Development of a Coupled Fluid-Structure Simulation Method in the Frequency Domain

Development of a Coupled Fluid-Structure Simulation Method in the Frequency Domain

Berthold, C.R.

Boersma, B.J. (mentor)

Mechanical, Maritime and Materials Engineering

Process and Energy (P&E)

2016-08-12

In this work a numerical method is developed to efficiently simulate limit cycle oscillations and forced response amplitudes of fluid-structure interaction (FSI) problems. The method computes a solution in the frequency-domain and can therefore only deal with periodic unsteadiness. As flow solver the Harmonic Balance method is used which is coupled to structural eigenmode dynamics. In this work the motion of the structure is approximated by one structural eigenmode only. The Harmonic Balance method is a nonlinear frequency-domain method. The newly developed method should be able to determine the resulting vibrational amplitude of a fluid-structure problem more efficiently than a coupled time-domain simulation. The resulting vibrational amplitude of the structure can then be used to evalute a mechanical design with respect to possible damage and/or High Cycle Fatigue. Possible applications of this method lie in the field of aeroelasticity, e.g. the investigation of flutter and forced response situations of blades in turbomachinery. To test the method it is applied to two 2D turbomachinery testcases and also to an elastically-mounted cylinder with vortex shedding. The main topics of this thesis are: 1) Analysis of the model equations and development of a numerical strategy which is solved with a pseudo time stepping method. 2) Investigation of the vibrational frequency of a coupled fluid-structure system which is in general not equal to the eigenfrequency of the structural eigenmode. 3) Application of the method to the testcases and validation against results from time- domain computations. It turns out that the developed method is able to predict forced response amplitudes (Synchronous Vibrations) very efficiently. The computational costs of the frequency-domain method are very promising. Non-Synchronous Vibrations (NSV) are also investigated with the developed method. The limit cycle oscillations of aerodynamically unstable modes of a blade row can be efficiently simulated. In case of a flutter investigation the method is able to predict the frequency of the coupled FSI problem as well as the resulting vibrational amplitude very efficiently. To investigate NSV which are dominated by a flow instability the method is applied to an elastically-mounted cylinder with vortex shedding in the lock-in regime. In this case the method fails in determining the frequency of the unsteadiness but if the correct frequency is known a priori the method is still able to compute the amplitude of the resulting limit cycle oscillations.

Fluid-Structure Interaction
Frequency Domain
Turbomachinery
Forced Response
Flutter
Aeroelasticity
Nonlinear Frequency Domain
Harmonic Balance

http://resolver.tudelft.nl/uuid:b9b9a646-0988-46fc-9e34-b750f5ecf3b1

Student theses

master thesis

(c) 2016 Berthold, C.R.