|Tipo di tesi||Tesi di dottorato di ricerca|
|Titolo||Sviluppo di modelli numerici e metodi sperimentali per l’analisi di flussi multifase in componenti per trasmissioni di potenza HVT ad alta efficienza energetica in applicazioni off-highway|
|Titolo in inglese||Development of numerical models and experimental methodologies for the analysis of multi-phase flows in components for high efficiency HVT power transmissions of off-highway vehicles|
|Settore scientifico disciplinare||ING-IND/09 - SISTEMI PER L'ENERGIA E L'AMBIENTE|
|Corso di studi||INGEGNERIA DELL'INNOVAZIONE INDUSTRIALE|
|Data inizio appello||2018-03-09|
|Disponibilità||Accessibile via web (tutti i file della tesi sono accessibili)|
Oggetto del lavoro di tesi è lo sviluppo di metodologie sperimentali e numeriche per l’analisi dei flussi multifase che caratterizzano i componenti per trasmissioni di potenza HVT ad alta efficienza energetica in applicazioni off-highway. Il fluido utilizzato per il processo di lubrificazione di tali componenti è infatti fortemente multi-fase, in quanto l’olio si miscela con l’aria presente al loro interno influenzando significativamente il comportamento meccanico e termico della trasmissione.
The object of this thesis is the investigation of the multiphase flow, which develops inside high efficiency HVT power transmissions components of off-highway vehicle, during the lubrication process. Objective of this thesis is the development of both experimental and numerical methodologies for the analysis of multi-phase flows within high efficiency HVT power transmissions for off-highway vehicles. The lubricating fluid is in fact often a mixture between oil and air within the components and the multi-phase nature of the flow influences significantly the mechanical and thermal behavior of the transmission. The study focuses on the multi-phase flow that characterizes wet-clutches and different methodologies are adopted for the prediction of the lubricating fluid distribution: experimental measurements on test rigs, multi-dimensional CFD analysis and lumped and distributed parameter numerical modeling. The experiments are initially carried out on industrial test rigs for fatigue testing of the whole transmission. Using this approach, several quantities can be directly measured, but the test rigs are usually expensive due to high capital costs, advanced control systems, time needed for testing; furthermore, it is extremely difficult to obtain measurements of the flow within the single component and to characterize the mixing process between lubricant and air. In fact, the multi-phase flow that develops within the wet-clutches makes it difficult to determine the flow pattern in the components and the complex geometry as well as the demanding operating conditions limits greatly the non-intrusive observation of the internal flow. Thus, new experimental methodologies are developed for the direct measurement of the flow distribution within wet clutches. A test rig equipped with transparent components is designed and used for reproducing as accurately as possible the real geometry of the clutch and run it under actual operating conditions. Fast imaging techniques are adopted for the measurement of the flow pattern within the component. The wet-clutches multi-phase flow within the HVT transmission is also analyzed by means of CFD simulation of the entire geometry. In order to accurately model the complex geometry, a modular approach is proposed for address the real fluid dynamics behavior. Multidimensional modeling demonstrates to be in good agreement with the measurements in terms of flow distribution and multi-flow field behavior. Even though this approach is very accurate in predicting the flow within the real geometry, the computational effort is remarkable and it can be employed only for a component focused analysis under specific operations. The CFD modeling of the entire systems for a sensitivity analysis with respect to varying operating conditions would be too demanding in terms of both computational resources and calculation time. Therefore, the thesis’s work is also focused on the development of lumped and distributed parameter numerical models for the simulation of the multi-phase flow under this modeling framework. The proposed models are characterized by a limited computational effort while predicting the flow pattern within a single component interacting with the whole system. The proposed models are implemented within the open source OpenModelica platform. The developed models accounts for the 3D nature of the flow by assuming a quasi 3D discretization of the fluid domain and the interface between the fluids is tracked by means of the PLIC (Piecewise Linear Interface Calculation) approach and of the balance of the centrifugal and gravitational forces acting on the flow. The implemented lumped and distributed models demonstrate to predict accurately the results obtained with both measurements and CFD calculations.