Student Theses

The flow near the stability limit shows unstationary phenomena. The aim of the investigations is to calculate these phenomena using CFD and to compare the results with experimental data.

Supervisors: Maiken Günther, Daniel Nagel

Type: Numerical

The aim of this thesis is to investigate the influence of mistuning on the flow of an axial compressor blisk. Mistuning is a specific effect that can occur in blade vibrations due to manufacturing inaccuracies in the rotor. This effect will be transferred to transient CFD simulations using Ansys CFX and compared with experimental data. Experience with Ansys FE and CFX is recommended but not essential.

Supervisors: Maiken Günther

Type: Numerical

The objective of this thesis is to numerically simulate a radial compressor test stand in closed-loop operation, including all components. In addition to the radial compressor, this includes the piping, a stilling chamber, a heat exchanger and a throttle. The CFD simulations are to be performed in steady-state conditions using Ansys CFX. The objective is to compare the results with a reduced model that includes only the radial compressor.

Supervisors: Maximilian Steffens, Max Bartholet

Type: Numerical

Introduction

In the development of modern turbomachinery, High Cycle Fatigue (HCF) induced by blade vibrations poses a major challenge for component lifetime. One approach to reduce vibration amplitudes—and thus the HCF ratio—is "Intentional Mistuning." This involves deliberately replacing the ideal, cyclically symmetric blading ("Tuned") with blades that have slight, targeted geometric deviations. While the structural dynamic goal of this specific geometry is to reduce the HCF ratio, it is essential to simultaneously investigate how these modifications affect the fluid flow. The goal is to evaluate purely the aerodynamic impact of these intentional geometric deviations using CFD. A structural mechanical calculation of the HCF ratio is not required here.

Tasks

In this study, two different blade geometries must be simulated and compared. For the intentionally mistuned blade geometry, an unstructured computational mesh must be generated using Cadence Hexpress, and a mesh independence study must be conducted. Subsequently, steady-state flow simulations are to be performed in Cadence FINE/Open. For a second, ideal baseline geometry ("Tuned"), a structured AutoGrid mesh already exists; a steady-state simulation must also be performed for this mesh. The objective is to present a detailed comparison of the results from both blade geometries and analyze how the flow field and the operating point of the machine change due to the mistuning.

Zusammenfassung

• Literature review on intentional mistuning and its aerodynamic effects
• Mesh generation (unstructured) in Cadence Hexpress for the mistuned geometry
• Execution of a systematic mesh independence study
• Performance of steady-state CFD simulations in Cadence FINE/Open
• Reference simulation using the existing structured AutoGrid mesh (tuned geometry)
• Detailed aerodynamic analysis of the flow field and losses
• Comparison of the operating points of both geometries

Kontaktdaten:

Abhishekkumar Shingala, M.Sc.

Tel.:             0711-685-69430

E-Mail:        abhishekkumar.shingala@itsm.uni-stuttgart.de

Introduction

In a traditional radial turbocharger, the shaft is supported by two journal bearings and one thrust bearing. These can be either oil-lubricated journal bearings or gas bearings. To perform a so-called pre-stressed modal analysis of the entire rotating system—which includes the turbine wheel, compressor wheel, and the shaft—precise values for the stiffness (Kxx, Kxy, Kyy, Kyx) and damping coefficients (Cxx, Cxy, Cyy, Cyx) must be determined. Because these values vary with rotational speed, the stiffness and damping parameters must be evaluated as a function of speed. This can be accomplished using CFD simulations. The resulting coefficients can subsequently be utilized to perform an accurate pre-stressed modal analysis of the entire rotor system, revealing system modes within the Campbell diagram and highlighting new resonance locations.

Tasks

This study requires a literature review on bearing designs. A basic CAD model of a suitable and realistic bearing must be created, followed by a detailed literature review on the modeling methodology. The objective is to perform a detailed CFD simulation and calculate the stiffness and damping coefficients. This can be computed for various configurations and bearing types, such as gas bearings or journal bearings. Realistic boundary conditions must be selected from the literature and a detailed analysis carried out.

Summary

• Literature review on bearing modeling methods
• Selection of a suitable ANSYS tool to perform the CFD simulation
• Selection of design parameters and boundary conditions
• Execution of simulations at various rotational speeds
• Determination of stiffness and damping coefficients
• Execution of a pre-stressed modal analysis (optional)
• Generation of Campbell diagrams (optional)
• Determination of new resonance locations (optional)

Contact Details:

Abhishekkumar Shingala, M.Sc.

Tel.:             0711-685-69430

E-Mail:        abhishekkumar.shingala@itsm.uni-stuttgart.de

Introduction

As the mobility and energy sectors transition toward zero-emission technologies, radial turbines are increasingly being deployed in novel applications such as Hydrogen Internal Combustion Engines (H2-ICE), Proton Exchange Membrane Fuel Cells (PEMFC), and alternative fuel blends (e.g., E100). These new applications fundamentally change the thermodynamic properties and density of the working fluid. A turbine geometry that is structurally safe in standard diesel exhaust may fail in a hydrogen or fuel cell environment due to critical shifts in aerodynamic forcing (wake excitations) and aerodynamic damping caused by High Cycle Fatigue (HCF). To prevent this, the aeroelastic behavior of turbines across different fluid media must be thoroughly understood.

Tasks

This study begins with a detailed literature review regarding thermodynamic fluid properties (such as H2-ICE exhaust, humid PEMFC air, and alternative fuels). Next, you will familiarize yourself with an existing, validated Cadence simulation environment and implement the corresponding real-gas and multi-component fluid models. In the main part of the thesis, you will use this setup to perform aerodynamic forcing and damping simulations (Forced Response and Aerodamping) for a baseline radial turbine across the various fluid cases. The goal is to evaluate how the respective working fluid alters the alternating stresses and HCF ratio, and to derive concrete aerodynamic and structural design guidelines for the design of future turbines.

Summary

• Literature review on fluid properties of H2-ICE exhaust, humid PEMFC air, and E100
• Familiarization with the existing Cadence setup for forced response and aerodamping analyses
• Implementation of the required fluid models into the simulation environment
• Execution of aerodynamic forcing and damping simulations for the different fluids
• Evaluation of aerodynamic forcing, damping, and alternating stresses
• Assessment of the impacts on the HCF safety margin
• Derivation of design guidelines for turbomachinery design in novel fluid media

Contact Details:

Abhishekkumar Shingala, M.Sc.

Tel.:             0711-685-69430

E-Mail:        abhishekkumar.shingala@itsm.uni-stuttgart.de

In transonic flow conditions, a shock wave exists within the rotor passages. This shock wave hits the trailing edge of the IGV blades, which are located upstream of the rotor. The aim of this thesis is to investigate the influence of this IGV-rotor interaction on compressor performance using numerical analysis. Please confirm the flow field obtained from the numerical analysis and investigate its impact on performance.

Supervisors: Toshihiko Azuma

Type: Numerical