Cavity Flows: Change Of Regime In The Ratio Between The Pressure And Kinetic Energy Flows Across The Cavity Mouth

The incompressible flow in a rectangular cavity located along one of the wall of a plane channel is studied. The focus is put on the flow in the cavity and on the energy dynamics, in particular on the pressure and kinetic energy exchange across the interface surface between the cavity and the channel. Moreover, using the incompressible formulation of fluid equations, we look for observable properties that can be associated to acoustic emission which is normally observed in this kind of flow beyond a critical value of Reynolds numbe

Dynamic models for Large Eddy Simulation of compressible flows with a high order DG method

The impact of dynamic models for applications to LES of compressible flows is assessed in the framework of a numerical model based on high order discontinuous finite elements. The projections onto lower dimensional subspaces associated with lower degree basis functions are used as LES filter, along the lines proposed in Variational Multiscale templates. Comparisons with DNS results available in the literature for plane and constricted channel flows at Mach numbers 0.2, 0.7 and 1.5 show clearly that the dynamic models are able to improve the prediction of most key features of the flow with respect to the Smagorinsky models employed so far in a VMS-DG context

Pressure and kinetic energy transport across the cavity mouth in resonating cavities

Basic properties of the incompressible fluid motion in a rectangular cavity located along one wall of a plane channel are considered. For Mach numbers of the order of 1 × 10−3 and using the incompressible formulation, we look for observable properties that can be associated with acoustic emission, which is normally observed in this kind of flow beyond a critical value of Reynolds number. The focus is put on the energy dynamics, in particular on the accumulation of energy in the cavity which takes place in the form of pressure and kinetic energy. By increasing the external forcing, we observe that the pressure flow into the cavity increases very rapidly, then peaks. However, the flow of kinetic energy, which is many orders of magnitude lower than that of the pressure, slowly but continuously grows. This leads to the pressure-kinetic energy flows ratio reaching an asymptotic state around the value 1000 for the channel bulk speed Reynolds number. It is interesting to note that beyond this threshold when the channel flow is highly unsteady—a sort of coarse turbulent flow—a sequence of high and low pressure spots is seen to depart from the downward cavity step in the statistically averaged field. The set of spots forms a steady spatial structure, a sort of damped standing wave stretching along the spanwise direction. The line joining the centers of the spots has an inclination similar to the normal to the fronts of density or pressure waves, which are observed to propagate from the downstream cavity edge in compressible cavity flows (at Mach numbers of 1 × 102 to 1 × 103, larger than those considered here). The wavelength of the standing wave is of the order of 1/8 the cavity depth and observed at the channel bulk Reynolds number, Re ∼ 2900. In this condition, the measure of the maximum pressure differences in the cavity field shows values of the order of 1 × 10−1 Pa.We interpret the presence of this sort of wave as the fingerprint of the noise emission spots which could be observed in simulations where the full compressible formulation is used. The flow is studied by means of a sequence of direct numerical simulations in the Reynolds number range 25-2900. This allows the study to span across the steady laminar regime up to a first coarse turbulent regime. These results are confirmed by the good agreement with a set of laboratory results obtained at a Reynolds number one order of magnitude larger in a different cavity geometry [M. Gharib and A. Roshko, J. Fluid Mech. 177, 501 (1987)]. This leaves room for a certain degree of qualitative universality to be associated with the present findings. DOI: 10.1103/PhysRevE.87.01301

Review of rheological behaviour of sewage sludge and its importance in the management of wastewater treatment plants

Abstract The process operation of wastewater treatment plants (WWTPs) is based on the proper set up of several physical, chemical and biological parameters. Often, issues and problems arising in the process are strictly linked to the rheological behaviour of sewage sludge (SeS). Therefore, rheological measurements, which recently have captured a growing interest, represent an important aspect to consider in the design and operation of WWTPs, especially in the sludge-handling processes. The knowledge of rheological behaviour of SeS represents a crucial step to better understand its flow behaviour and therefore optimize the performance of the processes, minimizing the costs. The SeS are non-Newtonian fluids and, to date, Bingham and Ostwald models are the most applied. This work presents an overview of scientific literature about the rheological properties of SeS and discusses the importance of its knowledge for the management of WWTPs

Electrify Italy

This study explores a possible pathway to implement a new energy paradigm in Italy based on electrification. The objectives are: • To build a forward-looking vision of possible scenarios at 2022, 2030 and 2050 by integrating a multi-focus perspective on the penetration of renewables and the electrification potential of the residential, industrial and transport sectors. • To estimate the potential benefits of further electrification through the calculation of Key Performance Indicators in four different areas: energy, economy, environment and society. The study shows how the electricity triangle, a paradigm based on clean generation by renewable sources, electrification of final uses, and electricity exchange through efficient smart grids, closes the loop of clean energy and efficient consumption. This leads to improvements in energy, environment, economy and social performances, and boosts the share of renewables in final consumption

A Mixed RANS/LES Model Applied to the Channel Flow

In the paper we present some preliminary results related to a new LES approach, the mixed RANS/LES modelling technique that should exploit both the experience accumulated in RANS modelling, particularly near the wall, and the LES capabilities. This new approach was first presented to the APS/DFD Meeting of Baltimore in 2012 [1] and represents a particular application of the general Hybrid RANS/LES filtering technique. Here in particular we have applied this new mixed RANS/LES modelling technique to the channel flow in the particular case of exact RANS databases as regards the RANS model and the no-model and the dynamic anisotropic model as regards the LES aspect. The results are interesting and promising for a simple implementation in different codes with different models