Large eddy simulations of Taylor-Couette-Poiseuille flows in a narrow-gap system

Abstract

International audienceThe present paper concerns Large-Eddy Simulations (LES) of turbulent Taylor-Couette-Poiseuille flows in a narrow-gap cavity for six different combinations of rotational and axial Reynolds numbers. The in-house numerical code has been first validated in a middle-gap cavity. Two sets of refined LES results, using the Wall-Adapting Local EddyViscosity(WALE) and theDynamic Smagorinsky subgrid-scale models availablewithin an in-house code based on high-order compact schemes, have been then compared with no noticeable difference on the mean flow field and theturbulent statistics. The WALE model enabling a saving of about 12% of computational effort has been finally used to investigate the influence on the hydrodynamics of the swirl parameter N within the range [1.49 − 6.71]. The swirl parameter N, which compares the effects of rotation of the inner cylinder and the axial flowrate, does not influence significantly the mean velocity profiles. Turbulence intensities are enhanced with increasing values of N with remarkably high peak values within the boundary layers. The inner rotating cylinder has a destabilizing effect inducing asymmetric profiles of the Reynolds stress tensor components. The rotor and stator boundary layers exhibit the main characteristics of two-dimensional boundary layers.Turbulence is also mainly at two-component there. Thin coherent structures appearing as negative (resp. positive) spiral rolls are observed along the rotor (resp. stator) side. Their inclination angle depends strongly on the value of the swirl parameter, which fixes the intensity of the crossflow. On the other hand, the intensity and the size of the coherent structures observed within the boundary layers are governed by the effective Reynolds number. For its highest value, they penetrate the whole gap. Finally, the results have been extended to the non-isothermal case in the forced convection regime. A correlation for the Nusselt number along the rotor has been provided showing a much larger dependence on the axial Reynolds number thanexpected from previous published works, while it depends classically on the Taylor number to the power 0.145 and on the Prandtl number to the power 0.3

A Direct Numerical Simulation Estimation of Viscous Energy Dissipation Rate in Taylor Vortex Reactor

“…In the bulk zone, the estimation by the numerical model is much better compared to the boundary layer, but still comparatively under-predicting. Chung & Sung [26], Poncet, Haddadi and Viazzo [27] and Poncet, Viazzo & Oguic [28] also observed similar results in the validation of their numerical models in both the boundary layer and bulk zone. For the VEDR of the mean flow kinetic energy (see Figure 4), it can be seen that the numerical model predicts the magnitude and the structure well in comparison with the experimental PIV estimations, especially in the boundary layer where the estimation is even comparatively higher.…”

“…Kobayashi et al [24] stated that this phenomenon is because of uniformity in the circumferential velocity, in which the velocity profiles apart from the ones in the outward and inward region are very similar to the one in the center of vortex region, which in turn is caused by convection of the secondary flow. In-fact, none of the numerical studies [18,20,[26][27][28] demonstrated the capability of the various numerical models to capture this phenomenon exhibited by experimental methods. In the case of the radial component (see Figure 2), though the magnitude is less than 3 % of the tangential component and the shape is well predicted by the numerical model, the maximum difference between the two axial heights is approximately 25 %.…”

CFD Study of Forced Air Cooling and Windage Losses in a High Speed Electric Motor

“…The numerical approach is based on the Reynolds Stress Modeling (RSM) where correlations for the averaged Nusselt numbers along both cylinders are finally provided according to the flow control parameters Reynolds number, friction coefficient and Prandtl number. In the work of Poncet et al [5] Large Eddy Simulations of Taylor-Couette-Poiseuille flows in a narrow gap system are presented together with a correlation for the Nusselt number along the rotor which shows a much larger dependence on the axial Reynolds number than expected from previous published works, while it depends classically on the Taylor number to the power 0.145 and on the Prandtl number to the power 0.3 i.e. Nu-Ta 0.145 Pr 0.3 .…”

On the Onset of Taylor Vortices in Finite-Length Cavity Subject to a Radial Oscillation Motion

“…In addition, the superposition of an axial flow, known as Taylor-Couette-Poiseuille flow, has been used as an efficient mechanism to stabilize the basic flow (Snyder, (1962); Meseguer and Marques, (2002);Campero and Vigil, (1999); Poncet et al, (2014)). …”