hydrodynamic `modelling of large-scale cooling water outfalls
TRANSCRIPT
Hydrodynamic modelling of large-scale cooling water outfalls with a dynamically coupled near field – far field modelling system ICDEMOS 2014 Robin Morelissen, Deltares
16 april 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
16 april 2014
Modelling outfalls
Outfall plume behaviour over different scales; close to outfall (turbulence, metres) to effects/impacts kilometres away (large scale ambient flow)
No single model can cover these different scales efficiently and
accurately
Source: MEDRC, Dr.-Ing. Tobias Bleninger & Prof. G.H. Jirka, Ph.D. and Domenichini et al.
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Coupling models
Cover different time and space scales by coupling near field and far field models
Coupling methods: - No coupling (direct insertion, undiluted source) - One-way, fixed near field solution - One-way, time-varying near field solution - Two-way, dynamic near field – far field coupling
Source: Choi & Lee 2007
Source: Bleninger 2006
Development of the Delft3D-CORMIX coupling
Coupling Delft3D with CORMIX: − physically suitable location for coupling to the far field model (including
boundary interaction) − include many different outfall configurations and flow conditions that
are included in CORMIX. Intermediate zone
Near-field
Far-field
Current Plume boundary
Near-field plume centreline
Typical coupling location
Preferred coupling location
DESA
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)
Case Study - Application of coupled modelling system
• New large submerged outfall diffusers and submerged intakes
• Existing surface outfalls
Case Study - Application of coupled modelling system
Design criteria in the Case Study: 1 – Minimised extent of the +1°C temperature contour at
the surface 2 – Safe design of intake, i.e. most conservative
temperature increase at the submerged intakes
Physical phenomena in field data and reproduced by coupled model 1 - Varying location where plume surfaces due to tide
Validation of coupled modelling system
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 of coupled modelling system
18°C
~19.5°C
Coupled
Traditional
Physical phenomena in field data and reproduced by coupled model 3 - Plume visibility at the surface and colder plume at the surface
(under stratified ambient conditions)
Validation of coupled modelling system
Physical phenomena in field data and reproduced by coupled model 4 – More realistic vertical mixing and safer prediction of intake temperature
Validation of coupled modelling system
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 field data and 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)
16 april 2014