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Numerical analysis of compressible turbulent helical flow in a Ranque-Hilsch vortex-tube
No full textNumerical analysis of the internal flow field in a Ranque-Hilsch vortex tube (RHVT) has been conducted in order to improve understanding of its fluid-dynamic behaviour. The flow field in an RHVT is compressible, turbulent and helical with a very high degree of swirl; hence its numerical simulation is a challenging task. Particular interest has been reserved for turbulence modelling, hence both RANS and LES approaches have been employed. In particular axial-symmetric RANS simulations have been conducted using RNG k-epsilon and a linear RSM (Reynolds Stress differential Model) closure models, while full three-dimensional LESS have been performed using Smagorinsky and Germano-Lilly sub-grid scales (SGS) models. Results showed, that turbulence closure models choice is a crucial issue in the prediction of the flow field in an RHVT. In fact, different simulations exhibit some differences in the description of the velocity vector components. In each simulation, flow government equations have been solved using the commercial finite volume code FLUEN (TM) 6.3.26.
Flow patterns in this device have been also investigated by means of the calculation of the Helical Flow Index or normalized helicity; Power Spectral Density (PSD) of velocity magnitude has been eventually calculated showing a good agreement with K41 theory. An improved understanding of the flow field inside the RHVT can lead to a correct prediction of fluid dynamic and thermal behaviour of outlet jets, fundamental information to define cooling performance of this device
Numerical Simulations of Turbulent Helical Flow in a Ranque-Hilsch Vortex Tube with different RANS closures and Sub-Grid Scales Models
No full textRaffreddamento di componenti elettronici di potenza mediante dispositivi ad effetto Ranque-Hilsch: simulazione numerica del flusso interno ed esterno
No full textUnsteady Aerodynamics of a Savonius wind rotor: a new computational approach for the simulation of energy performance
No full textWhen 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”
Modellazione e realizzazione dello strato limite atmosferico in galleria del vento ambientale. Prime prove sperimentali e numeriche
No full textNumerical Simulations of Turbulent Helical Flow in a Ranque-Hilsch Vortex Tube with different RANS closures and Sub-Grid Scales Models
No full textNumerical simulation of turbulent flow in a Ranque-Hilsch vortex tube
No full textThe 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
Raffreddamento di componenti elettronici di potenza mediante dispositivi ad effetto Ranque-Hilsch: caratterizzazione sperimentale realizzazione di un prototipo
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