Development of a partially premixed combustion model

In this work, a possible extensions of the TFC model to imperfectly premixed cases has been introduced and validated, even if in a purely qualitative way. The proposed IPM model has given results physically consistent and it seems able to describe in more correct terms actual combustor, in which it is far from real any assumption of having perfectly premixed mixtures feeding the combustion chamber. Nevertheless, a proper validation of the proposed IPM model and of the TFC model over a realistic industrial case is still to come and it will be an essential part of the future work. Finally, the quite general lines of how to get a partially premixed model (premixed plus diffusion) have been drawn, showing that, in principle, no new modeling is needed and that it would be probably enough to assembly already existent premixed and diffusion models. The actual implementation of the idea above into ARES could be also a future development of this work

Development and implementation of turbulence models in the combustion code Ares

This report describes the R&D activities carried out under the ENEA-MURST programme , objective 4. Three more turbulence models (the RNG K – ε, the one-equation Spalart & Allmaras and the Wilcox K – ω) have been implemented into the Ares combustion code. They represent state-of-the-art models that have demonstrated over the past decade their superior accuracy , robustness as well as ease of implementation with respect to the class of K – ε models. The first chapter describes the models formulations. In chapter 2 the three models have been validated against three well known test cases. Particular attention has been dedicated to coupling the one-equation turbulence model by Spalart & Allmaras to the TFC premixed combustion model, for two computed turbulence scales are needed to evaluate the turbulent flame velocity and one-equation models provide one turbulent scale only. For validating the correct models implementations, two simple cold test cases have been chosen, namely the turbulent boundary layer over a flat plate, and a well documented turbulent flow over a backward facing step. Finally the Moreau combustor test case have been used for the validation of the models for premixed combustion flow. The state-of-the-art turbulence models implemented should allow the combustion code Ares to increase its ability to correctly compute complex turbulent premixed reactive flows in real combustors, which is the objective of the next project tasks

Numerical simulations on the TEFLU sodium jet experiment using the CFD code Karalis

The TEFLU experiments were performed at the Karlsruhe Forschungszentrum in order to investigate the behaviour of a low-Prandtl number jet under various flow condition, from forced flow to purely buoyant. Here, numerical simulations are presented and results compared with the experimental data. The computation are made within the Benchmark Working Group activities in order to test the capabilities of CFD codes to simulate Heavy Liquid Metal flows with heat transfer. The simulation are performed with the CFD code Karalis

Assessment of fission fragments enhancement for nuclear thermal propulsion

A novel concept of Nuclear Thermal Rocket (NTR) propulsion is presented. It is based onthe direct conversion of the kinetic energy of the Fission Fragments (FFs) into the propellantenthalpy. The FFs can escape from an extremely thin layer of fissionable material: a sufficiently large surface coated with few micrometers of Americium 242m, confined by a neutron diffuser, may become a critical reactor. The novel FF NTR propulsion concept may allow the propellant to achieve temperatures higher than the nuclear fuel, thus overcoming the limit in the specific enthalpy achievable by the propellant in the conventional solid-core NTR propulsion. Such a limit comes from the need to keep the temperature of the fuel material within a safe interval by using conventional convective heat transfer mechanism. A preliminary assessment of the FF NTR concept’s propulsion characteristics has been carried out using an in-house developed software system which integrates a Computational Fluid Dynamic code, a neutronic code and a Monte Carlo code. The assessment shows the potential to reach specific impulses of about 15,000 m/s and thrust levels in the range 4,000 to 6,000 N, with a trhust to weight ratio of a few percent of the acceleration of gravity. Such performances may make the FF propulsion a candidate for human missions to the planet Mars.645-652Pubblicat

Assessment of the boussinesq approximation for buoyancy-driven flows

The numerical simulation of buoyant flows often makes use of the Boussinesq approximation. This is particularly true when Direct Numerical Simulation is used for the analysis of heat transfer loops or other applications of natural convection flows. Boussinesq approximation consists of considering the density strictly constant, adding the buoyant force to the momentum balance and coupling an equation for the temperature to the incompressible Navier-Stokes system that has to be solved. In this paper, the validity of the Boussinesq approximation is investigated in some details via numerical simulations. The test cases chosen include a differentially heated cavity and two buoyant heated loops with internal heating. Results show clearly that the error on some performance parameters depends linearly on the compressibility parameter βΔΤ The error in some cases can be 20% or higher, but it is drastically reduced to a few percent by the use of a 2ⁿͩ order formulation of the Boussinesq source term. Nevertheless, some flow features are strictly tied to the compressible coupling and are not captured in a Boussinesq framework

The CFD code karalis

Karalis is a paralle MPI, Finite-Volume, multiblock CFD code which solves the fully compressible Euler and Navier-Stokes equations where all couplings between dynamics and thermodynamics are allowed. This the most general mathematical model for all fluid flows. The code solves the coupled system of continuity, momentum and full energy equation for the velocity components, pressure and temperature. Once, u, v, w, p are and T are updated, arbitrary thermodynamics is supplied. The second order Roe’s upwind TVD scheme is used to compute convective fluxes through the Finite-Volume cell interfaces. A V-cycle Coarse Grid Correction Multi-Grid algorithm is used, together with a 5-stage Runge-Kutta explicit time-marching method, to accelerate convergence to a steady state. This formulation, typical of aerodynamic flows, shows an eccellent efficiency even for incompressible flows as well as for flows of incompressible fluids (typically buoyancy flows), once equipped with a preconditioner. Merkel’s preconditioner has been chosen because it can be easily formulated for arbitrary equations of state given as a functional relation of two independent thermodynamic variables (typically the pressure p and the temperature T), or even in tabular form, read in as an input file and used with bilinear interpolation. Karalis implement two among the most popular turbulence models, namely the one-equation model by Spalart and Allmaras and the two-equations model by Wilcox, the k-ω model, which allow a good compromise between accuracy, robustness and stability of turbulent calculations. Code validation is presented for some typical benchmark test cases of incompressible fluid dynamics. Comparison with solutions obtained with a few popular commercial CFD codes is also presented

Displacements of an Active Moderately Rapid Landslide\u2014A Dataset Retrieved by Continuous GNSS Arrays

This paper describes a dataset of continuous GNSS positioning solutions referring to slope movements in the Ca’ Lita landslide (Northern Apennines, Italy). The dataset covers the period from 24 March 2016 to 17 July 2019 and includes time-series of the daily position of three GNSS rovers located in different parts of the landslide: head zone, upper track zone, and lower track zone. Two different types of continuous GNSS arrays have been used: one is based on high-end Leica geodetic receivers, and the other is based on low-cost effective Emlid receivers. Displacements captured in the dataset are up to more than a hundred meters and are characterized by prolonged phases of slow movement and moderately rapid acceleration phases. The data presented in this contribution were used to underline slope processes and validate displacements retrieved by the application of digital image correlation to a stack of a satellite images

FE modelling of the Streicker Footbridge

The Streicker footbridge was completed in 2010 at the Princeton University Campus, over the Washington Road. It is about 104 m long and consists of a central main span supported by a steel arch and four lateral approaching legs. The deck is a post-tensioned high-performance concrete girder. Steel columns with “Y” shape support four lateral legs that connect the bridge to the lateral bearings on the ground and the whole system results a slender varying cross section main girder. The original shape in the horizontal plane provides horizontal stability to the footbridge despite the intrinsic slenderness of the steel supporting columns. Vertical stability is provided also by the arch in the central main-span and by the supporting columns under the legs. Cross section width increases from the midpoint of the main span to the connections with the legs and then remains constant up to the ground bearings. This work is focused on the development of a finite element analysis of the footbridge at different levels of refinement from the essential implementation of beam elements to more refined FE solutions for the prestressed concrete deck. The models are identified with respect to the available operational modal parameters. This deck discretization could further allow simulating the motion of a running/walking pedestrian along different trajectories

Systematic Review and Meta-Analysis of Health-Related Quality of Life in Patients with β-Thalassemia Underwent Hematopoietic Stem Cell Transplantation

Abstract: Background: β-Thalassemia major (β-TM) represents one of the most important hemoglobinopathies worldwide. Remarkable improvements have been achieved in supportive therapy based on blood transfusions and iron chelation, and nowadays, this approach is capable of assuring a long life in these patients in industrialized countries. The only curative treatment is represented by hematopoietic stem cell transplantation (HSCT). However, this treatment may be burdened by deterioration in the Health-Related Quality of Life (HRQoL). This paper aimed to evaluate the role of HRQoL in transplanted β-TM patients with a systematic review and meta-analysis. Methods: PubMed database, Web of Science, and Scopus were systematically searched for studies published between January 1st, 2000 to September 2020. The following terms were entered in the database queries: β-thalassemia, HRQoL, and HSCT. The study was carried out according to the Preferred Reporting Items for Systematic and Meta-analyses (PRISMA) statement. Results: We identified a total of 33 potential studies. Among these, 10 were finally considered in the systematic review and 5 in the meta-analysis. Overall, good scores in the principal domains of HRQoL were reported by transplanted patients. These data were confirmed by results of meta-analysis that showed significant difference between transplanted and β-TM patients treated with conventional therapy in the physical and emotional dimension, with a medium effect size [d=0.65, 95% CI (0.29-1.02), z = 3.52, p =0.0004, I2 =75%; and d=0.59, 95% CI (0.43-0.76), z = 6.99, p <0.00001,I 2 =0%, respectively]. Conclusion: HRQoL is generally good in β-TM transplanted patients and may significantly contribute in deciding whether or not to transplant a β-TM patient treated with conventional therapy