Direct simulations of low-Reynolds-number turbulent flow in a rotating channel (original) (raw)
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Science China Physics, Mechanics and Astronomy, 2010
We investigates the effect of Taylor-Görtler vortex on the Reynolds stress transport in the rotating turbulent channel flow by direct numerical simulation. The Taylor-Görtler vortex is detected by longitudinal average of velocity fluctuation in the channel and defined as TG fluctuation. It has been found that turbulent diffusion is significant in the Reynolds stress transportation at the suction side of rotating turbulent channel in contrast with the turbulent channel flow without rotation and Taylor-Görtler vortex plays an important role in the turbulent diffusion in Reynolds stress transport. The paper focuses on the low and moderate rotation number, but the effect of the rotation number on the Reynolds stress transport is also reported. Taylor-Görtler vortex, rotating turbulent channel flow, turbulent diffusion, budget of Reynolds stress transportation
PAMM, 2006
In this work a turbulent channel flow rotating about the streamwise direction is presented. The theory is based on the investigations of [3] employing the symmetry group theory. It was found that a cross flow in the spanwise direction is induced. Statistical evaluations have shown that all six components of the Reynolds stress tensor are non-zero. A series of direct numerical simulations (DNS) has been conducted at rotation number Ro=20 for different Reynolds numbers. In this paper the results of the DNS are presented and discussed.
The effects of system rotation with three orthogonal rotating axes on turbulent channel flow
The effect of Coriolis force on turbulent channel flow has been sought in a more general manner by taking into account the alignment between the rotation axis and the direction of mean pressure gradient and the rotation rate as well. Three different, but orthogonal rotation vectors coincident with the Cartesian coordinates have been imposed on a plane channel, in which homogeneity is presumed in the planes parallel to the wall. A series of DNS has been performed for each case starting from the non-rotating plane channel, while increasing the rotation number and keeping the Reynolds number based on the friction velocity at 150. Detailed statistics are obtained including mean quantities, turbulent intensities, vorticities, and higher-order moments. The budgets of transport equations of the quantities relevant to turbulence modeling are prepared for the three orthogonal cases in order to help assessing turbulence models. An attempt to investigate the near-wall structures has been tried.
Physics of Fluids
The influence of rotation about the streamwise axis on a turbulent channel flow is discussed by analyzing and comparing numerical and experimental data. The numerical study uses direct numerical simulations ͑DNS͒, while the experiments were based on particle-image velocimetry ͑PIV͒. The flow properties in the numerical and experimental analyses were maintained as similar as possible. For comparability with data from the literature the nonrotating channel flow at a Reynolds number Re = 180 serves as a reference problem. Depending on the rotation rate of the channel the development of a secondary flow perpendicular to the main flow has been found in both investigations. The rotation primarily influences those components of the Reynolds shear stresses, which contain the spanwise velocity component. The size of the correlation areas and thus the length scales of the flow increase in all three coordinate directions, leading to longer structures. The increased momentum exchange can be deducted from the behavior of the mean main velocity profile, which shows a decreased centerline velocity and an increased velocity near the wall at growing rotation rates. The qualitative development of the mean flow and the statistical flow properties is similar for the simulation and the experiment. The growth of the coherent turbulent structures with the rotation rate is confirmed by both investigations.
The effect of spanwise system rotation on Dean vortices
Journal of Fluid Mechanics, 1994
An experimental study is reported of the flow in a high-aspect-ratio curved air channel with spanwise system rotation, utilizing hot-wire measurements and smoke visualization. The experiments were made at two different Dean numbers (De), approximately 2 and 4.5 times the critical De for which the flow becomes unstable and develops streamwise vortices. For the lower De without system rotation the primary Dean instability appeared as steady longitudinal vortices. It was shown that negative spanwise system rotation, i.e. the Coriolis force counteracts the centrifugal force, could cancel the primary Dean instability and that for high rotation rates it could give rise to vortices on the inner convex channel wall. For positive spanwise system rotation, i.e. when the Coriolis force enhanced the centrifugal force, splitting and merging of vortex pairs were observed. At the higher De secondary instabilities occurred in the form of travelling waves. The effect of spanwise system rotation on the secondary instability was studied and was found to reduce the amplitude of the twisting and undulating motions for low negative rotation. For low positive rotation the amplitude of the secondary instabilities was unaffected for most regions in parameter space.
Direct numerical simulation of Taylor-Couette flows in the fully turbulent regime
Computational Fluid Dynamics 2006, 2009
Direct numerical simulations have been performed to study the Taylor-Couette (TC) flow between two rotating, coaxial cylinders in the presence of a radial temperature gradient. Specifically, the influence of the buoyant force and the outer cylinder rotation on the turbulent TC flow system with the radius ratio η = 0.912 was examined. For the co-rotating TC flows with Re i (inner cylinder) = 1000 and Re o (outer cylinder) = 100, a transition pathway to highly turbulent flows is realized by increasing σ, a parameter signifying the ratio of buoyant to inertial force. This nonlinear flow transition involves four intriguing states that emerge in sequence as chaotic wavy vortex flow for σ = 0, wavy interpenetrating spiral flows for σ = 0.02 and 0.05, intermittent turbulent spirals for σ = 0.1 and 0.2, and turbulent spirals for σ = 0.4. Overall, the fluid motion changes from a centrifugally driven flow regime characterized by large-scale wavy Taylor vortices (TVs) to a buoyancy-dominated flow regime characterized by small-scale turbulent vortices. Commensurate changes in turbulence statistics and heat transfer are seen as a result of the weakening of large-scale TV circulations and enhancement of turbulent motions. Additionally, the influence of variation of the outer cylinder rotation, −500 < Re o < 500 in presence of buoyancy (σ = 0.1) with Re i = 1000, has been considered. Specifically, it is demonstrated that this variation strongly influences the azimuthal and axial mean flows with a weaker influence on the fluctuating fluid motions. Of special interest, here are the turbulent dynamics near the outer wall where a marked decrease of turbulence intensity and a sign inversion of the Reynolds stress R r z are observed for the strongly counter-rotating regimes (Re o = −300 and −500). To this end, it has been shown that the underlying flow physics for this drastic modification are associated with the modification of the correlation between the radial and axial fluctuating motions. In turn, the intriguing effects of this modification on the mean axial flow, turbulent statistics, force balance, and dynamic processes such as turbulence production and dissipation are discussed.
From natural to forced counter-rotating streamwise vortices in boundary layers
Journal of Physics: Conference Series, 2008
Counter-rotating streamwise vortices (CRSVs) are ubiquitous in Fluid Mechanics, and especially in boundary layer and shear layer flows. A short review is presented showing how the CRSVs are naturally generated in boundary layer flows and how they can be artificially generated in the purpose of efficient flow control experiments.
Nonlinear vortex development in rotating flows
Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, 2008
We present the results of a combined experimental and numerical investigation into steady secondary vortex flows confined between two concentric right circular cylinders. When the flow is driven by the symmetric rotation of both end walls and the inner cylinder, toroidal vortex structures arise through the creation of stagnation points (in the meridional plane) at the inner bounding cylinder or on the mid-plane of symmetry. A detailed description of the flow regimes is presented, suggesting that a cascade of such vortices can be created. Experimental results are reported, which visualize some of the new states and confirm the prediction that they are stable to (mid-plane) symmetry-breaking perturbations. We also present some brief results for the flows driven by the rotation of a single end wall. Vortex structures may also be observed at low Reynolds numbers in this geometry. We show that standard flow visualization methods lead to some interesting non-axisymmetric particle paths in...
Turbulent rotating convection: an experimental study
Journal of Fluid Mechanics, 2002
We present experimental measurements of velocity and temperature fields in horizontal planes crossing a cylindrical Rayleigh-Bénard convection cell in steady rotation about its vertical axis. The range of dimensionless rotation rates Ω is from zero to 5 × 10 4 for a Rayleigh number R = 3.2 × 10 8 . The corresponding range of convective Rossby numbers is ∞ > Ro > 0.06. The patterns of velocity and temperature and the flow statistics characterize three basic flow regimes. For Ro 1, the flow is dominated by vortex sheets (plumes) typical of turbulent convection without rotation. The flow patterns for Ro ∼ 1 are cyclone-dominated, with anticyclonic vortices rare. As the Rossby number continues to decrease, the number of anticyclonic vortex structures begins to grow but the vorticity PDF in the vicinity of the top boundary layer still shows skewness favouring cyclonic vorticity. Velocity-averaging near the top of the cell suggests the existence of a global circulation pattern for Ro 1.
Development of pre-set counter-rotating streamwise vortices in wavy channel
Experimental Thermal and Fluid Science, 2016
Development of counter-rotating streamwise vortices in a rectangular channel with onesided wavy surface has been experimentally quantified using hot-wire anemometry. The wavy surface has fixed amplitude of 3.75 mm. The counter-rotating vortices are pre-set by means of a sawtooth pattern cut at the leading edge of the wavy surface. Variations of the central streamwise velocity U c with a channel gap H = 35 mm and 50 mm (corresponding to a Reynolds number from 1600 to 4400) change the instability of the flow which can be distinguished from the velocity contours at a certain spanwise plane. The streamwise velocity contours and turbulence intensity for Reynolds number Re = 3100 and H = 35 mm show the disappearance of the mushroom-like vortices prior to turbulence near the second peak of the wavy surface, while for higher Re, this phenomenon occurs earlier. Under certain conditions, for example, for Re = 4400 and H = 50 mm, the splitting of the vortices can also be observed.