FLUID–STRUCTURE INTERACTION AND INVERSE DESIGN SIMULATIONS FOR FLEXIBLE TURBOMACHINERY

open_access
Open Access
Author:
Campbell, Robert Lee
Graduate Program:
Mechanical Engineering
Degree:
Doctor of Philosophy
Document Type:
Dissertation
Date of Defense:
June 30, 2010
Committee Members:
Eric Paterson, Dissertation Advisor/Co-Advisor
Eric G Paterson, Committee Chair/Co-Chair
Robert Francis Kunz, Committee Chair/Co-Chair
John Michael Cimbala, Committee Member
Stephen A Hambric, Committee Member
Boris Leschinsky, Committee Member
Keywords:
Viscoelastic impeller
Viscoelastic hydrofoil
Flexible hydrofoil
Flexible turbomachinery
Turbomachinery
Expandable impeller pump
FSI
Fluid-structure interaction
Viscoelasticity
Pump
Expandable pump
Flexible pump
Inverse analysis
Abstract:
Highly flexible turbomachinery comprised of soft polymeric impellers, exhibit large, time-dependent deformation when subjected to fluid stresses during operation. The large deformations of the impeller blades and the close proximity of the blades to the pump casing require simulations that consider the interaction of the fluid flow and the structural deformations. This thesis explores the use of fluid–structure interaction (FSI) modeling to perform time-accurate simulations of flexible polymeric turbomachinery and also explores the use of an inverse structural analysis to account for blade deformations over an initial startup period. The purpose of the inverse analysis is to determine the shape of a blade that, when acted on by fluid stresses, will deform into the design shape. A partitioned FSI solver is developed, using the OpenFOAM software and an author-developed finite element (FE) structural solver, to perform FSI simulations of flexible turbomachinery. The flow and structural solvers are tightly coupled using fixed-point iterations to ensure fully converged structural and flow solvers for each solution time step. The solver interface supports disparate flow and structural meshes through interpolation and load mapping algorithms. A water tunnel test of a modified NACA 66 viscoelastic fin is performed at multiple angles of attack to generate validation data for the FSI solver. The validated solver is applied to an expandable impeller pump to simulate time-accurate performance changes that result from impeller elastic and viscoelastic deformation under application of the fluid stresses. An inverse FE structural solver is developed and used to compute inverted structural shapes that account for deformations due to fluid loads so that the structures deform into their design shapes after elastic and viscoelastic deformations occur. The inverse solver is validated for several cases based on numerical simulations. Time-accurate performance estimates of the expandable impeller pump for the inverted impeller shape demonstrate the accuracy of the inverse procedure when subjected to time-varying fluid forces. FSI simulation results for inverted modified NACA 66 fins are also presented. The deformed inverse shapes show good agreement with the intended (design) shapes, but slight discrepancies exist between the prescribed and simulated time at which these shapes are achieved. The slight discrepancies in the target times are attributed to inaccuracies in the load histories assumed during the inverse analyses.