Drag reduction on grooved cylinders in the critical Reynolds number regime

Quintavalla, Steven J.; Angilella, Alexander J.; Smits, Alexander J.

doi:10.1016/j.expthermflusci.2013.01.018

Cited by 49 publications

(16 citation statements)

References 11 publications

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“…Increasing the ratio, A * , between the area of all the grooves and the area of the cylinder decreased the critical Reynolds number and increased the minimum drag coefficient. This finding was robust regardless of whether A * was increased by increasing the groove depth, groove width or shape factor [21].…”

Section: Introductionsupporting

confidence: 49%

“…The results showed that both triangular and arc-shaped grooves induced the drag crisis at the same value of Re, but the triangular-grooved cylinders exhibited a lower value of the minimum drag coefficient [19]. A more recent study [21] focused on catenary shaped grooves in the critical Reynolds number regime (2 Re [×10 4 ] 12). The experiments were performed with cylinders of varying groove depth, width and area.…”

Section: Introductionmentioning

confidence: 99%

“…Also motivated by the cactus analogy, a series of previous studies have addressed the aerodynamics of cylinders with longitudinal grooves [4,6,10,[16][17][18][19][20][21]. For example, Refs.…”

Section: Introductionmentioning

confidence: 99%

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Active aerodynamic drag reduction on morphable cylinders

Guttag

Reis

2017

Phys. Rev. Fluids

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We study a mechanism for active aerodynamic drag reduction on morphable grooved cylinders, whose topography can be modified pneumatically. Our design is inspired by the morphology of the Saguaro cactus (Carnegiea gigantea), which possesses an array of axial grooves, thought to help reduce aerodynamic drag, thereby enhancing the structural robustness of the plant under wind loading. Our analog experimental samples comprise a spoked rigid skeleton with axial cavities, covered by a stretched elastomeric film. Decreasing the inner pressure of the sample produces axial grooves, whose depth can be accurately varied, on demand. First, we characterize the relation between groove depth and pneumatic loading through a combination of precision mechanical experiments and finite element simulations. Second, wind tunnel tests are used to measure the aerodynamic drag coefficient (as a function of Reynolds number) of the grooved samples, with different levels of periodicity and groove depths. We focus specifically on the drag crisis and systematically measure the associated minimum drag coefficient and the critical Reynolds number at which it occurs. The results are in agreement with the classic literature of rough cylinders, albeit with an unprecedented level of precision and resolution in varying topography using a single sample. Finally, we leverage the morphable nature of our system to dynamically reduce drag for varying aerodynamic loading conditions. We demonstrate that actively controlling the groove depth yields a drag coefficient that decreases monotonically with Reynolds number and is significantly lower than the fixed sample counterparts. These findings open the possibility for the drag reduction of grooved cylinders to be operated over a wide range of flow conditions.

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Section: Introductionsupporting

confidence: 49%

Section: Introductionmentioning

confidence: 99%

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Active aerodynamic drag reduction on morphable cylinders

Guttag

Reis

2017

Phys. Rev. Fluids

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“…The following ideas have been previously tested: grooves, [3][4][5] bumps and dimples, [6][7][8] and screens, [9,10] among others. These studies showed that surface manipulation can effectively delay the separation point.…”

Section: Discussionmentioning

confidence: 99%

Surface pressure distribution on patterned cylinders under simulated atmospheric boundary layer winds

Ferreira

Amirinia

Jung

2017

Structural Design Tall Build

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SummaryExtensive research has been previously conducted on pressure distribution of cylindrical models under uniform and laminar flow conditions. However, typical civil structures such as high-rise buildings or towers are under the atmospheric boundary layer (ABL) conditions. Knowing this, the present research aims to quantify the effectiveness of surface patterns in reducing the suction zone under a simulated ABL condition. Two different surface patterns, U-grooved and V-grooved, were selected to be tested in wind tunnel. In addition to patterned cylinders, tests were also conducted on a smooth-surfaced cylinder, serving as the control of the experiment. An array of roughness elements was placed at the upstream end of the test section with the purpose of inducing ABL winds within the test section. Without the ABL wind, the cylinder covered in V-grooved riblets was most effective in reducing the suction zone followed by the U-grooved cylinder. With the simulated ABL condition, V-grooved cylinder continued to show decreased suction although the amount of decrease was less. Both grooved cylinders showed decreased peak pressure coefficients under the ABL condition compared to the non-ABL condition.KEYWORDS atmospheric boundary layer, cylinder, flow separation, pressure coefficient, surface pattern, wind tunnel 1 | INTRODUCTION High-rise buildings, categorized as any structure requiring the use of a mechanical vertical transportation system (i.e., elevators), can vary greatly in size, from a common 10-story office building to the 828-m-tall Burj Khalifa in Dubai. Although each structure faces its own design challenges, wind is a major determining factor in high-rise buildings.As wind strikes a structure, flow may remain attached or be separated from the surface of the structure. The windward side experiences a positive pressure whereas the leeward side experiences a negative pressure, often referred to as suction. [1] Flow separation typically causes an increase in pressure drag that is the form of drag caused by the pressure differences between the front (windward) and rear (leeward) surface of a structure. By delaying the separation point (occurring at a leeward point), pressure drag can be reduced.All experiments related to delaying the flow separation can be grouped into 2 major categories, passive or active. A passive mechanism is one that is related to the building architecture, where features are intentionally incorporated into a design in order to dictate fluid flow around a particular surface. Oppositely, an active mechanism requires that external energy be added into a particular system. [2] The current paper will deal strictly with passive mechanisms.The majority of techniques researched with cylindrical structures involves surface manipulation, such as added roughness or patterns. The following ideas have been previously tested: grooves, [3][4][5] bumps and dimples, [6][7][8] and screens, [9,10] among others. These studies showed that surface manipulation can effectively delay the separation point. Delay...

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“…Flow over a rough surface is known to display an early transition to turbulence, which means that a rough cylinder may have a lower drag coefficient than a smooth cylinder at a certain range of Reynolds numbers [3]. Different types of roughness pattern have been considered by previous researchers, for example dimples and grooves [2,3], surface trip wire [9,14], roughness strips [10], dimples [4,12], grooves [8,7,13], helical strakes [18], screened surface [11], and periodic blowing and suction [6], among others.…”

Section: Introductionmentioning

confidence: 98%