Practical trainings, student assistants and theses

Test of the HZDR baseline model in OpenFOAM

Student practical training / Bachelor theses / Master theses / Diploma theses / Student Assistant

Bubbly flows are commonly encountered in process and power industry. CFD has becoming a popular tool for studying such kind of flow configurations. The department of Computational Fluid Dynamics at HZDR has yearlong experience in modelling and simulation of bubbly flow. Need of closures as well as their insufficiency is a known issue in the Eulerian modelling of multiphase flow. To avoid uncertainties and inconvenience brought by arbitrary adjustment of models or model constants, a baseline model with a unified set of closures has been recently proposed for further development and evaluation of the models. It has been tested for a broad range of flow configurations flows in the commercial CFD code ANSYS CFX. With consideration of the recent achievements in OpenFOAM, it is intended to extend the validation in OpenFOAM.

Main tasks:
• Create a database and an overview of the test cases
• Prepare and run the test cases in OpenFOAM
• Analyse simulation results
• Extend the database by finding new suitable cases in the literature

Department: Computational Fluid Dynamics

Contact: Dr. Liao, Yixiang

Requirements

• Basic knowledge of fluid dynamics, numerical algorithm and CFD
• Systematic way of working
• Good C++ and other programming skills
• Good English in writing and reading
• Experience with OpenFOAM is an advantage

Conditions

• Duration: 4-6 months
• Begin: from now on

Online application

Please apply online: english / german

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A correlation of critical void fraction on/near the wall under the boiling crisis (CHF)

Student practical training / Master theses / Diploma theses / Student Assistant / compulsory internship

Nucleation boiling is commonly known as a most efficient way of transferring heat into a liquid, as it combines a large uptake of latent heat by the steam bubbles, convective transfer via bubble motion and a most effective mixing of the thermal boundary layers. However, when the heat flux becomes higher and reaches a critical value (CHF), parts of the heater surface become irreversibly covered by vapor and nucleation boiling turns into film boiling. In cases of power controlled heating this can potentially lead to a meltdown of the heater structure. Understanding and predicting the complex phenomena involved in the CHF is necessary for the efficient operation, safety and development of industrial applications like boiler, nuclear reactor, electronic/microchips system. However even with decades’ heavy investigations, the mechanism of forming CHF especially how the CHF is initiated from nucleation is still without a consensus explanation.
Recently a model of near critical heat flux (CHF-) is raised in our group, that is, the moment, when CHF is initiated, is inferred. This model gives to our opinion both a definite explanation on how CHF is initiated and secondly a quantitative value for the onset of CHF, which has been validated with a number of test cases from literature. Computational fluid dynamics (CFD) is an attractive way to support engineering design by 3D flow simulation in the future. It would be beneficial, if occurrence of CHF could be simulated with CFD codes. In last years an extended RPI model was developed and tested by ANSYS and HZDR CFD group together which requires the critical void fraction as a criterion. In the preliminary test, this value is set to 80% but which is confirmed should be case dependent.
The main tasks for this work are:
1. Simulate the multiphase flow in subcooled boiling process with standard RPI model where the CHF value calculated by CHF- model is considered as a input boundary condition.
2. Capturing the critical void fraction from the simulations.
3. Processing and analysis the captured results to generate an empirical correlations using MATLAB.
4. Applying the correlations to predict the boiling crisis with extended RPI model.

Department: Computational Fluid Dynamics

Contact: Dr. Ding, Wei

Requirements

1. Study of mechanical engineering, process engineering or similar
2. Knowledge of CFD
3. Basic knowledge of heat transfer
4. Knowledge of program/script language (e.g. MATLAB)

Conditions

Duration: >= 3 months
Begin: from now on

Online application

Please apply online: english / german

Druckversion


Erweiterung und Validierung von Simulationsmodellen für Mehrphasenströmungen in OpenFOAM

Bachelor theses / Master theses / Diploma theses / Student Assistant / compulsory internship

Die Anwendung von Methoden der CFD („Computational fluid dynamics“) für Scale-up und Intensivierung verfahrenstechnischer Prozesse bietet die Möglichkeit, Energie- und Ressourcen-effiziente Lösungen zu identifizieren, deren Untersuchung mit konventionellen halb-empirischen Methoden kostspielig und langwierig wäre. Eine solche Simulation im großtechnischen Maßstab ist im Rahmen der Euler-Euler Beschreibung möglich, in der die Prozesse auf der Skala einzelner Blasen modelliert werden.Von besonderem Interesse ist die Implementierung und Validierung solcher Modelle in Open-Source Software, die von industriellen Anwendern zunehmend genutzt wird.
Ein am HZDR entwickeltes Baseline-Modell für die Fluiddynamik von Blasenströmungen wurde bereits in OpenFOAM implementiert und validiert. Dies soll nun um die Betrachtung des Stofftransports erweitert werden. Entsprechende Modelle ebenso wie zur Validierung geeignete Testfälle sind aus früheren Untersuchungen verfügbar. Damit sind beste Voraussetzungen für ein zügiges Gelingen gegeben.

Die durchzuführenden Teilaufgaben umfassen:
• Implementierung der Modelle in OpenFOAM 5.0
• Vorstudien zur Auffindung geeigneter Simulations-Setups
• Durchführung von Simulationsrechnungen
• Auswertung und Dokumentation der Ergebnisse
• Diskussion der erzielten Übereinstimmung

Department: Computational Fluid Dynamics

Contact: Dr. Rzehak, Roland

Requirements

• Kenntnisse in Strömungsmechanik
• Kenntnisse in der Programmierung in C++ oder C
• Erfahrung mit OpenFOAM ist von Vorteil, kann aber bei entsprechendem Einsatz auch erworben werden
• Englischkenntnisse in Schrift und Wort
• Freude am wissenschaftlichen Arbeiten

Conditions

• Bearbeitungszeit: 4-6 Monate
• Beginn: Jan-Mar 2018
• Vergütung der Arbeit

Online application

Please apply online: english / german

Druckversion