The effect of spanwise system rotation on Dean vortices

1994 ◽  
Vol 274 ◽  
pp. 243-265 ◽  
Author(s):  
O. John E. Matsson ◽  
P. Henrik Alfredsson
Keyword(s):  
Centrifugal Force ◽  
Coriolis Force ◽  
Travelling Waves ◽  
Streamwise Vortices ◽  
Longitudinal Vortices ◽  
Smoke Visualization ◽  
Rotation Rates ◽  
Dean Vortices ◽  
System Rotation ◽  
Secondary Instabilities

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.

scholarly journals Numerical Flow Analysis in a Rotating Square Duct and a Rotating Curved-Duct

2000 ◽  
Vol 6 (1) ◽  
pp. 1-9
Author(s):  
Je Hyun Baekt ◽  
Chang Hwan Ko
Keyword(s):  
Laminar Flow ◽  
Viscous Fluid ◽  
Secondary Flow ◽  
Centrifugal Force ◽  
Coriolis Force ◽  
Axial Velocity ◽  
Numerical Study ◽  
Axial Direction ◽  
Square Duct ◽  
Rotation Rates

A numerical study is conducted on the fully-developed laminar flow of an incompressible viscous fluid in a square duct rotating about a perpendicular axis to the axial direction of the duct. At the straight duct, the rotation produces vortices due to the Coriolis force. Generally two vortex cells are formed and the axial velocity distribution is distorted by the effect of this Coriolis force. When a convective force is weak, two counter-rotating vortices are shown with a quasi-parabolic axial velocity profile for weak rotation rates. As the rotation rate increases, the axial velocity on the vertical centreline of the duct begins to flatten and the location of vorticity center is moved near to wall by the effect of the Coriolis force. When the convective inertia force is strong, a double-vortex secondary flow appears in the transverse planes of the duct for weak rotation rates but as the speed of rotation increases the secondary flow is shown to split into an asymmetric configuration of four counter-rotating vortices. If the rotation rates are increased further, the secondary flow restabilizes to a slightly asymmetric double-vortex configuration. Also, a numerical study is conducted on the laminar flow of an incompressible viscous fluid in a90°-bend square duct that rotates about axis parallel to the axial direction of the inlet. At a90°-bend square duct, the feature of flow by the effect of a Coriolis force and a centrifugal force, namely a secondary flow by the centrifugal force in the curved region and the Coriolis force in the downstream region, is shown since the centrifugal force in curved region and the Coriolis force in downstream region are dominant respectively.

Effects of System Rotation on Vortical Structure in Wall Turbulence

2014 ◽  
Vol 137 (2) ◽  
Author(s):  
Oaki Iida
Keyword(s):  
High Speed ◽  
Vortical Structure ◽  
Wall Turbulence ◽  
Deformation Tensor ◽  
Streamwise Vortices ◽  
Longitudinal Vortices ◽  
Homogeneous Shear ◽  
System Rotation ◽  
Homogeneous Shear Flow ◽  
Vortex Axis

Direct numerical simulations (DNSs) of rotating turbulent Poiseuille flows are performed to study the effects of both cyclonic and anticyclonic system rotation on the kinematics of the quasi-streamwise vortices. By using the second invariant of the deformation tensor, a number of streamwise vortices are detected and averaged in the wall vicinity where the intense sweep motion, i.e., the inrush motion of high-speed fluid toward the wall, is related to the quasi-streamwise vortices. The effects of the system rotation on the angle of vortex axis are clearly observed as studied in longitudinal vortices of the homogeneous shear flow. Moreover, by calculating the probability of the emergence of the counterclockwise vortices (CCVs) around a clockwise vortex (CV), we find that with increase in the anticyclonic system rotation, the probability increases and decreases in the ejection and sweep sides of a CV, respectively. In contrast, cyclonic system rotation attenuates CCVs in both sides of a CV, though it increases at the top of the CV. This distribution of CCVs is found to affect sweep motion related to the quasi-streamwise vortices.

Turbulent flow over a backward-facing step. Part 1. Effects of anti-cyclonic system rotation

2010 ◽  
Vol 665 ◽  
pp. 382-417 ◽  
Author(s):  
MUSTAFA BARRI ◽  
HELGE I. ANDERSSON
Keyword(s):  
Turbulent Flow ◽  
Shear Layer ◽  
Coriolis Force ◽  
Bulk Flow ◽  
Sudden Expansion ◽  
Backward Facing Step ◽  
Recirculation Bubble ◽  
Rotation Rates ◽  
Recirculating Flow ◽  
System Rotation

The effects of rotation on turbulent flow with separation and reattachment are investigated by means of direct numerical simulations. The backward-facing step configuration is rotated about a spanwise axis such that the sudden expansion of the channel is on the pressure side. The upstream flow is a fully developed plane Poiseuille flow subjected to orthogonal-mode rotation, which subsequently detaches from the step corner and eventually reattaches further downstream. The size of the resulting separation bubble with recirculating flow diminishes monotonically with increasing rotation rates and the reattachment distance is reduced from about 7 to 3 step heights. This is ascribed to the augmentation of the cross-stream turbulence intensity in theanti-cyclonicshear layer formed between the bulk flow and the recirculating eddy due to the destabilizing influence of the Coriolis force. The spanwise-oriented vortex cells or roller eddies found in non-rotating shear layers were disrupted by the enhanced turbulence. The flow along the planar wall is subjected to an adverse pressure gradient induced by the sudden expansion. The stabilizing influence of the system rotation in thiscyclonicshear layer tends to damp the turbulence, the flow becomes susceptible to flow separation, and a substantial cyclonic recirculation bubble is observed at the highest rotation rates. The resulting meandering of the bulk flow is associated with interactions between the anti-cyclonic shear layer at the stepped side and the cyclonic shear flow along the planar surface. These give rise to enhanced turbulence levels at the cyclonic side in spite of the otherwise stabilizing influence of the Coriolis force. Exceptionally high velocity fluctuations in the spanwise direction are observed in the vicinity of flow reattachment behind the step and ascribed to longitudinal Taylor–Görtler-like roll cells which extend into the backflow region. These roll cells arise from a centrifugal instability mechanism associated with the convex streamline curvature in the reattachment zone.

scholarly journals Asymmetric travelling waves in a square duct

2012 ◽  
Vol 693 ◽  
pp. 57-68 ◽  
Author(s):  
Shinya Okino ◽  
Masato Nagata
Keyword(s):  
Cross Sections ◽  
Mirror Symmetry ◽  
Symmetric Solution ◽  
Travelling Waves ◽  
Edge State ◽  
Duct Flow ◽  
Streamwise Vortices ◽  
Square Duct ◽  
Geometrical Difference ◽  
Asymmetric Solution

AbstractTwo types of asymmetric solutions are found numerically in square-duct flow. They emerge through a symmetry-breaking bifurcation from the mirror-symmetric solutions discovered by Okino et al. (J. Fluid Mech., vol. 657, 2010, pp. 413–429). One of them is characterized by a pair of streamwise vortices and a low-speed streak localized near one of the sidewalls and retains the shift-and-reflect symmetry. The bifurcation nature as well as the flow structure of the solution show striking resemblance to those of the asymmetric solution in pipe flow found by Pringle & Kerswell (Phys. Rev. Lett., vol. 99, 2007, A074502), despite the geometrical difference between their cross-sections. The solution seems to be embedded in the edge state of square-duct flow identified by Biau & Bottaro (Phil. Trans. R. Soc. Lond. A, vol. 367, 2009, pp. 529–544). The other solution deviates slightly from the mirror-symmetric solution from which it bifurcates: the shift-and-rotate symmetry is retained but the mirror symmetry is broken.

The Effect of Centrifugal Force and Coriolis Force on Vehicle-Flexible Bridge Vertical Vibration

2012 ◽  
Vol 455-456 ◽  
pp. 1480-1485
Author(s):  
Xiang Xiao ◽  
Wei Xin Ren ◽  
Wen Yu He
Keyword(s):  
Centrifugal Force ◽  
Coriolis Force ◽  
Mass Matrix ◽  
Interaction Model ◽  
Vertical Motion ◽  
Vertical Vibration ◽  
Time Deformation ◽  
Damping Matrix ◽  
Load Vector ◽  
Bridge System

Considering centrifugal force and Coriolis force caused by the real-time deformation of bridge, a vehicle-bridge interaction model is established. Take simply supported bridge subjected to an one-axle vehicle for example, the mass matrix, damping matrix, stiffness matrix and load vector of the vehicle-bridge system are derived via modal analysis method, thus the vertical motion equation of vehicle-bridge system, which can better reflect the operation characteristics of vehicles running on the bridge, has been established.

Sensorimotor aspects of high-speed artificial gravity: III. Sensorimotor adaptation

2003 ◽  
Vol 12 (5-6) ◽  
pp. 291-299
Author(s):  
Paul DiZio ◽  
James R. Lackner
Keyword(s):  
Side Effects ◽  
Coriolis Force ◽  
High Speed ◽  
Motor Adaptation ◽  
Vestibular Stimulation ◽  
Head Movements ◽  
Artificial Gravity ◽  
Slow Rotation ◽  
Movement Trajectory ◽  
Rotation Rates

As a countermeasure to the debilitating physiological effects of weightlessness, astronauts could live continuously in an artificial gravity environment created by slow rotation of an entire spacecraft or be exposed to brief daily "doses" in a short radius centrifuge housed within a non-rotating spacecraft. A potential drawback to both approaches is that head movements made during rotation may be disorienting and nauseogenic. These side effects are more severe at higher rotation rates, especially upon first exposure. Head movements during rotation generate aberrant vestibular stimulation and Coriolis force perturbations of the head-neck motor system. This article reviews our progress toward distinguishing vestibular and motor factors in side effects of rotation, and presents new data concerning the rates of rotation up to which adaptation is possible. We have studied subjects pointing to targets during constant velocity rotation, because these movements generate Coriolis motor perturbations of the arm but do not involve unusual vestibular stimulation. Initially, reaching paths and endpoints are deviated in the direction of the transient lateral Coriolis forces generated. With practice, subjects soon move in straighter paths and land on target once more. If sight of the arm is permitted, adaptation is more rapid than in darkness. Initial arm movement trajectory and endpoint deviations are proportional to Coriolis force magnitude over a range of rotation speeds from 5 to 20 rpm, and there is rapid, complete motor adaptation at all speeds. These new results indicate that motor adaptation to high rotation rates is possible. Coriolis force perturbations of head movements also occur in a rotating environment but adaptation gradually develops over the course of many head movements.

On longitudinal vortices in curved channel flow

1993 ◽  
Vol 251 ◽  
pp. 627-660 ◽  
Author(s):  
Alessandro Bottaro
Keyword(s):  
High Speed ◽  
Curved Channel ◽  
Longitudinal Vortices ◽  
Dean Vortices ◽  
Vortex Pairs ◽  
Spatial Approach ◽  
Temporal Model ◽  
Inlet Conditions ◽  
Curved Channel Flow ◽  
Good Agreement

The laminar flow in a curved channel is studied numerically to analyse the initial formation, development and interaction phenomena of an array of centrifugally induced longitudinal vortices arranged across the span of the channel. Simulations employing streamwise periodic boundary conditions (temporal model) as well as inlet-outlet conditions (spatial model) are carried out. In the temporal approach the interactions (pairing of vortices and growth of new vortex pairs) of fully developed vortex pairs are time-dependent, whereas in the spatial approach these events are inherently steady and concern vortices not in their fully developed state. The initial spatial development of the vortices is in excellent agreement with results of a linear stability analysis up to fairly large disturbance amplitudes. In the nonlinear regime a good agreement with experimental results has also been found. The receptivity of the flow is very important in a convectively unstable situation such as the present one and different behaviour is found at fixed Reynolds number (equal to 2.43 times the critical value for the onset of Dean vortices): the flow can be either steady or undergo a continuous sequence of merging and splitting events, depending on the inlet conditions. In the latter situation decorrelated patterns of low- and high-speed streaks are produced in streamwise-spanwise planes and they bear several similarities to near-wall coherent structures of turbulent boundary layers.

Experimental Investigation of a Free Round Jet with Dean Vortices

2014 ◽  
Vol 9 (2) ◽  
pp. 128-135
Author(s):  
Maria Litvinenko ◽  
Yuriy Litvinenko ◽  
Grigory Kozlov ◽  
Valentin Vikhorev
Keyword(s):  
Experimental Investigation ◽  
Three Dimensional ◽  
Experimental Investigations ◽  
Acoustic Excitation ◽  
Hot Wire ◽  
Curved Channel ◽  
Mean Velocity ◽  
Round Jet ◽  
Smoke Visualization ◽  
Dean Vortices

Results of the experimental investigations of free round jet with Dean vortices formed in curved channel are presented. Hot-wire anemometry measurements of three-dimensional mean velocity profile were performed, smoke visualization pictures cross and longitudinal sections at nozzle exit and downstream were obtained. The features of jet development at acoustic excitation of 40 Hz are shown

Turbulent plane Couette flow subject to strong system rotation

1997 ◽  
Vol 347 ◽  
pp. 289-314 ◽  
Author(s):  
KNUT H. BECH ◽  
HELGE I. ANDERSSON
Keyword(s):  
Flow Field ◽  
Couette Flow ◽  
Turbulence Level ◽  
Streamwise Vortices ◽  
Plane Couette Flow ◽  
Mean Flow ◽  
Cell Pattern ◽  
System Rotation ◽  
The Mean ◽  
Turbulent Plane

System rotation is known to substantially affect the mean flow pattern as well as the turbulence structure in rotating channel flows. In a numerical study of plane Couette flow rotating slowly about an axis aligned with the mean vorticity, Bech & Andersson (1996a) found that the turbulence level was damped in the presence of anticyclonic system rotation, in spite of the occurrence of longitudinal counter-rotating roll cells. Moreover, the turbulence anisotropy was practically unaffected by the weak rotation, for which the rotation number Ro, defined as the ratio of twice the imposed angular vorticity Ω to the shear rate of the corresponding laminar flow, was ±0.01. The aim of the present paper is to explore the effects of stronger anticyclonic system rotation on directly simulated turbulent plane Couette flow. Turbulence statistics like energy, enstrophy and Taylor lengthscales, both componental and directional, were computed from the statistically steady flow fields and supplemented by structural information obtained by conditional sampling.The designation of the imposed system rotation as ‘high’ was associated with a reversal of the conventional Reynolds stress anisotropy so that the velocity fluctuations perpendicular to the wall exceeded those in the streamwise direction. It was observed that the anisotropy reversal was accompanied by an appreciable region of the mean velocity profile with slope ∼2Ω, i.e. the absolute mean vorticity tended to zero. It is particularly noteworthy that these characteristic features were shared by two fundamentally different flow regimes. First, the two-dimensional roll cell pattern already observed at Ro=0.01 became more regular and energetic at Ro=0.10 and 0.20, whereas the turbulence level was reduced by about 50%. Then, when Ro was further increased to 0.50, a disordering of the predominant roll cell pattern set in during a transient period until the flow field settled at a new statistically steady state substantially less affected by the roll cells. This was accompanied by a substantial amplification of the streamwise turbulent vorticity and an anomalous variation of the mean turbulent kinetic energy which peaked in the middle of the channel rather than near the walls. While the predominant flow structures of the non-rotating flow were longitudinal streaks, system rotation generated streamwise vortices, either ordered secondary flow or quasi-streamwise vortices. Eventually, at Ro=1.0, the turbulent fluctuations were completely suppressed and the flow field relaminarized.

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