Numerical Study on the Propagation of Turbulent Fronts in Dilute Polymer Solutions

This work explores the mechanics of turbulent propagation in dilute polymer solutions with the objective of increasing the current understanding on turbulent propagation not only of this particular kind of flow, but also of Newtonian turbulent flows in general. By means of Direct Numerical Simulations of planar turbulent/non-turbulent interfaces, the phenomenon of turbulence propagation has been studied in its full range of turbulent scales

Numerical investigation of turbulent/non-turbulent interface

The subject of this work is the diffusion of turbulence in a non-turbulent flow. Such phenomenon can be found in almost every practical case of turbulent flow: all types of shear flows (wakes, jet, boundary layers) present some boundary between turbulence and the non-turbulent surround; all transients from a laminar flow to turbulence must account for turbulent diffusion; mixing of flows often involve the injection of a turbulent solution in a non-turbulent fluid. The mechanism of what Phillips defined as “the erosion by turbulence of the underlying non-turbulent flow”, is called entrainment. It is usually considered to operate on two scales with different mechanics. The small scale nibbling, which is the entrainment of fluid by viscous diffusion of turbulence, and the large scale engulfment, which entraps large volume of flow to be “digested” subsequently by viscous diffusion. The exact role of each of them in the overall entrainment rate is still not well understood, as it is the interplay between these two mechanics of diffusion. It is anyway accepted that the entrainment rate scales with large properties of the flow, while is not understood how the large scale inertial behavior can affect an intrinsically viscous phenomenon as diffusion of vorticity. In the present work we will address then the problem of turbulent diffusion through pseudo-spectral DNS simulations of the interface between a volume of decaying turbulence and quiescent flow. Such simulations will give us first hand measures of velocity, vorticity and strains fields at the interface; moreover the framework of unforced decaying turbulence will permit to study both spatial and temporal evolution of such fields. The analysis will evidence that for this kind of flows the overall production of enstrophy , i.e. the square of vorticity omega^2 , is dominated near the interface by the local inertial transport of “fresh vorticity” coming from the turbulent flow. Viscous diffusion instead plays a major role in enstrophy production in the outbound of the interface, where the nibbling process is dominant. The data from our simulation seems to confirm the theory of an inertially stirred viscous phenomenon proposed by others authors before and provides new data about the inertial diffusion of turbulence across the interface

A numerical study of the shear-less turbulent/non-turbulent interface

A DNS simulation of an interface between a decaying turbulent flow without mean shear and a quiescent non-turbulent region is presented here. The analysis of the instantaneous fields highlight a complex multi-scale behaviour at the turbulent/non-turbulent interface. According to previous results in the literature, by analysing the enstrophy budgets it is possible to observe that enstrophy propagate from the turbulent region mainly by inviscid process while viscous diffusion is relevant only at the interface

PARMA CITTÀ FUTURA VOLUME II Il libro bianco

Secondo volume di Parma Città Futura Il libro bianco raccoglie il lavoro di riflessione strategica organizzato in dieci tavoli di discussione che si sono spontaneamente attivati grazie all’impegno di docenti di vari Dipartimenti dell’Università di Parma che si sono dedicati a elaborare proposte collegate all’attuazione del Progetto Urbano Strategico documentato nel primo volume. Come le varie politiche urbane possono orientarsi e svilupparsi nella prospettiva di concretizzare una idea di città verde accessibile ed accogliente come quella prefigurata? Cultura con la proposta di realizzare un museo/laboratorio della città, Sport e tempo libero orientato all’uso consapevole e condiviso dello spazio pubblico, cittadi- nanza attiva, comunicazione scientifica come nuovo cromosoma nel DNA della città, musica come identità e risorsa, economia di territorio ed area integrata, mobilità sostenibile, tecnologie innovative per la casa e la città, salute e benessere, strategie di attuazione, sono i temi affrontati da oltre 130 persone provenienti da 66 enti, fondazioni, istituzioni e associazioni per elaborare progettualità di settore mirate e complementari. Oltre alle proposte dei vari tavoli offerte alla città ed alla sua amministrazione comunale, l’esperienza di un network flessibile di lavoro collettivo come quello coagulatosi nel 2016 viene presentato come strumento di riflessione operativa e di confronto permanente da mantenere in vita e rilanciare per stimolare un processo prezioso quanto raro di democrazia deliberativa