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Development of advanced models for transition to turbulence in hypersonic flows and prediction of transition under uncertainties Serino, Gennaro ; Terrapon, Vincent ; et al in Serino, Gennaro (Ed.) Review of the VKI Doctoral Research 2012-2013 (2013, March) Detailed reference viewed: 139 (10 ULg)Integrating Experimental and Computational Fluid Dynamics approaches using Proper Orthogonal Decomposition Techniques Andrianne, Thomas ; ; Guissart, Amandine et al in Progress in Aerospace Sciences (2013) The concept of Proper Orthogonal Decomposition (POD) is used to integrate Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) approaches. The key idea is to take advantage of the ... [more ▼] The concept of Proper Orthogonal Decomposition (POD) is used to integrate Experimental Fluid Dynamics (EFD) and Computational Fluid Dynamics (CFD) approaches. The key idea is to take advantage of the optimality of the POD technique and its capability to extract the most energetic patterns of complex aerodynamic flow fields. First, the concept of Modal Assurance Criterion (MAC) is used to obtain a simple quantitative criterion to compare EFD measurements to CFD results. The comparison is based on the POD modes, extracted from each set of data. The analysis of the energy content of the modes allows to draw important conclusions about the role of the latter. The method is applied in the study of the flow field around a rectangular cylinder, which is either static or oscillating in a low-speed flow field. The second EFD/CFD integration technique deals with the reconstruction of a flow field from measured data, making use of CFD simulation results. The POD modes are first extracted from several CFD data sets, using a snapshot POD approach. Then the entire flow field of measured data can be reconstructed using a gappy POD method. The technique is applied to the transonic flow around a civil aircraft type wind tunnel model. The EFD measurements consist in pressure coefficient data from pressure ports or pressure-sensitive paint. It is shown that the complete flow field can be reconstructed from the pressure data with satisfactory accuracy and at relatively low computational cost. The work demonstrates the potential of the POD technique to integrate EFD and CFD data, leading to a combined, validated and complete analysis of the flow under consideration. [less ▲] Detailed reference viewed: 325 (42 ULg)Radiation Modeling of a Hydrogen Fueled Scramjet ; ; Terrapon, Vincent in Journal of Thermophysics and Heat Transfer (2013), 27(1), 11-21 With the difficulty and cost of full-scale flight experiments, the design of scramjet engines relies heavily on computational simulations. Radiation may play an important role in the wall heating and flow ... [more ▼] With the difficulty and cost of full-scale flight experiments, the design of scramjet engines relies heavily on computational simulations. Radiation may play an important role in the wall heating and flow cooling of scramjets. However, very few studies have focused on such. The present analysis is based on three-dimensional turbulent reacting flow simulations of the HyShot II hydrogen fueled scramjet engine running at flight conditions of Mach 7.4. A three-dimensional discrete ordinates method analysis with a narrowband averaged spectral model is employed to determine wall heating and flow cooling from thermal radiation. The discrete ordinates method is verified against a three-dimensional ray tracing method. The radiative species considered are H2O and OH. The radiative heat flux is on the order of 10 kW∕m2, which is 0.1–0.6% of the total convective wall heat flux. Flow cooling due to radiation is found to be on the order of 3 K. Sensitivity analysis shows that radiation is highly dependent on chamber size, temperature, pressure, and radiative species mole fraction. Variations in these factors can explain the differences between previous analyses in the literature that studied hypothetical engines and the current work that models an existing scramjet. [less ▲] Detailed reference viewed: 53 (6 ULg)Dynamics of Elasto-Inertial Turbulence in Flows with Polymer Additives Terrapon, Vincent ; ; Scientific conference (2012, December 07) Elasto-inertial turbulence is a new state of turbulence that may occur in certain viscoelastic flows, in particular flows with polymer additives. The dynamics of elasto-inertial turbulence is here ... [more ▼] Elasto-inertial turbulence is a new state of turbulence that may occur in certain viscoelastic flows, in particular flows with polymer additives. The dynamics of elasto-inertial turbulence is here investigated numerically from the perspective of the coupling between polymer dynamics and flow structures. The resulting mechanism helps resolve a long standing controversy in the understanding of polymer drag reduction and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows, previously observed in polymeric flows. In particular, we show that the introduction of small perturbations into the polymeric flow excites the unstable nature of the nonlinear advection term, resulting in the formation of sheets or cliffs of polymer stretch. These sheets of high polymer stretch, hosting a significant increase in extensional viscosity, create a strong local anisotropy, with a formation of local low-speed jet-like flow. The response of the flow is through pressure, whose role is to redistribute energy across components of momentum, resulting in the formation of waves, or trains of alternating rotational and straining motions. The mechanism shares some similarity with the Kelvin-Helmholtz instability, except that the thickness of these sheets is too close to the Kolmogorov scale for vortices to be created. Once triggered, EIT is self-sustained since the elastic instability creates the very velocity fluctuations it feeds upon. [less ▲] Detailed reference viewed: 53 (17 ULg)Using Proper Orthogonal Decomposition Methods for Comparing CFD Results to Experimental Measurements Andrianne, Thomas ; Guissart, Amandine ; Terrapon, Vincent et al Scientific conference (2012, December 07) This work presents a method for quantitative comparison of numerical results to experimental measurements. It is based on the concept of Proper Orthogonal Decomposition. This technique is selected in ... [more ▼] This work presents a method for quantitative comparison of numerical results to experimental measurements. It is based on the concept of Proper Orthogonal Decomposition. This technique is selected in order to compare the unsteady aerodynamic flows around static and oscillating bodies obtained from wind tunnel testing and numerical simulations. Two dimensional Time-resolved Particle Image Velocimetry measurements are carried out on the upper surface a 4:1 rectangular cylinder. Simulations are performed using unsteady Reynolds-Averaged Navier-Stokes and an unsteady Discrete Vortex Method. It is demonstrated that the proposed technique is a good preliminary step for comparing the main characteristics of unsteady aerodynamic data. [less ▲] Detailed reference viewed: 67 (25 ULg)Studying the Topology and Dynamics of Elasto-inertial Channel Flow Turbulence Using the Invariants of the Velocity Gradient Tensor and Dynamic Mode Decomposition ; Terrapon, Vincent ; Conference (2012, November 20) Direct numerical simulations (DNS) of the transition to and fully developed elasto-inertial turbulence (EIT) of a polymer solution in a channel flow has been used as a basis for the study of the topology ... [more ▼] Direct numerical simulations (DNS) of the transition to and fully developed elasto-inertial turbulence (EIT) of a polymer solution in a channel flow has been used as a basis for the study of the topology and dynamics of these flows. The Reynolds number in these DNS ranged from 500 to 5000. The topology of these flows was studied through the joint probability density functions (JPDFs) of the second and third invariants of the velocity gradient tensor (VGT), $Q_A$ and $R_A$ respectively and the JPDFs of the second invariants of the rate-of-strain tensor and the rate-of-rotation tensor, $Q_S$ and $Q_W$ respectively. The results suggest that these transitional and fully developed EIT flows are predominantly made up of vortex sheets. Dynamic mode decomposition has been undertaken on the second invariant of the VGT, $Q_A$, which reveals that the most amplified mode is a two-dimensional structure located in the near-wall region. A ``discontinuity'' is observed close to the wall, which corresponds closely to the location of extrema of the mean polymer extension and is hypothesized to be a critical layer. [less ▲] Detailed reference viewed: 59 (6 ULg)A New State of Turbulence: Elasto-Inertial Turbulence ; ; et al Conference (2012, November 20) The elasticity of polymer solutions is found to generate a new state of turbulence, elasto-inertial turbulence (EIT), characterized by an interplay between elastic and flow instabilities. Experiments and ... [more ▼] The elasticity of polymer solutions is found to generate a new state of turbulence, elasto-inertial turbulence (EIT), characterized by an interplay between elastic and flow instabilities. Experiments and direct numerical simulations (DNS) in pipe and channel flows demonstrate the emergence of EIT at Reynolds numbers much lower than the critical Reynolds number for transition to turbulence in Newtonian flows. EIT causes the friction factor to deviate from the laminar solution and subsequently transition to the maximum drag reduction asymptote around Re=1800. EIT is a self-sustained mechanism that arises from the interactions between fluctuations of extensional viscosity, velocity and pressure. The polymer solution elasticity controls the growth of flow instability, resulting in transitional-like flows at high Reynolds numbers. The existence of EIT is not limited to pipe, channel or boundary layer flows, and evidence of EIT will be discussed in other flows, including natural convection using DNS. [less ▲] Detailed reference viewed: 94 (9 ULg)Mechanics and characteristics of transition to turbulence in elasto-inertial turbulence Terrapon, Vincent ; ; Conference (2012, November 20) Numerical experiments of transition in elasto-inertial turbulent channel flows are used to highlight the mechanisms of transition and characterize the MDR regime. Specifically, the pressure kernel from ... [more ▼] Numerical experiments of transition in elasto-inertial turbulent channel flows are used to highlight the mechanisms of transition and characterize the MDR regime. Specifically, the pressure kernel from the generalized pressure Poisson equation is used to demonstrate the role of elastic instabilities in inducing and sustaining a turbulent-like flow. Additionally, dynamic mode decomposition is applied to statistically steady viscoelastic flows at different Reynolds number to identify the relative contributions of elastic and inertial instabilities. It is shown that elastic instabilities can be triggered through long-range interactions from disturbances in the free-stream, similarly to by-pass transition, and are then sufficient to self-sustain. When the Reynolds number is increased, the relative contribution of inertial instabilities becomes more important, and the flow demonstrates features that are characteristic to Newtonian turbulent flows (e.g., streaks, quasi-streamwise vortices), although at lower intensity. [less ▲] Detailed reference viewed: 45 (13 ULg)A Numerical Study of Fiber Glass Drawing Process Chouffart, Quentin ; Terrapon, Vincent Scientific conference (2012, October 19) The industrial glass fiber process is very sensitive to disturbances as they can lead to fibers break during the extrusion step. To identify and better characterize the relevant underlying physics and the ... [more ▼] The industrial glass fiber process is very sensitive to disturbances as they can lead to fibers break during the extrusion step. To identify and better characterize the relevant underlying physics and the possible causes of fiber break, the glass behavior from the die exit to the winder is investigated numerically. In a first step, simulations of the glass fiber extrusion process are performed where the fluid is considered Newtonian. The full Navier-Stokes equations including the energy equation for the temperature are solved with a finite-element method. The solution is then compared to previous results from the literature. In a second step, we conducted a sensitivity analysis of the key process variables, such as glass height above the tip, viscosity and flow rate at the tip exit, winder velocity... Additionally, the importance of an accurate physical representation of the heat transfers, i.e., conduction within the fiber, radiation of the fiber, and convection around the fiber, is investigated. This model shows very good agreement with cases from the literature. It was found that bushing temperature and fiber environment have a significant impact on forming fiber shape. This demonstrates that numerical simulations can provide a useful tool to adjust the process operating window. [less ▲] Detailed reference viewed: 157 (24 ULg)Using Proper Orthogonal Decomposition Methods for Comparing CFD Results to Experimental Measurements Andrianne, Thomas ; Guissart, Amandine ; Terrapon, Vincent et al in Proceedings of the 5th Symposium on Integrating CFD and Experiments in Aerodynamics (Integration 2012) (2012, October 03) This work presents a method for quantitative comparison of numerical results to experimental measurements. It is based on the concept of Proper Orthogonal Decomposition. This technique is selected in ... [more ▼] This work presents a method for quantitative comparison of numerical results to experimental measurements. It is based on the concept of Proper Orthogonal Decomposition. This technique is selected in order to compare the unsteady aerodynamic flows around static and oscillating bodies obtained from wind tunnel testing and numerical simulations. Two dimensional Time-resolved Particle Image Velocimetry measurements are carried out on the upper surface a 4:1 rectangular cylinder. Simulations are performed using unsteady Reynolds-Averaged Navier-Stokes and an unsteady Discrete Vortex Method. It is demonstrated that the proposed technique is a good preliminary step for comparing the main characteristics of unsteady aerodynamic data. [less ▲] Detailed reference viewed: 258 (47 ULg)Reynolds-Averaged Navier-Stokes Simulations of the HyShot II Scramjet ; Terrapon, Vincent ; et al in AIAA Journal (2012), 50(8), 1717-1732 The internal flow in the HyShot II scramjet is investigated through numerical simulations. A computational infrastructure to solve the compressible Reynolds-Averaged Navier-Stokes equations on ... [more ▼] The internal flow in the HyShot II scramjet is investigated through numerical simulations. A computational infrastructure to solve the compressible Reynolds-Averaged Navier-Stokes equations on unstructured meshes is introduced. A combustion model based on tabulated chemistry is considered to incorporate a detailed chemical kinetics mechanics while retaining a low computational cost. Both non-reactive and reactive simulations have been performed and results are compared with ground test measurements obtained at DLR. Different turbulence models were tested and the dependence on the mesh is assessed through grid refinement. The comparison with experimental data shows good agreement, although for the reactive case the computed heat fluxes at the wall are higher than measurements. A sensitivity analysis on the turbulent Schmidt and Prandtl numbers shows that the choice of these parameters has a strong influence on the results. In particular, variations of the turbulent Prandtl number lead to large changes in the heat flux at the walls. Finally, the inception of thermal choking is investigated by increasing the equivalence ratio, whereby a normal shock is created locally and moves upstream leading to a large increase in the maximum pressure. Nevertheless a large portion of the flow is still supersonic. [less ▲] Detailed reference viewed: 292 (10 ULg)Computational Fluid Mechanics for Civil Engineering Applications Terrapon, Vincent Scientific conference (2012, May 23) Detailed reference viewed: 35 (9 ULg)Analysis of transitional polymeric flows and elastic instabilities ; Terrapon, Vincent ; in Center for Turbulence Research, Proceedings of the Summer Program (2012) The dynamics of turbulence generated and controlled by polymer additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of ... [more ▼] The dynamics of turbulence generated and controlled by polymer additives is investigated from the perspective of the coupling between polymer dynamics and flow structures. Direct numerical simulations of channel flow with Reynolds numbers ranging from 1,000 to 10,000 (based on the bulk and the channel height) are used to study the formation and dynamics of elastic instabilities and their effects on the flow. The resulting mechanism of interactions between polymer dynamics and the flow helps resolve a long-standing controversy in the understanding of polymer drag reduction and explains the phenomenon of early turbulence, or onset of turbulence at lower Reynolds numbers than for Newtonian flows, previously observed in polymeric flows. [less ▲] Detailed reference viewed: 91 (14 ULg)A flamelet-based combustion model for high-speed flows! Terrapon, Vincent Scientific conference (2011, December 13) Detailed reference viewed: 17 (4 ULg)Towards a better understanding of polymer drag reduction in turbulent wall-bounded flows Terrapon, Vincent ; ; et al Scientific conference (2011, November 14) Detailed reference viewed: 45 (6 ULg)Polymer Maximum Drag Reduction: A Unique Transitional State ; ; et al E-print/Working paper (2011) The upper bound of polymer drag reduction is identified as a unique transitional state between laminar and turbulent flow corresponding to the onset of the nonlinear breakdown of flow instabilities. Detailed reference viewed: 20 (6 ULg)Radiation Modeling of a Hydrogen-Fueled Scramjet ; ; Terrapon, Vincent in 42nd AIAA Thermophysics Conference 2011, Vol. 3; No AIAA 2011-3769 (2011, June) With the difficulty and cost of full-scale flight experiments, the design of scramjet engines relies heavily on computational simulations. Radiation may play an important role in wall heating and flow ... [more ▼] With the difficulty and cost of full-scale flight experiments, the design of scramjet engines relies heavily on computational simulations. Radiation may play an important role in wall heating and flow cooling of scramjets. However, very few studies have focused on such. The present analysis is based on three-dimensional turbulent reacting flow simulations of the HyShot II hydrogen fueled scramjet engine running at flight conditions of Mach 7.4. A one-dimensional Discrete Ordinates Method analysis with a narrow band averaged spectral model is employed to determine wall heating and flow cooling from thermal radiation. The one-dimensional Discrete Ordinates Method is verifi ed against a three-dimensional ray tracing method. The radiative species considered are H2O and OH. The radiative heat flux is on the order of 10 kW/m2, which is 0.1-0.2% of the total convective wall heat flux. Flow cooling due to radiation is found to be on the order of 2 K. Sensitivity analysis shows that radiation is highly dependent on chamber size, temperature, pressure and radiative species mole fraction. Variations in these factors can explain the differences between previous analyses in the literature that studied hypothetical engines and the current work that models an existing scramjet. [less ▲] Detailed reference viewed: 47 (7 ULg)Balancing sources of errors and uncertainties - Application to failure mode analysis of scramjets Terrapon, Vincent Scientific conference (2011, May 14) Detailed reference viewed: 25 (2 ULg)Introduction to uncertainty analysis and uncertainty representations Terrapon, Vincent ; Scientific conference (2011, May 13) Detailed reference viewed: 28 (4 ULg)Full-system simulation of the HyShot II scramjet Terrapon, Vincent Scientific conference (2011, May) The renewed interest in high-speed flight has recently demonstrated the need for the development of hypersonic air-breathing propulsion systems, i.e., in which the ambient air is used as oxidizer. Because ... [more ▼] The renewed interest in high-speed flight has recently demonstrated the need for the development of hypersonic air-breathing propulsion systems, i.e., in which the ambient air is used as oxidizer. Because the internal flow in a scramjet is supersonic, it has a very short residence time during which air and fuel must mix on a molecular level, and chemical reactions have to be completed before leaving the engine. Moreover, the kinetic energy of the free stream of air entering the propulsion engine is of the same order of magnitude as the combustion heat re- lease. This results in a small net thrust compared to the aerodynamic drag. On the other hand, an excessive heat release can lead to the unstart phenomenon, i.e., the choking of the engine, that causes a sudden drop in thrust and large mechanical loads on the structure. Performance optimization requires thus maximizing thrust without crossing the unstart bound. To achieve predictive computations, the quantification of margins and uncertainties (QMU) with respect to this unstart bound is critical. Recent advances within the PSAAP program at Stanford University to develop computational tools to study the unstart phenomenon will be presented. In the first part, an overview of the program will be given. The second part will focus on the combustion model. Since heat release is at the heart of a scramjet operation and the main contributor to unstart, it is also the major source of uncertainties. A novel model for supersonic combustion based on a flamelet/progress variable approach has been developed. This approach allows the use of com- plex chemistry with only 2 or 3 additional scalar transport equations. The model is applied in a RANS computation of the hydrogen fueled HyShot II scramjet and simulation results are compared with experimental data. LES results for a jet in a supersonic crossflow will also be presented. [less ▲] Detailed reference viewed: 84 (10 ULg) |
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