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Journal of Hydrodynamics
Ser.B,2007,1 9(1):78-83 sdlj.chinajourna1.net.cn
CALCULATIoN oF FLOW FIELD AND ANALYSiS OF Sn WNING SITES
FoR CHINESE STURGEoN IN THE Do、ⅣNSTREAM oF GEZHoUBA
DAM
FU Xiao-li,LI Da-mei,JIN Guo-yu
School of Water Resource and Hydropower,Wuhan University,Wuhan 430072,China,
E-mail:fuxiaoli 1 979@yahoo.corn
(Received October 25,2005;Revised April 1 9,2006)
ABSTRACT:The Chinese sturgeon(Acipenser Sinensis)is
one of the unique and important fishery resources in China.
Since the construction of the Gezhouba Dan3,the traditional
migration route of the sturgeon has been blocked;consequently,
the len础of natural spawning sites is reduced from 800 km in
thepasttolessthan 5 km atpresent.As an endangered species,
the Chinese sturgeon has become one of the most conserved
aquatic species.In this article,the flow field of its spawning
states in the downstream ofGezhouba Dam was simulated and
analyzed using N.S equations and k一8 turbulence mode1.
Volume Of Fluid(VOF、method with the Finite Volume
Method(FVM)was used to simulate the water-air two-phase
flow to examine the computed area.On the basis of the
ecologica1.hydraulic characteristics of Chinese sturgeon,the
features of the flow field were investigated to provide
theoretical support for the proper managemeut of the Three
Gorges Reservoir.
KEYWORDS:Chinese sturgeon(Acipenser Sinensis),Finite
Volume Method(FVM),Volume Of Fluid(VOF),natural
spawning site,three—dimensional river channel
1.1NTRoDUCTloN
1.1 Researchproblem
The Chinese sturgeon(Acipenser Sinensis)
belongs to the sturgeon family ’ .They ale a type of
anadromous,bosom-feeding fish.Between October
and November each year in natural spawning sites in
the eight-hundred-kilometer river area between
Pingshan and Mudong in the upper reaches of the
Yangtze River.The fish typically lay eggs in deep
waters and rock heaps in the riverbed.The
construction of the Gezhouba Dam in 1 98 l blocked
the migration route of tllis fish.and this raised a
significant threat against the reproduction and survival
of the fish and substantially reduced this fishery
resource.Despite the fact that Chinese sturgeons can
travel only 21 0 km ups ̄eam.because of their
strong viability, sensitivity, selectivity, and
adaptability with regard to the changes in the
conditions of flow field. they have found new
spawning sites in the river area 5 km downstream of
the Gezhouba Dam.However,their spawning rate is
less than 20%of the normal spawning rate.Therefore.
the Chinese sturgeon has been considered as an
endangered species. More seriously,the river
structures of the spawning sites are constantly
threatened by the flood discharge of the e
Georges Reservoir and dredging of the waterways.
The environment for the spawning and reproduction
of Chinese sturgeons is very fragile.
1.2ResearchontheChineseSturgeon
Some research institutions in China are devoted
to the protection of Chinese sturgeons.For example。
the I中秋月饼图片大全 nstitute of Hydrobiology of the Chinese Academy
of Sciences has been involved in the biological studies
of Chinese sturgeons.The Yangtze River Institute of
Aquatic Products of the Chinese Academy of Aquatic
Sciences has produced Chinese sturgeons through
artificial incubation.Each year a number of Chinese
★Project supported by the Three Georges Construction Commission and the National Natur童孙未解供耕织下一句 al Science Foundation of China
(Grant No.30490231).
Biography:FU Xiao—li(1979一),Female,Ph.D.
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sturgeon fry and breeding sturgeon with 0.2 m size are
putintotheYangtzeRiver.
1_3 D/stribution ofthe spawning sites ofChinese
sturgeon
The records on the spawning sites of Chinese
sturgeons collected since 1 983 indicate that these sites
have been concentrated in the 1 0 km river area
betweenthe Gezhouba Dam and the Yanzhiba Dalil.L
Figure l shows the diferent districts of the river aFea.
The results obtained by tracking the spawning
sturgeons with ultrasonic telemetering devices and
directly gathering the zygotes of the fish from the
riverbed indicate that the fish’s eggs are mainly found
in the districts III and IV.with small distributions in
the districts I.B,II.B,II.C,and V.B.Dislributions of
eggs in other districts are extremely rare.To
understand the patterns of the fish’s spawning,this
article aims to simulate the features of the river
channel and the f1ow velocity distributions.Because
the natural fiver channel is winding.it is dif行cult to
present it exactly as it is in the three.dimensional
mathematical mode1.Therefore, some
conceptualization is necessary.With the topographic
map(see Fig.2)ofthe spawning sites for sturgeons,a
computational diagram is given in Fig.3.
Fig.1 Layout of spawning sites of Acipenser Sinensis
Fig.2 Map of spawning sites ofAcipenser Sinensis
2. NUMERICAL SIMULATIoN AND
CoMPUTATIoNAL MIETHoDS
The natural fiver channel鹊桥仙表达了怎样的情感 has several
uncertainties such as the complex boundaries and
turbulentflow.Therefore,the computation at the
79
Fig.3 Sketch of the boundaries of the spawning site of
Acipenser Sinensis
boundaries of river channels has been a hot but
dimcult subject.Since Launder and Spalding L)J
established the k一 mode1.it has become the most
widely used model of turbulent flow and has been
successfully used to simulate several complex flow
prOblems.Although the Reynolds stress model or the
algebraic stress model is more accurate than the
k一 model for the simulation ofnonuniform flows.
with the introduction of the two.phase flow Volume
Of Fluid(VOF)method for the computation of river
channe1.the k一 model provide results that are
more similar to the on-site measu
,…
red values compared
with the Reynolds stress model,t Therefore
.in this
study.the k一 turbulent flow model is employed
for the nUlTlerical simulation of the whole flow field.
The obvious dividing interface between water flow
and air in the river channel makes simulation possible
by using the two.phase flow model in water.air
two-phase flow.At present,the method of volume of
fluid created bv Hirt and Nichols 】is considered as
an ideal method for dealing with the problems related
to free surface flow.Using this method,two or three
immiscible flows can be simulated via the solutions of
individual momentum equations and the examination
ofthe volume ratio of each flow passing through the
area.This method is suitable for the simulation of
flows in natural river channels.Given the fact that two
or more flows(or phases)are not mixed,the VOF
formulae considers the new variable of each phase
mat is added to the model to compute the volume ratio
of the phase in the element.Wimin each controlled
volume.the sumofthevolume ratiosofallphasesis 1.
A11 variables and their a衔liated areas are shared by
every phase.They represent the mean volumes as long
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as the volume ratio of every phase at each position is
nown.Hence,a volume ratio equation in addition to
the continuity equation,the momentum equation,and
the k, equations are used to solve the free surface
problems,as follows.
Volume ratio equation:
The interface between tracking phases is
established by the solutions of single—phase or
multiphase continuous volume ratio equations.For the
phase q,the equation is expressed as
o
at (1)
Generally,the volume ratio equation is not used for
the solution of the primary phase.The computation of
the volume ratio of the primary phase is based on the
following constraint:
∑ =1
q=l
Continuity equation:
+ ( ):o a
t a)C:、。
Momentum equation:
—
OP ui
+考 一筹+毒 +
k equation:
O(pk)
equation:
(2)
(3)
(4)
:( + )当+G一 ax
i ok a)ci
(5)
一
o(pe)+
: ( + +O t
f f o Oxf
Cl 丢G (6)
where f is the time,uf and xi are the velocity
components and the coordinate components,
respectively,P is the density, is the molecular
viscosity coefficient,and P is the moderated stress.
t
is the turbulence viscosity represented as:
k
t
p乙u一
where C is an empirical constant( 0.09),o- and
a are the Prandtl turbulence constants for
k andE(o- =1.0, =1.3),Cl and C2 are the
constants for (C1 =1.44,C2 =1.92),G is the
turbulence momentum product caused by the average
velocity scale as defined below:
G -O uy]
J
Oui
Boundary conditions:
Atinlet
The boundary conditions at the inlet for the case
isthatonlytheErjiangPowerPlantisin operationand
the Dajiang Power Plant and the ship lock are closed.
These conditions,as shown in Figs.1 and 2,are
identical with the case that the Gezhouba Dam
operates during the spawning period of Chinese
sturgeons.On the basis of the information collected
and those provided by the Institute of Hydrobiology of
the Chinese Academy of Sciences,the inlet of the
model is placed in front of the outlet of the Gezhouba
Power Station.and it is the furthest possible place
where the surveying ship can reach.The inlet flow
velocity at the Erjiang Power Plant is 2.55 m/s.
whereas the flow velocity at the Dajiang Power Plant
and at the ship lock is 0.32 rn/s.The depth of the
water at the inlet ofthe model is 8 meters and the rest
is all air.k and at the inlet are given using the
empirical formula.
At outlet:
The normal derivatives of all variables are 0.tl1at
is,the second boundary condition is:
:o
On
Atfree surface:
The free surface is treated as a pressure boundary
atwhich the pressure valuep=0.
Atwall:
Use the standard wall function.
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Construction of mesh:
In this article,the nonstructural mesh
.which iS
well suited for complex computed areas
.iS combined
with the finite volume method to divid却看妻子愁何在翻译 e the computed
area.Similar to a fmite element。the nonstructural
mesh relies on the relationship between nodes and
elements to mark their positions and the connections
between adjacent elements[13-15].For three—
dimensional problems,tetrahedron,prism,cube and
other flexible spatial shapes Can be used to divide the
computed area.A tetrahedral or prismatic element can
be used in the irregular areas,whereas a cubic element
Can be used In the regular areas.Figure 4 shows the
construction of surface mesh for the computed area
.
Fig.4 Computation mesh
3.ANALYSIS oF THE COMPUTATIONAL
RESULTS
The th感恩母亲的诗歌 ree—dimensional flow field iS unique for
analyzing the model at diferent sections
.The
lnformation with regard to the distribution of flow
velocity can be obtained by the examination of the
diferent sections of the fiver channe1
.Figures 5一ll
present the flow fields and streamlines of different
sections.
O
一20
Fig.5 Velocity at section x=85m
The topographical m印shows a big,deep‘'hole”
at the river bend resulting from water discharging and
scounng for years by the discharge from the Dajiang
Power Plant and the Erjiang Power Plant since the
construction of the Gezhouba Dam.It iS around this
sturgeons are concentrated.Therefore,the flow field
8l
around the deep hole iS the focus ofthe computation
. The horizontal flow direction of the river channel is
given in Figs.9’10.For the case that only the Erjiang
Power Plant IS in opermion,a strong backflow area is
formed near the Dajiang Power Plant and the ship
lockgate.Additionally.there iS a small backflow area
at the riverbend.The backflow becomes weaker and
the flow tUI ̄s to be more stable near the boRom ofthe
river.Down In the hole there印pears a vo ̄ex that
exhibits a complicated flow behavior
.
5
lO
l5
Fig.6 Underwater velocity distribution at measured section
O
。lO
一20
Fig.7 Velocity at section y=3m
95
9o
85
8O
75
Fig.8 Streamline at section .1
.5m
Figure 7 shows the flow velocity at the vertical
section of the deep hole
.When the main flow passes
through the deep hole of the simulated river channel-
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82
vortices with opposite directions are formed at the
bottom ofthe hole and at the upper and lower parts of
the main flow(clockwise atthe bottom ofthe hole and
counterclockwise in the upper part of the flow).11le
air atthe upperpart ofthe flow is irregularbecause of
the influence of the water flow.Figure 5 shows the
flow velocity of the passing water section at the center
of the deep hole.A demarcation line between the air
and the water can be easily seen.The flow is turbulent.
Small vortices near the wall and a huge vortex in the
whole flow area are found.Figure 6 represents the
distribution offlow velocity ofunderwater at the river
section measured with the Acoustic Doppler Current
Profiler(ADCP).It is obvious that the velocity
distributions in Figs.5 and 6 are similar.Figure 8 is
also obtained by sectioning at the bottom ofthe hole
the water plane at the center of which vortices are
spotted.Finally.Fig.1l shows the general similarities
between the computed results and the on.site
measurements of the flow velocity distribution at the
underwater sections.
0 50 lo0
Fig.9 Streamline at section z=-8m
4o
20
0
-20
0 50 lo0
Fig.10 Streamline at section z=-4m
4.CoNCLUSIoNS
(1)The numerical simulation ofthe flow field in
the spawning sites for sturgeons in the downstream of
the Gezhouba Dam shows very complex
characteristics. en only the Erjian Power Plant is in
operation,the velocity of the main surface flow is
high,and a deep hole i泊秦淮 杜牧 n the river area is formed.
enthewaterflowpassesthroughthe deephole,the
flow field ofthe vortices at the bottom of the hole is
extremely beneficial for the sedimentation ofthe fish
eggs.In addition,the strong viscosity of the fish eggs
enables them to stick to the crevices ofpiled rocks at
the bottom ofthe river without being washed away or
devoured by other fishes.thus effectively protecting
theincubationofthe eggs.
40
20
0
_20
Fig.1 1 Calculated velocity
(2)The on.site measurements and computational
results indicate that Chinese sturgeons tend tO lav eggs
among piled rocks ofthe deep hole,where the surface
flow velocity is high,the flow velocity at the bottom
is low.and the flow is relatively stable.This result is
in accordance with the hydrodynamic characteristics
of spawning sites for Chinese sturgeon.
(3)The spawning sites for Chinese sturgeons in
the downstream ofthe Gezhouba Dam are very shaky,
therefore,Chinese sturgeons can become extinct at
any time,and this is attributed to the water discharge
fromthedamandthedredgingofthewaterways.
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维普资讯
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