pptx

sisterpurpleΜηχανική

24 Οκτ 2013 (πριν από 3 χρόνια και 1 μήνα)

51 εμφανίσεις

(
a.y.
2012/13,
9 credits


90 hours)

Environmental Fluid Mechanics


Hydropower Plants

Transport processes and impacts

Marco Toffolon

e
-
mail:
marco.toffolon@ing.unitn.it

Laboratorio

Didattico


di
Modellistica

Idrodinamica

(2
nd

floor, central corridor)

tel.: 0461 28

2480

Hydrology and water resources

prof. Alberto Bellin

e
-
mail:
alberto.bellin@ing.unitn.it

Constructions

prof. Maurizio Righetti

e
-
mail:
maurizio.righetti@ing.unitn.it

Part II: Transport processes in the environment

II
-
1. Introduction
(10 hours)

Basic concepts: definition of concentration, mass balance, diffusion. Turbulent mixing. Gaussian
model for diffusion processes: basic solution and typical scales. Advection
-
diffusion equation
and analytical solutions in the one
-
dimensional context. Phases of mixing: near field,
intermediate field, far field. Dispersion resulting from non
-
uniform advection. Dynamics of
reactive tracers (including temperature): zero
-

and one
-
dimensional models.



II
-
2. Transport processes in rivers and effects of hydropower production
(9 hours)

Review of basic hydraulic concepts. Estimates of turbulent diffusion and dispersion coefficients.
Flood waves due to sudden releases from hydropower plants (hydropeaking). Temperature
waves due to the temperature differences between rivers and hydropower releases
(thermopeaking). Introduction to river morphology. Hints on biological effects of hydro
-

and
thermo
-
peaking. Modification of habitats in impacted rivers. Numerical models for longitudinal
dispersion: examples.



II
-
3. Thermal dynamics of reservoirs
(9 hours)

Heat budget in closed basins. Stratification cycle and implications on vertical mixing.

Effect of
withdrawals and inflows on the temperature profile.

Hints on biological aspects and water
quality.

Numerical models for hydro
-
thermodynamics of reservoirs: examples.

Application to a
real case: reservoir management and impact on downstream river.

~28 hours

Lecture notes
.



Suggested textbook (transport processes):


S.A
. Socolofsky & G.H. Jirka, dispense del corso
Special Topics on Mixing and Transport in the
Environment
, Texas A&M University, 2005.






Further reading on environmental fluid mechanics:


Fischer
H.B., Koh J., List J., Imberger J., Brooks H.,
Mixing in Inland and Coastal Waters
, Academic
Press, New York, 1988.


Rutherford
J.C.,
River Mixing
, John Wiley & Sons, Chichester, 1994
.


J.L. Martin, S.C. McCutcheon,
Hydrodynamic and transport for water quality modeling
,
Lewis Publishers
CRC Press


About HP impacts
on the
environment:


Journal papers

Main references

link

on website:
http://www.ing.unitn.it/~toffolon/ (“Materiale didattico”)

Environmental fluid
mechanics:

An emblematic case

21/04/2010

http://earthobservatory.nasa.gov/NaturalHazards/event.php?id=43733

Deepwater

Horizon

oil spill

http://fastfreenews.com/wp
-
content/uploads/2010/06/gul f
-
oil
-
spill1.jpg

25/04/2010

01/05/2010

09/05/2010

17/05/2010

24/05/2010

12/06/2010

19/06/2010

Impacts of hydropower production

Reservoirs

Rivers

Ecosystems

Thermal structure

Macro
-
benthos

Fishes

Sediments

Infilling

Clogging

Coasts

Eco
-
hydraulics

in Trento: a multi
-
disciplinary research group

Guido
Zolezzi

Nunzio

Siviglia

M. Cristina Bruno

Bruno
Maiolini

Department of Civil and Environmental Engineering

University of Trento,
Italy

Typical medium
-
term
behaviour:

daily cycle
+
weekly cycle

due to the production of
peaks of electricity.

Sunday

Monday

Friday

Thursday

Wednesday

Tuesday

Saturday

Sunday

Stage variations are very rapid
(order of
cm/min

or m/h)

both
in the rising
and in the
decreasing phase



travelling waves.


Simplifying assumption:

waves have approximately a
square shape.

Hydropeaking
: qualitative description

http://www.raci ne.ra.i t/europa/uno/esame2003/terzaf/vcv/html/due.htm

… and what is
thermopeaking
?

temperature of reservoir

Hydropeaking


thermal alteration

Intensity changes during the year

temperature of river



Main concepts

Transport in the environment

1.
mass is conserved
(non
-
reactive tracers)




2.
concentration tends to become
spatially homogeneous

1

2

3

passive tracer

flow field

concentration:

“diffusion”

(
exceptions
:

reactive tracer


oxygen, nutrients,

and
temperature
)

Diffusion

Diffusive flux works against
concentration gradient

Fick law

(1855)

200 “balls”, probability of movement 0.2, single boxes

Phenomenological explanation:

random displacement rightward or leftward

N

steps (time)

Main features of diffusive processes

1

2

3

Characteristic dimension of the cloud

L(t
1
)

L(t
3
)

L(t
2
)

Self
-
similar Gaussian solution

with variance

(1D, infinite domain)

±




68.3%

±
2




95.5%

±
3




99.7%

“mass” between
extreme points:

How an advective process becomes diffusive…

Turbulence

(“random” advection)

Turbulent
d
iffusion

(property of the flow field,
and not of the
tracer+fluid
)

for times long enough

(longer than the integral
scals

of turbulence)

Non
-
uniform

advective motion

+ diffusion

orthogonal
to the flow


Dispersion

(combined mechanism)

for times long enough

(longer than the characteristic scale of orthogonal diffusion)

Thermal oscillations

Molecular diffusion

(property of
tracer+fluid
)

typical values

in water ~ 10
-
5

cm
2
/s = 10
-
9

m
2
/s


in air ~ 10
-
5

m
2
/s

Dispersion:
phenomenological description

Lagrangian

model
: following particles

deterministic
component

(assigned flow field)

random component

(turbulence or thermal oscillation)

y

u(y)

non
-
uniform
advective motion



cloud
distortion along x

x

orthogonal
diffusion



“compacts”
the cloud along y

dispersion



enhanced
“diffusion” along x

concentration C(x)

particles in the
x,y

domain

C(y)

zoom

zoom

x

y

particles

Numerical simulation

x

y

River mixing

hp. shallow water, large width (B>>Y)

z

y

B

Y

vertical mixing is much faster than
transverse mixing

Mixing phases

source

completed vertical mixing

completed transverse mixing

near field
: 3D model, turbulent diffusion
(+ molecular)

intermediate field
: 2D model
(depth
-
averaged)
,
dispersion + turbulent diffusion
(+ molecular)

far field
: 1D model
(cross
-
section
-
averaged)
, dispersion
(+
turbulent diffusion
+

molecular)

Gallery of images

Point source in a river 1/2

flow direction

Tracciante rilasciato in un fiume. Il mescolamento verticale viene
raggiunto molto velocemente (a distanza di circa 10 volte la
profondità); il mescolamento trasversale è molto più lento.

Point source in a river
2/2

Le curve incrementano fortemente il mescolamento trasversale a
causa delle correnti secondarie.

Confluence

Confluenza di tre fiumi: a sinistra, con una concentrazione molto alta
di particolato; al centro con una concentrazione intermedia; a destra
(più scuro), più pulito. Contorni ben definiti separano di diversi flussi.
[Inn a sinistra, Danubio al centro, Passau DE]

Un caso concreto:

Scarico accidentale in un corso d’acqua

Fasi del problema

rio Sorne

fase 2:

confluenza

fase 1:

mixing nel rio Sorne

fase 3:

mixing nell’Adige

fase 4:

cosa succede a valle?

fiume Adige

scarico massa M