Papers by Matteo Montecchia
Experimental analysis of a separation control device based on plasma technology
In this thesis effects of plasma actuators based on Dielectric Barrier Discharge (DBD) technology... more In this thesis effects of plasma actuators based on Dielectric Barrier Discharge (DBD) technology over a NACA 0015 bidimensional airfoil have been analyzed in an experimental way, at low Reynolds number. Work developed on thesis has been carried on in partnership with the Department of Electrical Engineering of Università di Bologna, inside Wind Tunnel of the Applied Aerodynamic Laboratory of Aerospace Engineering faculty. In order to verify the effectiveness of these active control devices, the analysis has shown how actuators succeed in prevent boundary layer separation only in certain conditions af angle of attack and Reynolds numbers. Moreover, in this thesis actuators’ chordwise position effect has been also analyzed, together with the influence of steady and unsteady operations
Capturing Reynolds number effects in the periodic hill flow by using LES with anisotropy-resolving sub-grid scale model
11th International Symposium on Turbulence and Shear Flow Phenomena (TSFP11), July 30 to August 2, 2019, Grand Harbour Hotel, Southampton, UK, 2019
Reynolds number effects in periodic hill flow: an LES study using OpenFOAM and the Explicit Algebraic SGS stress model
Development and testing of an anisotropy-resolving model for hybrid RANS-LES computations of turbulent incompressible flows
In the present work a new model for hybrid RANS-LES computations based on the improved-delayed-de... more In the present work a new model for hybrid RANS-LES computations based on the improved-delayed-detached eddy simulation (IDDES) approach is proposed.The model combines the Explicit Algebraic Reynol ...
Can anisotropy-resolving SGS models relax the resolution requirements in hybrid RANS-LES ?
Anisotropy-resolving Reynolds stress turbulence modelling in a RANS context has been shown to be ... more Anisotropy-resolving Reynolds stress turbulence modelling in a RANS context has been shown to be superior to standard eddy-viscosity models (EVM) in flows that are more complex than simple plane shear flows. Differential Reynolds stress models (DRSM) as well as their algebraic counterpart (EARSM) have been shown to be able to capture effects of rotation, curvature, swirl, secondary flows, non-equilibrium and separation onset somewhat better than EVMs. Still massive separation and flows around blunt bodies cannot be well captured by RANS models mainly because of non-local effects, which is the primary motivation for hybrid RANS LES approaches. EARSM has been applied also in hybrid approaches for the attached RANS part, see e.g. Jaffrézic & Breuer [1], but the LES part is modelled using more standard EVM SGS modelling. It is commonly believed that the SGS turbulence is quite isotropic, which is true when the small scales are purely driven by an energy cascade in equilibrium. However, ...
Physical Review Fluids, 2017
Properly resolved large-eddy simulations of wall-bounded high Reynolds number flows using standar... more Properly resolved large-eddy simulations of wall-bounded high Reynolds number flows using standard subgrid-scale (SGS) models requires high spatial and temporal resolution. We have shown that a more elaborate SGS model taking into account the SGS Reynolds stress anisotropies can relax the requirement for the number of grid points by at least an order of magnitude for the same accuracy. This was shown by applying the recently developed explicit algebraic subgrid-scale model (EAM) [Marstorp et al., J. Fluid Mech. 639, 403 (2009)] to fully developed high Reynolds number channel flows with friction Reynolds numbers of 550, 2000, and 5200. The near-wall region is fully resolved, i.e., no explicit wall modeling or wall functions are applied. A dynamic procedure adjusts the model at the wall for both low and high Reynolds numbers. The resolution is reduced, from the typically recommended 50 and 15 wall units in the stream-and spanwise directions respectively, by up to a factor of 5 in each direction. It was shown by comparison with direct numerical simulations that the EAM is much less sensitive to reduced resolution than the dynamic Smagorinsky model. Skin friction coefficients, mean flow profiles, and Reynolds stresses are better predicted by the EAM for a given resolution. Even the notorious overprediction of the streamwise fluctuation intensity typically seen in poorly resolved LES is significantly reduced when EAM is used on coarse grids. The improved prediction is due to the capability of the EAM to capture the SGS anisotropy, which becomes significant close to the wall.
Sub-grid scale (SGS) models are required in order to model the influence of the unresolved small ... more Sub-grid scale (SGS) models are required in order to model the influence of the unresolved small scales on the resolved scales in large-eddy simulations (LES), the flow at the smallest scales of turbulence. In the following work two SGS models are presented and deeply analyzed in terms of accuracy through several LESs with different spatial resolutions, i.e. grid spacings. The first part of this thesis focuses on the basic theory of turbulence, the governing equations of fluid dynamics and their adaptation to LES. Furthermore, two important SGS models are presented: one is the Dynamic eddy-viscosity model (DEVM), developed by \cite{germano1991dynamic}, while the other is the Explicit Algebraic SGS model (EASSM), by \cite{marstorp2009explicit}. In addition, some details about the implementation of the EASSM in a Pseudo-Spectral Navier-Stokes code \cite{chevalier2007simson} are presented. The performance of the two aforementioned models will be investigated in the following chapters, ...
Journal of Turbulence
There is a rapidly growing interest in using general-purpose CFD codes based on second-order fini... more There is a rapidly growing interest in using general-purpose CFD codes based on second-order finite volume methods for Large-Eddy Simulation (LES) in a wide range of applications, and in many cases involving wall-bounded flows. However, such codes are strongly affected by numerical dissipation and the accuracy obtained for typical LES resolutions is often poor. In the present study, we approach the problem of improving the LES capability of such codes by reduction of the numerical dissipation and use of an anisotropycapturing subgrid-scale (SGS) stress model. The latter is of special importance for wall-resolved LES with resolutions where the SGS anisotropy can be substantial. Here we use the Explicit Algebraic (EA) SGS model [Marstorp L, Brethouwer G, Grundestam O, et al. Explicit algebraic subgrid stress models with application to rotating channel flow. J Fluid Mech. 2009;639:403-432], and comparisons are made for channel flow at friction Reynolds numbers up to 934 with the dynamic Smagorinsky model. The numerical dissipation is reduced by using an OpenFOAM based custom-built flow solver that modifies the Rhie and Chow interpolation and allows to control and minimise its effects without causing numerical instability (in viscous, fully turbulent flows). Different resolutions were used and large improvements of the LES accuracy were demonstrated for skin friction, mean velocity and other flow statistics by use of the new solver in combination with the EA SGS model. By reducing the numerical dissipation and using the EA SGS model the resolution requirements for wall-resolved LES can be significantly reduced.
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Papers by Matteo Montecchia