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At least 307 records · Page 17

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NASA NTRS1984

Axisymmetric bluff-body drag reduction through geometrical modifications

The effect of shoulder radiusing and grooving (longitudinally or circumferentially) the afterbodies of bluff bodies of reduce the base drag at low speeds is discussed. Shoulder radii as large as 2.75 body diameters are examined. Reynolds number based on body diameter varied from 20,000 to 200,000. Results indicate that increasing the shoulder radius to 2.75 body diameters can reduce the drag levels to those of a streamline body having 67 percent greater fineness ratio. For the relatively sharp shoulder case, body drag reductions as large as 50% are obtained using circumferential or longitudinal grooves.

Howard, F. G.↗

NASA NTRS1986

Wall temperature control of low-speed body drag

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.

Lin, J. C.↗

NASA NTRS1987

Unsteady transonic flow simulation on a full-span-wing-body configuration

The presence of a body influences both the aerodynamic and aeroelastic performance of wings. Such effects are more pronounced in the transonic regime. To accurately account for the effect of the body, particularly when the wings are experiencing asymmetric modal motions, it is necessary to model the full configuration in the nonlinear transonic regime. In this study, full-span-wing-body configurations are simulated for the first time by a theoretical method that uses the unsteady potential equations based on the small-disturbance theory. The body geometry is modeled exactly as the physical shape, instead of as a rectangular box, which has been done in the past. Steady pressure computations for wing-body configurations compare well with the available experimental data. Unsteady pressure computations when the wings are oscillating in asymmetric modes show significant influence of the body.

Guruswamy, Guru P.↗

NASA NTRS1988

Drag measurements on a laminar flow body of revolution in Langley's 13 inch magnetic suspension and balance system

Low-speed wind tunnel drag force measurements were taken on a laminar flow body of revolution free of support interference. This body was tested at zero incidence in the NASA Langley 13 inch Magnetic Suspension and Balance System (MSBS). The primary objective of these tests was to substantiate the drag force measuring capabilities of the 13 inch MSBS. A secondary objective was to obtain support interference free drag measurements on an axisymmetric body of interest. Both objectives were met. The drag force calibrations and wind-on repeatability data provide a means of assessing the drag force measuring capabilities of the 13 inch MSBS. The measured drag coefficients for this body are of interest to researchers actively involved in designing minimum drag fuselage shapes. Additional investigations included: the effects of fixing transition; the effects of fins installed in the tail; surface flow visualizations using both liquid crystals and oil flow; and base pressure measurements using a one-channel telemetry system. Two drag prediction codes were used to assess their usefulness in estimating overall body drag. These theoretical results did not compare well with the measured values because of the following: incorrect or non-existent modeling of a laminar separation bubble on the body and incorrect of non-existent estimates of base pressure drag.

Dress, David A.↗

NASA NTRS1989

Supersonic aerodynamic characteristics of a proposed Assured Crew Return Capability (ACRC) lifting-body configuration

An investigation was conducted in the Langley Unitary Plan Wind Tunnel at Mach numbers from 1.6 to 4.5. The model had a low-aspect-ratio body with a flat undersurface. A center fin and two outboard fins were mounted on the aft portion of the upper body. The outboard fins were rolled outboard 40 deg from the vertical. Elevon surfaces made up the trailing edges of the outboard fins, and body flaps were located on the upper and lower aft fuselage. The center fin pivoted about its midchord for yaw control. The model was longitudinally stable about the design center-of-gravity position at 54 percent of the body length. The configuration with undeflected longitudinal controls trimmed near 0 deg angle of attack at Mach numbers from 1.6 to 3.0 where lift and lift-drag ratio were negative. Longitudinal trim was near the maximum lift-drag ratio (1.4) at Mach 4.5. The model was directionally stable over Mach number range except at angles of attack around 4 deg at M = 2.5. Pitch control deflection of more than -10 deg with either elevons or body flaps is needed to trim the model to angles of attack at which lift becomes positive. With increased control deflection, the lifting-body configuration should perform the assured crew return mission through the supersonic speed range.

Ware, George M.↗

NASA NTRS1991

Flexible body dynamic stability for high performance aircraft

Dynamic equations which include the effects of unsteady aerodynamic forces and a flexible body structure were developed for a free flying high performance fighter aircraft. The linear and angular deformations are assumed to be small in the body reference frame, allowing the equations to be linearized in the deformation variables. Equations for total body dynamics and flexible body dynamics are formulated using the hybrid coordinate method and integrated in a state space format. A detailed finite element model of a generic high performance fighter aircraft is used to generate the mass and stiffness matrices. Unsteady aerodynamics are represented by a rational function approximation of the doublet lattice matrices. The equations simplify for the case of constant angular rate of the body reference frame, allowing the effect of roll rate to be studied by computing the eigenvalues of the system. It is found that the rigid body modes of the aircraft are greatly affected by introducing a constant roll rate, while the effect on the flexible modes is minimal for this configuration.

Goforth, E. A.↗

NASA NTRS1991

A recursive approach to the equations of motion for the maneuvering and control of flexible multi-body systems

Interest lies in a mathematical formulation capable of accommodating the problem of maneuvering a space structure consisting of a chain of articulated flexible substructures. Simultaneously, any perturbations from the 'rigid body' maneuvering and any elastic vibration must be suppressed. The equations of motion for flexible bodies undergoing rigid body motions and elastic vibrations can be obtained conveniently by means of Lagrange's equations in terms of quasi-coordinates. The advantage of this approach is that it yields equations in terms of body axes, which are the same axes that are used to express the control forces and torques. The equations of motion are nonlinear hybrid differential quations. The partial differential equations can be discretized (in space) by means of the finite element method or the classical Rayleigh-Ritz method. The result is a set of nonlinear ordinary differential equations of high order. The nonlinearity can be traced to the rigid body motions and the high order to the elastic vibration. Elastic motions tend to be small when compared with rigid body motions.

Kwak, Moon K.↗

NASA NTRS1990

Numerical investigation of the origin of vortex asymmetry of flows over bodies at large angle of attack

The occurrence of the flow about a slender body of revolution placed at incidence to an incoming stream is numerically examined for angles of attack ranging from 20 to 80 degrees and a Reynolds number of 200,000 based on maximum body diameter. Over a certain range of Reynolds numbers, the trend of flowfields around slender bodies at incidence can be roughly divided into three main categories: (1) at alpha = 0-30 deg, the flow is steady and symmetric; (2) at alpha = 30-60 deg, the flow under normal conditions is usually asymmetric, but the level of the asymmetry depends on the amount of disturbances present on the tip of the body; and (3) at alpha 60-90 deg, the flow in the wake of the body acts in a fashion similar to that of the Karman vortex shedding behind a two-dimensional circular cylinder. For each of these categories the range of incidence may change by + or - 10 degrees, depending on the quality of flow, or body finish.

Degani, David↗

NASA NTRS1991

Altered sensorimotor control of the body as an etiological factor in space motion sickness

Exposure to nonterrestrial force levels affects the activity of gravitoinertial force sensitive receptors of the body, both of labyrinthine and nonlabyrinthine origin. It also disrupts the normal patterning of motor control of body orientation and movement. The patterns and levels of muscle innervation necessary to achieve particular body configurations and to bring about particular body movements are greatly affected by background force level and body orientation relative to the force vector. The present studies demonstrate that such altered sensorimotor control of head and body posture along with altered vestibulomotor control are evocative of motion sickness. This observation has explanatory significance both for space motion sickness and the re-entry disturbances that occur after prolonged spaceflight.

Lackner, James R.↗

NASA NTRS2012

Body weight of advanced concept hypersonic aircraft

In this paper, preliminary qualitative and quantitative comparisons of the body weight of five hypersonic aircraft configurations are conducted. The five configurations are briefly described as follows: (1) a wing-and-body arrangement with a power-law, circular cross-section body and a delta wing; (2) an all-body vehicle with delta planform and elliptical cross-sections; (3) a wingless wave rider configuration; (4) a winged wave rider configuration; and (5) the spacewing concept, an oblique flying wing at low speed that yaws to 90 deg sweep and flies end-on at hypersonic speeds. The vehicles are defined by their external moldline geometries and by the interior arrangement of their fuel tanks and other components. Intersecting, circular-lobed tankage is used in vehicles with noncircular bodies. The nonusable volume of such concepts is calculated. The structural concept, structural materials, Thermal Protection System, and heat load are allowed to vary with vehicle longitudinal station. Relative strengths and weaknesses of the various hypersonic aircraft concepts in terms of body weight are summarized.

Mark D Ardema↗

NASA NTRS1992

Effect of planform and body on supersonic aerodynamics of multibody configurations

An experimental and theoretical investigation of the effect of the wing planform and bodies on the supersonic aerodynamics of a low-fineness-ratio, multibody configuration has been conducted in the Langley Unitary Plan Wind Tunnel at Mach numbers of 1.60, 1.80, 2.00, and 2.16. Force and moment data, flow-visualization data, and surface-pressure data were obtained on eight low-fineness-ratio, twin-body configurations. These configurations varied in inboard wing planform shape, outboard wing planform shape, outboard wing planform size, and presence of the bodies. The force and moment data showed that increasing the ratio of outboard wing area to total wing area or increasing the leading-edge sweep of the inboard wing influenced the aerodynamic characteristics. The flow-visualization data showed a complex flow-field system of shocks, shock-induced separation, and body vortex systems occurring between the side bodies. This flow field was substantially affected by the inboard wing planform shape but minimally affected by the outboard wing planform shape. The flow-visualization and surface-pressure data showed that flow over the outboard wing developed as expected with changes in angle of attack and Mach number and was affected by the leading-edge sweep of the inboard wing and the presence of the bodies. Evaluation of the linear-theory prediction methods revealed their general inability to consistently predict the characteristics of these multibody configurations.

Mcmillin, S. Naomi↗

NASA NTRS1992

An investigation of the effects of aft blowing on a 3.0 caliber tangent ogive body at high angles of attack

An experimental investigation of the effects of aft blowing on the asymmetric vortex flow of a slender, axisymmetric body at high angles of attack was conducted. A 3.0 caliber tangent ogive body fitted with a cylindrical afterbody was tested in a wind tunnel under subsonic, laminar flow test conditions. Asymmetric blowing from both a single nozzle and a double nozzle configuration, positioned near the body apex, was investigated. Aft blowing was observed to alter the vortex asymmetry by moving the blowing-side vortex closer to the body surface while moving the non-blowing-side vortex further away from the body. The effect of increasing the blowing coefficient was to move the blowing-side vortex closer to the body surface at a more upstream location. The data also showed that blowing was more effective in altering the initial vortex asymmetry at the higher angles of attack than at the lower. The effects of changing the nozzle exit geometry were investigated and it was observed that blowing from a nozzle with a low, broad exit geometry was more effective in reducing the vortex asymmetry than blowing from a high, narrow exit geometry.

Gittner, Nathan M.↗

NASA NTRS1992

Evaluation of conformal and body-axis attitude information for spatial awareness

The traditional head-up display (HUD) used in most modern fighter aircraft presents attitude information that is both conformal to the outside world and aligned with the body-axis of the aircraft. The introduction of helmet-mounted display (HMD) technology into simulated and actual flight environments has introduced an interesting issue regarding the presentation of attitude information. This information can be presented conformally or relative to the aircraft's body-axis, but not both (except in the special case where the pilot's line of sight is directly matched with the aircraft's body-axis). The question addressed with this study was whether attitude information displayed in an HMD should be presented with respect to the real world (conformally) or to the aircraft's body-axis. To answer this, both conformal and body-axis attitude symbology were compared under simulated air combat situations. The results of this study indicated that the body-axis concept was a more effective HMD display. A detailed description of the flight task and results of this study will be presented.

Jones, Denise R.↗

NASA NTRS1951

Results of Flight Tests to Determine Drag of Parabolic and Cone-cylinder Bodies of Very Large Fineness Ratios at Supersonic Speeds

Results of a free-flight investigation at supersonic speeds to determine zero-lift drag of a series of bodies of revolution are presented. Configurations tested included two parabolic bodies with fineness ratios of 17.78 and 24.5 and two 8 degree cone-cylinder bodies with fineness ratios of 17.2 and 21.2. Results of previous tests of similar parabolic bodies but with lower fineness ratios are included in this paper for comparison. All bodies for which data are presented in this paper had a base-to-maximum-diameter ratio of 0.437. Calculated drag coefficients are shown for all bodies for which data are presented. (author)

Welsh, Clement J↗

NASA NTRS1951

Flight Investigation of the Drag of Round-nosed Bodies of Revolution at Mach Numbers from 0.6 to 1.5 Using Rocket-propelled Test Vehicles

Values of total drag coefficient were measured for four round-nosed bodies of revolution in free flight at Mach numbers from 0.6 to 1.5 and Reynolds numbers from 10 x 10(6) to 50 x 10(6). The bodies were designed by rounding off the sharp, fineness-ratio-3.56 nose of a previously tested configuration. The nose radii tested were 27.4, 38.7, 80.6, and 100 percent of the maximum body radius and corresponded to values of 0.075, 0.150, 0.650, and 1.000, respectively, for the ratio of nose-sphere frontal area to body frontal area. The body having least bluntness did not differ appreciably in drag from the pointed-nose body. The others showed marked increases in supersonic drag with increasing bluntness. (author)

Hart, Roger G↗

NASA NTRS1954

Average Skin-Friction Drag Coefficients from Tank Tests of a Parabolic Body of Revolution (NACA RM-10)

Average skin-friction drag coefficients were obtained from boundary-layer total-pressure measurements on a parabolic body of revolution (NACA rm-10, basic fineness ratio 15) in water at Reynolds numbers from 4.4 x 10(6) to 70 x 10(6). The tests were made in the Langley tank no. 1 with the body sting-mounted at a depth of two maximum body diameters. The arithmetic mean of three drag measurements taken around the body was in good agreement with flat-plate results, but, apparently because of the slight surface wave caused by the body, the distribution of the boundary layer around the body was not uniform over part of the Reynolds number range.

Mottard, Elmo J↗

NASA NTRS1956

A Study of the Zero-Lift Drag-Rise Characteristics of Wing-Body Combinations Near the Speed of Sound

Comparisons have been made of the shock phenomena and drag-rise increments for representative wing and central-body combinations with those for bodies of revolution having the same axial developments of cross-sectional areas normal to the airstream. On the basis of these comparisons, it is concluded that near the speed of sound the zero-lift drag rise of a low-aspect-ratio thin-wing and body combination is primarily dependent on the axial development of the cross-sectional areas normal to the airstream. It follows that the drag rise for any such configuration is approximately the same as that for any other with the same development of cross-sectional areas. Investigations have also been made of representative wing-body combinations with the body so indented that the axial developments of cross-sectional areas for the combinations were the same as that for the original body alone. Such indentations greatly reduced or eliminated the zero-lift drag-rise increments associated with the wings near the speed of sound.

Whitcomb, Richard T↗

NASA NTRS1942

High-speed Tests of a Ducted Body with Various Air-outlet Openings

Test of a ducted body with Internal flow were made in the 8-foot high-speed wind tunnel for the purpose of studying the effects on external drag and an critical speed of the addition of efficient inlet and outlet openings to a basic streamline shape. Drag tests of a 13.6- inch-diameter streamline body of fineness ratio 6.14 were made at Mach numbers ranging from 0.20 to 0.75. The model was centrally mounted on a 9-percent-thick airfoil and was designed to have an efficient airfoil-body juncture and a high critical speed. An air inlet at the nose and various outlets at the tail were added: drag and internal-flow data were obtained over the given speed range. The critical speed of the ducted bodies was found to be as high as that of the streamline body. The external - drag with air flow through the body did not exceed the drag of the basic streamline shape. No appreciable variation in the efficiency of the diffuser section of the internal duct occurred throughout the Mach number range of the tests.

Becker, John V.↗