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

Abstract

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.