Gabriele Bedon

Innovative Discrete-Vortex Model for Dynamic Stall Simulations

An innovative model based on the vortex theory is presented with the aim of simulating the two-dimensional airfoil dynamic behavior at pitching reduced frequencies related to vertical axis wind-turbine operative conditions. The model relies on the introduction of a second separated wake from the suction side to correctly account for the aerodynamic effects of stall conditions and is provided with correction models whose aim is to consider the dynamic evolution of the shed vortices and of the separation point. The model receives as input experimental data to estimate the nonoscillating steady-state separation point for different angles of attack. A validation procedure confirmed the model capabilities to provide reliable numerical estimations of the lift coefficient for a pitching airfoil compared to experimental tests and computational-fluid-dynamics approaches based on the unsteady Reynolds-averaged Navier–Stokes equations complemented with the k-ω shear-stress transport turbulence model. In particular, ...

Surrogate-Based Shape Optimization of Stall Margin and Efficiency of a Centrifugal Compressor

Centrifugal compressors are required to increase their operating range and efficiency, which are limited at low mass flow rates by the rotating stall and surge. This paper presents a surrogate-based multi-objective optimization of a centrifugal compressor to improve its efficiency and stall margin. Curvatures of the blade, the impeller shroud, and the diffuser hub are selected as optimization parameters since they influence highly both the efficiency and the stall limit. The implemented optimization procedure starts by the construction of a metamodel, which is the radial basis function that uses a database composed of a well-selected set of geometries and their corresponding computational fluid dynamics predicted objectives using the Ansys-CFX 12 code. The NSGA-II optimization algorithm is used afterward to search the Pareto front based on radial basis function approximations. To improve the accuracy of the radial basis function and subsequently the Pareto front, a database refinement is sequentially achi...

Numerical performance and stress prediction for a vertical-axis wind turbine as a function of the aerodynamic control strategy

A combined performance/stress numerical analysis is proposed for a three-bladed vertical-axis wind turbine (VAWT) adopting a Blade Element-Momentum (BE-M) algorithm as a simulation tool. After determining the operational curves of the turbine, the aerodynamic forces acting on rotor blades, as well as the global thrust acting on the whole machine, are evaluated as a function of the aerodynamic control strategy of the rotor, obtaining a first estimation to be used for the structural sizing of both rotor blades and shaft.