M.Sc Thesis


M.Sc StudentAlexander Shousterman
SubjectAeroelastic Loads Calculation for a Cascade Blade of Jet
Engine Compressors and Gas Turbines
DepartmentDepartment of Aerospace Engineering
Supervisor Professor Raveh Daniella
Full Thesis text - in Hebrew Full thesis text - Hebrew Version


Abstract

The study introduced a novel methodology for aeroelastic analysis of cascade blades of jet-engine compressors, turbines, and propellers. The aeroelastic analysis is used to compute time-domain dynamical responses of a cascade blade to different aerodynamic excitations, which may be due to the vicinity of an upstream stator cascade, or due to alteration of the cascade operating conditions (e.g., acceleration of the cascade).


The aeroelastic analysis consists of two elements that are treated in the current study with new approaches. The first element, which tackles the structural dynamics, employs the modal approach for the analytical evaluation of the blade stiffening due to rotation, using the natural frequencies and modes of the static blade. The second element, which entails of the computation of the aerodynamic forces, offers to calculate the time domain blade aerodynamic response to arbitrary flow disturbances using Computational Fluid Dynamics (CFD) tools.


The structural stiffening due to blade rotation is evaluated analytically, by use of energy considerations. The stiffness and mass matrices are computed using the Lagrange equations and the Hamilton principle. The equations of motion of the homogeneous rotating blade system are formulated in generalized coordinates, where the modes of the static blade serve as the systems' degrees of freedom. Time-domain aerodynamic forces are computed by means of convolution, using the cascade's lift responses to a step angle-of-attack, and to a step sharp-edge gust inputs. In the current study these are calculated by the EZNSS CFD software on a 2D section of the cascade. The three-dimensional wing aerodynamic model is obtained using the Strip Theory.


The method is based on the use of high-fidelity disciplinary models, i.e., CFD and finite-elements, but at the same time is very computationally efficient. That results from the fact that the method requires a single run of the FE software, and only few runs of the CFD code. These provide the modal and aerodynamic models which are then used in a semi-analytical aeroelastic computation. The method allows for the examination of many aeroelastic responses of the cascade in a rapid manner, where cases in which the response is found to be irregular can be further examined by full CFD aeroelastic simulation.