Aerodynamic Forcing Investigations of a Transonic Compressor

This thesis aspires to provide a preliminary analysis of unsteady forcing in a transonic compressor. The study and research conducted is placed within the Advanced Research Into Aeromechanical Solutions (ARIAS) project: the experimental results obtained from the Technische Universität Darmstadt (TUD) compressor test rig are used as a starting point of the work. A critical pattern of wake generator is taken into account, with staggered blades and attention is devoted to the first mode excited by engine order 3. This configuration leads to high stresses in the first mode and for this reason simulations are necessary to predict possible failures without compromising the experimental setup. The engineering simulation software ANSYS and its packages are used to run the simulations. A preliminary setup is carried out before starting the simulations: this includes the staggered configuration generation with DesignModeler and the creation of the IGV mesh with ICEM CFD. The mesh can be coarse or more refined based on the number of constituent elements and nodes: in order to choose the best mesh, i.e. accurate enough but not too fine, a grid dependence analysis is performed. Three meshes are generated: COARSE, MEDIUM and FINE: for each, a proper y+ value is chosen by means of an iterative procedure. As a next step, some simple steady state simulations of the IGV are executed and the MEDIUM mesh has resulted to be a good compromise between accuracy and number of elements. The MEDIUM mesh is then imported in CFX with rotor, stator and OGV, whose meshes in TubroGrid are taken from the ARIAS project literature. To run the correct Steady State (SS) simulation, the compressor operating point at this specific configuration is calculated. Starting from the experimental Campbell diagram, the intersection between the curve related to the third engine order and to the first mode gives the operational speed. The compressor curve is determined by running several SS simulation by varying the outlet static pressure. The intersection with the working line in the TUD pre­tests performance map gives the operating point of the case study. The operating point is obtained also in the case of reference configuration, i.e. no staggered blade, and the results are compared with the case study. Some sensitive differences are found in the blade loading and total pressure, in particular in the wake region and at the rotor leading edge, where shocks are identified. The thesis ends with the transient simulation with the Time Transformation method in CFX: first, an appropriate SS simulation is set, taking into account pitch unequalities between IGV, stator and rotor. Second, the transient simulation is run, obtaining the time evolution of certain quantities (total pressure, Mach number,...) and in particular the excitation force value decomposed in Fourier coefficients. The excitation corresponding to the mode of interest can be selected and used for future investigations, such as the forced response analysis.