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

Inviscid supersonic minimum length nozzle design

An aerospace vehicle is accelerated by a propulsion system to a given velocity. A nozzle is used to extract the maximum thrust from high pressure exhaust gases generated by the propulsion system. The nozzle is responsible for providing the thrust necessary to successfully accomplish the mission while its design efficiency translates to greater payload and reduction in propellant consumption. Specifically, the nozzle is that portion of the engine beyond the combustion chamber. Typically, the combustion chamber is a constant area duct into which propellants are injected, mixed and burned. Its length is sufficient to complete the combustion of the propellant before the nozzle accelerates the gas products. The nozzle is said to begin at the point where the chamber diameter begins to decrease. This paper exploits the De Laval nozzle, a convergent divergent nozzle invented by Carl De Laval toward the end of the 19th century, and it tries to give a practical procedure to design the nozzle of minimum length. The basic assumption made is that the boundary layer thickness is small compared to the characteristic length, i.e. nozzle radius, so that the nozzle flow field can be treated as inviscid for the purpose of designing the aerodynamic lines. Ones the aerodynamic lines are determined, a correction can be made to account for the displacement thickness of the boundary layer. This second step of the designing procedure is not treated in here. This basic procedure has been applied successfully to many supersonic nozzle

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

Flusso tridimensionale e viscoso nei ventilatori assiali: confronto fra risultati sperimentali e numerici

La conoscenza del flusso tridimensionale a valle della girante dei ventilatori assiali è di fondamentale importanza per valutare la distribuzione delle perdite fluidodinamiche nella macchina e per intervenire con proposte di modifiche della conformazione dei condotti palari in fase di progettazione. Per raggiungere questo obiettivo è particolarmente utile poter affiancare ai metodi di indagine sperimentale codici di calcolo evoluti ed affidabili. Per verificare la validità di tale impostazione nel presente lavoro si è effettuato il confronto fra i risultati dell’indagine sperimentale condotta con sonde ad alta risposta in frequenza e quelli derivanti dalla simulazione del flusso con un codice di calcolo su un ventilatore assiale di tipo industriale.The knowledge of detailed 3-D flow field downstream of rotor blade in industrial axial flow fan is important both to evaluate the aerodynamic losses and to improve the aerodynamic design of these machines. To achieve these goals it is very important to use a reliable fluid dynamic computational code. In this paper a comparison between experimental and numerical results downstream an axial fan are presented

Numerical simulation of premixed combustion flows: a comparative study

In this work four different commercial and research CFD codes have been compared for the simulation of two combustion test cases. The aim was to get an overview of the capabilities of these different tools to simulate combustion flows in premixed regimes. Codes tested were Fluent, CFX, StarCD and Tanit. Three combustion models have been applied, namely the Eddy Break Up, the Eddy Dissipation Model and the Turbulent Flame Closure, the turbulence model used being the standard k-epsilon. Numerical results have been found to fairly fit experiments and helped to show some drawbacks of combustion models. In its theoretically correct range of applicability the TFC model has been found to give the better agreement with experiments

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

Thermal insulation coating using natural stone powder-epoxy composite for room temperature reduction

The ability of a roof to absorb heat is crucial for maintaining temperature stability within a room. Therefore, natural material composite coatings utilization offers a viable option for modern roof development. This research investigates how using natural stone mixed with epoxy, and applied as a coating on a galvalume surface, influences thermal conductivity and reduces room temperature. Temperature measurements were collected around a small room with a composite-coated roof, utilizing different types of rock in the composition. Thermocouples were placed 20 cm above the roof's surface, attached to the roofing composite, positioned beneath the galvalume layer, and within the small room. The results demonstrate a reduction in thermal conductivity and room temperature when natural stone powder is added to the roof. Experiments using composite coatings with various stone types exhibit varying degrees of room temperature reduction. Consequently, this research concludes that the unique properties of natural stone can effectively lower the thermal conductivity of roofs and decrease room temperature

Development of a non-adiabatic premixed model into the Ares combustion code

The present report somehow represents the summa of the activities which have been carried out during the third and conclusive year of the project. In the necessity of modifying the original goal of the present task, has emerged. In fact, the research work carried out in has shown that the original adiabatic formulation of the TFC model was not sufficient to achieve a qualitatively and quantitatively fair description of the fluid dynamic fields (velocity and temperature) inside a combustion chamber whenever the energy diffusion phenomena cannot be neglected, which is the case in the actual industrial burners. In the same report it was discussed the how the TFC model formulation could be modified in order to take into account the diffusion of thermal energy, and the non adiabatic version of the TFC model available in the code Fluent was tested against the ENSMA experimental combustor test case. The obtained results were such to make advisable to reformulate the original conclusive task of the project in order to implement the non adiabatic version of the TFC model into the codes Ares

Implementazione e utilizzazione di modelli di turbolenza avanzati in un codice CFD per il calcolo del flusso nei ventilatori assiali

Dottorato di ricerca in progettazione meccanicaConsiglio Nazionale delle Ricerche - Biblioteca Centrale - P.le Aldo Moro, 7, Rome; Biblioteca Nazionale Centrale - P.za Cavalleggeri, 1, Florence / CNR - Consiglio Nazionale delle RichercheSIGLEITItal

Vento di Sardegna. Messa a punto del codice di calcolo cfd rans

Il presente documento illustra i risultati ottenuti nell’ambito dell’attività 1.3 dell’Obiettivo Realizzativo 1 del progetto Vento di Sardegna: “messa a punto e integrazione dei diversi software per la simulazione”. In particolare viene presentato il lavoro svolto per la realizzazione dell’attività di messa a punto del codice di calcolo CFD RANS. L’attività di analisi fluidodinamica fatta mediante l’uso del calcolo nell’ambito del progetto di ricerca costituisce di fatto una sorta di galleria del vento virtuale. Allo stesso modo di ogni altro strumento di analisi, anche il codice di simulazione necessita di una fase di “taratura”. In altre parole, per lo specifico problema e per le specifiche condizioni di flusso, si deve cercare di ottimizzare l’insieme dei parametri della simulazione (estensione del dominio di calcolo, condizioni al contorno, dimensione della griglia, modellistica fisica utilizzata), al fine di avere uno strumento in grado non solo di riprodurre le evidenze sperimentali in condizioni note, ma anche di fornire utili indicazioni per lo sviluppo di nuove soluzioni progettuali