Magnetic Resonance Velocimetry for Unsteady Flows

Magnetic Resonance Imaging (MRI) is an established tool for clinical diagnostics. The measurement technique can be used to measure blood flow, then denoted Flow MRI or Magnetic Resonance Velocimetry (MRV). MRV has in recent years also found increasing consideration in the field of fluid mechanics, where it is esteemed for its unique capabilities of measuring fully volumetric velocity fields without the need for optical access and without manipulating the flow under investigation. MRV is typically used for the acquisition of mean velocity fields in water flows. This study deals with the possibility of acquiring velocity fields in steady, unsteady and turbulent flows. Besides the application of the different MR techniques in selected test cases, validation of the acquired measurement data is a main topic of this thesis. Mean flow measurements are acquired within steady flow model of a modern IC engine. The acquired flow data is validated by means of PIV data and excellent agreement is found. The three-dimensional nature of the acquired flow field enables new insights into the volumetric flow field distribution. Unsteady periodic flows are analyzed by means of the 4D MRV measurement sequence,which acquires phase-averaged, volumetric velocity fields. The acquired flow data is extensively validated by means of Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) data and valid flow regions are identified. A comprehensive understanding of the unsteady, periodic flow field evolution during intake stroke is enabled for the measurements inside the modified engine flow model. MR turbulence measurements, for the acquisition of normal and shear stresses within the flow field, are conducted within a Backward Facing Step (BFS) geometry, which provides optical access for comparative LDV validation measurements through a perspex insert. MR turbulence measurements inside the engine flow model demonstrate the potential of the measurements regarding their application in complex geometries. Validation of the measurements shows a reasonable agreement for normal stresses, while the determination of shear stresses remains still rather inaccurate

Magnetic Resonance Velocimetry for Unsteady Flows

Magnetic Resonance Imaging (MRI) is an established tool for clinical diagnostics. The measurement technique can be used to measure blood flow, then denoted Flow MRI or Magnetic Resonance Velocimetry (MRV). MRV has in recent years also found increasing consideration in the field of fluid mechanics, where it is esteemed for its unique capabilities of measuring fully volumetric velocity fields without the need for optical access and without manipulating the flow under investigation. MRV is typically used for the acquisition of mean velocity fields in water flows. This study deals with the possibility of acquiring velocity fields in steady, unsteady and turbulent flows. Besides the application of the different MR techniques in selected test cases, validation of the acquired measurement data is a main topic of this thesis. Mean flow measurements are acquired within steady flow model of a modern IC engine. The acquired flow data is validated by means of PIV data and excellent agreement is found. The three-dimensional nature of the acquired flow field enables new insights into the volumetric flow field distribution. Unsteady periodic flows are analyzed by means of the 4D MRV measurement sequence,which acquires phase-averaged, volumetric velocity fields. The acquired flow data is extensively validated by means of Particle Image Velocimetry (PIV) and Laser Doppler Velocimetry (LDV) data and valid flow regions are identified. A comprehensive understanding of the unsteady, periodic flow field evolution during intake stroke is enabled for the measurements inside the modified engine flow model. MR turbulence measurements, for the acquisition of normal and shear stresses within the flow field, are conducted within a Backward Facing Step (BFS) geometry, which provides optical access for comparative LDV validation measurements through a perspex insert. MR turbulence measurements inside the engine flow model demonstrate the potential of the measurements regarding their application in complex geometries. Validation of the measurements shows a reasonable agreement for normal stresses, while the determination of shear stresses remains still rather inaccurate