Delft3D-FLOW and CORMIX near-field modelling

1. 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

2. 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

3. 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.

4. 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/

5. 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)

6. 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

7. 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

8. 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)

9. Validation 1: Mass conservation

10. 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

11. Validation 2: Entrainment rate

12. 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)

13. Validation 4: Case Study - Application of coupled modelling system to a large Power Plant
Existing Units
New Units

14. Validation 4: Example

15. 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)

16. 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

17. 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)

18. 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)

19. 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

20. 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