Acoustic treaming visualization in elastic spherical cavities

Flow visualizations are presented for acoustic streaming occurring inside spherical elastic cavities oscillating in an acoustic field. Streaming flows are visualized using Particle Image Velocimetry (PIV) and results are observed for a range of values of a dimensionless frequency parameter,M=120-306. Over the frequency range investigated, streaming flow fields remain steady at a given value ofM. The magnitude of the flows circulating inside the cavity remains small (<1 mm/s) and follows a non-linear dependency with respect to the acoustic power of the sound wave. The present boundary-driven cavity flows may enhance particle fluid transport mechanisms, leading ultimately to potential fluid mixing application

Flow in near-critical fluids induced by shock and expansion waves

Abstract.: Unsteady shock and expansion waves are proposed as means to produce flows near the liquid-vapor critical-point without imposing pressure gradients. By choosing appropriate initial conditions and wave speeds, near-critical post-wave conditions can be obtained. The post-shock conditions are shown to be stable with respect to perturbations in the pre-shock conditions. The initial conditions are sufficiently far from the critical-point to allow fast thermal equilibration, permitting the use of larger fluid volumes. Example calculations for the cases of an impulsively accelerated piston, of a shock tube, and of a Ludwieg-like tube are presented yielding flows up to 20 m/s in sulfur hexafluoride (SF6), where the limit is due to the region of validity of the equation of state. The proposed setup also allows one to study shock wave propagation into near-critical fluid

Optical density and velocity measurements in cryogenic gas flows

This paper presents the application of optical measurement techniques in dense-gas flows in a heavy-gas channel to determine planar two-component (2C) velocity profiles and two-dimensional (2D) temperature profiles. The experimental approach is rather new in this area, and represents progress compared with the traditional techniques based on thermocouple measurements. The dense-gas flows are generated by the evaporation of liquid nitrogen. The optical measurement of both the velocity and density profiles is accomplished by the implementation of particle image velocimetry (PIV) and background-oriented schlieren (BOS) systems. Supplemental thermocouple measurements are used as independent calibrations to derive temperatures from the density data measured with the BOS system. The results obtained with both systems are used to quantify the dilution behavior of the propagating cloud through a global entrainment parameter β. Its value agrees well with the results obtained by earlier studie

Visualization of respiratory flows from 3D reconstructed alveolar airspaces using X-ray tomographic microscopy

A deeper knowledge of the three-dimensional (3D) structure of the pulmonary acinus has direct applications in studies on acinar fluid dynamics and aerosol kinematics. To date, however, acinar flow simulations have been often based on geometrical models inspired by morphometrical studies; limitations in the spatial resolution of lung imaging techniques have prevented the simulation of acinar flows using 3D reconstructions of such small structures. In the present study, we use high-resolution, synchrotron radiation-based X-ray tomographic microscopy (SRXTM) images of the pulmonary acinus of a mouse to reconstruct 3D alveolar airspaces and conduct computational fluid dynamic (CFD) simulations mimicking rhythmic breathing motion. Respiratory airflows and Lagrangian (massless) particle tracking are visualized in two examples of acinar geometries with varying size and complexity, representative of terminal sacculi including their alveoli. The present CFD simulations open the path towards future acinar flow and aerosol deposition studies in complete and anatomically realistic multi-generation acinar trees using reconstructed 3D SRXTM geometries

Acoustic treaming visualization in elastic spherical cavities

ISSN:1343-8875ISSN:1875-897

Three-dimensional particle tracking velocimetry using dynamic vision sensors

A fast-flow visualization method is presented based on tracking neutrally buoyant soap bubbles with a set of neuromorphic cameras. The “dynamic vision sensors” register only the changes in brightness with very low latency, capturing fast processes at a low data rate. The data consist of a stream of asynchronous events, each encoding the corresponding pixel position, the time instant of the event and the sign of the change in logarithmic intensity. The work uses three such synchronized cameras to perform 3D particle tracking in a medium sized wind tunnel. The data analysis relies on Kalman filters to associate the asynchronous events with individual tracers and to reconstruct the three-dimensional path and velocity based on calibrated sensor information