Presentation on theme: "1. Early studies. 2. The era of Corrsin, Townsend and company 3. Active grids 4. Review of advances and outstanding problems Zellman Warhaft, Cornell University."— Presentation transcript:
1. Early studies. 2. The era of Corrsin, Townsend and company 3. Active grids 4. Review of advances and outstanding problems Zellman Warhaft, Cornell University “Finally, if we are to list the reasons for studying homogeneous turbulence, we should add that it is a profoundly interesting physical phenomenon which still defies satisfactory mathematical analysis; this is, of course, the most compelling reason” G.K. Batchelor, The Theory of Homogeneous Turbulence, 1953. “ Why on earth are you studying grid turbulence?” Statement of a turbulence researcher to ZW, conference on “Structure and Mechanisms of turbulence.” Berlin, 1976.
Corrsin and Townsend “Corrsin carried on a correspondence with Townsend for several years regarding the isotropy of grid turbulence. Corrsin’s measurements indicated that turbulence in Baltimore was not quite isotropic, while Townsend continued to refer to his turbulence as isotropic. At one point, Corrsin wrapped up one of his grids and sent it to Townsend. There was no reply. Ultimately, the difference was traced to X- wire calibration and the hot-wire length correction. In fact, as Corrsin has claimed, the grid turbulence was not quite isotropic (see below) ”. From “A Century of Turbulence” by J.L. Lumley and A.M. Yaglom. Flow, Turbulence and Combustion, 66: 241-286, 2001
Partial list of other passive grid turbulence experiments Diffusion from line sources: Uberoi, M.S. & Corrsin, S. 1953 NACA Rep. 1142 Townsend, A.A. 1954 Proc. Roy. Soc.Lon. A, 224 Stapuntsis, Hunt et al. JFM 1986, W. 1984 JFM Axisymmetric strain: Uberoi, M.S. 1956, J. Aero. Sc. 23. Mills, R. R. & Corrsin, S. 1959 NASA memo 5-5-59 W. 1980. JFM 99 Heated grids & homogeneous scalars: Yeh, T.T. & van Atta, C.W. 1973 J. Fluid Mech. 58 Mills, R. R. & Corrsin, S. 1959 NASA memo 5-5-59 W Lumley, J.L. & W. J. Fluid Mech. 1978 Sreeninvasan, K.R., Tavoularis, S. Henry, R. & Corrsin, S. J. 1980 Fluid Mech. 100 Lagrangian: Snyder, W.H. & Lumley, 1971, J. Fluid Mech. 48., Qureshi, Bourgoin PRL 2007. Homogeneous Shear: S. Corrsin and Co-workers Turbulence mixing layer: Gilbert, Veeravalli & W...,....................
Active Grids Gad-El-Hak, M. Corrisin, S. J. Fluid Mech. (1974) [jets, co-& counter flow] H.Makita, K. Sassa,. I Iwasaki & A. Iidu (1987), Trans. Japan Soc. Mech. Engng 1987 H.Makita (1991) Fluid Dynamics Research (Japan) Mydlarski & W* (1996), J. Fluid Mech. Poorte R.E.G. & Biesheuvel (2002) J. Fluid Mech.[ gas bubbles] Kang, H.S.Chester, S. Meneveau, C. (2003) J. Fluid Mech. [decaying turbulence and LES] Kang, H.S. Meneveau, C. (2008) Phys. Fluids [shearless mixing layer] Mordant, N (2008) American J. Physics [teaching tool] Savelsber R & Van de Water, w. (2009) J. Fluid Mech. [ free surface turbulence] *Z.W and Mydlarski, L, Shen, X, Ayyalasomayajula S, Gylfason,A, Gerashchenko, S. Sharpe, N.Neuscaman S, [Passive scalars, homogeneous shear, inertial particles, boundary layer, axisymmetric strain] Turbulence intensity ~ drag coeff. ~ solidity. Solidity > 0.4, unstable
Active vs. passive grids The issue of isotropy and integral scale
Large and Small Scales Passive grid experiments, particularly those of Corrsin and Townsend, were focused on seeking large scale isotropy to test kinematics and theories of isotropic turbulence. Active grid experiments are focused on achieving high Reynolds numbers at the expense of large scale isotropy, and of having the largest eddies significantly smaller than that of the tunnel. There is more and more reason to suggest that the large and small scales are (directly) related.
Other new ways of generating “isotropic” turbulence Meng et al. Digital holographic imaging Bodenschatz et al. Stereoscopic 3D tracking Eaton et al. laser sheetCornell (Makita) et al. Sled/laser sheet Bodenschatz et al. Pinton et al. Doppler sonar
Perhaps! We still do not know the values of important constants well (von Karman constant, a_0 etc. ). Reynolds number dependencies, pre-factors are not well documented. But, as we have seen at this meeting, a great deal IS understood. And soon much more with the PMI-SF6 tunnel.