Unsteady Aerodynamics of a Savonius wind rotor: a new computational approach for the simulation of energy performance

When compared with of other wind turbine the Savonius wind rotor offers lower performance in terms of power coefficient, on the other hand it offers a number of advantages as it is extremely simple to built, it is self-starting and it has no need to be oriented in the wind direction. Although it is well suited to be integrated in urban environment as mini or micro wind turbine it is inappropriate when high power is requested. For this reason several studies have been carried-out in recent years in order to improve its aerodynamic performance. The aim of this research is to gain an insight into the complex flow field developing around a Savonius wind rotor and to evaluate its performance. A mathematical model of the interaction between the flow field and the rotor blades was developed and validated by comparing its results with data obtained at Environmental Wind Tunnel (EWT) laboratory of the “Polytechnic University of Marche”

Numerical simulation of turbulent flow in a Ranque-Hilsch vortex tube

The present work is about numerical simulations of the internal flow in a commercial model of a Ranque– Hilsch vortex tube (RHVT) operating in jet impingement. Simulation of the turbulent, compressible, high swirling flow was performed by both RANS and LES techniques. The effect of different turbulence closure models have been tested in RANS simulations using a first order closure RNG k–e and, for the first time in this kind of flow, a second order RSM (Reynolds Stress differential Model) closure. RANS computations have been executed on an axis-symmetric two-dimensional mesh and results have been compared with LES ones, obtained over a three-dimensional computational grid. Smagorinsky sub-grid scale model was used in LES. All the calculations were performed using FLUENTTM 6.3.26. The use of a common code for the different simulations allowed the comparison of the performances of the different techniques and turbu- lence models, avoiding the introduction of other variables. In all the simulations performed, consistency with the real commercial vortex tube model in jet impingement operation has been followed by substituting an axial hot computational exit to the usual radial one. Comparison of the results between RANS simulations performed on both a traditional radial hot outlet computational domain and one with an axial hot outlet, demonstrates the suitability of the computational model adopted in this work, closer to the real geometry of the device, particularly in RANS RSM simulations. Results in different sections of the tube show significant differences in the velocity pro- files, temperature profiles and secondary vortex structures, varying turbulence model. The accurate numerical simulation of the flow in a RHVT, resulting in an improved prediction capability of the kinematic and thermal properties of outgoing jets, could allow a correct estimation of the cooling performance of this device in jet impingement operation

Mechanical Design and Rotor-dynamic Analysis of the ORCHID Turbine

The ORCHID turbine is a 10 kW, high-speed (~100 krpm) radial-inflow organic Rankine cycle (ORC) turbine, under realization in the Propulsion and Power laboratory of Delft University of Technology. The turbine will be installed and tested in the Organic Rankine Cycle Hybrid Integrated Device (ORCHID) facility, the setup for fundamental and applied studies on ORC technology currently in operation in the same lab. Experimental data from future measurement campaigns will be employed to validate numerical tools and develop best practices for designing and operating these unconventional machines. This work documents the recent design efforts to define the functional requirements, the necessary components, and the mechanical assessment of the turbine test bed. In particular, the detailed design of the rotor assembly, carried out in cooperation with the Rotor-dynamic research group of Politecnico di Milano, is described with emphasis on three main aspects. First, the derivation of the damping characteristics of a squeeze-film-damper cartridge for turbochargers, which has been selected as support bearing for the turbine shaft. Secondly, the estimation of the stiffness and damping coefficients of a labyrinth gas seal with swirl breakers, using 3D CFD simulations of the flow path. Finally, linear elastic rotordynamic simulations were performed on a finite beam element model of the resulting turbine shaft. The bearing stiffness, initially estimated using Hertz contact theory, was varied to investigate the sensitivity of the rotor critical speeds to it