arXiv subjects

Carlos Junqueira-Junior

Publications and source records attributed to Carlos Junqueira-Junior.

14 recordsLinked to original sources

arXiv2026

Assessment of jet inflow conditions on the development of supersonic jet flows

In the present work, large-eddy simulations of free supersonic jet flows are performed to investigate the influence of inflow conditions on the jet flow field and its turbulent properties. A high-order nodal discontinuous Galerkin method is employed to solve the governing equations on the generated mesh. Three different inflow profiles are evaluated to represent the nozzle-exit conditions, namely, inviscid, steady viscous, and unsteady viscous profiles. Velocity and shear stress tensor component profiles obtained from the simulations are compared with experimental data. Among the investigated profiles, the steady viscous inflow shows the most significant deviation from the inviscid case, particularly in the near-field region of the jet inlet. The steady viscous profile also leads to reduced peak velocity fluctuations, showing better agreement with experimental results. Further downstream, the influence of the inflow condition diminishes, with all three profiles converging toward the experimental reference. In addition, power spectral density analyses of streamwise velocity fluctuations reveal that the inflow conditions have little effect on spectral distributions, with numerical results showing consistent agreement with experimental data within the accessible Strouhal range. Beyond these findings, the study provides a highly detailed, high-fidelity database of supersonic jet flow simulations, encompassing six large-eddy computations with different meshes, polynomial refinements, and inflow conditions. The database includes high-frequency data in relevant regions of the jet flow field and is openly available in the Zenodo repository, ensuring accessibility and reusability for the scientific community.

physics.flu-dyn↗

arXiv2025

A Comparison of LES Inlet Boundary Conditions for Supersonic Jet Flows

The present work evaluates the effects of three inflow boundary conditions on large-eddy simulations of supersonic jet flows. The three inlet flow configurations considered are an inviscid profile, a stationary turbulent profile extracted from a RANS calculation, and a time-dependent tripped turbulent profile. The study applies the nodal discontinuous Galerkin spatial discretization to perform the supersonic jet flow simulations. Initially, a mesh and polynomial resolution study is performed to identify the requisites for simulating the supersonic jet flow. The velocity profiles resulting from the three numerical simulations with the different inflow conditions are compared with experimental data. The velocity profiles extracted from the calculation results indicate a major role of the steady turbulent inlet profile on the jet flow behavior, even for the tripped inlet condition. The imposition of a steady turbulent inlet profile could approximate the velocity distributions in the region close to the jet inlet section with the experimental reference. Negligible changes were observed to the velocity profiles far from the inlet section, where a good agreement with the experimental reference was already obtained from the simulations even with the inviscid profile.

physics.flu-dyn↗

arXiv2025

Characterization of boundary layers on isothermal and adiabatic curved surfaces of a supersonic turbine cascade

The effects of adiabatic and isothermal boundary conditions are investigated on the shock-boundary layer interactions (SBLIs) in a supersonic turbine cascade. Special attention is given to the characterization of the incoming boundary layers over the convex and concave walls of the blade and their impact in the SBLIs. Large eddy simulations (LES) are performed for an inlet Mach number of $\mathbf{M_\infty = 2.0}$ and Reynolds number based on the axial chord $\mathbf{Re = 200\,000}$. For the isothermal condition, the wall to inlet temperature ratio is $\mathbf{T_w/T_{\infty}=0.75}$, representing a cooled wall. Different incident shock wave topologies occur on the suction and pressure sides of the airfoil. For the former, an oblique shock impinges on the boundary layer leading to a larger separation bubble. On the other hand, a normal shock from a Mach reflection induces a small separation region near the wall for the pressure side. Results are presented in terms of mean velocity and temperature contours, and the incoming boundary layers are characterized by looking at the Clauser parameter, shape factor, dilatation and turbulent kinetic energy (TKE) profiles. Inspection of the shape factors show that the adiabatic wall boundary layers are more prone to separate than the isothermal ones. This is indeed observed in the airfoil suction side, but not on the pressure side, where the flow separates in the same chord position regardless of the thermal boundary condition. This is a topic for investigation in the final version of the paper. An assessment of the dilatation and TKE profiles explains the disparities of the bubble sizes on the pressure and suction sides of the airfoil.

physics.flu-dyn↗

arXiv2025

Characterization of supersonic boundary layers of adiabatic and isothermal curved surfaces with shock interactions

Boundary layers of adiabatic and isothermal curved walls are investigated for a supersonic turbine cascade, including the effects of shock-boundary layer interactions (SBLIs). Wall-resolved large eddy simulations (LES) are performed for a linear cascade of blades with an inlet Mach number of $M_\infty = 2.0$ and Reynolds number based on the axial chord $Re_\infty = 200\,000$. The wall to inlet temperature ratio of the isothermal case is $T_w/T_{\infty}=0.75$, representing a cooled wall. An assessment of the effects of pressure gradient, thermal boundary conditions and SBLIs is presented in terms of the downstream variation of mean flow quantities such as density, temperature, and momentum profiles. The different thermal boundary conditions affect the density and temperature profiles along the boundary layer, where cooling increases the density of the gas near the wall, and reduces its temperature and viscosity. Both of these effects make the momentum profiles fuller and, hence, the boundary layer of the isothermal case is less prone to separate than that of the adiabatic wall. The mean density profiles are also affected by pressure gradients induced by the convex and concave curvatures of the blade, which lead to expansion and compression of the flow, respectively. The analysis of separate terms from the momentum balance equation explains the behavior of various physical mechanisms in the inner and outer regions of the supersonic boundary layers. The importance of mean flow advection, compressibility, and Reynolds stresses is presented in terms of flow acceleration and deceleration. The impact of the SBLIs in the momentum balance mechanisms is also investigated, showing that a combination of compressions and expansions impact the boundary layers by redirecting the flow toward the wall due to the shock formations.

physics.flu-dyn↗

arXiv2024

Accuracy Assessment of Discontinuous Galerkin Spectral Element Method in Simulating Supersonic Free Jets

The study performs large-eddy simulations of supersonic free jet flows using the Discontinuous Galerkin Spectral Element Method (DGSEM). The main objective of the present work is to assess the resolution requirements for adequate simulation of such flows with the DGSEM approach. The study looked at the influence of the mesh and the spatial discretization accuracy on the simulation results. The present analysis involves four simulations, incorporating three different numerical meshes and two different orders of spatial discretization accuracy. The numerical meshes are generated with distinct mesh topologies and refinement levels. Detailed descriptions of the grid generation and refinement procedures are presented. The study compares flow property profiles and power spectral densities of velocity components with experimental data. The results show a consistent improvement in the computed data as the simulation resolution increases. This investigation revealed a trade-off between mesh and polynomial refinement, striking a balance between computational cost and the accuracy of large-eddy simulation results for turbulent flow analyses.

physics.flu-dyn↗

arXiv2023

Dynamic Mode Decomposition of High Reynolds Number Supersonic Jet Flows

Current design constraints have encouraged the studies of aeroacoustic fields around compressible jet flows. The present work addresses the numerical study of unsteady turbulent jet flows as a preparation for future aeroacoustic analyses of main engine rocket plumes. An in-house large eddy simulation tool is used in order to reproduce high fidelity results of compressible jet flows. The large eddy simulation formulation is written using a second order numerical scheme for a finite difference spatial discretization. Numerical simulations of perfectly expanded jets are performed and the results are compared to the literature. Dynamic mode decompositions (DMD) of the jet flow, using large size three-dimensional snapshots, are performed. Three variables are analyzed, namely, the velocity magnitude, the vorticity magnitude and the divergence of velocity. In particular, two frequencies are identified and they are linked to flow structures observed in experiments performed by other authors in the literature. The spatial shapes of the corresponding dynamic modes are also discussed.

physics.flu-dyn↗

arXiv2023

Comparison of Shock-Boundary Layer Interactions in Adiabatic and Isothermal Supersonic Turbine Cascades

Wall-resolved large eddy simulations are employed to investigate the shock-boundary layer interactions (SBLIs) in a supersonic turbine cascade. An analysis of the suction side separation bubbles forming due to the SBLIs is presented for adiabatic and isothermal (cooled) walls. Flow snapshots indicate that the separation bubble contracts and expands in a similar fashion for both thermal boundary conditions. However, the skin-friction coefficient distributions reveal a downstream displacement of the separation region when cooling is applied. The separation bubble is also smaller for this setup compared to the adiabatic one. A steeper pressure rise is observed for the isothermal wall downstream of the incident oblique shock, and this occurs because the incident shock wave gets closer to the blade surface when cooling is applied. The Reynolds stresses are computed to investigate the effects of wall temperature on the turbulence activity. While the levels of the tangential stresses are similar for the cases analyzed, those for the wall-normal component are higher for the cooled wall.

physics.flu-dyn↗

arXiv2023

Influence of Different Subgrid Scale Models in LES of Supersonic Jet Flows

Current design constraints have encouraged the studies of aeroacoustics fields around compressible jet flows. The present work addresses the numerical study of subgrid scale modeling for unsteady turbulent jet flows as a preliminary step for future aeroacoustic analyses of main engine rocket plumes. An in-house large eddy simulation (LES) tool is developed in order to reproduce high fidelity results of compressible jet flows. In the present study, perfectly expanded jets are considered because the authors want to emphasize the effects of the jet mixing phenomena. The large eddy simulation formulation is written using the finite difference approach, with an explicit time integration and using a second order spatial discretization. The energy equation is carefully discretized in order to model the energy equation of the filtered Navier-Stokes formulation. The classical Smagorinsky model, the dynamic Smagorinsky model and the Vreman models are the chosen subgrid scale closures for the present work. Numerical simulations of perfectly expanded jets are performed and compared with the literature in order to validate and compare the performance of each subgrid closure in the solver.

physics.flu-dyn↗

arXiv2023

Computational Performance of a LES Solver for Supersonic Jet Flow Applications

An in-house large eddy simulation tool is developed in order to reproduce high fidelity results of compressible jet flows. The large eddy simulation formulation is written using the finite difference approach, with an explicit time integration and using a second order spatial discretization. The energy equation is carefully discretized in order to model the energy equation of the filtered Navier-Stokes formulation. Such nu\-me\-ri\-cal studies are very expensive and demand high performance computing. Message passage interface protocols are implemented into the code in order to perform parallel computations. The present work addresses the computational performance of the solver running on up to 400 processors in parallel. Different mesh configurations, whose size varies from approximately 5.9 million points to approximately 1.0 billion points, are evaluate in the current paper. Speedup and efficiency curves are evaluated in order to assess the strong scalability of the solver.

physics.flu-dyn↗

arXiv2022

Influence of different subgrid-scale models in low-order LES of supersonic jet flows

The present work is concerned with a study of large eddy simulations (LES) of unsteady turbulent jet flows. In particular, the present analysis is focused on the effects of the subgrid-scale modeling used when a second-order spatial discretization methodology is employed for the numerical simulations. The present effort addresses perfectly expanded supersonic jets, because the authors want to emphasize the effects of the jet mixing phenomena. The LES formulation is discretized using the finite difference approach, after the equations are rewritten in a generalized coordinate system. Both space and time discretizations are second-order accurate and an explicit time march is adopted. Special care is dedicated to the discretization of the energy equation to appropriately model the set of filtered equations appearing in the LES formulation. The classical Smagorinsky, the dynamic Smagorinsky and the Vreman models are the subgrid-scale closures selected for the present work. The computational results are compared to data in the literature to validate the present simulation tool. Results indicate that the characteristics of numerical discretization can be as important as the effects of the subgrid-scale models for such low-order spatial discretization schemes. A detailed analysis is presented for the performance of each subgrid closure in the numerical context here considered.

physics.flu-dyn↗

arXiv2022

Large Eddy Simulations of Supersonic Jet Flows for Aeroacoustic Applications

Current design constraints have encouraged the studies of aeroacoustics fields around compressible jet flows. The present work addresses the numerical study of unsteady turbulent jet flows for aeroacoustic analyses of main engine rocket plumes. A novel large eddy simulation (LES) tool is developed in order to reproduce high fidelity results of compressible jet flows which could be used for aeroacoustic studies with the Ffowcs Williams and Hawkings approach. The numerical solver is an upgrade of an existing Reynolds-averaged Navier-Stokes solver previously developed in the group. The original framework is rewritten in a modern fashion and intensive parallel computation capabilities have been added to the code. The LES formulation is written using the finite difference approach. The energy equation is carefully discretized in order to model the energy equation of the filtered Navier-Stokes formulation. The classical Smagorinsky model is the chosen subgrid scale closure for the present work. Numerical simulations of perfectly expanded jets are performed and compared with the literature in order to validate the new solver. Moreover, speedup and the computational performance of the code are evaluated and discussed. Flow results are used for an initial evaluation of the noise radiated from the rocket plume.

physics.flu-dyn↗

arXiv2021

Numerical investigation of three-dimensional partial cavitation in a Venturi geometry

Sheet cavitation appears in many hydraulic applicationss and can lead to technical issues. Some fundamental outcomes such as the complex topology of 3-Dimensional cavitation pockets and their associated dynamics need to be carefully visited.In the present paper, the dynamics of partial cavitation developing in a 3-D Venturi geometry and the interaction with sidewalls are numerically investigated. The simulations are performed usinf a one-fluid compressible Reynolds-Averaged Navier-Stokes (RANS solver associated to a non-linear turbulence model and a void transport-equation model. A detailed analysis of this cavitating flow is carried out using innovative tools such as Spectral Proper Orthogonal Decompositions. Particular attenttion is paid in the study of 3-D effects by comparing numerical results obtained with sidewalls and periodic conditions. A three-dimensional dynamics of the sheet cavitation, unrelated to the presence of sidewalls, is identified and discussed.

physics.flu-dyn↗

arXiv2020

Strong Scaling of Numerical Solver for Supersonic Jet Flow Configuration

Acoustics loads are rocket design constraints which push researches and engineers to invest efforts in the aeroacoustics phenomena which is present on launch vehicles. Therefore, an in-house computational fluid dynamics tool is developed in order to reproduce high-fidelity results of supersonic jet flows for aeroacoustic analogy applications. The solver is written using the large eddy simulation formulation that is discretized using a finite-difference approach and an explicit time integration. Numerical simulations of supersonic jet flows are very expensive and demand efficient high-performance computing. Therefore, non-blocking message passage interface protocols and parallel input/output features are implemented into the code in order to perform simulations which demand up to one billion degrees of freedom. The present work evaluates the parallel efficiency of the solver when running on a supercomputer with a maximum theoretical peak of 127.4 TFLOPS. Speedup curves are generated using nine different workloads. Moreover, the validation results of a realistic flow condition are also presented in the current work.

cs.CE↗

arXiv2020

On the scalability of CFD tool for supersonic jet flow configurations

New regulations are imposing noise emissions limitations for the aviation industry which are pushing researchers and engineers to invest efforts in studying the aeroacoustics phenomena. Following this trend, an in-house computational fluid dynamics tool is build to reproduce high fidelity results of supersonic jet flows for aeroacoustic analogy applications. The solver is written using the large eddy simulation formulation that is discretized using a finite difference approach and an explicit time integration. Numerical simulations of supersonic jet flows are very expensive and demand efficient high-performance computing. Therefore, non-blocking message passage interface protocols and parallel Input/Output features are implemented into the code in order to perform simulations which demand up to one billion grid points. The present work addresses the evaluation of code improvements along with the computational performance of the solver running on a computer with maximum theoretical peak of 2.727 PFlops. Different mesh configurations, whose size varies from a few hundred thousand to approximately one billion grid points, are evaluated in the present paper. Calculations are performed using different workloads in order to assess the strong and weak scalability of the parallel computational tool. Moreover, validation results of a realistic flow condition are also presented in the current work.

cs.DC↗