The 4 th Japan-Korea Mn-ymposm on Modelng and Measrement of Hydralc Flow March 28, 2014, Yonse Unversty, Korea Prmary Velocty Dstrbton n Open Channels wth Dfferent Vegetaton Layot - Eperment and Nmercal mlaton - Yoshhsa KAWAHARA Dept. of Cvl and Envronmental Engneerng Hroshma Unversty, Japan Hroshma Unversty The Ohta Rver n Hroshma cty
OUTLINE OF PREENTATION Introdcton Epermental setp & condtons Nmercal model Comparson between eperment and nmercal smlaton mmary Hroshma Unversty
BACKGROUND OF THE TUDY Vegetaton s a ey factor n rver management. It has mltfnctons, sch as To change magntde and drecton of flood flow To stablze allval channels To create dfferent habtats stable for bodversty Wash-ot of vegetaton and eroson of floodplan n Ota Rver de to a bg flood n 2005. Hroshma Unversty
BACKGROUND OF THE TUDY Vegetaton eerts sgnfcant effects on the morphologcal behavors of allval channels by stablzng channels and bans. Vegetaton growth n the Tama Rver after dam constrcton (photos by Kehn wor offce, MLIT) Hroshma Unversty
BACKGROUND OF THE TUDY Many stdes have been carred ot to reveal the effects of vegetaton on mass and momentm transfer n open channels wth vegetaton. Compond channels flows wth vegetaton have been stded by researchers, sch as Pasche and Rove (1985), Naot et al. (1996), Bennett (2002), Kang and Cho (2006), Rameshwaran and hono (2007), etc. There stll reman many nnowns wth respect to flowvegetaton nteracton modelng, n partclar n the presence of large horzontal vortces and patched vegetaton belts. Hroshma Unversty
OBJECTIVE OF THE TUDY To gan nsght nto mean flow feld and large vortces n a prsmatc open channel n the presence of emergent vegetaton, To clarfy the performance of a non-lnear -ε model copled wth a vegetaton model for trblent flows n a straght channel wth dfferent layot of vegetaton. We need a relable nmercal method that can predct momentm and sedment transfer n the presence of vegetaton whch may topple or be washed ot drng floods. Hroshma Unversty
EXPERIMENTAL ETUP y Flow 80 cm y d Vegetaton Belt Bed slope: 1/555 27 cm Flow 2,200 cm Vegetaton Unt Length: 99 cm Wdth: 27 cm Case-1 Vegetaton: contnos, along the channel center Model Vegetaton Emergent rgd cylnders Dameter: 3.0 mm Heght: 6.0 cm pacng: 3.0 cm Hroshma Unversty
EXPERIMENTAL ETUP & CONDITION y Flow 80 cm 26.5 cm Vegetaton Belt 27 cm Case-1 Vegetaton: contnos, along the channel center y Flow 80 cm 27 cm Case-2 Vegetaton: contnos, along a sde wall y 9.5 cm Flow 80 cm 27 cm Case-3 Vegetaton: contnos, off the channel center y Flow 80 cm 26.5 cm 99.0 cm 99.0 cm Case-4 27 cm Vegetaton: patched, along the channel center Hroshma Unversty
EXPERIMENTAL CONDITION & RATING CURVE Case Dscharge (l/s) Normal Depth (cm) 1 4.78 2 4.00 9.0 3 4.30 4 4.71 Case-1 Case-4 Patched vegetaton belts show larger carryng capacty of flow than contnos ones. Ths reslt has been confrmed for dfferent ntervals of vegetaton patches.
FLOW VIUALIZATION Case-1 Vegetaton: contnos, along the channel center Large Vorte L: 80~100 cm T: 3.5~4.5 sec Case-2 Vegetaton: contnos, along a sde wall Large Vorte L=80~100 L: 90~110 cm cm T=3.5~4.5 T: 4.0~5.0 sec sec Case-3 Vegetaton: contnos, off the channel center Large Vorte L (rght): 80~100 cm L (left): 30~40 cm T(rght): 4.0~5.0 sec T(left): 3.0~4.0 sec Hroshma Unversty
FLOW VIUALIZATION Case-1 Vegetaton: contnos, along the channel center Large Vorte L: 80~100 cm T: 3.5~4.5 sec Case-4 Vegetaton: patched, along the channel center Large Vorte L=80~100 L: cm cm T=3.5~4.5 T: sec sec Hroshma Unversty
p P g t 2 2 ' ' 1 1 BAIC EQUATION WITH RAN MODEL Momentm eqatons: D F U U C p 2 1 1 2 U Doble-averaged velocty: 0 λ= D/d*dy ; D:Dameter of stem X Y d dy ' '' ' U U U Contnty eqaton: Hroshma Unversty (λ : vegetaton densty, ) 0.9 C D
TURBULENCE MODEL t 3 2 ' ' Lnear -ε Model Non-Lnear -ε Model (Kmra-Hosoda) 2 2 0.09 1 0.3 0.09, mn ; M C C t ) 3 1 ( 3 2 ' ' 3 1 t t C U U U U ; 2 1 ; 2 1 ), ma( M The non-lnear terms are fond to be necessary to prodce secondary crrents of the second nd, large horzontal vortces at the nterface between vegetaton and flow regon. Hroshma Unversty
TURBULENCE ENERGY AND DIIPATION RATE rod m t m P U t C P C U t rod m t m 2 1 Transport eqatons for and ε : U C FU D 2 orce/ n term for : orce/ n term for ε : U C FU D 4 1. 2 3 Hroshma Unversty
DICRETIZATION & COMPUTATIONAL CONDITION Dscretzaton: Fnte Volme Method +Flly mplct scheme Algorthm: IMPLE algorthm Convecton terms: QUICK scheme for momentm eqs. Power-law scheme for and ε eqs. Bondary condtons: Wall fncton technqe for sold walls, ymmetry condton for free srfac, Gven vales at nlet, Otflow condton at downstream end. Nmber of grd ponts: 238 36 17 Tme nterval: 0.01 sec Hroshma Unversty
INTANTANEOU VELOCITY & WATER LEVEL 20cm/s 20cm/s Case 1 (z=1.9cm) Case 1 20cm/s 20cm/s A seres of large vortces develop along the nterface. The calclated sze of large vortces are slghtly nderestmated. Case 2 (z=2.1cm) Case 2 The core of large vortces has low water level. 20cm/s 20cm/s Case 3 (z=1.8cm) Case 3 Velocty vectors mean streamwse velocty at nterface Hroshma Unversty
FLUCTUATION OF WATER LEVEL y 53.5 cm 26.5 cm 2.0 cm Flow Case-1 (cm) h (s) h (cm) Ether sde of flow regon Ether sde of flow regon h (s) h Ether sde of vegetaton belt Eperment Ether sde of vegetaton belt Nmercal mlaton
FLUCTUATION OF VELOCITY COMPONENT y Flow 26.5 cm Case-1 (cm/s) ' v (s) ' v Eperment (z=2.5cm) Nmercal mlaton (z=2.9cm) and v at the nterface between vegetaton belt and flow regon (y=26.5cm) Hroshma Unversty
FLUCTUATION OF WATER LEVEL AND VELOCITY COMPONENT y 53.5 cm Flow Case-2 h' h' Water level Water level ' v and v (z=2.0cm) Eperment ' and v (z=2.1cm) Nmercal mlaton
FLUCTUATION OF VELOCITY COMPONENT y 44.5 cm Flow Case-3 ' v ' v and v (z=2.2cm) Eperment ' and v (z=2.2cm) Nmercal mlaton Hroshma Unversty
FLUCTUATION OF WATER LEVEL y 26.5 cm =1260cm =1360cm 99 cm 99 cm 53.5 cm 26.5 cm 2.0 cm 27 cm Case-4 h' h' Ot of phase h' h' In phase
FLUCTUATION OF VELOCITY COMPONENT y 26.5cm =1260cm =1360cm 99cm 99cm 26.5 cm 27 cm Case-4 ' v' ' v' =1260cm, y=26.5cm, z=2.5cm =1360cm, y=26.5cm, z=2.5cm
MEAN VELOCITY (U/UM) Case-1 Case-1 Case-2 Case-2 Case-3 Case-3 Eperment Nmercal mlaton Hroshma Unversty
MEAN VELOCITY (U/UM) y =1203cm =1250cm =1296cm =1200cm =1203cm =1250cm =1296cm =1302cm =1349cm =1302cm =1349cm Hroshma Unversty
UMMARY 1. Large vortces have developed along the edge of vegetaton belt. Ther scale and domnant freqency depend on the vegetaton layot. 2. The present nmercal model can reprodce mean flow feld and large vortces reasonably well even when the prmary velocty shows large dfference across the vegetaton belt. However, t tends to nderestmate the flctatng prmary velocty, whch needs frther dscsson. 3. The nmercal model needs frther valdaton for flows wth large coherent vortces and patched vegetaton belts. Hroshma Unversty
Than yo for yor nd attenton. Any qestons? H Rver wth actve sand movement Hroshma Unversty