Visualization study and quantitative velocity measurements in turbulent taylor-couette flow by phantomm flow tagging: a description of the transition to turbulence

Abstract

A visualization study and Quantitative velocity measurements have been performed in Taylor-Couette flow with a medium-gap (ç= 0.356), over a large range of Taylor numbers (2.1x10(4) < Ta < 1.1x10(11)), with the outer cylinder fixed and the inner cylinder rotating about its axis. Quantitative velocity measurements were carried out using the PHANTOMM flow tagging technique. Two techniques were used for visualization study: the PHANTOMM technique that allowed flow structure visualization from small to moderate Taylor numbers, and the Particle Streak Imaging, PSI (the flow was seeded with neutrally buoyant polystyrene micro spheres) that permitted the flow structure visualization from moderate to high Taylor numbers. The results illustrate the expected three-dimensional features of flow and presence of Taylor cells at low Taylor numbers. Our study examined the interplay between small and large scales present in the flow as well as showed the gradual transition to turbulence with increasing Taylor numbers. Taylor cells were found for Taylor numbers less than 1.13 x 10(10). At low Taylor numbers, the flow in the cells appeared to be a rotational laminar flow with a high degree of coherence. At higher Taylor numbers, the cells aspect became more irregular, and the flow inside them became turbulent. The Görtler instability developed inside Taylor cells and close to the inner cylinder wall. At the highest Taylor numbers, turbulence increased up to the point where no Taylor cells could be detected. For the flow in our study, at Ta = 1.13 x 10(10), the homogenization by turbulence spread across the gap, and the flow structure sharply changed its pattern as a toroidal vortex in helical motion developed in a thin layer on the inner cylinder wall. Instantaneous velocities, average velocities, angular-momentum ratio and spectral density function were computed for all ranges of Taylor numbers in the range studied. These quantitative results show the same conclusions as the ones presented by the visualization stud

Turbulent Couette–Taylor flows with endwall effects: A numerical benchmark

“…persist along the inner cylinder, with a structure similar to the toroidal vortices observed by Biage and Campos [4] for Re = 2.04 × 10 5 , η = 0.38 and Γ = 10. At Re = 10 5 , the iso-values of the Q-criterion obtained by DNS ( Fig.2d) show that the flow is clearly turbulent with even thinner turbulent structures.…”

“…The radius ratio remains in the range 0.33 < η < 0.67, so that the cavity is considered as a middle gap cavity [4]. For enclosed systems characterized by a low aspect ratio Γ, such as in the experiment of Burin et al [5], the choice of the boundary conditions on the endcap disks is primordial and can favour the development of large Ekman recirculations…”

“…where R 1 and R 2 are the radii of the inner and outer cylinders respectively and H is the cavity height. Biage and Campos [4] proposed a classification of the systems depending on the value of their radius ratio η as follows: narrow-gap cavities for η > 0.67, middle-gap cavities for 0.33 < η < 0.67 and wide-gap cavities for η < 0.33. Most of the experiments up to now including the seminal one of Taylor [26] have considered cavities with an aspect ratio larger than 100.…”

Velocity and temperature measurements in a turbulent water-filled Taylor–Couette–Poiseuille system

“…The outer Plexiglas cylinder of radius b ¼ 9 cm is stationary. The cavity is thus defined by an aspect ratio equal to G ¼ h/(bÀa) ¼ 50 and a radius ratio equal to h ¼ a/b ¼ 0.89 (narrow gap cavity [19]). The outer cylinder is made of PMMA to allow optical velocimetry measurements.…”

Numerical and Experimental Identification of the Aerodynamic Power Losses of the ISWEC

“…Considering the full operative range for both pressure and velocity, the maximum torque, shown in Figure 5, is about 200 times the minimum value, highlighting once more how crucial it is to model such losses, already in the preliminary design stage. For the particular configuration considered in this work, where the radii ratio is R 1 /R 2 = 0.94 and the gap between the two cylinders is classified as small [30], the torque at atmospheric pressure (p i = 100 kPa) is about 20 times greater than the torque at vacuum conditions (p i = 1 kPa), for the lowest rotational speed (200 rpm), and about 30 times greater, for the maximum rotational speed (800 rpm). On the other hand, Figure 6 shows that the total torque at a given pressure is about linearly proportional to the flywheel velocity, with a ratio between the lowest and the highest torques (M high /M low ) equal to 12.…”