Pressure-relief valves are safety devices widely used in industrial applications to prevent that the working-fluid operating pressure exceeds the safety levels. Due to their significance they have been addressed by several studies and publications aimed at analyzing the flow field during relieving conditions. In those studies, based on CFD simulations, the difficulty in rendering the complex internal shape of the valves has been bypassed by means of two-dimensional axisymmetric meshes, or three-dimensional unstructured grids generated using commercial codes. The current thesis work, based on an internship at AST S.p.A. Company, pursues the goal of realizing for the first time in scientific literature a three-dimensional model of a spring-loaded pressure-relief safety valve on a structured grid for CFD analyses run with an open source code. The work is carried out using OpenFOAM, an open-source toolbox comprising utilities for mesh generation, calculation setup and solution. Following the creation of the three-dimensional model of the valve to be analyzed, attention is being focused on the complexity of generating a three-dimensional structured mesh and how some obstacles have been taken on exploiting the Company’s experience and the tools offered by OpenFOAM. After generating a satisfactory grid, a calculation for the transient simulation of a compressible flow of air is set up. Not only do the outcomes of the analysis highlight the supersonic nature of the flow within the valve, but also allow to study the behavior of an open source code for industrial applications, proving its suitability. Further simulations examine in depth the effect of the turbulence model and the numerical schemes on the solution, pointing out that the best accuracy is reached with second-order schemes and k-epsilon turbulence model. Eventually, the numerical results of the simulation have been validated by experiments that prove their reliability.
Le valvole di scarico sono dispositivi di sicurezza ampiamente utilizzati in ambito industriale per evitare che la pressione di esercizio superi i livelli di sicurezza. Data la loro importanza sono state oggetto di svariati studi e pubblicazioni mirati ad analizzare il campo di moto durante le condizioni di funzionamento. In questi studi, basati su simulazioni CFD, la difficoltà di riprodurre la complessa geometria interna delle valvole è stata aggirata tramite mesh bidimensionali con geometrie assialsimmetriche, o griglie tridimensionali non strutturate generate tramite codici commerciali. Il presente lavoro di tesi, basato su un’esperienza di tirocinio per conto dell’azienda AST S.p.A., si pone come obiettivo quello di realizzare per la prima volta nella letteratura scientifica un modello tridimensionale di una valvola di sicurezza a molla su griglia strutturata per analisi CFD eseguite tramite un codice open source. Il lavoro è svolto utilizzando OpenFOAM, un pacchetto software open-source che offre strumenti per generare mesh, impostare calcoli CFD e risolverli. Dopo aver riprodotto il modello tridimensionale contenente la geometria della valvola da analizzare, l’attenzione è focalizzata sulla complessità di realizzare una mesh strutturata tridimensionale e su come talune criticità siano state affrontate sfruttando l’esperienza dell’azienda e gli strumenti messi a disposizione da OpenFOAM. A seguito della generazione di una griglia soddisfacente, viene messo a punto un modello di calcolo per la simulazione transiente di un flusso comprimibile di aria. I risultati dell’analisi non solo evidenziano la natura supersonica del flusso all’interno della valvola, ma permettono anche di studiare il comportamento di un codice open source per un’applicazione industriale confermandone l’adeguatezza. Ulteriori simulazioni approfondiscono l’effetto del modello di turbolenza e degli schemi numerici sulla soluzione del calcolo, sottolineando come la migliore accuratezza si ottenga con schemi del secondo ordine e modello di turbolenza k-epsilon. Infine, i risultati numerici dell’analisi sono stati validati tramite prove sperimentali che ne confermano l’affidabilità.
Development of a CFD model to simulate the compressible flow within a pressure-relief safety valve
BANFI, RICCARDO ATTILIO
2018/2019
Abstract
Pressure-relief valves are safety devices widely used in industrial applications to prevent that the working-fluid operating pressure exceeds the safety levels. Due to their significance they have been addressed by several studies and publications aimed at analyzing the flow field during relieving conditions. In those studies, based on CFD simulations, the difficulty in rendering the complex internal shape of the valves has been bypassed by means of two-dimensional axisymmetric meshes, or three-dimensional unstructured grids generated using commercial codes. The current thesis work, based on an internship at AST S.p.A. Company, pursues the goal of realizing for the first time in scientific literature a three-dimensional model of a spring-loaded pressure-relief safety valve on a structured grid for CFD analyses run with an open source code. The work is carried out using OpenFOAM, an open-source toolbox comprising utilities for mesh generation, calculation setup and solution. Following the creation of the three-dimensional model of the valve to be analyzed, attention is being focused on the complexity of generating a three-dimensional structured mesh and how some obstacles have been taken on exploiting the Company’s experience and the tools offered by OpenFOAM. After generating a satisfactory grid, a calculation for the transient simulation of a compressible flow of air is set up. Not only do the outcomes of the analysis highlight the supersonic nature of the flow within the valve, but also allow to study the behavior of an open source code for industrial applications, proving its suitability. Further simulations examine in depth the effect of the turbulence model and the numerical schemes on the solution, pointing out that the best accuracy is reached with second-order schemes and k-epsilon turbulence model. Eventually, the numerical results of the simulation have been validated by experiments that prove their reliability.File | Dimensione | Formato | |
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https://hdl.handle.net/10589/150337