Immersed Boundary Technique Research Articles

Pairwise interaction of in-line spheroids settling in a linearly stratified fluid

AbstractThis study investigates the transport of particles in density-stratified fluids, a prevalent natural phenomenon. In the ocean, particles and marine snow descend through fluids with significant density variations due to salinity and temperature gradients. Such heterogeneity in the background fluid affects the settling or rising rates of particles, often leading to accumulation at transitional density layers. Previous research has primarily focused on spherical particles, examining their isolated motion, pairwise interactions, and collective transport in stratified fluids. This work, however, extends the investigation to the interaction between two spheroidal particles settling in-line in a linearly stratified fluid. This study employs an immersed-boundary technique to perform particle-resolved numerical simulations in a three-dimensional Cartesian domain. The results showcase the effects of varying the stratification strength through the Froude number, the particles’ aspect ratios, and the initial separation distance between the particles on the interaction dynamics between the settling spheroids.

Improved diffuse interface-immersed boundary method for three-dimensional multiphase fluids–structure interaction with moving contact lines

In the realm of numerical algorithms for investigating interactions between multiphase fluids and structure, the accurate computation of moving contact lines (MCLs) dynamics and the substantial computational resource demands bring challenges in three-dimensional simulations. In this study, an improved diffuse interface-immersed boundary method is proposed to efficiently investigate three-dimensional multiphase fluids–structure interactions. The present work commences with the development of the explicit correction scheme and the simplified Dirac function coefficient, designed to efficiently implement the immersed boundary technique. To validate the effectiveness and accuracy of the proposed method, the simulations of water entry and exit for a half-buoyant sphere are carried out, which conclusively demonstrate that the proposed method offers significant advantages in terms of both efficiency and accuracy, faithfully capturing the dynamic response of solid structures and the substantial deformation of free surfaces at the three-dimensional scale. Additionally, a comparative analysis of the results obtained using the proposed method for the free water exit of a hollow sphere against previous experimental data is conducted, highlighting the promising potential of the proposed method for applications.

A sharp MLS penalty immersed finite element method for fluid-structure interaction of highly deformable slender body in turbulent flow

This paper presents a new computational approach to simulate challenging fluid-structure interactions (FSI) between fluids and slender deformable structures. Key innovations address limitations of standard immersed boundary methods, including spurious forces, stability at low density ratios, and accuracy at high Reynolds numbers. The method couples a sharp interface immersed boundary technique with detached eddy simulation turbulence modelling to enable precise FSI for high Reynolds number flows. A strong coupling partitioned algorithm stabilized by Aitken relaxation significantly enhances stability for low density ratios down to 1. A moving least square compact support domain approximation reduces spurious oscillations from moving geometries while providing second-order accuracy. Adaptive mesh refinement imposes jump conditions on slim deformable bodies and minimizes grid leakage. The proposed method is evaluated on three conventional FSI benchmarks and four experimental cases, confirming its robustness, accuracy, and stability in low and significantly high Reynolds numbers. A more complex fluids engineering case is considered last to test the solution under challenging conditions with fast moving solid boundaries and fast flowing fluid. A thin deformable membrane is forced through a submersible centrifugal pump under standard operating conditions. The solution is shown to produce a stable solution with good collision handling ability.

Implementation of a level-set-based volume penalization method for solving fluid flows around bluff bodies

A volume penalization-based immersed boundary technique is developed and thoroughly validated for fluid flow problems, specifically flow over bluff bodies. The proposed algorithm has been implemented in an open source field operation and manipulation (OpenFOAM), a computational fluid dynamics solver. The immersed boundary method offers the advantage of inserting a complex solid object inside a Cartesian grid system, and therefore, the governing equations can be applied to such a simpler grid arrangement. For capturing the fluid–solid interface more accurately, the grid is refined near the solid surface using topoSetDict and refineMeshDict utilities in OpenFOAM. In order to avoid any numerical oscillation and to compute the gradients accurately near the interface, the present volume penalization method (VPM) is integrated with a signed distance function, which is also referred to as a level-set function. Benchmark problems, such as flows around a cylinder and a sphere, are considered and thoroughly validated with the results available in the literature. For the flow over a stationary cylinder, the Reynolds number is varied so that it covers from a steady two-dimensional flow to an unsteady three-dimensional flow. The capability of the present solver has been further verified by considering the flow past a vibrating cylinder in the cross-stream direction. In addition, a flow over a sphere, which is inherently three-dimensional due to its geometrical shape, is validated in both steady and unsteady regimes. The results obtained by the present VPM show good agreement with those obtained by a body-fitted grid using the same numerical scheme as that of the VPM, and also with those reported in the literature. The present results indicate that the VPM-based immersed boundary technique can be widely applicable to scientific and engineering problems involving flow past stationary and moving bluff bodies of arbitrary geometry.

Direct Numerical Simulation of liquid metal forced and mixed convection in a square rod bundle

This paper reports results of Direct Numerical Simulations of fully developed, forced and mixed convection of Liquid Lead Bismuth Eutectic (LBE) around four vertical cylindrical rods arranged in a square lattice at Pr = 0.031. The solutions provided here are placed in a context where very few data are available for low-Prandtl flows, especially in mixed convection conditions, and can hence be useful for the development and validation of advanced turbulent heat transfer models. The equations are discretized using a Finite Volume implementation of a second order projection method. The irregular cylindrical boundaries are handled with an original Immersed Boundary technique. A single friction Reynolds number value is set (Reτ = 180) and buoyancy effects are accounted for by imposing the Rayleigh number, under the Boussinesq approximation. A Ra-value Ra = 2.5 ×104 is selected in order to investigate the main differences between forced and mixed convection at low Prandtl number values. Time-averaged velocity and temperature fields are shown, in order to discuss the main features of the flow and thermal fields. First order statistics are also presented, highlighting the effect of aiding buoyancy on turbulent heat and momentum transport.

A High-Order Immersed Moving Boundary Method Using Ghost Points and Characteristics for Acoustics

Realistic acoustic problems often involve interactions between arbitrary-shaped moving objects at the interface with a fluid domain. The present work aims at developing numerical methods to take into account moving boundaries for acoustic problems, with a high order of convergence. The reference problem considered in this work is the solution of the non-linear Euler equations by a finite-difference time-domain method, describing the formation of one-dimensional waves created by a moving piston. The most suitable class of methods to solve this type of problem in the case of complex moving boundaries is the ghost-point method for sharp interface with 4th order reconstruction. 1 In order to accurately formulate the immersed boundaries with ghost points, the boundary conditions are formulated in terms of characteristic waves of the non-linear equations. The proposed approach is also extended to represent moving boundaries with a prescribed acoustic impedance. This is achieved by coupling a time-domain acoustic impedance model to the immersed boundary technique. The method is also applied to a two-dimensional example, where an acoustic pulse is reflected by a moving wall.

Code verification of immersed boundary techniques using the method of manufactured solutions

Code verification plays a crucial role for all finite element applications, especially for non-standard ones, such as immersed boundary approaches, which are typically based on novel algorithms and often error-prone in-house implementations. Instead of relying on rarely available analytical solutions or overkill FEM simulations, in this article, the capabilities of the method of manufactured solutions (MoMS) are explored, enabling an easy and straightforward derivation of closed-form reference solutions. The focus is kept on immersed problems, in particular, on the finite cell method (FCM), and manufactured solutions are derived for 2D and 3D problems involving voids and single/multiple inclusions. We propose several approaches for the construction of the manufactured solutions, where zero traction conditions for void regions and continuous normal stresses along material interfaces are directly fulfilled. Thus, no weak boundary conditions are required for reproducing the manufactured solution via FCM. This not only enables code verification for FCM implementations that lack the option of applying weak boundary conditions, but also keeps the simulation complexity low, when testing other relevant features, e.g., different integration schemes or the implementation of enrichment functions. The flexibility and wide application range of the MoMS in the context of immersed boundary simulations is demonstrated using static, quasi-static, and transient problems in the context of linear elasticity. Finally, the analytical derivations of the manufactured solutions used in this paper are provided as supplementary material.

A fluid-structure interaction method for soft particle transport in curved microchannels

A numerical framework is presented to predict the transport of soft elastic capsules immersed in an incompressible fluid with the aim of simulating inertial microfluidics applications. The flow evolution is modeled by a fully incompressible lattice Boltzmann method whereas a finite element model is considered for describing the dynamics of deformable structures. An immersed boundary technique is adopted to reconstruct the solution in the vicinity of the immersed surface and the time integration of the fluid-structure interaction problem is obtained by following an explicit procedure. The effectiveness of the framework is validated by means of several test cases involving: flows between two parallel plates for Reynolds numbers in the range 1÷100; capsules immersed in a fluid at Stokes regime exhibiting small and large deformations under shear; capsules migrating in a long straight microchannel with square cross-section at low-to-moderate Reynolds number. A very good agreement between the present results and literature data obtained using different numerical methods is found for all test cases. Finally, the method allowed to accurately simulate incompressible flows subjected to large pressure difference between the inlet and the outlet, characteristic of long curved microchannels, obtaining very smooth particle dynamics.

The effect of segmentation depth in a helical fin tube bundle on the anisotropic turbulence state

The large eddy simulation approach was used to perform a numerical simulation of a flow around a helical segmented-fin tube bundle. This work focuses on the study of turbulence and the effect of segment depth on it. The simulation was conducted in an area away from the boundaries of the tube bundle, where the flow is fully-developed, and the use of periodic boundary conditions is possible. The computer-aided design of the helical segmented-fin tube geometry is incorporated into the computational grid from the immersed boundary technique. The Reynolds stress tensor was used to analyze the anisotropic state of turbulence. This flow is characterized by an anisotropic state generated by a flow with a preferential direction. A transfer of momentum in the inter-segment space and contiguous zones was observed. This intersegment flow generates a less anisotropic state of turbulence. This study aimed to understand a possible transformation of heat transfer with marginal geometrical changes and pressure drop increases.

A versatile immersed boundary method for high-fidelity simulation of Conjugate Heat Transfer

A numerical strategy based on an immersed boundary method (IBM) is presented for performing high-fidelity simulation of thermal hydraulics while including Conjugate Heat Transfer (CHT). The well documented pipe flow is considered which, despite its academic nature, can be seen as a prototype of complex geometry in the sense that the computational mesh, only regular and Cartesian, is not in any way designed to fit the wall. An original strategy is proposed to impose Neumann boundary conditions in this generic situation where the wall geometry is disconnected from the mesh organization. As a first validation step, the technique is used in the context of heat transfer in pipe flow with isoflux conditions (IF). The actual order of accuracy is assessed in laminar regime and then direct numerical simulation (DNS) results are compared to turbulent data of reference, including first- and second-order one-point statistics, as well as budgets of temperature variance for a Reynolds number Re=5300 and two Prandtl numbers Pr=0.025,0.71. The technique is then used to develop a versatile methodology for CHT simulations, where the coupling between fluid and solid thermal solution is performed by an immersed boundary technique that translates the information from the normal and tangential surface directions into the Cartesian grid directions. Consistent results are presented in laminar and turbulent regimes, through the check of the accuracy order for the former and the analysis of turbulent statistics for the latter, including the assessment of the discontinuity of the temperature variance dissipation across the fluid-solid interface.

A critical assessment of the immersed boundary method for modeling flow around fixed and moving bodies

This paper reports the verification and validation of the immersed boundary methods implemented in the open-source toolbox FOAM-Extend version 4.0 and 4.1. Five test cases with increasing complexity are studied and the simulation results are compared with the experimental and numerical data found in the literature. A solver is developed based on the Immersed Boundary Surface Method (IBS) which is an advanced cut-cell finite volume immersed boundary technique. By integrating the Lagrangian equations of motion with the IBS, this solver is capable of simulating fluid–particle interactions. The benchmark studies indicated that the IBS yields excellent results for stationary immersed bodies. Even though the flow field is captured satisfactorily for moving bodies, spurious force oscillations are present in these cases. Simulating different size particles in a channel flow shows that the spurious force oscillations can negatively affect the prediction of particle dynamic motion, although the severity depends on the value of the particle Stokes number.

: A high-order discontinuous Galerkin solver for flow simulations and multi-physics applications

We present the latest developments of our High-Order Spectral Element Solver (▪), an open source high-order discontinuous Galerkin framework, capable of solving a variety of flow applications, including compressible flows (with or without shocks), incompressible flows, various RANS and LES turbulence models, particle dynamics, multiphase flows, and aeroacoustics. We provide an overview of the high-order spatial discretisation (including energy/entropy stable schemes) and anisotropic p-adaptation capabilities. The solver is parallelised using MPI and OpenMP showing good scalability for up to 1000 processors. Temporal discretisations include explicit, implicit, multigrid, and dual time-stepping schemes with efficient preconditioners. Additionally, we facilitate meshing and simulating complex geometries through a mesh-free immersed boundary technique. We detail the available documentation and the test cases included in the GitHub repository. Program summaryProgram Title:▪CPC Library link to program files:https://doi.org/10.17632/738py2shk4.1Developer's repository link:https://github.com/loganoz/horses3d.Licensing provisions: MITProgramming language: Fortran 2008External routines/libraries: METIS, MPI, HDF5, MKL, PETSc (all are optional).Nature of problem:▪ is a high-order discontinuous Galerkin framework, capable of solving a variety of flow applications, including compressible flows (with or without shocks), incompressible flows, various RANS and LES turbulence models, particle dynamics, multiphase flows, and aeroacoustics.Solution method: high-order discontinuous Galerkin Spectral Element (DGSEM) and explicit/implicit time-steppers.Additional comments including restrictions and unusual features:▪ is a multiphysics environment where the compressible Navier-Stokes equations, the incompressible Navier–Stokes equations, the Cahn–Hilliard equation and entropy–stable variants are solved. Arbitrary high–order, p–anisotropic discretisations are used, including static and dynamic p–adaptation methods (feature-based and truncation error-based). Explicit and implicit time-steppers for steady and time-marching solutions are available, including efficient multigrid and preconditioners. Numerical and analytical Jacobian computations with a colouring algorithm have been implemented. Multiphase flows are solved using a diffuse interface model: Navier–Stokes/Cahn–Hilliard. Turbulent models implemented include RANS: Spalart-Allmaras and LES: Smagorinsky, Wale, Vreman; including wall models. Immersed boundary methods can be used, to avoid creating body fitted meshes. Acoustic propagation can be computed using Ffowcs-Williams and Hawkings models. ▪ supports curvilinear, hexahedral, conforming meshes in GMSH, HDF5 and SpecMesh/HOHQMesh format. A hybrid CPU-based parallelisation strategy (shared and distributed memory) with OpenMP and MPI is followed.

Numerical analysis of heat and mass transfer through beds of spherical and non-spherical elements

Many issues related to mass and heat transfer through beds of granular materials are still not fully understood. In this work, non-isothermal turbulent flow is analysed within granular layers of spherical and non-spherical elements. We apply a volume penalization (VP) approach formulated in the framework of an immersed boundary technique (IB) on Cartesian computational meshes. It allows modelling flows around solid objects with almost arbitrarily complex shapes and in any form of contact. The validation of the solution accuracy is performed against ANSYS Fluent simulations using body-fitted meshes and experimental literature data. It shows the capability of the IB-VP approach for the simulations of flows in complex geometries. The main research focuses on the comparison of the influence of various types of particles and their temperature on vorticity, turbulence level and pressure drop inside and behind the granular bed. In particular, we analyse how the shape of the solid particles affects the efficiency of heat transfer in different flow conditions. The obtained results reveal the occurrence of very complex flow structures (recirculation and stagnation regions) inside beds. Comparison of results also point out preferred configurations of the beds.

Numerical Investigation of Regime Transition in Canopy Flows

We have carried out highly resolved simulations of turbulent open channel flows. The channel wall is covered with different filamentous layers sharing the same thickness (h=0.1H, where H is the open channel height) and bulk Reynolds number (i.e., Re_b=U_bH/nu , , U_b is the bulk velocity and nu the kinematic fluid viscosity). The layers are composed of rigid, slender cylindrical filaments mounted perpendicular to the bottom wall. We have selected two layer configurations characterised by filament spacing ratios of Delta S/H=pi /24simeq 0.13 and Delta S/H=pi /32simeq 0.098. The geometrical features of the two layers, allow to classify them as transitional canopies (lambda =dh/Delta S^2simeq 0.15, where d is the filament diameter, i.e. dh is the filament frontal area) (Monti et al. 2020), which is defined as the separation between the sparse-dense asymptotic regimes, proposed by Nepf (2012). While the physical characterisation of the two asymptotic regimes is fairly understood, the transitional conditions remain an open question since the physical characteristics unique to the sparse and dense scenarios coexist in the transitional regime. By resolving every single filament with the aid of an immersed boundary technique in the framework of a Large Eddy formulation, we report the physical mechanisms that emerge at the onset of different regimes (chosen values of lambda fall on the verge between a dense and a sparse condition) and verify the criterion associated with the inception of the transition regime.

XIGA: An eXtended IsoGeometric analysis approach for multi-material problems

Multi-material problems often exhibit complex geometries along with physical responses presenting large spatial gradients or discontinuities. In these cases, providing high-quality body-fitted finite element analysis meshes and obtaining accurate solutions remain challenging. Immersed boundary techniques provide elegant solutions for such problems. Enrichment methods alleviate the need for generating conforming analysis grids by capturing discontinuities within mesh elements. Additionally, increased accuracy of physical responses and geometry description can be achieved with higher-order approximation bases. In particular, using B-splines has become popular with the development of IsoGeometric Analysis. In this work, an eXtended IsoGeometric Analysis (XIGA) approach is proposed for multi-material problems. The computational domain geometry is described implicitly by level set functions. A novel generalized Heaviside enrichment strategy is employed to accommodate an arbitrary number of materials without artificially stiffening the physical response. Higher-order B-spline functions are used for both geometry representation and analysis. Boundary and interface conditions are enforced weakly via Nitsche’s method, and a new face-oriented ghost stabilization methodology is used to mitigate numerical instabilities arising from small material integration subdomains. Two- and three-dimensional heat transfer and elasticity problems are solved to validate the approach. Numerical studies provide insight into the ability to handle multiple materials considering sharp-edged and curved interfaces, as well as the impact of higher-order bases and stabilization on the solution accuracy and conditioning.

OpenFOAM solver for thermal and chemical conversion in porous media

We present the porousGasificationFoam solver and libraries, developed in the open-source C++ code OpenFOAM, for the comprehensive simulation of the thermochemical conversion in porous media.The code porousGasificationFoam integrates gas flow through a porous media with the models of heterogeneous (drying, gasification, pyrolysis, solid combustion, precipitation) and homogeneous (gas combustion) chemical reactions. Inside porous media transport equations are formulated applying the spatial averaging methodology. The mass and enthalpy transfer between solid and gas phases is suitable for systems out of the thermal equilibrium. The convection and radiation modes of the heat transfer are included for gas and solid phases, and the immersed boundary technique is applied for the porous media inside the computational domain.We validate the elements of the model against a set of experimental and theoretical results. Amongst them, Thermogravimetric Analysis experiments of thermal conversions of two wooden particles: one of millimeter size the other of centimeter size. Simulations feature reaction schemes and physical parameters established in the literature. We show the influence of the porous media size on the gasification process. The millimeter particle remains uniform, while for the centimeter setup, the pyrolysis front is reproduced. The spatial patterns in physical conditions modify the course of chemical reactions and influence media composition and structure evolution. Another important example is a gasifier where we obtain a self-sustaining front propagation because of an exothermic heterogeneous reaction. Program summaryProgram Title: porousGasificationFoamCPC Library link to program files:https://doi.org/10.17632/s6sj9kgp69.1Developer's repository link:https://github.com/pjzuk/porousGasificationFoam (foam-extend-4.1); https://github.com/btuznik/porousGasificationFoam (OpenFOAM 8)Licensing provisions: GNU General Public Licence version 3Programming language: C++External routines/libraries: OpenFOAM 8, foam-extend-4.1Nature of problem: The developed software is a solver and a set of libraries for simulating the thermal conversion in porous media, including drying, pyrolysis, gasification, and combustion. The model includes the flow of the reactive gas mixture and the transfer of mass and enthalpy between the gas and solid phases. The porous medium can change during the process. The model is transient and enables three-dimensional simulations.Solution method:: The finite-volume method is used in the code for equation discretization. A set of governing equations is solved for the gas and solid phases, including mass conservation of gas species and solid components, momentum conservation in the gas phase, and equations of enthalpy conservation in both phases. The porous media region inside the whole computational domain is defined using the immersed boundary approach.

Numerical investigation of turbulent features past different mechanical aortic valves

Flow through mechanical aortic valves (MAVs) has been constantly associated to higher haemolysis and platelet activation levels with respect to native valves, due to non-physiologic haemodynamic features. Both computational and experimental investigations have correlated the blood damage to augmented levels of turbulent stress downstream of MAVs. This study provides a computational estimation, drawn from high-resolution direct numerical simulations, of turbulent and fluctuating viscous stresses in three different MAV configurations, at subsequent stages of the cardiac cycle. The configurations comprise a St. Judes Medical Regent valve (SJMV), a Lapeyre-Triflo FURTIVA valve (LTFV) with three leaflets, and a SJMV with vortex generators (VGs). Non-standard configurations are expected to mitigate the mean stress level on blood constituents reducing the turbulent production. Computations are carried out by means of a finite-difference flow solver with a direct-forcing immersed boundary technique to handle fixed and moving bodies. The VGs are found to provide instabilities which corrupt the Kármán-like vortex shedding downstream of the leaflets, reducing the intensity of turbulent kinetic energy at the peak flow rate, thus lowering the local Reynolds shear stress. Conversely, the LTFV configuration provides comparable haemodynamic performance at peak flow rate but further reduced stress level in the deceleration phase. These interpretations are supported by probability density distributions from three-dimensional fields, and further corroborated by a pointwise mapping of the Taylor length scale and local energy spectra. The outcomes of this study might potentially be exploited to improve the design of new-generation MAVs, with the aim of decreasing the risk of thromboembolic complications.

Combined influences of radiation and inclined magnetic field on natural convection in a cavity with complex geometry

In the current study, the influence of inclined magnetic field and optical thickness on the natural convection heat transfer of participating magnetic fluid flow in a complex geometry are investigated, for the first time. The physical model is a 2D square enclosure with an internal elliptical heater. The radiative transfer equation is used instead of the Roseland approximation to calculate the divergence of the radiative heat flux. The multiple-time-relaxation lattice Boltzmann method is adopted to calculate the velocity and temperature fields. The complex boundary conditions are treated using the immersed boundary technique and the radiative transfer equation by the finite volume method. The findings are accessible in terms of streamlines, isotherms, Nusselt number, percentage reduction of the heat transfer, and correlation of Nusselt number for a wide range of optical thicknesses (0 ≤ τ ≤ 100), Hartmann numbers (0 ≤ Ha ≤ 500), and magnetic field inclinations (0° ≤ γ ≤ 90°) in fixed values of Rayleigh number (Ra = 106) and Planck number (Pl = 0.1). The results showed that at Ha = 500, in an optically thin medium (τ ≤ 1), the maximum reduction of the heat transfer because of the magnetic effect is less than 15%, while this is 61% and 66% for τ = 100 and the non-radiative state, respectively.

An updated Gappy-POD to capture non-parameterized geometrical variation in fluid dynamics problems

In this work, we propose a new method to fill the gap within an incomplete turbulent and incompressible data field in such a way to satisfy the topological and intensity changes of the fluid flow after a non-parameterized geometrical variation in the fluid domain. This work extends the one that has been published as a conference proceeding to the 2018 AIAA Scitech Forum and Exposition (Akkari et al. in Geometrical reduced order modeling (ROM) by proper orthogonal decomposition (POD) for the incompressible navier stokes equations. In: 2018 AIAA Aerospace Sciences Meeting, AIAA SciTech Forum, (AIAA 2018-1827), 2018). A single baseline large eddy simulation (LES) is assumed to be performed prior geometrical variations. The proposed method is an enhancement of the Gappy-POD method proposed by Everson and Sirovich in 1995, in the case where the given set of empirical eigenfunctions is not sufficient and is not interpolant for the recovering of the modal coefficients for each Gappy snapshot by a least squares procedure. This happens when the available data cannot be written as an interpolation of the baseline POD modes. This is typically the case when we introduce non-parameterized geometrical modifications in the fluid domain. Here, after the baseline simulation, additional solutions of the incompressible Navier–Stokes equations are solely performed over a restricted fluid domain, that contains the geometrical modifications. These local LESs that we will call hybrid simulations are performed by using the immersed boundary technique, which uses of a fluid boundary condition and the baseline velocity field. Then, we propose to update the POD modes using a local modification of the baseline POD modes in the restricted fluid domain. Furthermore, we will propose a physical correction of the latter enhanced Gappy-POD modal coefficients thanks to a Galerkin projection of the Navier–Stokes equations upon the new modes of the available data. This enhancement procedure on the global velocity reconstruction by the physical constraint was tested on a 3D semi-industrial test case of a typical aeronautical injection system and, a 2D laminar and unsteady incompressible test case. The speed-up relative to this new technique is equal to 100, which allows us to perform an exploration of two new designs of the aeronautical injection system.

Secondary Flow in Smooth and Rough Turbulent Circular Pipes: Turbulence Kinetic Energy Budgets

Direct Numerical Simulations have been performed for turbulent flow in circular pipes with smooth and corrugated walls. The numerical method, based on second-order finite discretization together with the immersed boundary technique, was validated and applied to various types of flows. The analysis is focused on the turbulence kinetic energy and its budget. Large differences have been found in the near-wall region at low Reynolds number. The change in the near-wall turbulent structures is responsible for increase of drag and turbulence kinetic energy. To investigatselinae the effects of wall corrugations, the velocity fields have been decomposed so as to isolate coherent and incoherent motions. For corrugated walls, we find that coherent motions are strongest for walls covered with square bars aligned with the flow direction. In particular, the coherent contribution is substantial when the bars are spaced apart by a distance larger than their height. Detailed analysis of the turbulence kinetic energy budget shows for this set-up a very different behavior than for the other types of corrugations.