• Available models for complex fluid flow modeling

 The picture below gives an overview of the different rheological models implemented and validated in ANANAS®. These models cover the overall needs of O&G industry and research : viscoplastic flow, viscoelastic fluids at high We number, time dependant thixotropic fluids and multiphase flow).

Rheological models implemented in ANANAS.

• Our partner for R&D in rheology and measurements

As measurement technics are also mandatory  to accuratly identify the constants in the numerical models, LEMMA has a strategic partnership with RHEONIS company, whose expertise and knowledge are based on high-level experienced engineers and research scientists in this field. See for further details http://www.rheonis.com/

• Example : coupling intelligent mesh and viscoplastic flow in sudden expansion

Ansitropic mesh adaptation in sudden expansion. Viscoplastic flow.

3D anisotropic mesh adaptation in sudden expansion. Viscoplastic flow.

ANANAS® is able to compute both newtonian and non-newtonian fluid flows in pipes, at several Reynolds numbers, ranging from stokes flow to fully turbulent (Re=1e7) pipe flow. For turbulent newtonian flows in pipe, many  models are available, from RANS to modern and innovative LES-VMS model. Hybrid RANS-VMS can also be used if necessary.

• Example of turbulent newtonian fluid flow in smooth pipe

Turbulent flow in pipe at high Reynolds number, using LES-VMS model.

LES-VMS velocity profiles in boundary layer zone.

• Paraffinic  oil (thixotropic oil flow in smooth pipe)

ANANAS® has been used in many practical situations where complex fluid flow are involved and must be solved accuratly. The following example (published in [Berton & al, CFM 2011]) gives a good idea of the striking results obtained using intelligent mesh coupled with non newtonian fluid (pseudoplastic with yield stress and thixotropic time dependant rheology) flow simulation. In the first part of the study, a classical spatial convergence is achieved using structured and fixed mesh. The second part shows how intelligent mesh technology allows us to perform a very accurate and converged simulation within less nodes (20% less nodes than M4 structured finest mesh).

Structured meshes and anisotropic adapted mesh used to simulate non newtonian flow in pipe.

Velocity profile obtained with different meshes.

Anisotropic mesh adaptation in pipe for viscoplastic flow. Contour of velocity.

The pictures below enable to show the time dependant evolution of the structure parameter used in the thixotropic model (Houska model). In the shear zone near from the wall, this parameter is descreasing, whereas its value remains constant and equal to 1 in the plug flow.

Evolution of the structure parameter during the simulation. From left to right : t=0 (init), t=2s, t=5s, t=7s.

• Two phase wall bounded turbulent flow (LES-VMS & Level-Set formulation)

• Transient PCP (Progressive Cavity Pump) simulation

ANANAS® was the first CFD code able to produce full transient 3D simulation of PCP pump within newtonian or viscoplastic fluid. FSI simulation are also performed. This work is published in [Berton & al, SPE Conference 2011]. This was a very challenging case because of the complex geometry and large structure deformation encountered during the simulation. Please see below few snapshots linked to this work , with courtesy of PCM S.A.

Full transient and 3D PCP simulation. Top right : structured mesh generation.

Please see below a validation result obtained with a viscoplastic and thixotropic fluid. The flow rate is accuratly predicted within an error less than 5%, including uncertainties.

PCP simulation : comparison with experimental results.

Animation of the PCP case

• Lobe pump

An other original case is the lobe pump simulation involving intelligent mesh (mesh is repaired automatically when skewness or size criterion is no longer respected). The prescribed metric allows us to handle transient simulation within very small rotor/stator gap (<0.3 mm). This simulation is shown with courtesy of PCM S.A.

Snapshot : lobe pump shear stress calculation.

Evolution of the mesh in the lobe pump application

Multiphase flows models have been implemented in ANANAS® to produce accurate resuts depending on the considered physics. Many fields have to be explored in this area, but ANANAS® is today able to simulate :

• • multiphase flows with particles from low to high concentration (eg one-way, two way or four-way coupling), with fast eulerian models. See below the  turbidity current simulation which is validated with DNS (Direct Numerical Simulations).

Turbidity current : experimental example. From Som Dutta & al.

Front position. DNS and ANANAS simulations comparison.

Velocity profiles in turbidity current. DNS and ANANAS simulation comparison.

Animation of flow with transient turbidity

• • multiphase flows involving N dispersed phases of rigid particles
  • multi-scale bubbly flows (improved Level-Set formulation and Rayleigh-Plesset model)
  • emulsion : models derived from kinetic theories are available to quantify emulsion specific area, break-up and collapse, and shape relaxation. Surface tension impact on stress tensor is also included. ANANAS® is the unique commercial CFD code having this kind of advanced model. Validation is quite difficult in this case, and it was decided to perform code to code comparisons (ANANAS® vs academic research code) to validate this approach. Results are presented below : the flow is laminar at the inlet and the shear stress is calculated at each time step. The model allows us to estimate the shape and droplets orientation in the domain. Blue colour enlights area where break up occurs (variation of the droplets specific area).

Shear rate and emulsion simulation in academic test case.

Example of emulsion computation

All the above models are also available when non newtonian flows are considered.

In fact, it is a very hard task to properly quantify if a mixing process can behave as promised. ANANAS® is today the only commercial software on the market to provide powerful tools derived from kinetic theory to better understand and predict complex mixing process behaviour. We are not talking about time residence simulations (that ANANAS® is also able to calculate anyway) to estimate the quality of a blending process. Our innovative tool is a step ahead. It allows the user to directly predict the specific interfacial area, which is by the way one of the most striking quantity available and calculated with ANANAS® to estimate the quality of a blend. See below two examples : the first is a 2D academic test case (Peclet number =100) to illustrate ANANAS® capabilities in predicting good and poor mixing areas and the second one is a complex 3D industrial process simulated with success.

•  Mixing process (batch mode)

Mixing process simulation & emulsion shape relaxation. Pe=100