The impact of static and dynamic roughness elements on flow separation

Servini, P.; Smith, F. T.; Rothmayer, A. P.

doi:10.1017/jfm.2017.577

Cited by 11 publications

(5 citation statements)

References 34 publications

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“…An isolated three-dimensional surface-mounted obstacle, in the form of a sufficiently high slender hump, is an effective means to force reattachment of an oncoming two-dimensional marginally separating boundary layer. Servini, Smith & Rothmayer (2017, 2018) studied the impact of a two-dimensional dynamic roughness element on a separating boundary layer. Recently, Karp & Hack (2020) showed, by numerical simulations, reduction of separation bubble size by the so-called optimal disturbances.…”

Section: Introductionmentioning

confidence: 99%

Elevated low-frequency free-stream vortical disturbances eliminate boundary-layer separation

2021

J. Fluid Mech.

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Section: Introductionmentioning

confidence: 99%

Elevated low-frequency free-stream vortical disturbances eliminate boundary-layer separation

2021

J. Fluid Mech.

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“…in a manner similar to that carried out in Servini et al (2017). The dynamic roughness function itself can be written as…”

Section: Methods Of Solutionmentioning

confidence: 99%

The impact of dynamic roughness elements on marginally separated boundary layers

2018

Self Cite

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It has been shown experimentally that dynamic roughness elements – small bumps embedded within a boundary layer, oscillating at a fixed frequency – are able to increase the angle of attack at which a laminar boundary layer will separate from the leading edge of an airfoil (Grager et al., in 6th AIAA Flow Control Conference, 2012, pp. 25–28). In this paper, we attempt to verify that such an increase is possible by considering a two-dimensional dynamic roughness element in the context of marginal separation theory, and suggest the mechanisms through which any increase may come about. We will show that a dynamic roughness element can increase the value of $\unicode[STIX]{x1D6E4}_{c}$ as compared to the clean airfoil case; $\unicode[STIX]{x1D6E4}_{c}$ represents, mathematically, the critical value of the parameter $\unicode[STIX]{x1D6E4}$ below which a solution exists in the governing equations and, physically, the maximum angle of attack possible below which a laminar boundary layer will remain predominantly attached to the surface. Furthermore, we find that the dynamic roughness element impacts on the perturbation pressure gradient in two possible ways: either by decreasing the magnitude of the adverse pressure peak or by increasing the streamwise extent in which favourable pressure perturbations exist. Finally, we discover that the marginal separation bubble does not necessarily have to exist at $\unicode[STIX]{x1D6E4}=\unicode[STIX]{x1D6E4}_{c}$ in the time-averaged flow and that full breakaway separation can therefore occur as a result of the bursting of transient bubbles existing within the length scale of marginal separation theory.

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“…When the fracture roughness was increased, the eddy volumes were increased, but the effective hydraulic conductivities were decreased, even though the Re values remained the same [8]. Servini et al [9] investigated the impact of static and dynamic roughness elements on the flow separation process. They found that both types of roughness can have an effect.…”

Section: Introductionmentioning

confidence: 99%

“…The researchers examined two distinct sizes and shapes of roughness elements. The first roughness element is relatively small and is located close to the point of vanishing skin friction, and the second roughness element is significantly larger and extends downstream [9]. Prasad et al [5] conducted a study on the effect of river discharges controlled by a dam and tidal currents on the salt wedge intrusion in the Godavari River estuary on the east coast of India.…”

Section: Introductionmentioning

confidence: 99%

Using CFD Modeling to Simulate the Control of the Propagation of Salt Wedge using Inclined Roughness Elements

Badr,

Azzubaidi

2023

E3S Web Conf.

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This research aims to simulate and use Computational Fluid Dynamics, CFD, to control the propagation of salt wedges. The flume has a cross-section of 25 cm in height and 7.5 cm in width with a length of 6 m and a zero slope. The simulated model is used to investigate the use of inclined roughness elements to control the propagation of salt wedges. The elements are blocks of 2 cm by 3 cm cross-sections having an inclined face in the direction of the flow, with a length of 2 and 3 cm. These elements were installed in two rows at both sides of the bed of the flume with variable spacing between them in the direction of the flow, and their centerline is inclined by an angle of 30 degrees in the direction of the flow. The simulation model was validated by comparing its output with a published laboratory experiment. Ten CFD model runs were conducted under two different discharges and five different spacing between the inclined roughness elements. The used discharges are 30 l/min and 45.3 l/min, and the spacing between elements was 3, 6, 9, 12, and 15 cm. The results demonstrated a good relationship between the obtained model runs and the observations of the laboratory experience under the same conditions. The result showed that when no roughness elements were used, the propagation of the salt wedge extended to 3.9 and 3.1 m at a discharge of 30 l/min and 45.31 l/min, respectively. The propagation of the salt wedge is reduced as the spacing increases to some limit and then starts to decrease when you use roughness elements. At the maximum applied discharge of 45.3 l/min, the propagation of the salt wedge was reduced by 82, 84, and 85% when the spacing between the blocks is 3, 6, and 9 cm, respectively. The percentage of reduction in the propagation of the salt wedge starts to reduce to 79% and 75% as the spacing between the blocks is increased to 12 and 15 cm, respectively. When the discharge is 30 l/min, the propagation of the salt wedge is reduced by 76, 74, and 78% at a spacing of 3, 6, and 9 cm, respectively. At the same time, the propagation is reduced by 58% at 12 cm and 53% as the spacing is increased to 12 and 15 cm.

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The impact of static and dynamic roughness elements on flow separation

Cited by 11 publications

References 34 publications

Elevated low-frequency free-stream vortical disturbances eliminate boundary-layer separation

Elevated low-frequency free-stream vortical disturbances eliminate boundary-layer separation

The impact of dynamic roughness elements on marginally separated boundary layers

Using CFD Modeling to Simulate the Control of the Propagation of Salt Wedge using Inclined Roughness Elements

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