On density effects and large structure in turbulent mixing layers
Tóm tắt
Plane turbulent mixing between two streams of different gases (especially nitrogen and helium) was studied in a novel apparatus. Spark shadow pictures showed that, for all ratios of densities in the two streams, the mixing layer is dominated by large coherent structures. High-speed movies showed that these convect at nearly constant speed, and increase their size and spacing discontinuously by amalgamation with neighbouring ones. The pictures and measurements of density fluctuations suggest that turbulent mixing and entrainment is a process of entanglement on the scale of the large structures; some statistical properties of the latter are used to obtain an estimate of entrainment rates. Large changes of the density ratio across the mixing layer were found to have a relatively small effect on the spreading angle; it is concluded that the strong effects, which are observed when one stream is supersonic, are due to compressibility effects, not density effects, as has been generally supposed.
Từ khóa
Tài liệu tham khảo
Sunyach, M. 1971 Contribution a l'étude des frontiéres d'écoulements turbulents libres. D.Sc. thesis,L'Université Claude Bernard de Lyon.
Sirieix, M. & Solionac, J.-L. 1966 Contributions a 1'étude experimentale de la couche de mélange turbulent isobare d'un écoulement supersonique.Symposium on Separated Flow, Agard Conf. Proc. p.4.
PUI, N. K. 1969 The plane mixing layer between parallel streams. M.A. Sc. thesis.University of British Columbia.
Sabin, C. M. 1965 An analytical and experimental study of the plane, incompressible, turbulent free-shear layer with arbitrary velocity ratio and pressure gradient.Trans. A.S.M.E. D 87,421.
Townsend, A. A. 1956 The Structure of Turbulent Shear Flow.Cambridge University Press.
Korst, H. H. , Page, R. H. & Childs, M. E. 1955 A theory for base pressures in transonic and supersonic flow.University of Illinois Eng. Expt. Station Rep. ME-TN-392-2.
Yule, A. J. 1972 Two-dimensional self-preserving turbulent mixing layers at different free stream velocity ratios.Aero. Res. Counc. R. & M. no. 3683.
Pierce, D. 1961 Photographic evidence of the formation and growth of vorticity behind plates accelerated from rest in still air.J. Fluid Mech. 11,460.
Ikawa, H. 1973 Turbulent mixing layer in supersonic flow. Ph.D. thesis,California Institute of Technology.
Mills, R. D. 1968 Numerical and experimental investigations of the shear layer between two parallel streams.J. Fluid Mech. 33,591.
Winant, C. D. & Browand, F. K. 1974 Vortex pairing: the mechanism of turbulent mixing-layer growth at moderate Reynolds numbers.J. Fluid Mech. 63,237.
Spencer, B. W. & Jones, B. G. 1971 Statistical investigation of pressure and velocity fields in the turbulent two-stream mixing layer.A.I.A.A. Paper, no. 71–613.
Browand, F. K. 1966 An experimental investigation of the instability of an incompressible, separated shear layer.J. Fluid Mech. 26,281.
Schlichting, H. 1960 Boundary Layer Theory,4th ed. McGraw-Hill.
Abramovich, G. N. , Yakovlevskp, O. V. , Smirnova, I. P. , Secundov, A. N. & Krasheninnikov, S. Yu. 1969 An investigation of the turbulent jets of different gases in a general stream.Astronautica Acta,14,229.
Damms, S. M. & Küchemann, D. 1972 Possible vortex motions in shear layers.Roy. Aircraft Establishment Tech. Memo. Aero. no. 1430.
Miles, J. B. & Shih, J. 1968 Similarity parameter for two-stream turbulent jet-mixing region.A.I.A.A. J. 6,1429.
Liepmann, H. W. & Laufer, J. 1947 Investigation of free turbulent mixing.N.A.C.A. Tech. Note, no. 1257.
Brown, G. L. & Roshko, A. 1971 The effect of density difference on the turbulent mixing layer.Turbulent Shear Flows,Agard-CP-93,23–1.
Jones, B. G. , Planchon, H. P. & Hammersley, R. J. 1973 Turbulent space-time correlation measurements in a plane two-stream mixing layer at velocity ratio 0·3.A.I.A.A. Paper, no. 73–225.
Abramovich, G. N. 1963 The Theory of Turbulent Jets.M.I.T. Press.
Rebollo, M. 1973 Analytical and experimental investigation of a turbulent mixing layer of different gases in a pressure gradient. Ph.D. thesis,California Institute of Technology.
Birch, S.F. & Ecgers, J. M. 1972 A critical review of the experimental data for developed turbulent free shear layers.Free Turbulent Shear Plows, Nasa SP-321, p.11.
Brown, G. L. & Rebollo, M. R. 1972 A small, fast-response probe to measure composition of a binary gas mixture.A.I.A.A. J. 10,649.
Bradshaw, P. 1966 The effects of initial conditions on the development of a free shear layer.J. Fluid Mech. 26,225.
Hirschfelder, J. O. , Curtiss, C. F. & Bird, R. B. 1954 Molecular Theory of Gases and Liquids.Wiley.