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The DSpace digital repository system captures, stores, indexes, preserves, and distributes digital research material.Wed, 24 Apr 2024 18:40:23 GMT2024-04-24T18:40:23ZA 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.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.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.Assessment of a high-order shock-capturing central-difference scheme for hypersonic turbulent flow simulations
http://hdl.handle.net/10985/21897
Assessment of a high-order shock-capturing central-difference scheme for hypersonic turbulent flow simulations
PASSIATORE, Donatella; CINELLA, Paola; GIUSEPPE, Pascazio; SCIACOVELLI, Luca
High-speed turbulent flows are encountered in most space-related applications (including exploration, tourism and defense fields) and represent a subject of growing interest in the last decades. A major challenge in performing high-fidelity simulations of such flows resides in the stringent requirements for the numerical schemes to be used. These must be robust enough to handle strong, unsteady discontinuities, while ensuring low amounts of intrinsic dissipation in smooth flow regions. Furthermore, the wide range of temporal and spatial active scales leads to concurrent needs for numerical stabilization and accurate representation of the smallest resolved flow scales in cases of under-resolved configurations. In this paper, we present a finite-difference high-order shock-capturing technique based on Jameson’s artificial diffusivity methodology. The resulting scheme is ninth-order-accurate far from discontinuities and relies on the addition of artificial dissipation close to large gradient flow regions. The shock detector is slightly revised to enhance its selectivity and avoid spurious activations of the shock-capturing term. A suite of test cases ranging from 1D to 3D configurations (namely, perfect-gas and chemically reacting shock tubes, Shu–Osher problem, isentropic vortex advection, under-expanded jet, compressible Taylor–Green Vortex, supersonic and hypersonic turbulent boundary layers)
is analyzed in order to test the capability of the proposed numerical strategy to handle a large variety of problems, ranging from calorically-perfect air to multi-species reactive flows. Results obtained on underresolved grids are also considered to test the applicability of the proposed strategy in the context of implicit Large-Eddy Simulations.
Mon, 01 Nov 2021 00:00:00 GMThttp://hdl.handle.net/10985/218972021-11-01T00:00:00ZPASSIATORE, DonatellaCINELLA, PaolaGIUSEPPE, PascazioSCIACOVELLI, LucaHigh-speed turbulent flows are encountered in most space-related applications (including exploration, tourism and defense fields) and represent a subject of growing interest in the last decades. A major challenge in performing high-fidelity simulations of such flows resides in the stringent requirements for the numerical schemes to be used. These must be robust enough to handle strong, unsteady discontinuities, while ensuring low amounts of intrinsic dissipation in smooth flow regions. Furthermore, the wide range of temporal and spatial active scales leads to concurrent needs for numerical stabilization and accurate representation of the smallest resolved flow scales in cases of under-resolved configurations. In this paper, we present a finite-difference high-order shock-capturing technique based on Jameson’s artificial diffusivity methodology. The resulting scheme is ninth-order-accurate far from discontinuities and relies on the addition of artificial dissipation close to large gradient flow regions. The shock detector is slightly revised to enhance its selectivity and avoid spurious activations of the shock-capturing term. A suite of test cases ranging from 1D to 3D configurations (namely, perfect-gas and chemically reacting shock tubes, Shu–Osher problem, isentropic vortex advection, under-expanded jet, compressible Taylor–Green Vortex, supersonic and hypersonic turbulent boundary layers)
is analyzed in order to test the capability of the proposed numerical strategy to handle a large variety of problems, ranging from calorically-perfect air to multi-species reactive flows. Results obtained on underresolved grids are also considered to test the applicability of the proposed strategy in the context of implicit Large-Eddy Simulations.Thermochemical non-equilibrium effects in turbulent hypersonic boundary layers
http://hdl.handle.net/10985/21900
Thermochemical non-equilibrium effects in turbulent hypersonic boundary layers
PASSIATORE, Donatella; CINNELLA, Paola; GIUSEPPE, Pascazio; SCIACOVELLI, Luca
A hypersonic, spatially evolving turbulent boundary layer at Mach 12.48 with a cooled wall is analysed by means of direct numerical simulations. At the selected conditions, massive kinetic-to-internal energy conversion triggers thermal and chemical non-equilibrium phenomena. Air is assumed to behave as a five-species reacting mixture, and a two-temperaturemodel is adopted to account for vibrational non-equilibrium.Wall cooling partly counteracts the effects of friction heating, and the temperature rise in the boundary layer excites vibrational energy modes while inducing mild chemical dissociation of oxygen. Vibrational non-equilibrium is mostly driven by molecular nitrogen, characterized by slower relaxation rates than the other molecules in the mixture. The results reveal that thermal non-equilibrium is sustained by turbulent mixing: sweep and ejection events efficiently redistribute the gas, contributing to the generation of a vibrationally under-excited state close to the wall, and an over-excited state in the outer region of the boundary layer. The tight coupling between turbulence and thermal effects is quantified by defining an interaction indicator. A modelling strategy for the vibrational energy turbulent
flux is proposed, based on the definition of a vibrational turbulent Prandtl number. The validity of the strong Reynolds analogy under thermal non-equilibrium is also evaluated.
Strong compressibility effects promote the translational–vibrational energy exchange, but no preferential correlation was detected between expansions/compressions and vibrational over-/under-excitation, as opposed to what has been observed for unconfined turbulent configurations.
Thu, 28 Apr 2022 00:00:00 GMThttp://hdl.handle.net/10985/219002022-04-28T00:00:00ZPASSIATORE, DonatellaCINNELLA, PaolaGIUSEPPE, PascazioSCIACOVELLI, LucaA hypersonic, spatially evolving turbulent boundary layer at Mach 12.48 with a cooled wall is analysed by means of direct numerical simulations. At the selected conditions, massive kinetic-to-internal energy conversion triggers thermal and chemical non-equilibrium phenomena. Air is assumed to behave as a five-species reacting mixture, and a two-temperaturemodel is adopted to account for vibrational non-equilibrium.Wall cooling partly counteracts the effects of friction heating, and the temperature rise in the boundary layer excites vibrational energy modes while inducing mild chemical dissociation of oxygen. Vibrational non-equilibrium is mostly driven by molecular nitrogen, characterized by slower relaxation rates than the other molecules in the mixture. The results reveal that thermal non-equilibrium is sustained by turbulent mixing: sweep and ejection events efficiently redistribute the gas, contributing to the generation of a vibrationally under-excited state close to the wall, and an over-excited state in the outer region of the boundary layer. The tight coupling between turbulence and thermal effects is quantified by defining an interaction indicator. A modelling strategy for the vibrational energy turbulent
flux is proposed, based on the definition of a vibrational turbulent Prandtl number. The validity of the strong Reynolds analogy under thermal non-equilibrium is also evaluated.
Strong compressibility effects promote the translational–vibrational energy exchange, but no preferential correlation was detected between expansions/compressions and vibrational over-/under-excitation, as opposed to what has been observed for unconfined turbulent configurations.Finite-rate chemistry effects in turbulent hypersonic boundary layers: A direct numerical simulation study
http://hdl.handle.net/10985/21899
Finite-rate chemistry effects in turbulent hypersonic boundary layers: A direct numerical simulation study
PASSIATORE, Donatella; CINELLA, Paola; GIUSEPPE, Pascazio; SCIACOVELLI, Luca
The influence of high-enthalpy effects on hypersonic turbulent boundary layers is investigated by means of direct numerical simulations (DNS). A quasiadiabatic flat-plate air flow at free-stream Mach number equal to 10 is simulated up to fully developed
turbulent conditions using a five-species, chemically reacting model. A companion DNS based on a frozen-chemistry assumption is also carried out, in order to isolate the effect of finite-rate chemical reactions and assess their influence on turbulent quantities. In order to reduce uncertainties associated with turbulence generation at the inlet of the computational domain, both simulations are initiated in the laminar flow region and the flow is let to evolve up to the fully turbulent regime. Modal forcing by means of localized suction and blowing is used to trigger laminar-to-turbulent transition. The high temperatures reached in the near-wall region including the viscous and buffer sublayers activate significant dissociation of both oxygen and nitrogen. This modifies in turn the thermodynamic and transport properties of the reacting mixture, affecting the first-order statistics of thermodynamic
quantities. Due to the endothermic nature of the chemical reactions in the forward direction, temperature and density fluctuations in the reacting layer are smaller than in the frozen-chemistry flow. However, the first- and second-order statistics of the velocity field are found to be little affected by the chemical reactions under a scaling that accounts for the modified fluid properties. We also observed that the Strong Reynolds Analogy remains well respected despite the severe hypersonic conditions and that the computed skin friction coefficient distributions match well the results of the Renard-Deck decomposition extended to compressible flows.
Sat, 01 May 2021 00:00:00 GMThttp://hdl.handle.net/10985/218992021-05-01T00:00:00ZPASSIATORE, DonatellaCINELLA, PaolaGIUSEPPE, PascazioSCIACOVELLI, LucaThe influence of high-enthalpy effects on hypersonic turbulent boundary layers is investigated by means of direct numerical simulations (DNS). A quasiadiabatic flat-plate air flow at free-stream Mach number equal to 10 is simulated up to fully developed
turbulent conditions using a five-species, chemically reacting model. A companion DNS based on a frozen-chemistry assumption is also carried out, in order to isolate the effect of finite-rate chemical reactions and assess their influence on turbulent quantities. In order to reduce uncertainties associated with turbulence generation at the inlet of the computational domain, both simulations are initiated in the laminar flow region and the flow is let to evolve up to the fully turbulent regime. Modal forcing by means of localized suction and blowing is used to trigger laminar-to-turbulent transition. The high temperatures reached in the near-wall region including the viscous and buffer sublayers activate significant dissociation of both oxygen and nitrogen. This modifies in turn the thermodynamic and transport properties of the reacting mixture, affecting the first-order statistics of thermodynamic
quantities. Due to the endothermic nature of the chemical reactions in the forward direction, temperature and density fluctuations in the reacting layer are smaller than in the frozen-chemistry flow. However, the first- and second-order statistics of the velocity field are found to be little affected by the chemical reactions under a scaling that accounts for the modified fluid properties. We also observed that the Strong Reynolds Analogy remains well respected despite the severe hypersonic conditions and that the computed skin friction coefficient distributions match well the results of the Renard-Deck decomposition extended to compressible flows.