Delft3D-FLOW and CORMIX

Coupling of different length scales;

An application to Cooling water discharges

Delft Software Days 2014

Theo van der Kaaij and Robin Morelissen, Deltares

7 november 2014

Introduction

Increasing amount of coastal activities/industries that use and discharge water world-wide; power plants, desalination plants, waste water outfalls, etc.

1 - Impact on the environment and need to comply with EIA criteria and regulations

2 - The design needs to be optimised for efficient/economic operation (e.g. recirculation)

Therefore, it is necessary to be able to assess the outfall plume behaviour accurately, e.g. by means of numerical modelling

7 november 2014

Modelling outfalls

Outfall plume behaviour over different scales;

close to outfall (near-field, metres)

to effects/impacts (far-field, 100 m towards several kilometers)

No single model can cover these different scales efficiently and

accurately

Typically CORMIX Typically Delft3D-FLOW

Source: MEDRC, Dr.-Ing. Tobias Bleninger

& Prof. G.H. Jirka, Ph.D. and Domenichini et al.

Something about CORMIX (1)

CORMIX is broadly accepted as an easy-to-use yet powerful tool for accurate and reliable point

source mixing analysis. Presently there are over 5000 registered CORMIX users worldwide, with

about one third within the United States. We have offered technical training to nearly 1000

individuals in the Americas, Europe, and Asia in workshops sponsored by USEPA and others

since 1990. CORMIX has been successfully applied by regulators, engineers, environmental

scientists, and students worldwide to the design and monitoring of wastewater disposal systems

in oceans, rivers, lakes, and estuaries. Because of it ability to simulate details of plume boundary

interaction, important for ecological and human health risk assessment, CORMIX is recognized

by regulatory authorities in all continents for environmental impact assessment.

• Based on the work of Prof. Gerhard Jirka (nowadays Rober Donneker

and prof Tobias Bleninger)

• Both surface discharges, single port an multi port diffusers are dealt with

• http://www.mixzon.com/ or http://www.cormix.info/

Something about CORMIX (2)

• No computational grid, No approximation of partial differential equations

• Rule based expert system. Depending on Ambient conditions and

discharge characteristics the flow is classified and the belonging

empirical/analytical formulations are applied (module)

5. About CORMIX (3)

Typical CORMIX output

BEGIN MOD274: ACCELERATION ZONE OF STAGED DIFFUSER

In this laterally contracting zone the diffuser plume becomes VERTICALLY FULLY

MIXED over the entire layer depth (HS = 15.00m).

Full mixing is achieved after a plume distance of about five

layer depths from the diffuser.

Profile definitions:

BV = layer depth (vertically mixed)

BH = Gaussian 1/e (37%) half-width in horizontal plane normal to trajectory

ZU = upper plume boundary (Z-coordinate)

ZL = lower plume boundary (Z-coordinate)

S = hydrodynamic centerline dilution

C = centerline concentration (includes reaction effects, if any)

TT = Cumulative travel time

X Y Z S C BV BH TT

0.00 -75.00 3.20 1.0 0.937E+01 0.00 0.00 .00000E+00

0.00 -60.00 3.63 2.6 0.355E+01 3.00 2.25 .35785E+02

0.00 -45.00 4.06 3.3 0.283E+01 6.00 4.50 .71570E+02

Cumulative travel time = 357.8521 sec ( 0.10 hrs)

Plume centerline may exhibit slight discontinuities in transition

to subsequent far-field module.

END OF MOD274: ACCELERATION ZONE OF STAGED DIFFUSER

----------------------------------------------------------------------------------------------

----------------------------------------------------------------------------------------------

BEGIN MOD252: DIFFUSER INDUCED PLUME IN WEAK CROSS-FLOW

Delft3D-FLOW - CORMIX coupling

Coupling Delft3D-FLOW with CORMIX:

DESA

DESA (Distributed Entrainment Sink Approach):

(Prof. Lee Hong Kong University)

Far Field impact of a jet/plume is that it entrains

water from its ambient which results in dilution.

Delft3D-FLOW:

- Number of entrainment sinks along the jet trajectory

- One single diluted source at the end of the jet trajectory

Working principle dynamically coupled models

Run several time steps in

far field model (Delft3D)

Translate ambient

conditions to

near field model

Run near field model

(CORMIX)

Translate near field

model results to far field

model (DESA)

Validation 1: Mass conservation

Validation 2: Entrainment rate

Experiment Eysink (1968):

Tank with linear density profile:

Density bed: 1015 kg/m3

Density surface:1000 kg/m3

Fresh water discharge through a small nozzle near the bed

Validation 2: Entrainment rate

Validation 3: Comparison with CORMIX Far Field

• Straight “unbounded” Channel, depth 15 m,

• Stationary flow velocity of 0.5 m/s,

• Cooling water discharge of 60 m3/s, dT = 10 oC,

• Discharged through a single port diffuser pointing (horizontally)

in flow direction (diameter 2.5 m)

Validation 4: Case Study - Application of coupled

modelling system to a large Power Plant

Existing Units New Units

Validation 4: Example

Physical phenomena in field data and reproduced by coupled model

1 - Varying location where plume surfaces due to tide

Validation 4: Comparison with measurements

(qualitatively, different periods)

Physical phenomena in field data and reproduced by coupled model

2 - Surface excess temperature in non-stratified conditions (+1.5°C at surface instead of +4°C in traditional (not coupled) modelling approach)

Validation 4: Comparison with measurements

(qualitatively, different periods)

18°C

~19.5°C

Coupled

Traditional

Physical phenomena in field data and reproduced by coupled model

3 - Plume visibility at the surface as colder than ambient surface temperature

(under stratified ambient conditions)

Validation 4: Comparison with measurements

(qualitatively, different periods)

Physical phenomena in field data and reproduced by coupled model

4 – More realistic vertical mixing and safer prediction of intake temperature

Validation 4: Comparison with measurements

(qualitatively, different periods)

Conclusions

Conclusions:

• Coupling of near and far field models is required to accurately and efficiently assess

the characteristics of the outfall plume on all spatial scales

• Validation: observed physical phenomena in both laboratory and field data are

reproduced by coupled model (and not in traditional modelling methods)

• The dynamically coupled modelling approach can make a substantial difference in the

development of plants

- Environmental impact not overestimated (smaller footprint)

- Safer design intake (for intake temperature)

Limitations:

• Not all relevant CORMIX modules are implemented yet. Implementation of new

module(s) requires same further validation aiming at that specific module(s).

• Parallel simulations not supported yet!

• Not (yet) included in the Open Source Version

Potential Further Developments (preferably jointly!):

• Implement more CORMIX modules

• More generic implementation aiming at coupling of models describing different

scales

- read table of x,y,z,value(s), table or tables can originate from some kind of

other model or educated expert guess or …… (whatever)

- translate the values into:

loss or gain of mass (water and/or substances)

loss or gain of momentum (for instance introduced by power generating

turbine)

Questions?

Contact information:

Robin.Morelissen@deltares.nl, or,

theo.vanderkaaij@deltares.nl