Validation of flow topologies within rotary Ventricular Assist Devices (VADs) remains challenging due to small geometric dimensions of these pumps. Blood damage induced by VADs is suspected to be correlated to local flow patterns and therefore numerical simulation techniques established as a powerful tool for investigating local flow phenomena. Consequently, deep understanding of these flow fields contributes significantly to the design of blood-preserving Ventricular Assist Devices and increase life span of affected patients.
Different methods for verification of numerical simulations are available, but validations of applied turbulence models have so far been lacking. To close this knowledge gap, it is essential to examine flow fields inside a rotary blood pump by optical investigations. To realize optical accessibility for investigation of flow fields, and to validate turbulence models, it is necessary to abandon drive and bearing/suspension originally used in appropriate VAD designs. To draw reliable conclusions about hydraulic and mechanical characteristics, precise and reproducible investigations with low measurement uncertainty are mandatory. Only very accurate experimental results can be used to validate numerical simulations due to geometrical dimensions, constraints on manufacturing techniques, sensor accuracies, and materials.
In this paper a methodology is presented how to design the bearing/suspension of the impeller to fulfill mandatory requirements needed for validation of flow topologies. Furthermore, Gaussian Error Propagation is used to quantify achieved precision and reproducibility.
The unique magnetic properties of magnetic nanoparticles (MNP) combined with their small size already led to numerous medical applications. Accurate determination of their magnetic properties is a key requirement enquired by users, that is impeded by the ever-present distribution of MNP sizes. Field flow fractionation (FFF) techniques may help to overcome these limitations by first separating the particles before characterization. In this study, we demonstrate the use of centrifugal FFF coupled to online detectors for fractionation, structural, and magnetic characterization of MNP. The primary goal is to establish a reproducible centrifugal FFF (CF3) method for MNP fractionation We show that CF3 has the same capability as other FFF techniques in resolving the bimodal hydrodynamic size distribution present in the commercial MNP system Resovist® but is faster and more straightforward through its technical approach.
Rotating Instability (RI) induces noise, triggers blade vibrations and is a potential indicator for critical operating conditions in axial compressors. Despite numerous studies, the source of RI is not completely understood. The objective of the present study is to give further insight into the basic mechanism of RI by means of advanced Stereo High-Speed Particle Image Velocimetry (PIV) applied to an annular compressor cascade without clearance. In particular, results of the PIV measurements visualize the predominant flow mechanism corresponding to RI. The experiments were conducted at an inflow Mach number of Ma = 0.4. Additional reference sensors captured the time-resolved pressure fluctuations synchronously to the optical measurements. By using correlation techniques between the PIV flow field and the reference sensor data, discrete vortex structures corresponding to the RI modes could be identified and localized. As a verification of the PIV results, the steady PIV flow velocity vectors are compared to results from an oil flow visualization technique. Overall, the present investigations point out that the general flow mechanism of RI is similar in compressor cascades with and without tip clearance. KEYWORDS ANNULAR CASCADE, COMPRESSOR, CIRCUMFERENTIAL MODES, ROTATING INSTABILITY, STEREO HIGH-SPEED PIV, UNSTEADY VORTEX STRUCTURES NOMENCLATURE f frequency i incidence m mode order Ma Mach number p pressure r radius Re Reynolds number u, v, w velocity components in x,y,z direction , , velocity fluctuation components in x,y,z direction
At the Department of Fluid System Dynamics, within the Collaborative Research Centre 1029 funded by the German Research Foundation (DFG), the influence of the rotor-stator interaction by four adaptive blade systems is studied. Using the adjustable stator vane, moveable stator vane, Gurney flaps and piezo actuators the flow losses are decreased by reducing the incidence. Therefore experimental investigations are carried out in a cascade, integrated in a water channel by means of the High-Speed PIV and time-resolved pressure measurement. The presented investigations show an enlargement of the operating range by using Gurney flaps in a rotating system and the adjustable front flap.
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