Mobile QR Code QR CODE : Journal of the Korean Society of Civil Engineers

  1. ์—ฐ์„ธ๋Œ€ํ•™๊ต ๋Œ€ํ•™์› ํ† ๋ชฉํ™˜๊ฒฝ๊ณตํ•™๊ณผ ์„๋ฐ•์‚ฌํ†ตํ•ฉ๊ณผ์ • (Yonsei University)
  2. ์—ฐ์„ธ๋Œ€ํ•™๊ต ๊ณต๊ณผ๋Œ€ํ•™ ํ† ๋ชฉํ™˜๊ฒฝ๊ณตํ•™๊ณผ ๊ต์ˆ˜ (Yonsei University)


๋‚œ๋ฅ˜, ์กฐ์ง๊ตฌ์กฐ, Bursting ํ˜„์ƒ, uw ์‚ฌ๋ถ„๋ฉด๊ธฐ๋ฒ•, ํฐ ์™€ ์ˆ˜์น˜๋ชจ์˜, OpenFOAM
Turbulence, Coherent structure, Bursting phenomena, uw quadrant threshold, Large eddy simulation, OpenFOAM

  • 1. ์„œ ๋ก 

  • 2. ์ง€๋ฐฐ๋ฐฉ์ •์‹

  •   2.1 ์œ ๋™๋ชจํ˜•

  •   2.2 Subgrid-scale ๋ชจํ˜•

  • 3. ์ˆ˜์น˜ํ•ด์„ ๋ฐฉ๋ฒ• ๋ฐ ์ ์šฉ

  • 4. Bursting ํ˜„์ƒ์˜ ๋ถ„์„

  •   4.1 ์‚ฌ๋ถ„๋ฉด๊ธฐ๋ฒ•

  •   4.2 Bursting ํ˜„์ƒ์ด ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ

  • 5. ๊ฒฐ ๋ก 

1. ์„œ ๋ก 

Kline et al. (1967)์€ ์ˆ˜์†Œ๊ธฐํฌ ๊ฐ€์‹œํ™”์‹คํ—˜(hydrogen-bubble visualization)์„ ์ด์šฉํ•ด ์ €์ธต(sublayer)์—์„œ ์ƒ๋Œ€์ ์œผ๋กœ ์œ ์†์ด ๋น ๋ฅธ ๊ณ ์†์˜์—ญ(high-velocity streaks)๊ณผ ์œ ์†์ด ๋А๋ฆฐ ์ €์†์˜์—ญ(low-velocity streaks)์œผ๋กœ ๊ตฌ๋ถ„์ด ๋˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•˜๊ณ , ์ €์†์˜์—ญ์—์„œ ์ƒ์Šน(lift-up), ์ง„๋™(oscillation), ๋ถ„์ถœํ˜„์ƒ(ejection)์˜ ์ผ๋ จ์˜ ๊ณผ์ •์„ ๋ฐํ˜€๋ƒˆ๋‹ค. Corino and Brodkey (1969)๋Š” Kline et al. (1967)๊ณผ ๋™์ผํ•œ ํ˜„์ƒ์„ ํ™•์ธํ•˜๊ณ , ์ถ”๊ฐ€๋กœ ๊ณ ์†์˜์—ญ์—์„œ ํ•˜๊ฐ•๋ฅ˜๊ฐ€ ๋‚˜ํƒ€๋‚˜๋Š” ํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ(sweep)์„ ๋ฐํ˜€๋ƒˆ๋‹ค. Kline et al. (1967)๊ณผ Corino and Brodkey (1969)๊ฐ€ ๋ฐํ˜€๋‚ธ ์ƒ์Šน, ์ง„๋™, ๋ถ„์ถœ, ์“ธ๊ธฐ์˜ ์ผ๋ จ์˜ ๊ณผ์ •์„ Bursting ํ˜„์ƒ(Bursting phenomena)์ด๋ผ๊ณ  ํ•œ๋‹ค.

๋‚œ๋ฅ˜์˜ Bursting ํ˜„์ƒ์€ ํ•˜์ƒ ํ† ๋ฆฝ์ž๋‚˜ ๋ถ€์œ ์‚ฌ์˜ ๋†๋„์™€ ๊ฐ™์€ ์Šค์นผ๋ผ๋Ÿ‰์˜ ์ด์†ก๊ณผ ๋ฐ€์ ‘ํ•œ ๊ด€๊ณ„๊ฐ€ ์žˆ๋Š” ๊ฒƒ์œผ๋กœ ๋ฐํ˜€์ง€๊ณ  ์žˆ๋‹ค. Niรฑo and Garcia (1996)์€ ์œ ์‚ฌ์˜ ๊ฑฐ๋™์€ Bursting ํ˜„์ƒ๊ณผ ๊ด€๋ จ์ด ์žˆ๋Š” ๊ฒƒ์œผ๋กœ ๋ฐํ˜”๊ณ , Gyr and Schmid (1997)์€ ๋ฒฝ ๊ทผ์ฒ˜์˜ ์œ ์‚ฌ์˜ ๊ฑฐ๋™์ด ์ €์† ์˜์—ญ์—์„œ ์ƒ์Šน๊ณผ ๋ถ„์ถœํ˜„์ƒ์— ์˜ํ•ด ์˜ํ–ฅ์„ ๋ฐ›๋Š”๋‹ค๊ณ  ๋ณด์˜€๋‹ค.

๊ณผ๊ฑฐ์˜ ์กฐ์ง๊ตฌ์กฐ์˜ ๋ถ„์„์€ ์ฃผ๋กœ ์‹คํ—˜์  ์—ฐ๊ตฌ์— ์˜ํ•ด ์ˆ˜ํ–‰๋˜์–ด ์™”๋‹ค. ์ตœ๊ทผ์—์„œ์•ผ ์ˆ˜์น˜๋ชจ์˜๋ฅผ ๊ธฐ๋ฐ˜์œผ๋กœ ํ•œ ์กฐ์ง๊ตฌ์กฐ ์—ฐ๊ตฌ๊ฐ€ ํ™œ๋ฐœํžˆ ์ง„ํ–‰๋˜๊ธฐ ์‹œ์ž‘ํ•˜์˜€๋‹ค. ๋‚œ๋ฅ˜๋ฅผ ๋ชจ์˜ํ•˜๋Š” ๋ฐฉ๋ฒ•์œผ๋กœ๋Š” ํฌ๊ฒŒ DNS (Direct Numerical Simulation), RANS (Reynolds Averaged Navier-Stokes) ๋ชจํ˜•, ๊ทธ๋ฆฌ๊ณ  LES (Large Eddy Simulation)๊ฐ€ ์žˆ๋‹ค. ์ž‘์€ ๊ทœ๋ชจ์˜ ์™€(ๆธฆ)๋Š” ๋ฌด์ž‘์œ„์„ฑ์„ ์ง€๋‹Œ ์•„์ฃผ ๋ฏธ์„ธํ•œ ๊ตฌ์กฐ์˜ ๋“ฑ๋ฐฉ์„ฑ ๋‚œ๋ฅ˜๋กœ ๊ตฌ์„ฑ๋˜์–ด ์žˆ๋‹ค, ํ•˜์ง€๋งŒ, ํฐ ๊ทœ๋ชจ์˜ ์™€(ๆธฆ)๋Š” ํ‰๊ท ํ๋ฆ„๊ณผ์˜ ์ƒํ˜ธ์ž‘์šฉ์— ์˜ํ•ด ์กฐ์ง์ ์œผ๋กœ ๋ณ€ํ•˜๋Š” ๊ตฌ์กฐ๋ฅผ ๊ฐ€์ง€๊ณ  ์žˆ๋‹ค. RANS์˜ ๊ฒฝ์šฐ ๋ชจ๋“  ํฌ๊ธฐ์˜ ๊ทœ๋ชจ์˜ ์™€๋ฅผ ๋Œ€ํ‘œํ•˜๋Š” ํฌ๊ธฐ๋ฅผ ํ™œ์šฉํ•ด์„œ ์‹œ๊ฐ„ ํ‰๊ท ๋œ Navier-Stokes ๋ฐฉ์ •์‹์„ ํ•ด์„ํ•˜๊ธฐ ๋•Œ๋ฌธ์—, ๋ณ€๋™์„ฑ๋ถ„์— ์˜ํ•œ ์กฐ์ง์  ๋ณ€๋™ ๊ตฌ์กฐ๋ฅผ ์ง€๋‹Œ ๋‚œ๋ฅ˜๋ฅผ ํ•ด์„ํ•˜๊ธฐ์—” ์ ํ•ฉํ•˜์ง€ ์•Š๋‹ค. LES ๋˜๋Š” DNS๋Š” ํฐ ๊ทœ๋ชจ์˜ ์™€(ๆธฆ)์— ๋Œ€ํ•ด์„œ Navier-Stokes ๋ฐฉ์ •์‹์„ ์ง์ ‘ ํ•ด์„ํ•˜๊ธฐ ๋•Œ๋ฌธ์— ์กฐ์ง๊ตฌ์กฐ๋ฅผ ๋ถ„์„ํ•˜๋Š”๋ฐ ์ ํ•ฉํ•œ ๋„๊ตฌ์ด๋‹ค. ํ•˜์ง€๋งŒ, ํฐ ๋ ˆ์ด๋†€์ฆˆ ์ˆ˜๋ฅผ ๊ฐ€์ง„ ํ๋ฆ„์—์„œ ๊ณ„์‚ฐ๋น„์šฉ์„ ๊ณ ๋ คํ•˜๊ฒŒ ๋œ๋‹ค๋ฉด DNS๋ณด๋‹ค LES ๋ชจํ˜•์ด ๋” ์ ํ•ฉํ•˜๋‹ค๊ณ  ํŒ๋‹จ๋œ๋‹ค.

์ตœ๊ทผ์— Nezu and Sanjou (2008)์€ ์นจ์ˆ˜์‹์ƒ ๊ฐœ์ˆ˜๋กœ ํ๋ฆ„์—์„œ ์‹คํ—˜ ๊ฒฐ๊ณผ๋ฅผ ํ† ๋Œ€๋กœ PIC4DE.gif์‚ฌ๋ถ„๋ฉด ๊ธฐ๋ฒ•์„ ์ ์šฉํ•˜์˜€๊ณ , ์ถ”๊ฐ€๋กœ LES ๋ชจํ˜•์„ ์ด์šฉํ•ด์„œ ์‹์ƒ์˜ ์บ๋…ธํ”ผ์—์„œ ๋ฐœ๋‹ฌํ•˜๋Š” ํฐ ๊ทœ๋ชจ์˜ ์™€(ๆธฆ) ์กฐ์ง์— ๋Œ€ํ•ด์„œ ์˜ˆ์ธกํ•˜์˜€๋‹ค. Okamoto and Nezu (2010)๋Š” ์นจ์ˆ˜์‹์ƒ ๊ฐœ์ˆ˜๋กœ ํ๋ฆ„์—์„œ ์‹คํ—˜๊ณผ LES ๋ชจํ˜•์„ ์ด์šฉํ•ด ์‹์ƒ์˜ ์บ๋…ธํ”ผ์—์„œ ๋ฐœ์ƒํ•˜๋Š” ์กฐ์ง๊ตฌ์กฐ์— ๋Œ€ํ•œ ๋น„๊ตยท๋ถ„์„ ์—ฐ๊ตฌ๋ฅผ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์ด๋Ÿฌํ•œ LES ๋ชจํ˜•์„ ํ™œ์šฉํ•œ ์กฐ์ง๊ตฌ์กฐ์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๊ฐ€ ํ™œ๋ฐœํ•œ ์ƒํ™ฉ์ธ๋ฐ, ๊ตญ๋‚ด์—์„œ๋Š” LES๋ฅผ ์ด์šฉํ•œ ํ๋ฆ„ ๋ชจ์˜ ๋ฐ ์ถ”๊ฐ€์ ์ธ ์กฐ์ง๊ตฌ์กฐ์— ๋Œ€ํ•œ ์—ฐ๊ตฌ๋Š” ๊ฑฐ์˜ ์—†๋Š” ์‹ค์ •์ด๋‹ค.

๋”ฐ๋ผ์„œ ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” LES ๋ชจํ˜•์„ ์ด์šฉํ•˜์—ฌ ๋งค๋ˆํ•œ ํ•˜์ƒ์˜ ์ง์‚ฌ๊ฐํ˜• ๊ฐœ์ˆ˜๋กœ ํ๋ฆ„์„ ๋ชจ์˜ํ•˜๊ณ , Bursting ํ˜„์ƒ์„ ๋ถ„์„ํ•˜๊ณ ์ž ํ•œ๋‹ค. Bursting ํ˜„์ƒ์˜ ๊ตฌ์กฐ๋ฅผ ๊ทœ๋ช…ํ•˜๊ธฐ ์œ„ํ•œ ๊ธฐ๋ฒ•์œผ๋กœ๋Š” ๋Œ€ํ‘œ์ ์œผ๋กœ Blackwelder and Kaplan (1976)์— ์˜ํ•ด ์ œ์•ˆ๋œ VITA (Variable Interval Time Average) ๊ธฐ๋ฒ•๊ณผ Lu and Willmarth (1973)์— ์˜ํ•ด ์ œ์•ˆ๋œ uw ์‚ฌ๋ถ„๋ฉด ๊ธฐ๋ฒ•(uw quadrant threshold)์ด ์žˆ๋‹ค. ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” Bursting ํ˜„์ƒ์„ ๋ถ„์„ํ•˜๊ธฐ ์œ„ํ•ด์„œ uw ์‚ฌ๋ถ„๋ฉด ๊ธฐ๋ฒ•์„ ์ด์šฉํ•˜๊ณ ์ž ํ•œ๋‹ค. ๋งค๋ˆํ•œ ํ•˜์ƒ์—์„œ LES๋ชจํ˜•์„ ์ด์šฉํ•œ ์กฐ์ง๊ตฌ์กฐ์˜ ๋ถ„์„์€ ํ–ฅํ›„ ๋‹ค๋ฐฉ๋ฉด์˜ ํ๋ฆ„์—์„œ์˜ ์กฐ์ง๊ตฌ์กฐ ์—ฐ๊ตฌ์— ๊ธฐ๋ฐ˜์ด ๋  ์ˆ˜ ์žˆ์„ ๊ฒƒ์ด๋‹ค.

2. ์ง€๋ฐฐ๋ฐฉ์ •์‹

2.1 ์œ ๋™๋ชจํ˜•

LES์˜ ์ง€๋ฐฐ๋ฐฉ์ •์‹์€ ์—ฐ์† ๋ฐฉ์ •์‹๊ณผ ์šด๋™๋Ÿ‰ ๋ฐฉ์ •์‹์„ ๊ณต๊ฐ„ ํ•„ํ„ฐ์— ์ ์šฉํ•˜์—ฌ ์—ฌ๊ณผ(spatial averaging)์‹œ์ผœ ์–ป์„ ์ˆ˜ ์žˆ๋‹ค. ์—ฌ๊ณผ๋œ ์—ฐ์†๋ฐฉ์ •์‹๊ณผ ์šด๋™๋Ÿ‰๋ฐฉ์ •์‹์€ ๊ฐ๊ฐ ๋‹ค์Œ๊ณผ ๊ฐ™๋‹ค.

PIC675.gif (1)

PIC731.gif (2)

์—ฌ๊ธฐ์„œ PIC780.gif๋Š” PIC7B0.gif ๋ฐฉํ–ฅ์œผ๋กœ์˜ ์ˆœ๊ฐ„์†๋„(instantaneous velocity), PIC7F0.gif๋Š” PIC810.gif ๋ฐฉํ–ฅ์œผ๋กœ์˜ ์—ฌ๊ณผ ์†๋„(filtered velocity), PIC840.gif๋Š” ์—ฌ๊ณผ๋œ ์••๋ ฅ(filtered pressure), PIC89F.gif๋Š” ๋ฌผ์˜ ๋ฐ€๋„, PIC8BF.gif๋Š” ๋ฌผ์˜ ๋™์ ์„ฑ ๊ณ„์ˆ˜์ด๋‹ค. Eq. (2)์˜ ์ขŒ์ธก ๋‘ ๋ฒˆ์งธ ํ•ญ์„ ์ž”์—ฌ ์‘๋ ฅํ•ญ(subgird-sclae stress) PIC8EF.gif์œผ๋กœ ๋‚˜ํƒ€๋‚ด๋ฉด ๋‹ค์Œ๊ณผ ๊ฐ™๋‹ค.

PIC94E.gif (3)

Eq. (3)์„ Eq. (2)์— ๋Œ€์ž…ํ•˜์—ฌ ์ •๋ฆฌํ•˜๋ฉด ๋‹ค์Œ๊ณผ ๊ฐ™์€ LES์˜ ์šด๋™๋Ÿ‰ ๋ฐฉ์ •์‹์„ ์–ป์„ ์ˆ˜ ์žˆ๋‹ค.

PICAA6.gif (4)

2.2 Subgrid-scale ๋ชจํ˜•

์ง€๋ฐฐ๋ฐฉ์ •์‹์˜ ์™„๊ฒฐ ๋ฌธ์ œ(closure problem)์„ ํ•ด๊ฒฐํ•˜๊ธฐ ์œ„ํ•ด ์—ฌ๊ณผ ๊ณผ์ •์—์„œ ๋ฐœ์ƒํ•œ ๋น„๋“ฑ๋ฐฉ์„ฑ ์ž”์—ฌ ์‘๋ ฅํ•ญ์— ๋Œ€ํ•œ ๋ชจ๋ธ๋ง์ด ํ•„์š”ํ•˜๋‹ค. ์ž”์—ฌ ์‘๋ ฅํ•ญ์€ ๋‹ค์Œ๊ณผ ๊ฐ™์ด ๋“ฑ๋ฐฉ์„ฑ ์š”์†Œ์™€ ๋น„๋“ฑ๋ฐฉ์„ฑ ์š”์†Œ๋กœ ๋‚˜๋‰˜๊ฒŒ ๋œ๋‹ค.

PICCAB.gif (5)

์—ฌ๊ธฐ์„œ PICCCB.gif๋Š” Kronecker delta์ด๋‹ค. ๋น„๋“ฑ๋ฐฉ์„ฑ ์ž”์—ฌ ์‘๋ ฅํ•ญ PICD1A.gif๋ฅผ ์™€์ ์„ฑ ๊ฐœ๋…(eddy-viscosity concept)์— ์˜ํ•ด ๋‚˜ํƒ€๋‚ด๋ฉด ๋‹ค์Œ๊ณผ ๊ฐ™๋‹ค.

PICD69.gif (6)

PICDC8.gif (7)

์—ฌ๊ธฐ์„œ PICE37.gif๋Š” ์—ฌ๊ณผ ์†๋„์— ๋Œ€ํ•œ ๋ณ€ํ˜•๋ฅ , PICEA5.gif๋Š” ์ž”์—ฌ์œ ์†์˜ ๋‚œ๋ฅ˜ ์ ์„ฑ๊ณ„์ˆ˜์ด๋‹ค. ํ˜ผํ•ฉ๊ฑฐ๋ฆฌ ๋ชจํ˜•์„ ์‚ฌ์šฉํ•˜์—ฌ ์ž”์—ฌ์œ ์†์˜ ๋‚œ๋ฅ˜ ์ ์„ฑ๊ณ„์ˆ˜๋ฅผ ์ •์˜ํ•˜๋ฉด ๋‹ค์Œ๊ณผ ๊ฐ™๋‹ค.

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์—ฌ๊ธฐ์„œ PICF92.gif๋Š” ํ•„ํ„ฐ์˜ ํฌ๊ธฐPICFD2.gif, ๊ทธ๋ฆฌ๊ณ  PIC1040.gif๋Š” Smagorinsky ์ƒ์ˆ˜์ด๋‹ค. ๋Œ€ํ‘œ์ ์ธ Smagoinky ์ƒ์ˆ˜ ๊ฒฐ์ • ๋ชจํ˜•์€ Smagorinsky (1963)๊ฐ€ ์ œ์•ˆํ•œ Smagorinksy ๋ชจํ˜•์ด ์žˆ๊ณ , Germano et al. (1991)์™€ Lilly (1992)๊ฐ€ ์ œ์•ˆํ•œ dynamic sub-grid ๋ชจํ˜•์ด ์žˆ๋‹ค. Smagorinksy ๋ชจํ˜•์˜ ๊ฒฝ์šฐ ์ „๋‹จํ๋ฆ„(shear flows)์—์„œ Smagorinksy ์ƒ์ˆ˜๋Š” ๋ฒ”์œ„๋กœ ์ œ์‹œ๋˜์–ด ์žˆ๊ณ , ๋ฒฝ ๊ทผ์ฒ˜์—์„œ๋Š” ์ถ”๊ฐ€์ ์œผ๋กœ ๊ฐ์‡„ํ•จ์ˆ˜ (damping function)๋ฅผ ์ ์šฉํ•˜๋Š” ๊ณผ์ •์ด ํ•„์š”ํ•˜๋‹ค. ๋”ฐ๋ผ์„œ ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” 2์ฐจ ์—ฌ๊ณผ๊ณผ์ •์„ ํ†ตํ•ด ์ž๋™์ ์œผ๋กœ Smagorinksy ์ƒ์ˆ˜๋ฅผ ๊ฒฐ์ •ํ•˜๋Š” ๋‹ค์Œ์˜ dynamic sub-grid ๋ชจํ˜•์„ ์‚ฌ์šฉํ•˜์˜€๋‹ค.

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์—ฌ๊ธฐ์„œ PIC1332.gif๋Š” ํ…Œ์ŠคํŠธ ํ•„ํ„ฐ์ด๊ณ , (PIC13B0.gif)๋Š” ํ…Œ์ŠคํŠธ ํ•„ํ„ฐ์— ์ ์šฉํ•˜์—ฌ ์—ฌ๊ณผ์‹œํ‚จ ํ•ญ์ด๋‹ค.

                              

3. ์ˆ˜์น˜ํ•ด์„ ๋ฐฉ๋ฒ• ๋ฐ ์ ์šฉ

๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ์—ฌ๊ณผ๋œ ์—ฐ์† ๋ฐฉ์ •์‹๊ณผ ์šด๋™๋Ÿ‰ ๋ฐฉ์ •์‹์„ ๊ณ„์‚ฐํ•˜๊ธฐ ์œ„ํ•ด์„œ OpenFOAM์—์„œ ์ œ๊ณตํ•˜๋Š” LES ์†Œ์Šค์ฝ”๋“œ๋ฅผ ์ด์šฉํ•˜์˜€๋‹ค. OpenFOAM์€ ์†Œ์Šค ์ฝ”๋“œ๊ฐ€ ๊ณต๊ฐœ๋œ ์ „์‚ฐ์œ ์ฒด์—ญํ•™ ํ•ด์„์„ ์œ„ํ•œ ์†Œํ”„ํŠธ์›จ์–ด ํŒจํ‚ค์ง€์ด๋‹ค. OpenFOAM์€ ์˜๊ตญ์˜ Imperial College์—์„œ 2004๋…„์— ๊ณต๊ฐœ ์ฝ”๋“œ๋กœ ๋ฐœํ‘œ ๋˜์—ˆ์œผ๋ฉฐ, ์ดํ›„ ๊พธ์ค€ํžˆ ์—…๊ทธ๋ ˆ์ด๋“œ๊ฐ€ ์ง„ํ–‰ํ•ด ์™”๋‹ค. OpenFOAM์˜ ์žฅ์ ์€ C ์–ธ์–ด๋ฅผ ์ด์šฉํ•˜์—ฌ ์–ด๋–ค ๊ธฐ๋Šฅ์ด๋“  ์ถ”๊ฐ€ํ•  ์ˆ˜ ์žˆ๋Š” ์šฐ์ˆ˜ํ•œ ์ ‘๊ทผ์„ฑ์„ ์ง€๋‹ˆ๊ณ  ์žˆ๊ธฐ ๋•Œ๋ฌธ์— ์—ฐ๊ตฌ๊ฐœ๋ฐœ์˜ ํ™•์žฅ์„ฑ์„ ๋ณด์žฅํ•œ๋‹ค. OpenFOAM์—์„œ ์ œ๊ณตํ•˜๋Š” ํ•ด์„์ฝ”๋“œ๋Š” ์ง๊ต์ขŒํ‘œ๊ณ„์—์„œ ์œ ํ•œ์ฒด์ ๋ฒ•์„ ์ด์šฉํ•˜๊ณ , ์ง€๋ฐฐ๋ฐฉ์ •์‹์„ ์ด์‚ฐํ™”ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ Harlow and Weich (1965)๊ฐ€ ์ œ์•ˆํ•œ ์—‡๊ฐˆ๋ฆฐ ๊ฒฉ์ž์ฒด๊ณ„(staggered Cartesian grid)๋ฅผ ์ด์šฉํ•œ๋‹ค. ์ฐจ๋ถ„ ๊ธฐ๋ฒ•์œผ๋กœ๋Š” ์••๋ ฅํ•ญ๊ณผ ํ™•์‚ฐํ•ญ์— ๋Œ€ํ•ด ์ค‘์•™ ์ฐจ๋ถ„๋ฒ•์„ ์‚ฌ์šฉํ•˜์˜€๊ณ , ์‹œ๊ฐ„ํ•ญ์— ๋Œ€ํ•ด ํ›„๋ฐฉ ์ฐจ๋ถ„๋ฒ•์„ ์‚ฌ์šฉํ•˜์˜€๋‹ค. ์œ ์†-์••๋ ฅ ์ƒ๊ด€๊ด€๊ณ„๋ฅผ ๊ณ„์‚ฐํ•˜๊ธฐ ์œ„ํ•˜์—ฌ Issa et al. (1986)์ด ์ œ์•ˆํ•œ PISO ์•Œ๊ณ ๋ฆฌ์ฆ˜์„ ์‚ฌ์šฉํ•˜์˜€๋‹ค.

Fig. 1์€ ๊ณ„์‚ฐ์˜์—ญ๊ณผ ๊ฒฝ๊ณ„์กฐ๊ฑด์„ ๋‚˜ํƒ€๋‚ธ ๊ทธ๋ฆผ์ด๋‹ค. ์ธก๋ฒฝ๊ณผ ๋ฐ”๋‹ฅ๋ฒฝ์˜ ๊ฒฝ๊ณ„์กฐ๊ฑด์œผ๋กœ๋Š” ๋น„ํ™œ๋™ ์กฐ๊ฑด(no-slip)์„ ์ด์šฉํ•˜์˜€๊ณ , ์ˆ˜๋ฉด์˜ ๊ฒฝ๊ณ„์กฐ๊ฑด์€ ๋Œ€์นญ ์กฐ๊ฑด(symmetry condition)์„ ์ด์šฉ, ์ฃผํ๋ฆ„๋ฐฉํ–ฅ์œผ๋กœ์˜ ์œ ์ž…ยท์œ ์ถœ๋ถ€์˜ ๊ฒฝ๊ณ„์กฐ๊ฑด์€ ์™„์ „ํžˆ ๋ฐœ๋‹ฌ๋œ ํ๋ฆ„์œผ๋กœ ๊ฐ€์ •ํ•˜๊ณ  ์ฃผ๊ธฐ ์กฐ๊ฑด(cyclic condition)์„ ์ ์šฉํ•˜์˜€๋‹ค. ๊ณ„์‚ฐ์˜์—ญ์€ PIC141F.gif์œผ๋กœ ๊ฐ๊ฐ ์ฃผํ๋ฆ„๋ฐฉํ–ฅ, ํšก๋ฐฉํ–ฅ, ์—ฐ์ง๋ฐฉํ–ฅ์„ ์˜๋ฏธํ•˜๊ณ , ์ฃผํ๋ฆ„๋ฐฉํ–ฅ์œผ๋กœ์˜ ๊ณ„์‚ฐ์˜์—ญ์˜ ๊ธธ์ด PIC151A.gif๋Š” ๋ชจ๋“  ์œ ์†์„ฑ๋ถ„์˜ ์ฃผํ๋ฆ„๋ฐฉํ–ฅ ์ƒ๊ด€์„ฑ(streamwise correlation)์ด ๊ฑฐ์˜ 0์ด ๋˜๊ธฐ์— ์ถฉ๋ถ„ํ•˜๋‹ค. ๊ณ„์‚ฐ์˜์—ญ์€ PIC15E6.gif๊ฐœ์˜ ์ ˆ์ ์œผ๋กœ ์ด์‚ฐํ™” ํ•˜์˜€์œผ๋ฉฐ, ๊ฒฉ์ž๊ฐ„ ๊ฑฐ๋ฆฌ๋Š” ๋ฌด์ฐจ์› ๊ฑฐ๋ฆฌ๋กœ PIC1635.gif, PIC16A3.gif์ด๋‹ค.

๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” Tominaga et al. (1989)์˜ ํญ-์ˆ˜์‹ฌ๋น„๊ฐ€ 2์ธ ๋งค๋ˆํ•œ ํ•˜์ƒ์˜ ์ง์‚ฌ๊ฐํ˜• ์‹คํ—˜์ˆ˜๋กœ์— ์ˆ˜์น˜๋ชจ์˜๋ฅผ ์ˆ˜ํ–‰ํ•˜๊ณ , ์ˆ˜๋กœ ์ค‘์•™์—์„œ ๋ฐ”๋‹ฅ๋ฉด์œผ๋กœ๋ถ€ํ„ฐ์˜ ๊ฑฐ๋ฆฌ๋ฅผ ๋‹ฌ๋ฆฌํ•˜์—ฌ ์œ ์†์˜ ์‹œ๊ณ„์—ด ์ž๋ฃŒ๋ฅผ ์ถ”์ถœํ•˜๊ณ  Bursting ํ˜„์ƒ์„ ๋ถ„์„ํ•˜์˜€๋‹ค. Table 1์€ Tominaga et al. (1989)์˜ ์‹คํ—˜์ˆ˜๋กœ์˜ ์ œ์›์ด๋‹ค. ํ‰๊ท ํ๋ฆ„ ๋ฐ ๋‚œ๋ฅ˜๋Ÿ‰์— ๋Œ€ํ•œ ๋ถ„์„์€ Ban and Choi (2014)์— ํฌํ•จํ•˜์˜€๋‹ค.

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Fig. 1. Computational Domain and Boundary Conditions for LES

Table 1. Experimental Conditions of Open-Channel Flow with Smooth Bed (Tominaga et al., 1989)

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0.2

0.4

2

0.192

0.244

7.31

0.18

4. Bursting ํ˜„์ƒ์˜ ๋ถ„์„

4.1 PIC28A3.gif ์‚ฌ๋ถ„๋ฉด๊ธฐ๋ฒ•

PIC2940.gif ์‚ฌ๋ถ„๋ฉด๊ธฐ๋ฒ•์€ Lu and Willmarth (1973)์— ์˜ํ•ด ์ œ์•ˆ๋œ ๊ธฐ๋ฒ•์œผ๋กœ, ์ง„๋™์†๋„(fluctuate velocity) PIC2980.gif์™€ PIC29CF.gif๋ฅผ ์ด์šฉํ•˜์—ฌ Bursting ํ˜„์ƒ์ด ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ๊ณผ Bursting ํ˜„์ƒ์˜ ์ฃผ๊ธฐ๋ฅผ ํŒŒ์•…ํ•  ์ˆ˜ ์žˆ๋‹ค. ์ˆœ๊ฐ„ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์€ ๊ฐ ์ง„๋™์†๋„์˜ ๋ถ€ํ˜ธ์™€ ์ž„์˜์˜ ๋ฐฐ์ œ์กฐ๊ฑด(threshold level)์— ์˜ํ•ด Fig. 2์™€ ๊ฐ™์ด ์™ธํ–ฅ์ƒํ˜ธ์ž‘์šฉ(outward interaction event), ๋ถ„์ถœํ˜„์ƒ(ejection event), ๋‚ดํ–ฅ์ƒํ˜ธ์ž‘์šฉ(inward interaction event), ์“ธ๊ธฐํ˜„์ƒ(sweep event), ๋ฐฐ์ œ์˜์—ญ(hole)์œผ๋กœ ์ด 5๊ฐœ์˜ ์˜์—ญ์œผ๋กœ ๋‚˜๋‰˜๊ฒŒ ๋œ๋‹ค. ๋ฐฐ์ œ์กฐ๊ฑด H๋Š” ์ž„์˜ ํฌ๊ธฐ์˜ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์„ ์‹œ๊ฐ„ ํ‰๊ท ๋œ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์œผ๋กœ ๋ฌด์ฐจ์›ํ™” ์‹œํ‚จ ๊ฐ’์œผ๋กœ ๋‹ค์Œ๊ณผ ๊ฐ™์ด ์ •์˜๋œ๋‹ค.

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Fig. 2. Schematic Division of the Four Quadrants

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๊ฐ ์˜์—ญ์— ํฌํ•จ๋˜๋Š” ์ˆœ๊ฐ„ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์ด(PIC2BF5.gif)์ด ์‹œ๊ฐ„ํ‰๊ท ๋œ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ(PIC2C63.gif)์— ๋ฏธ์น˜๋Š” ๊ธฐ์—ฌ์œจ(contribution rate) PIC2CB2.gif์€ ๋‹ค์Œ์˜ ์‹์œผ๋กœ๋ถ€ํ„ฐ ๊ณ„์‚ฐ๋œ๋‹ค.

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์—ฌ๊ธฐ์„œ 1์‚ฌ๋ถ„๋ฉด๊ณผ 3์‚ฌ๋ถ„๋ฉด์— ํ•ด๋‹นํ•˜๋Š” PIC32B0.gif๊ณผ PIC32D1.gif์€ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์ƒ์„ฑ ์ค‘ ์Œ์˜ ์ƒ์„ฑ(negative production)์— ๊ธฐ์—ฌํ•˜๋Š” ๋น„์œจ์ด๊ณ , 2์‚ฌ๋ถ„๋ฉด๊ณผ 4์‚ฌ๋ถ„๋ฉด์— ํ•ด๋‹นํ•˜๋Š” PIC3301.gif์™€ PIC3350.gif๋Š” ์–‘์˜ ์ƒ์„ฑ์—(positive production)์— ๊ธฐ์—ฌํ•˜๋Š” ๋น„์œจ์ด๋‹ค. PIC33AE.gif(PIC340D.gif)๋Š” ์ˆœ๊ฐ„ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์„ ์‹œ๊ฐ„ํ‰๊ท  ๋œ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์œผ๋กœ ๋ฌด์ฐจ์›ํ™” ์‹œํ‚จ ๋ณ€์ˆ˜์ด๊ณ , PIC346C.gif๋Š” ๊ฐ ์‚ฌ๋ถ„๋ฉด์— ํฌํ•จ๋˜๋Š” ์ˆœ๊ฐ„ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์กฐ๊ฑด๋ถ€ ํ™•๋ฅ ์ด๋‹ค. ๋˜ํ•œ ์ˆœ๊ฐ„ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์ด ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์— ๋ฏธ์น˜๋Š” ์‹œ๊ฐ„๋น„(fraction time) PIC349C.gif๋Š” ๋‹ค์Œ์˜ ์‹์œผ๋กœ๋ถ€ํ„ฐ ๊ณ„์‚ฐ๋œ๋‹ค.

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์—ฌ๊ธฐ์„œ PIC3868.gif๊ณผ PIC38C6.gif์€ ์ „์ฒด ํ˜„์ƒ์˜ ์ธก์ •์‹œ๊ฐ„ ์ค‘์— ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์–‘์˜ ์ƒ์„ฑ์— ๊ธฐ์—ฌํ•˜๋Š” ํ˜„์ƒ์˜ ์‹œ๊ฐ„๋น„๋ฅผ ์˜๋ฏธํ•˜๊ณ , PIC3AEA.gif์™€ PIC3B0A.gif๋Š” ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์Œ์˜ ์ƒ์„ฑ์— ๊ธฐ์—ฌํ•˜๋Š” ์‹œ๊ฐ„๋น„๋ฅผ ์˜๋ฏธํ•œ๋‹ค.

4.2 Bursting ํ˜„์ƒ์ด ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ

Fig. 3์€ PIC3B4A.gif ์‚ฌ๋ถ„๋ฉด ๊ธฐ๋ฒ•์„ ๋ฐ”๋‹ฅ๊ณผ ๊ฐ€๊นŒ์šด ์ง€์ (PIC3C06.gif)๊ณผ ์ˆ˜์‹ฌ์˜ ์ค‘์•™(PIC3C56.gif)๊ณผ ๊ทธ๋ฆฌ๊ณ  ์ˆ˜๋ฉด์— ๊ทผ์ ‘ํ•œ ์ง€์ (PIC3DFC.gif)์—์„œ์˜ ์ง„๋™์†๋„ PIC3E8A.gif์™€ PIC3F37.gif์— ์ ์šฉํ•œ ๊ฒฐ๊ณผ์ด๋‹ค. Figs. 3(a) and 3(b)๋ฅผ ์‚ดํŽด๋ณด๋ฉด 2์‚ฌ๋ถ„๋ฉด๊ณผ 4์‚ฌ๋ถ„๋ฉด์— ํ•ด๋‹นํ•˜๋Š” ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ ์ง€๋ฐฐ์ ์œผ๋กœ ๋ฐœ์ƒํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ๋‹ค. ํŠนํžˆ ๋ฐ”๋‹ฅ์—์„œ๋Š” ์ „์ฒด ๋ฐœ์ƒํšŸ์ˆ˜์˜ 70% ์ด์ƒ์ด ๋ถ„์ถœ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์ธ ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๊ณ , ์ˆ˜์‹ฌ์˜ ์ค‘์•™์—์„œ๋Š” ์•ฝ 65% ์ด์ƒ์ด ๋ถ„์ถœ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์ธ ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ์ˆ˜๋ฉด์— ๊ฐ€๊นŒ์›Œ์งˆ์ˆ˜๋ก ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์˜ ๋ฐœ์ƒํšŸ์ˆ˜๊ฐ€ ๊ฐ์†Œํ•˜์—ฌ ์ƒํ˜ธ์ž‘์šฉ๊ณผ ๊ฑฐ์˜ ๋น„์Šทํ•œ ๋ฐœ์ƒํšŸ์ˆ˜๋ฅผ ๋‚˜ํƒ€๋‚ด๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค.

Fig. 4๋Š” ๋ฐฐ์ œ์กฐ๊ฑด์— ๋”ฐ๋ฅธ ์ˆœ๊ฐ„ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ๊ธฐ์—ฌ์œจ์„ ๋„์‹œํ•œ ๊ทธ๋ฆผ์ด๋‹ค. ์ ์šฉ ์ง€์ ์€ Fig. 3๊ณผ ๋™์ผํ•˜๊ฒŒ ๋ฐ”๋‹ฅ๊ณผ ์ค‘๊ฐ„์˜์—ญ ๊ทธ๋ฆฌ๊ณ  ์ˆ˜๋ฉด์— ๊ทผ์ ‘ํ•œ ์ง€์ ์œผ๋กœ ํ•˜์˜€๋‹ค. ๊ทธ๋ฆผ์—์„œ ๊ฐ€๋กœ์ถ•์€ ๋ฐฐ์ œ์กฐ๊ฑด์ด๊ณ , ์„ธ๋กœ์ถ•์€ ๊ธฐ์—ฌ์œจ์ด๋‹ค. ๋ฐ”๋‹ฅ๊ณผ ๊ฐ€๊นŒ์šด ์ง€์ (PIC3F76.gif)์„ ์‚ดํŽด๋ณด๋ฉด ๋ถ„์ถœํ˜„์ƒ์ด ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์ƒ์„ฑ์— ๊ฐ€์žฅ ํฐ ๊ธฐ์—ฌ๋ฅผ ํ•˜๋ฉฐ ๊ทธ ๋‹ค์Œ์œผ๋กœ ์“ธ๊ธฐํ˜„์ƒ์ด ํฌ๊ฒŒ ๊ธฐ์—ฌํ•œ๋‹ค. ๋ฐฐ์ œ์กฐ๊ฑด์ด ์ปค์ง€๋ฉด์„œ ๊ธ‰ํ•˜๊ฒŒ ๊ฐ์†Œํ•˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ์ฆ‰, ์•ฝํ•œ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ๊ธฐ์—ฌ์œจ์ด ํฐ ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ์ƒํ˜ธ์ž‘์šฉ์— ์˜ํ•œ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์ƒ์„ฑ(์Œ์˜ ์ƒ์„ฑ)์€ ๊ฑฐ์˜ ์—†๋Š” ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค. ๋งค๋ˆํ•œ ํ•˜์ƒ์˜ ๊ฒฝ์šฐ ์ ์„ฑ์ €์ธต(viscous sublayer)์—์„œ ์“ธ๊ธฐํ˜„์ƒ์ด ์ง€๋ฐฐ์ ์œผ๋กœ ๋‚˜ํƒ€๋‚œ๋‹ค๊ณ  ์•Œ๋ ค์ ธ ์žˆ๋‹ค(Wallace et al., 1972), ๋˜ํ•œ, ์ ์„ฑ์ €์ธต ๋ฐ”๋กœ ์œ„์˜ ์™„์ถฉ์ธต(buffer layer)์—์„œ๋Š” ์“ธ๊ธฐํ˜„์ƒ๊ณผ ๋ถ„์ถœํ˜„์ƒ์ด ๋™๋“ฑํ•œ ๊ธฐ์—ฌ์œจ์„ ๋ณด์ด๋ฉฐ, ๊ทธ ์ดํ›„์˜ ๊ตฌ๊ฐ„์—์„œ๋Š” ๋ถ„์ถœํ˜„์ƒ์ด ์ง€๋ฐฐ์ ์œผ๋กœ ๋‚˜ํƒ€๋‚œ๋‹ค๊ณ  ์•Œ๋ ค์ ธ ์žˆ๋‹ค(Raupach and Thom, 1981). ๋ฐ”๋‹ฅ๊ณผ ๊ฐ€๊นŒ์šด ์ง€์ (PIC40A0.gif)์€ ๋ฌด์ฐจ์› ๊ฑฐ๋ฆฌ PIC4286.gif๋กœ ์™„์ถฉ์ธต์— ํ•ด๋‹นํ•˜๊ณ , ์ด ๊ตฌ๊ฐ„์—์„œ ๋ถ„์ถœํ˜„์ƒ์ด ์“ธ๊ธฐํ˜„์ƒ๋ณด๋‹ค ๋” ์šฐ์„ธํ•˜๊ฒŒ ๋ฐœ์ƒํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธ ํ•  ์ˆ˜ ์žˆ๋‹ค. ์ˆ˜์‹ฌ์˜ ์ค‘์•™(PIC42D5.gif) ๋ถ€๋ถ„์˜ ๊ธฐ์—ฌ์œจ์„ ์‚ดํŽด๋ณด๋ฉด ๋ฐ”๋‹ฅ๊ณผ ๊ฐ€๊นŒ์šด ์ง€์ ๊ณผ ๋งˆ์ฐฌ๊ฐ€์ง€๋กœ ๋ถ„์ถœํ˜„์ƒ์ด ์“ธ๊ธฐํ˜„์ƒ๋ณด๋‹ค ํฌ๊ฒŒ ๋‚˜ํƒ€๋‚˜๊ณ , ๋ฐฐ์ œ์กฐ๊ฑด์ด ์ž‘์€ ๊ฒฝ์šฐ์˜ ๊ธฐ์—ฌ์œจ์ด ๋” ํฐ ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ์ƒํ˜ธ์ž‘์šฉ์˜ ๊ธฐ์—ฌ์œจ์€ ๋ฐ”๋‹ฅ์— ๋น„ํ•ด ์•ฝ๊ฐ„ ์ฆ๊ฐ€ํ•˜์˜€์ง€๋งŒ ๋ถ„์ถœ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์— ๋น„ํ•ด ๊ฑฐ์˜ ์˜ํ–ฅ์ด ์—†๋Š” ๊ฒƒ์œผ๋กœ ํŒ๋‹จ๋œ๋‹ค. ๋งˆ์ง€๋ง‰์œผ๋กœ ์ˆ˜๋ฉด์— ๊ทผ์ ‘ํ•œ ์ง€์ (PIC4382.gif)์˜ ๊ธฐ์—ฌ์œจ์„ ์‚ดํŽด๋ณด๋ฉด ์ƒํ˜ธ์ž‘์šฉ์— ์˜ํ•œ ์˜ํ–ฅ์ด ํฌ๊ฒŒ ์ฆ๊ฐ€ํ•˜์—ฌ ๋ถ„์ถœ๊ณผ ์“ธ๊ธฐํ˜„์ƒ๊ณผ ๋น„์Šทํ•œ ์ •๋„์˜ ๊ธฐ์—ฌ์œจ์„ ๋ณด์—ฌ์ฃผ๊ณ  ์žˆ๋‹ค. ํ•˜์ง€๋งŒ ๋ฐ”๋‹ฅ๊ณผ ์ˆ˜์‹ฌ์˜ ์ค‘์•™์— ๋น„ํ•ด ํฐ ๋ฐฐ์ œ์กฐ๊ฑด์—์„œ์˜ ๊ธฐ์—ฌ์œจ์ด ํฐ ๊ฒƒ์œผ๋กœ, ํฐ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ๊ธฐ์—ฌ์œจ์ด ์ปค์ง์„ ์•Œ ์ˆ˜ ์žˆ๋‹ค.

Fig. 5๋Š” ๋ฐฐ์ œ์กฐ๊ฑด PIC684F.gif์ผ ๋•Œ ์ˆ˜์‹ฌ์— ๋”ฐ๋ฅธ ๊ฐ ์‚ฌ๋ถ„๋ฉด์˜ ๊ธฐ์—ฌ์œจ์„ ๋ฌด์ฐจ์› ๊ฑฐ๋ฆฌ(PIC6969.gif)๋กœ ๋‚˜ํƒ€๋‚ด์–ด ๋„์‹œํ•œ ๊ฒƒ์ด๋‹ค. ๋งค์šฐ ์ž‘์€ ํฌ๊ธฐ์˜ ์ˆœ๊ฐ„ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ๋„ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์ƒ์„ฑ์— ์˜ํ–ฅ์„ ๋ฏธ์น˜๋ฏ€๋กœ, ์ด๋ฅผ ๊ณ ๋ คํ•˜๊ธฐ ์œ„ํ•ด์„œ ๊ธฐ์—ฌ์œจ์— ๋ชจ๋“  ํฌ๊ธฐ์˜ ์ˆœ๊ฐ„ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์„ ๋ฐ˜์˜ํ•  ํ•„์š”๊ฐ€ ์žˆ๋‹ค. ๊ธฐ์กด์˜ ์‹คํ—˜์—ฐ๊ตฌ(Lu and Willmarth, 1973; Brodkey, 1974; Nakagawa and Nezu, 1977)์™€ Kim et al. (1987)์˜ DNS ๊ฒฐ๊ณผ์™€ ํ•จ๊ป˜ ๋„์‹œํ•˜์˜€๋‹ค. Brodkey et al. (1974)์™€ Kim et al. (1987)์˜ ๊ฒฐ๊ณผ PIC6A93.gif์ธ ์˜์—ญ์—์„œ ์“ธ๊ธฐํ˜„์ƒ์ด ๋ถ„์ถœํ˜„์ƒ์— ๋น„ํ•ด ํฌ๊ฒŒ ๋‚˜ํƒ€๋‚ฌ์ง€๋งŒ, ๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ๋ถ„์ถœํ˜„์ƒ์ด ์“ธ๊ธฐํ˜„์ƒ๋ณด๋‹ค ํฌ๊ฒŒ ๋‚˜ํƒ€๋‚ฌ๋‹ค. ์ด๋Š” ๊ฒฉ์ž๊ฐ„ ๊ฑฐ๋ฆฌ๊ฐ€ PIC6B5F.gif๋กœ ์ด๋Ÿฌํ•œ ๋ฒฝ์—์„œ ๊ฐ€๊นŒ์šด ์ง€์ ์˜ ๋‚œ๋ฅ˜๊ตฌ์กฐ๋ฅผ ๋ฐํ˜€๋‚ด๊ธฐ์—” ์ถฉ๋ถ„ํ•˜์ง€ ์•Š๋‹ค๊ณ  ํŒ๋‹จ๋œ๋‹ค. ์™„์ถฉ์ธต ์ดํ›„(PIC6BCE.gif)์—๋Š” ๊ธฐ์กด ์‹คํ—˜ ๋ฐ ์ˆ˜์น˜๋ชจ์˜ ๊ฒฐ๊ณผ์™€ ์ž˜ ์ผ์น˜ํ•œ๋‹ค. Nakagawa and Nezu (1977)์˜ ๊ฒฐ๊ณผ๋ฅผ ๋ณด๋ฉด ์ˆ˜๋ฉด(PIC715C.gif)์— ๊ทผ์ ‘ํ• ์ˆ˜๋ก ๋ถ„์ถœ๊ณผ ์“ธ๊ธฐ ํ˜„์ƒ์˜ ๊ธฐ์—ฌ์œจ์ด ๊ธ‰์ฆํ•˜๋Š”๋ฐ, ๋ณธ ์—ฐ๊ตฌ์—์„œ์˜ ์ˆ˜๋ฉด์˜ ๋ฌด์ฐจ์› ๊ฑฐ๋ฆฌ PIC71DA.gif๋Š” ์•ฝ 2,200์œผ๋กœ ์ˆ˜๋ฉด์— ๊ทผ์ ‘ํ•˜๋ฉด์„œ ๋งˆ์ฐฌ๊ฐ€์ง€ ๊ฒฝํ–ฅ์„ ๋ณด์—ฌ์ฃผ๋Š” ๊ฒƒ์„ ์•Œ ์ˆ˜ ์žˆ๋‹ค. Table 2๋Š” Nezu and Nakagawa (1993)๊ฐ€ ์ œ์‹œํ•œ ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์˜ ๊ธฐ์—ฌ์œจ๊ณผ Kim et al. (1987)์˜ DNS ์ˆ˜์น˜๋ชจ์˜ ๊ฒฐ๊ณผ์ด๋‹ค. ์™„์ถฉ์ธต ์ดํ›„์˜ ๊ตฌ๊ฐ„(PIC722A.gif)์—์„œ ๋ถ„์ถœํ˜„์ƒ์— ์˜ํ•œ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์ƒ์„ฑ์€ ์•ฝ 71%๋ฅผ ์ฐจ์ง€ํ•˜๊ณ  ์“ธ๊ธฐํ˜„์ƒ์— ์˜ํ•œ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์ƒ์„ฑ์€ ์•ฝ 55%๋ฅผ ์ฐจ์ง€ํ•˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ๋ณธ ์—ฐ๊ตฌ์˜ ๊ฒฐ๊ณผ ๋‹ค์†Œ ์ž‘์ง€๋งŒ ์ „๋ฐ˜์ ์œผ๋กœ ์ž˜ ์ผ์น˜ํ•˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์˜ ๊ธฐ์—ฌ์œจ์˜ ํ•ฉ์ด 1์ด ๋„˜๋Š” ๊ฒƒ์€ ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์€ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์–‘์˜ ์ƒ์„ฑ์— ๊ธฐ์—ฌํ•˜๊ณ  ์ƒํ˜ธ์ž‘์šฉ์€ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์Œ์˜ ์ƒ์„ฑ์— ๊ธฐ์—ฌํ•˜๊ธฐ ๋•Œ๋ฌธ์ด๋‹ค.

PIC4DA4.gif

PIC4F4B.gif

PIC57A9.gif

(a) PIC5AD6.gif

(b) PIC5B64.gif

(c) PIC5C01.gif

Fig. 3. Distributions of Fluctuating Velocity PIC5CCD.gif and PIC5D3C.gif

PIC5E27.gif

PIC5F41.gif

PIC6405.gif

(a) PIC64B2.gif

(b) PIC6669.gif

(c) PIC6725.gif

Fig. 4. Contribution Rate with Threshold Level

Fig. 6์€๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์˜ ๊ธฐ์—ฌ์œจ์˜ ๋น„(PIC81DA.gif)๋ฅผ ๊ฑฐ๋ฆฌ์— ๋”ฐ๋ผ ๋„์‹œํ•œ ๊ฒƒ์ด๋‹ค. ๋งค๋ˆํ•œ ํ•˜์ƒ์—์„œ์˜ ์‹คํ—˜๊ฒฐ๊ณผ์™€ DNS ์ˆ˜์น˜๋ชจ์˜ ๊ฒฐ๊ณผ๋ฅผ ํ•จ๊ป˜ ๋„์‹œํ•˜์˜€๋‹ค. PIC8313.gif์˜ ๊ตฌ๊ฐ„๊ณผ PIC8353.gif์—์„œ ๋ชจ๋‘ ๊ธฐ์กด ์‹คํ—˜ ๋ฐ ์ˆ˜์น˜๋ชจ์˜ ๊ฒฐ๊ณผ์™€ ์ž˜ ์ผ์น˜ํ•˜๋Š” ๊ฒฐ๊ณผ๋ฅผ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ๋ฒฝ์—์„œ ๊ฐ€๊นŒ์›Œ ์งˆ์ˆ˜๋ก(PIC840F.gif) ๋ถ„์ถœํ˜„์ƒ์— ๋น„ํ•ด ์“ธ๊ธฐํ˜„์ƒ์˜ ํฌ๊ธฐ๊ฐ€ ์ฆ๊ฐ€ํ•˜๋Š” ๊ฒฝํ–ฅ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ๋˜ํ•œ Nezu and Nakagawa (1993)๋Š” PIC850A.gif์—์„œ PIC8634.gif๋ฅผ 0.74๋กœ ์ œ์‹œํ•˜์˜€๋Š”๋ฐ, ๋น„์Šทํ•œ ๊ฒฐ๊ณผ๋ฅผ ์–ป์„ ์ˆ˜ ์žˆ์—ˆ๋‹ค. ์ฆ‰, ์™„์ถฉ์ธต ์ดํ›„์˜ ๊ตฌ๊ฐ„(PIC86B2.gif)์—์„œ ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์˜ ๊ธฐ์—ฌ์œจ์˜ ํฌ๊ธฐ์™€ ๋…๋ฆฝ์ ์œผ๋กœ ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์ด ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์–‘์˜ ์ƒ์„ฑ์— ์ฐจ์ง€ํ•˜๋Š” ๋น„์œจ์€ ์ผ์ •ํ•˜๋‹ค.

PIC7315.gif

Fig. 5. Distributions of Contribution Rate PIC7364.gif and PIC7365.gif

Table 2. Comparison of Contributions Rate PIC7654.gif

Present LES

Nezu and Nakagawa (1993)

Kim et al. (1987)

PIC7701.gif

PIC7740.gif

PIC77ED.gif

PIC782D.gif

PIC786C.gif

PIC7996.gif

PIC7A43.gif

PIC7AB1.gif

PIC80BD.gif

Fig. 6. Distributions of Ratio PIC80DE.gif/PIC817B.gif

Fig. 7์€ ๋ฐฐ์ œ์กฐ๊ฑด PIC87BD.gif์ผ ๋•Œ ์ˆ˜์‹ฌ์— ๋”ฐ๋ฅธ ๊ฐ ์‚ฌ๋ถ„๋ฉด์˜ ์‹œ๊ฐ„๋น„๋ฅผ ๋ฌด์ฐจ์› ๊ฑฐ๋ฆฌ๋กœ ๋‚˜ํƒ€๋‚ด์–ด ๋„์‹œํ•œ ๊ฒƒ์ด๋‹ค. Nakgawa and Nezu (1977)์™€ Brodkey et al. (1974)์˜ ์‹คํ—˜ ๊ฒฐ๊ณผ์™€ ํ•จ๊ป˜ ๋„์‹œํ•˜์˜€๋‹ค. ๋ฐ”๋‹ฅ ๊ทผ์ฒ˜๋ฅผ ์ œ์™ธํ•˜๋ฉด ์ˆ˜์น˜๋ชจ์˜ ๊ฒฐ๊ณผ ๊ธฐ์กด ์‹คํ—˜ ์—ฐ๊ตฌ์˜ ๊ฒฐ๊ณผ์™€ ๋Œ€์ฒด๋กœ ์ผ์น˜ํ•˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. Table 3์€ Nezu and Nakagawa (1993)๊ฐ€ PIC8935.gif (PIC89C2.gif)์—์„œ ์ œ์‹œํ•œ ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์˜ ์‹œ๊ฐ„๋น„์ด๋‹ค. ์ œ์‹œํ•œ ๋ฒ”์œ„์—์„œ์˜ ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์˜ ๊ฐ๊ฐ์˜ ์‹œ๊ฐ„๋น„๋Š” ์•ฝ 0.29์™€ 0.33์œผ๋กœ, ๋ณธ ์—ฐ๊ตฌ์—์„œ ๋™์ผํ•œ ๋ฒ”์œ„์—์„œ์˜ ์‹œ๊ฐ„๋น„๋ฅผ ํ™•์ธํ•ด๋ณธ ๊ฒฐ๊ณผ ์ž˜ ์ผ์น˜ํ•˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ์‹œ๊ฐ„๋น„๋Š” ์ „์ฒด ์ธก์ • ์‹œ๊ฐ„์ค‘ ๊ฐ ํ˜„์ƒ์ด ์ฐจ์ง€ํ•˜๋Š” ์‹œ๊ฐ„์„ ๋‚˜ํƒ€๋‚ด๋Š” ๊ฒƒ์œผ๋กœ, ๋ถ„์ถœํ˜„์ƒ์€ ์ „์ฒด ์‹œ๊ฐ„์ค‘ 29% ์ •๋„ ๋ฐœ์ƒํ•˜๊ณ , ์“ธ๊ธฐํ˜„์ƒ์€ 33% ์ •๋„ ๋ฐœ์ƒํ•˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ๋‹ค. ์ด๋Š” ๋ฐ”๋‹ฅ์„ ์ œ์™ธํ•˜๊ณ  ์ „์ฒด์ ์œผ๋กœ ์“ธ๊ธฐํ˜„์ƒ์˜ ๋ฐœ์ƒ์‹œ๊ฐ„์ด ๋” ๋งŽ์€ ๊ฒƒ์„ ์•Œ ์ˆ˜ ์žˆ๋‹ค.

PIC8AFC.gif

Fig. 7. Distributions of fraction time PIC94D0.gif and PIC952F.gif

Table 3. Comparison of Fraction Time PIC957E.gif

Present LES

Nezu and Nakagawa (1993)

PIC95CD.gif

PIC965B.gif

PIC96C9.gif

PIC9728.gif

PIC993C.gif

PIC99CA.gif

5. ๊ฒฐ ๋ก 

๋ณธ ์—ฐ๊ตฌ์—์„œ๋Š” ๋งค๋„๋Ÿฌ์šด ํ•˜์ƒ ๊ฐœ์ˆ˜๋กœ ํ๋ฆ„์—์„œ์˜ ์กฐ์ง๊ตฌ์กฐ๋ฅผ ๋ถ„์„ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ LES ๋ชจํ˜•์„ ์ด์šฉํ•˜์—ฌ ์ˆ˜์น˜ ๋ชจ์˜๋ฅผ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. ์กฐ์ง๊ตฌ์กฐ์˜ ์ „๋ฐ˜์ ์ธ ๋ถ„์„์„ ์œ„ํ•˜์—ฌ Bursting ํ˜„์ƒ์— ์ดˆ์ ์„ ๋‘์–ด ๋ถ„์„์„ ์ˆ˜ํ–‰ํ•˜์˜€๋‹ค. Bursting ํ˜„์ƒ์„ ๋ถ„์„์€ PIC9A77.gif ์‚ฌ๋ถ„๋ฉด ๊ธฐ๋ฒ•์„ ์ด์šฉํ•˜์—ฌ Bursting ํ˜„์ƒ์ด ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์— ๋ฏธ์น˜๋Š” ์˜ํ–ฅ์„ ํŒŒ์•…ํ•˜์˜€๋‹ค.

PIC9B81.gif ์‚ฌ๋ถ„๋ฉด ๊ธฐ๋ฒ•์„ ์ง„๋™์†๋„์— ์ ์šฉํ•œ ๊ฒฐ๊ณผ ๋ฐ”๋‹ฅ์— ๊ฐ€๊นŒ์šด ์ง€์ ์—์„œ ๋ถ„์ถœ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์ด ์ง€๋ฐฐ์ ์œผ๋กœ ๋ฐœ์ƒํ•˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ์—ˆ๊ณ , ์ˆ˜๋ฉด์— ๊ทผ์ ‘ํ• ์ˆ˜๋ก ์ƒํ˜ธ์ž‘์šฉ์˜ ๋ฐœ์ƒ์ด ์ฆ๊ฐ€ํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธ ํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค. ๋ถ„์ธจํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์€ ๋ ˆ์ด๋†€์ฆˆ ์‘๋ ฅ์˜ ์–‘์˜ ์ƒ์„ฑ์— ๊ธฐ์—ฌํ•˜๋ฏ€๋กœ ์ด๋ฅผ ๋ถ„์„ํ•˜๊ธฐ ์œ„ํ•˜์—ฌ ๊ฐ ํ˜„์ƒ์˜ ๊ธฐ์—ฌ์œจ๊ณผ ์‹œ๊ฐ„๋น„๋ฅผ ๋ถ„์„ํ•˜์˜€๋‹ค. ์™„์ถฉ์ธต ์ดํ›„์˜ ๊ตฌ๊ฐ„์—์„œ ๋ถ„์ถœํ˜„์ƒ์˜ ๊ธฐ์—ฌ์œจ์ด ์“ธ๊ธฐํ˜„์ƒ์˜ ๊ธฐ์—ฌ์œจ์— ๋น„ํ•ด ํฌ๊ฒŒ ๋ฐœ์ƒํ•˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ์—ˆ๊ณ , ๋ถ„์ถœํ˜„์ƒ๊ณผ ์“ธ๊ธฐํ˜„์ƒ์˜ ๊ธฐ์—ฌ์œจ์˜ ๋น„๋Š” ์ผ์ •ํ•˜๊ฒŒ ๋‚˜ํƒ€๋‚˜๋Š” ๊ฒƒ์„ ๋ณผ ์ˆ˜ ์žˆ์—ˆ๋‹ค. ๋˜ํ•œ ์™„์ถฉ์ธต ์ดํ›„์˜ ๊ตฌ๊ฐ„์—์„œ ๋ถ„์ถœํ˜„์ƒ์˜ ์‹œ๊ฐ„๋น„๊ฐ€ ์“ธ๊ธฐํ˜„์ƒ์˜ ์‹œ๊ฐ„๋น„๋ณด๋‹ค ์ž‘์€ ๊ฐ’์„ ๊ฐ€์ง€๋Š” ๊ฒƒ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค. ์ด๋Š” ๊ธฐ์กด ์‹คํ—˜์—ฐ๊ตฌ์™€ ์ˆ˜์น˜๋ชจ์˜์™€ ์ผ์น˜ํ•˜๊ณ , Nezu and Nakagawa (1993)๊ฐ€ ์ œ์•ˆํ•œ ๋ฒ”์œ„์™€๋„ ์ผ์น˜ํ•˜๋Š” ๊ฒƒ์„ ํ™•์ธํ•  ์ˆ˜ ์žˆ์—ˆ๋‹ค.

Acknowledgements

์ด ๋…ผ๋ฌธ์€ 2013๋…„๋„ ์ •๋ถ€(๋ฏธ๋ž˜์ฐฝ์กฐ๊ณผํ•™๋ถ€)์˜ ์žฌ์›์œผ๋กœ ํ•œ๊ตญ์—ฐ๊ตฌ์žฌ๋‹จ์˜ ์ง€์›์„ ๋ฐ›์•„ ์ˆ˜ํ–‰๋œ ์—ฐ๊ตฌ์ž„(NRF-2012R1A2A2A02047 549). ์—ฐ๊ตฌ๋น„ ์ง€์›์— ๊ฐ์‚ฌ๋“œ๋ฆฝ๋‹ˆ๋‹ค.

References

1 
Blackwelder, R. F. and Kaplan, R. E. (1976). โ€œOn the wall structure of the turbulent boundary layer.โ€ Journal of Fluid Mechanics, Vol. 76, No. 1, pp. 89-112.10.1017/S0022112076003145Blackwelder, R. F. and Kaplan, R. E. (1976). โ€œOn the wall structure of the turbulent boundary layer.โ€ Journal of Fluid Mechanics, Vol. 76, No. 1, pp. 89-112.DOI
2 
Brodkey, R. S., Wallace, J. M. and Eckelmann, H. (1974). โ€œSome properties of truncated turbulence signals in bounded shear flows.โ€ Journal of Fluid Mechanics, Vol. 63, No. 2, pp. 209-224.10.1017/S0022112074001108Brodkey, R. S., Wallace, J. M. and Eckelmann, H. (1974). โ€œSome properties of truncated turbulence signals in bounded shear flows.โ€ Journal of Fluid Mechanics, Vol. 63, No. 2, pp. 209-224.DOI
3 
Corino, E. R. and Brodkey, R. S. (1969). โ€œA visual investigation of the wall region in turbulent flow.โ€ Journal of Fluid Mechanics, Vol. 37, No. 1, pp. 1-30.10.1017/S0022112069000395Corino, E. R. and Brodkey, R. S. (1969). โ€œA visual investigation of the wall region in turbulent flow.โ€ Journal of Fluid Mechanics, Vol. 37, No. 1, pp. 1-30.DOI
4 
Germano, M., Piomelli, U., Moin, P. and Cabot, W. H. (1991). โ€œA dynamic subgrid-scale eddy viscosity model.โ€ Physics of Fluids A: Fluid Dynamics (1989-1993), Vol. 3, No. 7, pp. 1760-1765.10.1063/1.857955Germano, M., Piomelli, U., Moin, P. and Cabot, W. H. (1991). โ€œA dynamic subgrid-scale eddy viscosity model.โ€ Physics of Fluids A: Fluid Dynamics (1989-1993), Vol. 3, No. 7, pp. 1760-1765.DOI
5 
Gyr, A. and Schmid, A. (1997). โ€œTurbulent flows over smooth erodible sand beds in flumes.โ€ Journal of hydraulic research, Vol. 35, No. 4, pp. 525-544.10.1080/00221689709498409Gyr, A. and Schmid, A. (1997). โ€œTurbulent flows over smooth erodible sand beds in flumes.โ€ Journal of hydraulic research, Vol. 35, No. 4, pp. 525-544.DOI
6 
Harlow, F. H. and Welch, J. E. (1965). โ€œNumerical calculation of time-dependent viscous incompressible flow of fluid with free surface.โ€ Physics of Fluids, 8, p. 2182.10.1063/1.1761178Harlow, F. H. and Welch, J. E. (1965). โ€œNumerical calculation of time-dependent viscous incompressible flow of fluid with free surface.โ€ Physics of Fluids, 8, p. 2182.DOI
7 
Issa, R. I., Gosman, A. D. and Watkins, A. P. (1986). โ€œThe computation of compressible and incompressible recirculating flows.โ€ Journal of Computational Physics, Vol. 62, No. 1, pp. 62-82.10.1016/0021-9991(86)90100-2Issa, R. I., Gosman, A. D. and Watkins, A. P. (1986). โ€œThe computation of compressible and incompressible recirculating flows.โ€ Journal of Computational Physics, Vol. 62, No. 1, pp. 62-82.DOI
8 
Kim, H. T., Kline, S. J. and Reynolds, W. C. (1971). โ€œThe production of turbulence near a smooth wall in a turbulent boundary layer.โ€ Journal of Fluid Mechanics, Vol. 50, No. 1, pp. 133-160.10.1017/S0022112071002490Kim, H. T., Kline, S. J. and Reynolds, W. C. (1971). โ€œThe production of turbulence near a smooth wall in a turbulent boundary layer.โ€ Journal of Fluid Mechanics, Vol. 50, No. 1, pp. 133-160.DOI
9 
Kim, J., Moin, P. and Moser, R. (1987). โ€œTurbulence statistics in fully developed channel flow at low Reynolds number.โ€ Journal of Fluid Mechanics, 177, pp. 133-166.10.1017/S0022112087000892Kim, J., Moin, P. and Moser, R. (1987). โ€œTurbulence statistics in fully developed channel flow at low Reynolds number.โ€ Journal of Fluid Mechanics, 177, pp. 133-166.DOI
10 
Kline, S. J., Reynolds, W. C., Schraub, F. A. and Runstadler, P. W. (1967). โ€œThe structure of turbulent boundary layers.โ€ Journal of Fluid Mechanics, Vol. 30, No. 4, pp. 741-773.10.1017/S0022112067001740Kline, S. J., Reynolds, W. C., Schraub, F. A. and Runstadler, P. W. (1967). โ€œThe structure of turbulent boundary layers.โ€ Journal of Fluid Mechanics, Vol. 30, No. 4, pp. 741-773.DOI
11 
Lilly, D. K. (1992). โ€œA proposed modification of the Germano subgrid-scale closure method.โ€ Physics of Fluids A: Fluid Dynamics (1989-1993), Vol. 4, No. 3, pp. 633-635.10.1063/1.858280Lilly, D. K. (1992). โ€œA proposed modification of the Germano subgrid-scale closure method.โ€ Physics of Fluids A: Fluid Dynamics (1989-1993), Vol. 4, No. 3, pp. 633-635.DOI
12 
Lu, S. S. and Willmarth, W. W. (1973). โ€œMeasurements of the structure of the Reynolds stress in a turbulent boundary layer.โ€ Journal of Fluid Mechanics, Vol. 60, No. 3, pp. 481-511.10.1017/S0022112073000315Lu, S. S. and Willmarth, W. W. (1973). โ€œMeasurements of the structure of the Reynolds stress in a turbulent boundary layer.โ€ Journal of Fluid Mechanics, Vol. 60, No. 3, pp. 481-511.DOI
13 
Nakagawa, H. and Nezu, I. (1977). โ€œPrediction of the contributions to the Reynolds stress from bursting events in open-channel flows.โ€ Journal of Fluid Mechanics, Vol. 80, No. 1, pp. 99-128.10.1017/S0022112077001554Nakagawa, H. and Nezu, I. (1977). โ€œPrediction of the contributions to the Reynolds stress from bursting events in open-channel flows.โ€ Journal of Fluid Mechanics, Vol. 80, No. 1, pp. 99-128.DOI
14 
Nezu, I. and Nakagawa, H. (1993). Turbulence in open-channel flows, Monograph, Balkema, Rotterdam, The Netherlands.Nezu, I. and Nakagawa, H. (1993). Turbulence in open-channel flows, Monograph, Balkema, Rotterdam, The Netherlands.Google Search
15 
Nezu, I. and Sanjou, M. (2008). โ€œTurburence structure and coherent motion in vegetated canopy open-channel flows.โ€ Journal of Hydro-environment Research, Vol. 2, No. 2, pp. 62-90.10.1016/j.jher.2008.05.003Nezu, I. and Sanjou, M. (2008). โ€œTurburence structure and coherent motion in vegetated canopy open-channel flows.โ€ Journal of Hydro-environment Research, Vol. 2, No. 2, pp. 62-90.DOI
16 
Niรฑo, Y. and Garcia, M. H. (1996). โ€œExperiments on particle- turbulence interactions in the near-wall region of an open channel flow: Implications for sediment transport.โ€ Journal of Fluid Mechanics, 326, pp. 285-319.10.1017/S0022112096008324Niรฑo, Y. and Garcia, M. H. (1996). โ€œExperiments on particle- turbulence interactions in the near-wall region of an open channel flow: Implications for sediment transport.โ€ Journal of Fluid Mechanics, 326, pp. 285-319.DOI
17 
Okamoto, T. A. and Nezu, I. (2010). โ€œLarge eddy simulation of 3-D flow structure and mass transport in open-channel flows with submerged vegetations.โ€ Journal of Hydro-environment Research, Vol. 4, No. 3, pp. 185-197.10.1016/j.jher.2010.04.015Okamoto, T. A. and Nezu, I. (2010). โ€œLarge eddy simulation of 3-D flow structure and mass transport in open-channel flows with submerged vegetations.โ€ Journal of Hydro-environment Research, Vol. 4, No. 3, pp. 185-197.DOI
18 
Raupach, M. R. and Thom, A. S. (1981). โ€œTurbulence in and above plant canopies.โ€ Annual Review of Fluid Mechanics, Vol. 13, No. 1, pp. 97-129.10.1146/annurev.fl.13.010181.000525Raupach, M. R. and Thom, A. S. (1981). โ€œTurbulence in and above plant canopies.โ€ Annual Review of Fluid Mechanics, Vol. 13, No. 1, pp. 97-129.DOI
19 
Smagorinsky, J. (1963). โ€œGeneral circulation experiments with the primitive equations: I. the Basic Experiment.โ€ Monthly Weather Review, Vol. 91, No. 3, pp. 99-164.10.1175/1520-0493(1963)091<0099:GCEWTP>2.3.CO;2Smagorinsky, J. (1963). โ€œGeneral circulation experiments with the primitive equations: I. the Basic Experiment.โ€ Monthly Weather Review, Vol. 91, No. 3, pp. 99-164.DOI
20 
Tominaga, A., Nezu, I., Ezaki, K.. and Nakagawa, H. (1989). โ€œThree- dimensional turbulent structure in straight open channel flows.โ€ Journal of Hydraulic Research, Vol. 27, No. 1, pp. 149-173.10.1080/00221688909499249Tominaga, A., Nezu, I., Ezaki, K.. and Nakagawa, H. (1989). โ€œThree- dimensional turbulent structure in straight open channel flows.โ€ Journal of Hydraulic Research, Vol. 27, No. 1, pp. 149-173.DOI
21 
Wallace, J. M., Eckelmann, H. and Brodkey, R. S. (1972). โ€œThe wall region in turbulent shear flow.โ€ Journal of Fluid Mechanics, Vol. 54, No. 1, pp. 39-48.10.1017/S0022112072000515Wallace, J. M., Eckelmann, H. and Brodkey, R. S. (1972). โ€œThe wall region in turbulent shear flow.โ€ Journal of Fluid Mechanics, Vol. 54, No. 1, pp. 39-48.DOI