Oleksandr Barannyk

The influence of the aortic root geometry on flow characteristics of a prosthetic heart valve.

In this paper, performance of aortic heart valve prosthesis in different geometries of the aortic root is investigated experimentally. The objective of this investigation is to establish a set of parameters, which are associated with abnormal flow patterns due to the flow through a prosthetic heart valve implanted in the patients that had certain types of valve diseases prior to the valve replacement. Specific valve diseases were classified into two clinical categories and were correlated with the corresponding changes in aortic root geometry while keeping the aortic base diameter fixed. These categories correspond to aortic valve stenosis and aortic valve insufficiency. The control case that corresponds to the aortic root of a patient without valve disease was used as a reference. Experiments were performed at test conditions corresponding to 70 beats/min, 5.5 L/min target cardiac output, and a mean aortic pressure of 100 mmHg. By varying the aortic root geometry, while keeping the diameter of the orifice constant, it was possible to investigate corresponding changes in the levels of Reynolds shear stress and establish the possibility of platelet activation and, as a result of that, the formation of blood clots.

Investigation of Diametral Acoustic Modes in a Model of a Steam Control Gate Valve

The objective of the present study is to provide an insight into mechanism of coupling between turbulent pipe flow and partially trapped diametral acoustic modes associated with a shallow cavity formed by the seat of a steam control gate valve. First, the effects of the internal pipe geometry immediately upstream and downstream of the shallow cavity on the characteristics of partially trapped diametral acoustic modes were investigated. The mode shapes were calculated numerically by solving a Helmholtz equation in a three-dimensional domain corresponding to the internal geometry of the pipe and the cavity. Second, the set of experiments were performed using a scaled model of a gate valve mounted in a pipeline that contained converging–diverging sections in the vicinity of the valve. Acoustic pressure measurements at three azimuthal locations at the floor of the cavity were performed for a range of geometries of the converging–diverging section and inflow velocities. The experimentally obtained pressure data were then used to scale the amplitude of the pressure in the numerical simulations. The present results are in good agreement with the results reported in earlier studies for an axisymmetric cavity mounted in a pipe with a uniform cross-section. The resonant response of the system corresponded to the second diametral mode of the cavity. Excitation of the dominant acoustic mode was accompanied by pressure oscillations corresponding to other acoustic modes. As the angle of the converging–diverging section of the main pipeline in the vicinity of the cavity increased, the trapped behavior of the acoustic diametral modes diminished, and additional antinodes of the acoustic pressure wave were observed in the main pipeline.

Effect of transverse perforations on fluid loading on a long, slender plate at zero incidence

Abstract This paper reports the results of experimental investigations of flow-induced loading on perforated and solid flat plates at zero incidence with respect to the incoming flow. The plates had a streamwise length to transverse thickness ratio of 23.5. The effect of the perforations was investigated for three different perforation diameters. The results corresponding to the perforated plates were compared with the reference case of the solid plate (no perforations) at five inflow velocities. We quantified the effect of the perforations on the unsteady fluid loading on the plate in terms of the variations of the corresponding Strouhal number, the mean drag coefficient and the fluctuating lift coefficient as functions of the Reynolds number and the perforation diameter. The results indicate that the loading was dominated by the dynamics of the wake. In particular, increasing the perforation diameter resulted in a wider wake, corresponding to the increase in mean drag coefficient and the decrease in the Strouhal number. Onset of coupling between the vortex shedding and the transverse oscillations of the plate was manifested as a rapid increase in the fluctuating lift coefficient, as the perforation diameter exceeds the plate thickness.

Design and application of nanoparticle coating system with decoupled spray generation and deposition control

Coatings are widely used in various biomedical applications to change the interaction of the surfaces with bioactive materials. The key factors that determine the quality of a spray-coated layer are the size (order of a few microns in diameter) and dimensional uniformity of droplets in the spray and the droplet impact velocity. For many applications, coating quality is strongly dependent on the method and equipment used during the application process. This paper presents the development of a decoupled system for spray coating and micro-printing, which includes an ultrasonic spray generation device and a nozzle for the spray deposition independently operated. Design and development of the system as well as testing for different applications are presented in this paper. The system design can be potentially used for large area coating, such as windows and solar panels, as well as micro-printing of electronic circuits and numerous other applications.

Experimental Investigation of Flow-Acoustic Coupling in a Deep Axisymmetric Cavity

In this paper, the phenomenon of self-sustained pressure oscillations due to the flow past a deep, circular, axisymmetric cavity is investigated. In many engineering applications, such as flows through open gate valves, there exists potential for coupling between the vortex shedding from the upstream edge of the cavity and a diametral mode of the acoustic pressure fluctuations. In the present study, the unsteady pressure was measured at several azimuthal locations at the bottom of the cavity walls, and the associated acoustic mode shapes were calculated numerically for the four representative cases of the internal cavity geometry, which involved a reference case with sharp, 90°edges as well as several modifications that involved chamfers of various length of the upstream and the downstream edges of the cavity. In addition, the flow velocity in the vicinity of the cavity opening in selected cases was measured using digital particle image velocimetry (PIV). The optical access to the highly confined internal flow was provided by implementing an endoscope attached to the camera. This global, quantitative imaging approach yielded patterns of velocity, streamlines and out-of-plane vorticity component. Instantaneous and time-averaged flow patterns provided insight into the mechanism of the flow tone generation. Among the considered cavity geometries, the configuration that corresponded to the most efficient noise suppression was identified.Copyright

Spinning Behaviour of Diametral Acoustic Modes in Deep Axisymmetric Cavities With Chamfered Edges

Spinning behaviour of diametral acoustic modes associated with self-sustained flow oscillations in a deep, axisymmetric cavity located in a long pipeline was investigated experimentally. High-amplitude pressure fluctuations resulted from the excitation of the diametral acoustic modes by the fully-turbulent flow in the pipeline. The unsteady pressure was measured at three equally spaced azimuthal locations at the bottom of the cavity. This arrangement allowed calculation of the azimuthal orientation of the acoustic modes, which were classified as stationary, partially spinning or spinning. Introduction of shallow chamfers to the upstream and the downstream edges of the cavity resulted in changes of azimuthal orientation and spinning behaviour of the acoustic modes. In addition, introduction of splitter plates in the cavity led to pronounced change in the spatial orientation and the spinning behaviour of the acoustic modes. The short splitter plates changed the behaviour of the dominant acoustic modes from partially spinning to stationary, while the long splitter plates enforced the stationary behaviour across all resonant acoustic modes.Copyright

Quantitative Visualization of Unstable, Acoustically Coupled Shear Layers in Deep Axisymmetric Cavities

High-amplitude acoustic pressure fluctuations associated with locked-on, resonant flow states frequently occur in engineering systems that involve internal cavities located in pipelines, such as components of gas transport systems, steam delivery pipelines and jet engines. This paper describes the evolution of fully turbulent, acoustically coupled shear layers that form across deep, axisymmetric cavities. Effects of geometric modifications of the cavity edges on the separated flow structure were investigated using digital particle image velocimetry (PIV). The internal flow was non-intrusively accessed by means of a borescope, which allowed illumination and optical recording of flow tracers inside the cavity. Instantaneous, phase- and time-averaged patterns of velocity and vorticity provided insight into the flow physics during flow tone generation and noise suppression by the geometric modifications. In particular, the first mode of the shear layer oscillations was significantly affected by shallow chamfers located at the upstream and, to a lesser degree, the downstream edges of the cavity. Specifically, the introduction of the chamfers affected the phase and the location of formation of large-scale vortical structures in the shear layer, which is associated with a maximum of the vorticity thickness across the cavity opening. In turn, these changes in the flow structure affected the amplitude of acoustic pressure pulsations.Copyright

In Vitro Study of the Influence of the Aortic Root Geometry on Flow Characteristics of a Prosthetic Heart Valve

In this paper, performance of aortic heart valve prosthesis in different geometries of the aortic root is investigated experimentally. The objective of this investigation is to establish a set of parameters, which are associated with abnormal flow patterns due to the flow through a prosthetic heart valve implanted to the patients that had certain types of valve diseases prior to the valve replacement. Specific valve diseases, classified into two clinical categories, were correlated with the corresponding changes of aortic root geometry. These categories correspond to aortic valve stenosis and aortic valve insufficiency. The control case that corresponds to the aortic root of a patient without valve disease was used as a reference. Experiments were performed at test conditions corresponding to 70 beats/min, 5.5 L/min target cardiac output and a mean aortic pressure of 100 mmHg. By varying the aortic root geometry, it was possible to investigate corresponding changes in the levels of Reynolds shear stress and establish the possibility of platelet activation and, as a result of that, the formation of blood clots.Copyright

Experimental Investigation of Flat Plates with Transverse Perforations at Zero Incidence

Particle Image Velocimetry (PIV) and direct force measurements are used to investigate the effect of transverse perforations on the flow-induced loading on and the associated flow structure around flat plates that are aligned with the oncoming flow. Plates with different characteristic diameter of the perforations, as well as a reference configuration without perforations are compared in terms of the spectra of the flow-induced forces, frequencies of the trailing edge vortex shedding and boundary layer profiles at the trailing edge at different planes across the perforation patterns for a range of inflow velocities. At high inflow velocities, boundary layer thickness increased as the diameter of the perforations increased and the distance from the perforation to the trailing edge of the plate decreased.

Experimental Investigation of Pulsatile Flow Through Prosthetic Heart Valves

Qualitative and quantitative flow visualization study was conducted for the case of a biomimetic pulsatile flow through an artificial heart valve placed into an asymmetric model of an aortic root with sinuses of Valsalva. A prototype trileaflet valve was tested alongside with a tilted disk valve and a bileaflet valve. The study was conducted in test conditions corresponding to 70 beats/min, 5.5 l/min target cardiac output and a mean aortic pressure of 100 mmHg. Flow visualization data obtained using digital particle image velocimetry (PIV) was phase-averaged in order to provide accurate, time-resolved patterns of flow velocity and viscous shear stress values. In the case of the tri-leaflet valve, during systole, a stable jet emanates from the valve, with vortical structures forming on the sides of the jet. These vortical structures entrain the surrounding fluid into the jet, which leads to development of a shear flow instability downstream of the valve. For all considered valve types, a recirculating flow was observed in the sinus area during both the systole and the diastole. No indication of a stagnating flow region was observed, as the fluid was completely washed out from the aortic sinus within each cardiac cycle.Copyright