Experimental method for investigating the formation of flow patterns in a very wide gap Taylor-Couette flow (<i>η</i> = 0.1).

Turbulent Taylor–Couette flow between two concentric independently rotating cylinders with a radius ratio of $\eta = 0.1$ is studied experimentally. While the scope is to study the counter-rotating cases between both cylinders, the radial and azimuthal velocity components are recorded at different horizontal planes with high-speed particle image velocimetry. The parametric study considered a set of different shear Reynolds numbers in the range of $20\,000 \leq Re_s \leq 1.31 \times 10^5$ , with different rotation ratios of $-0.06 \leq \mu \leq +0.008$ . The observed flow fields had a clear dependence on the rotation ratio, where flow patterns evolved with a more pronounced axial dependence. The angular momentum transport is computed as a result of the recorded flow fields and given by a quasi-Nusselt number. The dependence of the Nusselt number on the different rotation ratios shows a maximum for the low counter-rotating case and $\mu _{max}$ is found between $-0.011 < \mu _{max} < -0.0077$ . The Nusselt number decreases for stronger counter-rotation until a minimum is reached, where it tends to increase again for higher counter-rotation rates. The space–time behaviour of the turbulent flow showed the existence of patterns propagating from the inner region towards the outer region for all studied counter-rotating cases. In addition, patterns have been found that tend to propagate from the outer region towards the inner region with a novel character at high counter-rotation cases. These patterns enhance the angular momentum transport where a second maximum in the transport mechanism has to be expected.

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Experimental investigation of turbulent counter-rotating Taylor–Couette flows for radius ratio η = 0.1

Hamede

Merbold

Egbers

2023

J. Fluid Mech.

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Dielectrophoretic force-enhanced thermal convection within a horizontal cylindrical annulus

Hamede,

Roller,

Meyer

et al. 2024

Physics of Fluids

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This study investigates, both experimentally and numerically the flow of a dielectric fluid confined between two concentric, differentially heated, horizontally aligned cylinders subjected to a 200 Hz alternating radial electric field. A wide-gap annular setup with a length 20 times larger than the gap size is utilized in this investigation. The study focuses exclusively on the outward heating configuration, meaning the inner cylinder is hotter than the outer one. The electric field, in conjunction with the temperature gradient, triggers thermal electro-hydrodynamic instability caused by the application of dielectrophoretic force. when the applied electric tension exceeds a critical value for specific temperature gradients between the cylinders, the flow symmetry in the gap is disturbed. The instability manifests as periodically oscillating vortices occurring on top of the gap. A notable increase in heat transfer efficiency accompanies the onset of instability. The experimental and numerical results demonstrate quantitative and qualitative agreement.

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Transition to the ultimate turbulent regime in a very wide gap Taylor-Couette flow (η = 0.1) with a stationary outer cylinder

Hamede

Merbold

Egbers

2023

EPL

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The boundary layers in turbulent Taylor-Couette flow are exposed to transitions fromlaminar to turbulent states if the flow is sufficiently sheared. The present study examines thisparticular transition from the so-called ’classical’ to ’ultimate’ regime experimentally for a verywide-gap Taylor-Couette flow with a radius ratio of η = 0.1 and shear Reynolds numbers of upto Re_s = 1.5 × 10^5. In order to determine the transition, the angular momentum transportis measured by using torque sensors at the inner wall. This is complemented by measuringthe radial and azimuthal velocities via a time-resolved Particle-Image-Velocimetry (PIV). Thetransition to the ultimate regime is found at 2.5 × 104 ≤ Re_s ≤ 3.7 × 104. The dimensionlessangular momentum flux showed an effective scaling of Nu_ω ∼ Re^0.76s for Re_s ≥ 2.5×10^4and is inagreement with the scaling laws used for the ultimate regime in narrow-gap Taylor-Couette flows.In addition, a spectral analysis was performed showing the existence of highly energetic small-scaleand large-scale patterns in the classical regime whereas only highly energetic large-scale patternswere observed in the ultimate regime.

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Experimental method for investigating the formation of flow patterns in a very wide gap Taylor-Couette flow (η = 0.1).

Cited by 4 publications

References 20 publications

Experimental investigation of turbulent counter-rotating Taylor–Couette flows for radius ratio η = 0.1

Experimental investigation of turbulent counter-rotating Taylor–Couette flows for radius ratio η = 0.1

Dielectrophoretic force-enhanced thermal convection within a horizontal cylindrical annulus

Transition to the ultimate turbulent regime in a very wide gap Taylor-Couette flow (η = 0.1) with a stationary outer cylinder

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