Particle Image Velocimetry Measurements over an Aerodynamically Open Two-Dimensional Cavity

An experimental study has been undertaken to characterise the low Reynolds number flow over an aerodynamically open two-dimensional cavity of rectangular cross-section. A series of water tunnel experiments have been performed in which the flow field was initially examined using dye flow visualisation, then particle image velocimetry (PIV) was used to obtain quantitative velocity measurements. For a laminar upstream boundary layer, the cavity flow structure has been characterised for a cavity length-to-depth ratio of 5 and Reynolds numbers, based on cavity depth, of 990, 1930, 3780 and 5710. Three different flow regimes were identified over the Reynolds number range tested. The mean PIV flow fields are presented and are found to compare well with the flow visualisation study and existing PIV literature

Pressure reconstruction from Lagrangian particle tracking with FFT integration

Volumetric time-resolved pressure gradient fields in unsteady flows can be estimated through flow measurements of the material acceleration in the fluid and the assumption of the governing momentum equation. In order to derive pressure, almost exclusively two numerical methods have been used to spatially integrate the pressure gradient until now: first, direct path integration in the spatial domain, and second, the solution of the Poisson equation with numerical methods. We propose an alternative method by integrating the pressure gradient field directly in Fourier space with a standard FFT function. The method is fast and easy to implement. We demonstrate the accuracy of the integration scheme on a synthetic pressure field and apply it to an experimental example based on acceleration data from Lagrangian particle tracking with high seeding density (Shake-The-Box method)

Anthropometrische, kraft-, ausdauer-und flexibilitätsmerkmale männlicher elite-eiskletterer und sportkletterer

Objective: Purpose of this study was to compare elite male ice climbers and sport climbers for their anthropometry, muscular strength, endurance, and flexibility. Although there is a certain overlap between these two activities, sport climbing, which recently became an Olympic discipline, has been studied significantly more than the ice climbing. Hence, the second aim was to indirectly determine whether sport climbing training processes and nutrition can be beneficial for the ice climbing athletes. › Methods: 23 male ice climbers of the Ice Climbing World Cup 2010 in Saas Fee (Switzerland) who all reached the final round were compared to 23 elite male sport climbers, which refers to “on sight” climbing grade of VII+/6b (UIAA/French) or higher. Measurements included anthropometry, three different tests for flexibility, two for strength and two for endurance. › Results: Ice climbers have more fat in the trunk region (Fat%-T), have significantly less handgrip strength in both hands, as well as strength to mass ratio (SMR) of the dominant hand. In the test “foot raise”, ice climbers showed significantly less flexibility. › Conclusion: Results indicate that ice climbers have not only higher body fat percentage, probably as an adaption to cold environment but also lower strength and flexibility than sport climbers. With such data, we can conclude that sport climbing training protocols for development of strength, endurance and flexibility can be potentially beneficial to ice climbers.Ziel: Ziel dieser Studie war es, männliche Elite-Eisk letterer und Sportk letterer hinsichtlich ihrer Anthropometrie, Muskelkraft, Ausdauer und Flexibilität zu vergleichen. Das zweite Ziel war zu bestimmen, ob Trainingsprozesse und Ernährung auf der Grundlage von Untersuchungen an Sportk letterern auch für Eiskletterer von Vorteil sein können.›Methoden: 23 männliche Eisk letterer des Ice Climbing World Cup 2010 in Saas Fee (Schweiz), die alle in die Finalrunde kamen, w urden mit 23 männlichen Elite-Sportkletterern verglichen, die „on sight“ einen K lettergrad von V II+/6b (UIA A/French) oder hö-her aufw iesen. Die Messungen umfassten die Anthropometrie, drei verschiedene Tests für Flexibilität, zwei für K raft und zwei für Ausdauer.›Ergebnisse: Eisk letterer haben mehr Fett im Rumpf bereich (Fat%-T), signifikant weniger Handgriff kraft in beiden Händen sowie Kraft-zu-Masse-Verhältnis (SMR) der dominanten Hand. Eiskletterer zeigten deutlich weniger Flexibilität imHüftbereich.›Schlussfolgerung: Die Ergebnisse zeigen, dass Eisk letterer nicht nur einen höheren Körperfettanteil haben, wahrscheinlich als Anpassung an eine kalte Umgebung, sondern auch eine gerin-gere Kraft und Flexibilität als Sportkletterer. Sportkletter-Trai-ningsprotokolle können zur Entw ick lung von Kraft, Ausdauer und Flexibilität für Eisk letterer potenziell von Vorteil sein

Development of new methods for analysis of LPT data and application to high-subsonic jet measurements

Lagrangian particle tracking enables the accurate measurement of the position, velocity and acceleration of particles moving within fluid flows. Beyond the particle positions in each time step, an actual track of the individual particle is available over time. This can be exploited for new analysis methods that use this continuous nature of the tracks to improve binned statistics of the flow. Instead of considering just particle positions at each sampling time instance the movement of the tracked particle between those time steps can provide additional information. In the case of binning based averaging methods this results in better convergence of the statistics for a given amount of data. We apply such methods to a multi-pulse Shake-The-Box (STB) measurement of a Mach 0.84 jet in air and generate high resolution two-point correlation maps of the flow. Coherent structures in the shear layer are further investigated using event orientated conditional averaging based on quadrant analysis. As a novel approach for using the Lagrangian nature of the measurement data, we additionally show a control volume balance based calculation approach, which together with bin based statistics could provide a pathway towards investigating balance equations of flow quantitie

3D Accelerations of a Subsonic Jet using Four-Pulse Shake-The-Box

Three-dimensional Lagrangian Particle Tracking (LPT) was performed using the Shake-The-Box (STB) algorithm on a subsonic jet flow at Mach 0.845. The STB technique for multi-pulse data was employed to reconstruct particle tracks along the four-pulse sequences providing highly resolved 3D flow velocity and material acceleration data. A description of the experimental methodology is given followed by instantaneous accelerations and averaged flow statistics

3D Lagrangian particle tracking of a subsonic jet using multi-pulse Shake-The-Box

Three-dimensional (3D) Lagrangian Particle Tracking (LPT) was performed on a subsonic jet flow at Mach 0.506 and 0.845 generated by a round nozzle with diameter-based Reynolds numbers of 1.7×105 and 3.1×105, respectively. The Multi-Pulse Shake-The-Box (MP-STB) technique was employed to reconstruct particle tracks along the four-pulse sequences, which were obtained by using orthogonally polarised light to separate the pulses on camera images. The MP-STB method applied here has a number of differences compared to previous publications, in particular, a new adaptive search radii approach and an iterative strategy and particle track validation criteria that have been customised for high subsonic/transonic flows. A description of this methodology is given followed by presentation of the instantaneous 3D flow velocity and material acceleration particle tracks. By ensemble-averaging the scattered instantaneous measurements extracted from individual particle tracks into small volumetric bins, highly resolved statistical quantities were obtained. The performance of MP-STB was assessed by comparing velocity profiles with published particle image velocimetry (PIV) data-sets. MP-STB was better able to resolve the steep velocity gradients, in particular the thin jet shear layer near the nozzle exit. At this location the MP-STB results also yielded higher turbulence intensities compared with the reported studies for similar flow conditions. The MP-STB acceleration flow statistics were compared for the two Mach numbers, and for the Mach 0.506 case, higher levels of normalised acceleration and fluctuations were found. The position accuracy of the 3D imaging system was quantified and it was found that the use of two different states of polarisation had a direct impact on the accuracy and the amount successfully tracked particles. Further assessment of the particle imaging quality of each camera revealed a significant disparity between cameras. This was attributed to the particle light scattering intensity variations, which were highly dependent on the particle size, camera angles and different states of polarised light. Despite these challenges, an average of40,000 individual particle tracks could be reconstructed from a typical particle image density of 0.02 particles per px (and an active sensor area of 1800×2200 px2). Furthermore, the accuracy of the measurement was shown to be relatively high, with respect to PIV

Comparation of morphological characteristics and motor skills between alpinists and other athletes

Alpinism is climbing to high mountains every season by hardly accessible and steep walls due to the discovery of the beauty of the natural environment, as well as the strengthening of physical strength, endurance and will. To ensure that alpinists are able to successfully and safely perform their ascents and achieve top sporting results, well-developed motor skills, as well as balanced morphological characteristics are necessary. Motor skills are the result of complex man's ability to manifest motor structures in certain activities, which integrate psychic characteristics, biochemical processes and functional changes. The aim of the research is to examine the differences in the morphological characteristics and motor skills of alpinists and other athletes, ages 16-26, both sexes. The sample of the respondents is 30 athletes, 15 alpinists (6 women and 9 men) and 15 other athletes (8 women and 7 men). It has been found that male alpinists are different from other athletes to the extent of BMI body composition. Women alpinists differ from other athletes in the capacity of the explosive muscle strength of the leg armpit. Alpinists, both sexes have better results than other athletes, both sexes in the relative strength and stamina of the upper body. Between alpinists and other athletes, both sexes have no difference in motor skills, agility and speed of movement, and ability to maintain balance on the front of the foot. The paper presents a good starting point for trainers to learn morphological characteristics and motor skills, as well as to plan the training process in the future

Lagrangian Particle Tracking in a Large-Scale Impinging Jet Using Shake-The-Box

The results presented in Sect. 18.3 demonstrate that combining helium-filled soap bubbles (HFSBs) as tracer particles with LED illumination allows for accurate particle tracking in large volumes using Shake-The-Box (STB) [31], see Sect. 9.4.3. Another experiment was created within the same cylindrical chamber, extending the concept to flows of higher speed. High-speed cameras were combined with arrays of high-power LEDs, being able to emit enough light within the short pulse widths required at flow velocities up to 16 m/s. The resulting tracks are used to reconstruct pressure fields, which are compared to the signal of wall mounted microphones

Towards high-resolution 3D flow field measurements at the cubic meter scale

We present results from two large-volume volumetric flow experiments. The first of these, investigating a thermal plume at low velocities (up to 0.35 m/s) demonstrates the abilities and requirements to reach volume sizes up to and probably beyond one cubic meter. It is shown that the use of Helium filled soap bubbles (HFSBs) as tracers, combined with pulsed LED illumination yields high particle image quality over large volume depths. A very uniform particle imaging, both in space as well as in time enables using high particle image concentrations (up to 0.1 ppp), while still being able to accurately reconstruct the flow using Shake-The-Box particle tracking. The experiment consisted of time-resolved volumetric flow measurements of a convectional plume within a volume of approx. 0.55 m3 (550 liters). The light yield needed for such a large scale measurement is realized by using HFSBs with 300 !m diameter as tracers and illuminating the measurement region using high-power, scalable arrays of white LEDs. Applying the Shake-The-Box algorithm, up to 275,000 bubbles could be tracked simultaneously. Interpolating the results on a regular grid (using ‘FlowFit’) reveals a multitude of flow structures. The setup can be scaled to larger volumes of several cubic meters, basically only being limited by the number and power of available LEDs and high-resolution cameras with sufficient frame-rate and pixel sizes. A second experiment showcases the possibilities to reach higher flow velocities, while still measuring within a comparatively large volume, by applying high-speed imaging and advanced LED illumination. An impinging turbulent jet was investigated in volumes ranging from 13 to 47 liters, depending on the repetition rate of the camera system. The results show that even at a repetition rate of 3.9 kHz and flow speeds up to 17 m/s the tested system was able to deliver images that allowed for a reliable and accurate tracking of bubbles