja, Anish

    2014-11-01

    The development of superhydrophobic surfaces (SHS) for skin-friction drag reduction in the laminar regime has shown great promise. A team led by the University of Michigan is examining the potential of similar SHS in high-speed naval applications. Specifically, we have developed a recirculating facility to investigate the reduction of drag along robustly engineered SHS in a fully-developed turbulent boundary layer flow. The facility can accommodate both small and large SHS samples in a test section 7 mm (depth) × 100 mm (span) × 1200 mm (length). Coupled with an 11.2 kilowatt pump and a 30:1 contraction, the facility is capable of producing an average flow velocity of 20 m/s, yielding a height based (7 mm) Reynolds number of 140,000. The SHS tested were designed for large-scale application. The present investigation shows skin-friction drag reduction for various sprayable and chemically developed SHS that were applied over a 100 mm (span) × 1100 mm (length) area. The drag measurement methods include pressure drop across the test specimen and PIV measured boundary layers. Additional SHS investigations include the implementation of active gas replenishment, providing an opportunity to replace gas-pockets that would otherwise be disrupted in traditional passive SHS due to high shear stress and turbulent pressure fluctuations. Gas is evenly distributed through a 90 mm (span) × 600 mm (length) sintered porous media with pore sizes of 10 to 100 microns. The impact of the active gas replenishment is being evaluated with and without SHS.

  9. Experiments examining drag in linear droplet packets

    NASA Astrophysics Data System (ADS)

    Nguyen, Q. V.; Dunn-Rankin, D.

    1992-01-01

    This paper presents an experimental study of vertically traveling droplet packets, where the droplets in each packet are aligned linearly, one behind another. The paper describes in detail, an experimental apparatus that produces repeatable, linearly aligned, and isolated droplet packets containing 1 6 droplets per packet. The apparatus is suitable for examining aerodynamic interactions between droplets within each packet. This paper demonstrates the performance of the apparatus by examining the drag reduction and collision of droplets traveling in the wake of a lead droplet. Comparison of a calculated single droplet trajectory with the detailed droplet position versus time data for a droplet packet provides the average drag reduction experienced by the trailing droplets due to the aerodynamic wake of the lead droplet. For the conditions of our experiment (4 droplet packet, 145 μm methanol droplets, 10 m/s initial velocity, initial droplet spacing of 5.2 droplet diameters, Reynolds number approx. 80) the average drag on the first trailing droplet was found to be 75% of the drag on the lead droplet.

  10. Turbulence and turbulent drag reduction in swirling flow: Inertial versus viscous forcing

    NASA Astrophysics Data System (ADS)

    Burnishev, Yuri; Steinberg, Victor

    2015-08-01

    We report unexpected results of a drastic difference in the transition to fully developed turbulent and turbulent drag reduction (TDR) regimes and in their properties in a von Karman swirling flow with counter-rotating disks of water-based polymer solutions for viscous (by smooth disks) as well as inertial (by bladed disks) forcing and by tracking just torque Γ (t ) and pressure p (t ) . For the viscous forcing, just a single TDR regime is found with the transition values of the Reynolds number (Re) Recturb=RecTDR≃(4.8 ±0.2 ) ×105 independent of ϕ , whereas for the inertial forcing two turbulent regimes are revealed. The first transition is to fully developed turbulence, and the second one is to the TDR regime with both Recturb and RecTDR depending on polymer concentration ϕ . Both regimes differ by the values of Cf and Cp, by the scaling exponents of the fundamental turbulent characteristics, by the nonmonotonic dependencies of skewness and flatness of the pressure PDFs on Re, and by the different frequency power spectra of p with the different dependencies of the main vortex peak frequency in the p power spectra on ϕ and Re. Thus our experimental results show the transition to the TDR regime in a von Karman swirling flow for the viscous and inertial forcings in a sharp contrast to the recent experiments [Phys. Fluids 10, 426 (1998), 10.1063/1.869532; Phys. Rev. E 47, R28(R) (1993), 10.1103/PhysRevE.47.R28; and J. Phys.: Condens. Matter 17, S1195 (2005), 10.1088/0953-8984/17/14/008] where the transition to TDR is observed in the same swirling flow with counter-rotating disks only for the viscous forcing. The latter result has led its authors to the wrong conclusion that TDR is a solely boundary effect contrary to the inertial forcing associated with the bulk effect, and this conception is currently rather widely accepted in literature.

  11. Numerical study on reduction of aerodynamic noise around an airfoil with biomimetic structures

    NASA Astrophysics Data System (ADS)

    Wang, Jing; Zhang, Chengchun; Wu, Zhengyang; Wharton, James; Ren, Luquan

    2017-04-01

    A biomimetic airfoil featuring leading edge waves, trailing edge serrations and surface ridges is proposed in this study, based on flow control with each section meeting the NACA 0012 airfoil profile. Numerical simulations have been conducted to compare aerodynamic and acoustic performances between the NACA 0012 and biomimetic airfoils. These simulations utilize the large eddy simulation (LES) method and aeroacoustic analogy at an angle of attack of 0° and a Reynolds number of 1.0×105, based on using the airfoil chord as the characteristic length. The simulation results reveal the overall sound pressure levels (OASPLs) for all frequencies and at the seven observer points around the biomimetic airfoil, and a decrease of 13.1-13.9 dB is observed, whereas the drag coefficient is almost unchanged. The biomimetic structures can transform the shedding vortices in laminar mode for the NACA 0012 airfoil to regular horseshoe-type vortices in the wake, and reduce the spanwise correlation of the large-scale vortices, thereby restrain the vortex shedding noise around the biomimetic airfoil.

  12. Phenomena of drag reduction on saltating sediment in shallow, supercritical flows

    Technology Transfer Automated Retrieval System (TEKTRAN)

    ABSTRACT: When a group of objects move through a fluid, it often exhibits coordinated behavior in which bodies in the wake of a leader generally experience reduced drag. Locomotion provides well known examples including the maneuvering and clustering of racing automobiles and bicyclists and queuing...

  13. Aircraft surface coatings study: Energy efficient transport program. [sprayed and adhesive bonded coatings for drag reduction

    NASA Technical Reports Server (NTRS)

    1979-01-01

    Surface coating materials for application on transport type aircraft to reduce drag, were investigated. The investigation included two basic types of materials: spray on coatings and adhesively bonded films. A cost/benefits analysis was performed, and recommendations were made for future work toward the application of this technology.

  14. Aerodynamic Design Opportunities for Future Supersonic Aircraft

    NASA Technical Reports Server (NTRS)

    Wood, Richard M.; Bauer, Steven X. S.; Flamm, Jeffrey D.

    2002-01-01

    A discussion of a diverse set of aerodynamic opportunities to improve the aerodynamic performance of future supersonic aircraft has been presented and discussed. These ideas are offered to the community in a hope that future supersonic vehicle development activities will not be hindered by past efforts. A number of nonlinear flow based drag reduction technologies are presented and discussed. The subject technologies are related to the areas of interference flows, vehicle concepts, vortex flows, wing design, advanced control effectors, and planform design. The authors also discussed the importance of improving the aerodynamic design environment to allow creativity and knowledge greater influence. A review of all of the data presented show that pressure drag reductions on the order of 50 to 60 counts are achievable, compared to a conventional supersonic cruise vehicle, with the application of several of the discussed technologies. These drag reductions would correlate to a 30 to 40% increase in cruise L/D (lift-to-drag ratio) for a commercial supersonic transport.

  15. Possible applications of soaring technology to drag reduction in powered general aviation aircraft

    NASA Technical Reports Server (NTRS)

    Mcmasters, J. H.; Palmer, G. M.

    1975-01-01

    A brief examination of the performance figures achieved by modern soaring machines and a little reflection on the often huge disparity in L/D values between sailplanes and GA aircraft indicates that careful attention to lessons learned in sailplane design and manufacture hold realistic promise for substantial gains in the aerodynamic efficiency of several GA types.

  16. Drag and heat reduction mechanism induced by a combinational novel cavity and counterflowing jet concept in hypersonic flows

    NASA Astrophysics Data System (ADS)

    Sun, Xi-wan; Guo, Zhen-yun; Huang, Wei; Li, Shi-bin; Yan, Li

    2016-09-01

    The drag and heat reduction problem of hypersonic reentry vehicles has always attracted the attention worldwide, and many novel schemes have been proposed recently. In the current study, the research progress of the combinational configuration of the forward-facing cavity and the counterflowing jet has been reviewed, and the conventional cavity configuration has been substituted by an approximate maximum thrust nozzle contour for better heat and surface pressure reduction efficiency. The Reynolds-average of Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been employed to calculate its surrounding flow fields. A validation metric and the grid convergence index (GCI) have been employed to conduct the turbulence model assessment and the grid independence analysis respectively. The axisymmetric assumption has been verified by three-dimensional computational results as well. The obtained results show that the SST k-ω model is more suitable for the novel drag and heat flux reduction scheme proposed in this article, and the axisymmetric assumption is approximately reasonable. After investigating the influence of jet pressure ratio, the novel combinational configuration has been verified to be more effective in heat and surface pressure reduction, and this is because the approximate maximum thrust nozzle contour contributes to better expansion and avoids total pressure loss of the jet.

  17. A Numerical Study of Novel Drag Reduction Techniques for Blunt Bodies in Hypersonic Flows

    DTIC Science & Technology

    2011-01-01

    Injection System and Operation. a) Sketch of Injector Nozzle and Reservoir. b-d) Distinct Modes of Injection. 9 Experimental investigations of...Paull, A., “ Numerical Investigation of a Spiked Blunt Nose Cone at Hypersonic Speeds,” Journal of Spacecraft and Rockets , Vol. 45, No. 3, 2008, pp. 449...both experimental and numerical ) have also shown that forward facing mass injection has the ability to significantly reduce drag on blunt bodies by

  18. Modeling the effect of head drag reduction for a cylinder with a protruding disk at high mach numbers

    NASA Astrophysics Data System (ADS)

    Isaev, S. A.; Baranov, P. A.; Mikhalev, A. N.; Sudakov, A. G.

    2014-11-01

    Various approaches to modeling super- and hypersonic turbulent airflow past cylindrical bodies with a nontraditional nose in the form of a protruding rod-supported disk have been compared. Aeroballistic experiments on a light-gas propulsion setup were combined with wind tunnel tests and numerical simulations using VP2/3 program package based on multiblock computational techniques and a model of shear stress transport with flow-line curvature corrections. The phenomenon of the head and wave drag reduction for the stepped body is analyzed at high Mach numbers (up to 10) and variation of the supporting rod length under conditions of existence of the frontal flow separation zone.

  19. Effect of Catalyst Film Thickness on Growth Morphology, Surface Wettability and Drag Reduction Property of Carbon Nanotubes

    NASA Astrophysics Data System (ADS)

    Ma, Weiwei; Zhou, Zhiping; Li, Gang; Li, Ping

    2016-10-01

    Nickel films were deposited on silicon substrates using magnetron sputtering method. The pretreatment process of nickel films under high temperature and ammonia atmosphere was investigated. The thickness of nickel film has a great influence on growth morphology of carbon nanotubes (CNTs). Too large or too small thickness would do harm to the orientated growth of CNTs. The inner structure, elements composition and growth mechanism have been confirmed by TEM and EDX characterization. The surface wettability and drag reduction property of CNTs were investigated. This paper can provide a new, effective method to further develop the practical application in micro/nano devices field.

  20. Flow through an Array of Superhydrophopic Pillars: The Role of the Air-Water Interface Shape on Drag Reduction

    NASA Astrophysics Data System (ADS)

    Kim, Jeong-Hyun; Rothstein, Jonathan

    2016-11-01

    In this study, measurements of the pressure drop and the velocity fields associated with the flow of water through a regular array of superhydrophobic pillars were systematically performed to investigate the role of the air-water interface shape on drag reduction. A microfluidic channel was created with circular and superhydrophobic apple-core-shaped pillars bridging across the entire channel. The apple-core-shaped pillars were designed to trap an air pocket along the side of the pillars. The shape of the interface was systematically modified from concave to convex by changing the static pressure within the microchannel. For superhydrophobic pillars having a circular cross section, D /D0 = 1.0, a drag reduction of 7% and a slip velocity of 20% the average channel velocity along the air-water interface were measured. At large static pressures, the interface was driven into the pillars resulting in a decrease in the effective size of the pillars, an increase in the effective spacing between pillars and a pressure drop reduction of as much as 18% when the interface was compressed to D /D0 = 0.8. At low static pressures, the pressure drop increased significantly even as the slip velocity increased as the expanding air-water interface constricted flow through the array of pillars. This research was supported by the National Science Foundation under Grant CBET-1334962.

  1. Large eddy simulation of the flow around bluff body with drag reduction device

    NASA Astrophysics Data System (ADS)

    Al-Anazi, Khalid Qaied

    This thesis focuses on the use of LES to simulate the flow around elliptical bluff body with blunt trailing edge fitted with open base cavity. The main objective of this study is to determine the effects of the cavity on the drag of the body. A secondary but important objective is to demonstrate that LES can provide accurate representation of the flow around this bluff body. Moreover, LES results can complement the available experimental results in order to provide a much better understanding of the flow. The simulations were carried out at a Reynolds number of 2.6×104 based on the height of the body using Spalart-Allmaras RANS model while the LES were performed using Smagorinsky dynamic model. A grid-independence test was conducted using three grids which contain 0.85M, 1.3M and 1.7M cells, respectively. This test shows that the results are grid-independent. The LES results predicted the mean flow field in the near wake with good accuracy as compared to the experimental mean flow field obtained. The base pressure results show that the base pressure coefficient for the base model was around -0.56, which agrees well with the experimental results .By attaching the cavity, the base pressure has increased. The increase in base pressure coefficient was around 44% using 1/3 h cavity and this agrees well with the experimental measurements. The RANS predicted drag coefficient of 0.56 for the base model and 0.471 for the cavity model. This represents a difference of 8% for the base model and 34% for the cavity model when compared with experiment drag coefficients (0.61 for the base model and 0.35 for the cavity model). For the LES, the drag coefficient of the base model was around 0.65 (6.5% difference) and using the cavity, the drag coefficient was reduced to around 0.37 (5.74% difference). Details of the mean velocity components have been compared with experimental data at various locations in the wake region of the flow. Observation on the comparison between LES and

  2. Wind tunnel experiments to assess the effect of back-mounted radio transmitters on bird body drag

    USGS Publications Warehouse

    Obrecht, H.H.; Pennycuick, C.J.; Fuller, M.R.

    1988-01-01

    The aerodynamic drag of bird bodies was measured in a wind tunnel, with and without back-mounted dummy radio transmitters. Flight performance estimates indicate that the drag of a large transmitter can cause a substantial reduction of a migrant's range, that is, the distance it can cover in non-stop flight. The drag of the transmitter can be reduced by arranging the components in an elongated shape, so minimizing the frontal area. The addition of a rounded fairing to the front end, and a pointed fairing behind, was found to reduce the drag of the transmitter by about onethird, as compared with an unfaired rectangular box.

  3. Transition delay and its implications for drag reduction in particle-laden channel flow

    NASA Astrophysics Data System (ADS)

    Sardina, G.; Brandt, L.

    2015-12-01

    Direct numerical simulations of a two-way coupled particle-laden channel flow are performed in the transitional and turbulent regime. Our aim is to investigate whether particles, assumed solid, spherical and heavy delay transition and diminish drag in wall bounded flows. We consider that the only interaction between the carrier and dispersed phase is due to the Stokes drag. The simulations have been performed with a pseudo-spectral solver for the incompressible Navier-Stokes equations while the particle equations are solved in a Lagrangian formulation. In the transitional regime, we study the evolution of disturbances added to a plane Poiseuille base flow with Reynolds number 2000, based on the channel half-height and centerline velocity. By fixing the Reynolds number, the only two free parameters are the particle Stokes number St and the particle mass fraction f. Two different scenarios are considered depending on the initial condition of the velocity field. The first scenario consists of counter-rotating streamwise vortices and one three-dimensional mode while the second is a nonlinear interaction of two symmetric oblique waves. The effects of the particles on the flow transition depend on the particle mass fraction. In particular, at lower concentrations, the transition is facilitated by the presence of the particles, conversely at higher mass fractions the particles tend to stabilize the flow. The results indicate that the particle can play an important role by influencing secondary instabilities and streaks breakdown. These effects can be linked to the reduced drag observed in turbulent channel flow laden with heavy particles and specific simulations in the turbulent regime have been performed.

  4. Wake analysis of drag components in gliding flight of a jackdaw (Corvus monedula) during moult.

    PubMed

    KleinHeerenbrink, Marco; Hedenström, Anders

    2017-02-06

    To maintain the quality of the feathers, birds regularly undergo moult. It is widely accepted that moult affects flight performance, but the specific aerodynamic consequences have received relatively little attention. Here we measured the components of aerodynamic drag from the wake behind a gliding jackdaw (Corvus monedula) at different stages of its natural wing moult. We found that span efficiency was reduced (lift induced drag increased) and the wing profile drag coefficient was increased. Both effects best correlated with the corresponding reduction in spanwise camber. The negative effects are partially mitigated by adjustments of wing posture to minimize gaps in the wing, and by weight loss to reduce wing loading. By studying the aerodynamic consequences of moult, we can refine our understanding of the emergence of various moulting strategies found among birds.

  5. Theoretical and numerical study of air layer drag reduction in two-phase Couette-Poiseuille flow

    NASA Astrophysics Data System (ADS)

    Kim, Dokyun; Moin, Parviz

    2008-11-01

    The objective of the present study is to predict and understand the air layer drag reduction (ALDR) phenomenon. Recent experiments (Elbing et al. 2008) have shown net drag reductions if air is injected beyond a critical rate next to the wall. The analysis is performed on a two-phase Couette-Poiseuille flow configuration, which mimics the far downstream region of boundary layer flow on a flat plate. Both theoretical and numerical approaches are employed to investigate the stability and mechanisms of ALDR. The linear stability of air-liquid interface is investigated by solving the Orr-Sommerfeld equations. From the stability analysis, the stability of the interface is reduced as the liquid free-stream velocity, Froude number and velocity gradients at the interface are increased, while the stability is enhanced as the gas flow rate and surface tension are increased. The Critical gas flow rates from stability theory are compared with experimental results, showing good agreement. Direct numerical simulations with a Refiend Level Set Grid technique has been performed to investigate the evolution of the interface, the turbulence interaction and nonlinear mechanisms of ALDR. It is observed that the Weber number has significant impact on the characteristics of the interface development.

  6. Unique fur and skin structure in harbour seals (Phoca vitulina)—thermal insulation, drag reduction, or both?

    PubMed Central

    Erdsack, Nicola; Dehnhardt, Guido; Witt, Martin; Wree, Andreas; Siebert, Ursula; Hanke, Wolf

    2015-01-01

    Vertebrate surface structures, including mammalian skin and hair structures, have undergone various modifications during evolution in accordance with functional specializations. Harbour seals rely on their vibrissal system for orientation and foraging. To maintain tactile sensitivity even at low temperatures, the vibrissal follicles are heated up intensely, which could cause severe heat loss to the environment. We analysed skin samples of different body parts of harbour seals, and expected to see higher hair densities at the vibrissal pads as a way to reduce heat loss. In addition to significantly higher hair densities around the vibrissae than on the rest of the body, we show a unique fur structure of hair bundles consisting of broad guard hairs along with hairs of a new type, smaller than guard hairs but broader than underhairs, which we defined as ‘intermediate hairs’. This fur composition has not been reported for any mammal so far and may serve for thermal insulation as well as drag reduction. Furthermore, we describe a scale-like skin structure that also presumably plays a role in drag reduction. PMID:25652462

  7. Unique fur and skin structure in harbour seals (Phoca vitulina)--thermal insulation, drag reduction, or both?

    PubMed

    Erdsack, Nicola; Dehnhardt, Guido; Witt, Martin; Wree, Andreas; Siebert, Ursula; Hanke, Wolf

    2015-03-06

    Vertebrate surface structures, including mammalian skin and hair structures, have undergone various modifications during evolution in accordance with functional specializations. Harbour seals rely on their vibrissal system for orientation and foraging. To maintain tactile sensitivity even at low temperatures, the vibrissal follicles are heated up intensely, which could cause severe heat loss to the environment. We analysed skin samples of different body parts of harbour seals, and expected to see higher hair densities at the vibrissal pads as a way to reduce heat loss. In addition to significantly higher hair densities around the vibrissae than on the rest of the body, we show a unique fur structure of hair bundles consisting of broad guard hairs along with hairs of a new type, smaller than guard hairs but broader than underhairs, which we defined as 'intermediate hairs'. This fur composition has not been reported for any mammal so far and may serve for thermal insulation as well as drag reduction. Furthermore, we describe a scale-like skin structure that also presumably plays a role in drag reduction.

  8. Aerodynamic Design of a Locomotive Fairing

    NASA Astrophysics Data System (ADS)

    Stucki, Chad; Maynes, Daniel

    2016-11-01

    Rising fuel cost has motivated increased fuel efficiency of freight trains. At cruising speed, the largest contributing factor to the fuel consumption is the aerodynamic drag. As a result of air stagnation at the front of the train and substantial flow separation behind, the leading locomotive and trailing railcar experience greater drag than intermediate cars. This work introduces the design of streamlined nose fairings to be attached to freight locomotives as a means of reducing the leading locomotive drag. The aerodynamic performance of each fairing design is modeled using a commercial CFD software package. The K-epsilon turbulence model is used, and fluid properties are equivalent to atmospheric air at standard conditions. A selection of isolated screening studies are performed, and a multidimensional regression is used to predict optimal-performing fairing designs. Between screening studies, careful examination of the flow field is performed to inspire subsequent fairing designs. Results are presented for 250 different nose fairings. The best performing fairing geometry predicts a nominal drag reduction of 17% on the lead locomotive in a train set. This drag reduction is expected to result in nearly 1% fuel savings for the entire train.

  9. Air flow testing on aerodynamic truck

    NASA Technical Reports Server (NTRS)

    1975-01-01

    After leasing a cab-over tractor-trailer from a Southern California firm, Dryden researchers added sheet metal modifications like those shown here. They rounded the front corners and edges, and placed a smooth fairing on the cab's roofs and sides extending back to the trailer. During the investigation of truck aerodynamics, the techniques honed in flight research proved highly applicable. By closing the gap between the cab and the trailer, for example, researchers discovered a significant reduction in aerodynamic drag, one resulting in 20 to 25 percent less fuel consumption than the standard design. Many truck manufacturers subsequently incorporated similar modifications on their products.

  10. Computation of H2/air reacting flowfields in drag-reduction external combustion

    NASA Technical Reports Server (NTRS)

    Lai, H. T.

    1992-01-01

    Numerical simulation and analysis of the solution are presented for a laminar reacting flowfield of air and hydrogen in the case of external combustion employed to reduce base drag in hypersonic vehicles operating at transonic speeds. The flowfield consists of a transonic air stream at a Mach number of 1.26 and a sonic transverse hydrogen injection along a row of 26 orifices. Self-sustained combustion is computed over an expansion ramp downstream of the injection and a flameholder, using the recently developed RPLUS code. Measured data is available only for surface pressure distributions and is used for validation of the code in practical 3D reacting flowfields. Pressure comparison shows generally good agreements, and the main effects of combustion are also qualitatively consistent with experiment.

  11. Aerodynamic design of electric and hybrid vehicles: A guidebook

    NASA Technical Reports Server (NTRS)

    Kurtz, D. W.

    1980-01-01

    A typical present-day subcompact electric hybrid vehicle (EHV), operating on an SAE J227a D driving cycle, consumes up to 35% of its road energy requirement overcoming aerodynamic resistance. The application of an integrated system design approach, where drag reduction is an important design parameter, can increase the cycle range by more than 15%. This guidebook highlights a logic strategy for including aerodynamic drag reduction in the design of electric and hybrid vehicles to the degree appropriate to the mission requirements. Backup information and procedures are included in order to implement the strategy. Elements of the procedure are based on extensive wind tunnel tests involving generic subscale models and full-scale prototype EHVs. The user need not have any previous aerodynamic background. By necessity, the procedure utilizes many generic approximations and assumptions resulting in various levels of uncertainty. Dealing with these uncertainties, however, is a key feature of the strategy.

  12. The Common Mechanism of Turbulent Skin-Friction Drag Reduction with Super-Hydrophobic Micro-Grooves and Riblets

    NASA Astrophysics Data System (ADS)

    Rastegari, Amirreza; Akhavan, Rayhaneh

    2016-11-01

    Drag Reduction (DR) with Super-Hydrophobic (SH) longitudinal Micro-Grooves (MGs) and riblets was investigated by DNS using lattice Boltzmann methods. The liquid/gas interfaces on the SH MGs were modeled as curved, stationary, shear-free boundaries, with the meniscus shape determined from the Young-Laplace equation. For comparison, the same geometries were also studied as riblets. DRs of 35% to 63% with SH MGs, and 10% to -17% with riblets, were realized in DNS in turbulent channel flow at Reb = 7200 , with MGs of size 14 <=g+0 <= 56 g+0 /w+0 = 7 , and protrusion angles of 0° to 90°, where g+0 and w+0 denote the widths and spacings of the MGs in base flow wall units. It was found that 100% of the DR with riblets, and 95% to 100% of the DR with SH MGs, arises from the effective slip on the walls and the resultant drop in the friction Reynolds number of the flow due to this effective slip. Modifications to the turbulence dynamics were always drag enhancing (DE) with riblets and generally DE with SH MGs. Increasing the riblet wall curvature significantly increased the wall slip velocity at the riblet tips. But this translated to an increase in DR only for g+0 14 , due to significant enhancement of turbulence production at larger MG widths.

  13. Active control of turbulence for drag reduction based on the detection of near-wall streamwise vortices by wall information

    NASA Astrophysics Data System (ADS)

    Ge, Mingwei; Xu, Chunxiao; Cui, Gui-Xiang

    2015-08-01

    The spatial relations between the measurable wall quantities (streamwise shear stress , spanwise shear stress , and pressure fluctuations ) and the near-wall streamwise vortices (NWSV) are investigated via direct numerical simulation (DNS) databases of fully developed turbulent channel flow at a low Reynolds number. In the standard turbulent channel flow, the results show that all the wall measurable variables are closely associated with the NWSV. But after applying a stochastic interference, the relation based on breaks down while the correlations based on and are still robust. Hence, two wall flow quantities based on and are proposed to detect the NWSV. As an application, two new control schemes are developed to suppress the near-wall vortical structures using the actuation of wall blowing/suction and obtain 16 % and 11 % drag reduction, respectively.

  14. Shortfin Mako Skin: A Possible Passive Flow Control Mechanism for Drag Reduction

    NASA Astrophysics Data System (ADS)

    Wheelus, Jennifer; Lang, Amy; Bradshaw, Michael; Motta, Phillip; Habegger, Maria

    2013-11-01

    The shortfin mako is one of the fastest and most agile ocean predators creating the need to minimize its pressure drag by controlling flow separation. One proposed method for flow control is the activation of small teeth-like denticles, on the order of 0.2 mm, that cover the skin of the shark. Biological studies of the shortfin mako skin have shown the passive bristling angle of their denticles to exceed 50 degrees in areas on the flank corresponding to the locations likely to experience separation first. It is proposed that reversing flow, as occurs at the onset of separation in a turbulent boundary layer, would activate denticle bristling and hinder local separation from leading to global separation over the shark. It has been shown on a biomimetic model that bristled denticles create cavities that support the formation of vortices that interact with the boundary layer. This interaction is thought to support momentum exchange and allow the flow to stay attached longer. This experiment focuses on the mechanism that triggers bristling of the real shark skin denticles and further explores the interaction those denticles foster with the boundary layer on a 3D biomimetic model using Digital Particle Image Velocimetry (DPIV). Support for this research by the NSF GRFP is gratefully acknowledged.

  15. Configuration Aerodynamics: Past - Present - Future

    NASA Technical Reports Server (NTRS)

    Wood, Richard M.; Agrawal, Shreekant; Bencze, Daniel P.; Kulfan, Robert M.; Wilson, Douglas L.

    1999-01-01

    The Configuration Aerodynamics (CA) element of the High Speed Research (HSR) program is managed by a joint NASA and Industry team, referred to as the Technology Integration Development (ITD) team. This team is responsible for the development of a broad range of technologies for improved aerodynamic performance and stability and control characteristics at subsonic to supersonic flight conditions. These objectives are pursued through the aggressive use of advanced experimental test techniques and state of the art computational methods. As the HSR program matures and transitions into the next phase the objectives of the Configuration Aerodynamics ITD are being refined to address the drag reduction needs and stability and control requirements of High Speed Civil Transport (HSCT) aircraft. In addition, the experimental and computational tools are being refined and improved to meet these challenges. The presentation will review the work performed within the Configuration Aerodynamics element in 1994 and 1995 and then discuss the plans for the 1996-1998 time period. The final portion of the presentation will review several observations of the HSR program and the design activity within Configuration Aerodynamics.

  16. Longitudinal aerodynamic performance of a series of power-law and minimum wave drag bodies at Mach 6 and several Reynolds numbers

    NASA Technical Reports Server (NTRS)

    Ashby, G. C., Jr.

    1974-01-01

    Experimental data have been obtained for two series of bodies at Mach 6 and Reynolds numbers, based on model length, from 1.4 million to 9.5 million. One series consisted of axisymmetric power-law bodies geometrically constrained for constant length and base diameter with values of the exponent n of 0.25, 0.5, 0.6, 0.667, 0.75, and 1.0. The other series consisted of positively and negatively cambered bodies of polygonal cross section, each having a constant longitudinal area distribution conforming to that required for minimizing zero-lift wave drag at hypersonic speeds under the geometric constraints of given length and volume. At the highest Reynolds number, the power-law body for minimum drag is blunter (exponent n lower) than predicted by inviscid theory (n approximately 0.6 instead of n = 0.667); however, the peak value of lift-drag ratio occurs at n = 0.667. Viscous effects were present on the bodies of polygonal cross section but were less pronounced than those on the power-law bodies. The trapezoidal bodies with maximum width at the bottom were found to have the highest maximum lift-drag ratio and the lowest mimimum drag.

  17. Preliminary flight-determined subsonic lift and drag characteristics of the X-29A forward-swept-wing airplane

    NASA Technical Reports Server (NTRS)

    Hicks, John W.; Huckabine, Thomas

    1989-01-01

    The X-29A subsonic lift and drag characteristics determined, met, or exceeded predictions, particularly with respect to the drag polar shapes. Induced drag levels were as great as 20 percent less than wind tunnel estimates, particularly at coefficients of lift above 0.8. Drag polar shape comparisons with other modern fighter aircraft showed the X-29A to have a better overall aircraft aerodynamic Oswald efficiency factor for the same aspect ratio. Two significant problems arose in the data reduction and analysis process. These included uncertainties in angle of attack upwash calibration and effects of maneuver dynamics on drag levels. The latter problem resulted from significantly improper control surface automatic camber control scheduling. Supersonic drag polar results were not obtained during this phase because of a lack of engine instrumentation to measure afterburner fuel flow.

  18. Atmospheric testing of wind turbine trailing edge aerodynamic brakes

    SciTech Connect

    Miller, L.S.; Migliore, P.G.; Quandt, G.A.

    1997-12-31

    An experimental investigation was conducted using an instrumented horizontal-axis wind turbine that incorporated variable span trailing-edge aerodynamic brakes. A primary goal was to directly compare study results with (infinite-span) wind tunnel data and to provide information on how to account for device span effects during turbine design or analysis. Comprehensive measurements were utilized to define effective changes in the aerodynamic coefficients, as a function of angle of attack and control deflection, for three device spans and configurations. Differences in the lift and drag behavior are most pronounced near stall and for device spans of less than 15%. Drag performance is affected only minimally (<70%) for 15% or larger span devices. Interestingly, aerodynamic controls with characteristic vents or openings appear most affected by span reductions and three-dimensional flow.

  19. High Reynolds Number Micro-Bubble and Polymer Drag Reduction Experiments

    DTIC Science & Technology

    2008-01-01

    to non-normal optical transmission at the vertical LCC sidewall windows. The resulting optical distortion and reduction in coincident bursts limited...remained relatively constant with respect to the distance from the plate for each free stream velocity. The coincident burst rates varied from 100 Hz...at 6.65 m/s to 170 Hz at 19.9 mis. The coincidence window varied from 0.02 ms at 6.65 m/s to 0.01 ms at 19.9 m/s, roughly translating to the ratio of

  20. A study of performance parameters on drag and heat flux reduction efficiency of combinational novel cavity and opposing jet concept in hypersonic flows

    NASA Astrophysics Data System (ADS)

    Sun, Xi-wan; Guo, Zhen-yun; Huang, Wei; Li, Shi-bin; Yan, Li

    2017-02-01

    The drag reduction and thermal protection system applied to hypersonic re-entry vehicles have attracted an increasing attention, and several novel concepts have been proposed by researchers. In the current study, the influences of performance parameters on drag and heat reduction efficiency of combinational novel cavity and opposing jet concept has been investigated numerically. The Reynolds-average Navier-Stokes (RANS) equations coupled with the SST k-ω turbulence model have been employed to calculate its surrounding flowfields, and the first-order spatially accurate upwind scheme appears to be more suitable for three-dimensional flowfields after grid independent analysis. Different cases of performance parameters, namely jet operating conditions, freestream angle of attack and physical dimensions, are simulated based on the verification of numerical method, and the effects on shock stand-off distance, drag force coefficient, surface pressure and heat flux distributions have been analyzed. This is the basic study for drag reduction and thermal protection by multi-objective optimization of the combinational novel cavity and opposing jet concept in hypersonic flows in the future.

  1. An investigation of drag reduction fairings on the space shuttle vehicle 5 configuration (model 74-OTS) in the MSFC 14 inch trisonic wind tunnel (FA14)

    NASA Technical Reports Server (NTRS)

    Ramsey, P. E.

    1976-01-01

    An experimental investigation was conducted in the MSFC 14-inch TWT (FA14, TWT 600) to determine the static stability and drag on a 0.004 scale model of the shuttle ascent configuration. The primary objective was to study the possibility of reducing the launch vehicle drag by using Orbiter/ET/SRB fairings, streamlined orbiter fore and aft attach structures, SRB and ET alternative nose configurations, and devices for modifying the flow between the orbiter and ET. The secondary objective was to determine the longitudinal and directional characteristics of the ascent configuration with the most promising of the drag reduction devices installed. Data were obtained for a Mach number range of 0.6 through 4.96 and angles of attack from -5 through 5 degrees at zero degrees side slip angle.

  2. Molecular drag model based on differential reduction of the Kruger-Shapiro equations

    NASA Astrophysics Data System (ADS)

    Helmer, J. C.; Levi, G.

    2002-07-01

    The history of the method of differential probability in molecular flow is reviewed, beginning with the little known derivation by D. Santeler (5th Annual Symposium on Space Environmental Simulation, Arnold Air Force Station, TN, May, 1964), based on the equation of C. W. Oatley [Br. J. Appl. Phys. 8, 15 (1957)]. This method contains the aperture correction within the theory, without phenomenological assumptions. A new equation of this type, for molecular pumping, is derived by differential reduction of the Kruger-Shapiro equations. A simple solution of the differential equations yields results of good accuracy for engineering use. The physical characteristics of molecular pumping are clarified by describing the pressure distribution within the pumping tube as if it were a conductance. By this method the calculated performance of a model pump is shown to be in satisfactory agreement with a Clausing-type solution from a previous publication. copyright 2002 American Vacuum Society.

  3. The rigid bi-functional sail, new concept concerning the reduction of the drag of ships

    NASA Astrophysics Data System (ADS)

    Țicu, I.; Popa, I.; Ristea, M.

    2015-11-01

    The policy of the European Union in the energy field, for the period to follow until 2020, is based on three fundamental objectives: sustainability, competitiveness and safety in energy supply. The “Energy - Climate Changes” program sets out a number of objectives for the EU for the year 2020, known as the “20-20-20 objectives”, namely: the reduction of greenhouse gas emissions by at least 20% from the level of those of 1990, a 20% increase in the share of renewable energy sources out of the total energy consumption as well as a target of 10% biofuels in the transports energy consumption. In this context, in order to produce or save a part of the propulsive power produced by the main propulsion machinery, by burning fossil fuels, we suggest the equipping of vessels designed for maritime transport with a bi-functional rigid sail. We consider that this device may have both the role of trapping wind energy and the role of acting as a deflector for reducing the resistance of the vessel's proceeding through the water by conveniently using the bow air current, as a result of the vessel's heading through the water with significant advantage in reducing the energy consumption for propulsion insurance.

  4. Multi-scale study on process of contravariant and covariant polymer elongation and drag reduction in viscoelastic turbulence

    NASA Astrophysics Data System (ADS)

    Horiuti, Kiyosi; Suzuki, Shu

    2014-11-01

    We study the elongation process of polymers released in the Newtonian homogeneous isotropic turbulence by connecting a mesoscopic description of ensemble of elastic dumbbells using Brownian dynamics (BDS) to the macroscopic description for the fluid using DNS. The dumbbells are allowed to be advected non-affinely with the macroscopically-imposed deformation. More drastic drag reduction is achieved when non-affinity is maximum than in the complete affine case. In the former case, the dumbbell is convected as a covariant vector, and in the latter as a contravariant vector. We derive the exact solution for the governing equation of the motion of dumbbells. The maximum stretching of dumbbell is achieved when the dumbbell aligns in the direction of vorticity in the contravariant case, and when the dumbbell directs outward perpendicularly on the vortex sheet in the covariant case. Alignment in the BDS-DNS data agrees with the theoretical results. In the mixture of contravariant and covariant dumbbells, the covariant dumbbells are transversely aligned with the contravariant dumbbells. Compared with the cases without mixture, stretching of covariant dumbbell is enhanced, while that of contravariant dumbbell is reduced. Application of this phenomenon is discussed.

  5. AFRODITE - passive flow control for skin-friction drag reduction using the method of spanwise mean velocity gradient

    NASA Astrophysics Data System (ADS)

    Fallenius, Bengt; Sattarzadeh, Sohrab; Downs, Robert; Shahinfar, Shahab; Fransson, Jens

    2015-11-01

    Over the last decade wind tunnel experiments and numerical simulations have shown that steady spanwise mean velocity gradients are able to attenuate the growth of different types of boundary layer disturbances. Within the AFRODITE research program different techniques to setup the spanwise mean velocity variations have been studied and their stabilizing effect leading to transition delay quantified. A successful boundary-layer modulator for transition delay has turned out to be the miniature-vortex generator and has been well documented during the past years. More recent ideas of setting up spanwise mean velocity gradients will be presented here. We show that, the non-linear interaction between a pair of oblique disturbance waves creating a streaky base flow, as well as the direct surface modulation by means of applying wavy surfaces in the spanwise direction, can both successfully be utilized for transition delay and hence skin-friction drag reduction. The European Research Council is gratefully acknowledged (ERC-StG-2010- 258339).

  6. Effect of Interface Curvature on Turbulent Skin-Friction Drag Reduction with Super-Hydrophobic Micro-Grooves

    NASA Astrophysics Data System (ADS)

    Akhavan, Rayhaneh; Rastegari, Amirreza

    2016-11-01

    Effect of interface curvature on Drag Reduction (DR) with Super-Hydrophobic (SH) Micro-Grooves (MGs) was investigated by DNS with lattice Boltzmann methods. The liquid/gas interfaces in the SH MGs were modeled as curved, stationary, shear-free boundaries, with the interface shape determined from the Young-Laplace equation. The full range of interface protrusion angles, ranging from 0° to -90o , were investigated. DRs of 35% to 63% were realized in DNS, in turbulent channel flows at a Rebulk = 7200 (Reτ0 222) with longitudinal MGs of size 14 <=g+0 <= 56 & g+0 /w+0 = 7 on both walls, where g+0 and w+0 denote the widths and spacings of the MGs, in wall units of the base flow, respectively. The presence of interface curvature led to increases of 2.3% to 4.5% in the magnitude of DR, and drops of -3.5% to -13.5% in the slip velocity, at low protrusion angles, and drops of -2.2% to -12.5% in the magnitude of DR, and either drops of up to -16.5% or increases of up to 6% in the slip velocity, at high protrusion angles, compared to flat interfaces. In addition, the instantaneous pressure fluctuations on curved SH interfaces at low protrusion angles were significantly lower (by a factor of 2) than those on flat interfaces.

  7. Proceedings of Workshop on Atmospheric Density and Aerodynamic Drag Models for Air Force Operations Held at Air Force Geophysics Laboratory on 20-22 October 1987. Volume 1

    DTIC Science & Technology

    1990-02-13

    Measurement of Upper Atmospheric Density 4.7 Determination of Atomic Oxygen Density and Temperature of the Thermosphere By Remote Sensing 4.8 Atmospheric...SENSING 1. Density 80-120 Km P. Hays (Univ. Mich) 2. Determination of Atomic Oxygen R. Sharna (AFGL/LSI) Density and Temperature of the Thermosphere by...Sydney) Effects of Surface Reflection Uncertainties 2. Direct Simulation Monte Carlo Drag J. Moss (NASA/LaRC) Predictions 3. In-Orbit Measurements of Atom

  8. Drag Control through Wrinkling on Curved Surfaces

    NASA Astrophysics Data System (ADS)

    Terwagne, Denis; Reis, Pedro

    2012-11-01

    We present the results of an experimental investigation on the wrinkling of positively curved surfaces and explore their use towards drag reduction applications. In our precision desktop-scale experiments we make use of rapid prototyping techniques to cast samples with custom geometry and material properties out of silicone-based rubbers. Our structures consist of a thin stiff shell that is chemically bonded to a thicker soft substrate. The substrate contains a spherical cavity that can be depressurized, under controlled volume conditions, to compress the ensemble structure. Under this compressive loading, the initially smooth outer-shell develops complex wrinkling patterns. We systematically characterize and quantify the morphology of the various patterns and study the phase diagram of the system. We consider both geometric and material quantities in the parameter space. Moreover, since the wrinkling patterns can be actuated dynamically using a pressure signal, we systematically characterize the aerodynamic behavior of our structures in the context of fluid drag reduction. An added advantage of the novel mechanism we introduce is that it allows for both dynamic switching and tuning of the surface morphology, thereby opening paths for drag control. D.T. thanks the B.A.E.F., the Fulbright Program and the WBI.World grants program for financial support.

  9. Drag Control through Wrinkling on Curved Surfaces

    NASA Astrophysics Data System (ADS)

    Terwagne, Denis; Reis, Pedro

    2013-03-01

    We present the results of an experimental investigation on the wrinkling of positively curved surfaces and explore their use towards drag reduction applications. In our precision model experiments we make use of rapid prototyping techniques to cast samples with custom geometry and material properties out of silicone-based rubbers. Our structures consist of a thin stiff shell that is chemically bonded to a thicker soft substrate. The substrate contains a spherical cavity that can be depressurized, under controlled volume conditions, to compress the ensemble structure. Under this compressive loading, the initially smooth outer-shell develops complex wrinkling patterns. We systematically characterize and quantify the morphology of the various patterns and study the phase diagram of the system. We consider both geometric and material quantities in the parameter space. Moreover, since the wrinkling patterns can be actuated dynamically using a pressure signal, we systematically characterize the aerodynamic behavior of our structures in the context of fluid drag reduction. An added advantage of our novel mechanism is that it allows for both dynamic switching and tuning of the surface morphology, thereby opening paths for drag control. D.T. thanks the B.A.E.F., the Fulbright Program and the WBI.World grants program for financial support.

  10. Aerodynamic Shutoff Valve

    NASA Technical Reports Server (NTRS)

    Horstman, Raymond H.

    1992-01-01

    Aerodynamic flow achieved by adding fixed fairings to butterfly valve. When valve fully open, fairings align with butterfly and reduce wake. Butterfly free to turn, so valve can be closed, while fairings remain fixed. Design reduces turbulence in flow of air in internal suction system. Valve aids in development of improved porous-surface boundary-layer control system to reduce aerodynamic drag. Applications primarily aerospace. System adapted to boundary-layer control on high-speed land vehicles.

  11. Hydrodynamic Drag Reduction

    DTIC Science & Technology

    2015-04-01

    different bow shapes could be "bolted on" at the shoulders of a physical model for towing- tank tests.) This implied that the box-like shape of nearly the...above. (Towing- tank test data for Baseline ACV model were used to validate the computational procedure.) (b) The next step was to determine the...34 at the shoulders of a physical model for towing- tank tests.) This implied that the box-like shape of nearly the entire hull (responsible for the

  12. Flight and wind-tunnel measurements showing base drag reduction provided by a trailing disk for high Reynolds number turbulent flow for subsonic and transonic Mach numbers

    NASA Technical Reports Server (NTRS)

    Powers, Sheryll Goecke; Huffman, Jarrett K.; Fox, Charles H., Jr.

    1986-01-01

    The effectiveness of a trailing disk, or trapped vortex concept, in reducing the base drag of a large body of revolution was studied from measurements made both in flight and in a wind tunnel. Pressure data obtained for the flight experiment, and both pressure and force balance data were obtained for the wind tunnel experiment. The flight test also included data obtained from a hemispherical base. The experiment demonstrated the significant base drag reduction capability of the trailing disk to Mach 0.93 and to Reynolds numbers up to 80 times greater than for earlier studies. For the trailing disk data from the flight experiment, the maximum decrease in base drag ranged form 0.08 to 0.07 as Mach number increased from 0.70 to 0.93. Aircraft angles of attack ranged from 3.9 to 6.6 deg for the flight data. For the trailing disk data from the wind tunnel experiment, the maximum decrease in base and total drag ranged from 0.08 to 0.05 for the approximately 0 deg angle of attack data as Mach number increased from 0.30 to 0.82.

  13. Supersonic aerodynamic characteristics of hypersonic low-wave-drag elliptical body-tail combinations as affected by changes in stabilizer configuration

    NASA Technical Reports Server (NTRS)

    Spencer, B., Jr.; Fournier, R. H.

    1973-01-01

    An investigation has been made at Mach numbers from 1.50 to 4.63 to determine systematically the effects of the addition and position of outboard stabilizers and vertical- and vee-tail configurations on the performance and stability characteristics of a low-wave-drag elliptical body. The basic body shape was a zero-lift hypersonic minimum-wave-drag body as determined for the geometric constraints of length and volume. The elliptical cross section had an axis ratio of 2 (major axis horizontal) and an equivalent fineness ratio of 6.14. Base-mounted outboard stabilizers were at various dihedral angles from 90 deg to minus 90 deg with and without a single center-line vertical tail or a vee-tail. The angle of attack was varied from about minus 6 to 27 deg at sideslip angles of 0 and 5 deg and a constant Reynolds number of 4.58 x one million (based on body length).

  14. Influence of satellite aerodynamics on atmospheric density determination.

    NASA Technical Reports Server (NTRS)

    Karr, G. R.; Smith, R. E.

    1972-01-01

    Discussion of aerodynamic factors which influence the interpretation of satellite dynamic response. These factors include: (1) the influence of satellite orientation and shape on the drag coefficient; (2) the effect of changes in the gas flow properties with altitude; and (3) the influence of upper atmospheric winds on the interpretation of data. These factors represent the greatest source of error in current data reduction. For this reason, an estimate is made of a possible correction to present density models.

  15. Using High Resolution Design Spaces for Aerodynamic Shape Optimization Under Uncertainty

    NASA Technical Reports Server (NTRS)

    Li, Wu; Padula, Sharon

    2004-01-01

    This paper explains why high resolution design spaces encourage traditional airfoil optimization algorithms to generate noisy shape modifications, which lead to inaccurate linear predictions of aerodynamic coefficients and potential failure of descent methods. By using auxiliary drag constraints for a simultaneous drag reduction at all design points and the least shape distortion to achieve the targeted drag reduction, an improved algorithm generates relatively smooth optimal airfoils with no severe off-design performance degradation over a range of flight conditions, in high resolution design spaces parameterized by cubic B-spline functions. Simulation results using FUN2D in Euler flows are included to show the capability of the robust aerodynamic shape optimization method over a range of flight conditions.

  16. Space shuttle: Aerodynamic stability, control effectiveness and drag characteristics of a shuttle orbiter configuration at Mach numbers from 0.6 to 4.96

    NASA Technical Reports Server (NTRS)

    Ramsey, P. E.

    1972-01-01

    Experimental aerodynamic investigations were conducted in the NASA/MSFC 14-inch Trisonic Wind Tunnel from Sept. 27 to Oct. 7, 1972 on a 0.004 scale model of the NR ATP baseline shuttle orbiter configuration. Six component aerodynamic force and moment data were recorded at 0 deg sideslip angle over an angle of attack range from 0 to 20 deg for Mach numbers of 0.6 to 4.96, 20 to 40 deg for Mach numbers of 0.6, 0.9, 2.99, and 4.96, and 40 to 60 deg for Mach numbers of 2.99 and 4.96. Data were obtained over a sideslip range of -10 to 10 deg at 0, 10, and 20 deg angles of attack over the Mach range and 30 and 50 deg at Mach numbers of 2.99 and 4.96. The purpose of the test was to define the buildup, performance, stability, and control characteristics of the orbiter configuration. The model parameters, were: body alone; body-wing; body-wing-tail; elevon deflections of 0, 10, -20, and -40 deg both full and split); aileron deflections of plus or minus 10 deg (full and split); rudder flares of 10 and 40 deg, and a rudder deflection of 15 deg about the 10 and 40 deg flare positions.

  17. Reduction of computer usage costs in predicting unsteady aerodynamic loadings caused by control surface motions: Analysis and results

    NASA Technical Reports Server (NTRS)

    Rowe, W. S.; Sebastian, J. D.; Petrarca, J. R.

    1979-01-01

    Results of theoretical and numerical investigations conducted to develop economical computing procedures were applied to an existing computer program that predicts unsteady aerodynamic loadings caused by leading and trailing edge control surface motions in subsonic compressible flow. Large reductions in computing costs were achieved by removing the spanwise singularity of the downwash integrand and evaluating its effect separately in closed form. Additional reductions were obtained by modifying the incremental pressure term that account for downwash singularities at control surface edges. Accuracy of theoretical predictions of unsteady loading at high reduced frequencies was increased by applying new pressure expressions that exactly satisified the high frequency boundary conditions of an oscillating control surface. Comparative computer result indicated that the revised procedures provide more accurate predictions of unsteady loadings as well as providing reduction of 50 to 80 percent in computer usage costs.

  18. Effect of Two Advanced Noise Reduction Technologies on the Aerodynamic Performance of an Ultra High Bypass Ratio Fan

    NASA Technical Reports Server (NTRS)

    Hughes, Christoper E.; Gazzaniga, John A.

    2013-01-01

    A wind tunnel experiment was conducted in the NASA Glenn Research Center anechoic 9- by 15-Foot Low-Speed Wind Tunnel to investigate two new advanced noise reduction technologies in support of the NASA Fundamental Aeronautics Program Subsonic Fixed Wing Project. The goal of the experiment was to demonstrate the noise reduction potential and effect on fan model performance of the two noise reduction technologies in a scale model Ultra-High Bypass turbofan at simulated takeoff and approach aircraft flight speeds. The two novel noise reduction technologies are called Over-the-Rotor acoustic treatment and Soft Vanes. Both technologies were aimed at modifying the local noise source mechanisms of the fan tip vortex/fan case interaction and the rotor wake-stator interaction. For the Over-the-Rotor acoustic treatment, two noise reduction configurations were investigated. The results showed that the two noise reduction technologies, Over-the-Rotor and Soft Vanes, were able to reduce the noise level of the fan model, but the Over-the-Rotor configurations had a significant negative impact on the fan aerodynamic performance; the loss in fan aerodynamic efficiency was between 2.75 to 8.75 percent, depending on configuration, compared to the conventional solid baseline fan case rubstrip also tested. Performance results with the Soft Vanes showed that there was no measurable change in the corrected fan thrust and a 1.8 percent loss in corrected stator vane thrust, which resulted in a total net thrust loss of approximately 0.5 percent compared with the baseline reference stator vane set.

  19. Initial Assessment of a Variable-Camber Continuous Trailing-Edge Flap System on a Rigid Wing for Drag Reduction in Subsonic Cruise

    NASA Technical Reports Server (NTRS)

    Ippolito, Corey; Nguyen, Nhan; Totah, Joe; Trinh, Khanh; Ting, Eric

    2013-01-01

    In this paper, we describe an initial optimization study of a Variable-Camber Continuous Trailing-Edge Flap (VCCTEF) system. The VCCTEF provides a light-weight control system for aircraft with long flexible wings, providing efficient high-lift capability for takeoff and landing, and greater efficiency with reduced drag at cruising flight by considering the effects of aeroelastic wing deformations in the control law. The VCCTEF system is comprised of a large number of distributed and individually-actuatable control surfaces that are constrained in movement relative to neighboring surfaces, and are non-trivially coupled through structural aeroelastic dynamics. Minimzation of drag results in a constrained, coupled, non-linear optimization over a high-dimension search space. In this paper, we describe the modeling, analysis, and optimization of the VCCTEF system control inputs for minimum drag in cruise. The purpose of this initial study is to quantify the expected benefits of the system concept. The scope of this analysis is limited to consideration of a rigid wing without structural flexibility in a steady-state cruise condition at various fuel weights. For analysis, we developed an optimization engine that couples geometric synthesis with vortex-lattice analysis to automate the optimization procedure. In this paper, we present and describe the VCCTEF system concept, optimization approach and tools, run-time performance, and results of the optimization at 20%, 50%, and 80% fuel load. This initial limited-scope study finds the VCCTEF system can potentially gain nearly 10% reduction in cruise drag, provides greater drag savings at lower operating weight, and efficiency is negatively impacted by the severity of relative constraints between control surfaces.

  20. Aerodynamics Research Revolutionizes Truck Design

    NASA Technical Reports Server (NTRS)

    2008-01-01

    During the 1970s and 1980s, researchers at Dryden Flight Research Center conducted numerous tests to refine the shape of trucks to reduce aerodynamic drag and improved efficiency. During the 1980s and 1990s, a team based at Langley Research Center explored controlling drag and the flow of air around a moving body. Aeroserve Technologies Ltd., of Ottawa, Canada, with its subsidiary, Airtab LLC, in Loveland, Colorado, applied the research from Dryden and Langley to the development of the Airtab vortex generator. Airtabs create two counter-rotating vortices to reduce wind resistance and aerodynamic drag of trucks, trailers, recreational vehicles, and many other vehicles.

  1. Characterization of the mechanism of drag reduction using a Karhunen-Loeve analysis on a direct numerical simulation of turbulent pipe flow

    NASA Astrophysics Data System (ADS)

    Duggleby, Andrew T.

    The objective of this study is to characterize the mechanism of drag reduction by comparing the dynamical eigenfunctions of a turbulent pipe flow against those of two known cases of drag reduced flows. The first is forced drag reduction by spanwise wall oscillation, and the second is natural drag reduction found in relaminarizing flow. The dynamics are examined through a Karhunen-Loeve (KL) expansion of the direct numerical simulation flow field results. The direct numerical simulation (DNS) is performed using NEK5000, a spectral element Navier-Stokes solver, the first exponentially convergent investigation of DNS of turbulence in a pipe. The base flow is performed at a Reynolds number of Retau = 150, resulting in a KL dimension of deltaKL = 2130. As in turbulent channel flow, propagating modes are found, characterized with constant phase speed, and contribute of 80.58% of the total fluctuating energy. Based upon wavenumber characteristics and coherent vorticity visualization, four subclasses of propagating modes and two subclasses of non-propagating modes are discovered, qualitatively similar to the horseshoe (hairpin) vortex structure reported in literature. The drag reduced case is performed at the same Reynolds number with a spanwise velocity A+ = 20, a period of T+ = 50, and is driven by a constant pressure gradient. This results in a increase of flow rate by 27 %, and the KL dimension is reduced to deltaKL = 102, a 96% reduction. The propagating modes, in particular the wall modes, are pushed away from the wall, resulting in a 34% increase in their advection speed, and a shift away from the wall of the root-mean-square and Reynolds stress peaks. The relaminarizing case observes the chugging motion of the mean flow rate when the Reynolds number is barely turbulent, at Retau = 95. This chugging motion is the relaminarization of the flow, resulting in an increased flow rate, and then before complete relaminarization, the flow regains its turbulent state. This

  2. Aerodynamics/ACEE: aircraft energy efficiency

    SciTech Connect

    Not Available

    1981-01-01

    An overview is presented of a 10 year program managed by NASA which seeks to make possible the most efficient use of energy for aircraft propulsion and lift as well as provide a technology that can be used by U.S. manufacturers of air transports and engines. Supercritical wings, winglets, vortex drag reduction, high lift, active control, laminar flow control, and aerodynamics by computer are among the topics discussed. Wind tunnel models in flight verification of advanced technology, and the design, construction and testing of various aircraft structures are also described.

  3. Aerodynamics/ACEE: Aircraft energy efficiency

    NASA Technical Reports Server (NTRS)

    1981-01-01

    An overview is presented of a 10 year program managed by NASA which seeks to make possible the most efficient use of energy for aircraft propulsion and lift as well as provide a technology that can be used by U.S. manufacturers of air transports and engines. Supercritical wings, winglets, vortex drag reduction, high lift, active control, laminar flow control, and aerodynamics by computer are among the topics discussed. Wind tunnel models in flight verification of advanced technology, and the design, construction and testing of various aircraft structures are also described.

  4. Charged aerodynamics of a Low Earth Orbit cylinder

    NASA Astrophysics Data System (ADS)

    Capon, C. J.; Brown, M.; Boyce, R. R.

    2016-11-01

    This work investigates the charged aerodynamic interaction of a Low Earth Orbiting (LEO) cylinder with the ionosphere. The ratio of charge to neutral drag force on a 2D LEO cylinder with diffusely reflecting cool walls is derived analytically and compared against self-consistent electrostatic Particle-in-Cell (PIC) simulations. Analytical calculations predict that neglecting charged drag in an O+ dominated LEO plasma with a neutral to ion number density ratio of 102 will cause a 10% over-prediction of O density based on body accelerations when body potential (ɸB) is ≤ -390 V. Above 900 km altitude in LEO, where H+ becomes the dominant ion species, analytical predictions suggest charge drag becomes equivalent to neutral drag for ɸB ≤ -0.75 V. Comparing analytical predictions against PIC simulations in the range of 0 < - ɸB < 50 V found that analytical charged drag was under-estimated for all body potentials; the degree of under-estimation increasing with ɸB. Based on the -50 V PIC simulations, our in-house 6 degree of freedom orbital propagator saw a reduction in the semi-major axis of a 10 kg satellite at 700 km of 6.9 m/day and 0.98 m/day at 900 km compared that caused purely by neutral drag - 0.67 m/day and 0.056 m/day respectively. Hence, this work provides initial evidence that charged aerodynamics may become significant compared to neutral aerodynamics for high voltage LEO bodies.

  5. Modeling of Reduction in the Drag and of Cessation of the Action of an Alternating Transverse Force on a Circular Cylinder due to the Throttling Effect

    NASA Astrophysics Data System (ADS)

    Isaev, S. A.; Sudakov, A. G.; Zhukova, Yu. V.; Usachovd, A. E.

    2014-07-01

    An analysis of the physical processes in unsteady fl ow past a circular cylinder surrounded by a sheath with ports for bleeding of the medium has been made by a factorized fi nite-volume method on the basis of numerical solution of Navier-Stokes equations closed with the Menter sheer-stress-transfer model. It has been shown that such arrangement of a circular cylinder ensures stabilization of the wake of the cylinder, and also the reduction in its drag and cessation of the action of an alternating transverse force at Reynolds numbers higher than 105.

  6. Nash equilibrium and multi criterion aerodynamic optimization

    NASA Astrophysics Data System (ADS)

    Tang, Zhili; Zhang, Lianhe

    2016-06-01

    Game theory and its particular Nash Equilibrium (NE) are gaining importance in solving Multi Criterion Optimization (MCO) in engineering problems over the past decade. The solution of a MCO problem can be viewed as a NE under the concept of competitive games. This paper surveyed/proposed four efficient algorithms for calculating a NE of a MCO problem. Existence and equivalence of the solution are analyzed and proved in the paper based on fixed point theorem. Specific virtual symmetric Nash game is also presented to set up an optimization strategy for single objective optimization problems. Two numerical examples are presented to verify proposed algorithms. One is mathematical functions' optimization to illustrate detailed numerical procedures of algorithms, the other is aerodynamic drag reduction of civil transport wing fuselage configuration by using virtual game. The successful application validates efficiency of algorithms in solving complex aerodynamic optimization problem.

  7. Aerodynamic Improvements to Cargo Carrying Rail Cars due to Roof Modifications

    NASA Astrophysics Data System (ADS)

    Condie, Robert; Maynes, Daniel

    2012-11-01

    The aerodynamic drag associated with the transport of commodities by rail is becoming increasingly important as the cost of diesel fuel increases. We provide an assessment of the influence of the roof structure on aerodynamic performance of two dissimilar rail cars, namely automobile carrying cars and coal carrying cars. Currently, the roof material for automobile carrying rail cars is corrugated steel, with the corrugation aligned perpendicular to the direction of travel. Coal cars are currently left uncovered for loading convenience and on the return leg from the power plant are empty. Aerodynamic drag data have been obtained through wind tunnel testing on 1/29 scale models to understand the savings that may be realized by judicious modification to the tops of both these car types. For the automobile-carrying cars, testing is performed for the corrugated and smooth roof configurations. This modification alone has the potential of reducing the car drag coefficient by nominally 25%. A broader study is performed for the coal cars, with data being acquired for coal filled models, empty models, and several cover prototype configurations. The results reveal that implementation of a cover may yield reductions in the aerodynamic drag for both coal filled (nominally 7%) and empty coal cars (nominally 30%).

  8. Bluff body drag manipulation using pulsed jets and Coanda effect

    NASA Astrophysics Data System (ADS)

    Barros, Diogo; Borée, Jacques; Noack, Bernd R.; Spohn, Andreas; Ruiz, Tony

    2016-10-01

    The impact of fluidic actuation on the wake and drag of a 3D blunt body is experimentally investigated. The wake is forced by jets pulsed tangentially to the main flow with variable frequency and velocity. Depending on the forcing conditions, two flow regimes can be identified. First, for a broadband range of frequencies comprising the natural wake instabilities, the convection of the jet structures enhances wake entrainment, shortening the recirculating flow length with an augmentation of the bluff body drag. Further increase of the actuation frequency induces a wake fluidic boat-tailing by shear-layer deviation. It additionally lowers turbulent intensity and entrainment of high momentum fluid in the shear layer, leading to an overall reduction of the wake fluctuating kinetic energy. The association of both mechanisms is responsible for a raise of base pressure and decrease of the model's drag. The physical features of such regimes are discussed on the basis of drag, pressure and velocity measurements at several upstream conditions and control parameters. By adding curved surfaces at the jet outlets to take advantage of the so-called Coanda effect, periodic actuation can be further reinforced leading to drag reductions of about 20 % in unsteady regime. In general, the unsteady Coanda blowing not only intensifies the base pressure recovery but also preserves the effect of unsteady high frequency forcing on the turbulent field. The present results encourage the development of fluidic control in road vehicles' aerodynamics as well as provide a complement to our current understanding of bluff body drag and its manipulation.

  9. Aerodynamic analysis of a helicopter fuselage with rotating rotor head

    NASA Astrophysics Data System (ADS)

    Reß, R.; Grawunder, M.; Breitsamter, Ch.

    2015-06-01

    The present paper describes results of wind tunnel experiments obtained during a research programme aimed at drag reduction of the fuselage of a twin engine light helicopter configuration. A 1 : 5 scale model of a helicopter fuselage including a rotating rotor head and landing gear was investigated in the low-speed wind tunnel A of Technische Universität a München (TUM). The modelled parts of the helicopter induce approxiu mately 80% of the total parasite drag thus forming a major potential for shape optimizations. The present paper compares results of force and moment measurements of a baseline configuration and modified variants with an emphasis on the aerodynamic drag, lift, and yawing moment coefficients.

  10. Some methods for reducing wing drag and wing-Nacelle interference

    NASA Technical Reports Server (NTRS)

    Kelly, T. C.

    1975-01-01

    Primary efforts directed toward drag reduction centered on the design of both supercritical and subcritical families of airfoils, the reduction of induced drag through the use of vortex diffusers, and the reduction of interference drag for executive-type aircraft.

  11. Void waves propagating in the bubbly two-phase turbulent boundary layer beneath a flat-bottom model ship during drag reduction

    NASA Astrophysics Data System (ADS)

    Park, Hyun Jin; Oishi, Yoshihiko; Tasaka, Yuji; Murai, Yuichi

    2016-12-01

    The injection of bubbles into a turbulent boundary layer can reduce the skin friction of a wall. Conventionally, the drag reduction rate is evaluated using time-averaged quantities of the mean gas flow rate or mean void fraction. Actually, as bubbles are subject to strong shear stresses near the wall, void waves and local bubble clusters appear. For pipe and channel flows, such wave-like behavior of the dispersed phase has been investigated intensely as an internal two-phase flow problem. We investigate how this wavy structure forms within the boundary layer as an external spatially developing two-phase flow along a horizontal flat plate. We describe how our model ship is designed to meet that purpose and report bubble-traveling behavior that accompanies unexpectedly strong wavy oscillations in the streamwise direction. A theoretical explanation based on a simplified two-fluid model is given to support this experimental fact, which suggests that void waves naturally stand out when drag reduction is enhanced through the local spatial gradient of the void fraction.

  12. GASP- General Aviation Synthesis Program. Volume 3: Aerodynamics

    NASA Technical Reports Server (NTRS)

    Hague, D.

    1978-01-01

    Aerodynamics calculations are treated in routines which concern moments as they vary with flight conditions and attitude. The subroutines discussed: (1) compute component equivalent flat plate and wetted areas and profile drag; (2) print and plot low and high speed drag polars; (3) determine life coefficient or angle of attack; (4) determine drag coefficient; (5) determine maximum lift coefficient and drag increment for various flap types and flap settings; and (6) determine required lift coefficient and drag coefficient in cruise flight.

  13. Aerodynamics of cyclist posture, bicycle and helmet characteristics in time trial stage.

    PubMed

    Chabroux, Vincent; Barelle, Caroline; Favier, Daniel

    2012-07-01

    The present work is focused on the aerodynamic study of different parameters, including both the posture of a cyclist's upper limbs and the saddle position, in time trial (TT) stages. The aerodynamic influence of a TT helmet large visor is also quantified as a function of the helmet inclination. Experiments conducted in a wind tunnel on nine professional cyclists provided drag force and frontal area measurements to determine the drag force coefficient. Data statistical analysis clearly shows that the hands positioning on shifters and the elbows joined together are significantly reducing the cyclist drag force. Concerning the saddle position, the drag force is shown to be significantly increased (about 3%) when the saddle is raised. The usual helmet inclination appears to be the inclination value minimizing the drag force. Moreover, the addition of a large visor on the helmet is shown to provide a drag coefficient reduction as a function of the helmet inclination. Present results indicate that variations in the TT cyclist posture, the saddle position and the helmet visor can produce a significant gain in time (up to 2.2%) during stages.

  14. Development of reduced drag concepts for acoustic liners using experimental methods

    NASA Astrophysics Data System (ADS)

    Jasinski, Christopher

    2016-11-01

    Commercial aircraft have used acoustic liners to reduce engine noise for many years, although their drag production has been largely unstudied. The next generation of aircraft may benefit from additional surface area covered by acoustic liner, thus understanding their drag production mechanism is crucial for future designs. An accurate direct aerodynamic drag measurement technique has been developed using a force balance with linear air bearings. Using 3D-printed and conventional liners, low-drag designs are being developed. This paper will investigate the underlying fluid mechanics governing the drag production in acoustic liners and describe new attempts to reduce aerodynamic drag.

  15. Aerodynamic characteristics of wheelchairs. [Langley V/STOL wind tunnel tests for human factors engineering

    NASA Technical Reports Server (NTRS)

    Coe, P. L., Jr.

    1979-01-01

    The overall aerodynamic drag characteristics of a conventional wheelchair were defined and the individual drag contributions of its components were determined. The results show that a fiftieth percentile man sitting in the complete wheelchair would experience an aerodynamic drag coefficient on the order of 1.4.

  16. The aerodynamics of hovering flight in Drosophila.

    PubMed

    Fry, Steven N; Sayaman, Rosalyn; Dickinson, Michael H

    2005-06-01

    Using 3D infrared high-speed video, we captured the continuous wing and body kinematics of free-flying fruit flies, Drosophila melanogaster, during hovering and slow forward flight. We then 'replayed' the wing kinematics on a dynamically scaled robotic model to measure the aerodynamic forces produced by the wings. Hovering animals generate a U-shaped wing trajectory, in which large drag forces during a downward plunge at the start of each stroke create peak vertical forces. Quasi-steady mechanisms could account for nearly all of the mean measured force required to hover, although temporal discrepancies between instantaneous measured forces and model predictions indicate that unsteady mechanisms also play a significant role. We analyzed the requirements for hovering from an analysis of the time history of forces and moments in all six degrees of freedom. The wing kinematics necessary to generate sufficient lift are highly constrained by the requirement to balance thrust and pitch torque over the stroke cycle. We also compare the wing motion and aerodynamic forces of free and tethered flies. Tethering causes a strong distortion of the stroke pattern that results in a reduction of translational forces and a prominent nose-down pitch moment. The stereotyped distortion under tethered conditions is most likely due to a disruption of sensory feedback. Finally, we calculated flight power based directly on the measurements of wing motion and aerodynamic forces, which yielded a higher estimate of muscle power during free hovering flight than prior estimates based on time-averaged parameters. This discrepancy is mostly due to a two- to threefold underestimate of the mean profile drag coefficient in prior studies. We also compared our values with the predictions of the same time-averaged models using more accurate kinematic and aerodynamic input parameters based on our high-speed videography measurements. In this case, the time-averaged models tended to overestimate flight

  17. Vapor layers reduce drag without the crisis

    NASA Astrophysics Data System (ADS)

    Vakarelski, Ivan; Berry, Joseph; Chan, Derek; Thoroddsen, Sigurdur

    2016-11-01

    The drag of a solid sphere moving in fluid is known to be only a function of the Reynolds number, Re and diminishes rapidly at the drag crisis around Re 3 ×105. A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect, can occur over a wide range of Re, from as low as 600. The Navier slip model with a viscosity dependent slip length captures the observed drag reduction and wake shape.

  18. Report of the Panel on Aerodynamics

    NASA Technical Reports Server (NTRS)

    Bradley, Richard G.; Bushnell, Dennis

    1984-01-01

    Progress in aerodynamics over the past 50 years has been evidenced by the development of increasingly sophisticated and efficient flight vehicles throughout the flight spectrum. Advances have generally arisen in an evolutionary manner from experience gained in wind tunnel testing, flight testing, and improvements in analytical and computational capabilities. As a result of this evolutionary development, both military and commercial vehicles operate at a relatively high efficiency level. This observation plus the fact that airplanes have not changed appreciably in outward appearance over recent years has led some skeptics to conclude incorrectly that aerodynamics is a mature technology, with little to be gained from further developments in the field. It is of interest to note that progress in aerodynamics has occurred without a thorough understanding of the fundamental physics of flow, turbulence, vortex dynamics, and separated flow, for example. The present understanding of transition, turbulence, and boundary layer separation is actually very limited. However, these fundamental flow phenomena provide the key to reducing the viscous drag of aircraft. Drag reduction provides the greatest potential for increased flight efficiency from the standpoint of both saving energy and maximizing performance. Recent advances have led to innovative concepts for reducing turbulent friction drag by modifying the turbulent structure within the boundary layer. Further advances in this basic area should lead to methods for reducing skin friction drag significantly. The current challenges for military aircraft open entirely new fields of investigation for the aerodynamicist. The ability through very high speed information processing technology to totally integrate the flight and propulsion controls can permit an aircraft to fly with "complete abandon," avoiding departure, buffet, and other undesirable characteristics. To utilize these new control concepts, complex aerodynamic

  19. Dynamic soaring: aerodynamics for albatrosses

    NASA Astrophysics Data System (ADS)

    Denny, Mark

    2009-01-01

    Albatrosses have evolved to soar and glide efficiently. By maximizing their lift-to-drag ratio L/D, albatrosses can gain energy from the wind and can travel long distances with little effort. We simplify the difficult aerodynamic equations of motion by assuming that albatrosses maintain a constant L/D. Analytic solutions to the simplified equations provide an instructive and appealing example of fixed-wing aerodynamics suitable for undergraduate demonstration.

  20. Aerodynamics: The Wright Way

    NASA Technical Reports Server (NTRS)

    Cole, Jennifer Hansen

    2010-01-01

    This slide presentation reviews some of the basic principles of aerodynamics. Included in the presentation are: a few demonstrations of the principles, an explanation of the concepts of lift, drag, thrust and weight, a description of Bernoulli's principle, the concept of the airfoil (i.e., the shape of the wing) and how that effects lift, and the method of controlling an aircraft by manipulating the four forces using control surfaces.

  1. Atmospheric tests of trailing-edge aerodynamic devices

    SciTech Connect

    Miller, L S; Huang, S; Quandt, G A

    1998-01-01

    An experiment was conducted at the National Renewable Energy Laboratory`s (NREL`s) National Wind Technology Center (NWTC) using an instrumented horizontal-axis wind turbine that incorporated variable-span, trailing-edge aerodynamic brakes. The goal of the investigation was to directly compare results with (infinite-span) wind tunnel data and to provide information on how to account for device span effects during turbine design or analysis. Comprehensive measurements were used to define effective changes in the aerodynamic and hinge-moment coefficients, as a function of angle of attack and control deflection, for three device spans (7.5%, 15%, and 22.5%) and configurations (Spoiler-Flap, vented sileron, and unvented aileron). Differences in the lift and drag behavior are most pronounced near stall and for device spans of less than 15%. Drag performance is affected only minimally (about a 30% reduction from infinite-span) for 15% or larger span devices. Interestingly, aerodynamic controls with vents or openings appear most affected by span reductions and three-dimensional flow.

  2. A computational study of the aerodynamic performance of a dragonfly wing section in gliding flight.

    PubMed

    Vargas, Abel; Mittal, Rajat; Dong, Haibo

    2008-06-01

    A comprehensive computational fluid-dynamics-based study of a pleated wing section based on the wing of Aeshna cyanea has been performed at ultra-low Reynolds numbers corresponding to the gliding flight of these dragonflies. In addition to the pleated wing, simulations have also been carried out for its smoothed counterpart (called the 'profiled' airfoil) and a flat plate in order to better understand the aerodynamic performance of the pleated wing. The simulations employ a sharp interface Cartesian-grid-based immersed boundary method, and a detailed critical assessment of the computed results was performed giving a high measure of confidence in the fidelity of the current simulations. The simulations demonstrate that the pleated airfoil produces comparable and at times higher lift than the profiled airfoil, with a drag comparable to that of its profiled counterpart. The higher lift and moderate drag associated with the pleated airfoil lead to an aerodynamic performance that is at least equivalent to and sometimes better than the profiled airfoil. The primary cause for the reduction in the overall drag of the pleated airfoil is the negative shear drag produced by the recirculation zones which form within the pleats. The current numerical simulations therefore clearly demonstrate that the pleated wing is an ingenious design of nature, which at times surpasses the aerodynamic performance of a more conventional smooth airfoil as well as that of a flat plate. For this reason, the pleated airfoil is an excellent candidate for a fixed wing micro-aerial vehicle design.

  3. Aerodynamic characteristics of flying fish in gliding flight.

    PubMed

    Park, Hyungmin; Choi, Haecheon

    2010-10-01

    , we find that the gliding performance of flying fish is comparable to those of bird wings such as the hawk, petrel and wood duck. However, the induced drag by strong wing-tip vortices is one of the dominant drag components. Finally, we examine ground effect on the aerodynamic forces of the gliding flying fish and find that the flying fish achieves the reduction of drag and increase of lift-to-drag ratio by flying close to the sea surface.

  4. Measuring the Drag Force on a Falling Ball

    ERIC Educational Resources Information Center

    Cross, Rod; Lindsey, Crawford

    2014-01-01

    The effect of the aerodynamic drag force on an object in flight is well known and has been described in this and other journals many times. At speeds less than about 1 m/s, the drag force on a sphere is proportional to the speed and is given by Stokes' law. At higher speeds, the drag force is proportional to the velocity squared and is…

  5. Apparatus And Method For Reducing Drag Of A Bluff Body In Ground Effect Using Counter-Rotating Vortex Pairs

    DOEpatents

    Ortega, Jason M.; Sabari, Kambiz

    2005-12-27

    An aerodynamic base drag reduction apparatus and method for bluff bodies, such as tractor-trailer trucks, utilizing a pair of lift surfaces extending to lift surface tips and located alongside the bluff body such as on opposing left and right side surfaces. In a flowstream substantially parallel to the longitudinal centerline of the bluff body, the pair of lift surfaces generate a pair of counter-rotating trailing vortices which confluence together in the wake of the bluff body in a direction orthogonal to the flowstream. The confluence draws or otherwise turns the flowstream, such as the flowstream passing over a top surface of the bluff body, in and around behind a trailing end of the bluff body to raise the pressure on a base surface at the trailing end and thereby reduce the aerodynamic base drag.

  6. Apparatus And Method For Reducing Drag Of A Bluff Body In Ground Effect Using Counter-Rotating Vortex Pairs

    DOEpatents

    Ortega, Jason M.; Salari, Kambiz

    2005-08-09

    An aerodynamic base drag reduction apparatus and method for bluff bodies, such as tractor-trailer trucks, utilizing a pair of lift surfaces extending to lift surface tips and located alongside the bluff body such as on opposing left and right side surfaces. In a flowstream substantially parallel to the longitudinal centerline of the bluff body, the pair of lift surfaces generate a pair of counter-rotating trailing vortices which confluence together in the wake of the bluff body in a direction orthogonal to the flowstream. The confluence draws or otherwise turns the flowstream, such as the flowstream passing over a top surface of the bluff body, in and around behind a trailing end of the bluff body to raise the pressure on a base surface at the trailing end and thereby reduce the aerodynamic base drag.

  7. Theoretical aerodynamics of upper-surface-blowing jet-wing interaction

    NASA Technical Reports Server (NTRS)

    Lan, C. E.; Campbell, J. F.

    1975-01-01

    A linear, inviscid subsonic compressible flow theory is formulated to treat the aerodynamic interaction between the wing and an inviscid upper-surface-blowing (USB) thick jet with Mach number nonuniformity. The predicted results show reasonably good agreement with some available lift and induced-drag data. It was also shown that the thin-jet-flap theory is inadequate for the USB configurations with thick jet. Additional theoretical results show that the lift and induced drag were reduced by increasing jet temperature and increased by increasing jet Mach number. Reducing jet aspect ratio, while holding jet area constant, caused reductions in lift, induced drag, and pitching moment at a given angle of attack but with a minimal change in the curve of lift coefficient against induced-drag coefficient. The jet-deflection effect was shown to be beneficial to cruise performance. The aerodynamic center was shifted forward by adding power or jet-deflection angle. Moving the jet away from the wing surface resulted in rapid changes in lift and induced drag. Reducing the wing span of a rectangular wing by half decreased the jet-circulation lift by only 24 percent at a thrust coefficient of 2.

  8. Dynamic Soaring: Aerodynamics for Albatrosses

    ERIC Educational Resources Information Center

    Denny, Mark

    2009-01-01

    Albatrosses have evolved to soar and glide efficiently. By maximizing their lift-to-drag ratio "L/D", albatrosses can gain energy from the wind and can travel long distances with little effort. We simplify the difficult aerodynamic equations of motion by assuming that albatrosses maintain a constant "L/D". Analytic solutions to the simplified…

  9. Drag calculations of wings using Euler methods

    NASA Technical Reports Server (NTRS)

    Van Dam, C. P.; Chang, I. C.; Vijgen, P. M. H. W.; Nikfetrat, Koorosh

    1991-01-01

    Several techniques for the calculation of drag using Euler-equation formulations are discussed and compared. Surface-pressure integration (a nearfield technique) as well as two different farfield calculation techniques are described and applied to three-dimensional flow-field solutions for an aspect-ratio-7 wing with attached flow. The present calculations are limited to steady, low-Mach-number flows around three-dimensional configurations in the absence of active systems such as surface blowing/suction and propulsion. Although the main focus of the paper is the calculation of aerodynamic drag, the calculation of aerodynamic lift is also briefly discussed. Three Euler methods are used to obtain the flowfield solutions. The farfield technique based on the evaluation of a wake-integral appears to provide the most consistent and accurate drag predictions.

  10. Performance and Design Investigation of Heavy Lift Tiltrotor with Aerodynamic Interference Effects

    NASA Technical Reports Server (NTRS)

    Yeo, Yyeonsoo; Johnson, Wayne

    2007-01-01

    The aerodynamic interference effects on tiltrotor performance in cruise are investigated using comprehensive calculations, to better understand the physics and to quantify the effects on the aircraft design. Performance calculations were conducted for 146,600-lb conventional and quad tiltrotors, which are to cruise at 300 knots at 4000 ft/95 deg F condition. A parametric study was conducted to understand the effects of design parameters on the performance of the aircraft. Aerodynamic interference improves the aircraft lift-to-drag ratio of the baseline conventional tiltrotor. However, interference degrades the aircraft performance of the baseline quad tiltrotor, due mostly to the unfavorable effects from the front wing to the rear wing. A reduction of rotor tip speed increased the aircraft lift-to-drag ratio the most among the design parameters investigated.

  11. The Effects of a Highly Cambered Low-Drag Wing and of Auxiliary Flaps on the High-Speed Aerodynamic Characteristics of a Twin-Engine Pursuit Airplane Model

    NASA Technical Reports Server (NTRS)

    Ganzer, Victor M

    1944-01-01

    Results are presented for tests of two wings, an NACA 230-series wing and a highly-cambered NACA 66-series wing on a twin-engine pursuit airplane. Auxiliary control flaps were tested in combinations with each wing. Data showing comparison of high-speed aerodynamic characteristics of the model when equipped with each wing, the effect of the auxiliary control flaps on aerodynamic characteristics, and elevator effectiveness for the model with the 66-series wing are presented. High-speed aerodynamic characteristics of the model were improved with the 66-series wing.

  12. PREFACE: Aerodynamic sound Aerodynamic sound

    NASA Astrophysics Data System (ADS)

    Akishita, Sadao

    2010-02-01

    The modern theory of aerodynamic sound originates from Lighthill's two papers in 1952 and 1954, as is well known. I have heard that Lighthill was motivated in writing the papers by the jet-noise emitted by the newly commercialized jet-engined airplanes at that time. The technology of aerodynamic sound is destined for environmental problems. Therefore the theory should always be applied to newly emerged public nuisances. This issue of Fluid Dynamics Research (FDR) reflects problems of environmental sound in present Japanese technology. The Japanese community studying aerodynamic sound has held an annual symposium since 29 years ago when the late Professor S Kotake and Professor S Kaji of Teikyo University organized the symposium. Most of the Japanese authors in this issue are members of the annual symposium. I should note the contribution of the two professors cited above in establishing the Japanese community of aerodynamic sound research. It is my pleasure to present the publication in this issue of ten papers discussed at the annual symposium. I would like to express many thanks to the Editorial Board of FDR for giving us the chance to contribute these papers. We have a review paper by T Suzuki on the study of jet noise, which continues to be important nowadays, and is expected to reform the theoretical model of generating mechanisms. Professor M S Howe and R S McGowan contribute an analytical paper, a valuable study in today's fluid dynamics research. They apply hydrodynamics to solve the compressible flow generated in the vocal cords of the human body. Experimental study continues to be the main methodology in aerodynamic sound, and it is expected to explore new horizons. H Fujita's study on the Aeolian tone provides a new viewpoint on major, longstanding sound problems. The paper by M Nishimura and T Goto on textile fabrics describes new technology for the effective reduction of bluff-body noise. The paper by T Sueki et al also reports new technology for the

  13. The Drag of Streamline Wires

    NASA Technical Reports Server (NTRS)

    Jacobs, Eastman N

    1933-01-01

    Preliminary results are given of drag tests of streamline wires. Full-size wires were tested over a wide range of speeds in the N.A.C.A. high speed tunnel. The results are thus directly applicable to full-scale problems and include any compressibility effects encountered at the higher speeds. The results show how protuberances may be employed on conventional streamline wires to reduce the drag, and also show how the conventional wires compare with others having sections more like strut or symmetrical airfoil sections. Because the new wire sections developed are markedly superior aerodynamically to conventional wires, it is recommended that some of them be tested in service in order to investigate their relative susceptibility to vibration and to fatigue failure.

  14. A closed-form trim solution yielding minimum trim drag for airplanes with multiple longitudinal-control effectors

    NASA Technical Reports Server (NTRS)

    Goodrich, Kenneth H.; Sliwa, Steven M.; Lallman, Frederick J.

    1989-01-01

    Airplane designs are currently being proposed with a multitude of lifting and control devices. Because of the redundancy in ways to generate moments and forces, there are a variety of strategies for trimming each airplane. A linear optimum trim solution (LOTS) is derived using a Lagrange formulation. LOTS enables the rapid calculation of the longitudinal load distribution resulting in the minimum trim drag in level, steady-state flight for airplanes with a mixture of three or more aerodynamic surfaces and propulsive control effectors. Comparisons of the trim drags obtained using LOTS, a direct constrained optimization method, and several ad hoc methods are presented for vortex-lattice representations of a three-surface airplane and two-surface airplane with thrust vectoring. These comparisons show that LOTS accurately predicts the results obtained from the nonlinear optimization and that the optimum methods result in trim drag reductions of up to 80 percent compared to the ad hoc methods.

  15. Multi-objective aerodynamic shape optimization of small livestock trailers

    NASA Astrophysics Data System (ADS)

    Gilkeson, C. A.; Toropov, V. V.; Thompson, H. M.; Wilson, M. C. T.; Foxley, N. A.; Gaskell, P. H.

    2013-11-01

    This article presents a formal optimization study of the design of small livestock trailers, within which the majority of animals are transported to market in the UK. The benefits of employing a headboard fairing to reduce aerodynamic drag without compromising the ventilation of the animals' microclimate are investigated using a multi-stage process involving computational fluid dynamics (CFD), optimal Latin hypercube (OLH) design of experiments (DoE) and moving least squares (MLS) metamodels. Fairings are parameterized in terms of three design variables and CFD solutions are obtained at 50 permutations of design variables. Both global and local search methods are employed to locate the global minimum from metamodels of the objective functions and a Pareto front is generated. The importance of carefully selecting an objective function is demonstrated and optimal fairing designs, offering drag reductions in excess of 5% without compromising animal ventilation, are presented.

  16. Cluster formation and drag reduction-proposed mechanism of particle recirculation within the partition column of the bottom spray fluid-bed coater.

    PubMed

    Wang, Li Kun; Heng, Paul Wan Sia; Liew, Celine Valeria

    2015-04-01

    Bottom spray fluid-bed coating is a common technique for coating multiparticulates. Under the quality-by-design framework, particle recirculation within the partition column is one of the main variability sources affecting particle coating and coat uniformity. However, the occurrence and mechanism of particle recirculation within the partition column of the coater are not well understood. The purpose of this study was to visualize and define particle recirculation within the partition column. Based on different combinations of partition gap setting, air accelerator insert diameter, and particle size fraction, particle movements within the partition column were captured using a high-speed video camera. The particle recirculation probability and voidage information were mapped using a visiometric process analyzer. High-speed images showed that particles contributing to the recirculation phenomenon were behaving as clustered colonies. Fluid dynamics analysis indicated that particle recirculation within the partition column may be attributed to the combined effect of cluster formation and drag reduction. Both visiometric process analysis and particle coating experiments showed that smaller particles had greater propensity toward cluster formation than larger particles. The influence of cluster formation on coating performance and possible solutions to cluster formation were further discussed.

  17. Aerodynamic Design Criteria for Class 8 Heavy Vehicles Trailer Base Devices to Attain Optimum Performance

    SciTech Connect

    Salari, K; Ortega, J

    2010-12-13

    Lawrence Livermore National Laboratory (LLNL) as part of its Department of Energy (DOE), Energy Efficiency and Renewable Energy (EERE), and Vehicle Technologies Program (VTP) effort has investigated class 8 tractor-trailer aerodynamics for many years. This effort has identified many drag producing flow structures around the heavy vehicles and also has designed and tested many new active and passive drag reduction techniques and concepts for significant on the road fuel economy improvements. As part of this effort a database of experimental, computational, and conceptual design for aerodynamic drag reduction devices has been established. The objective of this report is to provide design guidance for trailer base devices to improve their aerodynamic performance. These devices are commonly referred to as boattails, base flaps, tail devices, and etc. The information provided here is based on past research and our most recent full-scale experimental investigations in collaboration with Navistar Inc. Additional supporting data from LLNL/Navistar wind tunnel, track test, and on the road test will be published soon. The trailer base devices can be identified by 4 flat panels that are attached to the rear edges of the trailer base to form a closed cavity. These devices have been engineered in many different forms such as, inflatable and non-inflatable, 3 and 4-sided, closed and open cavity, and etc. The following is an in-depth discussion with some recommendations, based on existing data and current research activities, of changes that could be made to these devices to improve their aerodynamic performance. There are 6 primary factors that could influence the aerodynamic performance of trailer base devices: (1) Deflection angle; (2) Boattail length; (3) Sealing of edges and corners; (4) 3 versus 4-sided, Position of the 4th plate; (5) Boattail vertical extension, Skirt - boattail transition; and (6) Closed versus open cavity.

  18. Effect of the Surface Condition of a Wing on the Aerodynamic Characteristics of an Airplane

    NASA Technical Reports Server (NTRS)

    Defrance, S J

    1934-01-01

    In order to determine the effect of the surface conditions of a wing on the aerodynamic characteristics of an airplane, tests were conducted in the N.A.C.A. full-scale wind tunnel on the Fairchild F-22 airplane first with normal commercial finish of wing surface and later with the same wing polished. Comparison of the characteristics of the airplane with the two surface conditions shows that the polish caused a negligible change in the lift curve, but reduced the minimum drag coefficient by 0.001. This reduction in drag if applied to an airplane with a given speed of 200 miles per hour and a minimum drag coefficient of 0.025 would increase the speed only 2.9 miles per hour, but if the speed remained the same, the power would be reduced 4 percent.

  19. The Aerodynamic Optimization of Wings at Subsonic Speeds and the Influence of Wingtip Design. Thesis

    NASA Technical Reports Server (NTRS)

    Zimmer, H.

    1987-01-01

    Some of the objectives of modern aircraft development are related to the achievement of reduced fuel consumption and aircraft noise. This investigation is mainly concerned with the aerodynamic aspects of aircraft development, i.e., reduction of induced drag. New studies of wing design, and in particular wing tips, are considered. Induced drag is important since, in cruising flight, it accounts for approximately one-third of the entire drag for the aircraft, and one-half while climbing. A survey is presented for the wing geometries and wing tip designs studied, and theoretical investigations of different planar wings with systematically varied wing tip forms are conducted. Attention is also paid to a theoretical study of some planar and nonplanar wings and their comparison with experimental data.

  20. Aerodynamic lift effect on satellite orbits

    NASA Technical Reports Server (NTRS)

    Karr, G. R.; Cleland, J. G.; Devries, L. L.

    1975-01-01

    Numerical quadrature is employed to obtain orbit perturbation results from the general perturbation equations. Both aerodynamic lift and drag forces are included in the analysis of the satellite orbit. An exponential atmosphere with and without atmospheric rotation is used. A comparison is made of the perturbations which are caused by atmospheric rotation with those caused by satellite aerodynamic effects. Results indicate that aerodynamic lift effects on the semi-major axis and orbit inclination can be of the same order as the effects of atmosphere rotation depending upon the orientation of the lift vector. The results reveal the importance of including aerodynamic lift effects in orbit perturbation analysis.

  1. Aircraft surface coatings reduce drag, may protect against corrosion

    SciTech Connect

    Kreitinger, R.L.; Middleton, D.B.

    1982-02-01

    The aerodynamic drag on an airplane is a very important design parameter. However, after exposure to the environment and accidental spills the surface of the airplane may become corroded or erode; thus the drag may change. Researchers at Boeing Commercial Airplane Co. and the NASA-Langley Research Center have been studying the possibility of using smooth surface coatings to help reduce drag and protect the surface of the airplane. Elastomeric polyurethanes on portions of a test airplane have reduced total drag by 0.2% (as compared to a bare surface) at cruise Reynolds number.

  2. Special Course on Skin Friction Drag Reduction Held in Rhode-St-Genese, Belgium on 2-6 March 1992 (Reduction de Trainee de Frottement)

    DTIC Science & Technology

    1992-03-01

    Hydrodynamic Studies Using Water Facilities AGARD CP-413, June 1987 Applications of Computational Fluid Dynamics in Aeronautics AGARD CP-412, November 1986...turbulent skin fiction reduction. At first, ature decreases. For water it is the contrary; the R.F.Blackwelder (University of Southern Cali- viscosity...tactical and strategic missiles, and technology should at least attempt to go beyond the (miltary/civilian) low- earth -orbit launch vphicles

  3. Multi-Objective Flight Control for Drag Minimization and Load Alleviation of High-Aspect Ratio Flexible Wing Aircraft

    NASA Technical Reports Server (NTRS)

    Nguyen, Nhan; Ting, Eric; Chaparro, Daniel; Drew, Michael; Swei, Sean

    2017-01-01

    As aircraft wings become much more flexible due to the use of light-weight composites material, adverse aerodynamics at off-design performance can result from changes in wing shapes due to aeroelastic deflections. Increased drag, hence increased fuel burn, is a potential consequence. Without means for aeroelastic compensation, the benefit of weight reduction from the use of light-weight material could be offset by less optimal aerodynamic performance at off-design flight conditions. Performance Adaptive Aeroelastic Wing (PAAW) technology can potentially address these technical challenges for future flexible wing transports. PAAW technology leverages multi-disciplinary solutions to maximize the aerodynamic performance payoff of future adaptive wing design, while addressing simultaneously operational constraints that can prevent the optimal aerodynamic performance from being realized. These operational constraints include reduced flutter margins, increased airframe responses to gust and maneuver loads, pilot handling qualities, and ride qualities. All of these constraints while seeking the optimal aerodynamic performance present themselves as a multi-objective flight control problem. The paper presents a multi-objective flight control approach based on a drag-cognizant optimal control method. A concept of virtual control, which was previously introduced, is implemented to address the pair-wise flap motion constraints imposed by the elastomer material. This method is shown to be able to satisfy the constraints. Real-time drag minimization control is considered to be an important consideration for PAAW technology. Drag minimization control has many technical challenges such as sensing and control. An initial outline of a real-time drag minimization control has already been developed and will be further investigated in the future. A simulation study of a multi-objective flight control for a flight path angle command with aeroelastic mode suppression and drag

  4. Preliminary Investigation of Stagnation Point Liquid Injection Influence on Blunt Body Aerodynamics

    NASA Technical Reports Server (NTRS)

    Woods, William C.; Jones, Kenneth M.; Genzel, Noah N.

    2002-01-01

    A preliminary investigation has been performed to determine the influence of stagnation point water injection on the hypersonic aerodynamic forces and moments for two-dimensional blunt bodies. This investigation was performed in the Langley 20-Inch Mach 6 Air Tunnel, and represents the qualitative first phase of a study to examine the potential benefits of water injection to reduce aerodynamic drag and aero-heating. Tests with a 4-inch diameter hemisphere cylinder and a 4-inch diameter cylinder with a span 1.5 times the diameter were performed over a range of free-stream unit Reynolds number from two million to six million per ft and of angle of attack (-5 deg to 5 deg) with water and gaseous nitrogen injection at the geometric stagnation point. The momentum flux ratio, that is, the ratio of the momentum flux of the jet to that of the free-stream flow, was varied from the non-blowing value of zero up to 0.00031 by maintaining the jet momentum fixed and varying the free-stream momentum, hence Reynolds number. The effect of water injection on the aerodynamic drag coefficient for the hemisphere cylinder was observed to be negligible as the momentum flux ratio was increased to 0.00017, but decreased significantly as this ratio increased above 0.00017; a nearly 50 percent reduction in drag occurred for a factor of two increase in momentum flux ratio.

  5. Aerodynamic Leidenfrost effect

    NASA Astrophysics Data System (ADS)

    Gauthier, Anaïs; Bird, James C.; Clanet, Christophe; Quéré, David

    2016-12-01

    When deposited on a plate moving quickly enough, any liquid can levitate as it does when it is volatile on a very hot solid (Leidenfrost effect). In the aerodynamic Leidenfrost situation, air gets inserted between the liquid and the moving solid, a situation that we analyze. We observe two types of entrainment. (i) The thickness of the air gap is found to increase with the plate speed, which is interpreted in the Landau-Levich-Derjaguin frame: Air is dynamically dragged along the surface and its thickness results from a balance between capillary and viscous effects. (ii) Air set in motion by the plate exerts a force on the levitating liquid. We discuss the magnitude of this aerodynamic force and show that it can be exploited to control the liquid and even to drive it against gravity.

  6. A parametric study of planform and aeroelastic effects on aerodynamic center, alpha- and q- stability derivatives. Appendix A: A computer program for calculating alpha- and q- stability derivatives and induced drag for thin elastic aeroplanes at subsonic and supersonic speeds

    NASA Technical Reports Server (NTRS)

    Roskam, J.; Lan, C.; Mehrotra, S.

    1972-01-01

    The computer program used to determine the rigid and elastic stability derivatives presented in the summary report is listed in this appendix along with instructions for its use, sample input data and answers. This program represents the airplane at subsonic and supersonic speeds as (a) thin surface(s) (without dihedral) composed of discrete panels of constant pressure according to the method of Woodward for the aerodynamic effects and slender beam(s) for the structural effects. Given a set of input data, the computer program calculates an aerodynamic influence coefficient matrix and a structural influence coefficient matrix.

  7. Prediction of Aerodynamic Loading

    DTIC Science & Technology

    1977-02-01

    predictable even with knowledge of the motion and the quasi- steady aerodynamic coefficients . It sems likely that the unsteady boundary-layer...build up, which are explainable 41 terams of the stability coefficients . More research is needed on the former type of undemanded manoeuvre. In some...drag 81, 82... B5 body sections I. kg lift St strdke 1M kg m pitching moment N kg normal force T kg axial force a 0 angle of attack Coefficie its: CD, cD

  8. Fairing Well: Aerodynamic Truck Research at NASA Dryden Flight Research Center. From Shoebox to Bat Truck and Beyond

    NASA Technical Reports Server (NTRS)

    Gelzer, Christian

    2011-01-01

    In 1973 engineers at Dryden began investigating ways to reduce aerodynamic drag on land vehicles. They began with a delivery van whose shape they changed dramatically, finally reducing its aerodynamic drag by more than 5 percent. They then turned their attention to tracator-trailers, modifying a cab-over and reducing its aerodynamic drag by nearly 25 percent. Further research identified additional areas worth attention, but in the intervening decades few of those changes have appeared.

  9. Study of potential aerodynamic benefits from spanwise blowing at wingtip. Ph.D. Thesis - George Washington Univ., 1992

    NASA Technical Reports Server (NTRS)

    Mineck, Raymond E.

    1995-01-01

    Comprehensive experimental and analytical studies have been conducted to assess the potential aerodynamic benefits from spanwise blowing at the tip of a moderate-aspect-ratio swept wing. Previous studies on low-aspect-ratio wings indicated that blowing from the wingtip can diffuse the tip vortex and displace it outward. The diffused and displaced vortex will induce a smaller downwash at the wing, and consequently the wing will have increased lift and decreased induced drag at a given angle of attack. Results from the present investigation indicated that blowing from jets with a short chord had little effect on lift or drag, but blowing from jets with a longer chord increased lift near the tip and reduced drag at low Mach numbers. A Navier-Stokes solver with modified boundary conditions at the tip was used to extrapolate the results to a Mach number of 0.72. Calculations indicated that lift and drag increase with increasing jet momentum coefficient. Because the momentum of the jet is typically greater than the reduction in the wing drag and the increase in the wing lift due to spanwise blowing is small, spanwise blowing at the wingtip does not appear to be a practical means of improving the aerodynamic efficiency of moderate-aspectratio swept wings at high subsonic Mach numbers.

  10. Skin friction drag measurements by LDV.

    PubMed

    Mazumder, M K; Wanchoo, S; McLeod, P C; Ballard, G S; Mozumdar, S; Caraballo, N

    1981-08-15

    A laser Doppler velocimeter employing a microscope objective as the receiving lens has been developed for measuring fluid velocity inside the boundary layer flow field with a spatial resolution of 40 microm. The method was applied for direct measurement of aerodynamic skin friction drag from the measured velocity gradient at the wall. Experimental results obtained on skin friction and on velocity components in a turbulent boundary layer on a low speed wind tunnel showed good agreement with previously reported data using conventional instruments such as hot-wire anemometers and Preston tubes. The method thus provides a tool for measurement and control of skin friction on aerodynamic bodies without perturbing the flow field.

  11. Aerodynamic Improvements of an Empty Timber Truck can Have the Potential of Significantly Reducing Fuel Consumption

    NASA Astrophysics Data System (ADS)

    Andersson, Magnus; Marashi, Seyedeh Sepideh; Karlsson, Matts

    2012-11-01

    In the present study, aerodynamic drag (AD) has been estimated for an empty and a fully loaded conceptual timber truck (TT) using Computational Fluid Dynamics (CFD). The increasing fuel prices have challenged heavy duty vehicle (HDV) manufactures to strive for better fuel economy, by e.g. utilizing drag reducing external devices. Despite this knowledge, the TT fleets seem to be left in the dark. Like HDV aerodynamics, similarities can be observed as a large low pressure wake is formed behind the tractor (unloaded) and downstream of the trailer (full load) thus generating AD. As TTs travel half the time without any cargo, focus on drag reduction is important. The full scaled TTs where simulated using the realizable k-epsilon model with grid adaption techniques for mesh independence. Our results indicate that a loaded TT reduces the AD significantly as both wake size and turbulence kinetic energy are lowered. In contrast to HDV the unloaded TTs have a much larger design space available for possible drag reducing devices, e.g. plastic wrapping and/or flaps. This conceptual CFD study has given an indication of the large AD difference between the unloaded and fully loaded TT, showing the potential for significant AD improvements.

  12. System technology analysis of aeroassisted orbital transfer vehicles - Moderate lift/drag

    NASA Technical Reports Server (NTRS)

    Florence, D. E.; Fischer, G.

    1983-01-01

    The utilization of procedures involving aerodynamic braking and/or aerodynamic maneuvering on return from higher altitude orbits to low-earth orbit makes it possible to realize significant performance benefits. The present study is concerned with a number of mission scenarios for Aeroassisted Orbital Transfer Vehicles (AOTV) and the impact of potential technology advances in the performance enhancement of the class of AOTV's having a hypersonic lift to drag ratio (L/D) of 0.75 to 1.5. It is found that the synergistic combination of a hypersonic L/D of 1.2, an advanced cryopropelled engine, and an LH2 drop tank (1-1/2 stage) leads to a single 65,000 pound shuttle, two-man geosynchronous mission with 2100 pounds of useful paylod. Additional payload enhancement is possible with AOTV dry weight reductions due to technology advances in the areas of vehicle structures and thermal protection systems and other subsystems.

  13. Advanced Aerodynamic Devices to Improve the Performance, Economics, Handling, and Safety of Heavy Vehicles

    SciTech Connect

    Robert J. Englar

    2001-05-14

    Research is being conducted at the Georgia Tech Research Institute (GTRI) to develop advanced aerodynamic devices to improve the performance, economics, stability, handling and safety of operation of Heavy Vehicles by using previously-developed and flight-tested pneumatic (blown) aircraft technology. Recent wind-tunnel investigations of a generic Heavy Vehicle model with blowing slots on both the leading and trailing edges of the trailer have been conducted under contract to the DOE Office of Heavy Vehicle Technologies. These experimental results show overall aerodynamic drag reductions on the Pneumatic Heavy Vehicle of 50% using only 1 psig blowing pressure in the plenums, and over 80% drag reductions if additional blowing air were available. Additionally, an increase in drag force for braking was confirmed by blowing different slots. Lift coefficient was increased for rolling resistance reduction by blowing only the top slot, while downforce was produced for traction increase by blowing only the bottom. Also, side force and yawing moment were generated on either side of the vehicle, and directional stability was restored by blowing the appropriate side slot. These experimental results and the predicted full-scale payoffs are presented in this paper, as is a discussion of additional applications to conventional commercial autos, buses, motor homes, and Sport Utility Vehicles.

  14. Influence of the postion of crew members on aerodynamics performance of two-man bobsleigh.

    PubMed

    Dabnichki, Peter; Avital, Eldad

    2006-01-01

    Bobsleigh aerodynamics has long been recognised as one of the crucial performance factors. Although the published research in the area is very limited, it is well known that the leading nations in the sport devote significant resources in research and development of sleds' aerodynamics. However, the rules and regulations pose strict design constraints on the shape modifications aiming at aerodynamics improvements. The reason for that is two-fold: (i) safety of the athletes and (ii) reduction of equipment impact on competition outcome. One particular area that has not been looked at and falls outside the current rules and regulations is the influence of the crew positioning and internal modifications on the aerodynamic performance. The current study presents results on numerical simulation of the flow in the cavity underpinned with some experimental measurements including flow visualisation of the air circulation around the bobsleigh. A simplified computational model was developed to assess the trends and its results validated by windtunnel tests. The results show that crew members influence the drag level significantly and suggest that purely internal modifications can be introduced to reduce the overall resistance drag.

  15. Reduction of computer usage costs in predicting unsteady aerodynamic loadings caused by control surface motions: Computer program description

    NASA Technical Reports Server (NTRS)

    Petrarca, J. R.; Harrison, B. A.; Redman, M. C.; Rowe, W. S.

    1979-01-01

    A digital computer program was developed to calculate unsteady loadings caused by motions of lifting surfaces with leading edge and trailing edge controls based on the subsonic kernel function approach. The pressure singularities at hinge line and side edges were extracted analytically as a preliminary step to solving the integral equation of collocation. The program calculates generalized aerodynamic forces for user supplied deflection modes. Optional intermediate output includes pressure at an array of points, and sectional generalized forces. From one to six controls on the half span can be accomodated.

  16. Drag bit construction

    DOEpatents

    Hood, M.

    1986-02-11

    A mounting movable with respect to an adjacent hard face has a projecting drag bit adapted to engage the hard face. The drag bit is disposed for movement relative to the mounting by encounter of the drag bit with the hard face. That relative movement regulates a valve in a water passageway, preferably extending through the drag bit, to play a stream of water in the area of contact of the drag bit and the hard face and to prevent such water play when the drag bit is out of contact with the hard face. 4 figs.

  17. Drag bit construction

    DOEpatents

    Hood, Michael

    1986-01-01

    A mounting movable with respect to an adjacent hard face has a projecting drag bit adapted to engage the hard face. The drag bit is disposed for movement relative to the mounting by encounter of the drag bit with the hard face. That relative movement regulates a valve in a water passageway, preferably extending through the drag bit, to play a stream of water in the area of contact of the drag bit and the hard face and to prevent such water play when the drag bit is out of contact with the hard face.

  18. Development of Pneumatic Aerodynamic Devices to Improve the Performance, Economics, and Safety of Heavy Vehicles

    SciTech Connect

    Robert J. Englar

    2000-06-19

    Under contract to the DOE Office of Heavy Vehicle Technologies, the Georgia Tech Research Institute (GTRI) is developing and evaluating pneumatic (blown) aerodynamic devices to improve the performance, economics, stability and safety of operation of Heavy Vehicles. The objective of this program is to apply the pneumatic aerodynamic aircraft technology previously developed and flight-tested by GTRI personnel to the design of an efficient blown tractor-trailer configuration. Recent experimental results obtained by GTRI using blowing have shown drag reductions of 35% on a streamlined automobile wind-tunnel model. Also measured were lift or down-load increases of 100-150% and the ability to control aerodynamic moments about all 3 axes without any moving control surfaces. Similar drag reductions yielded by blowing on bluff afterbody trailers in current US trucking fleet operations are anticipated to reduce yearly fuel consumption by more than 1.2 billion gallons, while even further reduction is possible using pneumatic lift to reduce tire rolling resistance. Conversely, increased drag and down force generated instantaneously by blowing can greatly increase braking characteristics and control in wet/icy weather due to effective ''weight'' increases on the tires. Safety is also enhanced by controlling side loads and moments caused on these Heavy Vehicles by winds, gusts and other vehicles passing. This may also help to eliminate the jack-knifing problem if caused by extreme wind side loads on the trailer. Lastly, reduction of the turbulent wake behind the trailer can reduce splash and spray patterns and rough air being experienced by following vehicles. To be presented by GTRI in this paper will be results developed during the early portion of this effort, including a preliminary systems study, CFD prediction of the blown flowfields, and design of the baseline conventional tractor-trailer model and the pneumatic wind-tunnel model.

  19. Assessment of aerodynamic performance of V/STOL and STOVL fighter aircraft

    NASA Technical Reports Server (NTRS)

    Nelms, W. P.

    1984-01-01

    The aerodynamic performance of V/STOL and STOVL fighter/attack aircraft was assessed. Aerodynamic and propulsion/airframe integration activities are described and small and large scale research programs are considered. Uncertainties affecting aerodynamic performance that are associated with special configuration features resulting from the V/STOL requirement are addressed. Example uncertainties relate to minimum drag, wave drag, high angle of attack characteristics, and power induced effects.

  20. Aerodynamic tailoring of the Learjet Model 60 wing

    NASA Technical Reports Server (NTRS)

    Chandrasekharan, Reuben M.; Hawke, Veronica M.; Hinson, Michael L.; Kennelly, Robert A., Jr.; Madson, Michael D.

    1993-01-01

    The wing of the Learjet Model 60 was tailored for improved aerodynamic characteristics using the TRANAIR transonic full-potential computational fluid dynamics (CFD) code. A root leading edge glove and wing tip fairing were shaped to reduce shock strength, improve cruise drag and extend the buffet limit. The aerodynamic design was validated by wind tunnel test and flight test data.

  1. Polymer Drag Reduction and Bioluminescence Reduction

    DTIC Science & Technology

    2007-09-30

    jet to cavitate is also reduced by the presence of trace amounts of polymer. Imaging of bioluminescence stimulated by a turbulent jet will assess...regulated by a computer-controlled pump system located downstream of the pipe. Upstream of the pipe is a tapered nozzle to assure laminar flow at the...inlet even at high flow rates. Flow rate is measured by a mass flow meter downstream of the pump and the pressure drop within the pipe is measured

  2. Polymer Drag Reduction and Bioluminescence Reduction

    DTIC Science & Technology

    2009-03-01

    2004). Flow through the pipe was regulated by a computer-controlled pump system located downstream of the pipe. Upstream of the pipe is a tapered...nozzle to assure laminar flow at the inlet even at high flow rates. Flow rate was measured by a mass flow meter downstream of the pump and the pressure...shown for one flow rate. (Bottom) " Pump Flow Control" module controls the flow rate, with a view of the settings for flow control during the

  3. Some lessons from NACA/NASA aerodynamic studies following World War II

    NASA Technical Reports Server (NTRS)

    Spearman, M. L.

    1983-01-01

    An historical account is presented of the new departures in aerodynamic research conducted by NACA, and subsequently NASA, as a result of novel aircraft technologies and operational regimes encountered in the course of the Second World War. The invention and initial development of the turbojet engine furnished the basis for a new speed/altitude regime in which numerous aerodynamic design problems arose. These included compressibility effects near the speed of sound, with attendant lift/drag efficiency reductions and longitudinal stability enhancements that were accompanied by a directional stability reduction. Major research initiatives were mounted in the investigation of swept, delta, trapezoidal and variable sweep wing configurations, sometimes conducted through flight testing of the 'X-series' aircraft. Attention is also given to the development of the first generation of supersonic fighter aircraft.

  4. Lewis icing research tunnel test of the aerodynamic effects of aircraft ground deicing/anti-icing fluids

    NASA Technical Reports Server (NTRS)

    Runyan, L. James; Zierten, Thomas A.; Hill, Eugene G.; Addy, Harold E., Jr.

    1992-01-01

    A wind tunnel investigation of the effect of aircraft ground deicing/anti-icing fluids on the aerodynamic characteristics of a Boeing 737-200ADV airplane was conducted. The test was carried out in the NASA Lewis Icing Research Tunnel. Fluids tested include a Newtonian deicing fluid, three non-Newtonian anti-icing fluids commercially available during or before 1988, and eight new experimental non-Newtonian fluids developed by four fluid manufacturers. The results show that fluids remain on the wind after liftoff and cause a measurable lift loss and drag increase. These effects are dependent on the high-lift configuration and on the temperature. For a configuration with a high-lift leading-edge device, the fluid effect is largest at the maximum lift condition. The fluid aerodynamic effects are related to the magnitude of the fluid surface roughness, particularly in the first 30 percent chord. The experimental fluids show a significant reduction in aerodynamic effects.

  5. Does Polishing a Rifle Bore Reduce Bullet Drag?

    DTIC Science & Technology

    2012-01-17

    thus lower drag. A Remington 700 5R Mil-Spec chambered in 300 Winchester Magnum was used. The bullets used were a 155.5 grain Berger Fullbore Boat...drag on the bullets. 15. SUBJECT TERMS Ballistic coefficient, aerodynamic drag, rifle bore, bore polishing, Remington 700 5R 16. SECURITY...A Remington 700 5R Mil-Spec chambered in 300 Winchester Magnum was used. The bullets used were a 155.5 grain Berger Fullbore Boat Tail and a 125

  6. 1997 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    Baize, Daniel G. (Editor)

    1999-01-01

    The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Aerodynamic Performance Workshop on February 25-28, 1997. The workshop was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, Flight Controls, Supersonic Laminar Flow Control, and Sonic Boom Prediction. The workshop objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientist and engineers working HSCT aerodynamics. In particular, single- and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT Motion Simulator results were presented along with executive summaries for all the Aerodynamic Performance technology areas.

  7. Comparisons of AEROX computer program predictions of lift and induced drag with flight test data

    NASA Technical Reports Server (NTRS)

    Axelson, J.; Hill, G. C.

    1981-01-01

    The AEROX aerodynamic computer program which provides accurate predictions of induced drag and trim drag for the full angle of attack range and for Mach numbers from 0.4 to 3.0 is described. This capability is demonstrated comparing flight test data and AEROX predictions for 17 different tactical aircraft. Values of minimum (skin friction, pressure, and zero lift wave) drag coefficients and lift coefficient offset due to camber (when required) were input from the flight test data to produce total lift and drag curves. The comparisons of trimmed lift drag polars show excellent agreement between the AEROX predictions and the in flight measurements.

  8. Theoretical and Experimental studies of aerodynamic interference effects. [aerodynamic forces on winglets and on wing nacelle configurations for the YC-14 and KC-135 aircraft

    NASA Technical Reports Server (NTRS)

    Rettie, I. H.

    1980-01-01

    Theoretical studies of aerodynamic forces on winglets shed considerable light on the mechanism by which these devices can reduce drag at constant total lift and on the necessity for proper alignment and cambering to achieve optimum favorable interference. Results of engineering studies, wind tunnel tests and performance predictions are reviewed for installations proposed for the AMST YC-14 and the KC-135 airplanes. The other major area of aerodynamic interference discussed is that of engine nacelle installations. Slipper and overwing nacelles have received much attention because of their potential for noise reduction, propulsive lift and improved ground clearance. A major challenge is the integration of such nacelles with the supercritical flow on the upper surface of a swept wing in cruise at high subsonic speeds.

  9. Vorticity confinement technique for drag prediction

    NASA Astrophysics Data System (ADS)

    Povitsky, Alex; Snyder, Troy

    2011-11-01

    This work couples wake-integral drag prediction and vorticity confinement technique (VC) for the improved prediction of drag from CFD simulations. Induced drag computations of a thin wing are shown to be more accurate than the more widespread method of surface pressure integration when compared to theoretical lifting-line value. Furthermore, the VC method improves trailing vortex preservation and counteracts the shift from induced drag to numerical entropy drag with increasing distance of Trefftz plane downstream of the wing. Accurate induced drag prediction via the surface integration of pressure barring a sufficiently refined surface grid and increased computation time. Furthermore, the alternative wake-integral technique for drag prediction suffers from numerical dissipation. VC is shown to control the numerical dissipation with very modest computational overhead. The 2-D research code is used to test specific formulations of the VC body force terms and illustrate the computational efficiency of the method compared to a ``brute force'' reduction in spatial step size. For the 3-D wing simulation, ANSYS FLUENT is employed with the VC body force terms added to the solver with user-defined functions (UDFs). VC is successfully implemented to highly unsteady flows typical for Micro Air Vehicles (MAV) producing oscillative drag force either by natural vortex shedding at high angles of attack or by flapping wing motion.

  10. Rarefaction effects on Galileo probe aerodynamics

    NASA Technical Reports Server (NTRS)

    Moss, James N.; LeBeau, Gerald J.; Blanchard, Robert C.; Price, Joseph M.

    1996-01-01

    Solutions of aerodynamic characteristics are presented for the Galileo Probe entering Jupiter's hydrogen-helium atmosphere at a nominal relative velocity of 47.4 km/s. Focus is on predicting the aerodynamic drag coefficient during the transitional flow regime using the direct simulation Monte Carlo (DSMC) method. Accuracy of the probe's drag coefficient directly impacts the inferred atmospheric properties that are being extracted from the deceleration measurements made by onboard accelerometers as part of the Atmospheric Structure Experiment. The range of rarefaction considered in the present study extends from the free molecular limit to continuum conditions. Comparisons made with previous calculations and experimental measurements show the present results for drag to merge well with Navier-Stokes and experimental results for the least rarefied conditions considered.

  11. Applicability of commercial CFD tools for assessment of heavy vehicle aerodynamic characteristics.

    SciTech Connect

    Pointer, W. D.; Sofu, T.; Chang, J.; Weber, D.; Nuclear Engineering Division

    2008-12-01

    In preliminary validation studies, computational predictions from the commercial CFD codes Star-CD were compared with detailed velocity, pressure and force balance data from experiments completed in the 7 ft. by 10 ft. wind tunnel at NASA Ames using a Generic Conventional Model (GCM) that is representative of typical current-generation tractor-trailer geometries. Lessons learned from this validation study were then applied to the prediction of aerodynamic drag impacts associated with various changes to the GCM geometry, including the addition of trailer based drag reduction devices and modifications to the radiator and hood configuration. Add-on device studies have focused on ogive boat tails, with initial results indicating that a seven percent reduction in drag coefficient is easily achievable. Radiator and hood reconfiguration studies have focused on changing only the size of the radiator and angle of the hood components without changes to radii of curvature between the radiator grill and hood components. Initial results indicate that such changes lead to only modest changes in drag coefficient.

  12. Aerodynamic Design of Heavy Vehicles Reporting Period January 15, 2004 through April 15, 2004

    SciTech Connect

    Leonard, A; Chatelain, P; Heineck, J; Browand, F; Mehta, R; Ortega, J; Salari, K; Storms, B; Brown, J; DeChant, L; Rubel, M; Ross, J; Hammache, M; Pointer, D; Roy, C; Hassan, B; Arcas, D; Hsu, T; Payne, J; Walker, S; Castellucci, P; McCallen, R

    2004-04-13

    Listed are summaries of the activities and accomplishments during this second-quarter reporting period for each of the consortium participants. The following are some highlights for this reporting period: (1) Experiments and computations guide conceptual designs for reduction of drag due to tractor-trailer gap flow (splitter plate), trailer underbody (wedges), and base drag (base-flap add-ons). (2) Steady and unsteady RANS simulations for the GTS geometry are being finalized for development of clear modeling guidelines with RANS. (3) Full geometry and tunnel simulations on the GCM geometry are underway. (4) CRADA with PACCAR is supporting computational parametric study to determine predictive need to include wind tunnel geometry as limits of computational domain. (5) Road and track test options are being investigated. All is ready for field testing of base-flaps at Crows Landing in California in collaboration with Partners in Advanced Transportation Highways (PATH). In addition, MAKA of Canada is providing the device and Wabash is providing a new trailer. (6) Apparatus to investigate tire splash and spray has been designed and is under construction. Michelin has offered tires with customized threads for this study. (7) Vortex methods have improved techniques for the treatment of vorticity near surfaces and spinning geometries like rotating tires. (8) Wind tunnel experiments on model rail cars demonstrate that empty coal cars exhibit substantial aerodynamic drag compared to full coal cars, indicating that significant fuel savings could be obtained by reducing the drag of empty coal cars. (9) Papers are being prepared for an exclusive conference session on the Heavy Vehicle DOE Aerodynamic Drag Project at the 34th AIAA Fluid Dynamics Conference in Portland, Oregon, June 28-July 1, 2004.

  13. Summary analysis of the Gemini entry aerodynamics

    NASA Technical Reports Server (NTRS)

    Whitnah, A. M.; Howes, D. B.

    1972-01-01

    The aerodynamic data that were derived in 1967 from the analysis of flight-generated data for the Gemini entry module are presented. These data represent the aerodynamic characteristics exhibited by the vehicle during the entry portion of Gemini 2, 3, 5, 8, 10, 11, and 12 missions. For the Gemini, 5, 8, 10, 11, and 12 missions, the flight-generated lift-to-drag ratios and corresponding angles of attack are compared with the wind tunnel data. These comparisons show that the flight generated lift-to-drag ratios are consistently lower than were anticipated from the tunnel data. Numerous data uncertainties are cited that provide an insight into the problems that are related to an analysis of flight data developed from instrumentation systems, the primary functions of which are other than the evaluation of flight aerodynamic performance.

  14. Physics of badminton shuttlecocks. Part 1 : aerodynamics

    NASA Astrophysics Data System (ADS)

    Cohen, Caroline; Darbois Texier, Baptiste; Quéré, David; Clanet, Christophe

    2011-11-01

    We study experimentally shuttlecocks dynamics. In this part we show that shuttlecock trajectory is highly different from classical parabola. When one takes into account the aerodynamic drag, the flight of the shuttlecock quickly curves downwards and almost reaches a vertical asymptote. We solve the equation of motion with gravity and drag at high Reynolds number and find an analytical expression of the reach. At high velocity, this reach does not depend on velocity anymore. Even if you develop your muscles you will not manage to launch the shuttlecock very far because of the ``aerodynamic wall.'' As a consequence you can predict the length of the field. We then discuss the extend of the aerodynamic wall to other projectiles like sports balls and its importance.

  15. Drag of wings with end plates

    NASA Technical Reports Server (NTRS)

    Hemke, Paul E

    1928-01-01

    In this report a formula for calculating the induced drag of multiplanes with end plates is derived. The frictional drag of the end plates are used, is sufficiently large to increase the efficiency of the wing. Curves showing the reduction of drag for monoplanes and biplanes are constructed; the influence of gap-chord ratio, aspect ratio, and height of end plate are determined for typical cases. The method of obtaining the reduction of drag for a multiplane is described. Comparisons are made of calculated and experimental results obtained in wind tunnel tests with airfoils of various aspect ratios and end plates of various sizes. The agreement between calculated and experimental results is good. Analysis of the experimental results shows that the shape and section of the end plates are important.

  16. Hypersonic bodies of maximum drag for a given lift-to-drag ratio.

    NASA Technical Reports Server (NTRS)

    Mcmillan, W., III; Hull, D. G.

    1971-01-01

    The problem considered in this paper is concerned with the aerodynamic design of the forebody shape of reentry vehicles in the blunt, homothetic, elliptic transversal contour, power-law longitudinal contour, raked-off configurational set. In particular, the forebody shape which maximizes the ratio of the forebody pressure drag to the free-stream dynamic pressure for a given lift-to-drag ratio and given geometric properties is determined. This problem is considered because recent survey articles indicate that its solution will provide useful qualitative design information about manned vehicles entering the earth's atmosphere from any of the foreseeable planetary missions. Single-integral equations relating the lift and drag in Newtonian hypersonic flow to the forebody geometry are derived and used to formulate the optimization problem which is solved by a direct numerical method.

  17. Experimental Study on Aerodynamic Characteristics of a Stepped-Nose Obstacle

    NASA Astrophysics Data System (ADS)

    Cakrawala, Anang; Umemura, Akira

    Wind tunnel experiments were conducted to obtain a comprehensive understanding of the aerodynamic characteristics of two-dimensional stepped-nose obstacles. In our previous numerical study on the flow around stepped-nose obstacles at a zero angle of attack, the following favorable properties have been found for such step configuration that the flow separating from the front corners reattaches to the leading edges of the side surfaces. (1) The strong vortices trapped in the step region produce the suction forces acting on the step walls to cancel the drag force acting the front surface. (2) The suppression of large-scale flow separation on the obstacle’s sides reduces not only the suction force acting on the back surface, but also the lateral force fluctuation to a great degree. (3) The resulting net drag coefficient is much smaller than that of square/rectangular obstacles. In the present experimental study, the drag coefficient of stepped-nosed obstacles with various step height and length, at zero angle of attack, was measured to identify the optimum step configuration for large drag reduction. The effect of attack angle on drag, lift and moment coefficients was examined to gain insight into the static and dynamic stability of stepped-nose obstacles. The effect of step configuration on the Strouhal number was also examined. It was found that the stepped nose brought about static stability to the obstacle with a rather large step length-to-height ratio, but neither static nor dynamic stability was derived for the optimal step configuration with maximum drag reduction.

  18. Statistical Analysis of CFD Solutions from the Drag Prediction Workshop

    NASA Technical Reports Server (NTRS)

    Hemsch, Michael J.

    2002-01-01

    A simple, graphical framework is presented for robust statistical evaluation of results obtained from N-Version testing of a series of RANS CFD codes. The solutions were obtained by a variety of code developers and users for the June 2001 Drag Prediction Workshop sponsored by the AIAA Applied Aerodynamics Technical Committee. The aerodynamic configuration used for the computational tests is the DLR-F4 wing-body combination previously tested in several European wind tunnels and for which a previous N-Version test had been conducted. The statistical framework is used to evaluate code results for (1) a single cruise design point, (2) drag polars and (3) drag rise. The paper concludes with a discussion of the meaning of the results, especially with respect to predictability, Validation, and reporting of solutions.

  19. The Effects of Streamwise-Deflected Wing Tips on the Aerodynamic Characteristics of an Aspect Ratio-2 Triangular Wing, Body, and Tail Combination

    NASA Technical Reports Server (NTRS)

    Peterson, Victor L.

    1959-01-01

    An investigation has been conducted on a triangular wing and body combination to determine the effects on the aerodynamic characteristics resulting from deflecting portions of the wing near the tips 900 to the wing surface about streamwise hinge lines. Experimental data were obtained for Mach numbers of 0.70, 1.30, 1.70, and 2.22 and for angles of attack ranging from -5 deg to +18 deg at sideslip angles of 0 deg and 5 deg. The results showed that the aerodynamic center shift experienced by the triangular wing and body combination as the Mach number was increased from subsonic to supersonic could be reduced by about 40 percent by deflecting the outboard 4 percent of the total area of each wing panel. Deflection about the same hinge line of additional inboard surfaces consisting of 2 percent of the total area of each wing panel resulted in a further reduction of the aerodynamic center travel of 10 percent. The resulting reductions in the stability were accompanied by increases in the drag due to lift and, for the case of the configuration with all surfaces deflected, in the minimum drag. The combined effects of reduced stability and increased drag of the untrimmed configuration on the trimmed lift-drag ratios were estimated from an analysis of the cases in which the wing-body combination with or without tips deflected was assumed to be controlled by a canard. The configurations with deflected surfaces had higher trimmed lift-drag ratios than the model with undeflected surfaces at Mach numbers up to about 1.70. Deflecting either the outboard surfaces or all of the surfaces caused the directional stability to be increased by increments that were approximately constant with increasing angle of attack at each Mach number. The effective dihedral was decreased at all angles of attack and Mach numbers when the surfaces were deflected.

  20. Flicking-wire drag tensioner

    NASA Technical Reports Server (NTRS)

    Dassele, M. A.; Fairall, H.

    1978-01-01

    Wire-drag system improves wire profile and applies consistent drag to wire. Wire drag is continuously adjustable from zero drag to tensile strength of wire. No-sag wire drag is easier to thread than former system and requires minimal downtime for cleaning and maintenance.

  1. Aerodynamic effects of wing corrugation at gliding flight at low Reynolds numbers

    NASA Astrophysics Data System (ADS)

    Meng, Xue Guang; Sun, Mao

    2013-07-01

    Corrugation gives an insect-wing the advantages of low mass, high stiffness, and low membrane stress. Researchers are interested to know if it is also advantageous aerodynamically. Previous works reported that corrugation enhanced the aerodynamic performance of wings at gliding flight. However, Reynolds numbers considered in these studies were higher than that of gliding insects. The present study showed that in the Reynolds number range of gliding insects, corrugation had negative aerodynamic effects. We studied aerodynamic effects of corrugation at gliding motion using the method of computational fluid dynamics, in the Reynolds number range of Re = 200-2400. Different corrugation patterns were considered. The effect of corrugation on aerodynamic performance was identified by comparing the aerodynamic forces between the corrugated and flat-plate wings, and the underlying flow mechanisms of the corrugation effects were revealed by analyzing the flow fields and surface pressure distributions. The findings are as follows: (1) the effect of corrugation is to decrease the lift, and change the drag only slightly (at 15°-25° angles of attack, lift is decreased by about 16%; at smaller angles of attack, the percentage of lift reduction is even larger because the lift is small). (2) Two mechanisms are responsible for the lift reduction. One is that the pleats at the lower surface of the corrugated wing produce relatively strong vortices, resulting in local low-pressure regions on the lower surface of the wing. The other is that corrugation near the leading edge pushes the leading-edge-separation layer slightly upwards and increases the size of the separation bubble above the upper surface, reducing the "suction pressure," or increasing the pressure, on the upper surface.

  2. Real-Time Adaptive Least-Squares Drag Minimization for Performance Adaptive Aeroelastic Wing

    NASA Technical Reports Server (NTRS)

    Ferrier, Yvonne L.; Nguyen, Nhan T.; Ting, Eric

    2016-01-01

    This paper contains a simulation study of a real-time adaptive least-squares drag minimization algorithm for an aeroelastic model of a flexible wing aircraft. The aircraft model is based on the NASA Generic Transport Model (GTM). The wing structures incorporate a novel aerodynamic control surface known as the Variable Camber Continuous Trailing Edge Flap (VCCTEF). The drag minimization algorithm uses the Newton-Raphson method to find the optimal VCCTEF deflections for minimum drag in the context of an altitude-hold flight control mode at cruise conditions. The aerodynamic coefficient parameters used in this optimization method are identified in real-time using Recursive Least Squares (RLS). The results demonstrate the potential of the VCCTEF to improve aerodynamic efficiency for drag minimization for transport aircraft.

  3. Covariance analysis of differential drag-based satellite cluster flight

    NASA Astrophysics Data System (ADS)

    Ben-Yaacov, Ohad; Ivantsov, Anatoly; Gurfil, Pini

    2016-06-01

    One possibility for satellite cluster flight is to control relative distances using differential drag. The idea is to increase or decrease the drag acceleration on each satellite by changing its attitude, and use the resulting small differential acceleration as a controller. The most significant advantage of the differential drag concept is that it enables cluster flight without consuming fuel. However, any drag-based control algorithm must cope with significant aerodynamical and mechanical uncertainties. The goal of the current paper is to develop a method for examination of the differential drag-based cluster flight performance in the presence of noise and uncertainties. In particular, the differential drag control law is examined under measurement noise, drag uncertainties, and initial condition-related uncertainties. The method used for uncertainty quantification is the Linear Covariance Analysis, which enables us to propagate the augmented state and filter covariance without propagating the state itself. Validation using a Monte-Carlo simulation is provided. The results show that all uncertainties have relatively small effect on the inter-satellite distance, even in the long term, which validates the robustness of the used differential drag controller.

  4. Reducing the pressure drag of a D-shaped bluff body using linear feedback control

    NASA Astrophysics Data System (ADS)

    Dalla Longa, L.; Morgans, A. S.; Dahan, J. A.

    2017-01-01

    The pressure drag of blunt bluff bodies is highly relevant in many practical applications, including to the aerodynamic drag of road vehicles. This paper presents theory revealing that a mean drag reduction can be achieved by manipulating wake flow fluctuations. A linear feedback control strategy then exploits this idea, targeting attenuation of the spatially integrated base (back face) pressure fluctuations. Large-eddy simulations of the flow over a D-shaped blunt bluff body are used as a test-bed for this control strategy. The flow response to synthetic jet actuation is characterised using system identification, and controller design is via shaping of the frequency response to achieve fluctuation attenuation. The designed controller successfully attenuates integrated base pressure fluctuations, increasing the time-averaged pressure on the body base by 38%. The effect on the flow field is to push the roll-up of vortices further downstream and increase the extent of the recirculation bubble. This control approach uses only body-mounted sensing/actuation and input-output model identification, meaning that it could be applied experimentally.

  5. Flight test evaluation of drag effects on surface coatings on the NASA Boeing 737 TCV airplane

    NASA Technical Reports Server (NTRS)

    George-Falvy, D.; Sikavi, D. A.

    1981-01-01

    A flight test program was conducted in which the effects of various surface coatings on aerodynamic drag were investigated; results of this program are described in this report. The tests were conducted at NASA-Langley Research Center on the terminal configured vehicle (TCV) Boeing 737 research airplane. The Boeing Company, as contractor with NASA under the Energy Efficient Transport (EET) program, planned and evaluated the experiment. The NASA-TCV Program Office coordinated the experiment and performed the flight tests. The principal objective of the test was to evaluate the drag reduction potential of an elastomeric polyurethane surface coating, CAAPCO B-274, which also has been considered for application on transport airplanes to protect leading edges from erosion. The smooth surface achievable with this type of coating held some promise of reducing the skin friction drag as compared to conventional production type aircraft surfaces, which are usually anodized bare metal or coated with corrosion protective paint. Requirements for high precision measurements were the principal considerations in the experiment.

  6. 1997 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    Baize, Daniel G. (Editor)

    1999-01-01

    The High-Speed Research Program and NASA Langley Research Center sponsored the NASA High-Speed Research Program Aerodynamic Performance Workshop on February 25-28, 1997. The workshop was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in area of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, Flight Controls, Supersonic Laminar Flow Control, and Sonic Boom Prediction. The workshop objectives were to (1) report the progress and status of HSCT aerodyamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientist and engineers working HSCT aerodynamics. In particular, single- and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT Motion Simulator results were presented along with executive summaries for all the Aerodynamic Performance technology areas.

  7. Aeroacoustic Study of a High-Fidelity Aircraft Model: Part 1- Steady Aerodynamic Measurements

    NASA Technical Reports Server (NTRS)

    Khorrami, Mehdi R.; Hannon, Judith A.; Neuhart, Danny H.; Markowski, Gregory A.; VandeVen, Thomas

    2012-01-01

    In this paper, we present steady aerodynamic measurements for an 18% scale model of a Gulfstream air-craft. The high fidelity and highly-instrumented semi-span model was developed to perform detailed aeroacoustic studies of airframe noise associated with main landing gear/flap components and gear-flap interaction noise, as well as to evaluate novel noise reduction concepts. The aeroacoustic tests, being conducted in the NASA Langley Research Center 14- by 22-Foot Subsonic Tunnel, are split into two entries. The first entry, completed November 2010, was entirely devoted to the detailed mapping of the aerodynamic characteristics of the fabricated model. Flap deflections of 39?, 20?, and 0? with the main landing gear on and off were tested at Mach numbers of 0.16, 0.20, and 0.24. Additionally, for each flap deflection, the model was tested with the tunnel both in the closed-wall and open-wall (jet) modes. During this first entry, global forces (lift and drag) and extensive steady and unsteady surface pressure measurements were obtained. Preliminary analysis of the measured forces indicates that lift, drag, and stall characteristics compare favorably with Gulfstream?s high Reynolds number flight data. The favorable comparison between wind-tunnel and flight data allows the semi-span model to be used as a test bed for developing/evaluating airframe noise reduction concepts under a relevant environment. Moreover, initial comparison of the aerodynamic measurements obtained with the tunnel in the closed- and open-wall configurations shows similar aerodynamic behavior. This permits the acoustic and off-surface flow measurements, planned for the second entry, to be conducted with the tunnel in the open-jet mode.

  8. A Method for Predicting Helicopter Hub Drag

    DTIC Science & Technology

    1976-01-01

    needed. Do not return it to the originirtor. .1g Uncles i fled AEP0RT DOCUMENTATI014 PAGE Nt"It COIIETJR Ft I hawba row OR*OVy ACCCUMNN. a mc mCIV~ur*6...using I I CDa = CDF + CDBS The total incremental drag of the rigid fairing is then I I D F = CDF + CDDS + ACDF (15) 24 AERODYNAMIC ANALYSIS TECIIQIOUE...panels and vortex lattices are stored on these units. These are working storage areas and are required for every , Job executed. 98 Unit(s) Description

  9. Space Shuttle Orbital Drag Parachute Design

    NASA Technical Reports Server (NTRS)

    Meyerson, Robert E.

    2001-01-01

    The drag parachute system was added to the Space Shuttle Orbiter's landing deceleration subsystem beginning with flight STS-49 in May 1992. The addition of this subsystem to an existing space vehicle required a detailed set of ground tests and analyses. The aerodynamic design and performance testing of the system consisted of wind tunnel tests, numerical simulations, pilot-in-the-loop simulations, and full-scale testing. This analysis and design resulted in a fully qualified system that is deployed on every flight of the Space Shuttle.

  10. 1999 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    Hahne, David E. (Editor)

    1999-01-01

    NASA's High-Speed Research Program sponsored the 1999 Aerodynamic Performance Technical Review on February 8-12, 1999 in Anaheim, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in the areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High Lift, and Flight Controls. The review objectives were to: (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working on HSCT aerodynamics. In particular, single and midpoint optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented, along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program. This Volume 1/Part 1 publication covers configuration aerodynamics.

  11. Vertical Landing Aerodynamics of Reusable Rocket Vehicle

    NASA Astrophysics Data System (ADS)

    Nonaka, Satoshi; Nishida, Hiroyuki; Kato, Hiroyuki; Ogawa, Hiroyuki; Inatani, Yoshifumi

    The aerodynamic characteristics of a vertical landing rocket are affected by its engine plume in the landing phase. The influences of interaction of the engine plume with the freestream around the vehicle on the aerodynamic characteristics are studied experimentally aiming to realize safe landing of the vertical landing rocket. The aerodynamic forces and surface pressure distributions are measured using a scaled model of a reusable rocket vehicle in low-speed wind tunnels. The flow field around the vehicle model is visualized using the particle image velocimetry (PIV) method. Results show that the aerodynamic characteristics, such as the drag force and pitching moment, are strongly affected by the change in the base pressure distributions and reattachment of a separation flow around the vehicle.

  12. Reduction of computer usage costs in predicting unsteady aerodynamic loadings caused by control surface motion. Addendum to computer program description

    NASA Technical Reports Server (NTRS)

    Rowe, W. S.; Petrarca, J. R.

    1980-01-01

    Changes to be made that provide increased accuracy and increased user flexibility in prediction of unsteady loadings caused by control surface motions are described. Analysis flexibility is increased by reducing the restrictions on the location of the downwash stations relative to the leading edge and the edges of the control surface boundaries. Analysis accuracy is increased in predicting unsteady loading for high Mach number analysis conditions through use of additional chordwise downwash stations. User guideline are presented to enlarge analysis capabilities of unusual wing control surface configurations. Comparative results indicate that the revised procedures provide accurate predictions of unsteady loadings as well as providing reductions of 40 to 75 percent in computer usage cost required by previous versions of this program.

  13. Rarefaction Effects in Hypersonic Aerodynamics

    NASA Astrophysics Data System (ADS)

    Riabov, Vladimir V.

    2011-05-01

    The Direct Simulation Monte-Carlo (DSMC) technique is used for numerical analysis of rarefied-gas hypersonic flows near a blunt plate, wedge, two side-by-side plates, disk, torus, and rotating cylinder. The role of various similarity parameters (Knudsen and Mach numbers, geometrical and temperature factors, specific heat ratios, and others) in aerodynamics of the probes is studied. Important kinetic effects that are specific for the transition flow regime have been found: non-monotonic lift and drag of plates, strong repulsive force between side-by-side plates and cylinders, dependence of drag on torus radii ratio, and the reverse Magnus effect on the lift of a rotating cylinder. The numerical results are in a good agreement with experimental data, which were obtained in a vacuum chamber at low and moderate Knudsen numbers from 0.01 to 10.

  14. Aerodynamic Analysis of Morphing Blades

    NASA Astrophysics Data System (ADS)

    Harris, Caleb; Macphee, David; Carlisle, Madeline

    2016-11-01

    Interest in morphing blades has grown with applications for wind turbines and other aerodynamic blades. This passive control method has advantages over active control methods such as lower manufacturing and upkeep costs. This study has investigated the lift and drag forces on individual blades with experimental and computational analysis. The goal has been to show that these blades delay stall and provide larger lift-to-drag ratios at various angles of attack. Rigid and flexible airfoils were cast from polyurethane and silicone respectively, then lift and drag forces were collected from a load cell during 2-D testing in a wind tunnel. Experimental data was used to validate computational models in OpenFOAM. A finite volume fluid-structure-interaction solver was used to model the flexible blade in fluid flow. Preliminary results indicate delay in stall and larger lift-to-drag ratios by maintaining more optimal angles of attack when flexing. Funding from NSF REU site Grant EEC 1358991 is greatly appreciated.

  15. Measuring the Drag Force on a Falling Ball

    NASA Astrophysics Data System (ADS)

    Cross, Rod; Lindsey, Crawford

    2014-03-01

    The effect of the aerodynamic drag force on an object in flight is well known and has been described in this and other journals many times. At speeds less than about 1 m/s, the drag force on a sphere is proportional to the speed and is given by Stokes' law. At higher speeds, the drag force is proportional to the velocity squared and is usually small compared with the gravitational force if the object mass is large and its speed is low. In order to observe a significant effect, or to measure the terminal velocity, experiments are often conducted with very light objects such as a balloon or coffee filter3 or muffin cup,4 or are conducted in a liquid rather than in air. The effect of the drag force can also be increased by increasing the surface area of the object.

  16. An Experimental Investigation of Helicopter Rotor Hub Fairing Drag Characteristics

    NASA Technical Reports Server (NTRS)

    Sung, D. Y.; Lance, M. B.; Young, L. A.; Stroub, R. H.

    1989-01-01

    A study was done in the NASA 14- by 22-Foot Wind Tunnel at Langley Research Center on the parasite drag of different helicopter rotor hub fairings and pylons. Parametric studies of hub-fairing camber and diameter were conducted. The effect of hub fairing/pylon clearance on hub fairing/pylon mutual interference drag was examined in detail. Force and moment data are presented in tabular and graphical forms. The results indicate that hub fairings with a circular-arc upper surface and a flat lower surface yield maximum hub drag reduction; and clearance between the hub fairing and pylon induces high mutual-interference drag and diminishes the drag-reduction benefit obtained using a hub fairing with a flat lower surface. Test data show that symmetrical hub fairings with circular-arc surfaces generate 74 percent more interference drag than do cambered hub fairings with flat lower surfaces, at moderate negative angle of attack.

  17. Validation of the virtual elevation field test method when assessing the aerodynamics of para-cyclists with a uni-lateral trans-tibial amputation.

    PubMed

    Dyer, Bryce; Disley, B Xavier

    2017-03-12

    Lower-limb amputees typically require some form of prosthetic limb to ride a bicycle for recreation or when competing. At elite-level racing speeds, aerodynamic drag can represent the majority of the resistance acting against a cyclists' forward motion. As a result, the reduction of such resistance is beneficial to an amputee whereby the form and function of the prosthetic limb can be optimized through engineering. To measure the performance of such limbs, field testing provides a cost-effective and context-specific method of aerodynamic drag measurement. However, few methods have been formally validated and none have been applied to amputees with lower-limb amputations. In this paper, an elite level para-cyclist wore two different prosthetic limb designs and had their total aerodynamic drag of a wind tunnel reference method statistically correlated against a velodrome-based virtual elevation field test method. The calculated coefficient of variation was in the range of 0.7-0.9% for the wind tunnel method and 2-3% for the virtual elevation method. A 0.03 m(2) difference was identified in the absolute values recorded between the two methods. Ultimately, both methods exhibited high levels of precision, yet relative results to each other. The virtual elevation method is proposed as a suitable technique to assess the aerodynamic drag of amputee para-cyclists. Implications for rehabilitation This assessment method will provide practitioners a reliable means of assessing the impact of changes made to prosthetics design for cyclists with limb absence. The proposed method offers a low cost and geographically accessible solution compared to others proposed in the past. This assessment method has significant potential for impact among prosthetic limb users looking to improve their cycling performance whereas previous attention in this field has been extremely limited.

  18. Numerical investigation of the aerodynamic and structural characteristics of a corrugated wing

    NASA Astrophysics Data System (ADS)

    Hord, Kyle

    Previous experimental studies on static, bio-inspired corrugated wings have shown that they produce favorable aerodynamic properties such as delayed stall compared to streamlined wings and flat plates at high Reynolds numbers (Re ≥ 4x104). The majority of studies have been carried out with scaled models of dragonfly forewings from the Aeshna Cyanea in either wind tunnels or water channels. In this thesis, the aerodynamics of a corrugated airfoil was studied using computational fluid dynamics methods at a low Reynolds number of 1000. Structural analysis was also performed using the commercial software SolidWorks 2009. The flow field is described by solving the incompressible Navier-Stokes equations on an overlapping grid using the pressure-Poisson method. The equations are discretized in space with second-order accurate central differences. Time integration is achieved through the second-order Crank-Nicolson implicit method. The complex vortex structures that form in the corrugated airfoil valleys and around the corrugated airfoil are studied in detail. Comparisons are made with experimental measurements from corrugated wings and also with simulations of a flat plate. Contrary to the studies at high Reynolds numbers, our study shows that at low Reynolds numbers the wing corrugation does not provide any aerodynamic benefit compared to a smoothed flat plate. Instead, the corrugated profile generates more pressure drag which is only partially offset by the reduction of friction drag, leading to more total drag than the flat plate. Structural analysis shows that the wing corrugation can increase the resistance to bending moments on the wing structure. A smoothed structure has to be three times thicker to provide the same stiffness. It was concluded the corrugated wing has the structural benefit to provide the same resistance to bending moments with a much reduced weight.

  19. Unsteady Aerodynamic Force Sensing from Measured Strain

    NASA Technical Reports Server (NTRS)

    Pak, Chan-Gi

    2016-01-01

    , velocity, and acceleration sensors. This research demonstrates the feasibility of obtaining induced drag and lift forces through the use of distributed sensor technology with measured strain data. An active induced drag control system thus can be designed using the two computed aerodynamic forces, induced drag and lift, to improve the fuel efficiency of an aircraft. Interpolation elements between structural finite element grids and the CFD grids and centroids are successfully incorporated with the unsteady aeroelastic computation scheme. The most critical technology for the success of the proposed approach is the robust on-line parameter estimator, since the least-squares curve fitting method depends heavily on aeroelastic system frequencies and damping factors.

  20. Operational considerations for aerodynamic testing of large-scale wing sections in a simulated natural rain environment

    NASA Technical Reports Server (NTRS)

    Campbell, Bryan A.; Bezos, Gaudy M.; Dunham, R. Earl, Jr.; Melson, W. Edward, Jr.

    1990-01-01

    One of the necessary areas of consideration for outdoor heavy rain testing is the effect of wind on both the simulated rain field and the quality and repeatability of the aerodynamic data. This paper discusses the data acquisition and subsequent reduction to nondimensional coefficients of lift and drag, with the appropriate correction for wind and rain field. Sample force data showing these effects are presented, along with estimates for accuracy and repeatability. The capability to produce high-quality data for rain drop size distribution using photographic and computerized image processing techniques was developed. Sample photographs depicting rain drop size are shown.

  1. Application of CAD/CAE class systems to aerodynamic analysis of electric race cars

    NASA Astrophysics Data System (ADS)

    Grabowski, L.; Baier, A.; Buchacz, A.; Majzner, M.; Sobek, M.

    2015-11-01

    Aerodynamics is one of the most important factors which influence on every aspect of a design of a car and car driving parameters. The biggest influence aerodynamics has on design of a shape of a race car body, especially when the main objective of the race is the longest distance driven in period of time, which can not be achieved without low energy consumption and low drag of a car. Designing shape of the vehicle body that must generate the lowest possible drag force, without compromising the other parameters of the drive. In the article entitled „Application of CAD/CAE class systems to aerodynamic analysis of electric race cars” are being presented problems solved by computer analysis of cars aerodynamics and free form modelling. Analysis have been subjected to existing race car of a Silesian Greenpower Race Team. On a basis of results of analysis of existence of Kammback aerodynamic effect innovative car body were modeled. Afterwards aerodynamic analysis were performed to verify existence of aerodynamic effect for innovative shape and to recognize aerodynamics parameters of the shape. Analysis results in the values of coefficients and aerodynamic drag forces. The resulting drag forces Fx, drag coefficients Cx(Cd) and aerodynamic factors Cx*A allowed to compare all of the shapes to each other. Pressure distribution, air velocities and streams courses were useful in determining aerodynamic features of analyzed shape. For aerodynamic tests was used Ansys Fluent CFD software. In a paper the ways of surface modeling with usage of Realize Shape module and classic surface modeling were presented. For shapes modeling Siemens NX 9.0 software was used. Obtained results were used to estimation of existing shapes and to make appropriate conclusions.

  2. Aerodynamics of a turbojet-boosted launch vehicle concept

    NASA Technical Reports Server (NTRS)

    Small, W. J.; Riebe, G. D.; Taylor, A. H.

    1980-01-01

    Results from analytical and experimental studies of the aerodynamic characteristics of a turbojet-boosted launch vehicle are presented. The success of this launch vehicle concept depends upon several novel applications of aerodynamic technology, particularly in the area of takeoff lift and minimum transonic drag requirements. The take-off mode stresses leading edge vortex lift generated in parallel by a complex arrangement of low aspect ratio booster and orbiter wings. Wind-tunnel tests on a representative model showed that this low-speed lift is sensitive to geometric arrangements of the booster-orbiter combination and is not predictable by standard analytic techniques. Transonic drag was also experimentally observed to be very sensitive to booster location; however, these drag levels were accurately predicted by standard farfield wave drag theory.

  3. Aerodynamic effects of flexibility in flapping wings.

    PubMed

    Zhao, Liang; Huang, Qingfeng; Deng, Xinyan; Sane, Sanjay P

    2010-03-06

    Recent work on the aerodynamics of flapping flight reveals fundamental differences in the mechanisms of aerodynamic force generation between fixed and flapping wings. When fixed wings translate at high angles of attack, they periodically generate and shed leading and trailing edge vortices as reflected in their fluctuating aerodynamic force traces and associated flow visualization. In contrast, wings flapping at high angles of attack generate stable leading edge vorticity, which persists throughout the duration of the stroke and enhances mean aerodynamic forces. Here, we show that aerodynamic forces can be controlled by altering the trailing edge flexibility of a flapping wing. We used a dynamically scaled mechanical model of flapping flight (Re approximately 2000) to measure the aerodynamic forces on flapping wings of variable flexural stiffness (EI). For low to medium angles of attack, as flexibility of the wing increases, its ability to generate aerodynamic forces decreases monotonically but its lift-to-drag ratios remain approximately constant. The instantaneous force traces reveal no major differences in the underlying modes of force generation for flexible and rigid wings, but the magnitude of force, the angle of net force vector and centre of pressure all vary systematically with wing flexibility. Even a rudimentary framework of wing veins is sufficient to restore the ability of flexible wings to generate forces at near-rigid values. Thus, the magnitude of force generation can be controlled by modulating the trailing edge flexibility and thereby controlling the magnitude of the leading edge vorticity. To characterize this, we have generated a detailed database of aerodynamic forces as a function of several variables including material properties, kinematics, aerodynamic forces and centre of pressure, which can also be used to help validate computational models of aeroelastic flapping wings. These experiments will also be useful for wing design for small

  4. On the lift induced drag in viscous flows

    NASA Astrophysics Data System (ADS)

    Tognaccini, Renato; Marongiu, Claudio; Ueno, Makoto

    2012-11-01

    As stated by Spalart (JFM, 2008): ``An ambition which will have to wait is a rigorous definition of induced drag in viscous flows.'' The idea that there is a link between the aerodynamic force and the Lamb vector, defined as the cross product of fluid vorticity and velocity dates back to Prandtl. Saffman (``Vortex Dynamics,'' 1992) and, more recently, Wu J.-Z. et al. (JFM, 2007) suggested an expression of the lift induced drag in terms of vortex force (the volume integral of the Lamb vector). In this paper we analyze the steady incompressible flow around a 3D lifting body at high Reynolds numbers. The suggested connection between vortex force and induced drag is discussed in detail. In particular, a rigorous definition of the lift induced drag in viscous flows without ambiguities is proposed. A numerical experiment: the analysis of the flow around an elliptic wing will confirm the theoretical analysis. The aerodynamic force and its lift and drag components are computed by integration of the Lamb vector field as obtained by a numerical solution and will be compared with classical expressions.

  5. System technology analysis of aeroassisted orbital transfer vehicles. Moderate lift/drag (0.75-1.5): Volume 1A, part 2: Executive summary, phase 2

    NASA Technical Reports Server (NTRS)

    1985-01-01

    Significant achievements and activities of Phase 2 of a study to assess aeroassisted orbit transfer vehicle (AOTV) system technology are summarized. Phase 2 was directed towards identification and prioritization of technology payoffs of representative space based mid lift/drag ratio (L/D) AOTV's and the cryofueled propulsion subsystem - configuration interactions. Enhancing technology areas were identified which could provide substantial transport cost reduction. These include: (1) improved lifetime of storable propellant engines; (2) avionics weight reduction; (3) external thermal protection system weight reduction; (4) decrease of uncertainties in aerodynamic and aerothermodynamic performance; electrical power subsystem weight reduction due to incorporation of advanced materials; and (6) structural shell weight reduction. Results indicated that advanced aerothermodynamic methodology and aft end configuring may provide an enlarged allowable zone for engine nozzle protrusions into the separated flow region. Payload manifesting and non-hydrogen propellant manifesting at the space station is recommended.

  6. Chaff Aerodynamics

    DTIC Science & Technology

    1975-11-01

    further improve the contrast all of the interior surfaces of the test chamber are painted flat black and the bac!-,ground walls in view of the cameras...to be adequate to eliminate wall effects on the chaff aerodynamics. Secondly, the chamber air mass had to be sufficiently small that it would damp out...independently- supported special rotating-shutter system to "strobe" the dipole images. The integral shutter in each lens assembly is also retained for

  7. Drag on Sessile Drops

    NASA Astrophysics Data System (ADS)

    Milne, Andrew J. B.; Fleck, Brian; Nobes, David; Sen, Debjyoti; Amirfazli, Alidad; University of Alberta Mechanical Engineering Collaboration

    2013-11-01

    We present the first ever direct measurements of the coefficient of drag on sessile drops at Reynolds numbers from the creeping flow regime up to the point of incipient motion, made using a newly developed floating element differential drag sensor. Surfaces of different wettabilities (PMMA, Teflon, and a superhydrophobic surface (SHS)), wet by water, hexadecane, and various silicone oils, are used to study the effects of drop shape, and fluid properties on drag. The relation between drag coefficient and Reynolds number (scaled by drop height) varies slightly with liquid-solid system and drop volume with results suggesting the drop experiences increased drag compared to similar shaped solid bodies due to drop oscillation influencing the otherwise laminar flow. Drops adopting more spherical shapes are seen to experience the greatest force at any given airspeed. This indicates that the relative exposed areas of drops is an important consideration in terms of force, with implications for the shedding of drops in applications such as airfoil icing and fuel cell flooding. The measurement technique used in this work can be adapted to measure drag force on other deformable, lightly adhered objects such as dust, sand, snow, vesicles, foams, and biofilms. The authours acknowledge NSERC, Alberta Innovates Technology Futures, and the Killam Trusts.

  8. An experimental and theoretical analysis of the aerodynamic characteristics of a biplane-winglet configuration. M.D. Thesis

    NASA Technical Reports Server (NTRS)

    Gall, P. D.

    1984-01-01

    Improving the aerodynamic characteristics of an airplane with respect to maximizing lift and minimizing induced and parasite drag are of primary importance in designing lighter, faster, and more efficient aircraft. Previous research has shown that a properly designed biplane wing system can perform superiorly to an equivalent monoplane system with regard to maximizing the lift-to-drag ratio and efficiency factor. Biplanes offer several potential advantages over equivalent monoplanes, such as a 60-percent reduction in weight, greater structural integrity, and increased roll response. The purpose of this research is to examine, both theoretically and experimentally, the possibility of further improving the aerodynamic characteristics of the biplanes configuration by adding winglets. Theoretical predictions were carried out utilizing vortex-lattice theory, which is a numerical method based on potential flow theory. Experimental data were obtained by testing a model in the Pennsylvania State University's subsonic wind tunnel at a Reynolds number of 510,000. The results showed that the addition of winglets improved the performance of the biplane with respect to increasing the lift-curve slope, increasing the maximum lift coefficient, increasing the efficiency factor, and decreasing the induced drag. A listing of the program is included in the Appendix.

  9. Calculated Drag of an Aerial Refueling Assembly Through Airplane Performance Analysis

    NASA Technical Reports Server (NTRS)

    Vachon, Michael Jacob; Ray, Ronald J.

    2004-01-01

    The aerodynamic drag of an aerial refueling assembly was calculated during the Automated Aerial Refueling project at the NASA Dryden Flight Research Center. An F/A-18A airplane was specially instrumented to obtain accurate fuel flow measurements and to determine engine thrust. A standard Navy air refueling store with a retractable refueling hose and paradrogue was mounted to the centerline pylon of the F/A-18A airplane. As the paradrogue assembly was deployed and stowed, changes in the calculated thrust of the airplane occurred and were equated to changes in vehicle drag. These drag changes were attributable to the drag of the paradrogue assembly. The drag of the paradrogue assembly was determined to range from 200 to 450 lbf at airspeeds from 170 to 250 KIAS. Analysis of the drag data resulted in a single drag coefficient of 0.0056 for the paradrogue assembly that adequately matched the calculated drag for all flight conditions. The drag relief provided to the tanker airplane when a receiver airplane engaged the paradrogue is also documented from 35 to 270 lbf at the various flight conditions tested. The results support the development of accurate aerodynamic models to be used in refueling simulations and control laws for fully autonomous refueling.

  10. Cruise aerodynamics of USB nacelle/wing geometric variations

    NASA Technical Reports Server (NTRS)

    Braden, J. A.; Hancock, J. P.; Burdges, K. P.

    1976-01-01

    Experimental results are presented on aerodynamic effects of geometric variations in upper surface blown nacelle configurations at high speed cruise conditions. Test data include both force and pressure measurements on two and three dimensional models powered by upper surface blowing nacelles of varying geometries. Experimental results are provided on variations in nozzle aspect ratio, nozzle boattail angle, and multiple nacelle installations. The nacelles are ranked according to aerodynamic drag penalties as well as overall installed drag penalties. Sample effects and correlations are shown for data obtained with the pressure model.

  11. 1998 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    McMillin, S. Naomi (Editor)

    1999-01-01

    NASA's High-Speed Research Program sponsored the 1998 Aerodynamic Performance Technical Review on February 9-13, in Los Angeles, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, and Flight Controls. The review objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working HSCT aerodynamics. In particular, single and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program.

  12. 1998 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    McMillin, S. Naomi (Editor)

    1999-01-01

    NASA's High-Speed Research Program sponsored the 1998 Aerodynamic Performance Technical Review on February 9-13, in Los Angeles, California. The review was designed to bring together NASA and industry HighSpeed Civil Transport (HSCT) Aerodynamic Performance technology development participants in areas of. Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High-Lift, and Flight Controls. The review objectives were to: (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working HSCT aerodynamics. In particular, single and multi-point optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program.

  13. 1999 NASA High-Speed Research Program Aerodynamic Performance Workshop. Volume 1; Configuration Aerodynamics

    NASA Technical Reports Server (NTRS)

    Hahne, David E. (Editor)

    1999-01-01

    NASA's High-Speed Research Program sponsored the 1999 Aerodynamic Performance Technical Review on February 8-12, 1999 in Anaheim, California. The review was designed to bring together NASA and industry High-Speed Civil Transport (HSCT) Aerodynamic Performance technology development participants in the areas of Configuration Aerodynamics (transonic and supersonic cruise drag prediction and minimization), High Lift, and Flight Controls. The review objectives were to (1) report the progress and status of HSCT aerodynamic performance technology development; (2) disseminate this technology within the appropriate technical communities; and (3) promote synergy among the scientists and engineers working on HSCT aerodynamics. In particular, single and midpoint optimized HSCT configurations, HSCT high-lift system performance predictions, and HSCT simulation results were presented, along with executive summaries for all the Aerodynamic Performance technology areas. The HSR Aerodynamic Performance Technical Review was held simultaneously with the annual review of the following airframe technology areas: Materials and Structures, Environmental Impact, Flight Deck, and Technology Integration. Thus, a fourth objective of the Review was to promote synergy between the Aerodynamic Performance technology area and the other technology areas of the HSR Program. This Volume 1/Part 2 publication covers the design optimization and testing sessions.

  14. Experimental investigation of hypersonic aerodynamics

    NASA Technical Reports Server (NTRS)

    Intrieri, Peter F.

    1988-01-01

    An extensive series of ballistic range tests were conducted at the Ames Research Center to determine precisely the aerodynamic characteristics of the Galileo entry probe vehicle. Figures and tables are presented which summarize the results of these ballistic range tests. Drag data were obtained for both a nonablated and a hypothesized ablated Galileo configuration at Mach numbers from about 0.7 to 14 and at Reynolds numbers from 1000 to 4 million. The tests were conducted in air and the experimental results were compared with available Pioneer Venus data since these two configurations are similar in geometry. The nonablated Galileo configuration was also tested with two different center-of-gravity positions to obtain values of pitching-moment-curve slope which could be used in determining values of lift and center-of-pressure location for this configuration. The results indicate that the drag characteristics of the Galileo probe are qualitatively similar to that of Pioneer Venus, however, the drag of the nonablated Galileo is about 3 percent lower at the higher Mach numbers and as much as 5 percent greater at transonic Mach numbers of about 1.0 to 1.5. Also, the drag of the hypothesized ablated configuration is about 3 percent lower than that of the nonablated configuration at the higher Mach numbers but about the same at the lower Mach numbers. Additional tests are required at Reynolds numbers of 1000, 500, and 250 to determine if the dramatic rise in drag coefficient measured for Pioneer Venus at these low Reynolds numbers also occurs for Galileo, as might be expected.

  15. Wind turbine trailing edge aerodynamic brakes

    SciTech Connect

    Migliore, P G; Miller, L S; Quandt, G A

    1995-04-01

    Five trailing-edge devices were investigated to determine their potential as wind-turbine aerodynamic brakes, and for power modulation and load alleviation. Several promising configurations were identified. A new device, called the spoiler-flap, appears to be the best alternative. It is a simple device that is effective at all angles of attack. It is not structurally intrusive, and it has the potential for small actuating loads. It is shown that simultaneous achievement of a low lift/drag ratio and high drag is the determinant of device effectiveness, and that these attributes must persist up to an angle of attack of 45{degree}. It is also argued that aerodynamic brakes must be designed for a wind speed of at least 45 m/s (100 mph).

  16. Aerodynamic shape optimization of arbitrary hypersonic vehicles

    NASA Technical Reports Server (NTRS)

    Dulikravich, George S.; Sheffer, Scott G.

    1991-01-01

    A new method was developed to optimize, in terms of aerodynamic wave drag minimization, arbitrary (nonaxisymmetric) hypersonic vehicles in modified Newtonian flow, while maintaining the initial volume and length of the vehicle. This new method uses either a surface fitted Fourier series to represent the vehicle's geometry or an independent point motion algorithm. In either case, the coefficients of the Fourier series or the spatial locations of the points defining each cross section were varied and a numerical optimization algorithm based on a quasi-Newton gradient search concept was used to determine the new optimal configuration. Results indicate a significant decrease in aerodynamic wave drag for simple and complex geometries at relatively low CPU costs. In the case of a cone, the results agreed well with known analytical optimum ogive shapes. The procedure is capable of accepting more complex flow field analysis codes.

  17. On a global aerodynamic optimization of a civil transport aircraft

    NASA Technical Reports Server (NTRS)

    Savu, G.; Trifu, O.

    1991-01-01

    An aerodynamic optimization procedure developed to minimize the drag to lift ratio of an aircraft configuration: wing - body - tail, in accordance with engineering restrictions, is described. An algorithm developed to search a hypersurface with 18 dimensions, which define an aircraft configuration, is discussed. The results, when considered from the aerodynamic point of view, indicate the optimal configuration is one that combines a lifting fuselage with a canard.

  18. Analysis of some aerodynamic characteristics due to wing-jet interaction

    NASA Technical Reports Server (NTRS)

    Fillman, G. L.; Lan, C. E.

    1979-01-01

    The results of two separate theoretical investigations are presented. A program was used which is capable of predicting the aerodynamic characteristics of both upper-surface blowing (USB) and over-wing blowing (OWB) configurations. A theoretical analysis of the effects of over-wing blowing jets on the induced drag of a 50 deg sweep back wing was developed. Experiments showed net drag reductions associated with the well known lift enhancement due to over-wing blowing. The mechanisms through which this drag reduction is brought about are presented. Both jet entrainment and the so called wing-jet interaction play important roles in this process. The effects of a rectangular upper-surface blowing jet were examined for a wide variety of planforms. The isolated effects of wing taper, sweep, and aspect ratio variations on the incremental lift due to blowing are presented. The effects of wing taper ratio and sweep angle were found to be especially important parameters when considering the relative levels of incremental lift produced by an upper-surface blowing configuration.

  19. AEROX: Computer program for transonic aircraft aerodynamics to high angles of attack. Volume 1: Aerodynamic methods and program users' guide

    NASA Technical Reports Server (NTRS)

    Axelson, J. A.

    1977-01-01

    The AEROX program estimates lift, induced-drag and pitching moments to high angles (typ. 60 deg) for wings and for wingbody combinations with or without an aft horizontal tail. Minimum drag coefficients are not estimated, but may be input for inclusion in the total aerodynamic parameters which are output in listed and plotted formats. The theory, users' guide, test cases, and program listing are presented.

  20. Aerodynamic Characteristics of a Flying-Boat Hull Having a Length-Beam Ratio of 15, TED No. NACA 2206

    NASA Technical Reports Server (NTRS)

    Riebe, John M.; Naeseth, Rodger L.

    1951-01-01

    An investigation was made in the Langley 300 MPH 7- by 10-foot tunnel to determine the aerodynamic characteristics of a flying-boat hull of a length-beam ratio of 15 in the presence of a wing. The investigation was an extension of previous tests made on hulls of length-beam ratios of 6, 9, and 12; these hulls were designed to have approximately the same hydrodynamic performance with respect to spray and resistance characteristics. Comparison with the previous investigation at lower length-beam ratios indicated a reduction in minimum drag coefficients of 0.0006 (10 peroent)with fixed transition when the length-beam ratio was extended from 12 to 15. As with the hulls of lower length-beam ratio, the drag reduction with a length-beam ratio of 15 occurred throughout the range of angle of attack tested and the angle of attack for minimum drag was in the range from 2deg to 3deg. Increasing the length-beam ratio from 12 to 15 reduced the hull longitudinal instability by an mount corresponding to an aerodynamic-center shift of about 1/2 percent of the mean aerodynamic chord of the hypothetical flying boat. At an angle of attack of 2deg, the value of the variation of yawing-moment coefficient with angle of yaw for a length-beam ratio of 15 was 0.00144, which was 0.00007 larger than the value for a length-beam ratio of 12.

  1. Aerodynamic design lowers truck fuel consumption

    NASA Technical Reports Server (NTRS)

    Steers, L.

    1978-01-01

    Energy-saving concepts in truck design are emerging from developing new shapes with improved aerodynamic flow properties that can reduce air-drag coefficient of conventional tractor-trailers without requiring severe design changes or compromising load-carrying capability. Improvements are expected to decrease somewhat with increased wind velocities and would be affected by factors such as terrain, driving techniques, and mechanical condition.

  2. Missile Aerodynamics

    DTIC Science & Technology

    1979-02-01

    desired properties. To this end, we shall make use of ex- perimental evidence, as obtained in wind or water tunnels by various flow visualization...based on the results of number of tests carried out in a water and various wind tunnels, as reported by H. Werl6 in Ref. 3. Vortex breakdown is found...of a triangular wing Rogachev, G.V. moving close to the earth ’ s surface. AD 785154, FTD-HC-23-1802-74. 25 Fox, C.H. Prediction of lift and drag for

  3. Analysis and design of planar and non-planar wings for induced drag minimization

    NASA Technical Reports Server (NTRS)

    Straussfogel, Dennis M.; Maughmer, Mark D.

    1991-01-01

    Improvements in the aerodynamic efficiency of commercial transport aircraft will reduce fuel usage with subsequent reduced cost, both monetary and environmental. To this end, the current research is aimed at reducing the overall drag of these aircraft with specific emphasis on reducing the drag generated by the lifting surfaces. The ultimate goal of this program is to create a wing design methodology which optimizes the geometry of the wing for lowest total drag within the constraints of a particular design specification. The components of drag which must be considered include profile drag, and wave drag. Profile drag is dependent upon, among other things, the airfoil section and the total wetted area. Induced drag, which is manifested as energy left in the wake by the trailing vortex system is mostly a function of wing span, but also depends on other geometric wing parameters. Wave drag of the wing, important in the transonic flight regime, is largely affected by the airfoil section, wing sweep, and so forth. The optimization problem is that of assessing the various parameters which contribute to the different components of wing drag, and determining the wing geometry which generates the best overall performance for a given aircraft mission. The primary thrust of the research effort to date was in the study of induced drag. Results from the study are presented.

  4. Improved Aerodynamic Analysis for Hybrid Wing Body Conceptual Design Optimization

    NASA Technical Reports Server (NTRS)

    Gern, Frank H.

    2012-01-01

    This paper provides an overview of ongoing efforts to develop, evaluate, and validate different tools for improved aerodynamic modeling and systems analysis of Hybrid Wing Body (HWB) aircraft configurations. Results are being presented for the evaluation of different aerodynamic tools including panel methods, enhanced panel methods with viscous drag prediction, and computational fluid dynamics. Emphasis is placed on proper prediction of aerodynamic loads for structural sizing as well as viscous drag prediction to develop drag polars for HWB conceptual design optimization. Data from transonic wind tunnel tests at the Arnold Engineering Development Center s 16-Foot Transonic Tunnel was used as a reference data set in order to evaluate the accuracy of the aerodynamic tools. Triangularized surface data and Vehicle Sketch Pad (VSP) models of an X-48B 2% scale wind tunnel model were used to generate input and model files for the different analysis tools. In support of ongoing HWB scaling studies within the NASA Environmentally Responsible Aviation (ERA) program, an improved finite element based structural analysis and weight estimation tool for HWB center bodies is currently under development. Aerodynamic results from these analyses are used to provide additional aerodynamic validation data.

  5. Some Advanced Concepts in Discrete Aerodynamic Sensitivity Analysis

    NASA Technical Reports Server (NTRS)

    Taylor, Arthur C., III; Green, Lawrence L.; Newman, Perry A.; Putko, Michele M.

    2001-01-01

    An efficient incremental-iterative approach for differentiating advanced flow codes is successfully demonstrated on a 2D inviscid model problem. The method employs the reverse-mode capability of the automatic- differentiation software tool ADIFOR 3.0, and is proven to yield accurate first-order aerodynamic sensitivity derivatives. A substantial reduction in CPU time and computer memory is demonstrated in comparison with results from a straight-forward, black-box reverse- mode application of ADIFOR 3.0 to the same flow code. An ADIFOR-assisted procedure for accurate second-order aerodynamic sensitivity derivatives is successfully verified on an inviscid transonic lifting airfoil example problem. The method requires that first-order derivatives are calculated first using both the forward (direct) and reverse (adjoint) procedures; then, a very efficient non-iterative calculation of all second-order derivatives can be accomplished. Accurate second derivatives (i.e., the complete Hessian matrices) of lift, wave-drag, and pitching-moment coefficients are calculated with respect to geometric- shape, angle-of-attack, and freestream Mach number

  6. Some Advanced Concepts in Discrete Aerodynamic Sensitivity Analysis

    NASA Technical Reports Server (NTRS)

    Taylor, Arthur C., III; Green, Lawrence L.; Newman, Perry A.; Putko, Michele M.

    2003-01-01

    An efficient incremental iterative approach for differentiating advanced flow codes is successfully demonstrated on a two-dimensional inviscid model problem. The method employs the reverse-mode capability of the automatic differentiation software tool ADIFOR 3.0 and is proven to yield accurate first-order aerodynamic sensitivity derivatives. A substantial reduction in CPU time and computer memory is demonstrated in comparison with results from a straightforward, black-box reverse-mode applicaiton of ADIFOR 3.0 to the same flow code. An ADIFOR-assisted procedure for accurate second-rder aerodynamic sensitivity derivatives is successfully verified on an inviscid transonic lifting airfoil example problem. The method requires that first-order derivatives are calculated first using both the forward (direct) and reverse (adjoinct) procedures; then, a very efficient noniterative calculation of all second-order derivatives can be accomplished. Accurate second derivatives (i.e., the complete Hesian matrices) of lift, wave drag, and pitching-moment coefficients are calculated with respect to geometric shape, angle of attack, and freestream Mach number.

  7. Simultaneous drag and flow measurements of Olympic skeleton athletes

    NASA Astrophysics Data System (ADS)

    Moon, Yae Eun; Digiulio, David; Peters, Steve; Wei, Timothy

    2009-11-01

    The Olympic sport of skeleton involves an athlete riding a small sled face first down a bobsled track at speeds up to 130 km/hr. In these races, the difference between gold and missing the medal stand altogether can be hundredths of a second per run. As such, reducing aerodynamic drag through proper body positioning is of first order importance. To better study the flow behavior and to improve the performance of the athletes, we constructed a static force balance system on a mock section of a bobsled track. Athlete and the sled are placed on the force balance system which is positioned at the exit of an open loop wind tunnel. Simultaneous drag force and DPIV velocity field measurements were made along with video recordings of body position to aid the athletes in determining their optimal aerodynamic body position.

  8. Drag-shield drop tower residual acceleration optimisation

    NASA Astrophysics Data System (ADS)

    Figueroa, A.; Sorribes-Palmer, F.; Fernandez De Pierola, M.; Duran, J.

    2016-07-01

    Among the forces that appear in drop towers for microgravity experiments, aerodynamic drag plays a crucial role in the residual acceleration. Buoyancy can also be critical, especially at the first instances of the drop when the low speed of the experimental platform makes the aerodynamic drag small compared with buoyancy. In this paper the perturbation method is used to formulate an analytical model which has been validated experimentally. The experimental test was conduced by undergraduate students of aerospace engineering at the Institute of Microgravity ‘Ignacio Da Riva’ of the Technical University of Madrid (IDR/UPM) microgravity tower. The test helped students to understand the influence of the buoyancy on the residual acceleration of the experiment platform. The objective of the students was to understand the physical process during the drop, identify the main parameters involved in the residual acceleration and determine the most suitable configuration for the next drop tower proposed to be built at UPM.

  9. Measuring the Effects of Lift and Drag on Projectile Motion

    ERIC Educational Resources Information Center

    Cross, Rod

    2012-01-01

    The trajectory of a projectile through the air is affected both by gravity and by aerodynamic forces. The latter forces can conveniently be ignored in many situations, even when they are comparatively large. For example, if a 145-g, 74-mm diameter baseball is pitched at 40 ms[superscript -1] (89.5 mph), it experiences a drag force of about 1.5 N.…

  10. Fourier functional analysis for unsteady aerodynamic modeling

    NASA Technical Reports Server (NTRS)

    Lan, C. Edward; Chin, Suei

    1991-01-01

    A method based on Fourier analysis is developed to analyze the force and moment data obtained in large amplitude forced oscillation tests at high angles of attack. The aerodynamic models for normal force, lift, drag, and pitching moment coefficients are built up from a set of aerodynamic responses to harmonic motions at different frequencies. Based on the aerodynamic models of harmonic data, the indicial responses are formed. The final expressions for the models involve time integrals of the indicial type advocated by Tobak and Schiff. Results from linear two- and three-dimensional unsteady aerodynamic theories as well as test data for a 70-degree delta wing are used to verify the models. It is shown that the present modeling method is accurate in producing the aerodynamic responses to harmonic motions and the ramp type motions. The model also produces correct trend for a 70-degree delta wing in harmonic motion with different mean angles-of-attack. However, the current model cannot be used to extrapolate data to higher angles-of-attack than that of the harmonic motions which form the aerodynamic model. For linear ramp motions, a special method is used to calculate the corresponding frequency and phase angle at a given time. The calculated results from modeling show a higher lift peak for linear ramp motion than for harmonic ramp motion. The current model also shows reasonably good results for the lift responses at different angles of attack.

  11. Drag of Several Gunner's Enclosures at High Speeds, Special Report

    NASA Technical Reports Server (NTRS)

    Stack, John; Moberg, Richard J.

    1941-01-01

    The drag of several types of gunner's turrets, windshields, blisters, and other protuberances, including projecting guns, was investigated at speeds from 75 to 440 miles per hour in the NACA 8-foot high-speed wind tunnel. The various gunner's enclosures were represented by 1/10 and 1/7 full-size models on a midwing-fuselage combination representative of bomber types. Most of the usual types of retractable turrets are very poor aerodynamically; they caused wind drag increments, dependent upon the size of the turret relative to the fuselage and upon the speed, up to twice the drag of the fuselage alone. A large streamline blister sufficient to enclose completely one type of rotating cylindrical turret caused a drag increment of approximately one-half that of the turret and at the same time provided space adequate for two gunners rather than for one gunner. A large portion of the drag increments for some types of turret appeared to be due to adverse effects on the fuselage flow caused by the turret rather than by the direct drag of the turret.

  12. Prediction of Aerodynamic Coefficients using Neural Networks for Sparse Data

    NASA Technical Reports Server (NTRS)

    Rajkumar, T.; Bardina, Jorge; Clancy, Daniel (Technical Monitor)

    2002-01-01

    Basic aerodynamic coefficients are modeled as functions of angles of attack and sideslip with vehicle lateral symmetry and compressibility effects. Most of the aerodynamic parameters can be well-fitted using polynomial functions. In this paper a fast, reliable way of predicting aerodynamic coefficients is produced using a neural network. The training data for the neural network is derived from wind tunnel test and numerical simulations. The coefficients of lift, drag, pitching moment are expressed as a function of alpha (angle of attack) and Mach number. The results produced from preliminary neural network analysis are very good.

  13. Comparison of aerodynamic coefficients obtained from theoretical calculations wind tunnel tests and flight tests data reduction for the alpha jet aircraft

    NASA Technical Reports Server (NTRS)

    Guiot, R.; Wunnenberg, H.

    1980-01-01

    The methods by which aerodynamic coefficients are determined and discussed. These include: calculations, wind tunnel experiments and experiments in flight for various prototypes of the Alpha Jet. A comparison of obtained results shows good correlation between expectations and in-flight test results.

  14. Rotating cylinder drag balance with application to riblets

    NASA Astrophysics Data System (ADS)

    Hall, T.; Joseph, D.

    2000-12-01

    Experimental results are reported and discussed for a rotating cylinder drag balance designed to predict drag reduction by surfaces like riblets. The apparatus functions by measuring the torque applied to the inner cylinder by a fluid, such as water, that is set in motion by the controlled rotation of the outer cylinder. The instrument was validated by calibration for laminar flow and comparison of turbulent flow results to the those of G. I. Taylor. The ability to predict drag reduction was demonstrated by testing 114 m symmetric sawtooth riblets, which gave a maximum reduction of about 5% and an overall drag reduction range of 5

  15. Effect of Ground Proximity on the Aerodynamic Characteristics of Aspect-Ratio-1 Airfoils With and Without End Plates

    NASA Technical Reports Server (NTRS)

    Carter, Arthur W.

    1961-01-01

    An investigation has been made to determine the effect of ground proximity on the aerodynamic characteristics of aspect-ratio-1 airfoils. The investigation was made with the model moving over the water in a towing tank in order to eliminate the effects of wind-tunnel walls and of boundary layer on ground boards at small ground clearances. The results indicated that, as the ground was approached, the airfoils experienced an increase in lift-curve slope and a reduction in induced drag; thus, lift-drag ratio was increased. As the ground was approached, the profile drag remained essentially constant for each airfoil. Near the ground, the addition of end plates to the airfoil resulted in a large increase in lift-drag ratio. The lift characteristics of the airfoils indicated stability of height at positive angles of attack and instability of height at negative angles; therefore, the operating range of angles of attack would be limited to positive values. At positive angles of attack, the static longitudinal stability was increased as the height above the ground was reduced. Comparison of the experimental data with Wieselsberger's ground-effect theory (NACA Technical Memorandum 77) indicated generally good agreement between experiment and theory for the airfoils without end plates.

  16. Measuring the Effects of Lift and Drag on Projectile Motion

    NASA Astrophysics Data System (ADS)

    Cross, Rod

    2012-02-01

    The trajectory of a projectile through the air is affected both by gravity and by aerodynamic forces. The latter forces can conveniently be ignored in many situations, even when they are comparatively large. For example, if a 145-g, 74-mm diameter baseball is pitched at 40 ms-1 (89.5 mph), it experiences a drag force of about 1.5 N. The gravitational force on the ball 1.42 N. Nevertheless, the trajectory of a baseball pitched without spin is not strongly affected by the drag force. Because the ball is relatively heavy and the flight distance is relatively small (about 60 ft), the drag force reduces the ball speed by only about 10% by the time it reaches the batter. As a result, the time taken for the ball to reach the batter is only about 5% longer than in a vacuum, and the actual trajectory is also very similar.2

  17. Acoustic Liner Drag: Measurements on Novel Facesheet Perforate Geometries

    NASA Technical Reports Server (NTRS)

    Howerton, Brian M.; Jones, Michael G.

    2016-01-01

    Interest in characterization of the aerodynamic drag of acoustic liners has increased in the past several years. This paper details experiments in the NASA Langley Grazing Flow Impedance Tube to quantify the relative drag of several perforate-over-honeycomb liner configurations at flow speeds of centerline flow Mach number equals 0.3 and 0.5. Various perforate geometries and orientations are investigated to determine their resistance factors using a static pressure drop approach. Comparison of these resistance factors gives a relative measurement of liner drag. For these same flow conditions, acoustic measurements are performed with tonal excitation from 400 to 3000 hertz at source sound pressure levels of 140 and 150 decibels. Educed impedance and attenuation spectra are used to determine the impact of variations in perforate geometry on acoustic performance.

  18. Acoustic Liner Drag: A Parametric Study of Conventional Configurations

    NASA Technical Reports Server (NTRS)

    Howerton, Brian M.; Jones, Michael G.

    2015-01-01

    Interest in the characterization of the aerodynamic drag performance of acoustic liners has increased in the past several years. This paper details experiments in NASA Langley's Grazing Flow Impedance Tube to quantify the relative drag of several conventional perforate-over-honeycomb liner configurations. For a fixed porosity, facesheet hole diameter and cavity depth are varied to study the effect of each. These configurations are selected to span the range of conventional liner geometries used in commercial aircraft engines. Detailed static pressure and acoustic measurements are made for grazing flows up to M=0.5 at 140 dB SPL for tones between 400 and 2800 Hz. These measurements are used to calculate a resistance factor (?) for each configuration. Analysis shows a correlation between perforate hole size and the resistance factor but cavity depth seems to have little influence. Acoustic effects on liner drag are observed to be limited to the lower Mach numbers included in this investigation.

  19. Magnon drag thermopile

    NASA Astrophysics Data System (ADS)

    Valenzuela, Sergio O.

    2013-03-01

    Thermoelectric effects in spintronics are gathering increasing attention as a means of controlling spin information by using heat flow. Thermal magnons (spin-wave quanta) are expected to play a major role, however, the coupling between electrons and magnons in ferromagnetic metals remains poorly understood. We demonstrate a conceptually new device that enables us to gather information on magnon-electron scattering and magnon-drag effects. The device resembles a thermopile formed by a large number of pairs of ferromagnetic wires placed between a hot and a cold source and connected thermally in parallel and electrically in series. By controlling the relative orientation of the magnetization in pairs of wires, the magnon drag can be studied independently of the electron and phonon drag thermoelectric effects. Measurements as a function of temperature reveal the effect on magnon drag following a variation of magnon and phonon populations. These results demonstrate the feasibility of directly converting magnon dynamics of nanomagnets into an electrical signal and could pave the way to novel thermoelectric devices for energy harvesting. This research was supported by the Spanish Ministerio de Ciencia e Innovación, MICINN (MAT2010-18065) and by the European Community's Seventh Framework Programme (FP7/2007-2013) under grant agreement NANOFUNCTION no 257375.

  20. Frame dragging and superenergy

    SciTech Connect

    Herrera, L.; Di Prisco, A.; Carot, J.

    2007-08-15

    We show that the vorticity appearing in stationary vacuum spacetimes is always related to the existence of a flow of superenergy on the plane orthogonal to the vorticity vector. This result, together with the previously established link between vorticity and superenergy in radiative (Bondi-Sachs) spacetimes, strengthens further the case for this latter quantity as the cause of frame dragging.

  1. Aerodynamic drag characterization and deposition studies of irregular particles

    SciTech Connect

    Celik, I.; Katragadda, S.; Nagarajan, R.

    1990-01-01

    An experimental and numerical analysis was performed of the temperature and flow field involved in co-axial, confined, non-reacting heated jets in a drop tube reactor. An electrically heated 2-inch (50.8 mm) diameter drop tube reactor was utilized to study the jet characteristics. Profiles of gas temperature, typically in the range of 800--1600 K were measured in the mixing zone of the jet with a K-Type thermocouple. Measured temperatures were corrected for conduction, convection, and radiation heat losses. Because of limited access to the mixing zone, characterization of the flow field at high temperatures with laser doppler or hot wire anemometry were impractical. A computer program which solves the full equations of motion and energy was employed to simulate the temperature and flow fields. The location of the recirculation region, the flow regimes and the mixing phenomena were studied. The wall heating, laminar and turbulent flow regimes were considered in the simulations. The predictions are in fairly good agreement with the corrected temperature measurements provided that the flow is turbulent. The results of this study demonstrate how a numerical method and measurement can be used together to analyze the flow conditions inside a reactor which has limited access because of very high temperatures. 37 refs., 37 figs., 8 tabs.

  2. The effect of aerodynamic parameters on power output of windmills

    NASA Technical Reports Server (NTRS)

    Wiesner, W.

    1973-01-01

    Aerodynamic results for a study on windpower generation are reported. Windmill power output is presented in terms that are commonly used in rotary wing analysis, namely, power output as a function of drag developed by the windmill. Effect of tip speed ratio, solidity, twist, wind angle, blade setting and airfoil characteristics are given.

  3. Grid Quality and Resolution Issues from the Drag Prediction Workshop Series

    NASA Technical Reports Server (NTRS)

    Mavriplis, Dimitri J.; Vassberg, John C.; Tinoco, Edward N.; Mani, Mori; Brodersen, Olaf P.; Eisfeld, Bernhard; Wahls, Richard A.; Morrison, Joseph H.; Zickuhr, Tom; Levy, David; Murayama, Mitsuhiro

    2008-01-01

    The drag prediction workshop series (DPW), held over the last six years, and sponsored by the AIAA Applied Aerodynamics Committee, has been extremely useful in providing an assessment of the state-of-the-art in computationally based aerodynamic drag prediction. An emerging consensus from the three workshop series has been the identification of spatial discretization errors as a dominant error source in absolute as well as incremental drag prediction. This paper provides an overview of the collective experience from the workshop series regarding the effect of grid-related issues on overall drag prediction accuracy. Examples based on workshop results are used to illustrate the effect of grid resolution and grid quality on drag prediction, and grid convergence behavior is examined in detail. For fully attached flows, various accurate and successful workshop results are demonstrated, while anomalous behavior is identified for a number of cases involving substantial regions of separated flow. Based on collective workshop experiences, recommendations for improvements in mesh generation technology which have the potential to impact the state-of-the-art of aerodynamic drag prediction are given.

  4. Leidenfrost Vapor Layers Reduce Drag without the Crisis in High Viscosity Liquids

    NASA Astrophysics Data System (ADS)

    Vakarelski, Ivan U.; Berry, Joseph D.; Chan, Derek Y. C.; Thoroddsen, Sigurdur T.

    2016-09-01

    The drag coefficient CD of a solid smooth sphere moving in a fluid is known to be only a function of the Reynolds number Re and diminishes rapidly at the drag crisis around Re ˜3 ×1 05 . A Leidenfrost vapor layer on a hot sphere surface can trigger the onset of the drag crisis at a lower Re. By using a range of high viscosity perfluorocarbon liquids, we show that the drag reduction effect can occur over a wide range of Re, from as low as ˜600 to 1 05. The Navier slip model with a viscosity dependent slip length can fit the observed drag reduction and wake shape.

  5. Aerodynamic Decelerators for Planetary Exploration: Past, Present, and Future

    NASA Technical Reports Server (NTRS)

    Cruz, Juna R.; Lingard, J. Stephen

    2006-01-01

    In this paper, aerodynamic decelerators are defined as textile devices intended to be deployed at Mach numbers below five. Such aerodynamic decelerators include parachutes and inflatable aerodynamic decelerators (often known as ballutes). Aerodynamic decelerators play a key role in the Entry, Descent, and Landing (EDL) of planetary exploration vehicles. Among the functions performed by aerodynamic decelerators for such vehicles are deceleration (often from supersonic to subsonic speeds), minimization of descent rate, providing specific descent rates (so that scientific measurements can be obtained), providing stability (drogue function - either to prevent aeroshell tumbling or to meet instrumentation requirements), effecting further aerodynamic decelerator system deployment (pilot function), providing differences in ballistic coefficients of components to enable separation events, and providing height and timeline to allow for completion of the EDL sequence. Challenging aspects in the development of aerodynamic decelerators for planetary exploration missions include: deployment in the unusual combination of high Mach numbers and low dynamic pressures, deployment in the wake behind a blunt-body entry vehicle, stringent mass and volume constraints, and the requirement for high drag and stability. Furthermore, these aerodynamic decelerators must be qualified for flight without access to the exotic operating environment where they are expected to operate. This paper is an introduction to the development and application of aerodynamic decelerators for robotic planetary exploration missions (including Earth sample return missions) from the earliest work in the 1960s to new ideas and technologies with possible application to future missions. An extensive list of references is provided for additional study.

  6. The influence of flight style on the aerodynamic properties of avian wings as fixed lifting surfaces

    PubMed Central

    Dimitriadis, Grigorios; Nudds, Robert L.

    2016-01-01

    The diversity of wing morphologies in birds reflects their variety of flight styles and the associated aerodynamic and inertial requirements. Although the aerodynamics underlying wing morphology can be informed by aeronautical research, important differences exist between planes and birds. In particular, birds operate at lower, transitional Reynolds numbers than do most aircraft. To date, few quantitative studies have investigated the aerodynamic performance of avian wings as fixed lifting surfaces and none have focused upon the differences between wings from different flight style groups. Dried wings from 10 bird species representing three distinct flight style groups were mounted on a force/torque sensor within a wind tunnel in order to test the hypothesis that wing morphologies associated with different flight styles exhibit different aerodynamic properties. Morphological differences manifested primarily as differences in drag rather than lift. Maximum lift coefficients did not differ between groups, whereas minimum drag coefficients were lowest in undulating flyers (Corvids). The lift to drag ratios were lower than in conventional aerofoils and data from free-flying soaring species; particularly in high frequency, flapping flyers (Anseriformes), which do not rely heavily on glide performance. The results illustrate important aerodynamic differences between the wings of different flight style groups that cannot be explained solely by simple wing-shape measures. Taken at face value, the results also suggest that wing-shape is linked principally to changes in aerodynamic drag, but, of course, it is aerodynamics during flapping and not gliding that is likely to be the primary driver. PMID:27781155

  7. The influence of flight style on the aerodynamic properties of avian wings as fixed lifting surfaces.

    PubMed

    Lees, John J; Dimitriadis, Grigorios; Nudds, Robert L

    2016-01-01

    The diversity of wing morphologies in birds reflects their variety of flight styles and the associated aerodynamic and inertial requirements. Although the aerodynamics underlying wing morphology can be informed by aeronautical research, important differences exist between planes and birds. In particular, birds operate at lower, transitional Reynolds numbers than do most aircraft. To date, few quantitative studies have investigated the aerodynamic performance of avian wings as fixed lifting surfaces and none have focused upon the differences between wings from different flight style groups. Dried wings from 10 bird species representing three distinct flight style groups were mounted on a force/torque sensor within a wind tunnel in order to test the hypothesis that wing morphologies associated with different flight styles exhibit different aerodynamic properties. Morphological differences manifested primarily as differences in drag rather than lift. Maximum lift coefficients did not differ between groups, whereas minimum drag coefficients were lowest in undulating flyers (Corvids). The lift to drag ratios were lower than in conventional aerofoils and data from free-flying soaring species; particularly in high frequency, flapping flyers (Anseriformes), which do not rely heavily on glide performance. The results illustrate important aerodynamic differences between the wings of different flight style groups that cannot be explained solely by simple wing-shape measures. Taken at face value, the results also suggest that wing-shape is linked principally to changes in aerodynamic drag, but, of course, it is aerodynamics during flapping and not gliding that is likely to be the primary driver.

  8. HSCT high lift system aerodynamic requirements

    NASA Technical Reports Server (NTRS)

    Paulson, John A.

    1992-01-01

    The viewgraphs and discussion of high lift system aerodynamic requirements are provided. Low speed aerodynamics has been identified as critical to the successful development of a High Speed Civil Transport (HSCT). The airplane must takeoff and land at a sufficient number of existing or projected airports to be economically viable. At the same time, community noise must be acceptable. Improvements in cruise drag, engine fuel consumption, and structural weight tend to decrease the wing size and thrust required of engines. Decreasing wing size increases the requirements for effective and efficient low speed characteristics. Current design concepts have already been compromised away from better cruise wings for low speed performance. Flap systems have been added to achieve better lift-to-drag ratios for climb and approach and for lower pitch attitudes for liftoff and touchdown. Research to achieve improvements in low speed aerodynamics needs to be focused on areas most likely to have the largest effect on the wing and engine sizing process. It would be desirable to provide enough lift to avoid sizing the airplane for field performance and to still meet the noise requirements. The airworthiness standards developed in 1971 will be the basis for performance requirements for an airplane that will not be critical to the airplane wing and engine size. The lift and drag levels that were required to meet the performance requirements of tentative airworthiness standards established in 1971 and that were important to community noise are identified. Research to improve the low speed aerodynamic characteristics of the HSCT needs to be focused in the areas of performance deficiency and where noise can be reduced. Otherwise, the wing planform, engine cycle, or other parameters for a superior cruising airplane would have to be changed.

  9. The aerodynamic analysis of the gyroplane rotating-wing system

    NASA Technical Reports Server (NTRS)

    Wheatley, John B

    1934-01-01

    An aerodynamic analysis of the gyroplane rotating-wing system is presented herein. This system consists of a freely rotating rotor in which opposite blades are rigidly connected and allowed to rotate or feather freely about their span axis. Equations have been derived for the lift, the lift-drag ratio, the angle of attack, the feathering angles, and the rolling and pitching moments of a gyroplane rotor in terms of its basic parameters. Curves of lift-drag ratio against lift coefficient have been calculated for a typical case, showing the effect of varying the pitch angle, the solidarity, and the average blade-section drag coefficient. The analysis expresses satisfactorily the qualitative relations between the rotor characteristics and the rotor parameters. As disclosed by this investigation, the aerodynamic principles of the gyroplane are sound, and further research on this wing system is justified.

  10. Aerodynamic characteristics of NACA 4412 airfoil sction with flap

    NASA Astrophysics Data System (ADS)

    Ockfen, Alex E.; Matveev, Konstantin I.

    2009-09-01

    Wing-in-Ground vehicles and aerodynamically assisted boats take advantage of increased lift and reduced drag of wing sections in the ground proximity. At relatively low speeds or heavy payloads of these craft, a flap at the wing trailing-ground-effect flow id numerically investigated in this study. The computational method consists of a steady-state, incompressible, finite volume method utilizing the Spalart-Allmaras turbulence model. Grid generation and solution of the Navier-Stokes equations are completed flow with a flap, as well as ground-effect motion without a flap. Aerodynamic forces are plain flap. Changes in the flow introduced with the flap addition are also discussed. Overall, the use of a flap on wings with small attack angles is found to be beneficial for small flap deflections up to 5% of the chord, where the contribution of lift augmentation exceeds the drag increase, yielding an augmented lift-to-drag ratio

  11. Satellite aerodynamics as a function of atmospheric properties.

    NASA Technical Reports Server (NTRS)

    Karr, G. R.

    1972-01-01

    Demonstration that satellite aerodynamic properties are a function of numerous factors associated with atmospheric properties. Among these factors, the gas composition has influence on the gas surface interaction which in turn has considerable influence on the satellite drag and lift properties. The drag and lift properties, which are also influenced by the orientation of the satellite with respect to the flow, are influenced by upper atmospheric winds which cause changes in the angle of attack of the satellite. Another strong influence on the aerodynamic properties is due to the speed ratio effect which is found to cause a systematic increase in drag coefficient with respect to altitude. The study of these factors is facilitated by the introduction of a generalized gas surface interaction model which is capable of representing a wide range of possible interactions.

  12. Prediction of nacelle aerodynamic interference effects at low supersonic Mach numbers

    NASA Technical Reports Server (NTRS)

    Kulfan, R. M.

    1980-01-01

    The accuracy of analytical predictions of nacelle aerodynamic interference effects at low supersonic speeds are studied by means of test versus theory comparisons. Comparisons shown include: (1) isolated wing body lift, drag, and pitching moments; (2) isolated nacelle drag and pressure distributions; (3) nacelle interference shock wave patterns and pressure distributions on the wing lower surface; (4) nacelle interference effects on wing body lift, drag, and pitching moments; and (5) total installed nacelle interference effects on lift, drag, and pitching moment. The comparisons also illustrate effects of nacelle location, nacelle spillage, angle of attack, and Mach numbers on the aerodynamic interference. The initial results seem to indicate that the methods can satisfactorily predict lift, drag, pitching moment, and pressure distributions of installed engine nacelles at low supersonic Mach numbers with mass flow ratios from 0.7 to 1.0 for configurations typical of efficient supersonic cruise airplanes.

  13. Flow pattern similarities in the near wake of three bird species suggest a common role for unsteady aerodynamic effects in lift generation.

    PubMed

    Gurka, Roi; Krishnan, Krishnamoorthy; Ben-Gida, Hadar; Kirchhefer, Adam J; Kopp, Gregory A; Guglielmo, Christopher G

    2017-02-06

    Analysis of the aerodynamics of flapping wings has yielded a general understanding of how birds generate lift and thrust during flight. However, the role of unsteady aerodynamics in avian flight due to the flapping motion still holds open questions in respect to performance and efficiency. We studied the flight of three distinctive bird species: western sandpiper (Calidris mauri), European starling (Sturnus vulgaris) and American robin (Turdus migratorius) using long-duration, time-resolved particle image velocimetry, to better characterize and advance our understanding of how birds use unsteady flow features to enhance their aerodynamic performances during flapping flight. We show that during transitions between downstroke and upstroke phases of the wing cycle, the near wake-flow structures vary and generate unique sets of vortices. These structures appear as quadruple layers of concentrated vorticity aligned at an angle with respect to the horizon (named 'double branch'). They occur where the circulation gradient changes sign, which implies that the forces exerted by the flapping wings of birds are modified during the transition phases. The flow patterns are similar in (non-dimensional) size and magnitude for the different birds suggesting that there are common mechanisms operating during flapping flight across species. These flow patterns occur at the same phase where drag reduction of about 5% per cycle and lift enhancement were observed in our prior studies. We propose that these flow structures should be considered in wake flow models that seek to account for the contribution of unsteady flow to lift and drag.

  14. Piloted Simulation Study of the Effects of High-Lift Aerodynamics on the Takeoff Noise of a Representative High-Speed Civil Transport

    NASA Technical Reports Server (NTRS)

    Glaab, Louis J.; Riley, Donald R.; Brandon, Jay M.; Person, Lee H., Jr.; Glaab, Patricia C.

    1999-01-01

    As part of an effort between NASA and private industry to reduce airport-community noise for high-speed civil transport (HSCT) concepts, a piloted simulation study was initiated for the purpose of predicting the noise reduction benefits that could result from improved low-speed high-lift aerodynamic performance for a typical HSCT configuration during takeoff and initial climb. Flight profile and engine information from the piloted simulation were coupled with the NASA Langley Aircraft Noise Prediction Program (ANOPP) to estimate jet engine noise and to propagate the resulting source noise to ground observer stations. A baseline aircraft configuration, which also incorporated different levels of projected improvements in low-speed high-lift aerodynamic performance, was simulated to investigate effects of increased lift and lift-to-drag ratio on takeoff noise levels. Simulated takeoff flights were performed with the pilots following a specified procedure in which either a single thrust cutback was performed at selected altitudes ranging from 400 to 2000 ft, or a multiple-cutback procedure was performed where thrust was reduced by a two-step process. Results show that improved low-speed high-lift aerodynamic performance provides at least a 4 to 6 dB reduction in effective perceived noise level at the FAA downrange flyover measurement station for either cutback procedure. However, improved low-speed high-lift aerodynamic performance reduced maximum sideline noise levels only when using the multiple-cutback procedures.

  15. A comparison of trim drag for conventional and supercritical wings

    NASA Technical Reports Server (NTRS)

    Jacobs, P. F.

    1983-01-01

    The magnitude of the trim drag incurred by advanced supercritical wings and conventional wide-body wings at cruise conditions are investigated. Experiments were performed in a transonic pressure tunnel at a Mach number of 0.82 with a conventional wide-body wing and supercritical wing with high aspect ratio (9.80) using one of three low-tail configurations or two T-tail configurations in order to determine the effects of horizontal tail size, location, camber and static margin. Drag measurements indicate trim drag for the supercritical wing not to be significantly higher than for the conventional wing, although the minimum drag values for the supercritical wing occurred at lower static margins than for conventional wings. Both wings exhibited a reduction in trim drag with reduced cambered tail size, and greater minimum drag increments for cambered tails than for symmetrical tails. Lower trim-drag increments were also observed for the T-tail configuration than the low tails. The increase in lift-drag ratio for the supercritical wing over the conventional wing amounted to 11% for the best tail configurations.

  16. Sphere Drag and Heat Transfer

    PubMed Central

    Duan, Zhipeng; He, Boshu; Duan, Yuanyuan

    2015-01-01

    Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body. PMID:26189698

  17. Sphere Drag and Heat Transfer.

    PubMed

    Duan, Zhipeng; He, Boshu; Duan, Yuanyuan

    2015-07-20

    Modelling fluid flows past a body is a general problem in science and engineering. Historical sphere drag and heat transfer data are critically examined. The appropriate drag coefficient is proposed to replace the inertia type definition proposed by Newton. It is found that the appropriate drag coefficient is a desirable dimensionless parameter to describe fluid flow physical behavior so that fluid flow problems can be solved in the simple and intuitive manner. The appropriate drag coefficient is presented graphically, and appears more general and reasonable to reflect the fluid flow physical behavior than the traditional century old drag coefficient diagram. Here we present drag and heat transfer experimental results which indicate that there exists a relationship in nature between the sphere drag and heat transfer. The role played by the heat flux has similar nature as the drag. The appropriate drag coefficient can be related to the Nusselt number. This finding opens new possibilities in predicting heat transfer characteristics by drag data. As heat transfer for flow over a body is inherently complex, the proposed simple means may provide an insight into the mechanism of heat transfer for flow past a body.

  18. Turbulence, Turbulence Control, and Drag Reduction.

    DTIC Science & Technology

    1987-08-01

    Onsager (1945) and Weizs~cker (1948). has made remarkable strides in advancing our understanding of turbulent flows. It is this description of turbulent...tujrbuilce Inl thle lar to thle Intermiittenit trans’ition to turbulence lus.t ,iedipen itlik. N\\N.tern onI the other. O pen0 * ~ ~ h 1 ~ kdinition10 po...Some Studies of Non-Simple Pipe Flows K R SREENIVASAN 2.AR’ .\\ variety o phenooena occrs ’.5’, ,sTecla’., f we stray,’ away from straight circ- lar i es a

  19. CFD Methods for Drag Prediction and Analysis Currently in Use in UK

    DTIC Science & Technology

    1988-09-01

    some extent -a- HIDA I rertiiltni, the lift on the main aeroroil being 0 EperimentI ovorc. time~ted wil tile lift on the other two ele- incur II n...evaluation report. AUARD-CP-124, Aerodynamic drag 1973. 2 F. H. Bailey , W. P. Ballhaus Jr. A large-scale computer facility for computational

  20. Low-drag events in transitional wall-bounded turbulence

    NASA Astrophysics Data System (ADS)

    Whalley, Richard D.; Park, Jae Sung; Kushwaha, Anubhav; Dennis, David J. C.; Graham, Michael D.; Poole, Robert J.

    2017-03-01

    Intermittency of low-drag pointwise wall shear stress measurements within Newtonian turbulent channel flow at transitional Reynolds numbers (friction Reynolds numbers 70 - 130) is characterized using experiments and simulations. Conditional mean velocity profiles during low-drag events closely approach that of a recently discovered nonlinear traveling wave solution; both profiles are near the so-called maximum drag reduction profile, a general feature of turbulent flow of liquids containing polymer additives (despite the fact that all results presented are for Newtonian fluids only). Similarities between temporal intermittency in small domains and spatiotemporal intermittency in large domains is thereby found.

  1. Wall temperature control of low-speed body drag

    NASA Technical Reports Server (NTRS)

    Lin, J. C.; Ash, R. L.

    1986-01-01

    The use of thermal means to control drag under turbulent boundary layer conditions is examined. Numerical calculations are presented for both skin friction and (unseparated) pressure drag for turbulent boundary-layer flows over a fuselage-like body with wall heat transfer. In addition, thermal control of separation on a bluff body is investigated. It is shown that a total drag reduction of up to 20 percent can be achieved for wall heating with a wall-to-total-freestream temperature ratio of 2. For streamlined slender bodies, partial wall heating of the forebody can produce almost the same order of total drag reduction as the full body heating case. For bluff bodies, the separation delay from partial wall cooling of the afterbody is approximately the same as for the fully cooled body.

  2. Skylon Aerodynamics and SABRE Plumes

    NASA Technical Reports Server (NTRS)

    Mehta, Unmeel; Afosmis, Michael; Bowles, Jeffrey; Pandya, Shishir

    2015-01-01

    An independent partial assessment is provided of the technical viability of the Skylon aerospace plane concept, developed by Reaction Engines Limited (REL). The objectives are to verify REL's engineering estimates of airframe aerodynamics during powered flight and to assess the impact of Synergetic Air-Breathing Rocket Engine (SABRE) plumes on the aft fuselage. Pressure lift and drag coefficients derived from simulations conducted with Euler equations for unpowered flight compare very well with those REL computed with engineering methods. The REL coefficients for powered flight are increasingly less acceptable as the freestream Mach number is increased beyond 8.5, because the engineering estimates did not account for the increasing favorable (in terms of drag and lift coefficients) effect of underexpanded rocket engine plumes on the aft fuselage. At Mach numbers greater than 8.5, the thermal environment around the aft fuselage is a known unknown-a potential design and/or performance risk issue. The adverse effects of shock waves on the aft fuselage and plumeinduced flow separation are other potential risks. The development of an operational reusable launcher from the Skylon concept necessitates the judicious use of a combination of engineering methods, advanced methods based on required physics or analytical fidelity, test data, and independent assessments.

  3. Techniques for estimating Space Station aerodynamic characteristics

    NASA Technical Reports Server (NTRS)

    Thomas, Richard E.

    1993-01-01

    A method was devised and calculations were performed to determine the effects of reflected molecules on the aerodynamic force and moment coefficients for a body in free molecule flow. A procedure was developed for determining the velocity and temperature distributions of molecules reflected from a surface of arbitrary momentum and energy accommodation. A system of equations, based on momentum and energy balances for the surface, incident, and reflected molecules, was solved by a numerical optimization technique. The minimization of a 'cost' function, developed from the set of equations, resulted in the determination of the defining properties of the flow reflected from the arbitrary surface. The properties used to define both the incident and reflected flows were: average temperature of the molecules in the flow, angle of the flow with respect to a vector normal to the surface, and the molecular speed ratio. The properties of the reflected flow were used to calculate the contribution of multiply reflected molecules to the force and moments on a test body in the flow. The test configuration consisted of two flat plates joined along one edge at a right angle to each other. When force and moment coefficients of this 90 deg concave wedge were compared to results that did not include multiple reflections, it was found that multiple reflections could nearly double lift and drag coefficients, with nearly a 50 percent increase in pitching moment for cases with specular or nearly specular accommodation. The cases of diffuse or nearly diffuse accommodation often had minor reductions in axial and normal forces when multiple reflections were included. There were several cases of intermediate accommodation where the addition of multiple reflection effects more than tripled the lift coefficient over the convex technique.

  4. Rotating flexible drag mill

    DOEpatents

    Pepper, W.B.

    1984-05-09

    A rotating parachute for decelerating objects travelling through atmosphere at subsonic or supersonic deployment speeds includes a circular canopy having a plurality of circumferentially arranged flexible panels projecting radially from a solid central disk. A slot extends radially between adjacent panels to the outer periphery of the canopy. Upon deployment, the solid disk diverts air radially to rapidly inflate the panels into a position of maximum diameter. Air impinging on the panels adjacent the panel slots rotates the parachute during its descent. Centrifugal force flattens the canopy into a constant maximum diameter during terminal descent for maximum drag and deceleration.

  5. Classical Aerodynamic Theory

    NASA Technical Reports Server (NTRS)

    Jones, R. T. (Compiler)

    1979-01-01

    A collection of papers on modern theoretical aerodynamics is presented. Included are theories of incompressible potential flow and research on the aerodynamic forces on wing and wing sections of aircraft and on airship hulls.

  6. Aerodynamics at NASA JSC

    NASA Technical Reports Server (NTRS)

    Vicker, Darby

    2006-01-01

    A viewgraph presentation describing aerodynamics at NASA Johnson Space Center is shown. The topics include: 1) Personal Background; 2) Aerodynamic Tools; 3) The Overset Computational Fluid Dynamics (CFD) Process; and 4) Recent Applicatoins.

  7. The NASA Langley laminar-flow-control experiment on a swept, supercritical airfoil - Drag equations

    NASA Technical Reports Server (NTRS)

    Brooks, Cuyler W., Jr.; Harris, Charles D.; Harvey, William D.

    1989-01-01

    The Langley Research Center has designed a swept, supercritical airfoil incorporating Laminar Flow Control for testing at transonic speeds. Analytical expressions have been developed and an evaluation made of the experimental section drag, composed of suction drag and wake drag, using theoretical design information and experimental data. The analysis shows that, although the sweep-induced boundary-layer crossflow influence on the wake drag is too large to be ignored and there is not a practical method for evaluating these crossflow effects on the experimental wake data, the conventional unswept 2-D wake-drag computation used in the reduction of the experimental data is at worst 10 percent too high.

  8. Drag Measurements of a Protruding .50-caliber Machine Gun with Barrel Jacket Removed

    NASA Technical Reports Server (NTRS)

    Luoma, Arvo A.

    1943-01-01

    Tests were made in 8-ft high-speed wind tunnel to determine the drag reduction possible by eliminating the barrel jacket of a protruding 50-caliber aircraft gun. It was found that the drag of a standard aircraft gun protruding into the air stream at right angles to the flow can be reduced by 23% by discarding the barrel jacket. At 300 mph and sea-level conditions, this amounts to a decrease in drag of from 83 to 64 pounds. A rough surface finish on the barrel was found to have no adverse effects on the drag of the barrel, the drag being actually less at high Mach Numbers.

  9. Active Control of Aerodynamic Noise Sources

    NASA Technical Reports Server (NTRS)

    Reynolds, Gregory A.

    2001-01-01

    Aerodynamic noise sources become important when propulsion noise is relatively low, as during aircraft landing. Under these conditions, aerodynamic noise from high-lift systems can be significant. The research program and accomplishments described here are directed toward reduction of this aerodynamic noise. Progress toward this objective include correction of flow quality in the Low Turbulence Water Channel flow facility, development of a test model and traversing mechanism, and improvement of the data acquisition and flow visualization capabilities in the Aero. & Fluid Dynamics Laboratory. These developments are described in this report.

  10. The elaborate plumage in peacocks is not such a drag.

    PubMed

    Askew, Graham N

    2014-09-15

    One of the classic examples of an exaggerated sexually selected trait is the elaborate plumage that forms the train in male peafowl Pavo cristatus (peacock). Such ornaments are thought to reduce locomotor performance as a result of their weight and aerodynamic drag, but this cost is unknown. Here, the effect that the train has on take-off flight in peacocks was quantified as the sum of the rates of change of the potential and kinetic energies of the body (P(CoM)) in birds with trains and following the train's removal. There was no significant difference between P(CoM) in birds with and without a train. The train incurs drag during take-off; however, while this produces a twofold increase in parasite drag, parasite power only accounts for 0.1% of the total aerodynamic power. The train represented 6.9% of body weight and is expected to increase induced power. The absence of a detectable effect on take-off performance does not necessarily mean that there is no cost associated with possessing such ornate plumage; rather, it suggests that given the variation in take-off performance per se, the magnitude of any effect of the train has little meaningful functional relevance.

  11. NASA aerodynamics program

    NASA Technical Reports Server (NTRS)

    Williams, Louis J.; Hessenius, Kristin A.; Corsiglia, Victor R.; Hicks, Gary; Richardson, Pamela F.; Unger, George; Neumann, Benjamin; Moss, Jim

    1992-01-01

    The annual accomplishments is reviewed for the Aerodynamics Division during FY 1991. The program includes both fundamental and applied research directed at the full spectrum of aerospace vehicles, from rotorcraft to planetary entry probes. A comprehensive review is presented of the following aerodynamics elements: computational methods and applications; CFD validation; transition and turbulence physics; numerical aerodynamic simulation; test techniques and instrumentation; configuration aerodynamics; aeroacoustics; aerothermodynamics; hypersonics; subsonics; fighter/attack aircraft and rotorcraft.

  12. An experimental study of the lift, drag and static longitudinal stability for a three lifting surface configuration

    NASA Technical Reports Server (NTRS)

    Ostowari, C.; Naik, D.

    1986-01-01

    The experimental procedure and aerodynamic force and moment measurements for wind tunnel testing of the three lifting surface configuration (TLC) are described. The influence of nonelliptical lift distributions on lift, drag, and static longitudinal stability are examined; graphs of the lift coefficient versus angle of attack, the pitching moment coefficient, drag coefficient, and lift to drag ratio versus lift coefficient are provided. The TLC data are compared with the conventional tail-aft configuration and the canard-wing configuration; it is concluded that the TLC has better lift and high-lift drag characteristics, lift to drag ratio, and zero-lift moments than the other two configurations. The effects of variations in forward and tail wind incidence angles, gap, stagger, and forward wind span on the drag, lift, longitudinal stability, and zero-lift moments of the configuration are studied.

  13. Theoretical solution of profile drag

    NASA Technical Reports Server (NTRS)

    Pretsch, J

    1942-01-01

    After a survey of the customary procedures for appraising the profile drag in which pressure drag was discounted and the methods for computing the laminar and turbulent friction flow, the author proposes a method by which the pressure drag can be computed with the aid of the displacement thickness of the frictional layer. The method is restricted to the case where the effects, caused by separation of frictional layer, are small. Then the total profile drag can be expressed solely by quantities derived from the velocity distribution in the frictional layer immediately at the trailing edge.

  14. Aerodynamics as a subway design parameter

    NASA Technical Reports Server (NTRS)

    Kurtz, D. W.

    1976-01-01

    A parametric sensitivity study has been performed on the system operational energy requirement in order to guide subway design strategy. Aerodynamics can play a dominant or trivial role, depending upon the system characteristics. Optimization of the aerodynamic parameters may not minimize the total operational energy. Isolation of the station box from the tunnel and reduction of the inertial power requirements pay the largest dividends in terms of the operational energy requirement.

  15. Backreaction of frame dragging

    SciTech Connect

    Herdeiro, Carlos A. R.; Rebelo, Carmen; Warnick, Claude M.

    2009-10-15

    The backreaction on black holes due to dragging heavy, rather than test, objects is discussed. As a case study, a five-dimensional regular black Saturn system where the central black hole has vanishing intrinsic angular momentum, J{sup BH}=0, is considered. It is shown that there is a correlation between the sign of two response functions. One is interpreted as a moment of inertia of the black ring in the black Saturn system. The other measures the variation of the black ring horizon angular velocity with the central black hole mass, for fixed ring mass and angular momentum. The two different phases defined by these response functions collapse, for small central black hole mass, to the thin and fat ring phases. In the fat phase, the zero area limit of the black Saturn ring has reduced spin j{sup 2}>1, which is related to the behavior of the ring angular velocity. Using the 'gravitomagnetic clock effect', for which a universality property is exhibited, it is shown that frame dragging measured by an asymptotic observer decreases, in both phases, when the central black hole mass increases, for fixed ring mass and angular momentum. A close parallelism between the results for the fat phase and those obtained recently for the double Kerr solution is drawn, considering also a regular black Saturn system with J{sup BH}{ne}0.

  16. Steady-state and transitional aerodynamic characteristics of a wing in simulated heavy rain

    NASA Technical Reports Server (NTRS)

    Campbell, Bryan A.; Bezos, Gaudy M.

    1989-01-01

    The steady-state and transient effects of simulated heavy rain on the subsonic aerodynamic characteristics of a wing model were determined in the Langley 14- by 22-Foot Subsonic Tunnel. The 1.29 foot chord wing was comprised of a NACA 23015 airfoil and had an aspect ratio of 6.10. Data were obtained while test variables of liquid water content, angle of attack, and trailing edge flap angle were parametrically varied at dynamic pressures of 10, 30, and 50 psf (i.e., Reynolds numbers of .76x10(6), 1.31x10(6), and 1.69x10(6)). The experimental results showed reductions in lift and increases in drag when in the simulated rain environment. Accompanying this was a reduction of the stall angle of attack by approximately 4 deg. The transient aerodynamic performance during transition from dry to wet steady-state conditions varied between a linear and a nonlinear transition.

  17. Aerodynamics of the Mars Microprobe Entry Vehicles

    NASA Technical Reports Server (NTRS)

    Mitcheltree, R. A.; Moss, J. N.; Cheatwood, F. M.; Greene, F. A.; Braun, R. D.

    1997-01-01

    The selection of the unique aeroshell shape for the Mars Microprobes is discussed. A description of its aerodynamics in hypersonic rarefied, hypersonic continuum, supersonic and transonic flow regimes is then presented. This description is based on Direct Simulation Monte Carlo analyses in the rarefied-flow regime, thermochemical nonequilibrium Computational Fluid Dynamics in the hypersonic regime, existing wind tunnel data in the supersonic and transonic regime, additional computational work in the transonic regime, and finally, ballistic range data. The aeroshell is shown to possess the correct combination of aerodynamic stability and drag to convert the probe's initial tumbling attitude and high velocity at atmospheric-interface into the desired surface-impact orientation and velocity.

  18. Aerodynamic characteristics of the HL-20

    NASA Astrophysics Data System (ADS)

    Ware, George M.; Cruz, Christopher I.

    1993-09-01

    Wind tunnel tests were made from subsonic to hypersonic speeds to define the aerodynamic characteristics of the HL-20 lifting-body configuration. The data have been assembled into an aerodynamic database for flight analysis of this proposed vehicle. The wind tunnel data indicates that the model is longitudinally and laterally stable (about a center-of-gravity location of 0.54 body length) over the test range from Mach 20 to 0.3. At hypersonic speeds, the HL-20 model trimmed at a lift/drag (L/D) ratio of 1.4. This value gives the vehicle a crossrange capability similar to that of the space shuttle. At subsonic speeds, the HL-20 has a trimmed L/D ratio of about 3.6. Replacing the flat-plate outboard fins with fins having an airfoil shape increased the maximum subsonic trimmed L/D to 4.2.

  19. The aerodynamic challenges of SRB recovery

    NASA Technical Reports Server (NTRS)

    Bacchus, D. L.; Kross, D. A.; Moog, R. D.

    1985-01-01

    Recovery and reuse of the Space Shuttle solid rocket boosters was baselined to support the primary goal to develop a low cost space transportation system. The recovery system required for the 170,000-lb boosters was for the largest and heaviest object yet to be retrieved from exoatmospheric conditions. State-of-the-art design procedures were ground-ruled and development testing minimized to produce both a reliable and cost effective system. The ability to utilize the inherent drag of the boosters during the initial phase of reentry was a key factor in minimizing the parachute loads, size and weight. A wind tunnel test program was devised to enable the accurate prediction of booster aerodynamic characteristics. Concurrently, wind tunnel, rocket sled and air drop tests were performed to develop and verify the performance of the parachute decelerator subsystem. Aerodynamic problems encountered during the overall recovery system development and the respective solutions are emphasized.

  20. Gliding flight: drag and torque of a hawk and a falcon with straight and turned heads, and a lower value for the parasite drag coefficient.

    PubMed

    Tucker, V A

    2000-12-01

    Raptors - falcons, hawks and eagles in this study - such as peregrine falcons (Falco peregrinus) that attack distant prey from high-speed dives face a paradox. Anatomical and behavioral measurements show that raptors of many species must turn their heads approximately 40 degrees to one side to see the prey straight ahead with maximum visual acuity, yet turning the head would presumably slow their diving speed by increasing aerodynamic drag. This paper investigates the aerodynamic drag part of this paradox by measuring the drag and torque on wingless model bodies of a peregrine falcon and a red-tailed hawk (Buteo jamaicensis) with straight and turned heads in a wind tunnel at a speed of 11.7 m s(-)(1). With a turned head, drag increased more than 50 %, and torque developed that tended to yaw the model towards the direction in which the head pointed. Mathematical models for the drag required to prevent yawing showed that the total drag could plausibly more than double with head-turning. Thus, the presumption about increased drag in the paradox is correct. The relationships between drag, head angle and torque developed here are prerequisites to the explanation of how a raptor could avoid the paradox by holding its head straight and flying along a spiral path that keeps its line of sight for maximum acuity pointed sideways at the prey. Although the spiral path to the prey is longer than the straight path, the raptor's higher speed can theoretically compensate for the difference in distances; and wild peregrines do indeed approach prey by flying along curved paths that resemble spirals. In addition to providing data that explain the paradox, this paper reports the lowest drag coefficients yet measured for raptor bodies (0.11 for the peregrine and 0.12 for the red-tailed hawk) when the body models with straight heads were set to pitch and yaw angles for minimum drag. These values are markedly lower than value of the parasite drag coefficient (C(D,par)) of 0.18 previously