Session RW: Experimental Techniques IV

Ultrasound Doppler Velocimetry Measurements in Turbulent Liquid Metal Channel Flow

Control of molten metal flow using magnetic fields is important in industrial applications. The Electromagnetic Flow Control Channel (EFCO) is an experimental test facility, located at Ilmenau University of Technology, for the development of such kind of control systems. The working fluid is the low-melting liquid metal alloy GaInSn in eutectic composition. In this channel, flow control is realized by combining and coupling the non-contact flow driving technology of electromagnetic pumps based on rotating permanent magnets and the non-contact flow rate measurement technology termed Lorentz Force Velocimetry (LFV). The flow rate is adjusted by controlling the rotation rate of the permanent magnet system. Physically, LFV is based on measuring the force acting on a magnet system. This force is induced by the melt flow passing through the static magnetic field generated by the system and is proportional to the flow. To calibrate such flow meters, we apply UDV technique to measure and analyse both turbulent hydrodynamic and MHD flow profiles in EFCO at various Reynolds numbers.   

Evaluation of a Penning Mixture for Use in Plasma Adaptive Optics

This research examines the use of a Penning gas mixture in a dielectric barrier discharge (DBD) plasma device to achieve stable plasmas at high pressures. Previous research suggests increasing pressure produces a larger dynamic range of refractive index, which is favorable for adaptive optics. As the pressure increases, however, plasma generation in air soon becomes impractical due to power requirements. Penning mixtures, such as neon with a small amount of argon, feature lower breakdown voltages and stronger ionization attributed to the presence of Penning ionization. Experimental measurements of voltage, current, power, and electron density are presented for a DBD plasma chamber containing the gas mixture. Results are evaluated against a previously developed empirical model. The work further motivates the creation of a plasma adaptive optics system.   

High-precision image-based tracking of a rigid body moving within a fluid

Precise measurement of the displacement, velocity and acceleration of a moving rigid body is of interest in many applications. The use of imaging techniques to obtain such information is an attractive option, particularly for movement within a fluid, as such measurements are inherently non-intrusive. Here we describe a class of imaging techniques based on edge detection and least-squares fitting for determining the displacement of a body, from which velocities and accelerations are readily derived. The use of edge-detection allows for potentially higher precision than correlation-based techniques. The accuracy of the techniques is estimated using both artificially generated images and calibrated measurements, and displacement errors of the order of a few thousandths of a pixel are shown to be obtainable for camera noise levels of a few percent. The resulting uncertainties in velocity and acceleration measurements are also analyzed. Several applications are then described, with particular emphasis on force measurements in short duration supersonic and hypersonic wind tunnels.   

Quantification of the Transient Behavior of Wind-driven Water Droplets and Rivulet Flows on a Substrate

Aircraft icing is widely recognized as a significant hazard to aircraft operations. The behavior of wind-driven water droplets and rivulet flows on cold airplane wings can directly and indirectly influence the formation and shape of the resulting ice accretion on the wings, which can significantly affect the surface roughness and the subsequent wing drag and overall aerodynamic performance. In this study, we report the progress made in our recent efforts in developing a novel digital fringe projection technique to achieve instantaneous measurements of the thickness distributions of water droplets and rivulet flows on a substrate to quantify the transient behavior of the wind-driven water droplets and rivulet flows. The effects of the surface properties of the substrate (e.g., hydrophobic, roughness and temperature) on the evolutions of the wind-driven water droplets and rivulet flows were investigated in great detail to elucidate underlying physics in order to improve our understanding about microphysical phenomena associated with aircraft icing phenomena.   

Wind tunnel experiment on investigating the times of ventilation in case of pollutant dispersion in an urban area

The times of ventilation, which is defined as how long pollutants take to arrive at and then vanish away in a distant place from the source point, were investigated in wind tunnel. In this study, rectangular shaped blocks were allocated in equally spaced interval in a wind tunnel. In order to cut off the disturbance of drift effect, which happens in symmetrical block alignment, the blocks array were tipped at 5-25 degrees. We defined semi-opened space between the blocks in the center of the modeled area as ``Void.'' Tracer gas was discharged at the center of the ``Void.'' The times of ventilation were measured in a boundary face of the ``Void.'' In addition, the distributions of velocity and concentration were measured in the `Void' simultaneously. We considered the results of times measurement based on the distributions of velocity and concentration. Concentration was disproportionately dispersed in the `Void' by unsymmetrical flow. With increasing angle, two factors of ventilation, horizontal transportation and vertical transportation, varied their features. Influenced by these feature, the times of ventilation shifted their peaks and distributions.   

Assessment of image correlation methods for the estimation of volume flow rates of subsea oil-gas plumes

The recent uncontrolled release of oil and gas from a failed well into the Gulf of Mexico in the wake of the Deep Water Horizons accident illustrated that the actual release rates are difficult to assess with established surface observation methods. To a large extent this has to with the great depth ($\sim$1500m) at which the oil was released and its subsequent dispersal throughout the vertical water column. Streaming video of the failure site was provided by subsea remotely operated vehicles (ROV) and allow, in principle, the quantification of the release rate on the basis of motion analysis image processing methods. Several correlation based approaches, commonly used in particle image velocimetry (PIV), are investigated with regard to estimating the propagation velocity of large scale features in the visible interface between sea water and oil plume. Together with time scale (video frame rate) and length scale (pipe diameter) the interface velocity of the plume can be estimated. Assuming the plume to be a turbulent free jet the actual volume flow rate of the oil/gas mixture can be then be recovered with reasonable accuracy.   

A Novel 3 Dimension 3 Component Micro-PIV System

We present a novel 3-dimension 3-component micro-PTV system which relies on a single view. This technique uses an axicon to determine the wavefront of a particle imaged by a microscope objective. The pattern produced by the axicon, a Bessel function of the first kind, is dependent on the three-dimensional location of the particle. A Hankel transform is used to characterize the patterns produced, making this particularly robust with respect to high particle loading. Once the particle coordinates are known for pairs of images, traditional PTV techniques are used to determine the velocity vectors.