van dyke_album of fluid motion excerpts

5/11/2018 Van Dyke_Album of Fluid Motion Excerpts

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AnAlbumof FluidMotion

Assem bled by M ilton Van DykeDepartment of Mechanical EngineeringStanford University, Stanford, California

THE PARABOLIC PRESS


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1. Creeping Flow

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L Hele-Shaw flow past a circle. Dye shows thestreamlines in water flowing at 1 mm per second betweenglass plates spaced 1 mm apart. It is at first sight paradox-ical that the best way of producing the unseparated pat-tern of plane potential flow past a bluff object, which

would be spoiled by separation in a real fluid of even thesHghtest viscosity, is to go to the opposite extreme of creep-ing flow in a narrow gap, which is dominated by viscousforces. Photograph by D. H. Peregrine


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2. Rete-Shaw flow past a Rankine half-body . A viscous fluid is introduced throughthe orifice at the left into a uniform streamof the same fluid flowing between glassplates spaced 0.5 mrn apart. Dye showsboth the external and internal streamlinesfor plane potential flow past a semi-infinitebody. The streamlines are slightly blurredbecause the rate of delivery of fluid to thesource was changing as the photograph wasmade. T aylor 1972

3. Hele-Shaw flow past an inclined plate. The Hele-Shaw analogy cannot represent a flow with circulation. Ittherefore shows the streamlines of potential flow past an

inclined plate with zero lift. Dye flows in water betweenglass plates spaced 1 mm apart. Photograph by D. H.Peregrine


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8. Sphere moving through a tube at R""O.10,relativemotion. A free sphere is falling steadily down the axis of atube of twice its diameter filled with glycerine. The camerais moved with the speed of the sphere to show the flow rel-

ative to it. The photograph has been rotated to show fbfrom left to right. Tiny magnesium cuttings are illuminateby a thin sheet of light, which casts a shadow of rl:sphere. Cout an ce a u 1 9 68

9. Sphere moving through a tube at R=O.10, absolutemotion. In contrast to the photograph above, here thecamera remains fixed with respect to the distant fluid. Dur-ing the exposure the sphere has moved from left to right

less than a tenth of a diameter, to show the absolute rtion of the fluid. At this small Reynolds number the flpattern, shown by magnesium cuttings in oil, looks ccpletely symmetric fore-and-aft. Co uta nc ea u 1 96 8

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15. Creeping flow past two circles in tandem. The gapis one diameter, and the Reynolds number is O . O L Stream-lines are shown by aluminum dust in glycerine. The inter-

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18. Creeping flow past two spheres in tandem. \Viththe same spacing and approximately the same Reynoldsnumber as the circles opposite, spheres show no sign ofseparation. This is consistent with the fact that separation

19. Creeping flow past closer spheres. At a spacing of0 .7 diameter, spheres in tandem show separation muchlike that between the circles spaced one diameter in figure15 . The diameter is 1. 6 em, and the Reynolds number 0.013 .T an ed a 1 97 9

20. Creeping flow past tangent spheres. At the sameReynolds number of 0 . 013 the two pairs of vortex ringsabove have now merged into a single pair. Theory pre-dicts, much as for the ~vedge in figure 10, an infinite se-quence of vortex rings nested toward the contact point.Taneda 1979

on an isolated sphere appears only above a Reynoldsnumber of 20, compared with 5 for a circle. Aluminumdust is illuminated in glycerine. T ane da 1 97 9

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2. Laminar F

21. Laminar wake of a slender body of revolution. Asharp-tailed slender body of revolution is supported by finetungsten wires and accurately aligned with the free streamin a water runnel. The Reynolds number is 3600 based onmaximum diameter. Dye released into the boundary layer

shows the core vi the wake, which remains laminar to thelimit of this photograph. Varicose instability and transi-tion to turbulence occur farther downstream. Phowgmphby F ran cis Hama

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22. Axisymmetric flow past a Ran-kine ogive. This is the body of revolu-tion that would be produced by a pointpmentird source in < 1 uniform stream ~t he axisymmetric coun terpart of theplane half-body of figure 2. Its shape is 50gentle that at zero incidence and aReynolds number of 6000 based 00di-ameter the flow remains attached amilaminar. Streamlines are made visible bytiny air bubbles in water, illuminated bya sheet of light in the mid-plane.ONERA p hoto gr af Al ., W e rl e 1 96 2

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23. Symmetric plane flow past an airfoil. An NACA64A015 profile is at zero incidence in a water tunnel. TheReynolds number is 7000 based on the chordlength.Streamlines are shown by colored fluid introduced up-

stream, The flow is evidently laminar and appears to beunseparated, though one might anticipate a small sepa-rated region near the trailing edge. ONERA photograph,W erle 1 97 4

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24. Circular cylinder at [1:=1.54. At this Reynoldsnumber the streamline patten> has dearly lost the fore-and-aft symmetry of figure 6. However, the flow has notyet separated at the rear. That begins at about R",S,

though the value is not known accurately. Streamlines aremade visible by aluminum powder in water. Photograph b yS ad ato sh i Tan ed a

25. Sphere at R=9.B. Here too, withwall effects negligible, the streamline pat-tern is distinctly asymmetric, I D contrastto the creeping flow of figure 8. The fluidis evidently moving very slowly at therem, making it difficult to estimate theonset of separation. The How is presum-ably attached here, because separation isbelieved to begin above R", 20 , Stream-lines are shown by magnesium cuttingsilluminated in water. Photograph byMadeleine Co uta nc em , a nd I vl ith e /e P a )'a rd

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26. Flow behind a sphere at R""8.15. A steel ball bear-ing supported laterally on a fine piano wire is towedthrough water containing suspended aluminum dust, andilluminated by 8 sheet of light in the cqu:-1t()ri8lplane. Theflow is dearly not yet separated. Photograph by SadatoshiTaneda

27. Flow behind a sphere at 1~=17.9.As the speed in-creases it is difficult to discern the onset of separation atthe rearrnost point. Here the flow must still be attached,because these experiments have indicated that separationbehind an isolated sphere begins at about R=2 4, T ar n.'d a1956b

28. Sphere moving through a tube at R= 6.9, absolutemotion. The sphere is one-fourth the diameter of thetube. It has moved to the left through one radius. In con-trast to the creeping motion of figure 9, there is at thismodest Reynolds number the beginning of a wake: the dis-

turbances extend considerably farther behind the spherethan ahead. Magnesium cuttings are illuminated in sili-cone oil. ATChi'w $ de I'AauW mie des Sciences de Patis. Cou-taneeau 1972

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3. Separa

32. Laminar separation on a thin ellipse. A 6:1ellipticcylinder is held at zero angle of attack in a wind tunnel.The Reynolds number is 4000 based on chord. Drops of ri-

tanium tetrachloride on the surface form white smoke,which shows the laminar boundary layer separating at therear. B r a.d sh aw 1970

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38. Laminar separation from a curved wall. Air bub-bles in water show the separation of a laminar boundarylayer whose Reynolds number is 20,000 based on distancefrom the leading edge (not shown). Because it is free ofbubbles, the boundary layer appears as a thin dark line at

the left. It separates tangentially near the start of the can."vex surface, remaining laminar for the distance to whichthe dark line persists, and then becomes unstable andturbulent. O NERA photograph , W erLe 1974

39. Turbulent separation over a rectangular block ona plate. The step height is large compared with thethickness of the oncoming laminar boundary layer. Theflow is effectively plane, so that the recirculating region

ahead of the step is dosed, whereas in the correspondingthree-dimensional flow of figure 92 it is open and drainsaround the sides. ONEHA p lw tog rap h, V7e r le 1 974

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40. Circular cylinder at R",,9.6. Here, in contrast tofigure 24 , the flow has clearly separated to form a pair of re-circulating eddies. The cylinder is moving through a tankof water containing aluminum powder, and is illuminated

by a sheet of light below the free surface. Extrapolation ofsuch experiments to unbounded flow suggests separationat R=4 or 5 , w h ere as most numerical computations giveR" " 5 to 7. P/wtograph by S ad aw sh i 1 cm ed a

41. Circular cylinder at R=13.1. The standing eddiesbecome elongated in the flow direction as the speed in-creases. Their length is found to increase linearly withReynolds number until the flow becomes unstable aboveR=40. Ta.)leda 19563

42. Circular cylinder at R=26. The downstream dis-tance to the cores of the eddies also increases linearly withReynolds number. However, the latera! distance betweenthe cores appears to grow more nearly as the square root.Photograph by S a da to sh i T an da

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43. Circular cylinder at R=24.3. A different view of theflow is obtained by moving a cylinder through oil. Tinymagnesium cuttings are illuminated by a sheet of lightfrom an arc projector. The two dark wedges below the cir-

ell' are an optical effect. The lengths of the particle trajec-tortes have been measured to find the velocitv field towithin two per cent. Coutanceau &E ou ar d 1 97 7

44. Circular cylinder at R",,30.2. Theflow is here still completely steady withthe recirculating wake more than onediameter long. The walls of the tank, 8diameters away, have litt]e effect at thesespeeds. Phorograj)h b ) Mad ele ine C ou tan ceau m ui RogeT B OU lTd

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55. Instantaneous flow past a sphere at R=15 ,OOO. Dyein water shows a laminar boundary layer separating aheadof the equator and remaining laminar for almost one

radius. It then becomes unstable and quickly turns tur-bulent. O NE RA p hotog rap h, Werl(; 1980

56 . Mean flow past a sphere at R=15.000. A timeexposure of air bubbles in water shows an averagedstreamline pattern in the meridian plane fo r the flowthat was photographed instantaneously above.O NE RA ph otog raph b)' H enri W erle

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59. Impulsive start of a circular cylinder. The cameramoves with the cylinder, of which only the lighted rearsurface is seen. The dark angle below results from a differ-ence in refractive index of the Plexiglas cylinder and the oil

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through which it is set in motion. The tracer particles afine magnesium cuttings. Photograph by M(hle1eineCOI.(taceau an d RogeT Bouard


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60. Impulsive start of a staggered array of circularcylinders. The Reynolds number is 3000 based on the

61. Impulsive start of a circular cylinder at R" , ,1700 ,Utld-=1.92. Aluminum dust in water gives a different view ofthe motion on the opposite page. It clearly shows the pair ofsmall secondary vortices upstream of each main one. Honji &T an ed a 1 96 9

diameter. The array has moved about ten diameters.O NERA photograph , W erle f'~Ga l/o n 1 97 3

62. Impulsive start of a circular cylinder atR= 1700, Urld"'4.0S. At this later stage the wakehas lost its original symmetry, and is beginning toshed vortices into the stream. Honji &T ane da 1 96 9

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6. Turbulence.,

151. Turbulent wake far behind a projectile. A bullethas been shot through the atmosphere at supersonicspeed, and is [lOW several hundred wake diameters to theleft. This short-duration shadowgraph shows the remark-able sharpness of the irregular boundary between the

highly turbulent wake produced by the bullet and thealmost quiescent air in irrotatio nal motion outside. Photo g rap h m ade at B alli.ltic Research Laboratories, A berdeen P rot'"ing Ground, in Corrsin &Kistler 1954

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152. Generation of turbulence by a grid. Smoke wiresshow a uniform laminar stream passing through a I/16-inchplate with -%--inchsquare perforations. The Reynolds num-

ber is 1500 based on the l-inch mesh size. Instability of theshear layers leads to turbulent flow downstream. Photo-graph by Thomas Corke and H asm n Nagib

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I153. Homogeneous turbulence behind a grid. Behinda finer grid than above, the merging unstable wakesquickly form a homogeneous field. As it decays down-

stream, it provides a useful approximation to the idealiza-tion of isotropic turbulence. Photograph b' T hom as C orkeand H assan N ag ib

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II~156. Comparison of laminar and turbulent boundarylayers. The laminar boundary layer in the upper photo-graph separates from the crest of a convex surface (cf.figure 38) , whereas the turbulent layer in the second

photograph remains attached; similar behavior is shownbelow for a sharp corner. (Cf. figures 55"58 for a sphere.)Titanium tetrachloride is painted on the forepart of themodel in a wind tunnel, H ead 1982

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van dyke_album of fluid motion excerpts

Documents

creeping flow

axisymmetric flow

streamlines of potential

real fluid

colored fluid

distant fluid

viscous fluid

symmetric plane flow