Hostname: page-component-7c8c6479df-r7xzm Total loading time: 0 Render date: 2024-03-18T07:45:28.845Z Has data issue: false hasContentIssue false

An experimental study of entrainment and transport in the turbulent near wake of a circular cylinder

Published online by Cambridge University Press:  20 April 2006

Brian Cantwell
Affiliation:
California Institute of Technology, Pasadena, California 91125
Donald Coles
Affiliation:
Stanford University, Stanford, California 94305

Abstract

This paper describes an experimental investigation of transport processes in the near wake of a circular cylinder at a Reynolds number of 140000. The flow in the first eight diameters of the wake was measured using X-array hot-wire probes mounted on a pair of whirling arms. This flying-hot-wire technique increases the relative velocity component along the probe axis and thus decreases the relative flow angle to usable values in regions where fluctuations in flow velocity and direction are large. One valuable fringe benefit of the technique is that rotation of the arms in a uniform flow applies a wide range of relative flow angles to the X-arrays, making them inherently self-calibrating in pitch. An analog circuit was used to generate an intermittency signal, and a fast surface-pressure sensor was used to generate a phase signal synchronized with the vortex-shedding process. The phase signal allowed sorting of the velocity data into 16 populations, each having essentially constant phase. An ensemble average for each population yielded a sequence of pictures of the instantaneous mean flow field, with the vortices frozen as they would be in a photograph. In addition to globally averaged data for velocity and stress, the measurements yield non-steady mean data (in the sense of an average a t constant phase) for velocity, intermittency, vorticity, stress and turbulent-energy production as a function of phase for the first eight diameters of the near wake. The stresses were resolved into a contribution from the periodic motion and a contribution from the random motion at constant phase. The two contributions are found to have comparable amplitudes but quite different geometries, and the time average of their sum (the conventional global Reynolds stress) therefore has a quite-complex structure. The non-steady mean-vorticity field is obtained with good resolution as the curl of the non-steady mean-velocity field. Less than half of the shed circulation appears in the vortices, and there is a slow decay of this circulation for each shed vortex as it moves downstream. In the discussion, considerable emphasis is put on the topology of the non-steady mean flow, which emerges as a pattern of centres and saddles in a frame of reference moving with the eddies. The kinematics of the vortex-formation process are described in terms of the formation and evolution of saddle points between vortices in the first few diameters of the near wake. One important conclusion is that a substantial part of the turbulence production is concentrated near the saddles and that the mechanism of turbulence production is probably vortex stretching at intermediate scales. Entrainment is also found to be closely associated with saddles and to be concentrated near the upstream-facing interface of each vortex.

Type
Research Article
Copyright
© 1983 Cambridge University Press

Access options

Get access to the full version of this content by using one of the access options below. (Log in options will check for institutional or personal access. Content may require purchase if you do not have access.)

References

Cantwell, B. J. 1976 A flying hot wire study of the turbulent near wake of a circular cylinder at a Reynolds number of 140,000. Ph.D. thesis, Calif. Inst. Tech.
Cantwell, B., Coles, D. & Dimotakis, P. 1978 Structure and entrainment in the plane of symmetry of a turbulent spot J. Fluid Mech. 87, 641672.Google Scholar
Coles, D. 1981 Prospects for useful research on coherent structure in turbulent shear flow Proc. Indian Acad. Sci. (Engng Sci.) 4, 111127.Google Scholar
Coles, D., Cantwell, B. & Wadcock, A. 1978 The flying hot wire and related instrumentation. NASA CR 3066.
Coles, D. & Wadcock, A. 1979 Flying-hot-wire study of flow past a NACA 4412 airfoil at maximum lift. AIAA J. 17, 321810 (AIAA Paper 78810).Google Scholar
Corcos, G. M. & Sherman, F. S. 1976 Vorticity concentration and the dynamics of unstable free shear layers J. Fluid Mech. 73, 241264.Google Scholar
Davies, M. E. 1976 A comparison of the wake structure of a stationary and oscillating bluff body, using a conditional averaging technique J. Fluid Mech. 75, 209231.Google Scholar
Drescher, H. 1956 Messung der auf querangeströmte Zylinder ausgeübten zeitlich veränderten Drücke Z. Flugwiss. 4, 1721.Google Scholar
Dyment, A., Gryson, P. & Ducruet, C. 1980 Unpublished paper at Euromech Colloq. no. 135; some photographs are included in M. Van Dyke An Album of Fluid Motion, pp. 130131 (Parabolic, 1982).
Gerrard, J. H. 1966 The mechanics of the formation region of vortices behind bluff bodies J. Fluid Mech. 25, 401413.Google Scholar
Gorecki, J. P. 1960 An investigation of temperature fluctuations on bluff bodies. Ph.D. thesis, Calif. Inst. Tech.
Gowen, F. E. & Perkins, E. W. 1953 Drag of circular cylinders for a wide range of Reynolds numbers and Mach numbers. NACA TN 2960.
Hooker, S. G. 1936 On the action of viscosity in increasing the spacing ratio of a vortex street. Proc. R. Soc. Lond A 154, 6789.Google Scholar
Hussain, A. K. M. F. 1980 Coherent structures and studies of perturbed and unperturbed jets. In The Role of Coherent Structures in Modelling Turbulence and Mixing (ed. J. Jimenez). Lecture Notes in Physics, vol. 136, pp. 252291. Springer.
Hussain, A. K. M. F. 1981 Role of coherent structures in turbulent shear flows Proc. Indian Acaa. Sci. (Engng Sci.) 4, 129175.Google Scholar
Hussain, A. K. M. F. & Zaman, K. B. M. Q. 1981 The ‘preferred mode’ of the axisymmetric jet. J. Fluid Mech. 110, 39810.Google Scholar
Kármán, T. 1912 Über den Mechanismus des Widerstandes, den ein bewegter Körper in einer Flüssigkeit erfährt. Göttingen Nachr., Math.-Phys. Klasse, pp. 547556.
Kline, S. J., Cantwell, B. J. & Lilley, G. M. 1981 1980-81 AFOSR-HTTM-Stanford Conf. on Complex Turbulent Flows, vol. I. Thermosciences Div., Mech. Engng Dept, Stanford Univ.
Kolmogorov, A. 1941 The local structure of turbulence in incompressible fluid for very large Reynolds numbers C.R. (Dokl.) Acad. Sci. URSS 30, 301305.Google Scholar
Matsui, T. 1981 Flow visualization studies of vortices Proc. Indian Acad. Sci. (Engng Sci.) 4, 239257.Google Scholar
Meijer, M. C. 1965 Pressure measurement on flapped hydrofoils in cavity flows and wake flows. Hydrodyn. Lab., Calif. Inst. Tech., Rep. E-133.2 (and private communication).Google Scholar
Naumann, A., Morsbach, M. & Kramer, C. 1966 The conditions for separation and vortex formation past cylinders. In Separated Flows; AGARD Conf. Proc. no. 4, part 2, pp. 539574.
Nielsen, K. W. 1970 Vortex formation in a two-dimensional periodic wake. Ph.D. thesis, Oxford Univ.
Owen, F. K. & Johnson, D. A. 1980 Measurements of unsteady vortex flow fields. AIAA J. 18, 1173810 (AIAA Paper 78810).Google Scholar
Peake, D. J. & Tobak, M. 1980 Three-dimensional interactions and vortical flows with emphasis on high speeds. AGARDograph 252.
Perry, A. E., Chong, M. S. & Lim, T. T. 1982 The vortex-shedding process behind two-dimensional bluff bodies J. Fluid Mech. 116, 7790.Google Scholar
Perry, A. E. & Morrison, G. L. 1971 A study of the constant-temperature hot-wire anemometer J. Fluid Mech. 47, 557599.Google Scholar
Perry, A. E. & Watmuff, J. H. 1981 The phase-averaged large-scale structures in threedimensional turbulent wakes J. Fluid Mech. 103, 3351.Google Scholar
Reynolds, W. C. & Hussain, A. K. M. F. 1972 The mechanics of an organized wave in turbulent shear flow. Part 3. Theoretical models and comparisons with experiments J. Fluid Mech. 54, 263288.Google Scholar
Roshko, A. 1954 On the drag and shedding frequency of two-dimensional bluff bodies. NACA TN 3169.
Ryan, L. F. 1951 Experiments on aerodynamic cooling. ETH Zürich, Inst. für Aerodyn., Mitt. nr. 18.
Schmidt, D. W. & Tilmann, P. M. 1972 Über die Zirkulations-entwicklung in Nachläufen von Rundstäben Acustica 27, 1422.Google Scholar
Stack, J. 1941 Compressibility effects in aeronautical engineering. NACA Confidential Rep. no. 246 (declassified 1967).Google Scholar
Thomann, H. 1959 Measurements of the recovery temperature in the wake of a cylinder and of a wedge at Mach numbers between 0.5 and 3. Aero. Res. Inst. Sweden (FFA) Rep. no. 84.Google Scholar
Tutu, N. And Chevray, R. 1975 Cross-wire anemometry in high intensity turbulence J. Fluid Mech. 71, 785800.Google Scholar
Wagner, W. J. 1976 Experimentelle Untersuchung der Nachlaufströmungen im Nahbereich hinter Rundstäben mittels Messung der Temperatureschwankungen. Mitt. MPI unde AVA, Göttingen, nr. 62.
Wlezien, R. W. & Way, J. L. 1979 Techniques for the experimental investigation of the near wake of a circular cylinder. AIAA J. 17, 563810 (AIAA Paper 78810).Google Scholar
Zdravkovich, M. M. 1969 Smoke observations of the formation of a Kármán vortex street J. Fluid Mech. 37, 491496.Google Scholar