Work in France - PD position
Offer: Post-doctoral position
Duration: 12 months
Salary: net 1850 €/month (including all medical cares)
Location: EDF R&D (Paris)
Laboratory: Saint Venant Laboratory for Hydraulics
Research Team: Sediment dynamics and morphodynamics
Supervisor: Prof. Dan Nguyen (01 30 87 79 57); kimdan_nguyen@yahoo.fr
Co-supervisor: Damien Pham Van Bang (01 30 87 84 37); damien.pham-van-bang@edf.fr
Subject: Two phase flow modelling and turbidity maximum
Abstract of the work
The turbidity maximum in estuaries is very important to consider as it strongly influence the propagation of tide, the conditions of navigability and the oxygenation in turbid water. On one hand, it damps the tidal wave by moving the sediment. On the other hand, it induces expensive operations to maintain the nautical bottom. Finally, the oxygenation is hindered in turbid water since suspended solid matter (SSM) are scattering the light.
Two-phase flow modelling for solid/liquid system have been recently developed for natural flows in river, estuaries. The new model enables a precise description of the sediment/liquid and the bottom/fluid interactions. The recent experimental observations on sedimentation and consolidation of estuarine mud are correctly simulated by introducing an effective permeability term. The model of turbulence in fluid/mud system that is coming from the COSINUS European project (based on the assumption of the passive tracers) is re-analysed in the light of two phase flow theory : more precisely, some aspects related to floculation, stratification, formation of the turbidity maximum, density current will be considered. An exploratory review on the floculation models (by Boltzmann and Smoluchowski’s equations) are realized simultaneously.
A new modelling of the turbulence in the NSMP (Navier Stokes Multi-Phase) numerical code is proposed. The validation and calibration are realized from available experimental data.
Objectives
The main purpose of the collaboration between Ecole des Ponts ParisTech/Saint Venant Lab. for Hydraulics, the CETMEF and the University of Caen is focused on the development of a two phase sediment/water applied to sediment dynamics and morphodynamics in estuarine and coastal zones. The NSMP model’s improvement (description of the turbulence in water in presence of solid particles) will enable to account for some processes (formation and dynamic of turbidity maximum in estuaries, damping/enhancement of the turbulence by a stable/unstable stratification) and further the turbulence/flocculation coupling.
The objective of this present study is: at first, to develop the theories as well as numerical schemes needed to correctly simulate erosion and scouring phenomenon; and then to extend the present width-averaged version to 3-D one with its application to real cases.
Methods
The development of the new model in two-phase flows follows four steps : (i) a literature review and a state of the art ; (ii) analysis and selection of the most relevant model for the applications in natural environment ; (iii) numerical developments and tests ; (iv) optimisation of the computational time.
The presentation of the state of the art will present an experimental part (describing the data obtained by the different research teams, a theoretical part (presenting based on both formulations, the passive tracers and the two-phase flow) and finally, a synthesis (exploratory only) on the turbulence/flocculation coupling.
The comparative analysis of identified models is realised to determine their weakness/strength and determine best compromise. The latter is then implemented in a FORTRAN routine and validated on test cases that are well-documented. Finally on the basis of the numerical experiment results some improvements (formulation and/or optimisation of computational time) are proposed.
Keywords
turbulence –sedimentation and consolidation –Erosion and scour, 3-D model
Geographical zone of interest
Estuaries, Bays, Deltas.
Required skills
- CFD (Computational Fluid Dynamics)
- Fluid mechanics, rheology
- Sediment transport
- Workgroup spirit
Some old and on-going researches performed by the Team
J. Chauchat (2007) : Contribution à la modélisation diphasique du transport sédimentaire en milieux côtiers et estuariens, Thèse de l’Université de Caen-Basse Normandie, 220p (in french).
N. Barbry, S. Guillou, K.D. Nguyen (2000). Une approche diphasique pour le calcul du transport sédimentaire en milieux estuariens. C.R. Acad. Sci., IIb, 328, pp 793–799.
J. Chauchat, S. Guillou, D. Pham Van Bang (2007) : Modélisation diphasique de la dispersion turbulente dans le transport en suspension de particules sédimentaires, Congrès Français de Mécanique, Grenoble, 6p
J. Chauchat & S. Guillou (2009) : Turbulence closure for sediment transport two-phase flow model in dilute flow, J. Geophys. Res., 113, C11017. [URL doi:10.1029/2007JC004708].
K.D. Nguyen, S. Guillou, J. Chauchat, N. Barbry (2009) : A two-phase numerical model for suspensed sediment transport in estuaries, Adv. In Water Ressources
S. Guillou, J. Chauchat, D. Pham Van Bang, D.H. Nguyen, K.D. Nguyen, (2010) : Simulation du clapage de sédiment avec un modèle à, deux phases, Journées Nationales Génie Civil – Génie Côtier (soumis)