The application of wind-generated energy is increasing at a great rate, about 11% per year, with ... more The application of wind-generated energy is increasing at a great rate, about 11% per year, with an installed capacity of 837 GW in 2021, and it is the primary non-hydro renewable technology; in many countries, it is the main source of electric energy [...]
Minimizing the aerodynamic drag and the lift of the train coach remains a key issue for high-spee... more Minimizing the aerodynamic drag and the lift of the train coach remains a key issue for high-speed trains. With the development of computing technology and computational fluid dynamics (CFD) in the engineering field, CFD has been successfully applied to the design process of high-speed trains. However, developing a new streamlined shape for high-speed trains with excellent aerodynamic performance requires huge computational costs. Furthermore, relationships between multiple design variables and the aerodynamic loads are seldom obtained. In the present study, the Kriging surrogate model is used to perform a multi-objective optimization of the streamlined shape of high-speed trains, where the drag and the lift of the train coach are the optimization objectives. To improve the prediction accuracy of the Kriging model, the cross-validation method is used to construct the optimal Kriging model. The optimization results show that the two objectives are efficiently optimized, indicating th...
ABSTRACT The necessity of a more complete definition of the turbulent wind acting on a train is s... more ABSTRACT The necessity of a more complete definition of the turbulent wind acting on a train is studied in this paper using computational fluid dynamics (CFD). A stochastic approach for the modeling of turbulent winds is proposed here. Synthetic winds are defined based on two different spectral models, namely the Kaimal spectrum and the Kraichnan spectrum. These are generated using and software, respectively. To complete the comparison, a third oncoming wind definition is considered, corresponding to a uniform (low-turbulence) wind. Large-Eddy Simulation (LES) and Scale-Adaptive Simulation (SAS) turbulence models have been used for the numerical simulation. Comparison is made of the average, standard deviations and extreme values of the loads calculated with the different methods. The corresponding flow fields are also studied and compared. The transient behavior is analyzed using the spectra of the velocity and loads, and the aerodynamic admittance curves. The results obtained for the last inlet condition are in good agreement with previous studies, while the importance of the spectral model choice is evidenced in the analysis of the velocity and force spectra, as well as in the aerodynamic admittance curves.
ABSTRACT A model proposed by García & Crespo (1997 and 2000) to study the modification of... more ABSTRACT A model proposed by García & Crespo (1997 and 2000) to study the modification of turbulence characteristics by dispersed particles is applied to several configurations appearing in the literature. The model is valid for dilute flows and small Stokes number. The classical k-e method is used, modified with additional terms in the k and epsilon equations, that take into account the effect of particles on the carrier phase. The additional dissipation term included in the equation for k is proportional to the mass centration of particles and to e, and has a proportionality constant equal to 3/2 of Kolmogorov constant, C_o. The additional source term for the e equation is taken as proportional to e/k, using a C_e3 coefficient. The model applies for particles small enough so that they increase the dissipation of turbulent kinetic energy. Previously, the model was applied to jets and mixing layers, and in this work is applied to homogeneous turbulence and channel flows, in order to further check its validity, and find the most appropriate values of C_o and C_e3. First, it is considered the case of decay of k and e in homogeneous and isotropic turbulence; the results of the direct numerical simulation of Elghobashi & Truesdell (1993) and the experiments of Schreck & Kleis (1993) are used for comparison. Comparison is also made with the results of Squires & Eaton (1994), that reproduce isotropic and homogeneous turbulence under forced conditions and steady state. Channel flow is also studied and a comparison is made with the measurements of Kulick et al. (1994). From the comparisons is deduced that C_e3 has to be very similar to the C_e2 coefficient of the k-e method, although with different values in each case. The trends are correctly predicted although quite different values of C_o are obtained.
The application of wind-generated energy is increasing at a great rate, about 11% per year, with ... more The application of wind-generated energy is increasing at a great rate, about 11% per year, with an installed capacity of 837 GW in 2021, and it is the primary non-hydro renewable technology; in many countries, it is the main source of electric energy [...]
Minimizing the aerodynamic drag and the lift of the train coach remains a key issue for high-spee... more Minimizing the aerodynamic drag and the lift of the train coach remains a key issue for high-speed trains. With the development of computing technology and computational fluid dynamics (CFD) in the engineering field, CFD has been successfully applied to the design process of high-speed trains. However, developing a new streamlined shape for high-speed trains with excellent aerodynamic performance requires huge computational costs. Furthermore, relationships between multiple design variables and the aerodynamic loads are seldom obtained. In the present study, the Kriging surrogate model is used to perform a multi-objective optimization of the streamlined shape of high-speed trains, where the drag and the lift of the train coach are the optimization objectives. To improve the prediction accuracy of the Kriging model, the cross-validation method is used to construct the optimal Kriging model. The optimization results show that the two objectives are efficiently optimized, indicating th...
ABSTRACT The necessity of a more complete definition of the turbulent wind acting on a train is s... more ABSTRACT The necessity of a more complete definition of the turbulent wind acting on a train is studied in this paper using computational fluid dynamics (CFD). A stochastic approach for the modeling of turbulent winds is proposed here. Synthetic winds are defined based on two different spectral models, namely the Kaimal spectrum and the Kraichnan spectrum. These are generated using and software, respectively. To complete the comparison, a third oncoming wind definition is considered, corresponding to a uniform (low-turbulence) wind. Large-Eddy Simulation (LES) and Scale-Adaptive Simulation (SAS) turbulence models have been used for the numerical simulation. Comparison is made of the average, standard deviations and extreme values of the loads calculated with the different methods. The corresponding flow fields are also studied and compared. The transient behavior is analyzed using the spectra of the velocity and loads, and the aerodynamic admittance curves. The results obtained for the last inlet condition are in good agreement with previous studies, while the importance of the spectral model choice is evidenced in the analysis of the velocity and force spectra, as well as in the aerodynamic admittance curves.
ABSTRACT A model proposed by García & Crespo (1997 and 2000) to study the modification of... more ABSTRACT A model proposed by García & Crespo (1997 and 2000) to study the modification of turbulence characteristics by dispersed particles is applied to several configurations appearing in the literature. The model is valid for dilute flows and small Stokes number. The classical k-e method is used, modified with additional terms in the k and epsilon equations, that take into account the effect of particles on the carrier phase. The additional dissipation term included in the equation for k is proportional to the mass centration of particles and to e, and has a proportionality constant equal to 3/2 of Kolmogorov constant, C_o. The additional source term for the e equation is taken as proportional to e/k, using a C_e3 coefficient. The model applies for particles small enough so that they increase the dissipation of turbulent kinetic energy. Previously, the model was applied to jets and mixing layers, and in this work is applied to homogeneous turbulence and channel flows, in order to further check its validity, and find the most appropriate values of C_o and C_e3. First, it is considered the case of decay of k and e in homogeneous and isotropic turbulence; the results of the direct numerical simulation of Elghobashi & Truesdell (1993) and the experiments of Schreck & Kleis (1993) are used for comparison. Comparison is also made with the results of Squires & Eaton (1994), that reproduce isotropic and homogeneous turbulence under forced conditions and steady state. Channel flow is also studied and a comparison is made with the measurements of Kulick et al. (1994). From the comparisons is deduced that C_e3 has to be very similar to the C_e2 coefficient of the k-e method, although with different values in each case. The trends are correctly predicted although quite different values of C_o are obtained.
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