Stability Analysis of Concentric Annular Passages Conducting Incompressible Turbulent Flows with Oscillatory Boundary

This paper presents an investigation of the response of a cylindrical structure within the fluidelastic coupling between an axial annular flow and a flexible vibrating duct. An unsteady programbased on a turbulence model called Baseline (BSL) k-omega model was conducted to simulate a turbulent annular flow between two initially concentric cylinders, the outer one of which executes aharmonic planar motion. Three turbulent flows with Re numbers of 4000, 8000 and 16000, wereinvestigated for the purpose of studying the stability of the outer cylinder with annular passages conducting incompressible turbulent flow. The effects of principal flow variables, i.e., mean axialvelocity and fluid temperature, also annular passage configuration, i.e., the radii of cylinders, on thepressure and circumferential velocity of a three dimensional turbulent flow were investigated. It is assumed that one side of the annulus, i.e., the inner cylinder is fixed and the outer cylindrical duct is flexibly supported. The outer cylinder is displaced from its equilibrium position and is then releasedto execute transverse vibrations. A second order backward Euler scheme is used to solve transientequations such as the Navier-Stokes and continuity equations. The employed method is validated with the available solutions in the literature and fairly good agreements are seen between the results.The comparison between results obtained for turbulent flows demonstrates that an increase inthe axial flow velocity results in smaller values for the unsteady pressure and the circumferential velocity amplitudes which affect the stability of the outer cylinder. For each of the turbulent flowsthe unsteady pressure amplitude increases with the fluid temperature, as well as the circumferentialvelocity amplitude. As the fluid temperature goes up, the amplitude and the coupled frequency of oscillation of the outer cylinder increase. By reducing the radii of cylinders, the amplitude of unsteadypressure and circumferential velocity decrease and then the outer cylinder oscillates withlarger amplitude. In this case the added damping is reduced but the coupled frequency of oscillationincreases. The results of this investigation are favorably used for Fluid-Structure Interaction (FSI) calculations in such configurations.

Keywords:

Fluid-Structure Interaction (FSI) , Fluidelastic Coupling , Annular Flow , Unsteady Pressure and Velocity