Compressor and Turbine Multidisciplinary Design for Highly Efficient Micro-gas Turbine

Multidisciplinary design optimization(MDO) is widely employed to enhance turbomachinery components efficiency. The aim of this work is to describe a complete tool for the aero-mechanical design of a radial inflow turbine and a centrifugal compressor. The high rotational speed of such machines and the high exhaust gas temperature(only for the turbine) expose blades to really high stresses and therefore the aerodynamics design has to be coupled with the mechanical one through an integrated procedure. The described approach employs a fully 3D Reynolds Averaged Navier-Stokes(RANS) solver for the aerodynamics and an open source Finite Element Analysis(FEA) solver for the mechanical integrity assessment. Due to the high computational cost of both these two solvers, a meta model, such as an artificial neural network(ANN), is used to speed up the optimization design process. The interaction between two codes, the mesh generation and the post processing of the results are achieved via in-house developed scripting modules. The obtained results are widely presented and discussed.

Experimental and Numerical Analysis of Cavity/Mean-Flow Interaction in Low Pressure Axial Flow Turbines

The increasing performance of modern aeroengines led the research towards the optimization of machine components not deeply analyzed in the past.In this context,the mechanisms driving the interaction process between the secondary flows evolving at the hub of low-pressure turbines with the rotor-stator cavity systems have been poorly investigated in the literature.In this work,an experimental and numerical analysis of the interaction between the endwall near wall flow and the leakage flow of a real cavity system is presented.The experimental results were carried out in the annular low-pressure axial flow turbine of the University of Genova.Experimental blade loading and pressure distributions into the cavity,as well as the measured total pressure loss coefficient,have been used for a proper validation of CFD results.Both steady and unsteady calculations were carried out through the commercial solver Numeca.Particularly,several numerical approaches have been tested into this work:RANS,Non Linear Harmonic(NLH),and URANS.The most promising CFD techniques have been firstly identified by comparison with experimental results and then systematically employed to extend the analysis of secondary flow-cavity flow interaction to positions and quantities not available from the experiments.Losses characterizing the mean flow-cavity flow interaction process will be shown to cover a great amount of the overall stage losses and should be properly accounted for the design of future optimized cavity configurations.

Large Eddy Simulation of the By-pass Transition Process under Different Inlet Turbulence Conditions

The transition process of the boundary layer developing over a flat plate with elevated inlet Free Stream Turbulence Intensity(FSTI)has been studied by means of Large Eddy Simulation(LES).To this purpose,four cases with different inflow disturbances have been tested varying the magnitude and the length scale of turbulence.LES has been performed by using the finite-volume ANSYS Fluent code.The computational domain,which was constituted by a rectangular domain with a zero thickness plate,was based on an ERCOFTAC test case in order to provide a validation with a well-known set of data by comparing the boundary layer integral parameters and mean and fluctuating streamwise velocity profiles.The four cases were discussed within the paper by looking at classical statistical properties as well as advanced post-processing tools.It was shown that the decrease in the free stream turbulence level postpones the transition location,whereas the variation of the integral length scale has a very low influence on the distribution of the time-mean flow properties.Proper Orthogonal Decomposition(POD)has been applied to the instantaneous LES flow fields in order to provide a statistical representation of the structures responsible for transition and their response to free-stream turbulence intensity and length scale.The presence of vortical filaments parallel to the wall,typically referred as boundary layer streaks,is clearly identified;their characteristic dimensions and how they change as a function of FSTI properties were analyzed within the paper.