Dekompozice dat získaných metodou PIV s aplikací na výzkum dynamiky odtržení mezní vrstvy

Separation of the turbulent boundary layer (BL) on a flat plate under adverse pressure gradient was studied experimentally using Time-Resolved PIV technique. The results of spatio-temporal analysis of flow-field in the separation zone are presented. For this purpose, the POD (Proper Orthogonal Decomposition) and its extension BOD (Bi-Orthogonal Decomposition) techniques are applied as well as dynamical approach based on POPs (Principal Oscillation Patterns) method. The study contributes to understanding physical mechanisms of a boundary layer separation process. The acquired information could be used to improve strategies of a boundary layer separation control.V článku jsou prezentovány výsledky prostorově-časové analýzy experimentů popisujících odtržení turbulentní mezní vrstvy na rovinné stěně při nepříznivém tlakovém gradientu. Pro měření byla použita rychlá metoda PIV, pro analýzu potom vlastní ortogonální dekompozice (POD) a její zobecnění biortogonální dekompozice (BOD). Dále pro výzkum dynamických vlastností byla aplikována metoda hlavních oscilačních struktur (POPs). Studie přispívá k pochopení fyzikálních mechanismů, které se uplatňují v procesu odtržení mezní vrstvy. Získané poznatky mohou být uplatněny při vylepšování strategie řízení odtržení mezní vrstvy

Passive scalar mixing downstream of a synthetic jet in crossflow

An experimental investigation on passive scalar mixing due to the interaction of a synthetic jet with a thermal boundary layer is presented. From velocity measurements, performed by particle image velocimetry, two jet behaviours were identified. For jet to crossflow velocity ratios less than 1.2, the velocity fluctuations due to the jet/crossflow interaction stayed close to the wall. At higher ratios, the fluctuations moved away from the wall. The thermal mixing was examined using laser induced fluorescence. During expulsion, the thickness of the downstream thermal boundary layer increased whilst the thermal boundary layer was annihilated immediately downstream of the jet during entrainment

Temperature field behind parallel-line heat source in turbulent flow

Paper presented at the 9th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Malta, 16-18 July, 2012.An interaction of the free turbulent shear flow and the steady temperature field, which develops to the homogeneity in the planes that are perpendicular to the main stream, was studied. The temperature field was generated by parallel thin heated wires. The isotropic grid turbulence is supposed. Heated wire generates large cross temperature gradients whereas unheated one does not affect the flow. Development of the temperature field was investigated experimentally.dc201

On 3D flow pattern behind a wall-mounted circular cylinder of finite-length

The wake behind a wall-mounted finite-length circular cylinder of the aspect ratio 2 stuck out of a wall was studied experimentally using stereo PIV technique. The cylinder was mounted normal to a ground plane and it was subjected to a cross-flow with thin boundary layer developed on the wall, the Reynolds number based on inflow velocity and cylinder diameter was 9.7 thousands. The time-averaged velocity and streamwise vorticity fields showed the development of the mean flow structure consisting of the tip vortex pair, the extent of the near-wake recirculation zone with back-flow, the downwash phenomenon and base vortex structures close to the wall

Wake flow past an ALUTEC profile

Aluminum construction profiles become a standard construction material for short-term stands in science and in industry as well. It has the shape of square prism with an groove in each side to easy connecting the nut or bolt in any location. We studied the wake past the profile of 45 mm side. We studied the topology of the wake in the dependence on the angle of attack by using the Particle Image Velocimetry technique

Hot-wire anemometry measurement of diffusion of air-carbon dioxide admixture in flow over two-dimensional hill

Paper presented at the 8th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Mauritius, 11-13 July, 2011.In experimental study of the diffusion there is commonly used an admixture gas as a tracer that enters the main airflow. The paper deals with the simultaneous measurement of the molar concentration in binary-gas mixture by means of hotwire anemometry. A special three-sensor probe has been manufactured and used for this task. A case of polynomial shaped 2D hill with the line source of tracer gas has been studied in detail. Geometry of the hill was taken from Almeida at al. Experimental study of the binary-mixture concentration field over the hill has been done.pm201

Turbulence topology behind different sections of the wind turbine blade

This work aimed to investigate the turbulence characteristics behind different parts of the wind turbine blade. Airfoils S807, S813, S817, and S803, which characterize the shape of the blade at different lengths, were selected for estimation. During the experiment, the chord-based Reynolds number was 2.6×105, while the angle of attack was zero. Measuring crosssections were placed behind the trailing edge at x·c-1≈0.2, 0.4 and 1.0. For the determination flow topology, we used a Hotwire anemometry with a split fiber probe 55R55 and a miniature X-wire probe 55P64. The obtained data allowed us to determine and compare the evolution of the wake behind different types of airfoils in streamwise and spanwise directions. Thus, the largest and smallest velocity deficit located behind S817 and S803 airfoils, respectively. This trend is also evident in the Normalized Reynolds shear stress distributions. Finally, we determined the spectrum and calculated the Integral length scale, the Taylor and Kolmogorov microscale of turbulent flow. According to the results, profile S817 contributes to the formation of a flow with a large scale of turbulence, while the S803 is contrary

Vorticity statistics in the near wake of asymmetric prismatic airfoil NACA 64-618 at negative angle of attack –10° at Reynolds numbers 1.6 ⋅ 104 and 1.6 ⋅ 105 in distance 0.0 – 0.4 × chord past trailing edge measured by Particle Image Velocimetry

The airfoil NACA 64-618 is realized by using two levels of quality: first the theoretical profile is printed on a 3D printer in a direct, “naive” way, this geometry has been scanned by using 3D scanner and based on the deviations, a better model has been processed. The flow within the turbulent wake is measured by using Particle Image Velocimetry (PIV) technique at two velocities separated by one order of magnitud