Showing papers on "Drag coefficient published in 1972"

An Investigation of the Flow around Rectangular Cylinders

Abstract: Measurements are presented of the base pressure coefficient, drag coefficient and Strouhal number of rectangular cylinders. The results confirm a finding in Japan that the drag coefficient rises to nearly 3 when the depth of the section is just over half the width. The flow around the sections is found to be strongly influenced by the presence of the trailing-edge corners.

Progress towards a method for the measurement of the components of the drag of a wing of finite span

Abstract: A theory is developed to relate the total drag of a wing of finite span - or other, more general lifting system - to measurements in a single transverse section of its wake. The theory is an extension of that due to Betz, for the measurement of profile drag, and is expected to provide a basis for the resolution of the total drag into vortex and profile drag components. Some results obtained in a first exploratory survey of the wake of a rectangular wing, of aspect ratio 6, are included, to indicate the nature of the experimental problems presented by the technique. But firm conclusions concerning the definition with which the drag components can be obtained will have to await the results of two further surveys.

Water-drop response to sudden accelerations

Abstract: The deformation of initially spherical drops of radius r0 subjected to an external flow of velocity u is experimentally examined for a large range of Weber and Bond numbers. Observations of the changes in the response are compared with recent analytical predictions. The data show that beyond a critical Weber number the response ceases to be vibratory and becomes monotonic with time. Subsequently, it is found that, although the response is unstable, the deformation imposed by the external aerodynamic pressure distribution remains the dominant factor. Measurements of the drag coefficient yield a mean value ofCD = 2·5 over a large Reynolds-number range. The time at which Taylor instability occurs is shown to be inversely proportional to Bond number to the one-quarter power. There is little evidence of the instability occurring until a normalized time is the real time.

Oscillatory Drag, Lift, and Torque on a Circular Cylinder in a Uniform Flow

Abstract: Numerical solutions of the equations governing time‐dependent, viscous, incompressible fluid flow past a circle are presented for Reynolds numbers 100, 400, and 1000. These solutions show the dramatic rise of the drag coefficient during the development of the Karman vortex street and reveal the oscillatory character of the drag, lift, and torque that are experienced by the circle. Contour plots of the vorticity and stream function are compared with histories of the pressure distribution, drag, lift, torque, and separation angles. These comparisons show how the pressure distribution, drag, lift, and torque on the circle are intimately and logically related to the well‐known flow pattern of the Karman street. A new method is described for implementing the infinity conditions. The use of this technique makes it possible to observe the motion of the upstream stagnation streamline and relate this effect to the lift on the circle. The fact that the drag is larger for the oscillatory wake than the symmetric wake is interpreted as a tendency toward an equilibrium state of maximum energy dissipation. Comparisons are made with experimental results. These comparisons suggest that the present results are a valid description of flow past a circular cylinder for Reynolds numbers in the range from 40 to 400.

The geostrophic drag coefficient and the ‘effective’ roughness length

Abstract: An ‘effective’ roughness length is defined for use over heterogeneous terrain as the roughness length which homogeneous terrain would have to give the correct surface stress over a given area. A method is suggested to compute geostrophic drag coefficient, wind-contour angle and surface heat flux, given this roughness length, latitude, geostrophic wind speed and insolation or ground-air temperature differences.

The optimum shaping of axisymmetric bodies for minimum drag in incompressible flow

Abstract: : The hydrodynamic problem is the design of submerged minimum drag axisymmetric vehicles for a specified enclosed volume and constant speed. Drag is to be minimized. Drag reduction is to be accomplished solely through manipulation of the vehicle shape; other means of drag reduction, such as polymer injection into the boundary layer, are not considered. A drag model, valid for nonseparating flows, consists of computer programs available in the literature, representative of state-of-the-art drag prediction methods.

Sphere Drag Coefficients for a Broad Range of Mach and Reynolds Numbers

Abstract: The purpose of the present investigation was to establish accurate values of sphere drag coefficient in the flight regime 0.1 < Mx < 6.0 and 2 x 10 < Re^ < 10 for TJT^ % 1.0. To this end, an extensive series of measurements was made in a ballistic range. These measurements, together with other published data, permit the derivation of sphere drag confidents with an uncertainty of + 2 % in this flight regime. In addition, sifficient information is presented such that reasonable estimates of sphere drag confident can be made for TJT^ ^ 1.0, 0.05 < M^ < 20.0, and 2 x 10~ < Re*, < W\

Some evaluations of drag and bulk transfer coefficients over water bodies of different sizes

Abstract: Three recent experiments allow evaluation of the bulk transfer coefficients for momentum, water vapour and sensible heat over water bodies of different sizes. As part of a study of evaporation rates from a swamp, measurements of latent and sensible heat fluxes were made over Lake Wyangan in southern N.S.W., Australia. This lake is of several kilometers diameter. In a later experiment, Reynolds stress and sensible heat transfer were measured from a natural-gas platform standing in Bass Strait, south of mainland Australia. The most recent experiment involved the direct measurement of each of these turbulent fluxes from a fixed tower erected in Lake Michigan, U.S.A. Perhaps the most important of the results is the finding that drag coefficients measured over Bass Strait are not significantly different from those over Lake Michigan, despite the obvious differences in depth, fetch, and hence surface wave structure. At both locations, drag coefficients are found to increase slightly with increasing wind speed, while at low wind speeds they are not significantly different from those corresponding to aerodynamic smoothness. Near-neutral bulk transfer coefficients for sensible heat and for water vapour are found to be similar. An average value of about 1.4 × 10−3 is obtained. It is emphasized that stability effects should be considered in any discussion of drag coefficients or bulk transfer coefficients. Large errors can result if near-neutrality is incorrectly assumed.

A Method for Reducing the Base Drag of Wings with Blunt Trailing Edge

Abstract: To study the possibilities of reducing the base drag of profiles with a blunt trailing edge, experiments were performed in two low-speed wind-tunnels at the DFVLR-AVA, Gottingen, some on models between walls and some on rectangular wings with an aspect ratio of 2.5. The results show that the mean base pressure can be increased, and so the base drag reduced, by using a special form of the blunt trailing edge. The variation of local base pressure along the span, and the way in which this variation is influenced by the form of the trailing edge, is also shown. Some results for the total drag and lift are also indicated.

On the Aerodynamics of Wake Vortices

Abstract: : The effect of wing span loading on the development of fully rolled up wing trailing vortices is discussed. It is shown that parabolic wing loadings produce potential flow maximum core rotary speeds which are finite and less than fifty percent of the downwash speeds at the plane of symmetry. The development of turbulent cores is analyzed and core growth is predicted to occur as the two thirds power of time whereas the peak velocities fall off as the inverse one third power. Axial flow effects of the wing profile drag and lifting system are shown to lead to axial jets on the vortex axis which may either follow the aircraft or exceed the free stream velocity depending on the ratio of profile drag to induced drag.

Aerodynamic Characteristics of Disk-Gap-Band Parachutes in the Wake of Viking Entry Forebodies at Mach Numbers from 0.2 to 2.6

Abstract: : Tests were conducted in wind tunnels to determine the drag and performance characteristics of various disk-gap-band parachute configurations in the wake of a 0.10-scale Viking entry vehicle. The parachutes were also tested behind a small faired body to obtain minimum interference parachute performance characteristics. Increasing the parachute trailing distance and suspension line length increased the parachute drag coefficient at each Mach number.

Wind Load on Cylinder with Spanwise Protrusion

Abstract: Drag and lift forces for circular cylindrical bodies with two types of spanwise protrusions were measured in a wind tunnel in the transition range of Reynolds numbers (10 4 to 10 5 ), with the protrusion size varying from 0.004 to 0.006 of the cylinder diameter. The data show that the two protuberance shapes, a trip-wire and an overlap, are nearly identical in their effect on the aerodynamic characteristics, and that their effect depends much more on location than on size. It was found that the drag coefficient could vary by ±40% and that the lift coefficient could be as high as 0.7, depending on the location of the protuberance, or equivalently on the angle of attack. By using hot-wire anemometry to study the flow field, these significant variations in C D and C L were revealed to be associated with fundamental changes in the boundary-layer flow, caused by the interaction of the protrusion with the surrounding fluid motion.

Drag Reduction by Ejecting Additive Solutions Into Pure-Water Boundary Layer

Abstract: Drag reduction caused by ejecting additive solutions from a slot into a pure-water boundary layer on a flat plate has been systematically studied. Results include drag measurements for a plane boundary, smooth and rough, with various openings of the slot and with various concentrations and discharges of the ejected additive solution. Conclusions have been drawn on the additive requirement in external flows and on the ejection technique for an optimum drag reduction.

Shock waves and drag in the numerical calculation of isentropic transonic flow

Abstract: Properties of the shock relations for steady, irrotational, transonic flow are discussed and compared for the full and approximate governing potential in common use. Results from numerical experiments are presented to show that the use of proper finite difference schemes provide realistic solutions and do not introduce spurious shock waves. Analysis also shows that realistic drags can be computed from shock waves that occur in isentropic flow. In analogy to the Oswatitsch drag equation, which relates the drag to entropy production in shock waves, a formula is derived for isentropic flow that relates drag to the momentum gain through an isentropic shock. A more accurate formula for drag, based on entropy production, is also derived, and examples of wave drag evaluation based on these formulas are given and comparisons are made with experimental results.

Atmospheric turbulent fluxes over snow

Abstract: On March 26, 1971, eddy fluxes of momentum, sensible heat and water vapour were measured over Lake Mendota, Wisconsin, U.S.A., which was covered by an extensive snowfall. An evaporation rate of about 0.7mm day−1 (2.2 mW cm−2) was detected. Wind speeds were light and the atmosphere near the surface was highly stable. In these conditions, the average sensible heat transfer and Reynolds stress were -0.9 mW cm−2 and 0.10 dyn cm−2, respectively. Comparison with measured gradients of wind speed, temperature and humidity yield a drag coefficient of about 0.54 × 10−3, and bulk transfer coefficients for sensible and latent heat of 0.41 × 10−3 and 0.78 × 10−3, respectively, applied to 10-m data. When corrected for the effect of atmospheric stability, these three coefficients become (in the same order) 1.2 × 10−3, 0.9 × 10−3 and 2.5 × 10−3. The errors in these estimates are such that the drag coefficient is not significantly different from that corresponding to an aerodynamically smooth surface, while the heat coefficients are similar to those normally applied over liquid water surfaces.

Windbreak drag calculated from the horizontal velocity field

Abstract: Several attempts have been made to calculate the drag coefficient of a windbreak from the known flow field around it. Here the complete horizontal-momentum balance equation, rather than parts of it, is used to calculate the drag from Nageli's field data. The vertical velocity, the horizontal shearing stress and the static pressure are all estimated from the horizontal velocity field.

Turbulence Effects on Drag of Sharp-Edged Bodies

Abstract: Contrary to popular opinion, wind tunnel tests showed that the drag coefficient of angular shaped bodies is significantly affected by the intensity of the free stream turbulence. For some bodies an increase in intensity causes an increase in C D while for others a decrease in C D results. Tests made on a vibrating body having a shape similar to an H beam showed that the amplitude of vibration was increased more than 200% with an increase in free stream turbulence. The change in coefficient of drag C D is attributed to two primary effects. The first is increased Reynolds stress in the region of the surface of separation which appears to cause an increase in C D and the other is reattachment of the flow to the body which may cause the C D to increase or decrease depending upon the shape of the body. The range of Reynolds numbers in these tests is limited to the relatively narrow span from approximately 5 x 103 to 7 x 104.

Wind stress and turbulence over a flat ice floe

Abstract: Wind velocity and temperature fluctuations have been recorded over a large, flat, snow covered ice floe in the Gulf of St. Lawrence using sonic anemometer-thermometers. Reynolds stresses and heat fluxes have been computed digitally by the eddy correlation method. The average drag coefficient, C10 = 0.0014, is the same as that of the sea surface and about half that of moderately rough ice. Spectra and cospectra of velocity and temperature fluctuations are expressed in dimensionless forms, and coherence cospectra of the fluctuations at various lateral separations are examined.

Velocity of Transient Cavities in an Acoustic Stationary Wave

Abstract: This paper concerns the high‐speed motion of transient cavities generated in an acoustic stationary wave in a cylinder filled with water. Time‐exposure photographs are presented of the cavities illuminated by a high‐speed stroboscope showing multiple exposures of an individual cavity as it was propelled outward from a region of large acoustic pressure amplitude. The photographs show several interesting details of the cavitation event. Velocities obtained by the cavities were on the order of 1 m/sec, pressure amplitudes on the order of 5 bars, and cavity lifetimes on the order of 10 msec. A theoretical analysis of the cavity motion is obtained by considering the cavity as a spherical inhomogeneity in an acoustic stationary wave. Comparison of theory and experiment show good agreement provided that a velocity‐squared drag law is used with a drag coefficient of 0.77.

Sting-free measurements of sphere drag in laminar flow

Abstract: An aerodynamic investigation was conducted to determine the laminar-flow drag coefficient of spheres of various sizes in a subsonic wind tunnel. The tests were conducted using the M.I.T.-N.A.S.A. prototype magnetic-balance system. By measuring the drag of different sized spheres without model support interference the tunnel wall effect can be deduced. The present results indicate that the classical wind tunnel correction does not completely account for the effects of model size and wall interference. That is, the corrected drag coefficient data for the different sphere sizes differ among themselves in the region of Reynolds number overlap.A comparison of the present sphere drag results with those of numerous other investigations including free-flight and ballistic-range data is given. The drag coefficients presented here are slightly lower than those of other workers for Reynolds numbers ranging from 20 000 to 150 000, but fall between the limits of experimental scatter for Reynolds numbers from 150 000 to 260 000.An analysis of the estimated error in the present data indicates the primary source to be measurement of the wind tunnel parameters rather than errors resulting from the balance system.

Geostrophic Drag, Heat and Mass Transfer Coefficients for the Diabatic Ekman Layer.

Abstract: The “asymptotic matching” principle has been applied to the equilibrium Ekman layer with vertical but flux. This principle requires that the properties of the “surface” or “inner” layer overlap asymptotically (at large z) with those of the “outer” layer, or rather, with the asymptotic behavior of the latter as z→0. In this manner, it is possible to derive relationships for the geostrophic drag, heat transfer, and mass transfer coefficients (i.e., relate surface fluxes to large-scale properties of the motion) without considering the detailed dynamics of the outer Ekman layer, by relying on the fairly accurately known surface, layer distributions of nondimensional velocity, temperature and humidity gradients. Such bulk transfer coefficients are presented as functions of nondimensional parameters involving large-scale measures of the flow only. Extrapolation of the calculated drag coefficients to strong stability suggests that the shear stress vanishes when the negative buoyant acceleration due to a...

Measurements of plasma velocity distributions in free-burning DC arcs up to 2160 A

Abstract: An experimental technique is described from which plasma velocity distributions have been determined. The technique consists of dropping a line of ball bearings of 3, 4 or 5 mm through a horizontal arc and recording the horizontal deflection of the balls by allowing them to strike a carbon paper. Multiple drops through repeated arcs enabled a deflection curve to be compiled. This curve was then subjected to an Abel inversion so that the radial variation of aerodynamic drag on the balls could be determined. By iterative techniques it was then possible to calculate a plasma velocity distribution compatible both with the Reynold's number and the radial deflection profile. A comparison with Wienecke's results obtained using photographic techniques on a 200 A arc showed good agreement, although the maximum deflection recorded was less than 3 mm with balls of 3 mm diameter. It was not possible to increase the deflection resolution by using smaller balls, since the scatter in striking position even in the absence of an arc increased unacceptably for balls of 2 mm diameter. An examination of the validity of the assumptions involved and associated errors is included. In particular the disturbing influence of the ball within the plasma is considered to be small. A more serious difficulty, pointed out by Kimura and Kanzawa concerns the difficulty of assigning the effective temperature and Reynold's number which determines the drag coefficient, since the ball and plasma boundary layer are necessarily at different temperatures. It is argued that the error involved in assigning the undisturbed plasma temperature is small. The overall error in the velocity distributions, which reach to 1500 m s−1 for the 2160 A arc, is considered to be about ±11%.

Drag Coefficient of Cylinders in Turbulent Flow

Abstract: The effects of free-stream turbulence on the drag coefficient of a circular cylinder were investigated experimentally in an air duct. The experiments were performed over a range of Reynolds number, based on mean velocity and cylinder diameter, from 1,350 < Re < 8,000. A constant temperature hot-film anemometer was used to determine the turbulence intensity which was between 1.2% < u′ < 21%. The range of the dimensionless turbulence scale was from 0.5 < ∂/D < 3.3, in which ∂ = the turbulence scale defined through the integral of auto-correlation function and D = the diameter of the cylinder. Two smooth circular cylinders were used. They were 1/4 in. and 1/2 in. 6.35 mm and 12.7 mm shell fraction. Quantitative results were obtained. Equations describing the relationship between the drag coefficient and turbulence characteristics were also obtained.

Drag force on a magnet moving near a thin conductor

Abstract: For a magnet moving with velocity ν over a conducting sheet, a proof of the relationship, drag force=(w/ν) (lift force), based upon Poynting's vector, is given. w is a characteristic velocity determined by the conductance of the sheet. A similar result for a right‐angle corner, drag force = (w/ν) (lift force + guidance force), is proved in the high‐speed limit by considering Maxwell's stress tensor.

Drag coefficient for particles in rarefied, low mach–number flows

Abstract: From international symposium on two-phase systems; Haifa, Israel (29 Aug 1971). See CONF-710836-. A parameter essential to the quantitative analysis of two-phase flows is the drag coefficient of the condensed phase particles. A review of the published drag data reveals that no results are available in the important flow region delimited by Mach numbers less than 2 and Reynolds numbers less than 100. A microballistic range was developed and utilized to measure particle-drag forces in this flow region. The results, reduced in terms of a normalized drag coefficient, are correlated with other drag data available over a wide range of flow conditions. Finally, an algebraic equation which provides a good data fit for all Mach numbers and for Reynolds numbers less than the critical Reynolds number is presented. (auth)

Transition to turbulence in pipe flow for water and dilute solutions of polyethylene oxide

Abstract: An experimental study of the transition from laminar to turbulent flow in a long 0·248in. I.D. pipe is reported for both water and dilute water solutions of polyethylene oxide which exhibit turbulent flow drag reduction (the Toms phenomenon). The drag-reducing solutions, ranging in effectiveness from near zero to the maximum attainable, are observed to undergo transition in a similar way to the Newtonian solvent in that the solutions exhibit intermittency and the growth rates of the turbulent patches are essentially equal to those of the pure solvent. The growth rate of turbulent patches indicates that drag reduction is associated with the small-scale structure of the turbulence near the pipe wall while patch growth is associated with the larger-scale turbulence in the outer flow. For low-disturbance pipe inlet conditions the strong drag-reducing solutions are observed to undergo transition at lower Reynolds numbers than the pure solvent.

Drag reduction in dilute flowing gas‐solid suspensions

Abstract: The effect of solids loading ratio, particle size, and gas Reynolds number on the pressure drop and flow characteristics of a dilute gas-solid suspension in turbulent pipe flow has been studied experimentally in both vertical and horizontal test sections. Glass beads of 10 to 60μ diameter were used at air Reynolds numbers of 10,000 to 25,000 and solids loading ratios of up to 2.5 Drag reduction was observed in the vertical test section for all of the particles studied, with the 30μ particles yielding a maximum drag reduction of about 75% at a loading ratio of 1.5. In the horizontal test section, drag reduction was observed only with the smallest sized particles, indicating a gravity effect. An explanation of these results based on the particles interacting with the turbulent structure of the gas near the wall has been proposed.