Development of flow structures over dimples

Tay, C. M.; Chew, Y. T.; Khoo, Boo Cheong; Zhao, Jincheng

doi:10.1016/j.expthermflusci.2013.10.001

Cited by 47 publications

(23 citation statements)

References 19 publications

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“…The presence of flow separation is intuitively likely to cause an increase in drag. In their numerical study, Isaev et al 6 found that dimples with depth to diameter ratios of less than 6% have no separated flow, though Tay et al 8 show that the exact depth to diameter ratio where flow separation appears depends not on just the dimple depth to diameter ratio but on the flow Reynolds number as well. These results suggest that shallow dimples have greater potential for drag reduction.…”

Section: Introductionmentioning

confidence: 97%

“…Burgess and Ligrani 2 further found that for dimples with a depth to diameter ratio of 30%, the friction factor increases with Reynolds numbers, but for dimples with depth to diameter ratios of 10% and 20%, the friction factors show little change as the Reynolds number varies. Isaev et al 6 and Tay et al 8 found that flow separation is minimised with decreasing dimple depth. The presence of flow separation is intuitively likely to cause an increase in drag.…”

Section: Introductionmentioning

confidence: 98%

“…The effect of the dimple depth to diameter ratio has been well studied both experimentally [1][2][3][4][5] and numerically. 6,7 Flow visualization 1,8 and numerical studies 6 show that dimples with depth to diameter ratios greater than 10% result in the generation of vertical and streamwise vortices. These vortices, which are sometimes periodic, greatly increase the mixing within the flow.…”

Section: Introductionmentioning

confidence: 98%

“…Sharp edged dimples encourage flow separation as the flow enters the dimple depression, further increasing mixing and heat transfer. 3,8 The majority of these studies involve dimples in an internal flow environment such as in a channel or pipe. Numerous empirical relations have been proposed relating practically useful parameters such as Nusselt numbers and friction factors with the dimple depth to diameter ratio, Reynolds number, inlet turbulence intensity, channel height, and even the channel aspect ratio.…”

Section: Introductionmentioning

confidence: 99%

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Mechanics of drag reduction by shallow dimples in channel flow

2015

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Arrays of shallow dimples with depth to diameter ratios of 1.5% and 5% are studied in a turbulent channel flow at Reynolds numbers between 5000 and 35 000. Pressure measurements show that drag reduction of up to 3% is possible. The mechanism of skin friction drag reduction with dimples is the same as that observed for flat surfaces using active methods such as spanwise wall motions or transverse wall jets. The three dimensional dimples introduce streamwise vorticity into the flow which results in spanwise flow components near the wall. The result is that the normal energy cascade to the smaller scales is suppressed, which leads to a reduction in turbulent skin friction drag because of the stabilized flow. Increasing the dimple depth from 1.5% to 5% of its diameter increases the streamwise vorticity introduced, which leads to a greater reduction in skin friction. However, increasing the dimple depth also results in flow separation which increases form drag. The net effect to the total drag depends on the relative dominance between the drag reducing streamwise vorticity and the drag increasing flow separation region. As the Reynolds number increases, the region of flow separation can shrink and result in increasing drag reduction. By understanding the flow physics of drag reduction in dimples, there is opportunity to minimize the form drag by passive contouring of the dimples using non-spherical shapes to optimize the dimple performance.

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Section: Introductionmentioning

confidence: 97%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 98%

Section: Introductionmentioning

confidence: 99%

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Mechanics of drag reduction by shallow dimples in channel flow

2015

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“…Xie et al [25,26] numerically investigated flow characteristics and heat transfer performance for a rectangular channel surface with internal-protruded dimples. Tay et al [27] applied the flow visualization method to study the various flow structures as Re D varied from 1000 to 28000.…”

Section: Introductionmentioning

confidence: 99%

Numerical Study on the Effect of Tube Rows on the Heat Transfer Characteristic of Dimpled Fin

Feng

Liu

et al. 2014

Advances in Mechanical Engineering

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The dimpled fin has excellent heat transfer performance and has attracted a lot of attention to apply on the fin and tube heat exchanger. A study presents to investigate the effects of number of tube rows on the air-side heat transfer characteristics of dimpled fin for velocity ranging from 1 to 3 m/s. The /Δ and /((Δ × )) are used to evaluate the heat transfer performance of the heat exchanger. The results show that the dimpled arrangement can change the mainstream direction, increase the disturbance, and enhance the heat transfer. With the increase of the number of tube rows, the average Nusselt number decreases and /Δ and /((Δ × )) increase gradually. Compared with the multipipe tube rows, the performance of two-row tube is better.

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