Flow past a rotating cylinder translating at different gap heights along a wall

Rao, Anil; Thompson, Mark C.; Leweke, Thomas; Hourigan, Kerry

doi:10.1016/j.jfluidstructs.2015.06.015

Cited by 34 publications

(44 citation statements)

References 51 publications

(112 reference statements)

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“…At high ξ, the pressure drag on the system is less than zero for some of the cases, indicating the generation of thrust. Thrust generation by the rotation of the control cylinders is consistent with the numerical simulations of a pair of counter-rotating cylinders conducted by van Rees et al (2015).…”

Section: Pressure Drag Reductionsupporting

confidence: 85%

“…In the flow past a rotating cylinder near a plane wall, the gap width is an important parameter in determining the forces on the cylinder, vortex shedding (Cheng & Luo 2007) and three-dimensional instability (Rao et al (2011) and Rao et al (2015)). In the application of rotating control cylinders to bluff body flow control, Mittal (2001) found that the gap between the main and control cylinders is a critical parameter and sensitivity to the gap changes with Reynolds number.…”

Section: Introductionmentioning

confidence: 99%

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Flow control with rotating cylinders

et al. 2017

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We study the use of small counter-rotating cylinders to control the streaming flow past a larger main cylinder for drag reduction. In a water tunnel experiment at a Reynolds number of 47, 000 with a three-dimensional and turbulent wake, Particle Image Velocimetry (PIV) measurements show that rotating cylinders narrow the mean wake and shorten the recirculation length. The drag of the main cylinder was measured to reduce by up to 45%. To examine the physical mechanism of the flow control in detail, a series of two-dimensional numerical simulations at a Reynolds number equal to 500 were conducted. These simulations investigated a range of control cylinder diameters in addition to rotation rates and gaps to the main cylinder. Effectively controlled simulated flows present a streamline that separates from the main cylinder, passes around the control cylinder, and reattaches to the main cylinder at a higher pressure. The computed pressure recovery from the separation to reattachment points collapse with respect to a new scaling, which indicates that the control mechanism is viscous.

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Section: Pressure Drag Reductionsupporting

confidence: 85%

Section: Introductionmentioning

confidence: 99%

Flow control with rotating cylinders

et al. 2017

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“…Figure 5(b) shows the spanwise perturbation vorticity contours for a cylinder translating along a wall at G/D = 0.5 at the specified parametric values. For more instances of perturbation contours of this mode, the reader is referred to figures 25 and 26 of Rao et al (2015b). The coalescing of the critical Reynolds numbers and the structure of the perturbation fields indicate that mode E and the three-dimensional modes observed in near-wall bluff-body studies are indeed identical.…”

Section: Cylinders In the Presence Of Wallsmentioning

confidence: 90%

A universal three-dimensional instability of the wakes of two-dimensional bluff bodies

2016

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Linear stability analysis of a wide range of two-dimensional and axisymmetric bluff-body wakes shows that the first three-dimensional mode to became unstable is always mode E. From the studies presented in this paper, it is speculated to be the universal primary 3D instability, irrespective of the flow configuration. However, since it is a transition from a steady two-dimensional flow, whether this mode can be observed in practice does depend on the nature of the flow set-up. For example, the mode E transition of a circular cylinder wake occurs at a Reynolds number of Re 96, which is considerably higher than the steady to unsteady Hopf bifurcation at Re 46 leading to Bénard-von-Kármán shedding. On the other hand, if the absolute instability responsible for the latter transition is suppressed, by rotating the cylinder or moving it towards a wall, then mode E may become the first transition of the steady flow. A well-known example is flow over a backward-facing step, where this instability is the first global instability to be manifested on the otherwise two-dimensional steady flow. Many other examples are considered in this paper. Exploring this further, a structural stability analysis (Pralits et al. J. Fluid Mech., vol. 730, 2013, pp. 5-18) was conducted for the subset of flows past a rotating cylinder as the rotation rate was varied. For the non-rotating or slowly rotating case, this indicated that the growth rate of the instability mode was sensitive to forcing between the recirculation lobes, while for the rapidly rotating case, it confirmed sensitivity near the cylinder and towards the hyperbolic point. For the non-rotating case, the perturbation, adjoint and structural stability fields, together with the wavelength selection, show some similarities with those of a Crow instability of a counter-rotating vortex pair, at least within the recirculation zones. On the other hand, at much higher rotation rates, Pralits et al. (J. Fluid Mech., vol. 730, 2013, pp. 5-18) have suggested that hyperbolic instability may play a role. However, both instabilities lie on the same continuous solution branch in Reynolds number/rotation-rate parameter space. The results suggest that this particular flow transition at least, and probably others, may have a number of different physical mechanisms supporting their development.

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“…For other bluff body configurations, for example a square cylinder [15], an elliptic cylinder [16], a circular ring [17], two circular cylinders in staggered arrangements [18], a rotating cylinder near a moving wall [19], and so on, similar Mode A and Mode B flows (as well as other modes) with similar spanwise wavelengths were obtained on the basis of stability analysis. In addition to bluff body flows, stability analysis of the flow over a backward-facing step [20] and the flow through a partially blocked channel [21] also found that the onset of the secondary instability was represented by a 3D mode with a specific spanwise wavelength.…”

Section: Introductionmentioning

confidence: 97%

On numerical aspects of simulating flow past a circular cylinder

Jiang

Cheng

2017

Numerical Methods in Fluids

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Three‐dimensional direct numerical simulation results of flow past a circular cylinder are influenced by numerical aspects, for example the spanwise domain length and the lateral boundary condition adopted for the simulation. It is found that inappropriate numerical set‐up, which restricts the development of intrinsic wake structure, leads to an over‐prediction of the onset point of the secondary wake instability (Recr). A best practice of the numerical set‐up is presented for the accurate prediction of Recr by direct numerical simulation while minimizing the computational cost. The cylinder span length should be chosen on the basis of the intrinsic wavelength of the wake structure to be simulated, whereas a long span length is not necessary. For the wake transitions above Recr, because the wake structures no longer follow particular wavelengths but become disordered and chaotic, a span length of more than 10 cylinder diameters (approximately three times the intrinsic wavelength) is recommended for the simulations to obtain wake structures and hydrodynamic forces that are not strongly restricted by the numerical set‐up. The performances of the periodic and symmetry lateral boundary conditions are compared and discussed. The symmetry boundary condition is recommended for predicting Recr, while the periodic boundary condition is recommended for simulating the wake structures above Recr. The general conclusions drawn through a circular cylinder are expected to be applicable to other bluff body configurations. Copyright © 2017 John Wiley & Sons, Ltd.

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Flow past a rotating cylinder translating at different gap heights along a wall

Cited by 34 publications

References 51 publications

Flow control with rotating cylinders

Flow control with rotating cylinders

A universal three-dimensional instability of the wakes of two-dimensional bluff bodies

On numerical aspects of simulating flow past a circular cylinder

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