Parallel implementation of a geometrical reconstruction interface algorithm over openFOAM(R)

Even when the Piecewise-Linear Interface Calculation algorithm is a well established tech- nique for interphase reconstruction related to the Volume of Fluid method and is implemented in sev- eral privative codes for arbitrary meshes, no freely-distributed version is available to the date for the OpenFOAM(R) libraries suite. This works presents implementation details of this technique over Open- FOAM(R) to be used on parallel platforms. Much of them are related with the underlying numerics and the fundamental requirement of local and global conservativeness. Two main aspects are covered in this work: the computation of face fluxes by intersection of swept volumes and interface cells and the calculation of curvatures in each cell. While the first aspect does not present much difficulties, curva- tures computation results in an interesting case in how to manage a problem not well suited for message passing parallelization.Publicado en: Mecánica Computacional vol. XXXV, no. 11Facultad de Ingenierí

Parallel implementation of a geometrical reconstruction interface algorithm over openFOAM(R)

Even when the Piecewise-Linear Interface Calculation algorithm is a well established tech- nique for interphase reconstruction related to the Volume of Fluid method and is implemented in sev- eral privative codes for arbitrary meshes, no freely-distributed version is available to the date for the OpenFOAM(R) libraries suite. This works presents implementation details of this technique over Open- FOAM(R) to be used on parallel platforms. Much of them are related with the underlying numerics and the fundamental requirement of local and global conservativeness. Two main aspects are covered in this work: the computation of face fluxes by intersection of swept volumes and interface cells and the calculation of curvatures in each cell. While the first aspect does not present much difficulties, curva- tures computation results in an interesting case in how to manage a problem not well suited for message passing parallelization.Publicado en: Mecánica Computacional vol. XXXV, no. 11Facultad de Ingenierí

Parallel implementation of a geometrical reconstruction interface algorithm over openFOAM(R)

Even when the Piecewise-Linear Interface Calculation algorithm is a well established tech- nique for interphase reconstruction related to the Volume of Fluid method and is implemented in sev- eral privative codes for arbitrary meshes, no freely-distributed version is available to the date for the OpenFOAM(R) libraries suite. This works presents implementation details of this technique over Open- FOAM(R) to be used on parallel platforms. Much of them are related with the underlying numerics and the fundamental requirement of local and global conservativeness. Two main aspects are covered in this work: the computation of face fluxes by intersection of swept volumes and interface cells and the calculation of curvatures in each cell. While the first aspect does not present much difficulties, curva- tures computation results in an interesting case in how to manage a problem not well suited for message passing parallelization.Publicado en: Mecánica Computacional vol. XXXV, no. 11Facultad de Ingenierí

On the error analysis for geometrical volume of fluid methods

The Piecewise-Linear Interface Calculation (PLIC) algorithm is a well known technique for interface reconstruction, widely used in several Volume of Fluid (VOF) codes both commercial and open-source. In this work, an unstructured mesh implementation of these tools in OpenFOAM(R) is described and tested. The underlying numerical features of this new solver are described, showing how the programmed schemes accomplish local and global conservativeness. An extension of geometrical schemes to the momentum equation is also discussed, remarking the advantages of using the so called momentum-conserving scheme instead of a standard algebraic TVD advection method. Several benchmark problems are solved, comparing the results with the ones available in literature and analytical solutions. Different error norms are used to evaluate the solver accuracy in problems involving advection of discontinuous functions. Finally, a simple atomization problem is solved, comparing these results with solutions obtained using original OpenFOAM(R) VOF formulation.Publicado en: Mecánica Computacional vol. XXXV, no. 19Facultad de Ingenierí

Transient numerical assessment of race car dry-sump oil under different maneuvers

A numerical assessment of a dry-sump oil system was performed by Computational Fluid Dynamics (CFD). Unlike conventional cars, race cars are subjected to high accelerations that induce oil sloshing. Hence, dry-sump oil systems are required to collect the oil outside of the engine prior to be pumped inside of it again. To avoid engine malfunctions, the dry-sump must guarantee continuously oil suction in every maneuver. To perform such simulations, the model was subjected to different car maneuvers extracted from data acquisition available from real race car, showing that single and combined maneuvers, such as acceleration, braking and turnings can induce downward, upward and lateral accelerations higher than 2g during several seconds. Therefore, four different single maneuvers (acceleration, deceleration, turn right and turn left) as well as a set of contaminated maneuvers (braking and turning) were studied. Simulations were achieved by mean of the Volume of Fluid Method (VOF) for a air-oil system. The influence of the turbulence modeling was also investigated. First a forerunner design was analyzed and both the race car tests and CFD simulations showed that for the most extreme maneuvers (pure braking and combined with braking with turning right) the original design failed before the end of the maneuvers by air suction in the pump inlet. In consequence, the dry-sump was redesigned and assessed under these extreme conditions until to ensure stable oil aspiration.Publicado en: Mecánica Computacional vol. XXXV, no. 7.Facultad de Ingenierí

Direct numerical simulations of a single drop in bag mode break-up

Secondary break-up consist on the decomposition of droplets, ligaments and rims into smaller droplets forming a spray. This phenomenon is driven by interface deformation given by the growth of hy- drodynamic instabilities, depending on Reynolds andWeber numbers. Bag mode break-up takes place at moderate gas Weber numbers, at which the drops turns into a film and inflates. Film thickness decreases until a hole forms and expands, giving place to decomposition in smaller droplets. This mechanism is present in several break-up processes and is of great interest to understand the underlying physics of liquid atomization. In this work, we present the Direct Numerical Simulations (DNS) results of a single liquid droplet submerged in an air stream in bag mode regime. Navier-Stokes equations for the two-phase flow are solved using a Volume of Fluid with a Piecewise Linear Interface Capturing (PLIC) formulation and geometrical advection schemes on the volume fraction and momentum equations, programmed in the Basilisk suite. The deformation of the drop into a film and the posterior evolution of its thickness is studied until the formation of a hole and the results are compared with experimental data.Publicado en: Mecánica Computacional vol. XXXV, no. 19Facultad de Ingenierí

Transient numerical assessment of race car dry-sump oil under different maneuvers

A numerical assessment of a dry-sump oil system was performed by Computational Fluid Dynamics (CFD). Unlike conventional cars, race cars are subjected to high accelerations that induce oil sloshing. Hence, dry-sump oil systems are required to collect the oil outside of the engine prior to be pumped inside of it again. To avoid engine malfunctions, the dry-sump must guarantee continuously oil suction in every maneuver. To perform such simulations, the model was subjected to different car maneuvers extracted from data acquisition available from real race car, showing that single and combined maneuvers, such as acceleration, braking and turnings can induce downward, upward and lateral accelerations higher than 2g during several seconds. Therefore, four different single maneuvers (acceleration, deceleration, turn right and turn left) as well as a set of contaminated maneuvers (braking and turning) were studied. Simulations were achieved by mean of the Volume of Fluid Method (VOF) for a air-oil system. The influence of the turbulence modeling was also investigated. First a forerunner design was analyzed and both the race car tests and CFD simulations showed that for the most extreme maneuvers (pure braking and combined with braking with turning right) the original design failed before the end of the maneuvers by air suction in the pump inlet. In consequence, the dry-sump was redesigned and assessed under these extreme conditions until to ensure stable oil aspiration.Publicado en: Mecánica Computacional vol. XXXV, no. 7.Facultad de Ingenierí

Transient numerical assessment of race car dry-sump oil under different maneuvers

A numerical assessment of a dry-sump oil system was performed by Computational Fluid Dynamics (CFD). Unlike conventional cars, race cars are subjected to high accelerations that induce oil sloshing. Hence, dry-sump oil systems are required to collect the oil outside of the engine prior to be pumped inside of it again. To avoid engine malfunctions, the dry-sump must guarantee continuously oil suction in every maneuver. To perform such simulations, the model was subjected to different car maneuvers extracted from data acquisition available from real race car, showing that single and combined maneuvers, such as acceleration, braking and turnings can induce downward, upward and lateral accelerations higher than 2g during several seconds. Therefore, four different single maneuvers (acceleration, deceleration, turn right and turn left) as well as a set of contaminated maneuvers (braking and turning) were studied. Simulations were achieved by mean of the Volume of Fluid Method (VOF) for a air-oil system. The influence of the turbulence modeling was also investigated. First a forerunner design was analyzed and both the race car tests and CFD simulations showed that for the most extreme maneuvers (pure braking and combined with braking with turning right) the original design failed before the end of the maneuvers by air suction in the pump inlet. In consequence, the dry-sump was redesigned and assessed under these extreme conditions until to ensure stable oil aspiration.Publicado en: Mecánica Computacional vol. XXXV, no. 7.Facultad de Ingenierí

Numerical simulation of partially premixed combustion using a flame surface density approach

Partially premixed combustion is characterized by a variable equivalence ratio of the mixture in space and time, and where there are both lean and rich mixture zones. Thus the reaction evolves along with a turbulent mixture process, which modifies the composition of reactants and products. In this situation a so-called triple flame could be encountered, in which a rich and a lean premixed flame front as well as a diffusion flame are present. The diffusion flame develops behind the premixed flame front due to turbulent mixing in the hot combustion products. This kind of combustion could be found in Direct Injection Spark Ignition (DISI) engines when they are operated in the stratified charge mode. The model considered in this work assumes a simplified one-step irreversible chemical reaction in which fuel and oxidant react together in stoichiometric proportions giving products with the composition corresponding to a complete combustion. A transport equation is solved for the oxidant and fuel, from which the amount of products and the combustion progress are computed, while the turbulence is modeled with RANS (Reynolds-Average Navier-Stokes). The reaction rate is assumed in the model as proportional to the product of the Flame Surface Density (FSD) by the local laminar flame speed. Aside from the state and composition of the mixture, the local laminar flame speed is afected by the turbulent mixing process. This mixing process is taken into account by means of the classical β-PDF (Probability Density Function), which is a function of the mixture fraction and its variance. A transport equation is solved for both, the mixture fraction and its variance, and the FSD is computed through a transport equation where several models are available for the source terms. The model is implemented in the open-source toolkit OpenFOAM®. Computational results are obtained for partially premixed combustions inside constant-volume vessels with several initial configurations, which are compared with numerical results available in the literature.Publicado en: Mecánica Computacional vol. XXXV, no. 16.Facultad de Ingenierí

Numerical simulation of partially premixed combustion using a flame surface density approach

Partially premixed combustion is characterized by a variable equivalence ratio of the mixture in space and time, and where there are both lean and rich mixture zones. Thus the reaction evolves along with a turbulent mixture process, which modifies the composition of reactants and products. In this situation a so-called triple flame could be encountered, in which a rich and a lean premixed flame front as well as a diffusion flame are present. The diffusion flame develops behind the premixed flame front due to turbulent mixing in the hot combustion products. This kind of combustion could be found in Direct Injection Spark Ignition (DISI) engines when they are operated in the stratified charge mode. The model considered in this work assumes a simplified one-step irreversible chemical reaction in which fuel and oxidant react together in stoichiometric proportions giving products with the composition corresponding to a complete combustion. A transport equation is solved for the oxidant and fuel, from which the amount of products and the combustion progress are computed, while the turbulence is modeled with RANS (Reynolds-Average Navier-Stokes). The reaction rate is assumed in the model as proportional to the product of the Flame Surface Density (FSD) by the local laminar flame speed. Aside from the state and composition of the mixture, the local laminar flame speed is afected by the turbulent mixing process. This mixing process is taken into account by means of the classical β-PDF (Probability Density Function), which is a function of the mixture fraction and its variance. A transport equation is solved for both, the mixture fraction and its variance, and the FSD is computed through a transport equation where several models are available for the source terms. The model is implemented in the open-source toolkit OpenFOAM®. Computational results are obtained for partially premixed combustions inside constant-volume vessels with several initial configurations, which are compared with numerical results available in the literature.Publicado en: Mecánica Computacional vol. XXXV, no. 16.Facultad de Ingenierí