[CCoE Notice] PhD Dissertation Defense -

[Khator, Suresh]

Three-dimensional Numerical Simulation for Combined Wavy and Steady Flows past a Vertical Circular Cylinder

Ph.D. Defense

Medhat Aly El-Nahas

Day and Time: Thursday, November 17, 2011 at 9:00 AM

Location: Department of Mechanical Engineering, Small Conference Room

Committee Members: Dr. Charels Dalton; Dr. Ralph W. Metcalfe; Dr. Stanley J. Kleis;Dr. Keh-Han Wang; Dr. Tsorng-Whay Pan.

Abstract

This study considered a numerical simulation with LES modeling of combined wavy and steady flows past a vertical circular cylinder. The numerical simulation considered the time-dependent, three-dimensional, incompressible Navier-Stokes equations in polar coordinates using primitive variables with a combined spatial approximation of the central differencing scheme and the Fourier spectral method. Fourier spectral methods were used in the circumferential and axial directions. A combination of Dirichlet and spatial Convective Projection boundary conditions is implemented to assure traveling waves, from the time-dependent flow structures formed at the cylinder surface, to be convected undisturbed outside the flow field. Verification and validation of the numerical model were conducted to ensure the accuracy and repeatability of the numerical model. The results obtained were compared to well-recognized numerical studies of a steady approach flow, a purely wavy flow, and two-dimensional combined steady and wavy flows past a circular cylinder, and were found in a good agreement with the previous work.
This study shows the significant effects of such combined flows on forces exerted on the cylinder, the effects of combining the steady flow and the wavy flow on the drag and inertia coefficients and the changes in vortex patterns due to that combination. It also extends the present understanding of the effects of the frequency parameter (*), the Keulegan-Carpenter Number (KC), and the strength of the steady flow (B) on the mechanics and the behavior of flow around the cylinder. It is noted that the drag and inertia coefficients of the combined flows are reduced with the increase of the strength of the steady flow. It is also noted that the KC value is the controlling parameter because the wake behavior seems to depend more on KC value. In addition to that, as KC and * increase, the randomness of the vortex shedding around the cylinder was noted, especially for pure wavy flow and combined flows at small values of B.

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