The accurate prediction of helicopter rotor aerodynamics and aeroacoustics using Computational Fl... more The accurate prediction of helicopter rotor aerodynamics and aeroacoustics using Computational Fluid Dynamics (CFD) techniques still remains a challenge, as the over-dissipation of numerical schemes results in a higher diffusive rate of rotor wake and vortices than what can be expected from the fluid governing equations. To alleviate this issue, a vortex feature-based vorticity confinement (FVC2-L2) method that combines the locally normalized λ2 vortex detection method with the standard second vorticity confinement (VC2) scheme is presented to counterbalance the truncation error introduced by the numerical discretization of the convective term while avoiding the over-confinement inside the boundary layer. The FVC2-L2 scheme is adopted for helicopter rotor aerodynamic and aeroacoustic predictions through its implementation in the multi-block structured grid CFD solver ROSITA and coupling with the aeroacoustic code ROCAAP based on the permeable surface Ffowcs Williams–Hawkings (PS-FWH...
An extension of the Roe linearization method to nonideal gases is described and applied to the pa... more An extension of the Roe linearization method to nonideal gases is described and applied to the particular case of the van der Waals gas. A supplementary relation connecting the thermodynamic variables is introduced to decouple the evaluation of the intermediate velocity and total specific enthalpy from the determination of the intermediate density, needed in the Jacobian matrix of the linearization due to the general thermodynamic character of the gas. The density value is obtained by solving the supplementary equation, which involves the Roe average of velocity and enthalpy, and that in the case of the polytropic van der Waals gas is a third-order algebraic equation. Numerical results are shown including classical and nonclassical behaviour in one-dimensional shock tube problems.
In order to improve the vortex resolution in aerodynamic wakes, a locally normalized vortex featu... more In order to improve the vortex resolution in aerodynamic wakes, a locally normalized vortex feature-based vorticity confinement method is implemented into the multi-block, structured computational fluid dynamics solver (ROSITA). In this method, the second vorticity confinement (VC2) scheme with two well-known vortex feature detection methods (non-dimensional Q criterion, non-dimensional $$\lambda _2$$ λ 2 criterion) is employed to counterbalance the truncation error introduced by the numerical discretization of the convective term. The flow field of two benchmark three-dimensional steady vortex-dominated cases, the NACA0015 wing and the Caradonna–Tung hovering rotor, is simulated with the implemented method. The improvements in aerodynamics prediction, vorticity preservation, computational stability, and efficiency are demonstrated. From the numerical results, the vortex feature-based confinement models significantly improve the computational stability, the aerodynamic loads predict...
ABSTRACT The accuracy of thermodynamic models in the computation of nonclassical gasdynamic pheno... more ABSTRACT The accuracy of thermodynamic models in the computation of nonclassical gasdynamic phenomena is discussed, to investigate their suitability in connection with the design of experimental apparatuses aimed at the observation of nonclassical wavefields. The Soave-Redlich-Kwong and the Peng-Robinson are preliminarily suggested as alternative thermodynamic models to the Martin-Hou usually considered in nonclassical gasdynamics of fluorinated substances. The validity of these models is assessed by comparisons to reference experimental data for fluorinated R13, R125, C318, FC-72, FC-75, and SF6 and to the Martin-Hou model itself. The three models are found to exhibit a comparable accuracy for reduced volumes ranging from 1.4 to 2.5 and near the critical isotherm, i.e., in the thermodynamic region where heavier fluorinated substances such as PP10 are expected to exhibit nonclassical gasdynamic phenomena. The Soave-Redlich-Kwong and the Peng-Robinson models are then used to supplement previous numerical results for a three-discontinuity nonclassical shock-tube experiment with fluid PP10, which was designed under the Martin-Hou model. Under the initial conditions chosen for the experiment, the three models agree in predicting the formation of a supersonic nonclassical rarefaction wave, with wave Mach number in the range 1.01-1.02, thus providing further confidence on the possibility of experimentally observing nonclassical gasdynamic behavior in fluid PP10.
ABSTRACT The accuracy of thermodynamic models in the computation of nonclassical gasdynamic pheno... more ABSTRACT The accuracy of thermodynamic models in the computation of nonclassical gasdynamic phenomena is discussed, to investigate their suitability in connection with the design of experimental apparatuses aimed at the observation of nonclassical wavefields. The Soave-Redlich-Kwong and the Peng-Robinson are preliminarily suggested as alternative thermodynamic models to the Martin-Hou usually considered in nonclassical gasdynamics of fluorinated substances. The validity of these models is assessed by comparisons to reference experimental data for fluorinated R13, R125, C318, FC-72, FC-75, and SF6 and to the Martin-Hou model itself. The three models are found to exhibit a comparable accuracy for reduced volumes ranging from 1.4 to 2.5 and near the critical isotherm, i.e., in the thermodynamic region where heavier fluorinated substances such as PP10 are expected to exhibit nonclassical gasdynamic phenomena. The Soave-Redlich-Kwong and the Peng-Robinson models are then used to supplement previous numerical results for a three-discontinuity nonclassical shock-tube experiment with fluid PP10, which was designed under the Martin-Hou model. Under the initial conditions chosen for the experiment, the three models agree in predicting the formation of a supersonic nonclassical rarefaction wave, with wave Mach number in the range 1.01-1.02, thus providing further confidence on the possibility of experimentally observing nonclassical gasdynamic behavior in fluid PP10.
The helicopter rotor flowfield is one of the most complex and challenging problems in theoretical... more The helicopter rotor flowfield is one of the most complex and challenging problems in theoretical aerodynamics. Its accurate analysis is essential for the design of rotors with increased performance, reduced vibratory loads and more environmentally friendly acoustic signatures. European rotorcraft manufacturers have an urgent requirement for a rotor aerodynamic prediction tool to be used within the design office on a routine basis and which is capable of capturing rotational phenomena, such as blade tip and wake vortices, and correctly predict the unsteady blade pressures over a range of different flight conditions. The EROS project addresses this requirement by developing a common European rotor aerodynamic system capable of analysing the inviscid rotor flow environment by solving the three-dimensional Euler equations. The method is based on a proven-technology time-accurate Euler formulation on overlapping structured grids (Chimera method). The grid generator provides an all-in-one capability for grid generation guiding the user from the generation of individual component grids to the Chimera domain decomposition through an interactive process which has embedded visualisation and animation capabilities. The cell-centered finite-volume solver adopts a dual-time implicit scheme on deforming grids. Non-conservative interpolation is used to transfer information across grid overlap regions. This article presents the main components of the system and reviews its capabilities through a number of applications.
A grid generator system for the modelling of complex multi-bladed rotors is under development in ... more A grid generator system for the modelling of complex multi-bladed rotors is under development in Europe as a part of the development of a complete rotorcraft simulation method:The Brite/EuRam EROS project. The grid generator [1] exploits a CHIMERA domain decomposition on structured grids. The development is being carried out by rotorcraft manufacturers (Agusta, ECD, GKN-Westland), research centres (CIRA, DERA, DLR, NLR, ONERA), and Universities (Polit. Milano, Univ. Bristol, Univ. Glasgow, Univ. Rome 3). It addresses the industrial need for a rotor aerodynamic prediction tool [2] able to capture rotational phenomena, such as blade tip and wake vortices, and to predict correctly the unsteady blade pressures over a range of flight conditions, from hover to high-speed forward flight. This paper presents and discusses the capabilities of the GEROS grid generator together with relevant results.
An experimental and theoretical activity has been carried out to investigate the influence of the... more An experimental and theoretical activity has been carried out to investigate the influence of the statistical description of temperature fluctuations on total NO emission predictions in a turbulent gas diffusion flame. A small cylindrical combustor has been simulated, using a commercial CFD code describing flow and combustion processes, integrated with a decoupled NO kinetics model that solves the transport equation of the average NO mass fraction. From the comparison of the computed results with in-flame measurements of temperature and species concentrations it can be concluded that modelling of the temperature variance transport equation is required to obtain correct NO predictions, and that results are sensitive to how the combustion contribution to the variance source term is handled.
ABSTRACT The present work discusses the implementation of a ki netic scheme based on the BGK mode... more ABSTRACT The present work discusses the implementation of a ki netic scheme based on the BGK model equation in the framework of a node-pair formulation for the conserva- tion laws to simulate compressible flows on unstructured hybrid meshes. A multidimensional second order scheme scheme is achieved by suitable modification to the original stencil of the node-pair approach. In the transitional regime, slip velocity condition at solid wall is automatically assured by the kinetic formulation of the node-pair boundary conditions. Flows at Knudsen number up to 0.01 have been considered for validation of the present approach.
The flow-structure interaction of a circular cylinder oscillating in the synchro-nization field a... more The flow-structure interaction of a circular cylinder oscillating in the synchro-nization field at 4 5 10 Re has been addressed both experimentally (unsteady pressures and oscillations measures) as well as by CFD simulations (2D DNS and k-RANS). DNS allowed simulation of the expected 2P vortex structures. The k-approach, although simulating the lock-in phenomenon, showed 2S vortex structures and quite lower unsteady lift C L values.
The class of entropy fixes originated by Harten and Hyman, as applied to Roe's linearization ... more The class of entropy fixes originated by Harten and Hyman, as applied to Roe's linearization of convex hyberbolic equations, is reformulated within a unified framework. By adopting a complementary viewpoint with respect to that of Harten, the entropy fix is recast in terms of expressions involving either the propagation speeds or the speed differences. The proposed formulation allows to analyze and compare several versions of this class of entropy fix and to elaborate some new variants thereof. In addition, this framework accommodates an interpretation of the HLL schemes which leads to the concept of a positivity preserving entropy fix and to a solution-dependent correction to Roe's scheme so as to assure positive solutions.
A grid generator system for the modelling of complex multi-bladed rotors is under development in ... more A grid generator system for the modelling of complex multi-bladed rotors is under development in Europe as a part of the development of a complete rotorcraft simulation method:The Brite/EuRam EROS project. The grid generator [1] exploits a CHIMERA domain decomposition on structured grids. The development is being carried out by rotorcraft manufacturers (Agusta, ECD, GKN-Westland), research centres (CIRA, DERA, DLR, NLR, ONERA), and Universities (Polit. Milano, Univ. Bristol, Univ. Glasgow, Univ. Rome 3). It addresses the industrial need for a rotor aerodynamic prediction tool [2] able to capture rotational phenomena, such as blade tip and wake vortices, and to predict correctly the unsteady blade pressures over a range of flight conditions, from hover to high-speed forward flight. This paper presents and discusses the capabilities of the GEROS grid generator together with relevant results.
The accurate prediction of helicopter rotor aerodynamics and aeroacoustics using Computational Fl... more The accurate prediction of helicopter rotor aerodynamics and aeroacoustics using Computational Fluid Dynamics (CFD) techniques still remains a challenge, as the over-dissipation of numerical schemes results in a higher diffusive rate of rotor wake and vortices than what can be expected from the fluid governing equations. To alleviate this issue, a vortex feature-based vorticity confinement (FVC2-L2) method that combines the locally normalized λ2 vortex detection method with the standard second vorticity confinement (VC2) scheme is presented to counterbalance the truncation error introduced by the numerical discretization of the convective term while avoiding the over-confinement inside the boundary layer. The FVC2-L2 scheme is adopted for helicopter rotor aerodynamic and aeroacoustic predictions through its implementation in the multi-block structured grid CFD solver ROSITA and coupling with the aeroacoustic code ROCAAP based on the permeable surface Ffowcs Williams–Hawkings (PS-FWH...
An extension of the Roe linearization method to nonideal gases is described and applied to the pa... more An extension of the Roe linearization method to nonideal gases is described and applied to the particular case of the van der Waals gas. A supplementary relation connecting the thermodynamic variables is introduced to decouple the evaluation of the intermediate velocity and total specific enthalpy from the determination of the intermediate density, needed in the Jacobian matrix of the linearization due to the general thermodynamic character of the gas. The density value is obtained by solving the supplementary equation, which involves the Roe average of velocity and enthalpy, and that in the case of the polytropic van der Waals gas is a third-order algebraic equation. Numerical results are shown including classical and nonclassical behaviour in one-dimensional shock tube problems.
In order to improve the vortex resolution in aerodynamic wakes, a locally normalized vortex featu... more In order to improve the vortex resolution in aerodynamic wakes, a locally normalized vortex feature-based vorticity confinement method is implemented into the multi-block, structured computational fluid dynamics solver (ROSITA). In this method, the second vorticity confinement (VC2) scheme with two well-known vortex feature detection methods (non-dimensional Q criterion, non-dimensional $$\lambda _2$$ λ 2 criterion) is employed to counterbalance the truncation error introduced by the numerical discretization of the convective term. The flow field of two benchmark three-dimensional steady vortex-dominated cases, the NACA0015 wing and the Caradonna–Tung hovering rotor, is simulated with the implemented method. The improvements in aerodynamics prediction, vorticity preservation, computational stability, and efficiency are demonstrated. From the numerical results, the vortex feature-based confinement models significantly improve the computational stability, the aerodynamic loads predict...
ABSTRACT The accuracy of thermodynamic models in the computation of nonclassical gasdynamic pheno... more ABSTRACT The accuracy of thermodynamic models in the computation of nonclassical gasdynamic phenomena is discussed, to investigate their suitability in connection with the design of experimental apparatuses aimed at the observation of nonclassical wavefields. The Soave-Redlich-Kwong and the Peng-Robinson are preliminarily suggested as alternative thermodynamic models to the Martin-Hou usually considered in nonclassical gasdynamics of fluorinated substances. The validity of these models is assessed by comparisons to reference experimental data for fluorinated R13, R125, C318, FC-72, FC-75, and SF6 and to the Martin-Hou model itself. The three models are found to exhibit a comparable accuracy for reduced volumes ranging from 1.4 to 2.5 and near the critical isotherm, i.e., in the thermodynamic region where heavier fluorinated substances such as PP10 are expected to exhibit nonclassical gasdynamic phenomena. The Soave-Redlich-Kwong and the Peng-Robinson models are then used to supplement previous numerical results for a three-discontinuity nonclassical shock-tube experiment with fluid PP10, which was designed under the Martin-Hou model. Under the initial conditions chosen for the experiment, the three models agree in predicting the formation of a supersonic nonclassical rarefaction wave, with wave Mach number in the range 1.01-1.02, thus providing further confidence on the possibility of experimentally observing nonclassical gasdynamic behavior in fluid PP10.
ABSTRACT The accuracy of thermodynamic models in the computation of nonclassical gasdynamic pheno... more ABSTRACT The accuracy of thermodynamic models in the computation of nonclassical gasdynamic phenomena is discussed, to investigate their suitability in connection with the design of experimental apparatuses aimed at the observation of nonclassical wavefields. The Soave-Redlich-Kwong and the Peng-Robinson are preliminarily suggested as alternative thermodynamic models to the Martin-Hou usually considered in nonclassical gasdynamics of fluorinated substances. The validity of these models is assessed by comparisons to reference experimental data for fluorinated R13, R125, C318, FC-72, FC-75, and SF6 and to the Martin-Hou model itself. The three models are found to exhibit a comparable accuracy for reduced volumes ranging from 1.4 to 2.5 and near the critical isotherm, i.e., in the thermodynamic region where heavier fluorinated substances such as PP10 are expected to exhibit nonclassical gasdynamic phenomena. The Soave-Redlich-Kwong and the Peng-Robinson models are then used to supplement previous numerical results for a three-discontinuity nonclassical shock-tube experiment with fluid PP10, which was designed under the Martin-Hou model. Under the initial conditions chosen for the experiment, the three models agree in predicting the formation of a supersonic nonclassical rarefaction wave, with wave Mach number in the range 1.01-1.02, thus providing further confidence on the possibility of experimentally observing nonclassical gasdynamic behavior in fluid PP10.
The helicopter rotor flowfield is one of the most complex and challenging problems in theoretical... more The helicopter rotor flowfield is one of the most complex and challenging problems in theoretical aerodynamics. Its accurate analysis is essential for the design of rotors with increased performance, reduced vibratory loads and more environmentally friendly acoustic signatures. European rotorcraft manufacturers have an urgent requirement for a rotor aerodynamic prediction tool to be used within the design office on a routine basis and which is capable of capturing rotational phenomena, such as blade tip and wake vortices, and correctly predict the unsteady blade pressures over a range of different flight conditions. The EROS project addresses this requirement by developing a common European rotor aerodynamic system capable of analysing the inviscid rotor flow environment by solving the three-dimensional Euler equations. The method is based on a proven-technology time-accurate Euler formulation on overlapping structured grids (Chimera method). The grid generator provides an all-in-one capability for grid generation guiding the user from the generation of individual component grids to the Chimera domain decomposition through an interactive process which has embedded visualisation and animation capabilities. The cell-centered finite-volume solver adopts a dual-time implicit scheme on deforming grids. Non-conservative interpolation is used to transfer information across grid overlap regions. This article presents the main components of the system and reviews its capabilities through a number of applications.
A grid generator system for the modelling of complex multi-bladed rotors is under development in ... more A grid generator system for the modelling of complex multi-bladed rotors is under development in Europe as a part of the development of a complete rotorcraft simulation method:The Brite/EuRam EROS project. The grid generator [1] exploits a CHIMERA domain decomposition on structured grids. The development is being carried out by rotorcraft manufacturers (Agusta, ECD, GKN-Westland), research centres (CIRA, DERA, DLR, NLR, ONERA), and Universities (Polit. Milano, Univ. Bristol, Univ. Glasgow, Univ. Rome 3). It addresses the industrial need for a rotor aerodynamic prediction tool [2] able to capture rotational phenomena, such as blade tip and wake vortices, and to predict correctly the unsteady blade pressures over a range of flight conditions, from hover to high-speed forward flight. This paper presents and discusses the capabilities of the GEROS grid generator together with relevant results.
An experimental and theoretical activity has been carried out to investigate the influence of the... more An experimental and theoretical activity has been carried out to investigate the influence of the statistical description of temperature fluctuations on total NO emission predictions in a turbulent gas diffusion flame. A small cylindrical combustor has been simulated, using a commercial CFD code describing flow and combustion processes, integrated with a decoupled NO kinetics model that solves the transport equation of the average NO mass fraction. From the comparison of the computed results with in-flame measurements of temperature and species concentrations it can be concluded that modelling of the temperature variance transport equation is required to obtain correct NO predictions, and that results are sensitive to how the combustion contribution to the variance source term is handled.
ABSTRACT The present work discusses the implementation of a ki netic scheme based on the BGK mode... more ABSTRACT The present work discusses the implementation of a ki netic scheme based on the BGK model equation in the framework of a node-pair formulation for the conserva- tion laws to simulate compressible flows on unstructured hybrid meshes. A multidimensional second order scheme scheme is achieved by suitable modification to the original stencil of the node-pair approach. In the transitional regime, slip velocity condition at solid wall is automatically assured by the kinetic formulation of the node-pair boundary conditions. Flows at Knudsen number up to 0.01 have been considered for validation of the present approach.
The flow-structure interaction of a circular cylinder oscillating in the synchro-nization field a... more The flow-structure interaction of a circular cylinder oscillating in the synchro-nization field at 4 5 10 Re has been addressed both experimentally (unsteady pressures and oscillations measures) as well as by CFD simulations (2D DNS and k-RANS). DNS allowed simulation of the expected 2P vortex structures. The k-approach, although simulating the lock-in phenomenon, showed 2S vortex structures and quite lower unsteady lift C L values.
The class of entropy fixes originated by Harten and Hyman, as applied to Roe's linearization ... more The class of entropy fixes originated by Harten and Hyman, as applied to Roe's linearization of convex hyberbolic equations, is reformulated within a unified framework. By adopting a complementary viewpoint with respect to that of Harten, the entropy fix is recast in terms of expressions involving either the propagation speeds or the speed differences. The proposed formulation allows to analyze and compare several versions of this class of entropy fix and to elaborate some new variants thereof. In addition, this framework accommodates an interpretation of the HLL schemes which leads to the concept of a positivity preserving entropy fix and to a solution-dependent correction to Roe's scheme so as to assure positive solutions.
A grid generator system for the modelling of complex multi-bladed rotors is under development in ... more A grid generator system for the modelling of complex multi-bladed rotors is under development in Europe as a part of the development of a complete rotorcraft simulation method:The Brite/EuRam EROS project. The grid generator [1] exploits a CHIMERA domain decomposition on structured grids. The development is being carried out by rotorcraft manufacturers (Agusta, ECD, GKN-Westland), research centres (CIRA, DERA, DLR, NLR, ONERA), and Universities (Polit. Milano, Univ. Bristol, Univ. Glasgow, Univ. Rome 3). It addresses the industrial need for a rotor aerodynamic prediction tool [2] able to capture rotational phenomena, such as blade tip and wake vortices, and to predict correctly the unsteady blade pressures over a range of flight conditions, from hover to high-speed forward flight. This paper presents and discusses the capabilities of the GEROS grid generator together with relevant results.
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Papers by Luigi Vigevano