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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Sun, 16 Jun 2024 06:35:03 GMT2024-06-16T06:35:03ZA high-order scheme for the numerical simulation of high-enthalpy hypersonic flows
http://hdl.handle.net/10985/23686
A high-order scheme for the numerical simulation of high-enthalpy hypersonic flows
PASSIATORE, Donatella; SCIACOVELLI, Luca; CINNELLA, Paola; PASCAZIO, Giuseppe
A high-order shock-capturing finite-difference scheme for scale-resolving numerical simulations of hypersonic high-enthalpy flows, involving thermal non-equilibrium effects, is presented. The suitability of the numerical strategy for such challenging configurations is assessed in terms of accuracy and robustness, with special focus on shock-capturing capabilities. The approach is demonstrated for a variety of thermochemical non-equilibrium configurations.
Fri, 01 Jul 2022 00:00:00 GMThttp://hdl.handle.net/10985/236862022-07-01T00:00:00ZPASSIATORE, DonatellaSCIACOVELLI, LucaCINNELLA, PaolaPASCAZIO, GiuseppeA high-order shock-capturing finite-difference scheme for scale-resolving numerical simulations of hypersonic high-enthalpy flows, involving thermal non-equilibrium effects, is presented. The suitability of the numerical strategy for such challenging configurations is assessed in terms of accuracy and robustness, with special focus on shock-capturing capabilities. The approach is demonstrated for a variety of thermochemical non-equilibrium configurations.Numerical investigation of hypersonic turbulent boundary layers with high-temperature effects
http://hdl.handle.net/10985/23685
Numerical investigation of hypersonic turbulent boundary layers with high-temperature effects
PASSIATORE, Donatella; SCIACOVELLI, Luca; CINNELLA, Paola; PASCAZIO, Giuseppe
A hypersonic turbulent boundary layer over a flat plate is numerically investigated. The large Mach number and temperature values in the freestream (M e = 12.48 and T e = 594.3 K, respectively) lead to a high-enthalpy regime and to the occurrence of thermochemical non-equilibrium effects. Vibrational relaxation phenomena are shown to be predominant with respect to chemical activity. In this context, high-fidelity results obtained by means of a Direct Numerical Simulation (DNS) are used as a benchmark to assess the quality of a Large-Eddy Simulation (LES) performed with a coarser wall-resolved grid. The wall-adapting local eddy viscosity approach is selected as sub-grid scale (SGS) model. The LES strategy is shown to capture the mean and fluctuating dynamic fields in the fully turbulent region quite satisfactorily, whereas transition to turbulence is slightly anticipated with respect to DNS. Both the chemical and vibrational source terms are evaluated with the filtered aerothermochemical quantities, resulting in an overestimation of the translational-vibrational energy exchange and an underestimation of dissociation chemical production rates. These results shed light on the necessity of developing more accurate closure models for the source terms, the SGS turbulence-thermochemistry interactions being important for the configuration under investigation.
Tue, 01 Nov 2022 00:00:00 GMThttp://hdl.handle.net/10985/236852022-11-01T00:00:00ZPASSIATORE, DonatellaSCIACOVELLI, LucaCINNELLA, PaolaPASCAZIO, GiuseppeA hypersonic turbulent boundary layer over a flat plate is numerically investigated. The large Mach number and temperature values in the freestream (M e = 12.48 and T e = 594.3 K, respectively) lead to a high-enthalpy regime and to the occurrence of thermochemical non-equilibrium effects. Vibrational relaxation phenomena are shown to be predominant with respect to chemical activity. In this context, high-fidelity results obtained by means of a Direct Numerical Simulation (DNS) are used as a benchmark to assess the quality of a Large-Eddy Simulation (LES) performed with a coarser wall-resolved grid. The wall-adapting local eddy viscosity approach is selected as sub-grid scale (SGS) model. The LES strategy is shown to capture the mean and fluctuating dynamic fields in the fully turbulent region quite satisfactorily, whereas transition to turbulence is slightly anticipated with respect to DNS. Both the chemical and vibrational source terms are evaluated with the filtered aerothermochemical quantities, resulting in an overestimation of the translational-vibrational energy exchange and an underestimation of dissociation chemical production rates. These results shed light on the necessity of developing more accurate closure models for the source terms, the SGS turbulence-thermochemistry interactions being important for the configuration under investigation.A priori tests of turbulence models for compressible flows
http://hdl.handle.net/10985/23684
A priori tests of turbulence models for compressible flows
CANNICI, Aron; PASSIATORE, Donatella; SCIACOVELLI, Luca; CINNELLA, Paola
The present work reports the results of a priori tests of Reynolds-Averaged Navier–Stokes (RANS) models based on Direct Numerical Simulations (DNS) data of zero-pressure-gradient flat-plate turbulent boundary layers. The DNS database covers a wide range of thermodynamic operating flow conditions, from supersonic (M∞ = 2.25) up to the high-enthalpy hypersonic regime (M ∞ = 12.48). The most common RANS closures and compressibility corrections in literature are assessed against the exact terms from the DNS. Particular attention has been paid to closure models for the turbulent heat fluxes and the dilatational dissipation, as well as to the analysis of turbulence/chemistry and turbulence/vibrational relaxation interactions for the high-enthalpy simulations.
Wed, 01 Mar 2023 00:00:00 GMThttp://hdl.handle.net/10985/236842023-03-01T00:00:00ZCANNICI, AronPASSIATORE, DonatellaSCIACOVELLI, LucaCINNELLA, PaolaThe present work reports the results of a priori tests of Reynolds-Averaged Navier–Stokes (RANS) models based on Direct Numerical Simulations (DNS) data of zero-pressure-gradient flat-plate turbulent boundary layers. The DNS database covers a wide range of thermodynamic operating flow conditions, from supersonic (M∞ = 2.25) up to the high-enthalpy hypersonic regime (M ∞ = 12.48). The most common RANS closures and compressibility corrections in literature are assessed against the exact terms from the DNS. Particular attention has been paid to closure models for the turbulent heat fluxes and the dilatational dissipation, as well as to the analysis of turbulence/chemistry and turbulence/vibrational relaxation interactions for the high-enthalpy simulations.Direct Numerical Simulation of a hypersonic boundary layer in chemical non-equilibrium
http://hdl.handle.net/10985/23688
Direct Numerical Simulation of a hypersonic boundary layer in chemical non-equilibrium
PASSIATORE, Donatella; SCIACOVELLI, Luca; CINNELLA, Paola; PASCAZIO, Giuseppe
The influence of high-enthalpy effects in hypersonic, spatially developing boundary layers is investigated by means of direct numerical simulations. The flow of a reacting mixture of nitrogen and oxygen over a flat plate at Mach 10, previously investigated in the literature using linear stability theory (LST), is simulated using a compu-tational domain encompassing the laminar, transitional and turbulent regimes. Transition is triggered by forcing Mack’s second mode through suction and blowing at the wall. In the laminar region, the solution matches reasonably well the locally self-similar profiles, computed under chemical non-equilibrium assumptions. Strong dissociation phenomena are observed, due to the high temperatures reached close to the (uncooled) plate surface. The transitional regime is investigated by means of modal analysis. Despite the significant chemical activity, the results confirm the classical transition scenario for high-Mach number boundary layers, for which the second-mode resonance is the main mechanism responsible for turbulent breakdown. In the turbulent region, first- and second-order statistics reveal that chemical reactions do not modify significantly dynamic quantities such as velocity and Reynolds stress profiles, but greatly affect thermal properties, due to their endothermic nature. For the configuration at hand, chemical dissociation is slower than the characteristic time-scale of the flow, and the peak of chemical activity is located in the viscous sublayer, leading to mild modifications of the turbulent field compared to a frozen-chemistry model.
Thu, 01 Apr 2021 00:00:00 GMThttp://hdl.handle.net/10985/236882021-04-01T00:00:00ZPASSIATORE, DonatellaSCIACOVELLI, LucaCINNELLA, PaolaPASCAZIO, GiuseppeThe influence of high-enthalpy effects in hypersonic, spatially developing boundary layers is investigated by means of direct numerical simulations. The flow of a reacting mixture of nitrogen and oxygen over a flat plate at Mach 10, previously investigated in the literature using linear stability theory (LST), is simulated using a compu-tational domain encompassing the laminar, transitional and turbulent regimes. Transition is triggered by forcing Mack’s second mode through suction and blowing at the wall. In the laminar region, the solution matches reasonably well the locally self-similar profiles, computed under chemical non-equilibrium assumptions. Strong dissociation phenomena are observed, due to the high temperatures reached close to the (uncooled) plate surface. The transitional regime is investigated by means of modal analysis. Despite the significant chemical activity, the results confirm the classical transition scenario for high-Mach number boundary layers, for which the second-mode resonance is the main mechanism responsible for turbulent breakdown. In the turbulent region, first- and second-order statistics reveal that chemical reactions do not modify significantly dynamic quantities such as velocity and Reynolds stress profiles, but greatly affect thermal properties, due to their endothermic nature. For the configuration at hand, chemical dissociation is slower than the characteristic time-scale of the flow, and the peak of chemical activity is located in the viscous sublayer, leading to mild modifications of the turbulent field compared to a frozen-chemistry model.Shock-wave/boundary layer interaction at high enthalpies
http://hdl.handle.net/10985/23683
Shock-wave/boundary layer interaction at high enthalpies
PASSIATORE, Donatella; SCIACOVELLI, Luca; CINNELLA, Paola; PASCAZIO, Giuseppe
The dynamics of a shock wave impinging on a freestream-perturbed high-enthalpy boundary layer is investigated by means of direct numerical simulation. The oblique shock impacts on a cooled flat-plate boundary layer with an angle of 10 degrees,
generating a reversal flow region. The combination of the freestream disturbances and the shock impingement is such that a transition to a fully turbulent regime occurs downstream of the interaction region. The analysis aims at qualifying and quantifying the role of thermochemical non-equilibrium conditions on the dynamics of the shock-wave/boundary-layer interaction.
Wed, 29 Mar 2023 00:00:00 GMThttp://hdl.handle.net/10985/236832023-03-29T00:00:00ZPASSIATORE, DonatellaSCIACOVELLI, LucaCINNELLA, PaolaPASCAZIO, GiuseppeThe dynamics of a shock wave impinging on a freestream-perturbed high-enthalpy boundary layer is investigated by means of direct numerical simulation. The oblique shock impacts on a cooled flat-plate boundary layer with an angle of 10 degrees,
generating a reversal flow region. The combination of the freestream disturbances and the shock impingement is such that a transition to a fully turbulent regime occurs downstream of the interaction region. The analysis aims at qualifying and quantifying the role of thermochemical non-equilibrium conditions on the dynamics of the shock-wave/boundary-layer interaction.DNS of turbulent flows of dense gases
http://hdl.handle.net/10985/23742
DNS of turbulent flows of dense gases
SCIACOVELLI, Luca; CINNELLA, Paola; GLOERFELT, Xavier; GRASSO, Francesco
The influence of dense gas effects on compressible turbulence is investigated by means of numerical simulations of the decay of compressible homogeneous isotropic turbulence (CHIT) and of supersonic turbulent flows through a plane channel (TCF). For both configurations, a parametric study on the Mach and Reynolds numbers is carried out. The dense gas considered in these parametric studies is PP11, a heavy fluorocarbon. The results are systematically compared to those obtained for a diatomic perfect gas (air). In our computations, the thermodynamic behaviour of the dense gases is modelled by means of the Martin-Hou equation of state. For CHIT cases, initial turbulent Mach numbers up to 1 are analyzed using mesh resolutions up to 5123. For TCF, bulk Mach numbers up to 3 and bulk Reynolds numbers up to 12000 are investigated. Average profiles of the thermodynamic quantities exhibit significant differences with respect to perfect-gas solutions for both of the configurations. For high-Mach CHIT, compressible structures are modified with respect to air, with weaker eddy shocklets and stronger expansions. In TCF, the velocity profiles of dense gas flows are much less sensitive to the Mach number and collapse reasonably well in the logarithmic region without any special need for compressible scalings, unlike the case of air, and the overall flow behaviour is midway between that of a variable-property liquid and that of a gas.
Sat, 01 Apr 2017 00:00:00 GMThttp://hdl.handle.net/10985/237422017-04-01T00:00:00ZSCIACOVELLI, LucaCINNELLA, PaolaGLOERFELT, XavierGRASSO, FrancescoThe influence of dense gas effects on compressible turbulence is investigated by means of numerical simulations of the decay of compressible homogeneous isotropic turbulence (CHIT) and of supersonic turbulent flows through a plane channel (TCF). For both configurations, a parametric study on the Mach and Reynolds numbers is carried out. The dense gas considered in these parametric studies is PP11, a heavy fluorocarbon. The results are systematically compared to those obtained for a diatomic perfect gas (air). In our computations, the thermodynamic behaviour of the dense gases is modelled by means of the Martin-Hou equation of state. For CHIT cases, initial turbulent Mach numbers up to 1 are analyzed using mesh resolutions up to 5123. For TCF, bulk Mach numbers up to 3 and bulk Reynolds numbers up to 12000 are investigated. Average profiles of the thermodynamic quantities exhibit significant differences with respect to perfect-gas solutions for both of the configurations. For high-Mach CHIT, compressible structures are modified with respect to air, with weaker eddy shocklets and stronger expansions. In TCF, the velocity profiles of dense gas flows are much less sensitive to the Mach number and collapse reasonably well in the logarithmic region without any special need for compressible scalings, unlike the case of air, and the overall flow behaviour is midway between that of a variable-property liquid and that of a gas.Numerical Investigation of Supersonic Dense-Gas Boundary Layers
http://hdl.handle.net/10985/23702
Numerical Investigation of Supersonic Dense-Gas Boundary Layers
SCIACOVELLI, Luca; PASSIATORE, Donatella; GLOERFELT, Xavier; CINNELLA, Paola; GRASSO, Francesco
A study of dense-gas effects on the laminar, transitional and turbulent characteristics of boundary layer flows is conducted. The laminar similarity solution shows that temperature variations are small due to the high specific heats of dense gases, leading to velocity profiles close to the incompressible ones. Nevertheless, the complex thermodynamics of the base flow has a major impact on unstable modes, which bear similarities with those obtained for a strongly cooled wall. Numerical simulations of spatially developing boundary layers yield turbulent statistics for the dense gas flow that remain closer to the incompressible regime than perfect gas ones despite the presence of strongly compressible structures.
Wed, 01 Jul 2020 00:00:00 GMThttp://hdl.handle.net/10985/237022020-07-01T00:00:00ZSCIACOVELLI, LucaPASSIATORE, DonatellaGLOERFELT, XavierCINNELLA, PaolaGRASSO, FrancescoA study of dense-gas effects on the laminar, transitional and turbulent characteristics of boundary layer flows is conducted. The laminar similarity solution shows that temperature variations are small due to the high specific heats of dense gases, leading to velocity profiles close to the incompressible ones. Nevertheless, the complex thermodynamics of the base flow has a major impact on unstable modes, which bear similarities with those obtained for a strongly cooled wall. Numerical simulations of spatially developing boundary layers yield turbulent statistics for the dense gas flow that remain closer to the incompressible regime than perfect gas ones despite the presence of strongly compressible structures.Analysis of Dense Gas Effects in Compressible Turbulent Channel Flows
http://hdl.handle.net/10985/23741
Analysis of Dense Gas Effects in Compressible Turbulent Channel Flows
SCIACOVELLI, Luca; CINNELLA, Paola; GLOERFELT, Xavier
In this work we investigate the influence of dense gas effects on compressible wall-bounded turbulence. Turbulent flows of dense gases represent a research field of great importance for a wide range of applications in engineering. Dense gases are single-phase fluids with a molecular complexity such that the fundamental derivative of gas dynamics [1], which measures the rate of change of the sound speed in isentropic transformations, is less than one in a range of thermodynamic conditions close to the saturation curve. In such conditions, the speed of sound increases in isentropic expansions and decreases in isentropic compressions, unlike the case of perfect gases. For dense gases, the perfect gas model is no longer valid, and more complex equations of state must be used to account for their peculiar thermodynamic behavior. Moreover, in the dense gas regime, the dynamic viscosity μ and the thermal conductivity λ depend on temperature and pressure through complex relationships. Similarly, the approximation of nearly constant Prandtl number Pr= μ c p / λ is no longer valid. Numerical simulations of turbulent dense gas flows of engineering interest are based on the (Reynolds-Averaged Navier–Stokes) RANS equations, which need to be supplemented by a model for the Reynolds stress tensor and turbulent heat flux. The accuracy of RANS models for dense-gas flows has not been properly assessed up to date, due to the lack of both experimental and numerical reference data. DNS databases [2, 3] are then needed to quantify the deficiencies of existing turbulence models and to develop and calibrate improved ones. In this work we first summarize some recent direct numerical simulation (DNS) results [4] for supersonic turbulent channel flows (TCF) of PP11, a heavy fluorocarbon representative of dense gases, at various bulk Mach and Reynolds numbers. The most relevant effects are represented by non-conventional variations of the fluctuating thermodynamic quantities, compared to perfect gases and a strong decoupling between thermal and dynamic effects almost everywhere in the flow, except in the immediate vicinity of the solid wall. Preliminary considerations about the validity of some currently-used models for the turbulent stresses and heat flux are carried out based on a priori comparisons between the exact terms computed from the DNS and their modeled counterparts.
Sat, 02 Feb 2019 00:00:00 GMThttp://hdl.handle.net/10985/237412019-02-02T00:00:00ZSCIACOVELLI, LucaCINNELLA, PaolaGLOERFELT, XavierIn this work we investigate the influence of dense gas effects on compressible wall-bounded turbulence. Turbulent flows of dense gases represent a research field of great importance for a wide range of applications in engineering. Dense gases are single-phase fluids with a molecular complexity such that the fundamental derivative of gas dynamics [1], which measures the rate of change of the sound speed in isentropic transformations, is less than one in a range of thermodynamic conditions close to the saturation curve. In such conditions, the speed of sound increases in isentropic expansions and decreases in isentropic compressions, unlike the case of perfect gases. For dense gases, the perfect gas model is no longer valid, and more complex equations of state must be used to account for their peculiar thermodynamic behavior. Moreover, in the dense gas regime, the dynamic viscosity μ and the thermal conductivity λ depend on temperature and pressure through complex relationships. Similarly, the approximation of nearly constant Prandtl number Pr= μ c p / λ is no longer valid. Numerical simulations of turbulent dense gas flows of engineering interest are based on the (Reynolds-Averaged Navier–Stokes) RANS equations, which need to be supplemented by a model for the Reynolds stress tensor and turbulent heat flux. The accuracy of RANS models for dense-gas flows has not been properly assessed up to date, due to the lack of both experimental and numerical reference data. DNS databases [2, 3] are then needed to quantify the deficiencies of existing turbulence models and to develop and calibrate improved ones. In this work we first summarize some recent direct numerical simulation (DNS) results [4] for supersonic turbulent channel flows (TCF) of PP11, a heavy fluorocarbon representative of dense gases, at various bulk Mach and Reynolds numbers. The most relevant effects are represented by non-conventional variations of the fluctuating thermodynamic quantities, compared to perfect gases and a strong decoupling between thermal and dynamic effects almost everywhere in the flow, except in the immediate vicinity of the solid wall. Preliminary considerations about the validity of some currently-used models for the turbulent stresses and heat flux are carried out based on a priori comparisons between the exact terms computed from the DNS and their modeled counterparts.Numerical Investigation of Hypersonic Boundary Layers of Perfect and Dense Gases
http://hdl.handle.net/10985/23691
Numerical Investigation of Hypersonic Boundary Layers of Perfect and Dense Gases
SCIACOVELLI, Luca; GLOERFELT, Xavier; CINNELLA, Paola; GRASSO, Francesco
Hypersonic turbulent boundary layers (HTBL) at Mach number M =6 of a dense gas (PP11) and a perfect gas (air) are investigated by means of Direct Numerical Simulations (DNS), from the laminar to fully turbulent state. The operating conditions are chosen in such a way to highlight dense gas effects, which profoundly alter the transition mechanisms and affect the turbulent flow properties significantly.
Fri, 01 May 2020 00:00:00 GMThttp://hdl.handle.net/10985/236912020-05-01T00:00:00ZSCIACOVELLI, LucaGLOERFELT, XavierCINNELLA, PaolaGRASSO, FrancescoHypersonic turbulent boundary layers (HTBL) at Mach number M =6 of a dense gas (PP11) and a perfect gas (air) are investigated by means of Direct Numerical Simulations (DNS), from the laminar to fully turbulent state. The operating conditions are chosen in such a way to highlight dense gas effects, which profoundly alter the transition mechanisms and affect the turbulent flow properties significantly.Direct Numerical Simulation of hypersonic boundary layers in chemical non-equilibrium
http://hdl.handle.net/10985/23687
Direct Numerical Simulation of hypersonic boundary layers in chemical non-equilibrium
PASSIATORE, Donatella; SCIACOVELLI, Luca; PASCAZIO, Giuseppe; CINNELLA, Paola
The influence of high-temperature effects on compressible wall-bounded turbulence is investigated by means of a direct numerical simulation of a hypersonic, chemically out-of-equilibrium, turbulent boundary layer. The analysis aims at assessing the effects of chemical reactions on turbulence, also by comparing the results with those of a frozen flow. We will present a detailed analysis of the turbulent statistics and near-wall dynamics; the validity of some classical scalings and Reynolds analogy will also be discussed.
Sun, 01 Aug 2021 00:00:00 GMThttp://hdl.handle.net/10985/236872021-08-01T00:00:00ZPASSIATORE, DonatellaSCIACOVELLI, LucaPASCAZIO, GiuseppeCINNELLA, PaolaThe influence of high-temperature effects on compressible wall-bounded turbulence is investigated by means of a direct numerical simulation of a hypersonic, chemically out-of-equilibrium, turbulent boundary layer. The analysis aims at assessing the effects of chemical reactions on turbulence, also by comparing the results with those of a frozen flow. We will present a detailed analysis of the turbulent statistics and near-wall dynamics; the validity of some classical scalings and Reynolds analogy will also be discussed.