samuel paul and haitham ghamry - nserc hydronet …€¦ · through bar racks in closed...

Numerical Investigation of Turbulent Flow Through Bar racks in Closed ConduitsThrough Bar racks in Closed Conduits

Samuel Paul and Haitham GhamrySamuel Paul and Haitham Ghamry

Fi h i & O C d (DFO)Fisheries & Oceans Canada (DFO)Freshwater Institute

Winnipeg, MB

Outline

• Background• Objective• Previous Work• Problem Definition• Methodology• Methodology• Results and Discussion• Concluding Remarks• Future WorkFuture Work

2Outline

What are Trash Racks?

bars and supporting beams

Protect t rbine from Protect turbine from debris

Reduce mortality of larger fishlarger fish

energy losses

Kelsey G.S.

Trash rack in closed conduitsTrash rack in closed conduits

Trash rack in open channelTrash rack in open channel

Fish injury or mortalityFish injury or mortality

Reducing fish injury or mortality depends on:• Species, sizes, abilities and behaviourp• Spacing between bars (physical exclusion)• Shape of the barsp• Flow conditions near barracks, particularly

magnitude and patterns of flow velocity, g p yacceleration and turbulence fields

• Turbine design

zFlow z' z"2B zFlow z' z"2B

Wch

Rounded leading edge (RD)

z

Square leading edge (SQ) inclined

x

bs

ba

x'x

bs

ba

x'x(e)x

(c)

Ud

h∆h

Salient feature of this flow is yU∞

Lch

h1 h2that it produces head loss.

• These energy losses can be partly attributed to the turbulent largescale flow structures generated by the bars.g

• Both from the fish protection and head loss perspectives, it isi l di h i d d fimportant to accurately predict the magnitude and patterns ofturbulent flow characteristics, and velocity fields around and betweenthe bars.

• The ability to correctly predict complex turbulent flows isfundamental to the design of trash racks as well as other fluidengineering systems.

Objectives

• To perform numerical investigation of turbulent flowthrough arrays of rectangular bar models of variousg y gconfigurations in closed conduits using a commercialCFD code, ANSYS CFX 12.1. .

• To evaluate and validate several turbulence models inorder to assess the most suitable model for predictingorder to assess the most suitable model for predictingturbulent flow through bar racks closed conduit model

• Assess the streamlines and contours of the meanvelocity, turbulence levels, pressure field. As well asthe profiles.

7Objective

Problem Description

Wall

W

Inlet

z

Outlet

WchU∞xy 0

P = ghWall

Ps = gh

LXup Xds

8

Schematic of the flow field around bar racks and solution domainnomenclature

Problem Description

Previous WorkExperimental

Authors RemarksMosonyi, 1963; Orsborn, 1968; Wahl, 1992; Meusburger et al (2001)

*Performed bulk flow measurements (i.e., average velocity and pressure ) using various bar shape, blockages etcp g*Developed correlations for calculating head losses, h

Tsikata et al 2008 *Studied the effects of bar shape depthTsikata et al. 2008Tsikata et al. 2009(a & b)

Studied the effects of bar shape, depth, thickness, spacing and inclination to the approach flow, on head losses.*Used Proper Orthogonal Decomposition toUsed Proper Orthogonal Decomposition to extract and study the role of the large scale structures in flow around TR.

Clark et al 2010 *Performed velocity and pressure

9

Clark et al. 2010 *Performed velocity and pressure measurement of flow through submerged TR

Previous Work

Previous Work

NumericalAuthors Model Code RemarksAuthors Model Code RemarksHermann et al. 1998

DNS, k- In-house *The DNS produced head losses that compared well with measured values at lo blockage ratios b t prod cedlow blockage ratios but produced higher losses than measured data at higher blockage ratios. *k ε were in good agreement with the

Meusburger et al. 1999

DNS, k-

*k-ε were in good agreement with the measured data, especially at higher blockage ratios.

N i S i I h *F d th t th t l f iNascimento et al. (2006)

Smagorinsy SGS

In-house *Found that the natural frequencies for a submerged bar-rack are about 30% smaller than the values of the natural frequencies of a non

10Previous Work

natural frequencies of a non-submerged bar-rack.

Present Work

Summary of geometric parameters and test conditions(University of Manitoba Experimental data for closed conduits by Clark et al.

TEST n s L b p U∞

( y p y2010, supported by Manitoba Hydro used for validation)

TEST[m]

L[m] [m]

p ∞

[m/s]

1 3 0 012 0 100 0 140 0 079 0 32 0 48 0 961 3 0.012 0.100 0.140 0.079 0.32, 0.48, 0.96,

1.12,1.37, 1.64

2 7 0.012 0.100 0.053 0.185 0.49, 0.98, 1.39

3 14 0.012 0 100 0.021 0.369 0.26, 0.78, 1.42

11Problem Description

3 14 0.012 0.100 0.021 0.369 0.26, 0.78, 1.42

Methodology Cont’d.

Governing EquationsA iAssumptions:

The fluid Newtonian

Steady, incompressible, and turbulent

Equations:Equations:Continuity and momentum conservation

iequations

Turbulence model equations: RANS 2-eqn, SMC(k-ε , k- , SST, LRR-IP, & SSG)

12Methodology

Methodology

Numerical Solution

Commercial CFD Code, ANSYS CFX v12.0:• Element based FVM• Element based FVM• Geometrical representation and integration points are based on FEM

• The coupled discretized mass and momentum equations with the turbulence model equations were solved iteratively using additive

i l i id l icorrection multi-grid acceleration. • Solutions were considered converged when the normalized maximum

residual of all the discretized equations was less than 1×10−4.residual of all the discretized equations was less than 1 10 .

13Methodology


Numerical Solution: Computational Mesh Numerical Solution: Computational Mesh

14Methodology

Sample coarse mesh (plan view)


Numerical Solution: Boundary conditions

I l tI l t O tl tO tl tInletInlet OutletOutlet• U = U∞, I = 0.05 Ps = gh

WallsWalls• N li• No-slip

• Low Reynolds number near-wall treatmentLow Reynolds number near wall treatmentfor all models

15Methodology

Results & Discussion

x/L = -0.5

x

x/L = 5x/L = 0

x/L = 1.0

x/L = 10x/L = 0.5

Geometrical layout showing a typical location at which sample results

x'

16

Geometrical layout showing a typical location at which sample results are presented


Results & Discussion Cont’d.

0 14

0.16

7bars, U = 0.49 m/s

Present Num. Study: k-

k-

0.16

E i t l d t

3bars, U = 0.48 m/s

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.50.12

0.14 k SST LRR O-Based

Expt.[Clark et al. 2010] (a)

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.50.12

0.14 Experimental data Present Num. Study: k- k- SST (d)

0 16

0.20

0.247bars, U

= 0.98 m/s

h[m]

016

0.20

0.24

h[m]

3bars, U = 0.96 m/s

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.50.12

0.16

(b)

0 28

0.327bars, U = 1.39 m/s

-1.5 -1.0 -0.5 0.0 0.5 1.0 1.50.12

0.16

(e)

0.283bars, U

= 1.37 m/s

0.16

0.20

0.24

0.28 7ba s, U

.39 /s

( )

0.16

0.20

0.24

(f)

17Results & Discussion

Comparison between profiles of predicted pressure head with measured values for selected approach velocity: (a, b, c) 7 bars and (e, f, g) 3 bars.

x[m]-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

0.12 (c)

x[m]-1.5 -1.0 -0.5 0.0 0.5 1.0 1.5

0.12(f)


N i l S d E

TableTable 11:: SummarySummary ofof headhead lossloss coefficientcoefficient forfor TestTest 22

Model L(m) np

U∞(m/s) Numerical Study Expt.∆h ∆h* ∆h*

k-ε0.10 7 0.185 0.49 0.0042 0.343 0.334

0.10 7 0.185 0.98 0.0170 0.343 0.334

0.10 7 0.185 1.39 0.0340 0.343 0.334

k-ω0.10 7 0.185 0.49 0.0044 0.360 0.3340.10 7 0.185 0.98 0.0180 0.360 0.3340.10 7 0.185 1.39 0.0350 0.360 0.334

SST0.10 7 0.185 0.49 0.0043 0.351 0.3340.10 7 0.185 0.98 0.0170 0.351 0.3340.10 7 0.185 1.39 0.0350 0.351 0.3340. 0 7 0. 85 .39 0.0350 0.35 0.334

LRR-IP0.10 7 0.185 0.49 0.0040 0.347 0.3340.10 7 0.185 0.98 0.0170 0.347 0.3340.10 7 0.185 1.39 0.034 0.347 0.334


SSG0.10 7 0.185 0.49 0.0040 0.351 0.3340.10 7 0.185 0.98 0.0172 0.351 0.3340.10 7 0.185 1.39 0.0346 0.351 0.334


Table 2: Summary of non-dimensional head loss coefficient for all test cases

Model Test s(m) n p U∞ (m/s)

∆h*

Expt

Eq.

(4.1)

Eq.

(4.2)

Eq.

(4.3)

0 079 0 48 0 085 0 091 0 044 0 072k-ε 1 0.012 3

0.079 0.48 0.085 0.091 0.044 0.0720.079 0.96 0.085 0.091 0.044 0.0720.079 1.37 0.085 0.091 0.044 0.0720.185 0.49 0.334 0.334 0.243 0.337

k-ε 2 0.012 7 0.185 0.98 0.334 0.334 0.243 0.3370.185 1.39 0.334 0.334 0.243 0.337

k-ε 3 0 012 14

0.369 0.26 1.089 1.148 0.967 1.2570 369 0 78 1 089 1 148 0 967 1 257k-ε 3 0.012 14 0.369 0.78 1.089 1.148 0.967 1.2570.369 1.42 1.089 1.148 0.967 1.257

sin)2/(/ 23/4 gUbsh

i)2/( 22 Ukh

Eq. (4.1): Kirschmer (1926)

E (4 2) F ll i d Li d i (1929)


sin)2/( 22 gUpkh

sin)2/(/tan1 2 gULbpBh DC

Eq. (4.2): Fellenius and Lindquist (1929)

Eq. (4.3): Meusburger et al. (2001)


(a) (b)

20

Contours of: (a) mean streamwise velocity and (b) static pressure field



(a) (d)

(b) (e)

(c) (f)


Contours of mean velocity (U* = U/U∞) for 3bars: (a) U = 0.48 m/s, (b), 0.96 m/s, and (c) 1.37 m/s, and for 14bars: (a) U = 0.26 m/s, (b), 0.78 m/s, and (c) 1.42 m/s

Results & Discussion Cont’d

(d)(a)

(e)(b)

(f)(c)


Contours of Tke (k* = k/U∞2) for 3bars: (a) U = 0.48 m/s, (b), 0.96 m/s, and (c) 1.37 m/s, and for

14bars: (a) U = 0.26 m/s, (b), 0.78 m/s, and (c) 1.42 m/s


05

1.0(a)U/U

(b) (c)

0.0

0.5 U = 0.48 m/s U = 0.96 m/s U = 1.37 m/s

U = 0.49 m/s U = 0.98 m/s U = 1.39 m/s

U = 0.26 m/s U = 0.78 m/s U = 1.42 m/s

0 5 10 150 5 10 15/

0 5 10 15 20

Mean velocity profile along the wake axes; (a) 3 bars , (b) 7 bars , and (c) 14 bars ; correspondingly, the blockage ratios are, respectively, 0.079, 0.185, and 0.369



0.08

0.12 U = 0.48 m/s U = 0.96 m/s U = 1.37 m/s

U = 0.49 m/s U = 0.98 m/s U = 1.39 m/s

U = 0.26 m/s U = 0.78 m/s U = 1.42 m/s

0.04k/U

2

( )

0 5 10 150 5 10 150.00 (a) (b)

0 5 10 15 20

(c)

Turbulence kinetic energy profile along the wake axes: (a) 3 bars , (b) 7 bars , and (c) 14 bars ; correspondingly, the blockage ratios are, respectively, 0.079, 0.185, and 0.369


p g y g p y

Results & Discussion Cont’d2.5

10.05.01.0x/L = 0

/Profiles of U/U∞ across the

k i f h b k

0.0

z/L wake axis of the bar racks atselected x/L locations

-2.51.01.01.01.0 2.00.00.00.0

U/U0.0

U/U2.5

z/L

10.05.01.0x/L = 0 Profiles of W/U∞ across the

wake axis of the bar racks atselected x/L locations

0.0se ected x/ ocat o s


-2.50.050.00.00.00.0 0.10.050.050.05

W/U

-0.05

Concluding Remarks The ANSYS-CFX reproduces the flow characteristics reasonably

well

k- models give better results than the other models

Present results were in good agreement with prior results

k- model predicted the mean velocity, turbulence kinetic energy, and pressure coefficient reasonably well. It was found that the head loss increases with blockage ratio as well as the independence of dimensionless pressure head (∆h*) on the Reynolds number.y

The recovery of mean velocity to its upstream value (U/U∞= 1) is most rapid at higher blockage ratio.

the level of turbulence increases with increasing blockage ratio26

Future works

Future Works

• Will provide further insight into the effects of bar leading andtrailing edges bar shape bar depth bar thickness bar spacing andtrailing edges, bar shape, bar depth, bar thickness, bar spacing andbar inclination to the approach flow, on head losses in model barracks using Flow 3-D software for improved bar rack design andfish survival at hydroelectric turbines.

• Influence of the following flow parameters on fish survival:• Influence of the following flow parameters on fish survival:– Turbulence and turbulence intensity (area upstream of bar racks)– Shear in flow (area upstream of bar racks)Shear in flow (area upstream of bar racks)– Acceleration (area upstream of bar racks)– Areas of maximum flow speed (area upstream of bar racks)will be fully examined.

27Future works

Acknowledgement

Profound gratitude to:

DFO-CHIF

UNIVERSITY OF MANITOBA

MANITOBA HYDROMANITOBA HYDRO

HYDRONET NSERC

for their support

28Acknowledgement

Question

29Question

samuel paul and haitham ghamry - nserc hydronet …€¦ · through bar racks in closed...

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