Research



Ph.D. Thesis M.E. Thesis B.S. Thesis Symposiums & Seminars Publications Useful Links


Ph.D Thesis

DNS of Turbulent Skin Friction Reduction with Wall Compliance

In this work we investigate the interaction of a compliant wall with turbulence for skin friction reduction by doing numerical simulations of turbulent flows in a minimal flow unit. The compliant wall is modeled as a membrane/plate with spring support. The DNS data are used to generate the POD eigenfunctions to construct the low-dimensional dynamical system model.

In the current DNS we use a time-dependent coordinate transformation to eliminate the deformation of the compliant boundary in the computational domain. The boundary conditions for pressure are determined indirectly from the incompressibility condition via an influence matrix technique. A Fourier-Galerkin and Chebyshev-Tau pseudospectral method for spatial discretization and a three-sub-step RK method for time advancement are used in solving the generalized NS equations.

Our preliminary results demonstrate no skin friction reduction on a compliant wall and no corresponding reductions in the magnitude of various statistical quantities of the turbulence near the compliant wall.



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M.E. Thesis

Modelling of a Coal Devolatilization Moving-Bed
A model of the coal devolatilization moving-bed in a Heat-Electricity-Gas tri-product plant was established. The supplying coal in the moving-bed is heated by the cycling ash from a fluidized-bed. The coal does not need to be very fine. Its particle size distribution is given as the input of the model. Marick model or Solomen model was used to simulate the coal devolatilization process. The limiting-diameter criterion was used to deal with the drying and heating process of coal particles. The model can predict the tempreature and gas component distributions in the moving-bed. The computed results for different kinds of coal and operating conditions match the experimental results resonably well.


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B.S. Thesis

Numerical Simulation of 2D Buoyant Flows in Cross Wind
The code TEAM was used to simulate 2-D buoyant flow in cross wind.


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Symposiums & Seminars

  1. The Turbulent Years: John Lumley at 70, A Symposium in honor of John L. Lumley on his Retirement. June 24 and 25, 2001. Cornell University, Ithaca, New York
  2. S. Xu, Wall Compliance Leading to Transition Delay and Turbulent Skin Friction Reduction. STTS Seminar. April 3, 2001. Cornell University, Ithaca, New York
  3. S. Xu, D. Rempfer and J.L. Lumley. Direct Numerical Simulation of the Interaction of Near-wall Turbulence with a Compliant Wall. IUTAM Symposium on FLow in Collapsible Tubes and Past Other Highly Compliant Boundaries. 26-30 March, 2001. University of Warwick and Cambridge University, England
  4. S. Xu, D. Rempfer, J.L.Lumley. Direct Numerical Simulation of the Interaction of Near-Wall Turbulence with a Compliant Boundary. The 53rd Annual Meeting of the American Physics Society, Division of Fluid Dynamics. November 19-21, 2000. Washington, D.C.
  5. S. Xu, D. Rempfer, J.L.Lumley and J. Mohd-Yusof. Direct Numerical Simulation of the Interaction of Near-Wall Turbulence with a Compliant Surface.The 52nd Annual Meeting of the American Physics Society, Division of Fluid Dynamics. November 21-23, 1999. New Orleans, Louisiana
  6. Fluid Mechanics and the Environment: Dynamical Approaches, A Symposium in honor of Sidney Leibovich on his 60th Birthday. August 23 and 24, 1999. Cornell University, Ithaca, New York


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Publications

  1. S. Xu, D. Rempfer and J. Lumley. Numerical Simulation of Turbulent Skin Friction Reduction by Wall Compliance. Under consideration for publication in J. Fluid Mech. (submitted)
  2. D. Rempfer, S. Xu, L. Parsons and J. Lumley. Theoretical Approaches to the Effect of Wall Compliance on Turbulent Flow. IUTAM Symposium Book on Flow in Collapsible Tubes and Past Highly Compliant Boundaries. (to be published)


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