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Environmental Fluid Mechanics – Hydropower Plants. ( a.y. 2012/13, 9 credits – 90 hours). Transport processes and impacts Marco Toffolon e-mail: [email protected] Laboratorio Didattico di Modellistica Idrodinamica (2 nd floor, central corridor) tel.: 0461 28 2480. - PowerPoint PPT Presentation
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(a.y. 2012/13, 9 credits – 90 hours)
Environmental Fluid Mechanics – Hydropower Plants
Transport processes and impactsMarco Toffolone-mail: [email protected] Didattico di Modellistica Idrodinamica(2nd floor, central corridor)tel.: 0461 28 2480
Hydrology and water resourcesprof. Alberto Belline-mail: [email protected]
Constructionsprof. Maurizio Righettie-mail: [email protected]
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/gulf-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-benthosFishes
Sediments
Infilling
CloggingCoasts
Eco-hydraulics in Trento: a multi-disciplinary research group
Guido ZolezziNunzio Siviglia
M. Cristina BrunoBruno Maiolini
Department of Civil and Environmental Engineering
University of Trento, Italy
Typical medium-term behaviour:daily cycle + weekly cycledue to the production of peaks of electricity.
Sund
ay
Mon
day
Frid
ay
Thur
sday
Wed
nesd
ay
Tues
day
Satu
rday
Sund
ay
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.racine.ra.it/europa/uno/esame2003/terzaf/vcv/html/due.htm
… and what is thermopeaking?
temperature of reservoir
Hydropeaking thermal alterationIntensity changes during the year
river
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
0dtdM
VMC
concentration:
“diffusion”
(exceptions: reactive tracer oxygen, nutrients, and temperature)
DiffusionDiffusive flux works against concentration gradient Fick law
(1855)CD
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 3Characteristic dimension of the cloud
L(t1)
L(t3)L(t2)
DttL )(
Self-similar Gaussian solution
2
2
21 2exp
2
xMxC D
with variance Dt22
(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 diffusion(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+ diffusionorthogonal 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 cm2/s = 10-9 m2/sin air ~ 10-5 m2/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
xorthogonal 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
Yvertical mixing is much faster than transverse mixing
Mixing phases
sourcecompleted 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