Methods and tools for fundamental research in fluid mechanics
Research focus
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The research activity in this area focuses on turbulent flows, super/hyper-sonic jets, gas dynamics of real gases, instability and bluff body aerodynamics, and computational fluid dynamics. Turbulent flows: direct numerical simulation and control for skin-friction reduction. Work focuses on turbulence control. Investigations have covered both open-loop techniques, including the energetic characterization of the spanwise-oscillating wall, and feedback-based techniques based on modern control theory. Distributed controllers have been synthesized with an innovative Wiener filter based on the mean impulse response of a turbulent channel flow. The main asset of the research unit is a computing environment, called the Personal Supercomputer, fully developed in-house, which comprises a computer language, a computer code and a computing system tailored towards the parallel Direct Numerical Simulation of wall turbulent flows in both cartesian and cylindrical coordinates. Experimental research on turbulence has recently started on the characterization of flows with wall curvature, and the test of innovative control methods via traveling waves. Super/Hyper-sonic jets. Work has been focused on the design and implementation of an experimental apparatus for studying free hypersonic jets over long scales, up to 200 times the initial radius. The jet/ambient ratio and Mach number can be controlled independently by using dissimilar gases in the jet and the ambient medium, while different nozzle configurations are employed to obtain nearly isentropic jets and under-expanded jets. Observations and measurements are performed by means of an in-house developed electron gun and high resolution pressure probes. Research has been conducted on under-dense jets, looking specifically at the mixing layer spreading and jet core fluctuations and destruction, and comparing the jet features when swapping the jet and ambient gases. Gas dynamics of real gases. The research is concerned with the study of flow fields of real gases near the critical point and the vapor-liquid saturation curve, specifically for high-molecular weight vapors (BZT fluids) for industrial applications, including Organic Rankine Cycle Engines. A collaboration is underway with the Aerospace Engineering Sciences Department of the Colorado University at Boulder, for the set-up of a shock tube experiment and of the supporting numerical simulations to demonstrate the existence of non classical gasdynamic phenomena in the vapor phase of fluid PP10 (C13F22). A second collaboration with the Technical University of Delft is directed towards the experimental verification of the existence of non classical gasdynamic phenomena for siloxanes. Extensive use of numerical simulations complement the experimental activities, and are conducted with a novel software tool based on an upwind scheme for unstructured grids, using improved modeling of the gas thermodynamic properties. Instability and bluff body aerodynamics. The bluff body problem at low Reynolds numbers has been tackled by means of matched asymptotic expansion theory, leading to a new analytic form of the base flow for the bluff body wakes and to an instability model for the circular cylinder wake including non-parallel effects. In the intermediate range of Reynolds numbers, the work has considered the different flow regimes of normal flat plates in tandem. In the high Reynolds numbers field, in collaboration with the Departments of Mathematics and Mechanics, a comprehensive study of the flowfield past freely-oscillating cylinders has been carried out to investigate flow instabilities and structural response of slender bodies, such as, for example, submarine cables. Numerical studies have been performed by means of proprietary codes running on an ad hoc cluster system, designed and assembled within this research unit. A novel Particle Image Velocimetry technique, working without laser sources, has been developed and tested on recirculating flows. Computational fluid dynamics. A continuing activity has been conducted in the development of basic numerical methods, applied to elliptic or parabolic problems. These developments can be considered as building blocks towards the accurate approximation of the Navier-Stokes equations for incompressible flows, to be applied in the simulation of highly separated and recirculating low-speed flows. The activity has focused on new formulations of spectral methods for elliptic problems and of Petrov-Galerkin finite element methods for advection–diffusion equations. The latter has been supplemented with the investigation of a posteriori error estimation procedures, to by applied with local adaptation of the computational grid. Lab infrastructures Turbulent flows: direct numerical simulation and control for skin-friction reduction. 2nd-generation Personal Supercomputer, made by 10 dual-CPU Xeon machines. Due to space constraints the 3rd- and 4thResearch topic 1.1 - Methods and tools for fundamental research in fluid mechanics 2-6 generation production machines are located at the University of Salerno, but DIA is the main testing site used for code development or architecture testing. The Personal Supercomputer architecture is tightly tuned to the code that runs on it, and is assembled with special connection topology from commodity hardware. A helically coiled pipe was designed for turbulence measurements up to Re=105, and equipped with an endoscopic PIV system. Super/Hyper-sonic jets. The experiments are performed in a 0.5m (diameter) x 5m (length) vacuum vessel, equipped with truncated and de Laval nozzles up to Mach 25. The jet stagnation pressure can reach 2MPa, the minimum ambient pressure is about 1 Pa. It is possible to use different ambient and jet gases. The measurement system consists of a 16kV/2mA electron gun and a high sensitivity camera, together with high resolution pressure transducers. Gas dynamics of real gases. A cluster made of 7 Linux PC with two AMD Athlon CPUs (2GHz) and 1 Gb of Ram is used for software development and for the simulations of real gas flows. Instability and bluff body aerodynamics. An open circuit wind tunnel with a 0.7x0.5m test section (max speed = 25 m/s). Velocity measurements are performed with 2D LDV anemometers ranging from 1mm/s to 300m/s, based on a 4W argon laser and equipped with a 5-axis positioning system. Complete multi-probe systems for pressure measurements in the range 0.01 Pa to 2MPa. Visualization are obtained by means of two smoke machines and an intensified camera, with exposure time as low as 1ms. The 1.5 x 1m test section of the Large Wind Tunnel (see Research Topic 2.2.1.2) is also used by the unit.
Dipartimento di afferenza
Dipartimento di Ingegneria Aerospaziale
Docenti afferenti
Arturo Baron (Full Professor)
Carlo Luigi Bottasso (Associate Professor)
Sergio De Ponte (Associate Professor)
Maurizio Quadrio (Associate Professor)
Luigi Quartapelle (Associate Professor)
Luigi Vigevano (Associate Professor)
Franco Auteri (Assistant Professor)
Marco Belan (Assistant Professor)
Maurizio Boffadossi (Assistant Professor)
Giuseppe Gibertini (Assistant Professor)